89. Supersymmetry, Part II (Experiment)

1

89. Supersymmetry, Part II (Experiment)
Revised August 2023 by M. D’Onofrio (Liverpool U.) and F. Moortgat (CERN; Ghent U.).

89.1 Introduction
Supersymmetry (SUSY), a transformation relating fermions to bosons and vice versa [1–9] is
one of the most compelling possible extensions of the Standard Model of particle physics (SM).
On theoretical grounds SUSY is motivated as a generalization of space-time symmetries. A lowenergy realization of SUSY, i.e., SUSY at the TeV scale, is, however, not a necessary consequence.
Instead, low-energy SUSY is motivated by the possible cancellation of quadratic divergences inradiative corrections to the Higgs boson mass [10–15]. Furthermore, it is intriguing that a weaklyinteracting, (meta)stable supersymmetric particle might make up some or all of the dark matter in
the Universe [16–18]. In addition, SUSY predicts that gauge couplings, as measured experimentallyat the electroweak scale, unify at an energy scale O(1016 ) GeV (“GUT scale”) near the Planckscale [19–25].
In the minimal supersymmetric extension to the Standard Model, the so called MSSM [11,26,27],a supersymmetry transformation relates every chiral fermion and gauge boson in the SM to asupersymmetric partner with half a unit of spin difference, but otherwise with the same properties(such as mass) and quantum numbers. The MSSM Higgs sector contains two doublets, which give
mass to the up-type and down-type quarks, respectively. After electroweak symmetry breaking,five Higgs bosons arise, of which two are charged. The supersymmetric partners of chiral fermions˜ ν̃), and the “gauginos” for gauge bosons. The supersymmetricare squarks (q̃) and sleptons (`,partners of the Higgs doublets are known as “higgsinos.” The weak gauginos and higgsinos mix,±
giving rise to charged mass eigenstates called “charginos” (χ̃ ), and neutral mass eigenstates called0“neutralinos” (χ̃ ). These are often collectively referred to as electroweakinos (EWkinos). The
SUSY partners of the gluons are known as “gluinos” (g̃). The fact that such particles are not yet
observed leads to the conclusion that, if supersymmetry is realized, it is a broken symmetry. A
description of SUSY in the form of an effective Lagrangian with only “soft” SUSY breaking terms
and SUSY particle masses of the order of T eV maintains the cancellation of quadratic divergencesof soft SUSY breaking scalar mass squared parameters.
The phenomenology of SUSY is to a large extent defined by the SUSY breaking mechanism
and the SUSY breaking scale. These determine the SUSY particle masses, the mass hierarchy, thefield contents of physical particles, and their decay modes. In addition, phenomenology cruciallydepends on whether the multiplicative quantum number of R-parity [27], R = (−1)3(B−L)+2S , where
B and L are baryon and lepton numbers and S is the spin, is conserved or violated. If R-parity
is conserved, SUSY particles (sparticles), which have odd R-parity, are produced in pairs and the
decays of each SUSY particle must involve an odd number of lighter SUSY particles. The lightest
SUSY particle (LSP) is then stable and often assumed to be a weakly interacting massive particle(WIMP). If R-parity is violated, new terms λijk , λ0ijk and λ00ijk appear in the superpotential, where
ijk are generation indices; λ-type couplings appear between lepton superfields only, λ00 -type are
between quark superfields only, and λ0 -type couplings connect the two. R-parity violation implies
lepton and/or baryon number violation. More details of the theoretical framework of SUSY are
discussed elsewhere in this volume [28].
The discovery of a Higgs boson with a mass around 125 GeV imposes constraints on SUSY
models, which are discussed elsewhere [28, 29]. Low-energy data from flavor physics experiments,
high-precision electroweak observables as well as astrophysical data also impose strong constraints
on the allowed SUSY parameter space. Recent examples of such data include measurements of
S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024)
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89. Supersymmetry, Part II (Experiment)

the rare B-meson decay Bs → µ+ µ− [30–32], measurements of the anomalous magnetic momentof the muon [33, 34], and accurate determinations of the cosmological dark matter relic density
constraint [35, 36].
Indirect constraints can be more sensitive to higher SUSY mass scales than experiments searching for direct sparticle production at colliders, but the interpretation of these results is often
strongly model dependent. In contrast, direct searches for sparticle production at collider experiments, which are the main topic of this review, are less subject to interpretation ambiguities andtherefore they play a crucial role in the search for SUSY. Further discussion on indirect constraints
can be found in 88.7.2.

89.2 Overview of the experimental search programme
The electron-positron collider LEP was operational at CERN between 1989 and 2000. In theinitial phase, center-of-mass energies around the Z-peak were probed, but after 1995 the LEP
experiments collected a significant amount of luminosity at higher center-of-mass energies, some√√
235 pb−1 per experiment at s ≥ 204 GeV, with a maximum s of 209 GeV. Searches for
new physics at e+ e− colliders benefit from the clean experimental environment and the fact thatmomentum balance can be measured not only in the plane transverse to the beam, but also inthe direction along the beam (up to the beam pipe holes), defined as the longitudinal direction.
Searches at LEP are dominated by the data samples taken at the highest center-of-mass energies.
The CDF and D0 experiments at the Tevatron, a proton-antiproton collider at a center-of-massenergy of up to 1.96 TeV, had an extensive search program for supersymmetric particles. CDF
and D0 collected integrated luminosities between 10 and 11 fb−1 each up to the end of collider
operations in 2011.
The electron-proton collider HERA provided collisions to the H1 and ZEUS experiments between 1992 and 2007, at a center-of-mass energy up to 318 GeV. A total integrated luminosityof approximately 0.5 fb−1 was collected by each experiment. Since at HERA baryons collide withleptons, SUSY searches typically look for R-parity violating production of single SUSY particles.
The Large Hadron Collider (LHC) at CERN started proton-proton operation at a center-ofmass energy of 7 TeV in 2010. By the end of 2011 the ATLAS and CMS experiments had collected
about 5 fb−1 of integrated luminosity each, and the LHCb experiment had collected approximately
1 fb−1 . In 2012, the LHC operated at a center-of-mass energy of 8 TeV, and ATLAS and CMS
collected approximately 20 fb−1 each, whereas LHCb collected 2 fb−1 . In 2015, the LHC started
Run 2, with a center-of-mass energy of 13 TeV. At the end of Run 2 in November 2018, ATLAS
and CMS had both collected approximately 140 fb−1 , and LHCb had collected almost 6 fb−1 . The
Run 3 of the LHC started in July 2022 with a center-of-mass energy of 13.6 TeV. Almost 70 fb−1of data have been collected by ATLAS and CMS at the time of writing (August 2023), and LHCb
collected around 1.3 fb−1 .
At the LHC, cross sections of QCD-mediated processes are the largest achievable at colliders,which is reflected in the higher sensitivity for SUSY particles carrying color charge, squarks andgluinos, with respect to LEP, Tevatron and HERA. In particular, proton-proton collisions at the
LHC differ from proton-antiproton collisions at the Tevatron in the sense that there are no valenceanti-quarks in the proton, and that gluon-initiated processes play a more dominant role. The
increased center-of-mass energy of the LHC compared to the Tevatron significantly extends the
kinematic reach for SUSY searches. This is reflected foremost in the sensitivity for squarks andgluinos, but also for SUSY particles produced via electroweak processes.
In this review we report results of direct searches for SUSY particles at colliders up to August
2023, mostly covering data analyses at the ATLAS and CMS experiments with reference to resultsfrom LEP, HERA and the Tevatron. For more details on LEP and Tevatron constraints, see earlier
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89. Supersymmetry, Part II (Experiment)

PDG reviews [37]. Analyses on the Run 3 datasets are still in progress hence the results reported
for ATLAS and CMS are based on Run 1 and Run 2 data. Results are categorized depending on thetargeted SUSY particles, the nature of their production and decays, and the assumption on R-parity.
Brief summaries of search techniques and approaches adopted for interpretation of the results are
given in Section 89.3 and 89.4, respectively. Sections 89.5-89.8 focus on results for promptlydecaying gluinos and first and second generation squarks, top and bottom squarks, electroweakinos(charginos, neutralinos) and sleptons. Limits obtained for sparticle masses assuming R-parity
violating models are also reported. Results of dedicated searches for long-lived (LL) SUSY particles
are reported in Section 89.9. Finally, Section 89.10 provides examples of global reinterpretations of
SUSY searches.

89.3 Experimental search techniques
Large background contributions from Standard Model processes pose challenges to the trigger
and analysis. Such backgrounds are dominated by multijet production processes, including, particularly at the LHC, those of top quark production, as well as jet production in association with
vector bosons. The proton’s momentum is shared between its parton constituents, and in eachcollision only a fraction of the total center-of-mass energy is available in the hard parton-parton
scattering. Since the parton momenta in the longitudinal direction are not known on an event-byevent basis, use of momentum conservation constraints in an analysis is restricted to the transverse
plane, leading to the definition of transverse variables, such as the missing transverse momentum,
and the transverse mass.
Under the assumption of R-parity conservation (RPC), the typical SUSY search signature forsquarks and gluinos at hadron colliders contains high-pT jets, which are produced in the decay
chains of heavy squarks and gluinos, and significant missing transverse momentum originatingfrom the two LSPs produced at the end of the decay chains, which escape experimental detection.
Electroweakino decays are often characterised by the presence of leptons, for instance from W andZ bosons in the decay chain, plus missing transverse momentum. Standard Model backgroundswith missing transverse momentum include leptonic W/Z-boson decays, associated production ofjets and a Z-boson decaying into neutrinos, semi-leptonic heavy-flavor decays to neutrinos, topquark pair production with one or both W bosons decaying leptonically, and multijet events that
may be affected by instrumental effects such as jet mis-measurement.
Selection variables designed to separate the SUSY signal from the Standard Model backgrounds
miss , and m . The quantities H and E miss refer to theinclude transverse variables such as HT , ET
eff
TT
measured transverse energy and the missing transverse momentum in the event, respectively. They
are usually defined as the scalar sum of the transverse jet momenta or of the transverse energies ofmiss ) of the negative vector
calorimeter clusters measured in the event (HT ), or the magnitude (ETsum of transverse momenta of reconstructed objects like jets and leptons in the event (~pmissT ). The
miss .
quantity meff is referred to as the effective mass of the event and is defined as meff = HT + ET
The peak of the meff distribution for SUSY signal events correlates with the SUSY mass scale, inparticular with the mass difference between the primary produced SUSY particle and the LSP [38],whereas the Standard Model backgrounds dominate at low meff . An additional reduction of multijet
backgrounds can be achieved by demanding isolated leptons or photons in the final states; insuch events the lepton or photon transverse momentum may be added to HT or meff for further
signal-background separation. Other kinematic variables and approaches developed to increase thesensitivity to pair production of heavy sparticles with TeV-scale masses focusing on the kinematicsof their decays are the αT [39–43], razor [44], stransverse mass (mT2 ) [45], and contransverse mass
(mCT ) [46] variables. The super-razor [47] and recursive jigsaw reconstruction [48] techniques are
topological event reconstruction methods also used in searches for sparticles with masses in the
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89. Supersymmetry, Part II (Experiment)

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TeV-range. In case massive, unstable SM particles such as top quarks, vector bosons or the Higgs
boson arise in the decay chain, dedicated procedures are employed for their reconstruction andidentification. If these are produced with a significant boost, their decay products will typicallyoverlap and become collimated (boosted) in the direction of the parent particle. Their hadronic
decay products can be reconstructed as a single large-radius jet (see studies from ATLAS [49]), andjet-substructure [50] techniques can be adopted. Machine-learning (ML) approaches are also used
to identify and classify hadronic decays of highly Lorentz-boosted bosons and top quarks, see as
example recent studies from CMS [51].
Most analyses still use simple combinations of selections on kinematic variables (often referred toas cut-and-count analyses) and exploit multiple signal regions defined by categorizing events on thebasis of several variables and their correlations. An example is provided in Fig. 89.1 from Ref. [52]:39 signal regions are set to search for top squarks in events with one lepton, jets and missing
transverse momentum. Regions depend on jet multiplicities, reconstructed top-quark candidates
and thresholds applied to the most discriminant variables used for optimisation.
137 fb-1 (13 TeV)

EventsCMS
103

Observed

Z→νν

Lost lepton

1l (from t)

1l (not from t)

Total Uncert.

102

10

Obs./Exp.

4
3
2
1
0

J:[550,750]
J:[750,+∞]

J:[350,450]
J:[450,550]

I:[750,+∞]
J:[250,350]

I:[450,550]
I:[550,750]

I:[250,350]
I:[350,450]

H:[250,500]
H:[500,+∞]G2:[350,450]
G3:[250,350]
G3:[350,450]

G1:[350,450]
G2:[250,350]

G0:[750,+∞]G1:[250,350]

G0:[450,550]
G0:[550,750]

F:[350,450]
F:[450,+∞]E3:[350,450]
F:[250,350]

E2:[350,450]
E3:[250,350]

E1:[350,450]
E2:[250,350]

E0:[600,+∞]E1:[250,350]

D:[600,+∞]E0:[450,600]

D:[350,450]
D:[450,600]

C:[800,+∞]
D:[250,350]

C:[550,650]
C:[650,800]

C:[350,450]
C:[450,550]

B:[250,450]
B:[450,700]
B:[700,+∞]A1:[450,600]
A2:[250,600]

A0:[750,+∞]A1:[350,450]

10−1

A0:[600,750]

1

NJ

t mod

A 2−3

> 10

≤ 175

B 2−3

> 10

> 175

C ≥4

≤0

≤ 175

D ≥4

≤0

> 175

Mlb [GeV]E ≥ 4 0−10≤ 175

F ≥ 4 0−10

> 175

G ≥4

> 10

≤ 175

H ≥4

> 10

> 175

X0: Inclusive
X1: Untagged
X2: Merged t quark tag
X3: Resolved t quark tag
I: NJ ≥ 5, Nb,med ≥ 1
J: NJ ≥ 3, Nb,soft ≥ 1

Signal Regions

Figure 89.1: Example of multiple signal regions set for a typical SUSY search at the LHC. For
definition of regions and acronyms specific for this search, see corresponding paper.
In recent years, shape analyses or analyses using more sophisticated techniques, e.g. machinelearning, have been also developed. ML techniques often allow analyses to better capture thecomplexity of the events and achieve improved sensitivity with respect to counting experiments. For
example, Boosted Decision Trees (BDTs) allow analyses to exploit simultaneously the discriminating
power of multiple variables and that of correlations among objects in the events. Deep Neural
Networks (NN) are also employed for objects reconstruction and to use directly detector-recordedenergies and momenta of produced particles instead of first deriving a restricted set of physicalvariables. Among others, currently in use are Convolutional NN for image classification techniques,
Recurrent NN, parametric NN and Generative Adversarial Networks.
Variables and approaches reported above are also used in searches for R-parity violating (RPV)SUSY models where signal events are often characterised by the presence of multiple leptons and/or
jets, and little or no missing transverse momentum. However, if R-parity violating couplings are
small, sparticles might be long-lived and may travel macroscopic distances before decaying. Similarly, long lifetimes may be due to small mass splittings, as in the case of pure higgsino/wino
scenarios, or to heavy mediators, as in Split SUSY models [53, 54]. The identification of long-lived
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particles requires dedicated tools and their signatures can be very diverse. At the LHC, customized
techniques (also based on NN) have been developed, for example, to reconstruct significantly displaced decay vertices or short track segments, and to identify tracks with atypical properties or
unusual ionization, small and localized deposits of energy inside of the calorimeters without associated tracks, or stopped particles that decay out of time with collisions. For an overview, see
Ref. [55].

89.4 Interpretation of search results
Since the mechanism by which SUSY is broken is unknown, a general approach to SUSY via
the most general soft SUSY breaking Lagrangian adds a significant number of new free parameters.
For the minimal supersymmetric standard model, MSSM, i.e., the model with the minimal particle
content, these comprise 105 new real degrees of freedom. A phenomenological analysis of SUSY
searches leaving all these parameters free is not feasible. For the practical interpretation of SUSY
searches at colliders several approaches are taken to reduce the number of free parameters.
One approach is to assume a SUSY breaking mechanism and lower the number of free parameters
through the assumption of additional constraints. Before the start of the LHC, interpretations ofexperimental results were often performed in constrained models of gravity mediated [56,57], gaugemediated [58–60], and anomaly mediated [61, 62] SUSY breaking. The most popular model wasthe constrained MSSM (CMSSM) [56, 63, 64], which in the literature is also referred to as minimal
supergravity, or MSUGRA. These constrained SUSY models are theoretically well motivated andprovide a rich spectrum of experimental signatures. However, with universality relations imposedon the soft SUSY breaking parameters, they do not cover all possible kinematic signatures and mass
relations of SUSY. Furthermore, the Higgs mass measurement from LHC Run 1, together with othercollider and non-collider measurements, limits substantially the allowed SUSY parameter space forthese models. This indicates that very constrained models like the CMSSM are no longer goodbenchmark scenarios to solely characterize the results of SUSY searches at the LHC and efforts
have been made to complement them with more flexible approaches.
A broader and more comprehensive subset of the MSSM can be studied via the so-called
phenomenological-MSSM, or pMSSM [65–68]. It is derived from the MSSM, using experimental data to eliminate parameters that are free in principle but have already been highly constrainedby measurements of e.g., flavor mixing and CP -violation. This effective approach reduces the number of free parameters in the MSSM to typically 19 or even less, making it a practical compromise
between the full MSSM and highly constrained models such as the CMSSM.
Even less dependent on fundamental assumptions are interpretations in terms of so-called simplified models [69–72]. Such models assume a limited set of SUSY particle production and decay modes
and leave open the possibility to vary masses and other parameters freely. Therefore, simplified
models enable comprehensive studies of individual SUSY topologies, and are useful for optimization of the experimental searches over a wide parameter space without limitations on fundamental
kinematic properties such as masses, production cross sections, and decay modes.
As a consequence, ATLAS and CMS have adopted simplified models as the primary framework
to provide interpretations of their searches. In addition to using simplified models that describe
prompt decays of SUSY particles, the experiments are now also focusing more on the use of simplified models that allow for decays of long-lived SUSY particles as they can arise in different SUSY
scenarios (see Section 89.9 for further discussion). Today, almost every individual search provides
interpretations of their results in one or several simplified models that are characteristic of SUSY
topologies probed by the analysis.
While simplified models are very convenient for the interpretation of individual SUSY production and decay topologies, care must be taken when applying these limits to more complex SUSY
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689. Supersymmetry, Part II (Experiment)

spectra. In particular, the branching ratio of SUSY particles into a specific final state is often
assumed to be 100% and in many of the quoted limits the LSP is assumed to be massless. Therefore, simplified model limits should be seen as an approximation of the constraints that can beplaced on sparticle masses in more complex SUSY spectra. Only on a case-by-case basis can it be
determined whether the limit of a given simplified model represents a good approximation of thetrue underlying constraint that can be applied on a sparticle mass in a complex SUSY spectrum.
In the following, we will point out explicitly the assumptions that have entered the limits when
quoting interpretations from simplified models.
Since none of the searches performed so far have shown significant excess above the SM background prediction, the interpretation of the presented results are exclusion limits on SUSY parameter space. Unless stated differently, all quoted exclusion limits are at the 95% confidence level.
Finally, we note that many of the recent publications by ATLAS and CMS also present resultsin terms of model-independent limits such that their discovery potential is statistically quantified
independently on a particular model.

89.5 Exclusion limits on gluino, first and second generation squark masses in
RPC scenarios
Colored SUSY particles such as squarks and gluinos are produced via the strong interaction andhave the highest cross sections at hadron colliders. Limits on squark masses of the order 100 GeV
have been set by the LEP experiments [73], in the decay to quark plus neutralino, and for a massdifference between squark and quark plus neutralino of typically at least a few GeV. However,
hadron collider experiments are able to set much more stringent mass limits.
The main production mechanisms at hadron colliders are squark-squark, squark-gluino andgluino-gluino production; when “squark” is used “antisquark” is also implied. Pair production
usually involves both the s-channel and t-channel parton-parton interactions. However, since there
is a negligible amount of bottom and top quark content in the proton, top and bottom squark
production proceeds through s-channel diagrams only. Experimental analyses of squark and/or
gluino production typically assume the first and second generation squarks to be approximately
degenerate in mass. Cross section calculations at the center-of-mass energy of 13 TeV shown in
Fig. 89.2 (from Ref. [74]) assume mass degeneracy of left- and right-handed u, d, s, c squarks.
Other sparticle masses are considered decoupled, i.e. their masses are assumed to have a very highvalue (above 10 TeV). The LHC experiments also provide simplified model limits on individual firstor second generation squarks. Top and bottom squarks have the same production cross section,
identical to that of a single light squark.
In this section, we focus on results assuming R-parity conservation. Limits set by the Tevatronexperiments on the gluino mass assume the framework of the CMSSM, with tan β = 5 (CDF) or
tan β = 3 (D0). Furthermore, the common trilinear term A0 is set to 0 and the higgsino mass term
µ is assumed to be less than 0. The resulting lower mass limits are about 310 GeV for all squark
masses, or 390 GeV for the case mq̃ = mg̃ [75, 76].
ATLAS and CMS limits on the gluino mass have been established in the framework of simplified
models. Assuming only gluino pair production, three main primary decay chains of the gluino havebeen considered by the LHC experiments for interpretations of their search results. The first decay0chain, g̃ → q q̄ χ̃1 , assumes gluino mediated production of first and second generation squarks (onshell or off-shell) which leads to four light flavor quarks in the final state. Therefore, inclusive
miss final states are utilized to put limits on
all-hadronic analyses searching for multijet plus ET
this simplified model. These limits are derived as a function of the gluino and neutralino (LSP)
mass. As shown in Fig. 89.3 (left)the CMS collaboration [77] excludes in this simplified model
gluino masses below approximately 2.1 TeV for a light neutralino mass below about 600 GeV. In
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89. Supersymmetry, Part II (Experiment)

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pp, s = 13 TeV, NNLOapprox+NNLL

104

gg
gq

qq *
tt * , bb *

1500

1750

cross section [pb]

102
100
10 2
10 4
10 6

250

500

750
1000 1250
particle mass [GeV]

2000

Figure 89.2: Cross sections for pair production of gluinos and squarks as a function of theirmass at the LHC for a center-of-mass energy of 13 TeV. They are calculated at approximately
next-to-next-to-leading-order (NNLO) including the resummation of soft gluon emission at the
next-to-next-to-leading logarithmic accuracy.

scenarios where neutralinos are not very light, the efficiency of the analyses is reduced by the factthat jets are less energetic, and there is less missing transverse momentum in the event. This leads
to weaker limits when the mass difference ∆m = mg̃ − mχ̃0 is reduced. For example, for neutralino
1
masses above about 1.2 TeV no limit on the gluino mass can be set for this decay chain. Therefore,
limits on gluino masses are strongly affected by the assumption of the neutralino mass. Similar
results for this simplified model have been obtained by ATLAS [78]. A second simplified model0
postulates a decay chain where g̃ → q q̄W χ̃1 , assuming that the intermediate (on-shell or off-shell)squark is left-handed and decays to a chargino and a quark, with the chargino decaying to a W
miss in theboson and the LSP. This leads to two W bosons and four light flavor quarks plus ET
final state. Both leptonic and hadronic decays of the W can be considered. In this scenario, the
ATLAS collaboration [79,80] excludes gluino masses below approximately 2.2 TeV for a sufficiently
light neutralino and assuming the chargino mass is halfway between the gluino and neutralinomass, see Fig. 89.3 (right). Again, for neutralino masses above about 1.2 TeV, there exists nolimit on the gluino mass for this decay chain. A similar reach has been obtained by the CMS
collaboration [81, 81, 82], where the most recent results are obtained using novel algorithms basedon deep neutral networks that identify hadronically decaying W bosons.
Gluino decays are not limited to first and second generation squarks: another important decay0chain of the gluino considered for interpretation in simplified models is g̃ → bb̄χ̃1 . In this casethe decay is mediated via bottom squarks and thus leads to four jets originating from b-quarks
miss in the final state. For this topology as well, inclusive all-hadronic searches provide theand EThighest sensitivity. In this case, the use of secondary vertex reconstruction for the identification ofjets originating from the b-quarks in the event provides a powerful handle to reject SM backgroundmiss signature these searches also require
contributions. Therefore, in addition to a multijet plus ET
between 1 and 4 jets to be tagged as b-jets. As shown in Fig. 89.4 (left), for this simplified model
CMS [77] excludes gluino masses below ≈ 2.3 TeV for a sufficiently light neutralino, while forneutralino masses above ≈ 1.5 TeV no limit on the gluino mass can be set. Comparable limits for
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1600

CMS

137 fb-1 (13 TeV)
miss

1704.07781 (HT ), 36 fb
miss1908.04722, 0-lep (HT )1909.03460 (MT2)-1

Expected
Observed

1400

1

1800

Moriond 20210m(∼χ ) [GeV]∼
pp → ~g~g, ~g → q q χ01

2000

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1

m χ∼ [GeV]

8

2200
2000
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±
m(∼
χ1) = 1×(m(~g)+m(∼
χ1))
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ATLAS Preliminary
0~g→ qqW∼
χ

1600
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1200

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s = 13 TeV
139 fb-1
0-lepton: arXiv:2010.14293
1-lepton: arXiv:2101.01629

800

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0-lepton: expected0-lepton: observed
1-lepton: expected
1-lepton: observed
Run 1 expected
Run 1 observed
All limits at 95% CL

Run 1: arXiv:1507.05525∼0χ )1
(
m

1000

800

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~g)<
(
m

600

400
400

200
200

0

800 1000 1200 1400 1600 1800 2000 2200 2400

mg~ [GeV]

600

800

1000 1200 1400 1600 1800 2000 2200 2400 2600m(~g) [GeV]Figure 89.3: Lower mass limits, at 95% C.L., on gluino pair production for various decay chains0in the framework of simplified models. Left: g̃ → q q̄ χ̃1 , result of the CMS collaboration. Right:
0g̃ → q q̄W χ̃1 , result of the ATLAS collaboration.

this simplified model are provided by searches from ATLAS [83, 84], with the most recent results
pushing the boundary of gluino masses to 2.44 TeV in the case of a massless neutralino.
If kinematically allowed, decays of gluinos to top squarks via g̃ → t̃t are also possible. This0defines the next important simplified model characterizing gluino pair production, g̃ → tt̄χ̃1 , which
0 0leads to a “four tops” final state, ttttχ̃1 χ̃1 . The topology of this decay is very rich in different
experimental signatures: as many as four isolated leptons, four b-jets, several light flavor quark
jets, and significant missing transverse momentum from the neutrinos in the W decay and fromthe two neutralinos. As shown in Fig. 89.4 (right), the ATLAS search [83] rules out gluinos with
masses below ≈ 2.4 TeV for light neutralinos in this model. For neutralino masses above ≈ 1.4 TeV,
no limit can be placed on the gluino mass. The CMS multiple b-jet search [85] and the search infull-hadronic events using identification techniques for boosted top-quarks in the final state [86]result in gluino mass limits of ≈ 2.3 TeV.
Assuming gluinos to be heavier than squarks, squarks will predominantly decay to a quark anda neutralino or chargino, if kinematically allowed. The decay may involve the lightest neutralino(typically the LSP) or chargino, but, depending on the masses and couplings of the gauginos and on
the handedness of the squarks, may involve heavier neutralinos or charginos. For pair productionof first and second generation squarks, the simplest decay modes involve two jets and missing
transverse momentum, with potential extra jets stemming from initial state or final state radiation(ISR/FSR) or from decay modes with longer decay chains (cascades). In cascades, isolated photons
or leptons may appear from the decays of sparticles such as neutralinos or charginos.
Limits on first and second generation squark masses set by the Tevatron experiments assume
the CMSSM, and amount to lower limits of about 380 GeV for all gluino masses, or 390 GeV
for the case mq̃ = mg̃ [75, 76]. At the LHC, limits on squark masses have been set using up to
approximately 140 fb−1 of data at 13 TeV. Interpretations in simplified models typically characterizesquark pair production considering only one decay chain at the time for the squark, for instance0
˜ s̃ and c̃ squarks are degenerateq̃ → q χ̃1 . It is usually assumed that the left and right-handed ũ, d,
31st May, 2024

1800 CMS
1600

Moriond 2021

137 fb-1 (13 TeV)
-11705.04650 (MT2), 36 fb
miss1908.04722, 0-lep (HT )1909.03460, 0-lep (MT2)March 2023

2500

1

2000

0
1

m χ∼ [GeV]∼
pp → ~g~g, ~g → b b χ010m(∼χ ) [GeV]

89. Supersymmetry, Part II (Experiment)

9

Expected
Observed1

36.1 - 140 fb-1
2000

1400

ATLAS Preliminary
0~g→ tt∼
χ , s = 13 TeV

All limits at 95% CL≥ 7-12 jets: 2008.06032≥ 3b jets: 2211.08028 + 1711.01901
SS leptons: 1706.03731
Run 1: 1507.05525

1200
1500

1000

≥ 7-12 jets expected≥ 7-12 jets observed≥ 3b jets expected≥ 3b jets observed
SS leptons expected
SS leptons observed
Run 1 expected
Run 1 observed

tt

∼0 )+
(χ 1

~ <m
(g)

800

m

1000

600
400
500

200
0

800 1000 1200 1400 1600 1800 2000 2200 2400

mg~ [GeV]

1000 1200 1400 1600 1800 2000 2200 2400 2600m(~g) [GeV]Figure 89.4: Lower mass limits, at 95% C.L., on gluino pair production for various decay chains00
in the framework of simplified models. Left: g̃ → bb̄χ̃1 . Right: g̃ → tt̄χ̃1 . Results from the CMS
and ATLAS collaborations.

in mass. Furthermore, it is assumed that the mass of the gluino is very high (above 10 TeV) andthus contributions of the corresponding t-channel diagrams to squark pair production are negligible.
Therefore, the total production cross section for this simplified model is eight times the production
cross section of an individual squark (e.g. ũL ). Under these assumptions, CMS obtains a lower
squark mass limit of ≈ 1.75 TeV for light neutralinos [85], as shown in Fig. 89.5 (left). Only forneutralino masses below ≈ 800 GeV can any squark masses be excluded. Searches for new physics
in monojet channels are sensitive to very compressed scenarios, and masses up to 900 GeV are
excluded for ∆m = mq̃ , mχ̃0 ≈ 5 GeV [87].
1
If the assumption of mass degenerate first and second generation squarks is dropped and only
the production of a single light squark is assumed, the limits weaken significantly. For example,
the CMS limit on degenerate squarks of 1750 GeV for light neutralinos drops to ≈ 1300 GeV for
pair production of a single light squark, and for neutralinos heavier than ≈ 600 GeV no squark
mass limit can be placed. It should be noted that this limit is not a result of a simple scaling of theabove mentioned mass limits assuming eight-fold mass degeneracy but it also takes into accountthat for an eight times lower production cross section the analyses must probe kinematic regionsof phase space that are closer to the ones of SM background production.
A summary of results of the ATLAS searches also targeting more complicated decay chains,
where e.g. intermediate bosons are produced as well, can be seen in Fig. 89.5 (right). Dependingon the topology, the exclusion limit can reach up to ≈ 2 TeV (this value is only reached in gauginomediated simplified models [88]). Recent results include a search in two-opposite-sign, same=flavor
dilepton final state events [89] targeting squarks decaying through the next-to-lightest neutralino
via a slepton or a Z boson and exclude mass up to ≈ 1550 GeV for a massless neutralino. Squarks
decaying via charginos and next-to-lightest neutralinos in long decay chains including W and Z
bosons are constrained with searches for same-sign dilepton or three-lepton final state events [90]:in this case, masses up to ≈ 1.7 TeV are excluded.
For single light squarks ATLAS also reports results of a dedicated search for pair production ofscalar partners of charm quarks [91]. Assuming that the scalar-charm state exclusively decays into
31st May, 2024

89. Supersymmetry, Part II (Experiment)∼
pp → ~q~q, ~q → q χ01

CMS
1200

Moriond 2021

3000
0
m(∼
χ1) [GeV]

1400

137 fb-1 (13 TeV)

1705.04650, 0-lep (MT2), 36 fb
1909.03460, 0-lep (MT2)
miss1908.04722, 0-lep (HT )01m ∼χ [GeV]

10

-1

2500

Expected
Observed

~ ~
~
q +~
q (~
u,d,~
s,c)
L
R

1000

s = 8-13 TeV, 20.3 - 140 fb-1
~= u
~, ~
q
d, ~
s, ~
c

March 2023

ATLAS Preliminary0~q → q∼
χ 0 lep. + mono-jet [2010.14293, 2102.10874]
10~
q → qW∼χ 0 lep. + 1 lep. [2010.14293, 2101.01629]
L

1

0~ → qZ(*)∼
q
χ1 2 lep. OS SF [2204.13072]
~
~ ~
0
~, b
q
, t → q(γ /Z)G via ∼χ ≥ 2 γ [1802.03158]
1

2000

0
~ → qWZ∼qχ ≥ 2 lep. SS [2307.01094]
L
1
~
0
~
q → q(ll/lν/ νν)∼χ via l/ ∼
ν ≥ 2 lep. SS [2307.01094]
L

1

0
~
q → q(ττ/ τν/ νν)∼χ via ∼τ/ ∼ν ≥ 1 τ [1507.05525]

800

L

1500

1

0
)
(∼χ 1

~q)<m
m(

Colours indicate different models
Observed limits at 95% CL

600

1000

400

one light ~
q

500

200
0

400

600

800

500

1000 1200 1400 1600 1800 2000

1000

m~q [GeV]

1500

2000
m(~
q) [GeV]Figure 89.5: Left: 95% C.L. exclusion contours in the framework of simplified models assuming
0
a single decay chain of q̃ → q χ̃1 , obtained by the CMS collaboration. Right: Assuming more
complicated decay chains including W or Z bosons, obtained by the ATLAS collaboration.
a charm quark and a neutralino, scalar-charm masses up to 800 GeV are excluded for neutralino
masses below 260 GeV.
Table 89.1: Summary of squark mass and gluino mass limits using different interpretation approaches assuming R-parity conservation. Masses
in this table are provided in GeV. Further details about the assumptions
and analyses from which these limits are obtained are discussed in thecorresponding sections of the text.
mq̃

mg̃

-

≈ 2300no limitmχ̃0 >≈ 1600-

≈ 2440no limitmχ̃0 =01mχ̃0 >≈ 1400-

≈ 2400no limit

Model
Assumption
Simplified models g̃g̃0g̃ → q q̄ χ̃1mχ̃0 =01mχ̃0 >≈ 1200
10g̃ → bb̄χ̃1mχ̃0 =01

10g̃ → tt̄χ̃1

1

Simplified models q̃ q̃
0q̃ → q χ̃10ũL → q χ̃1mχ̃0 =0≈ 19001mχ̃0 >≈ 800 no limit-mχ̃0 =0≈ 13001mχ̃0 >≈ 600 no limit

-

1

1

A summary of the most important squark and gluino mass limits for different interpretation
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11

89. Supersymmetry, Part II (Experiment)

approaches assuming R-parity conservation is shown in Table 89.1. For gluino masses rather similar
limits of about 2.3−2.4 TeV are obtained from different model assumptions, indicating that the LHC
is indeed probing direct gluino production at the TeV scale and beyond. However, for neutralino
masses above approximately 1.2 to 1.6 TeV, even in the best case scenarios, ATLAS and CMS
searches do not place any limits on the gluino mass. Limits on direct squark production, on theother hand, depend strongly on the chosen model. For neutralino masses above ≈ 600 GeV nolimits on any direct squark pair production scenario are placed by the LHC.

89.6 Exclusion limits on bottom and top squarks masses in RPC scenarios
Besides placing stringent limits on first and second generation squark masses, the LHC experiments also search for the production of third generation squarks. SUSY at the TeV-scale is often
motivated by naturalness arguments, most notably as a solution to cancel quadratic divergences inradiative corrections to the Higgs boson mass. In this context, the most relevant terms for SUSY
phenomenology arise from the interplay between the masses of the third generation squarks andthe Yukawa coupling of the top quark to the Higgs boson. This motivates a potential constraint
on the masses of the top squarks and the left-handed bottom squark. Due to the large top quark
mass, significant mixing between t̃L and t̃R is expected, leading to a lighter mass state t̃1 and aheavier mass state t̃2 . In the MSSM, the lightest top squark (t̃1 ) can be the lightest squark.
0
Bottom squarks are expected to decay predominantly to bχ̃1 giving rise to the characteristic
missmulti b-jet and ET signature. Direct production of bottom squark pairs has been searched forat the Tevatron and at the LHC. Limits from the Tevatron are mb̃ > 247 GeV for a masslessneutralino [92, 93]. ATLAS has set a lower limit of mb̃ > 1250 GeV for massless neutralinos in thismodel [94] exploiting the two b-jets and missing transverse momentum analysis. For mχ̃0 ≈ 800 GeV
1or higher no limit can be placed on direct bottom squark pair production in this simplified model.
Limits from CMS are comparable [85]. Reinterpretations of the monojet analysis results can beused to constrain very compressed scenarios, with exclusion of masses up to 550 GeV in case of∆m = mb̃ − mχ̃0 ≈ 5 GeV [87]. Further bottom squark decay modes have also been searched1
for by ATLAS [95–97] and CMS [77, 98, 99], for instance targeting more complex decay chains that
include Higgs bosons in the cascade.
The top squark decay modes depend on the SUSY mass spectrum, and on the t̃L -t̃R mixture
0of the top squark mass eigenstate. If kinematically allowed, the two-body decays t̃ → tχ̃1 (which±
requires mt̃ − mχ̃0 > mt ) and t̃ → bχ̃ (which requires mt̃ − mχ̃± > mb ) are expected to dominate.
10
If not, the top squark decay may proceed either via the two-body decay t̃ → cχ̃1 or through0t̃ → bf f¯0 χ̃1 (where f and f¯0 denote a fermion-antifermion pair with appropriate quantum numbers).
For mt̃ − mχ̃0 > mb the latter decay chain represents a four-body decay with a W boson, charged1
˜ or light flavor squark q̃, exchange. If the exchanged W boson and/or sleptons
Higgs H ± , slepton `,0˜
are kinematically allowed to be on-shell, the three-body decays t̃ → W bχ̃1 and/or t̃ → bν `(ν̃`)
will
become dominant. For further discussion on top squark decays see for example Ref. [100].
Limits from LEP on the t̃1 mass are mt̃ > 96 GeV in the charm plus neutralino final state, and> 93 GeV in the lepton, b-quark and sneutrino final state [73].
The Tevatron experiments have performed a number of searches for top squarks, often assuming
direct pair production. In the b`ν̃ decay channel, and assuming a 100% branching fraction, limits
are set as mt̃ > 210 GeV for mν̃ < 110 GeV and mt̃ − mν̃ > 30 GeV, or mt̃ > 235 GeV for0mν̃ < 50 GeV [101, 102]. In the t̃ → cχ̃1 decay mode, a top squark with a mass below 180 GeV
is excluded for a neutralino lighter than 95 GeV [103, 104]. In both analyses, no limits on the top±
squark can be set for heavy sneutrinos or neutralinos. In the t̃ → bχ̃1 decay channel, searches fora relatively light top squark have been performed in the dilepton final state [105, 106]. The CDF
31st May, 2024

89. Supersymmetry, Part II (Experiment)12

s = 8,13 TeV, 20.3-140 fb -1

ATLAS Preliminary60~~
t1t1 production, limits at 95% CL

40
30

180

200

220

Expected limits
Data 15-18, s = 13 TeV, 140 fb -1~∼0
monojet, t1 → bff' χ
1[2102.10874]
~
∼0 ~
∼0 ~
∼0
0L, t1 → t χ / t1 → bWχ / t1 → bff' χ1

1

1[2004.14060]
~
∼0 ~
∼0 ~
∼0
1L, t1 → t χ / t1 → bWχ / t1 → bff' χ

∆

10
0

m ~
(t
1 , χ∼ 0
1 )=

700 20t

800 50600

August 2023
Observed limits

70

0
m ~
(t
,
∼
1 χ 0
∆
m ~ 1 )=(tm
1 , χ∼ 0
b +
m
1 )=
m
W

900

∆

0
m(∼
χ 1) [GeV]0experiment sets limits in the t̃ − χ̃1 mass plane for various branching fractions of the chargino decay
to leptons and for two values of mχ̃± . For mχ̃± = 105.8 GeV and mχ̃0 = 47.6 GeV, top squarks
1
1
1
between 128 and 135 GeV are excluded for W -like leptonic branching fractions of the chargino.
The LHC experiments have improved these limits substantially and developed dedicated searches
for all potential top-squark decay mode. This is well depicted in Fig. 89.6, where a summary of the0limits on the top squark mass are reported for the single decay chain of t̃ → tχ̃1 as well as for thethree-body and four-body decay modes. Interpretations are carried out in simplified models hencecare must be taken when interpreting these limits in the context of more complete SUSY models.

1

1

1

[2012.03799]
~
∼0 ~
∼0
1L NN, t1 → t χ / t1 → bWχ

500

1

1

[ATLAS-CONF-2023-043]
~
∼0 ~
∼0 ~
∼0
2L, t1 → t χ / t1 → bWχ / t1 → bff' χ
1

400

1

1

[2102.01444]
Data 15-16, s = 13 TeV, 36.1 fb -1
~
∼0 ~
∼0 ~
∼0
t1 → t χ / t1 → bWχ / t1 → bff' χ

300

1

1

1

[1709.04183, 1711.11520,

200

1708.03247, 1711.03301]~∼0
tt, t1 → t χ
1[1903.07570]

100

Data 12, s = 8 TeV, 20.3 fb -1
~
∼0 ~
∼0 ~
∼0
t1 → t χ / t1 → bWχ / t1 → bff' χ
1

200

400

600

800

1000 1200~m( t1 ) [GeV]

1

1[1506.08616]

Figure 89.6: A summary of the 95% C.L. exclusion contours in the stop-neutralino mass plane forvarious possible decay chains, including two-, three- and four-body decays, as obtained in dedicatedanalyses by ATLAS.
The most important searches for the top squark decay topology are dedicated searches requiring
miss , and four or more jets out of which at least one jet must be
zero or one isolated lepton, modest ET
reconstructed as a b-jet [52, 77, 85, 86, 107–109]. For example, using an all-hadronic analysis, CMS
excludes top squarks with masses below about 1300 GeV in this model for light neutralinos, while
for mχ̃0 > 700 GeV no limits can be provided [86]. Equivalent constraints are set by the ATLAS
1
all-hadronic search [107]. Analyses targeting final state events characterised by the presence of one
0
lepton (electron or muon) have similar albeit lower sensitivity in the t̃ → tχ̃1 decay mode, see for
instance the recent ATLAS result [109] using NN methods.
Single and di-lepton analyses are most sensitive to models where the top squark decay exclusively±±0
proceeds via the chargino mediated decay chain t̃ → bχ̃1 , χ̃1 → W ±(∗) χ̃1 . In this case, top squark±
0mass exclusion limits vary strongly with the assumptions made on the t̃ − χ̃1 − χ̃1 mass hierarchy.
0
For example, for mχ̃± = (mt̃ + mχ̃0 )/2, a stop mass below ≈ 1150 GeV for a light χ̃1 is excluded
1
1
by CMS, while no limit can be placed for mχ̃0 > 550 GeV [52]. These limits, however, can weaken
1significantly when other assumptions about the mass hierarchy or the decay of the charginos are
imposed [52, 110–112].
Other analyses with zero, one or two leptons target this kinematic region [113–119], also pro31st May, 2024

13

89. Supersymmetry, Part II (Experiment)

viding sensitivity in the case of alternative decay modes of the top squark, i.e. including tau
sleptons [112, 120–122] or Higgs and Z bosons in the decay chain [123].
±±
00
If the decays t̃ → tχ̃1 and t̃ → bχ̃1 , χ̃1 → W ±(∗) χ̃1 are kinematically forbidden, the decay chains00t̃ → W bχ̃1 and t̃ → cχ̃1 can become important. The one-lepton ATLAS search [108] provides forthe kinematic region mt̃ − mχ̃± > mb + mW lower limits on the top squark mass of ≈ 700 GeV
for a neutralino lighter than ≈ 570 GeV, as also shown in Fig. 89.6. For the kinematic regionin which even the production of real W bosons is not allowed, ATLAS and CMS improve the0
Tevatron limit on t̃ → cχ̃1 substantially. Based on a monojet analysis [87] ATLAS excludes top
0squark masses below mχ̃0 ≈ 550 GeV along the kinematic boundary for the t̃ → cχ̃1 decay. The
1
ATLAS monojet analysis also places similar boundaries for the other decay chain relevant in this0phase region, t̃ → bf f¯0 χ̃1 . Other analyses, such as the search in events with one leptons and jets,
are also sensitive to this decay mode: the ATLAS one-lepton analysis excludes up to ≈ 650 GeV for∆m = mt̃ , mχ̃0 ≈ 50 GeV [108]. The CMS collaboration uses the hadronic searches [86,114,116] to1place constraints on stop decay into charm-quark and excludes mt̃ ≈ 630 GeV for ∆m = mt̃ , mχ̃0 ≈1
050 GeV [86]. Constraints are also set in case of t̃ → bf f¯0 χ̃1 , with CMS excluding masses up to 480
and 700 GeV for ∆m = mt̃ , mχ̃0 ≈ 10 and 80 GeV, respectively [124].
10
In general, the variety of top squark decay chains in the phase space region where t̃ → tχ̃1 iskinematically forbidden represents a challenge for the experimental search program but more data
and refined analyses in Run 2 have further improved the sensitivity in this difficult but importantregion of SUSY parameter space, and more is expected for future Runs of the LHC. Precision
SM measurements can also provide important insights to such challenging regions. For instance,
analyses of tt̄ spin correlations can be used to set constraints on top squark masses close to the
top-quark mass. ATLAS [125] excludes the mass region between 150 and 230 GeV for kinematicallyallowed values of the neutralino mass. CMS [126] results cover a similar mass range.
Table 89.2: Summary of bottom and top squark mass limits using different interpretation approaches assuming R-parity conservation. Masses
in this table are provided in GeV. Further details about the assumptions
and analyses from which these limits are obtained are discussed in thecorresponding sections of the text.
Model0b̃ → bχ̃1

Assumptionmχ̃0 =01mχ̃0 >≈ 700mq̃
≈ 1250no limit0mχ̃0 =01mχ̃0 >≈ 600≈ 1300no limitmχ̃0 =01mχ̃0 >≈ 550≈ 1150no limit

1t̃ → tχ̃11±

t̃ → bχ̃1(mχ̃± = (mt̃ − mχ̃0 )/2)1
10t̃ → W bχ̃1

mχ̃0 <≈ 570(mt̃ − mχ̃0 < mW )mt̃ ≈ mχ̃0

1

≈ 700
1
(mW < mt̃ − mχ̃0 < mt )0t̃ → cχ̃1
mt̃ − mχ̃0 ≈ 50 ≈ 630
1
mt̃ ≈ mχ̃0
≈ 550
1
0
0
t̃ → bf f χ̃1mt̃ − mχ̃0 ≈ 50 ≈ 650
1

31st May, 2024

1

≈ 550

14

89. Supersymmetry, Part II (Experiment)

89.7 Exclusion limits on the masses of charginos, neutralinos and sleptons in
RPC scenarios
Charginos, neutralinos and sleptons are produced through electroweak interactions and theircross sections depend on the assumptions made for mass and mixing parameters.
Charginos and neutralinos carry no color charge and the mixing of the charged wino and higgsino
states (for charginos), and the neutral bino, wino and higgsino states (for neutralinos), is determinedby a limited number of parameters. For charginos these are the wino mass parameter M2 , thehiggsino mass parameter µ, and tan β, and for neutralinos these are the same parameters plus
the bino mass parameter M1 . If one of the parameters M1 , M2 or µ is substantially smaller thanthe others, the chargino/neutralino composition would be dominated by specific states, which arereferred to as bino-like (M1  M2 , µ), wino-like (M2  M1 , µ), or higgsino-like (µ  M1 , M2 ).
If gaugino mass unification at the GUT scale is assumed, a relation between M1 and M2 at theelectroweak scale follows: M1 = 5/3 tan2 θW M2 ≈ 0.5M2 , with θW the weak mixing angle. The
largest production rates at hadron machines are obtained when the LSP is bino-like and the lightest
chargino and next-to-lightest neutralino are wino-like, forming an approximately mass degenerateSU(2) triplet. If the higgsino mass is much smaller than the gaugino masses, the two lightest
neutralinos and the lightest chargino form an approximately mass degenerate Dirac SU(2) doublet,
production rates are lower and the mass spectrum is compressed.
In models with slepton and gaugino mass unification at the GUT scale, the superpartner ofthe right-handed lepton, `˜R , is expected to be lighter than the left-handed one, `˜L . Cross sections
depend on the L-R mixing which in turn depends on the mass of the fermion and other parameters.
For tau sleptons there may be considerable mixing between the L and R states, leading to asignificant mass difference between the lighter τ̃1 and the heavier τ̃2 .
Fig. 89.7 [127,128] (see also Ref. [74] for further details) shows typical production cross sectionsat hadron colliders for electroweakinos under various assumptions and considering a center-of-massenergy of 13 TeV. For masses of several hundreds of GeV, they are at least two orders of magnitude
smaller than for colored SUSY particles. Thanks to the large data samples collected at the LHC,
the sensitivity of LEP and Tevatron searches for direct chargino/neutralino or slepton production
has been surpassed in several regions of SUSY parameter space.
89.7.1 Exclusion limits on chargino masses±
The lightest chargino χ̃1 is searched for either considering pair production, or through associated±0
production of χ̃1 and the next-to-lightest neutralino, χ̃2 , if they are assumed to be degenerate in±˜ aremass. If kinematically allowed, two body decay modes such as χ̃ → f˜f¯0 (including `ν̃ and `ν)±00dominant. If not, three-body decays χ̃ → f f¯ χ̃1 , mediated through virtual W bosons or sfermions,become dominant. If sfermions are heavy, the W mediation dominates, and f f¯0 are distributedwith branching fractions similar to W decay products (barring phase space effects for small mass±0
gaps between χ̃ and χ̃ ). If, on the other hand, sleptons are light enough to play a significant rolein the decay, leptonic final states will be enhanced.
+ −At LEP, χ̃1 χ̃1 is the dominant production process. Charginos have been searched for in fullyhadronic, semi-leptonic and fully leptonic decay modes [129, 130]. A general lower limit on thelightest chargino mass of 103.5 GeV is derived, except in corners of phase space with low electron
sneutrino mass, where destructive interference in chargino production, or two-body decay modes,±
0play a role. The limit is also affected if the mass difference between χ̃1 and χ̃1 is small; dedicatedsearches for such scenarios set a lower limit of 92 GeV.
± 0
At the Tevatron, charginos have been searched for via associated production of χ̃1 χ̃2 [131,132].
Decay modes involving multilepton final states provide the best discrimination against the large
multijet background. Analyses have looked for at least three charged isolated leptons, for two
31st May, 2024

89. Supersymmetry, Part II (Experiment)

15

pp, s = 13 TeV, NLO+NLL(higgsino)

cross section [pb]LL+
1 1 (wino)± 0
1 2 (wino)

100

RR
L, R L, R

10 2

10 4

10 6
100

200

300

400

500 600 700
particle mass [GeV]

800

900

1000

Figure 89.7: Cross sections for pair production of charginos, neutralinos and sleptons calculated
for 13 TeV centre-of-mass energy at NLO plus next-to-leading-log (NLL) precision. Wino-like
±
+ −
0
0
0
χ̃±
1 χ̃2 and χ̃1 χ̃1 productions are calculated in a limit of mass-degenerate χ̃1 and χ̃2 , light bino χ̃1 ,and with all the other sparticles assumed to be heavy and decoupled. Higgsino-like cross sections±
00
assume mass-degenerate χ̃1 , χ̃2 and χ̃1 . For slepton pair cross sections, left(right)-handed only or
50% mixed states are considered.
leptons with missing transverse momentum, or for two leptons with the same charge. Depending±0
0
0
on the (χ̃1 − χ̃1 ) and/or (χ̃2 − χ̃1 ) mass differences, leptons may have soft transverse momentum.
At the LHC, the search strategy is similar to that at the Tevatron but it also exploits the large+ −datasets collected to target missing momentum and fully-hadronic final states and consider χ̃1 χ̃1±0
production only i.e. releasing the assumption of χ̃1 , χ̃2 mass degeneracy. Furthermore, compressed
SUSY spectra are searched for considering low-momentum leptons recoiling against an ISR jet.
Chargino pair production is searched for in the dilepton plus missing momentum final state.
+ −In a simplified model interpretation of the results where only the χ̃1 χ̃1 process is considered andassuming mediation of the chargino decay by light sleptons (ẽ and µ̃), ATLAS [133] and CMS [134]set limits on the chargino mass up to 1 TeV for massless LSPs, but no limits on the chargino mass0can be set for χ̃1 heavier than 480 GeV. Limits are fairly robust against variation of the slepton
mass, unless the mass gap between sparticles becomes small enough that the charged lepton has a
too low-momentum to be reconstructed. For decays mediated through τ̃ or ν̃τ , limits of 630 GeV
are set by ATLAS [135] for LSPs not heavier than 200 GeV. The CMS experiment provides similar
limits [136].
In case slepton masses are higher than the mass of the chargino, searches are performed forcharginos decaying via a W boson. ATLAS sets limits on this kind of simplified models [133] forpure-wino charginos: masses below 420 GeV are excluded for massless LSPs, but no limits are set
for LSPs heavier than 120 GeV. In the challenging case where the difference between chargino
and LSP masses is close to that of the W boson, dedicated searches have been carried out by
ATLAS [137], excluding chargino masses up to 140 GeV. Searches have also been carried out inthe single lepton final state. ATLAS excludes chargino masses between 260 and 520 GeV for a
massless LSP [138].
Further extension of the sensitivity in the high-mass region is achieved by ATLAS [139] and31st May, 2024

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89. Supersymmetry, Part II (Experiment)

CMS [140] exploiting the large branching ratio of fully-hadronic final states and the identificationof boosted W bosons through large-radius jets and jet substructure information. Considering only
wino-like chargino pair production in case of a massless LSP, ATLAS excludes a region between
630 GeV and 760 GeV, while CMS excludes between 290 GeV and 670 GeV. No limits are set for
LSP masses above 200 GeV.
Several final states characterised by the presence of missing transverse momentum are studied± 0±
to set limits on the chargino mass through χ̃1 χ̃2 associated production. Usually, wino-like χ̃100and χ̃2 and bino-like χ̃1 are assumed with mχ̃± = mχ̃0 , leaving mχ̃± and mχ̃0 free. Again, the1211
branching fraction of leptonic final states is determined by the slepton masses. If the decay is
predominantly mediated by a light `˜L , i.e. `˜R is assumed to be heavy, the three charged-lepton
flavors will be produced in equal amounts, and a multi-lepton signature is favored. It is assumed
that `˜L and sneutrino masses are equal, and diagrams with sneutrinos are included. In this scenario,
ATLAS [141] and CMS [142] exclude chargino masses below 1450 GeV for massless LSPs; no limits
are set for LSP masses above 1 TeV. If the decay is dominated by a light `˜R , the chargino
cannot be a pure wino but needs to have a large higgsino component, preferring the decays totau leptons. Limits are set in various scenarios. If, like for `˜L , a flavor-democratic scenario isassumed (τ -enriched scenario), CMS sets limits of 1150 GeV on the chargino mass for massless±
0LSPs, but under the assumption that both χ̃1 and χ̃2 decay leads to tau leptons in the final state(τ -dominated scenario), the chargino mass limit deteriorates to 970 GeV for massless LSPs [142].
ATLAS assumes a simplified model in which staus are significantly lighter than the other sleptons
and search for a similar multi-tau final state, setting a lower limit on the chargino mass of 760 GeV
in this model [135].
0
If sleptons are heavy, the chargino is assumed to decay to a W boson plus LSP, and the χ̃2 into
Z plus LSP (W Z searches) or H plus LSP (W H searches). Searches for the W Z channel exploit
events with either two same-sign leptons or three leptons, a single lepton, or with no leptons (all0hadronic). If χ̃2 decays through a Higgs boson with mH = 125 GeV, search strategies depend on the
SM-like Higgs decay modes and branching fractions. Higgs bosons in the final state are identified
by either two jets originating from bottom quarks (h → bb̄), two photons (h → γγ), or leptons from0
the W W , ZZ or τ τ decay modes. Interpretations are also provided in scenarios where the χ̃2 does
not decay exclusively into a Z or H boson and the LSP.
± 0
ATLAS has searched for χ̃1 χ̃2 production in events with three leptons and missing momentum
and wino-like chargino masses below 640 GeV are excluded for massless LSPs [143]. Results havealso been reported for searches including same-sign lepton signal regions [144] and single lepton
searches [138]. Limits are reduced in case of higgsino-like scenarios, with exclusion down to
210 GeV. CMS [142] excludes chargino masses below 650 GeV for massless LSPs using events with
two leptons of the same sign, or with three or more leptons targeting final states with W and Z
0bosons. No constraints are set for χ̃1 masses above 300 GeV.
Additional constraints on the chargino mass are placed exploiting all-hadronic analyses. A
wino-like (higgsino-like) chargino with mass up to 1060 (900) GeV is excluded by ATLAS [139]when the LSP mass is below 400 (240) GeV and the mass splitting is larger than 400 (450) GeV.
CMS [140] excludes wino-like charginos with mass up to 970 GeV for massless LSP.
Searches exploiting the presence of b-jets are most sensitive in the high-mass chargino region ifχ̃02 decays through a Higgs boson, while analyses targeting photon pair or leptonic decays provide
the best sensitivity in the region of low masses. CMS [145] sets lower limits on the chargino mass
up to 820 GeV for massless LSPs, but vanish for LSP masses above 350 GeV using events with atleast one lepton and missing transverse momentum in the final state. Similar sensitivity is achievedby the ATLAS analyses [146–148].
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89. Supersymmetry, Part II (Experiment)

In both the wino region (a characteristic of anomaly-mediated SUSY breaking models) and the±0
higgsino region of the MSSM, the mass splitting between χ̃1 and χ̃1 is small. The chargino decay
products are very soft and may escape detection. These compressed spectra are hard to detect, andhave triggered dedicated search strategies. ATLAS [149] and CMS [150] have performed searches
for charginos and neutralinos in a compressed mass spectrum using initial state radiation and two±
0or three low-momentum (soft) leptons. For wino-like charginos, assuming degenerate χ̃1 and χ̃2 ,±0exclusion contours in the chargino-mass versus ∆m(χ̃1 − χ̃1 ) plane are derived. As an example,±
0such charginos are excluded by CMS (ATLAS) below 280 (240) GeV for ∆m(χ̃1 − χ̃1 ) = 10 GeV.
Considering the higgsino model, the masses probed by CMS reach up to 215 GeV for a massdifference of 7.5 GeV and 150 GeV in the highly compressed region with a mass difference of
3 GeV. CMS has also searched for chargino-pair production through vector-boson-fusion [151],±0also targeting compressed mass spectra. Assuming degenerate χ̃1 and χ̃2 , charginos with a mass±0
below 112 GeV are excluded for ∆m(χ̃1 − χ̃1 ) = 1 GeV. CMS has published further searches forsuch compressed spectra with a soft tau lepton [152].
89.7.2 Exclusion limits on neutralino masses
In a considerable part of the MSSM parameter space, and in particular when demanding that the0
LSP carries no electric or color charge, the lightest neutralino χ̃1 is the LSP. If R-parity is conserved,
0such a χ̃1 is stable. Since it is weakly interacting, it will typically escape detectors unseen. Limits
on the invisible width of the Z boson apply to neutralinos with a mass below 45.5 GeV, but dependon the Z-neutralino coupling. Such a coupling could be small or even absent; in such a scenario
there is no general lower limit on the mass of the lightest neutralino [153]. In models with gaugino
mass unification and sfermion mass unification at the GUT scale, a lower limit on the neutralinomass is derived from limits from direct searches, notably for charginos and sleptons, and amounts
to 47 GeV [154]. Assuming a constrained model like the CMSSM, this limit increases to 50 GeV
0at LEP; however the strong constraints now set by the LHC increase such CMSSM-derived χ̃1
mass limits to well above a few hundred GeV (the latest reinterpretation only uses Run 1 data andindicates 200 GeV [155–157]).
In gauge-mediated SUSY breaking models (GMSB), the LSP is typically a gravitino, and thephenomenology is determined by the nature of the next-to-lightest supersymmetric particle (NLSP).
A NLSP neutralino will decay to a gravitino and a SM particle whose nature is determined by theneutralino composition. Final states with two high pT photons and missing momentum are searched
for, and interpreted in gauge mediation models with bino-like neutralinos [158–164].
Assuming the production of at least two neutralinos per event, neutralinos with large non-binocomponents can also be searched for by their decay in final states with missing momentum plus
any two bosons out of the collection γ, Z, H. A number of searches at the LHC have tried to0cover the rich phenomenology predicted by the general gauge mediation model (GGM) where χ̃1might decay with various BR in the Z and H decay modes [98, 147, 161, 165–175]. As an example,
strong constraints for decay modes involving Z and H bosons arise from full-hadronic searcheson higgsino-like scenarios: ATLAS [139] excludes higgsino production with decays into a masslessgravitino LSP in a mass range between 450 (500) GeV and 940 (850) GeV assuming BR = 1 (0.5)
for the Z plus gravitino decay mode. Assuming only H plus gravitino decays, CMS [176] excludes
a higgsino mass range between 175 GeV and 1025 GeV. Assuming a mix of γ, Z, H decays, a CMS
search [164] in the photonic final state excludes higgsinos up to 1.05 TeV.
0
Heavier neutralinos, in particular χ̃2 , have been searched for in their decays to the lightest±
0
neutralino plus a γ, a Z boson or a Higgs boson. Limits on electroweak production of χ̃2 plus χ̃1from all-hadronic, same-sign dilepton and trilepton analyses have been discussed in the section on±
0
charginos; the assumption of equal mass of χ̃2 and χ̃1 make the limits on chargino masses apply to
31st May, 2024

89. Supersymmetry, Part II (Experiment)18χ̃02 as well. Multilepton analyses have also been used to set limits on χ̃02 χ̃03 production; assuming
equal mass and decay through light sleptons, limits are set up to 680 GeV for massless LSPs [177].
Again, compressed spectra with small mass differences between the heavier neutralinos and the
LSP form the most challenging region.
00
In χ̃2 decays to χ̃1 and a lepton pair, the lepton pair invariant mass distribution may show a00structure that can be used to measure the χ̃2 − χ̃1 mass difference in case of a signal [38]. This
structure, however, can also be used in the search strategy itself, as demonstrated by ATLAS[178, 179] and CMS [98, 180].
Fig. 89.8 summarizes some of the most recent results from ATLAS and CMS for chargino
pair or chargino and next-to-lightest neutralino pair productions comparing results obtained withvarious assumptions. The limits on weak gauginos in simplified models are also summarized inTable 89.3. Only results for promptly decaying charginos and neutralinos are included: limits fromsearches focusing on long-lived particle scenarios are reported in Section 89.9. A combination ofseveral searches for the electroweak production of winos, binos, higgsinos, and sleptons has also
been recently been presented by CMS [181].
Interpretations of the search results outside simplified models, such as in the phenomenological
MSSM [182–187], show that the simplified model limits can translate into accurate constraints but
must also be interpreted with care. Electroweak gauginos in models that are compatible with therelic density of dark matter in the Universe, for example, have particularly tuned mixing parametersand mass spectra, which are not always captured by the simplified models used.
~∼ ) = 1 [ m( χ∼0 ) + m( χ∼± , χ
∼0 ) ]
m( lL/ ∼τL/ ν
1
1
2
2

137 fb (13 TeV)

SUS-21-008, Combination (WZ)
Expected
SUS-21-008, Combination (WH)∼∼
Observed
2106.14246, 2l SS +≥ 3l (χ±1χ02→∼τ ν~τ∼
τ , xl=0.5)∼∼∼
02106.14246, 2l SS +≥ 3l (χ1±χ2→lν ll, BF(ll)=0.5, xl=0.5)

1000

m
∼+
mχ
0

∼0 1
m χ 0+m Z
∼χ 1
=

800

∼ ±1
mχ ±= m
∼χ 1

=
∼
mχ
±

H

450

March 2023

s=13 TeV, 36.1-139 fb-1

All limits at 95% CL
Expected limits

400
350
300

1

ATLAS Preliminary

1

Observed limits
m( ∼
χ0
2 )=
m( ∼
m( ∼
χ0
χ 0
1 )
m( ∼2 ) =
m( ∼
χ0
2 )=
χ 0
m( ∼1 ) +
m(
χ 0
Z
1 )+
m( )
h)

1200

CMS Preliminary

June 2023-1m( ∼χ10 ) [GeV]

1400

0
1

m ∼χ [GeV]∼ ∼pp → χ02 χ±1

± 0
∼
χ1 ∼
χ2 viaWZ 0l, 2l, 3l
arXiv:1806.02293
arXiv:1911.12606
arXiv:2106.01676

250

arXiv:2108.07586

m

arXiv:2204.13072

200

600

Wh lbb, 0l
arXiv:1909.09226

150

400

arXiv:2108.07586∼
χ+1 ∼χ1− via100200

WW 0l, 2l
arXiv:1908.08215

500

arXiv:2209.13935
arXiv:2108.07586

200

400

600

800

1000

1200

1400

0
100 200 300 400 500 600 700 800 900 1000 1100

∼ ,∼
m( χ
χ20 ) [GeV]1±m∼χ =m∼χ [GeV]
0
2

±
1

Figure 89.8: LHC exclusion limits on chargino and neutralino masses in a number of simplified
models. Left: CMS limits on chargino and neutralino masses for pair production of charginos, pair
production of heavier neutralinos, or pair production of chargino and neutralino, under a varietyof assumptions including light sleptons mediating the decays. Right: ATLAS limits on chargino
and neutralino masses for pair production of chargino and neutralino, under the assumption of
decoupled sleptons, and chargino/neutralino decay through on- or off-shell W and Z or H.
89.7.3 Exclusion limits on slepton masses
The most model-independent searches for selectrons, smuons and staus originate from the LEP
experiments [188]. Smuon production only takes place via s-channel γ ∗ /Z exchange. Search results
are often quoted for µ̃R , since it is typically lighter than µ̃L and has a weaker coupling to the0
Z boson; limits are therefore conservative. Decays are expected to be dominated by µ̃R → µχ̃1 ,31st May, 2024

89. Supersymmetry, Part II (Experiment)

19

Table 89.3: Summary of weak gaugino mass limits in simplified models, assuming R-parity conservation. Masses in the table are provided in
GeV. Further details about assumptions and corresponding analyses are
discussed in the text. Details on constraints for compressed scenarios fromsoft-lepton searches are not represented in the table.
mχ> 92> 103.5

Assumption±0χ̃±
1 , all ∆m(χ̃1 , χ̃1 )χ̃±
1 ∆m > 5, mν̃ > 300

χ̃±= (m ± + mχ̃0 )/2
1 , m(`,ν̃)
˜
χ̃1

1

mχ̃0 ≈ 0> 10001χ̃±
1 , mχ̃0 > 480
1χ̃±
1 , m`˜ > mχ̃±1

no LHC limitmχ̃0 ≈ 01
χ̃±
1 , mχ̃0 > 120> 420 and 290 − 760
no LHC limit1mχ̃± = mχ̃0 , m`˜L = (mχ̃± + mχ̃0 )/2
2
1
1
1mχ̃0 ≈ 01
mχ̃0 > 10001mχ̃± = mχ̃0 , m`˜R = (mχ̃± + mχ̃0 )/2
2
1
1
1mχ̃0 ≈ 01
mχ̃0 > 700
1mχ̃± = mχ̃0 , mτ̃ = (mχ̃± + mχ̃0 )/2
2
1
1
1mχ̃0 ≈ 01
mχ̃0 > 4501mχ̃± = mχ̃0 , m`˜ > mχ̃± , BF(W Z) = 1
2
1
1mχ̃0 ≈ 01
mχ̃0 > 300
1mχ̃± = mχ̃0 , m`˜ > mχ̃± , BF(W H) = 1
2
1
1±mχ̃0 ≈ 0, wino-like χ̃1> 1450no LHC limit
flavor-democratic> 1150no LHC limitτ̃ -dominated> 970
no LHC limit> 960
no LHC limit> 10601±mχ̃0 ≈ 0, higgsino-like χ̃11mχ̃0 > 400(240)1> 900
no LHC limit wino(higgsino)-likeleading to two non-back-to-back muons and missing momentum. Slepton mass limits are calculated
in the MSSM under the assumption of gaugino mass unification at the GUT scale, and depend on0
the mass difference between the smuon and χ̃1 . A µ̃R with a mass below 94 GeV is excluded formµ̃R − mχ̃0 > 10 GeV. The selectron case is similar to the smuon case, except that an additional
1
production mechanism is provided by t-channel neutralino exchange. The ẽR lower mass limit is
100 GeV for mχ̃0 < 85 GeV. Due to the t-channel neutralino exchange, ẽR ẽL pair production1
was possible at LEP, and a lower limit of 73 GeV was set on the selectron mass regardless ofthe neutralino mass by scanning over MSSM parameter space [189]. The potentially large mixing
between τ̃L and τ̃R not only makes the τ̃1 light, but can also make its coupling to the Z boson
0
small. LEP lower limits on the τ̃ mass range between 87 and 93 GeV depending on the χ̃1 mass,for mτ̃ − mχ̃0 > 7 GeV [188].
1

31st May, 2024

20

89. Supersymmetry, Part II (Experiment)m(χ01̃ ) [GeV]At the LHC, pair production of sleptons is not only heavily suppressed with respect to pair
production of colored SUSY particles but the cross section is also almost two orders of magnitude
smaller than the one of pair production of charginos and neutralinos. With the full data sets ofRun 1 and Run 2, however, ATLAS and CMS have surpassed the sensitivity of the LEP analyses
under certain assumptions.
ATLAS and CMS have searched for direct production of selectron pairs and smuon pairs at0
the LHC, with each slepton decaying to its corresponding SM partner lepton and the χ̃1 LSP. In
simplified models, ATLAS [133] and CMS [180] set lower mass limits on sleptons of 700 GeV for0degenerate `˜L and `˜R , for a massless χ̃1 and assuming equal selectron and smuon masses, as shown
0
in Fig. 89.9. The limits deteriorate with increasing χ̃1 mass due to decreasing missing momentum0
and lepton momentum. As a consequence, no limits are set for χ̃1 masses above 400 GeV. Limits
are also derived without the assumption of slepton mass degeneracy [133, 190]. A dedicated search0for sleptons with small mass difference between `˜ and χ̃1 is performed by ATLAS [149] demanding
the presence of ISR jets. Although no sensitivity is achieved for intermediate mass differences
between the slepton and the LSP, slepton masses up to 260 GeV are excluded for slepton-LSP
mass differences of 10-20 GeV. ATLAS [137] followed up with a dedicated search in the challenging
regime where the mass difference between the slepton and the LSP is close to the W mass. Sleptons
with masses up to 150 GeV are excluded for a mass-splitting between the sleptons and the LSP of
50 GeV.
600
500
400

August 2023

ATLAS
Preliminaryps = 13 TeV, 140 fb−1

̃ χ0̃
pp→ℓL,̃+ RℓL,̃− R, ℓ→ℓ
1

All limits at 95% CL
Observed limits
Expected limits

300)<

8 TeV, 20.3 fb−1

Soft 2ℓ2ℓ
2ℓ, Δm ≈ m(W)ℓ ̃ ∈ [e,̃ μ]̃

arXiv:1403.5294ℓ ̃ ∈ [e,̃ μ]̃
ℓ ̃ ∈ [e,̃ μ]̃

arXiv:1911.12606
arXiv:1908.08215ℓ ̃ ∈ [e,̃ μ]̃

arXiv:2209.14035

2τ hadronicℓ ̃= τ ̃
LEP μR̃ excluded

ATLAS-CONF-2023-029

0̃ )
(χ 1
m

̃ ,R
(ℓ L
m

200
100
0

100

200

300

400

500

600

700

800

m(ℓL,̃ R) [GeV]

Figure 89.9: LHC exclusion limits on slepton (selectron, smuon and stau) masses, assuming
equal masses of selectrons and smuons, degeneracy of `˜L and `˜R , and a 100% branching fraction0for `˜ → `χ̃1 .
ATLAS and CMS have also searched for τ̃ -pair production. In simplified models, ATLAS
0
excludes τ̃ masses between 120 and 390 GeV assuming light χ̃1 , combining the production ofdegenerate left- and right-handed τ̃ s [191]. The CMS analysis [192] covers lower masses and closes
the mass gap with LEP. In a search for hadronic final states, CMS [193] excludes purely left-handedτ̃ s with masses between 115 and 340 GeV for massless LSP. A recent ATLAS search [194] for staupair production in the fully hadronic final state excludes, for a massless LSP, degenerate left- andright-handed τ̃ s with masses up to 480 GeV, purely left-handed τ̃ s with masses up to 410 GeV andpurely right-handed τ̃ s with masses up to 330 GeV.
31st May, 2024

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89. Supersymmetry, Part II (Experiment)

In gauge-mediated SUSY breaking models, sleptons can be (co-)NLSPs, i.e., the next-to-lightest
SUSY particles and almost degenerate in mass, decaying to a lepton and a gravitino. This decay caneither be prompt, or the slepton can have a non-zero lifetime. Combining several analyses, lower
mass limits on µ̃R of 96.3 GeV and on ẽR of 66 GeV are set for all slepton lifetimes at LEP [195]. In
a considerable part of parameter space in these models, the τ̃ is the NLSP. The LEP experiments
have set lower limits on the mass of such a τ̃ between 87 and 97 GeV, depending on the τ̃ lifetime.
ATLAS and CMS have searched for final states with τ s, jets and missing transverse momentum,
and have interpreted the results in GMSB models setting limits on the model parameters [196,197].
CMS has interpreted a multilepton analysis in terms of limits on gauge mediation models withslepton NLSP [198]. CDF has put limits on gauge mediation models at high tan β and slepton
NLSP using an analysis searching for like-charge light leptons and taus [199].
The invisible width of the Z boson puts a lower limit on the sneutrino mass of about 45 GeV.
Tighter limits are derived from other searches, notably for gauginos and sleptons, under the assumption of gaugino and sfermion mass universality at the GUT scale, and amount to approximately
94 GeV in the MSSM [200].
The limits on sleptons in simplified models are summarized in Table 89.4.
Table 89.4: Summary of slepton mass limits from LEP and LHC, as0
suming R-parity conservation and 100% branching fraction for `˜ → `χ̃1 .
Masses in this table are provided in GeV.
Assumptionm`˜
0µ̃R , ∆m(µ̃R , χ̃1 ) > 10
> 94
0ẽR , ∆m(ẽR , χ̃1 ) > 10
> 94
ẽR , any ∆m> 730τ̃R , ∆m(τ̃R , χ̃1 ) > 7
> 87
0
χ̃
ν̃e , ∆m(ẽR , 1 ) > 10
> 94
mẽL,R = mµ̃L,R , mχ̃0 ≈ 0> 700
1mχ̃0 >≈ 400
no LHC limit
1mτ̃L = mτ̃R , mχ̃0 ≈ 0> 480
1mχ̃0 >≈ 200
no LHC limit
1mτ̃L , mχ̃0 ≈ 0> 410
1mχ̃0 >≈ 150
no LHC limit
1mτ̃R , mχ̃0 ≈ 0> 330
1mχ̃0 >≈ 100
no LHC limit
189.8 Exclusion limits on promptly decaying sparticle masses in RPV scenarios
The large variety of possible configurations for non-zero λ, λ0 and λ00 couplings in RPV SUSY
scenarios leads to a huge number of potential signatures to be investigated in the strong andelectroweak sectors. The lightest supersymmetric particle can be any particle, although most of themodels considered at the LHC assume that to be the lightest neutralino, and can decay promptly or
displaced. Cascade decays of sparticles down to the LSP can also be prompt or displaced dependingon the strength of the couplings involved, although typically such cascades are dominated by gauge
couplings which are prompt. In this section, we review dedicated searches for scenarios with small
non-zero RPV couplings but still large enough to allow prompt decays of the sparticles involved(see Section 89.9 for examples of dedicated signatures searches for non-prompt decays).
31st May, 2024

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89. Supersymmetry, Part II (Experiment)

Prompt RPV gluino and squark decays are searched for in final states generally characterisedby the presence of multiple leptons or jets and moderate or no missing transverse momentum.
Searches in multilepton final states [90, 166, 201–205] set lower gluino mass limits between 1
and 2.5 TeV for decays mediated by λ and λ0 couplings, with strong dependence on the couplings
involved, the neutralino mass and the lepton flavor. Multijet final states have been used to search
for fully hadronic gluino decays involving λ00 couplings, by CDF [206], ATLAS [96, 207–210] andCMS [211–213]. Lower gluino mass limits range between 600 and 2000 GeV depending on neutralinomass and flavor content of the final state. ATLAS [214] also searched in events characterised byhigh jet multiplicity, at least one isolated light lepton and either zero or at least three b-tagged
jets, reaching as high as 2.4 TeV in gluino mass. If gluinos decay via top squark into tbd final
states through a non-zero λ00313 coupling, a search for same-sign/three-lepton events can be effective.
ATLAS [90] sets a lower limit of 1.65 TeV for a top squark with a mass below 1.45 TeV.
RPV production of single squarks via a λ0 -type coupling has been studied at HERA. In suchmodels, a lower limit on the squark mass of the order of 275 GeV has been set for electromagneticstrength-like couplings λ0 = 0.3 [215]. At the LHC, prompt [202,205,216] R-parity violating squark
decays have been searched for, with mass limits very model-dependent.
Dedicated searches for RPV top squarks (at production and/or in decays) have been carried out
in the past decades. Production of single top squarks has been searched for at LEP, HERA, andthe Tevatron. For example, an analysis from the ZEUS collaboration [217] makes an interpretation±of its search result assuming top squarks to be produced via a λ0 coupling and decay either to bχ̃1or R-parity-violating to a lepton and a jet. Limits are set on λ0131 as a function of the top squark
mass in an MSSM framework with gaugino mass unification at the GUT scale. CMS and ATLAS
have performed several searches for top squarks using a variety of multilepton and/or multijet final
states and Run 2 data. The λ0 -mediated top squark decay t̃ → b` has been studied by ATLAS for
prompt decays [218], and by ATLAS and CMS for non-prompt decays [219–221], setting limits up
to 1.4 − 1.6 TeV in simplified models for this mode. CMS also searched for the λ0 -mediated decayt̃ → b`qq, setting lower stop mass limits of 890 GeV (e) or 1000 GeV (µ) [222]. The fully hadronic
R-parity violating top squark decays t̃ → bs, t̃ → ds, and t̃ → bd, involving λ00 , have been searched
for by ATLAS [202, 208, 223–225], and CMS [226, 227]. Other recent searches target top squarks
decaying through cascades into several b− and light-quarks, for example as in [228]. The mostrecent results set lower top squark mass limits up to 1.35 TeV in top-squark mass [214] if decays
include top- and b-quarks [214] lower top squark mass limits are up to 1.35 TeV in top-squark
mass. Constraints on masses up to 670 GeV are found if the top squarks decays include top- andlight-quarks [229].
Various searches for multi-lepton and lepton plus jets events are interpreted in a model with RPV
decays of charginos and neutralinos (including the LSP) involving a non-zero λ [166, 201, 205] or
λ0 [202,210,230,231] coupling. Neutralino decays involving non-zero λ00 lead to fully hadronic final
states, and searches for multi-jet events and jet-pair resonances are used to set limits, typicallyon the production of colored particles like top squarks or gluinos, which are assumed to be theprimary produced sparticles in these interpretations, as discussed earlier. For instance, the ATLAS
search [214] in events with one lepton and high jet multiplicity excludes up to 320 (365) GeV in
higgsino (wino) masses. If top quarks arise in the decay of the neutralino, lepton-enriched final
state events are also relevant, see for example preliminary results in [144]. The multilepton searchin [232] set limits on the production of charginos and neutralinos for a minimal SUSY model with
an approximate B − L symmetry. In this case, charginos and neutralinos with masses between
100 GeV and 1.1 TeV are excluded depending on the assumed decay BR into a lepton plus a W, Z
or H boson. Finally, recent results from ATLAS [144] set the first experimental constraints on
31st May, 2024

89. Supersymmetry, Part II (Experiment)

23

bilinear RPV models (bRPV) with degenerate higgsino masses exploiting same-sign/three-lepton
signatures, excluding masses smaller than 440 GeV.
Limits also exist on sleptons in RPV models, both from LEP and the Tevatron experiments.
From LEP, lower limits on µ̃R and ẽR masses in such models are 97 GeV, and the limits on thestau mass are very close: 96 GeV [233]. CMS has searched for resonant smuon production in a
modified CMSSM scenario [234], putting limits on λ0211 as a function of m0 , m1/2 . Production ofpairs of sneutrinos in R-parity violating models has been searched for at LEP [233]. Assuming
fully leptonic decays via λ-type couplings, lower mass limits between 85 and 100 GeV are set. At
the Tevatron [235, 236] and at the LHC [234, 237–239], searches have focused on scenarios withresonant production of a sneutrino decaying to eµ, µτ and eτ final states. Limits have been set on
sneutrino masses as a function of the value of relevant RPV couplings. As an example, the LHC
experiments exclude a resonant tau sneutrino with a mass below 3.9 TeV for λ312 = λ321 > 0.07
and λ0311 > 0.11 [240].
Formulating a general assessment of the existing bounds on RPV SUSY models is becoming increasingly important in order to evaluate loopholes and potential new search directions. A
classification of all potential RPV signatures at the LHC for small couplings has been recently
published [241] to evaluate the coverage of the most general RPV-MSSM setup, without making
any assumptions about the sparticle spectrum details. Small RPV couplings imply that sparticles
are pair-produced at the LHC as in the RPC-MSSM case. Figure 89.10 shows a summary of the
95% C.L. limits on sparticle masses in RPV models for two types of λ couplings, compared to thedirect production mass bound when the sparticle under consideration is the LSP. This is done toquantify the impact of possible assumptions made on the nature, mass and coupling choices for the
LSP which in turn might lead to different leptons, jets and top-quark multiplicities. As underlinedin [241], changes in exclusion limits on sparticle masses are at most around 20%.
eµe
Ip̃→q̃

eµe
Ip̃→
W̃

eµe
Ip̃→
B̃

eµe
Ip̃→τ̃

eµe
Ip̃→q̃
3

eµe
Ip̃→
H̃

eµe
Ip̃→
`˜

Dp̃eµe

mg̃

mg̃

mq̃

mq̃

mq̃3

mq̃3

mW̃

mW̃

mH̃

mH̃

m`/ν̃
˜

m`/ν̃
˜

mτ̃ /ν̃τmτ̃ /ν̃τ
0.5

1.0

1.5
[TeV]

2.0

2.5

0.0

τ eτ
Ip̃→q̃

τ eτ
Ip̃→
W̃

τ eτ
Ip̃→
B̃

τ eτ
Ip̃→τ̃

τ eτ
Ip̃→q̃
3

τ eτ
Ip̃→
H̃

τ eτ
Ip̃→
`˜

Dp̃τ eτ

0.5

1.0
1.5
[TeV]

2.0

2.5

Figure 89.10: Summary of 95% C.L. limits on sparticle masses in RPV models, for λ121 (left),and for λ313 (right). The vertical red line represents the direct production mass bound when thesparticle under consideration is the LSP.
Finally, RPV signatures are often similar to signatures of Stealth SUSY [242–244]. In these
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89. Supersymmetry, Part II (Experiment)

scenarios, squarks can decay to a quark and a chargino (neutralino), which can subsequently decay
to a singlino S̃ and a W ± (photon), with the S̃ decaying to two gluons and a soft gravitino G̃.
Dedicated CMS searches [245, 246] exclude squark masses up to 1.85 TeV in the photon channel
and up to 550 GeV in the charged lepton channel. Gluino masses up to 2.1 TeV are excluded in thedi-photon channel [246]. Limits have also been placed on top squarks in stealth SUSY scenarios,
where the top squark decays to a top quark, a gluon and a S̃, and the S̃ subsequently decays to aG̃ and two gluons. In such a scenario, top squark masses up to 870 GeV have been excluded by
CMS [229].

89.9 Exclusion limits on long-lived sparticles
Long-lived sparticles arise in many different SUSY models. In particular in co-annihilation
scenarios, where the NLSP and LSP are nearly mass-degenerate, this is rather common in orderto obtain the correct Dark Matter relic density. Prominent examples are scenarios featuring stau
co-annihilation, or models of SUSY breaking, e.g. minimal anomaly-mediated SUSY breaking(AMSB), in which the appropriate Dark Matter density is obtained by co-annihilation of the LSP
with an almost degenerate long-lived wino. R-parity violating SUSY models might also lead to nonprompt decays. Searches for events with a displaced hadronic vertex, with or without a matched
lepton, are for instance interpreted in a model with RPV neutralino decays involving a non-zero
λ0 coupling [231]. However, in general, other sparticles can also be long-lived and it is desirable toestablish a comprehensive search program for these special long-lived cases, which lead to distinct
experimental search signatures. Past experiments have performed dedicated searches for long-lived
SUSY signatures, but given the absence of any experimental evidence for SUSY so far, more effort
and focus has gone into such searches at the LHC recently. Signatures interpreted in terms of SUSY
models include disappearing tracks, identification of tracks with atypical properties or unusual
ionization, small and localized deposits of energy inside of the calorimeters without associatedtracks, or stopped particles that decay out of time with collisions. Some examples are reported
below with interpretations provided for gluinos, squarks and electroweak SUSY particles in a varietyof SUSY models.
If the decay of gluinos is suppressed, for example if squark masses are high, gluinos may live
longer than typical hadronization times. It is expected that such gluinos will hadronize to long-living
strongly interacting particles known as R-hadrons. In particular, if the suppression of the gluino
decay is strong, as in the case that the squark masses are much higher than the TeV scale, these Rhadrons can be (semi-)stable in collider timescales. Searches for such R-hadrons exploit the typicalsignature of stable charged massive particles in the detector. R-hadrons decaying in the detector
are searched for using dE/dx measurements and searches for displaced vertices. As shown in the left
plot of Fig. 89.11, the ATLAS experiment excludes semi-stable gluino R-hadrons with masses below
1.9 − 2.3 TeV for all lifetimes in a simplified model where such gluinos always form R-hadrons,
and decay into jets and a light neutralino, by combining a number of analyses [208, 247–250].
A combination of CMS searches for long-lived particles, as shown in Fig. 89.12, reaches similar
limits [251–255].
Alternatively, since such R-hadrons are strongly interacting, they may be stopped in thecalorimeter or in other material, and decay later into energetic jets. These decays are searched
for by identifying the jets [256–258] or muons [258] outside the time window associated with bunchbunch collisions. As shown in Fig. 89.12, the CMS collaboration sets limits on such stopped
R-hadrons over 13 orders of magnitude in gluino lifetime, up to masses of 1390 GeV [258]. Recent
results from ATLAS [259] sets constraint on the mass of gluino R-hadrons using large out-of-timeenergy deposits in the calorimeters. Also in this case, masses of up to 1.4 TeV are excluded for
gluino lifetimes of 10−5 − 103 s.
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89. Supersymmetry, Part II (Experiment)

1

3000

August 2023

1

-1

RPC 0L 2-6 jets (36 fb )-1
RPC 0L 2-6 jets (36 fb )Displaced vertices (33 fb-1)
Pixel dE/dx (140 fb-1)
Pixel dE/dx, calo ToF (140 fb-1)-1
Stable charged (36 fb )-1
Stopped gluino (103 fb )ATLAS Preliminary

arXiv:1712.02332
ATLAS-CONF-2018-003
arXiv:1710.04901
arXiv:2205.06013
ATLAS-CONF-2023-044
arXiv:1902.01636
arXiv:2104.03050

Expected
Observed0±~ ± → π± ∼
~0
∼
χ [~W
χ [~W
]
]
1

1600

March 2022

1

ATLAS Preliminary

Expected limits
Observed limits

136 fb-1, s=13 TeV
Disappearing track arXiv:2201.02472

95% CL limits
σSUSY
not included
theory1~) [GeV]
Lower limit on m(g00~g (R-hadron) → qq ∼
χ ; m( ∼χ ) = 100 GeV±
Lower limit on m(∼χ ) [GeV]25-1

s=13 TeV, 36-140 fb
95% CL limits

2500

2000

1400

36 fb-1, s=13 TeV
Stable charged

arXiv:1902.01636

140 fb-1, s=13 TeV

1200

Pixel dE/dx

arXiv:2205.06013

1000
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1500

10−2

10−1

1

103

102

10

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10−2

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(r for η=0, βγ =1)(r for η=0, βγ =1) Beampipe Inner Detector Calo MS

10−3

StableStable1000

Prompt

400

−2

1

10

103

102

−1

10

104
cτ [m]

10

Inner Detector

10

Calo

1

MS

τ [ns]

10cτ [m]

Figure 89.11: Limits at 95% C.L. on the gluino mass in R-hadron models (left), and on the
chargino mass in a model where the wino-like chargino is almost degenerate with the LSP (right),
as a function of gluino or chargino lifetime, as obtained by ATLAS.

Overview of CMS long-lived particle searches
SUSY RPV

UDD, g tbs, mg = 2500 GeV
UDD, g tbs, mg = 2500 GeV
UDD, t dd, mt = 1600 GeV
UDD, t dd, mt = 1600 GeV
LQD, t bl, mt = 600 GeV
LQD, t bl, mt = 460 GeV
LQD, t bl, mt = 1600 GeV

SUSY RPCGMSB, g gG, mg = 2450 GeVg
GMSB, g gG, mg = 2100 GeVgSplit SUSY, g qq 10, mg = 2500 GeVg
0Split SUSY, g qq 1 , mg = 1300 GeVgSplit SUSY (HSCP), fgg = 0.1, mg = 1600 GeV
g
mGMSB (HSCP) tan = 10, > 0 , m = 247 GeV
0
Stopped t, t t 1 , mt = 700 GeVt
Stopped g, g qq 10, fgg = 0.1, mg = 1300 GeVg
Stopped g, g qq 20( 10), fgg = 0.1, mg = 940 GeVg±
AMSB, ± 10 ± , m ± = 700 GeV
g qq 10 or qu/d qd/u 1±, 1± 10 ± , mg = 1600GeV,m 10 = 1575GeV 1±
0
0 ±
±
0
±
q q 1 or q 1 , 1 1 , mq = 2000 GeV, m 10 = 1000 GeV 1±±
t t 10 or b 1± , 1± 10 ± , mt = 1100 GeV, m 10 = 1000 GeV
1
0
GMSB, 10 HG(50%)/ZG(50%), m 10 = 600 GeV
1
0
GMSB, 10 HG(50%)/ZG(50%), m 10 = 300 GeV
1
0GMSB SPS8, 10 G, m 10 = 400 GeV
1
GMSB, co-NLSP, l lG, ml = 270 GeVlHiggs+OtherCMS Preliminary

H ZDZD(0.1%), ZD , mH = 125 GeV, mX = 20 GeV
H ZDZD(0.1%), ZD (15.7%), mH = 125 GeV, mX = 5 GeV
H XX(10%), X ee, mH = 125 GeV, mX = 20 GeV
H XX(0.03%), X ll, mH = 125 GeV, mX = 30 GeV
H XX(10%), X bb, mH = 125 GeV, mX = 40 GeV
H XX(10%), X bb, mH = 125 GeV, mX = 40 GeV
H XX(10%), X bb, mH = 125 GeV, mX = 40 GeV
H XX(10%), X , mH = 125 GeV, mX = 7 GeV
dark QCD, m DK = 5 GeV, mXDK = 1200 GeVMarch 2023

2104.13474 (Jets with displaced vertices)
0.0006 0.09 m
2012.01581 (Displaced jets)
0.003 1 m
2104.13474 (Jets with displaced vertices)
0.00035 0.08 m
2012.01581 (Displaced jets)
0.002 1.32 m
1808.05082 (2 + 2 jets)<0.031 m
2110.04809 (Displaced leptons)
0.0001 10 m
2012.01581 (Displaced jets)
0.005 0.24 m

g
g
t
t
t
t
t
10 7

10 5

1802.02110 (Jets + MET)

2012.01581 (Displaced jets)
c 0.006[m] 0.55 m
1906.06441 (Delayed jet + MET)
0.32 34 m
2012.01581 (Displaced jets)
0.007 0.36 m<1 m
CMS-PAS-EXO-16-036 (dE/dx)
CMS-PAS-EXO-16-036 (dE/dx + TOF)
1801.00359 (Delayed jet)
1801.00359 (Delayed jet)
1801.00359 (Delayed )2004.05153 (Disappearing track)
0.7 30 m
1909.03460 (Disappearing tracks + jets with MT2)
0.11 10 m
1909.03460 (Disappearing tracks + jets with MT2)
0.26 2 m
1909.03460 (Disappearing tracks + jets with MT2)
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2212.06695 (Trackless jets + MET)
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0.05 24 m
1909.06166 (Delayed ( ))0.2 6 m2110.04809 (Displaced leptons)
5e-05 2.65 m
10 3

10 1

2205.08582 (Displaced dimuon)Xc [m]0.0001 0.25 m
X 2112.13769 (Displaced dimuon using scouting)1411.6977 (Displaced dielectron)X
2110.04809 (Displaced leptons)
0.001 0.12 m
X
2012.01581 (Displaced jets)
0.001 0.53 m
X
2110.13218 (Displaced jets + Z)
0.004 0.248 m
X
2107.04838 (Hadronic decays in CSCs)
X
2107.04838 (LLP decays in CSCs)
X
1810.10069 (Emerging jet + jet)0.0022 0.3 m
XDK
10 7

10 7

10 5

10 5

140 fb 1
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36 fb 1
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10 3

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c [m]

101

5e-05 5 m

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0.00012 25 m

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101

0.12 450 m>0.7 m
>7.5 m60 1.5e+13 m
50 3e+13 m
600 3.3e+12 m

132 fb 1
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13 fb 139 fb 139 fb 139 fb 1140 fb 1
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118 fb 1
132 fb 1
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137 fb 1
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16 fb 1

103

Selection of observed exclusion limits at 95% C.L. (theory uncertainties are not included). The y-axis tick labels indicate the studied long-lived particle.

Figure 89.12: Excluded regions, at 95% C.L., in the lifetimes of long-lived particles in several
models, as obtained by CMS.

Top squarks can also be long-lived and hadronize to a R-hadron, for example in the scenario
where the top squark is the next-to-lightest SUSY particle, with a small mass difference to the
LSP. Searches for massive stable charged particles are sensitive to such top squarks. Tevatron
limits are approximately mt̃ > 300 GeV [260, 261]. ATLAS sets a limit of 1340 GeV on such top
squarks [249], the CMS limits are comparable [253]. Intermediate lifetimes of top squarks decaying
through RPV coupling into a quark and a lepton are also targeted by ATLAS and CMS. Limits
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89. Supersymmetry, Part II (Experiment)

on top squarks decaying into a quark and a muon are set by ATLAS [262] using events that pass amuon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced
vertex. Masses up to 1.7 TeV are excluded for a lifetime of 0.1 ns, and masses below 1.3 TeV are
excluded for lifetimes between 0.01 ns and 30 ns. CMS [263] utilizes events with two leptons withtransverse impact parameter values between 0.01 and 10 cm not required to form a common vertex
to exclude top squarks with masses between 100 and at least 460 GeV for 0.01 < cτ0 < 1000 cm,
where cτ0 is the proper decay length.
In addition to colored sparticles, sparticles like charginos may also be long-lived, especially in
scenarios with compressed mass spectra. Charginos decaying in the detectors away from the primaryvertex could lead to signatures such as kinked-tracks, or apparently disappearing tracks, since, for±0example, the pion in χ̃1 → π ± χ̃1 might be too soft to be reconstructed. At the LHC, searches
have been performed for such disappearing tracks, and interpreted within anomaly-mediated SUSY
breaking models [264–267]. The right plot of Fig. 89.11 shows constraints for different ATLAS
searches on the chargino mass-vs-lifetime plane for an AMSB model (tan β = 5, µ > 0) in which a±0wino-like χ̃ decays to a soft pion and an almost mass-degenerated wino-like χ̃1 [249,250,265–268].
The disappearing track search [267] provides constraints also for higgsino-like models. Resultsfrom [268] exploiting anomalously large specific ionisation losses dE/dx are extrapolated to thestable regime. For a similar AMSB-like model, CMS excludes cτ values between 0.15 and 18 m
for a chargino mass of 505 GeV [264], see Fig. 89.12. Their most recent results [269] expand andimprove the constraints on masses of charginos as well as of colored sparticles by making use ofelectron and muon plus disappearing track signatures, measurements of the dE/dx ionization energy
loss of candidate tracks, and by re-analyzing the fully hadronic signatures using ML techniques.
Charginos with a lifetime longer than the time needed to pass through the detector appear as
charged stable massive particles. Limits have been derived by the LEP experiments [270], by D0
at the Tevatron [261], and by the LHC experiments [249, 271], and such charginos with mass below
1090 GeV are excluded.
In gauge mediation models, NLSP neutralino decays need not be prompt, and experiments have0
searched for late decays with photons in the final state. CDF has searched for delayed χ̃1 → γ G̃decays using the timing of photon signals in the calorimeter [272]. CMS has used the same techniqueat the LHC [273]. Results are given as exclusion contours in the neutralino mass versus lifetime
plane, and for example in a GMSB model with a neutralino mass of 300 GeV, cτ values between 10
and 2000 cm are excluded [273]. D0 has looked at the direction of showers in the electromagnetic
calorimeter with a similar goal [274], and ATLAS has searched for photon candidates that do not
point back to the primary vertex, as well as for delayed photons [275].
Charged slepton decays may be kinematically suppressed, for example in the scenario of a NLSP
slepton with a very small mass difference to the LSP. Such a slepton may appear to be a stablecharged massive particle. Interpretation of searches at LEP for such signatures within GMSB
models with a stau NLSP or slepton co-NLSP exclude masses up to 99 GeV [270]. Searches forstable charged particles at the Tevatron [260, 261] and at the LHC [249, 253] are also interpreted
in terms of limits on stable charged sleptons. The limits obtained at the LHC exclude stable staus
with masses below 430 GeV when produced directly in pairs, and below 660 GeV when staus areproduced both directly and indirectly in the decay of other particles in a GMSB model. Recent
results from ATLAS and CMS set constraints on long-lived charged slepton with intermediate
lifetimes. ATLAS searches for charged leptons with large impact parameters and exclude selectron,
smuon and stau masses up to 720 GeV, 680 GeV, and 340 GeV, respectively, in case of lifetimesof 0.1 ns. They also exclude smuons with lifetimes down to 1 ps for a smuon mass of 100 GeV, andsmuon masses up to 520 GeV are excluded for a proper lifetime of 10 ps [276]. CMS [193] targets
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89. Supersymmetry, Part II (Experiment)

long-lived stau with cτ of about 0.1 mm excluding masses between 115 and 220 GeV for the casethat the LSP is nearly massless.

89.10 Global interpretations
Apart from the interpretation of direct searches for sparticle production at colliders in terms oflimits on masses of individual SUSY particles, model-dependent interpretations of allowed SUSY
parameter space are derived from global SUSY fits. Typically these fits combine the results fromcollider experiments with indirect constraints on SUSY as obtained from low-energy experiments,
flavor physics, high-precision electroweak results, and astrophysical data.
In the pre-LHC era these fits were mainly dominated by indirect constraints. Even for very
constrained models like the CMSSM, the allowed parameter space, in terms of squark and gluino
masses, ranged from several hundreds of GeV to a few TeV. Furthermore, these global fits indicatedthat squarks and gluino masses in the range of 500 to 1000 GeV were the preferred region ofparameter space, although values as high as a few TeV were allowed with lower probabilities [277–284].
With ATLAS and CMS now probing mass scales around 1 TeV and beyond, the importance ofthe direct searches for global analyses of allowed SUSY parameter space has increased. For example,
imposing the new experimental limits on constrained supergravity models pushes the most likely
values of first generation squark and gluino masses significantly beyond 2 TeV, typically resulting inoverall values of fit quality much worse than those in the pre-LHC era [155–157, 185, 285–292]. The
measured value of mh pushes the sparticle masses upwards. Although these constrained models are
not yet ruled out, the extended experimental limits impose very tight constraints on the allowed
parameter space.
For this reason, the emphasis of global SUSY fits has shifted towards less-constrained SUSY
models. Interpretations in the pMSSM [183–187, 271, 285, 293] as well as in simplified models, havebeen useful to generalize SUSY searches, for example to redesign experimental analyses in order
to increase their sensitivity for compressed spectra, where the mass of the LSP is much closer tosquark and gluino masses than predicted by the CMSSM. As shown in Table 89.1, for neutralino
masses above 0.5 − 1 TeV the current set of ATLAS and CMS searches, interpreted in simplified
models, cannot exclude the existence of squarks or gluinos with masses only marginally above theneutralino mass. However, as these exclusion limits are defined in the context of simplified models,
they are only valid for the assumptions in which these models are defined.
Fig. 89.13 shows graphically the LHC exclusion power in the pMSSM based on searches per√formed at s = 7 and 8 TeV as reported by ATLAS [183] and CMS [184]. The plot on the left shows
the survival probability in the gluino-neutralino mass plane, which is a measure of the parameter
space that remains after inclusion of the relevant CMS search results. As can be seen, gluino masses
below about 1.2 TeV are almost fully excluded. This result agrees well with the typical exclusion
obtained at 8 TeV in simplified models for gluino production. However, as shown in the right plotof Fig. 89.13, when a similar analysis for other sparticles is performed it becomes apparent that
exclusions on the pMSSM parameter can be significantly less stringent than simplified model limits
might suggest. This is especially apparent for the electroweak sector, where even at rather low√
masses several of the pMSSM test points still survive the constraint of ATLAS searches at s =7 and 8 TeV. This again indicates that care must be taken when interpreting results from the
LHC searches and there are still several scenarios where sparticles below the 1 TeV scale are not√excluded, even when considering the most recent results at s = 13 TeV. Interpretations in thepMSSM of searches performed on the full Run 2 dataset are in preparation and will offer further
insights on the validity of constraints obtained with simplified models and, thus, guidance towards
the future LHC runs and beyond.
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1.4

0.9

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0.8
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survival probability∼0 mass [TeV]χ
1Combined, 7 + 8 TeV

Mass [GeV]

CMS

pMSSM

2000

s = 8 TeV, 20.3 fb−1

ATLAS

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89. Supersymmetry, Part II (Experiment)

28

0.1
0

~
g

~
t1

~
t2

~
b1

~
b2

~
q

0
∼
χ
1

0
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χ
2

0
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χ
3

0
∼
χ
4

∼
τ1

∼τ
2

~
l

±
∼
χ

1

±
∼
χ

0

2

Sparticle

Figure 89.13: The plot on the left shows the survival probability of a pMSSM parameter spacemodel in the gluino-neutralino mass plane after the application of the relevant CMS search results.
The plot on the right shows a graphical representation of the ATLAS exclusion power in a pMSSM
model. Each vertical bar is a one-dimensional projection of the fraction of models points excluded
for each sparticle by ATLAS analyses. The experimental results are obtained from data taken at√s = 7 and 8 TeV.

Furthermore, the discovery of a Higgs boson with a mass around 125 GeV has triggered manystudies regarding the compatibility of SUSY parameter space with this new particle (see for example [294,295]). Much of it is still work in progress and it will be interesting to see how the interplay
between the results from direct SUSY searches and more precise measurements of the properties ofthe Higgs boson will unfold in the future.

89.11 Summary and Outlook√
The absence of any observation of new phenomena at the first run of the LHC at s = 7/8 TeV,√
and after the second run at s = 13 TeV, places significant constraints on SUSY parameter
space. An overview of the current landscape of SUSY searches and limits at the LHC is shownin Figure 89.14, where a summary of results from the ATLAS experiment [296] (CMS results are
similar [297]), is reported for illustration purposes. Inclusive searches probe production of gluinos
at about 2.45 TeV, first and second generation squarks in the range of about 1 to 1.9 TeV, third
generation squarks at scales around 600 GeV to 1.2 TeV, electroweak gauginos at scales around400 − 1100 GeV, and sleptons around 700 GeV. However, depending on the assumptions made on
the underlying SUSY spectrum these limits can also weaken considerably.
√With the LHC having reached almost its maximum energy of about s = 14 TeV and analyses
explored the full Run 2 dataset, future sensitivity improvements will have to originate from moredata, the improvement of experimental analysis techniques and the focus on special signatures likethe ones arising in long-lived sparticle decays. Therefore, it is expected that the current landscapeof SUSY searches and corresponding exclusion limits at the LHC, especially for strongly produced
sparticles in RPC scenarios, will not change as rapidly anymore as it did in the past, when the
LHC underwent several successive increases of collision energy.
The interpretation of results at the LHC has moved away from constrained models like the
CMSSM towards a large set of simplified models, or the pMSSM. Quoted limits in simplified
models are only valid under the explicit assumptions made in these models. The addition of morecomprehensive interpretations in the pMSSM complement those and therefore enable an even morerefined understanding of the probed SUSY parameter space.
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ATLAS Preliminary√

ATLAS SUSY Searches* - 95% CL Lower Limits
August 2023
Model

Signature

Inclusive Searches

00 e, µmono-jet

2-6 jets
1-3 jets

ETmissETmiss

140
140

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q̃

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g̃g̃, g̃→qq̄χ̃10 e, µ2-6 jets

ETmiss140g̃g̃

1 e, µETmissETmiss

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g̃

ee, µµ0 e, µSS e, µ2-6 jets
2 jets7-11 jets
6 jetsg̃
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0-1 e, µSS e, µ3b
6 jetsETmiss

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g̃

0

g̃g̃, g̃→qq̄W χ̃10g̃g̃, g̃→qq̄(ℓℓ)χ̃10g̃g̃, g̃→qqWZ χ̃10g̃g̃, g̃→t¯t χ̃1

140

b̃1
b̃1

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b̃1

0
t˜1 t˜1 , t˜1 →tχ̃10t˜1 t˜1 , t˜1 →Wbχ̃1
˜t1 t˜1 , t˜1 →τ̃1 bν, τ̃1 →τG̃00t˜1 t˜1 , t˜1 →cχ̃1 / c̃c̃, c̃→cχ̃1ETmissETmiss0-1 e, µ1 e, µ1-2 τ0 e, µ0 e, µ≥ 1 jet

3 jets/1 b
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mono-jet

140
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140

t̃ 1

0
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t˜1 t˜1 , t˜1 →tχ̃2 , χ̃2 →Z/hχ̃1t˜2 t˜2 , t˜2 →˜t1 + Z

ETmissETmissETmissETmissETmiss

1-2 e, µ3 e, µ1-4 b
1bETmissETmiss

140
140

t̃ 1

140
140

χ̃±1 /χ̃02±
0

3rd gen. squarks
direct production

EW
directH̃ H̃ , H̃→hG̃/ZG̃+ −±Disapp. trk

0Long-lived
particles

Direct χ̃1 χ̃1 prod., long-lived χ̃1Stable g̃ R-hadron

Metastable g̃ R-hadron, g̃→qqχ̃1ℓ̃ℓ̃, ℓ̃→ℓG̃

± ∓

0

±

ETmiss140

pixel dE/dx
pixel dE/dx
Displ. lep

ETmissETmissETmiss

140
140
140

pixel dE/dx

ETmiss140χ̃1 χ̃1 /χ̃1 , χ̃1 →Zℓ→ℓℓℓ
χ̃±1 χ̃∓1 /χ̃02 → WW/Zℓℓℓℓνν00g̃g̃, g̃→qqχ̃1 , χ̃1 → qqq
00t˜t˜, t˜→tχ̃1 , χ̃1 → tbs±±
t˜t˜, t˜→bχ̃1 , χ̃1 → bbs
t˜1 t˜1 , t˜1 →bst˜1 t˜1 , t˜1 →qℓ

3 e, µ4 e, µχ̃±1 /χ̃02 /χ̃01 , χ̃0 →tbs, χ̃+1 →bbs

1-2 e, µ

1,2

140
140
140
140

1 jet

0 jets≥8 jets

ETmissMultiple≥ 4b2 e, µ1µ2 jets + 2 b
2bDV≥6 jets*Only a selection of the available mass limits on new states or
phenomena is shown. Many of the limits are based on
simplified models, c.f. refs. for the assumptions made.

Forbidden

0.55

Forbidden
0.85

2204.13072
2008.06032
2307.01094

m(χ̃1 )<500 GeV
0m(g̃)-m(χ̃1 )=300 GeV

02211.08028
1909.08457

0m(χ̃1 )<400 GeV
010 GeV<∆m(b̃1 ,χ̃1 )<20 GeV

2101.12527
2101.12527

00∆m(χ̃2 , χ̃1 )=130 GeV, m(χ̃1 )=100 GeV
0 0
0∆m(χ̃2 , χ̃1 )=130 GeV, m(χ̃1 )=0 GeV

χ̃±1

χ̃±1 /χ̃02
χ̃±1

0.34

χ̃±1
χ̃±1

0
m(χ̃1 )=0, wino-bino0m(χ̃1 )=70 GeV, wino-bino±0m(ℓ̃ ,ν̃)=0.5(m(χ̃1 )+m(χ̃1 ))
0m(χ̃1 )=00m(χ̃1 )=00χ̃m(ℓ̃ )-m( 1 )=10 GeV
0

140

χ̃01

χ̃±1 /χ̃02

0.625[BR( Zτ)=1, BR( Ze)=1][λi33 , 0, λ12k , 0]

0

323

t̃
t̃ 1

[ qq, bs]

t̃ 1
t̃ 1

[1e-10< λ′

23k

0.55
Forbidden
0.42
0.61

<1e-8, 3e-10< λ′23k <3e-9]

1.05
0.95

1.55
1.6

2.25

1.05
0.95

1908.08215
ATLAS-CONF-2023-029
1908.08215
1911.12606

BR(χ̃1 → Z G̃)=BR(χ̃1 → hG̃)=0.5

02204.13072

Pure Wino
Pure higgsino

2201.02472
2201.02472

2.05
2.2

[m(χ̃1 )=50 GeV, 1250 GeV][λ′′ =2e-4, 1e-2]

1908.08215
2004.10894, 2108.07586

To appear2103.11684
2108.07586

2205.06013
0m(χ̃1 )=100 GeV
τ(ℓ̃) = 0.1 nsτ(ℓ̃) = 0.1 nsτ(ℓ̃) = 10 ns

0.7

0.34
0.36

2106.01676, 2108.07586
1911.12606

BR(χ̃1 → hG̃)=10
BR(χ̃1 → Z G̃)=10
BR(χ̃1 → Z G̃)=10g̃
g̃ [τ( g̃) =10 ns]ẽ, µ̃
τ̃τ̃χ̃∓1 /χ̃01

0±0m(χ̃1 )=0, wino-binom(χ̃1 )-m(χ̃1 )=5 GeV, wino-bino

0.66

0.21

140
140
140
36.1
140
36.7
36.1
136

2006.05880

0.45-0.93
0.77

H̃

2108.07665

2006.05880

0.94

0.55

1805.01649
2102.10874

0

0.7

H̃
H̃
H̃

2012.03799, ATLAS-CONF-2023-043

0

0

0.48

0.26

m(χ̃1 )=500 GeVm(τ̃1 )=800 GeVm(χ̃2 )=500 GeV

0

1.06
1.0

[τ̃R , τ̃R,L ]ℓ̃ℓ̃

2004.14060, 2012.03799

m(χ̃1 )=360 GeV, m(t˜1 )-m(χ̃1 )= 40 GeV

0.42

Forbidden0m(χ̃1 )=0 GeV
0m(t˜1 ,c̃)-m(χ̃1 )=5 GeV

0.96

0.205

χ̃1 /χ̃2

1908.03122
2103.08189

m(χ̃1 )=1 GeV
01.4

0.067-1.18
0.86

Forbidden

t̃ 2

g̃
t̃

0

0

2.45

0

2101.01629

m(χ̃1 )<700 GeV

1.05

t̃ 1

2010.14293
2010.14293

m(χ̃1 ) <600 GeV
0m(g̃)-m(χ̃1 )=200 GeV

1.25

t̃ 1

2010.14293
2102.10874

0m(χ̃1 )=0 GeV
0m(χ̃1 )=1000 GeV
00.23-1.35

0.13-0.85m(χ̃1 )<400 GeV
0m(q̃)-m(χ̃1 )=5 GeVm(χ̃1 )<600 GeV

1.255

0.68

Forbidden

c̃
t̃ 1

τ̃

2.3

1.97

1.25

2b

140
140
140
140
140
140

1.15-1.95

1.15

6b
2b

χ̃±1 χ̃∓1 via WWχ̃±1 χ̃02 via Wh
χ̃±1 χ̃∓1 via ℓ̃L /ν̃0τ̃τ̃, τ̃→τχ̃10ℓ̃L,R ℓ̃L,R , ℓ̃→ℓχ̃1

0

1.85

g̃

0 e, µ2τ

Multiple ℓ/jets
ETmissee, µµ≥ 1 jetETmiss2 e, µETmissMultiple ℓ/jets
ETmiss2 e, µETmissETmiss2τ2 e, µ0 jetsETmissee, µµ≥ 1 jetETmiss0 e, µETmiss≥3b4 e, µ0 jetsETmiss0 e, µ ≥ 2 large jets ETmiss
2 e, µ≥ 2 jets ETmiss

1.0

2.2
2.2

0 e, µχ̃±1 χ̃02 via WZ

0.9

Forbiddenb̃1 b̃1 , b̃1 →bχ̃2 → bhχ̃10Reference[1×, 8× Degen.][8× Degen.]ETmiss0

s = 13 TeV

Mass limit

L dt [fb−1 ]q̃q̃, q̃→qχ̃1b̃1 b̃1

RPV

R

2205.06013
2011.07812
2011.07812
2205.06013

Pure Wino

2011.10543m(χ̃1 )=200 GeV
Large λ′′112

02103.11684m(χ̃1 )=200 GeV, bino-like

ATLAS-CONF-2018-003

0±

To appearm(χ̃1 )=500 GeV

2010.01015

BR(t˜1 →be/bµ)>20%
BR(t˜1 →qµ)=100%, cosθt =1

1710.05544
2003.11956

1710.07171

1.0

0.4-1.45
1.6

0.2-0.32

Pure higgsino

1

10−1

2106.09609

Mass scale [TeV]

Figure 89.14: Overview of the current landscape of SUSY searches at the LHC (updated on August 2023). The plot shows exclusion mass limits of ATLAS for different searches and interpretation
assumptions. The corresponding results of the CMS experiment are similar.

In this context, the limit range of 1.5 − 2.45 TeV on generic colored SUSY particles only holds
for light neutralinos, in the R-parity conserving MSSM. Limits on third generation squarks andelectroweak gauginos also only hold for light neutralinos, and under specific assumptions for decay
modes and slepton masses. Constraints in R-parity violating SUSY models strongly depend also
on the assumed non-zero couplings.
√
The next LHC runs, with s between 13 and 14 TeV and significantly larger integrated luminosities (notably the High-Luminosity LHC), will provide a large data sample for future SUSY
searches. As mentioned above, the improvement in sensitivity will largely have to come from alarger data set, and evolution of trigger and analysis techniques, since there will be no significant
energy increase at the LHC anymore. Although the sensitivity for colored sparticles will increase
somewhat as well, the expanded data set will be particularly beneficial for electroweak gaugino
searches, and for the more difficult final states presented by compressed particle spectra, stealth
SUSY, long-lived sparticles, or R-parity violating scenarios.
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