Supersymmetryat ATLASDan Tovey
University of SheffieldDan
Dan Tovey
Tovey

11

Kyoto,
Kyoto, January
January 2005
2005

Supersymmetry•

Supersymmetry (SUSY) fundamental
continuous symmetry connecting
fermions and bosons
Qα|F> = |B>,•

Qα|B> = |F>{Qα,Qβ}=-2γμαβpμ: generators of SUSY ~‘square-root’ of translations– Connection to space-time symmetry•

SUSY stabilises Higgs mass against loop
corrections (gauge hierarchy/fine-tuning
problem)– Leads to Higgs mass ≤ 135 GeV– Good agreement with LEP constraints from
EW global fits•

SUSY modifies running of SM gauge
couplings ‘just enough’ to give Grand
Unification at single scale.
Dan
Dan Tovey
Tovey

22

Kyoto,
Kyoto, January
January 2005
2005

SUSY Spectrum•

SUSY gives rise to partners of SM states with opposite spin-statistics
but otherwise same Quantum Numbers.

•

Expect SUSY
partners tohave same
masses as SM
states– Notobserved(despite best
efforts!)– SUSY must
be a broken
symmetry at
low energy•

Higgs sector
also expanded
Dan
Dan Tovey
Tovey

33

Kyoto,
Kyoto, January
January 2005
2005

SUSY & Dark Matter
m1/2 (GeV) mSugra with tanβ = 10, A = 0, μ < 001750– e.g. protects proton from1500
rapid decay via SUSY states

•

•

•

16

Universe Over-Closed

14

12
1250
Causes Lightest SUSY
Particle (LSP) to be
10
1000
absolutely stable
8
LSP neutral/weakly
750
interacting to escape6
astroparticle bounds on
500
4
anomalous heavy elements.
No REWSB
2
Naturally provides solution to 250
dark matter problem of
0
0
0
1000
2000
3000
4000
5000
6000
astrophysics / cosmologymBaer
m0 (GeV)0 (GeV)et al.
R-Parity violating models still
LEP2 excluded
possible Î not covered here. mh=114.1GeV

m1/2 (GeV)

•

18

Dan
Dan Tovey
Tovey

GENIUS
44

CDMSIIKyoto,
CDMS
2005
Kyoto, January
January2005

ln(χ2/DOF)

2000

~

R-Parity Rp = (-1)3B+2S+L
Conservation of Rp(motivated e.g. by stringmodels) attractive

Ζ1 not LSP••SUSY @ ATLAS••

LHC will be a 14 TeV proton-proton
collider located inside the LEP
tunnel at CERN.
Luminosity goals:– 10 fb-1 / year (first 3 years)– 100 fb-1/year (subsequently).

••First data in 2007.
Higgs & SUSY main goals.
•

Much preparatory work carried out
historically by ATLAS– Summarised in Detector andPhysics Performance TDR (1998/9).

•

Work continuing to ensure ready totest new ideas in 2007.
Concentrate here on more recent
work.

•
Dan
Dan Tovey
Tovey

55

Kyoto,
Kyoto, January
January 2005
2005

Model Framework•

Minimal Supersymmetric Extension of the Standard Model (MSSM)
contains > 105 free parameters, NMSSM etc. has more J difficult tomap complete parameter space!
• Assume specific well-motivated model framework in which genericsignatures can be studied.
• Often assume SUSY broken by gravitational interactions J
mSUGRA/CMSSM framework : unified masses and couplings at the
GUT scale J 5 free parameters
LHCC(m0, m1/2, A0, tan(β), sgn(μ)).
mSUGRA• R-Parity assumed to be conserved.
Points• Exclusive studies use benchmark
3
points in mSUGRA parameter space:••••

LHCC Points 1-6;
Post-LEP benchmarks (Battaglia et al.);Snowmass Points and Slopes (SPS);
etc…

Dan
Dan Tovey
Tovey

66

5

1

2

4

Kyoto,
Kyoto, January
January 2005
2005

SUSY Signatures••

Q: What do we expect SUSY events @ LHC to look like?
A: Look at typical decay chain:

p

p
~
g
q
•
•
•

~
q

~
χ02

q

~
χ01

~
l
l

l

Strongly interacting sparticles (squarks, gluinos) dominate
production.
Heavier than sleptons, gauginos etc. J cascade decays to LSP.
Long decay chains and large mass differences between SUSY states– Many high pT objects observed (leptons, jets, b-jets).

•

If R-Parity conserved LSP (lightest neutralino in mSUGRA) stable
and sparticles pair produced.
– Large ETmiss signature (c.f. WJlν).

•Closest equivalent SM signature tJWb.
Dan
Dan Tovey
Tovey

77

Kyoto,
Kyoto, January
January 2005
2005

Inclusive Searches••••

Use 'golden' Jets + n leptons + ETmiss discovery channel.
Map statistical discovery reach in mSUGRA m0-m1/2 parameter space.
Sensitivity only weakly dependent on A0, tan(β) and sign(μ).
Syst.+ stat. reach harder to assess: focus of current & future work.

Dan
Dan Tovey
Tovey

5σ

5σ

ATLAS

ATLAS

88

Kyoto,
Kyoto, January
January 2005
2005

SUSY Mass Scale•

First measured SUSY parameter
likely to be mass scale:Jets + ETmiss + 0 leptons– Defined as weighted mean ofmasses of initial sparticles.

•

•
•
•

ATLAS

Calculate distribution of 'effective
mass' variable defined as scalarsum of masses of all jets (or four
hardest) and ETmiss:
Meff=Σ|pTi| + ETmiss.
Distribution peaked at ~ twice
SUSY mass scale for signal events.
Pseudo 'model-independent'
measurement.
Typical measurement error(syst+stat) ~10% for mSUGRA
models for 10 fb-1.
Dan
Dan Tovey
Tovey

99

10 fb-1

ATLAS

10 fb-1

Kyoto,
Kyoto, January
January 2005
2005

Exclusive Studies••

With more data will attempt to measure weak scale SUSY parameters(masses etc.) using exclusive channels.
Different philosophy to TeV Run II (better S/B, longer decay chains)
J aim to use model-independent measures.

p

p
~
q

~g
q
•

~
χ02
q

~
lR
l

~0
χ1
l

Two neutral LSPs escape from each event– Impossible to measure mass of each sparticle using one channel alone•••

Use kinematic end-points to measure combinations of masses.
Old technique used many times before (ν mass from β decay
spectrum, W (transverse) mass in WJlν).
Difference here is we don't know mass of neutral final state particles.
Dan
Dan Tovey
Tovey

10
10

Kyoto,
Kyoto, January
January 2005
2005

Dilepton Edge Measurements•••

When kinematically~0 can undergo
accessible χ2sequential two-body decayto ~χ01 via a right-slepton(e.g. LHC Point 5).
Results in sharp OS SF
dilepton invariant massedge sensitive to
combination of masses ofsparticles.
Can perform SM & SUSY
background subtraction
using OF distribution

χ~02
l

χ~01
l
e+e- + μ+μ- e+μ- - μ+e-

e+e- + μ+μPoint 5
ATLAS

~
l

30 fb-1
atlfastPhysics
TDR

5 fb-1
FULL SIM

ATLAS
Modified
Point 5(tan(β) = 6)e+e- + μ+μ- - e+μ- - μ+e-•

Position of edge measured
with precision ~ 0.5%
(30 fb-1).
Dan
Dan Tovey
Tovey

11
11

Kyoto,
Kyoto, January
January 2005
2005

Measurements With Squarks• Dilepton edge starting point for reconstruction of decay chain.
• Make invariant mass combinations of leptons and jets.
• Gives multiple constraints on combinations of four masses.
• Sensitivity to individual sparticle masses.

~
qL
~
q χ02

l

~
l

l

q~L

~
χ01

~
q χ02

llq thresholdlq edge

1% error(100 fb-1)

1% error(100 fb-1)

TDR,
Point 5

TDR,
Point 5ATLAS

DanDan Tovey
Tovey

ATLAS

h
b

llq edge

2% error(100 fb-1)
TDR,
Point 5
ATLAS

12
12

~
χ01
b
bbq edge
1% error(100 fb-1) TDR,
Point 5

ATLAS

Kyoto,
Kyoto, January
January 2005
2005

‘Model-Independent’ Masses•

Combine measurements from edges
from different jet/lepton
combinations to obtain ‘modelindependent’ mass measurements.

~
χ0

ATLAS

ATLAS

Mass (GeV)

Mass (GeV)

~χ0
2

LHCC
Point 5

~
lR

1

~
q
L

ATLAS

ATLAS

Mass (GeV)

Mass (GeV)

Sparticle Expected precision (100 fb-1)
~
± 3%
qL
~χ02
± 6%
~
± 9%
lR
~χ0
± 12%
1
Dan
Dan Tovey
Tovey

13
13

Kyoto,
Kyoto, January
January 2005
2005

Sbottom/Gluino Mass

•
•

•

p

p
~g ~
b
b

Dan
Dan Tovey
Tovey

~
χ02

~
lR

33.76

l

Constant
Mean
Sigma

Events/10 GeV/300 fb-1

80

/ 29
63.70
587.6
57.43

2.709
2.227
1.577

60

300 fb-1

40

20

0

400

600
m(χbb) (GeV)

ATLAS

800

SPS1a

~
~
m(g)-m(b1)= (103.3 ± 1.8) GeV~~
m(g)-m(b2)= (70.6 ± 2.6) GeV

ATLAS

300 fb-1

~0
χ1

25.24

/ 20
70.68
98.12
24.15
15.67
63.87
6.167

P1
P2
P3
P4
P5
P6

100

3.501
1.338
1.102
6.262
2.386
1.913

75

50

25

0

b

~
~0 )
m(g)-0.99m(χ1= (500.0 ± 6.4) GeV-1•

Following measurement of squark, sleptonand neutralino masses move up decay
chain and study alternative chains.
One possibility: require b-tagged jet in
addition to dileptons.
Give sensitivity to sbottom mass (actually
two peaks) and gluino mass.
~0 mass
Problem with large error on input χ1remains J reconstruct difference of gluino
and sbottom masses.
~~
Allows separation of b1 and b2 with 300 fb-1.

Events/5 GeV/300 fb

•

l

SPS1a
0

50
100
m(χbb)-m(χb) (GeV)

150




Figure 8: Distribution of
for an integrated luminosity of 300 fb
perimposed is the ﬁt performed assuming the sum of two gaussian distributions.


O

,

Q

H





O

,

Q

H

H





+

+

5

. Su-

10

14
14

Kyoto,
Kyoto, January
January 2005
2005

Stop Mass
•
•

•
•

Look at edge in tb mass distribution.
Contains contributions frommtbmax = (443.2 ± 7.4stat) GeV
Expected = 459 GeV~ ~ Îtbχ~+– gÎtt1
1~~~+– gÎbb1Îbtχ 1– SUSY backgrounds

120 fb-1

Measures weighted mean of end-points
Require m(jj) ~ m(W), m(jjb) ~ m(t)

LHCC Pt 5(tan(β)=10)

ATLAS

mtbmax = (510.6 ± 5.4stat) GeV
Expected = 543 GeV•
120 fb-1
ATLAS

Subtract sidebands from m(jj)distribution• Can use similar approach with~~
gÎtt1Îttχ~0i– Di-top selection with sideband
subtraction

LHCC Pt 5(tan(β)=10)•Dan
Dan Tovey
Tovey

Also use ‘standard’ bbll analyses(previous slide)15
15

Kyoto,
Kyoto, January
January 2005
2005

RH Squark Mass•

Right handed squarks difficult as rarely decay via ‘standard’ ~χ02 chain~ J~– Typically BR (qχ01q) > 99%.
R••

Instead search for events with 2 hard jets and lots of ETmiss.
Reconstruct mass using ‘stransverse mass’ (Allanach et al.):mT22 =

•
•

min

χ(1)
T

χ(2)
T

miss
T

[max{mT2(pTj(1),qTχ(1);mχ),mT2(pTj(2),qTχ(2);mχ)}]

q
+q
=E
~
0
Needs χ 1 mass measurement as input.
Also works for sleptons.

~
χ01
q
ATLAS

ATLAS

30 fb-1
RightsquarkSPS1a~qR

30 fb-1

100 fb-1

ATLAS

SPS1a

SPS1a
Right
squarkLeft slepton

Precision ~ 3%Dan
Dan Tovey
Tovey

16
16

Kyoto,
Kyoto, January
January 2005
2005

Heavy Gaugino Measurements•••

Also possible to identify dilepton edges fromdecays of heavy gauginos.
Requires high stats.
Crucial input to reconstruction of MSSM
neutralino mass matrix (independent of
SUSY breaking scenario).

ATLAS

SPS1a

ATLAS
100 fb-1

Dan
Dan Tovey
Tovey

ATLAS
100 fb-1

17
17

ATLAS
100 fb-1
SPS1a

Kyoto,
Kyoto, January
January 2005
2005

•
•

Mass Relation Method

New idea for reconstructing SUSY masses!
‘Impossible to measure mass of each sparticle using one channel
alone’ (Slide 10).
– Should have added caveat: Only if done event-by-event!

••

Assume in each decay chain 5 inv. mass constraints for 6 unknowns (4~0 momenta + gluino mass + sbottom mass).
χ
1Remove ambiguities by combining different events analytically J‘mass relation method’ (Nojiri et al.).
Also allows all events to be used, not just those passing hard cuts
(useful if background small, buts stats limited – e.g. high scale SUSY).
Preliminary

ATLAS

•

Dan
Dan Tovey
Tovey

ATLAS
SPS1a

18
18

Kyoto,
Kyoto, January
January 2005
2005

Chargino Mass Measurement~•

Mass of lightest chargino very
difficult to measure as does notparticipate in standard dilepton
SUSY decay chain.
• Decay process via ν+slepton
gives too many extra degrees
of freedom - concentrate~+ J W χ~0 .
instead on decay χ1
1• Require dilepton ~χ02 decaychain on other ‘leg’ of eventand use kinematics to calculate
chargino mass analytically.
• Using sideband subtraction
technique obtain clear peak attrue chargino mass (218 GeV).
• ~ 3 σ significance for 100 fb-1.
Dan
Dan Tovey
Tovey

~0
χ
1

χ +1

W
q q q

~
q q~
g
p

p
~
g

~
q
q

~ χ~01
lR

~
χ02
q

l

PRELIMINARY
Modified
LHCC Point 5:
m0=100 GeV;
m1/2=300 GeV;
A0=300 GeV;
tanß=6 ; μ>0100 fb-1

19
19

Kyoto,
Kyoto, January
January 2005
2005lMeasuring Model Parameters••

Alternative use for SUSY observables (invariant mass end-points,
thresholds etc.).
Here assume mSUGRA/CMSSM model and perform global fit of model
parameters to observables– So far mostly private codes but e.g. SFITTER, FITTINO now on the market;– c.f. global EW fits at LEP, ZFITTER, TOPAZ0 etc.
Point
LHC Point 5
SPS1a

Parameterm0m1/2
tan(β)A0
Dan
Dan Tovey
Tovey

m0 m1/2 A0
100 300 300
100 250 -100tan(β) sign(μ)
2
+1
10
+1

Expected precision (300 fb-1)± 2%± 0.6%
± 9%
± 16%
20
20

Kyoto,
Kyoto, January
January 2005
2005

SUSY Dark Matter•Can use parameter measurements
for many purposes, e.g. estimate
LSP Dark Matter properties (e.g.
for 300 fb-1, SPS1a)– Ωχh2 = 0.1921 ± 0.0053– log10(σχp/pb) = -8.17 ± 0.04
Micromegas 1.1(Belanger et al.)+ ISASUGRA 7.69

Dan
Dan Tovey
Tovey

Baer et al. hep-ph/0305191

LHC Point 5: >5σ error (300 fb-1)
SPS1a: >5σerror (300 fb-1)
σχp=10-11 pb

DarkSUSY 3.14.02(Gondolo et al.)+ ISASUGRA 7.69σχp=10-10 pb

Ωχh2

σχp

300 fb-1

300 fb-1

ATLAS

ATLAS

σχp=10-9 pb

21
21

LEP 2

No REWSB

Kyoto,
Kyoto, January
January 2005
2005

SUSY Dark Matter•

SUSY (e.g. mSUGRA) parameter space strongly constrained bycosmology (e.g. WMAP satellite) data. mSUGRA A0=0, Slepton Cotan(β) = 10, μ>0'Focus point'
region: significant~
h component to
LSP enhances
annihilation togauge bosons'Bulk' region: tchannel slepton
exchange - LSP
mostly Bino.
'Bread and Butter'region for LHC
Expts.

Dan
Dan Tovey
Tovey

DC1/2
Rome

Ellis et al. hep-ph/0303043
Disfavoured by BR (b → sγ) =(3.2 ± 0.5) • 10-4 (CLEO, BELLE)

χ~01
~0
χ
1

22
22

l
~
lR

l

χ~01

τ

~
τ1

τ~1
γ/Z/h

annihilation
region: LSP ~pure Bino. Small
slepton-LSP
mass difference
makes
measurements
difficult.

Also 'rapid
annihilation funnel'
at Higgs pole at
0.094 ≤ Ω χ h2 ≤ 0.129(WMAP)
high tan(β), stop
co-annihilation
region at large A0
Kyoto,
Kyoto, January
January 2005
2005

Coannihilation Signatures•

Small slepton-neutralino massdifference gives soft leptons
100 fb-1– Low electron/muon/tau energy
thresholds crucial.

•

Study point chosen within region:– m0=70 GeV; m1/2=350 GeV; A0=0;
tanß=10 ; μ>0;
– Same model used for DC2 study.

•

Preliminary~~
Decays of ~χ02 to both lL and lR
kinematically allowed.

– Double dilepton invariant massedge structure;– Edges expected at 57 / 101 GeV

•

ATLAS

• ETmiss>300 GeV• 2 OSSF leptons
PT>10 GeV• >1 jet with PT>150
GeV• OSSF-OSOF
subtraction applied

100 fb-1

Stau channels enhanced (tanβ)– Soft tau signatures;– Edge expected at 79 GeV;
– Less clear due to poor tau visibleenergy resolution.
Dan
Dan Tovey
Tovey

Preliminary

23
23

ATLAS

• ETmiss>300 GeV• 1 tau PT>40
GeV;1 tau PT<25
GeV• >1 jet with
PT>100 GeV• SS tausubtraction

Kyoto,
Kyoto, January
January 2005
2005

Focus Point Models•••

Large m0 Î sfermions are heavy
Most useful signatures from heavy neutralino decay
Study point chosen within focus point region :– m0=3000 GeV; m1/2=215 GeV; A0=0; tanß=10 ; μ>0~0 → χ
~0 ll
Direct three-body decays χn1~0 )-m(χ~0 )~Edges give m(χχ02 → ~
χ01 lln
1

events/1.5 GeV

dilepton invariant mass
160

ATLAS

e+e-+μ+μe+μ-+e+μ-

140
120

EntriesMean
RMS
χ2 / ndf
Prob
p0
p1
p2
p3
p4
p5
p6
p7

120
100

30 fb-1

60

60

40

40

20

20

0

0
0

ATLAS

Preliminary

80

20

40

60

Dan
Dan Tovey
Tovey

80

Z0 → ll
graph

80

100

~0 → ~
χ01 llχ
3

Flavour subtracted
Events/2 Gev••

0

100 120 140 160 180 200
M (GeV)

24
24

61
50.06
25.08
36.25 / 30
0.199978.62 ± 1.74
-8.202e-05 ± 3.536e-01
0.2682 ± 0.0354
47.66
47.66± ±0.620
0.62
0.0266 ± 1.5081
3.982 ± 0.843
97.33 ± 7.85
-19.05 ± 2.50

Preliminary
20

40

60

80

100

120
M (GeV)

Kyoto,
Kyoto, January
January 2005
2005

SUSY Spin Measurement•

Q: How do we know that a SUSY signal is really due to SUSY?
– Other models (e.g. UED) can mimic SUSY mass spectrum••

A: Measure spin of new particles.
One proposal – use ‘standard’ two-body slepton decay chain– charge asymmetry of lq pairs measures spin of ~χ02
– relies on valence quark contribution to pdf of proton (C asymmetry)– shape of dilepton invariant mass spectrum measures slepton spin
Spin-0MeasureAngle

ASpin-½+−l+ − l−= + −l +lPoint 5

Point 5ATLAS
150 fb -1

mlq
spin-0=flat
PolariseSpin-½,
Spin-0mostly winoDan
Dan Tovey
Tovey

150 fb -1

ATLAS

Straight
line distn(phase-space)Spin-½,
mostly bino
25
25

Kyoto,
Kyoto, January
January 2005
2005

DC1 SUSY Challenge••First attempt at large-scale simulation of
SUSY signals in ATLAS (100 000 events:~5 fb-1) in early 2003.
Tested Geant3 simulation and ATHENA(C++) reconstruction software framework
thoroughly.

ll endpoint

ATLAS
Preliminary

No b-tagWith b-tag
llj endpoint

Modified
LHCC Point 5:
ATLAS
Preliminary m0=100 GeV;
m1/2=300 GeV;
A0=300 GeV;
tanß=6 ; μ>0
SUSY
Mass
Scale

Dijet mT2
distribution

ATLAS

Preliminary

ATLAS
PreliminaryDan
Dan Tovey
Tovey

26
26

Kyoto,
Kyoto, January
January 2005
2005

DC2 SUSY Challenge••

DC2 testing new G4 simulation andreconstruction.
Points studied:

μ+μ- endpoint– DC1 bulk region point (test G4)– Stau coannihilation point (rich in signatures test reconstruction)

•

ATLAS
Preliminary
DC1 Point

Further studies planned in run up to Rome
Physics Workshop (Focus Point model etc.)

Work in Progress!
μ+μ- endpoint

ll endpoint

DC1 Point

ATLAS
Coannihilation
Point

Preliminary

ATLAS

Coannihilation
Point

Preliminary

ll endpointDan
Dan Tovey
Tovey

27
27

Kyoto,
Kyoto, January
January 2005
2005

Preparations for 1st Physics•

Preparations needed to ensure efficient/reliable searches
for/measurements of SUSY particles in timely manner:– Initial calibrations (energy scales, resolutions, efficiencies etc.);– Minimisation of poorly estimated SM backgrounds;– Estimation of remaining SM backgrounds;– Development of useful tools.

• Different situation to Run II (no previous σ measurements at same √s)• Will need convincing bckgrnd. estimate with little data as possible.
• Background estimation techniques will change depending on
integrated lumi.
• Ditto optimum search channels & cuts.
• Aim to use combination of– Fast-sim;– Full-sim;– Estimations from data.

••

Use comparison between different techniques to validate estimatesand build confidence in (blind) analysis.
Aim to study with full-sim (DC2) dataDan
Dan Tovey
Tovey

28
28

Kyoto,
Kyoto, January
January 2005
2005

Background Estimation•

Main backgrounds:

•

Also:
– Single top– WW/WZ/ZZ– Z + n jets
– W + n jets
– ttbar– QCD•

Jets + ETmiss + 0 leptons
ATLAS

10 fb-1

Generic approach :– Select low ETmiss background calibration
samples;– Extrapolate into high ETmiss signal region.
QCD
W+jet
Z+jet
ttbar

ATLAS

Dan
Dan Tovey
Tovey

•
•

Used by CDF / D0
Extrapolation non-trivial.
– Must find variables uncorrelated with ETmiss••

Several approaches developed.
Most promising: Use Z (Î ll) + jets toestimate Z (Î νν) / W (Î lν) + jets
29
29

Kyoto,
Kyoto, January
January 2005
2005

Top Background
•

•
•

•

•
•
•

Estimation using simulation possible(normalised to data ttbar selection) –cross-check with data
Isolate clean sample of top eventsusing mass constraint(s).
Then plot ETmiss distribution (large
statistical errors), compare with same
technique applied to SUSY events(SPS1a benchmark model).
Reconstruct leptonic W momentum
from ETmiss vector and W massconstraint (analytical approach –quadratic ambiguity).
Select solution with greatest W pT.
Select b-jet with greatest pT.
Plot invariant mass of combination.

Dan
Dan Tovey
Tovey

30
30

ATLAS

ttbar

Preliminary

SUSY

ATLAS
Preliminary

Kyoto,
Kyoto, January
January 2005
2005

Top Background•••

Select events in peak and examine
ETmiss distribution.
Subtract combinatorial background withappropriately weighted (from MC)
sideband subtraction.
Good agreement with top background
distribution in SUSY selection.

ttbar
ATLAS
Preliminary

SUSY

•
ATLAS
Preliminary•

With this tuning does not selectSUSY events (as required)
Promising approach but more workneeded (no btag etc.)
Histogram – 1 lepton SUSY selection (no b-tag)
Data points – background estimate

Dan
Dan Tovey
Tovey

31
31

Kyoto,
Kyoto, January
January 2005
2005

Supersummary
•
•
•
•
•
•
•

The LHC will be THE PLACE to search for, and hopefully study, SUSY
from 2007 onwards (at least until ILC).
SUSY searches will commence on Day 1 of LHC operation.
Many studies of exclusive channels already performed.
Lots of input from both theorists (new ideas) and experimentalists(new techniques).
Renewed emphasis on use of full simulation tools.
Big challenge for discovery will be understanding systematics.
Big effort ramping up now to understand how to exploit first data intimely fashion– Calibrations– Background rejection– Background estimation– Tools•

Massive scope for further work!
Dan
Dan Tovey
Tovey

32
32

Kyoto,
Kyoto, January
January 2005
2005

BACK-UP SLIDESDanDan Tovey
Tovey

33
33

Kyoto,
Kyoto, January
January 2005
2005

llq Edge••

Dilepton edges provide starting point for other measurements.
Use dilepton signature to tag presence of ~
χ02 in event, then work backup decay chain constructing invariant mass distributions ofcombinations of leptons and jets.

~qL

e.g. LHC Point 5

q

~0
χ2
l

•
•

~
l

~0
χ1
l

ATLAS

1% error(100 fb-1)

Hardest jets in each event produced
by RH or LH squark decays.
Select smaller of two llq invariant
masses from two hardest jets

Physics
TDR
Point 5– Mass must be < edge position.

•

Edge sensitive to LH squark mass.
Dan
Dan Tovey
Tovey

34
34

Kyoto,
Kyoto, January
January 2005
2005

lq Edge•••

Complex decay chain at LHC Point 5 gives
additional constraints on masses.
Use lepton-jet combinations in addition tolepton-lepton combinations.
Select events with only one dilepton-jet
pairing consistent with slepton hypothesis
J Require one llq mass above edge and one
below (reduces combinatorics).
ATLAS•
1% error(100 fb-1)•

Physics
TDR
Point 5Dan
Dan Tovey
Tovey

35
35

ATLAS

Point 5
Physics
TDR

Construct distribution ofinvariant masses of 'slepton'
jet with each lepton.
'Right' edge sensitive toslepton, squark and ~χ 02
masses ('wrong' edge notvisible).
Kyoto,
Kyoto, January
January 2005
2005

hq edge•••

If tan(β) not too large can also observe two body decay of ~χ02 to~0 .
higgs and χ
1Reconstruct higgs mass (2 b-jets) and combine with hard jet.
Gives additional mass constraint.

~
qL

ATLAS

q

~
χ02

~
χ01

h
b

b

Point 51% error(100 fb-1)
Physics
TDR

Dan
Dan Tovey
Tovey

36
36

Kyoto,
Kyoto, January
January 2005
2005

llq Threshold••

Two body kinematics of sleptonmediated decay chain also provides
still further information (Point 5).
Consider case where ~χ01 produced~0 frame.
near rest in χ
2
x
x

ATLAS
Physics
TDR
Point 5

Dilepton mass near maximal.
~ 0 ).
p(ll) determined by p(χ2
ATLAS

Physics
TDR•

Point 52% error(100 fb-1)•

Dan
Dan Tovey
Tovey

37
37

Distribution of llq invariant
masses distribution has
maximum and minimum (whenquark and dilepton parallel).
llq threshold important as
contains new dependence onmass of lightest neutralino.
Kyoto,
Kyoto, January
January 2005
2005

Mass Reconstruction•

Combine measurements fromedges from different
jet/lepton combinations.

•Dan
Dan Tovey
Tovey

38
38

Gives sensitivity to masses(rather than combinations).

Kyoto,
Kyoto, January
January 20052005

High Mass mSUGRA••ATLAS study of sensitivity to models
with high mass scales
E.g. CLIC Point K Î Potentiallyobservable … but hard!

ATLAS
1000 fb -1

•
•
•
Dan
Dan Tovey
Tovey

Characteristic double peak in signal
Meff distribution (Point K).
Squark and gluino production crosssection reduced due to high mass.
Gaugino production significant
39
39

Kyoto,
Kyoto, January
January 2005
2005

AMSB
•

•
•

Examined RPC model withtan(β) = 10, m3/2=36 TeV, m0=500
GeV, sign(μ) = +1.
~~
χ+/-1 near degenerate with χ01.
~~
Search for χ+/-1 J π+/-χ01(Δm = 631 MeV J soft pions).

•
•

Dan
Dan Tovey
Tovey

Also displaced vertex due to phasespace (cτ=360 microns).
Measure mass difference between
chargino and neutralino using mT2
variable (from mSUGRA analysis).

40
40

Kyoto,
Kyoto, January
January 2005
2005

GMSB
•
•
•
•

Kinematic edges also useful for GMSB models when neutral
LSP or very long-lived NLSP escapes detector.
Kinematic techniques using invariant masses ofcombinations of leptons, jets and photons similar.
Interpretation different though.
E.g. LHC Point G1a (neutralino NLSP with prompt decay togravitino) with decay chain:

~0
χ2
l

Dan
Dan Tovey
Tovey

~
l

~0
χ1

l

41
41

γ

~
G

Kyoto,
Kyoto, January
January 2005
2005

GMSB
•
•
•

Use dilepton edge as before (but different position in chain).
Use also lγ, llγ edges (c.f. lq and llq edges in mSUGRA).
Get two edges (bonus!) in lγ as can now see edge from 'wrong' lepton(from χ02 decay). Not possible at LHCC Pt5 due to masses.

•

Interpretation easier as can assume gravitino massless:Dan
Dan Tovey
Tovey

42
42

Kyoto,
Kyoto, January
January 2005
2005

R-Parity Violation••

Missing ET for events at
SUGRA point 5 with andwithout R-parity violation
RPV removes the classic
SUSY missing ET signature•

Use modified effective mass
variable taking into account pT of
leptons and jets in event

mT ,cent = ∑ pT

jet ,lepton

η< 2

Dan
Dan Tovey
Tovey

43
43

Kyoto,
Kyoto, January
January 2005
2005

R-Parity Violation•

Baryon-Parity violating casehardest to identify (no leptons).

Phase space
sample 8j +2l– Worst case: λ"212 - no heavy-quark jets•

Test model studied with decay
chain:
00q˜ L → χ˜ 2 q → l˜Rlq → χ˜ 1 llq•

Lightest neutralino decays via BPV
coupling:χ˜ 10 → cds•

Reconstruct neutralino mass from
3-jet combinations (but large
combinatorics : require > 8 jets!)Dan
Dan Tovey
Tovey

44
44

Kyoto,
Kyoto, January
January 2005
2005

R-Parity Violation••

Use extra information from
leptons to decrease background.
0
Sequential decay of q~L to χ˜ 1~
0through χ˜ 2 and lR producing
Opposite Sign, Same Family(OSSF) leptons

q~L

χ˜ 20
q

Dan
Dan Tovey
Tovey

Test point~lRl

Decay via ~lR allowed where0~m( χ˜ 2 ) > m( lR )

χ˜ 10
l

q

q
q

45
45

Kyoto,
Kyoto, January
January 2005
2005

R-Parity Violation•

Perform simultaneous (2D) fit to 3jet and 3jet + 2lepton combination(measures mass of χ~02).

No peak inphase space
sampleGaussian fit:0m( χ˜ 1 ) = 118.9 ± 3 GeV, (116.7 GeV)
0m( χ˜ 2 ) = 218.5 ± 3 GeV (211.9 GeV)•

Jet energy scale
uncertainty ≈ 3%
⇒ 3 GeV systematic
Can also measure squark and slepton masses.

Dan
Dan Tovey
Tovey

•

46
46

Kyoto,
Kyoto, January
January 2005
2005

R-Parity Violation•

Distinguishingλ " ijk from λ " lmn
uds
udb
usb
cds
cdb
csb
udb
usb
cds
cdb
csb
usb
cds
cdb
csb
cds
cdb
csb
cdb
csb

Different λ”ijk RPV couplings
cause LSP decays to different
quarks:01
1 2 3

χ˜ → q q q

Identifying the dominant λ”
gives insight into flavour
structure of model.
• Use vertexing and non-isolatedmuons to statistically separatec- and b- from light quark jets.
• Remaining ambiguity from d s• Dominant coupling could be
identified at > 3.5 σ•

DanDan Tovey
Tovey

47
47

Vertexing2
χ / df P / %59.1/1 73.0/1 30.5/1 106.9/1 113.4/1 1.6/2 44
10.3/2 1
18.3/2 16.3/2 17.5/2 12.1/2 9.9/2
1
56.1/2 55.8/2 0.6/2 72

Muons
Combined2
χ / df P / %σ
28.7/1
9.4
31.7/1
10.2
4.0/1
4
5.9
47.2/1
12.4
49.2/1
12.8
0.4/1
54
1.4
13.0/1
4.8
6.8/2
3
5
5.1/2
8
4.6
17.2/1
5.9
5.1/1
2
4.2
3.1/1
8
3.6
37.4/1
9.7
35.3/1
9.5
1.3/2
51
1.4

Kyoto,
Kyoto, January
January 20052005