# Presentation: 252023

## New String-Motivated Phenomenological Signals at the Tevatron and LHC

- Matt Strassler
- University of Washington
- - hep-ph/0604261,0605193   w/ K Zurek
- - hep-ph/0607160
- - in preparation

## Theoretical Motivation

- Many beyond-the-standard-model theories contain ***new sectors***.
- Common in top-down constructions (especially in string theory)
- Increasingly common in bottom-up constructions (twin Higgs, folded supersymmetry...)
- Could be home of dark matter
- Could be related to SUSY breaking, flavor, etc.
- New sectors may decouple from our own at low energy
- SUSY breaking scale?
- TeV scale?
*Learning about these sectors, which may contain many particles, could open up an entirely new view of nature.*.
- Missing these sectors experimentally would be to miss a huge opportunity
*Therefore we should ensure that we understand their phenomenological manifestations.*

## We are at a crucial moment for both the Tevatron and the LHC:

Tevatron:

2 more years at forefront
Few deviations from standard model at 2 sigma at 1 inv. fb.
But many searches have not been carried out yet
Large data set: what’s hiding?

 LHC:

1 year left to adjust systems, software
Last chance to optimize before flooded with data

Both: wise to consider models with unusual phenomenology

_**Tevatron:**_
- 2 more years at forefront
- Few deviations from standard model at 2 sigma at 1 inv. fb.
***But many searches have not been carried out yet***
- Large data set: what’s hiding?
-  _**LHC:**_
- 1 year left to adjust systems, software
- Last chance to optimize before flooded with data
- Both: wise to consider models with unusual phenomenology

-  Experimental Motivation

## LHC

- Hardware largely finished
- Software still in development
- Time-sensitive hard-to-alter software in
- Trigger
- First-pass reconstruction
- Tracking algorithms
- Detectors designed for minimal-SUSY-like expectations
- High-energy isolated jets
- Moderate-energy isolated leptons/photons
- All emerging from the interaction point
*But what if signal doesn’t have this form?*
- Must ensure trigger does not reject
- Must ensure reconstruction can find
**Important to investigate models that pose a severe but not impossible challenge to this paradigm**
***Only a few months left for this kind of work***

## Hidden Valleys – Preview 

- “Hidden Valley” sectors
- Coupling not-too-weakly to our sector
- Containing not-too-heavy particles
-  		may be observable at Tev/LHC
- Possible subtle phenomena include
- High-multiplicity final states (possibly all-hadronic)
- Highly variable final states
- Many low-momentum partons
- Unusual parton clustering
- Breakdown of jet/parton matching
- Sharp alteration of Higgs decays;
- new discovery modes
- Sharp alteration of SUSY events
- Usual search strategies may fail, need replacements
- Possibly low cross-sections; high efficiency searches needed
- Predictions may require understanding non-perturbative dynamics in new sector – theoretical challenge

## Hidden Valley Models (w/ K. Zurek)

- Basic minimal structure

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- Gv with v-matter

- April 06

## A Conceptual Diagram

**A Conceptual Diagram**

- Energy

- Inaccessibility

## Hidden Valley Models (w/ K. Zurek)

- Basic minimal structure

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- Gv with v-matter

## Communicators

- Standard Model
- SU(3)xSU(2)xU(1)

- New Z’ from
- U(1)’

- Hidden Valley
- Gv with v-matter

## Communicators

- Standard Model
- SU(3)xSU(2)xU(1)

- Higgs Boson
- Or Bosons

- Hidden Valley
- Gv with v-matter

## Communicators

- Standard Model
- SU(3)xSU(2)xU(1)

- Lightest Standard
- Model Superpartner

- Hidden Valley
- Gv with v-matter

## Communicators

- Standard Model
- SU(3)xSU(2)xU(1)

- Heavy Sterile
- Neutrinos

- Hidden Valley
- Gv with v-matter

## Communicators

- Standard Model
- SU(3)xSU(2)xU(1)

- Loops of Particles
- Charged Under
- SM* and *HV

- Hidden Valley
- Gv with v-matter

## 
Note that the communicator for production need not be the communicator for the decays...

- Note that the communicator for production need not be the communicator for the decays...

- Standard Model
- SU(3)xSU(2)xU(1)

- Hidden Valley
- Gv with v-matter

- New Z’ from
- U(1)’

- Higgs Bosons

- Communicators

## The Hidden Valley (“v”-)Sector

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- QCD-like Theory

## The Hidden Valley (“v”-)Sector

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- QCD-like Theory
- With N Colors
- With n1 Light Quarks
- And n2 Heavy Quarks

## The Hidden Valley (“v”-)Sector

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- Gluons only

## The Hidden Valley (“v”-)Sector

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- Gluons Plus
- Adjoint Matter

## The Hidden Valley (“v”-)Sector

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- KS Throat/RS Model

## The Hidden Valley (“v”-)Sector

- Standard Model
- SU(3)xSU(2)xU(1)

- Communicator

- Hidden Valley
- Multiple Gauge Groups

## Many Models, Few Constraints

- Number of possibilities is ***huge***!
- Constraints are limited
**LEP** : production rare or absent
**Precision tests**: new sector appears at 2 loops
**Cosmology**: few constraints if
- Efficient mixing of species
- One species with lifetime < 1 second to decay to SM
- In general, complexities too extreme for purely analytic calculation
***Event Generation Software Needed!***
- Reasonable strategy:
- Identify large class of models with similar experimental signatures
- Select a typical subset of this class
- Compute properties
- Write event generation software
- Explore experimental challenges within this subset
- Infer lessons valid for entire class, and beyond

## This talk

- Carry out above program for simplest subset of simplest class
- General setup
- Simulation and results
- Easier case: long-lived (neutral) particles
- Harder case: no long-lived particles
- Different communicators with simple v-sector
- Effects on Higgs
- [more generally, discovering Higgs via highly-displaced vertices]
- Effect on SUSY
- [more generally, on any model with new global sym]
- Others...
- Other physics in the v-sector
- Heavy v-quarks
- One light v-quark
- Pure YM plus heavy v-quarks
- SUSY YM
- And beyond...

## Simplest Class of Models

- Easy subset of models
- to understand
- to find experimentally
- to simulate
- to allow exploration of a wide range of phenomena
- This subset is part of a wide class of QCD-like theories

- Standard Model
- SU(3)xSU(2)xU(1)

- New Z’ from
- U(1)’

- Hidden Valley
- v-QCD with
- 2 (or 3) light v-quarks

## Two-flavor (v)QCD

- A model with N colors and two light v-quarks serves as a starting point.
- The theory is asymptotically free and becomes strong at a scale v
- All v-hadrons decay immediately to v-pions and v-nucleons.
- All v-hadrons are electric and color neutral, since v-quarks are electric and color-neutral
- If v-baryon number is conserved, v-baryons are stable (and invisible)

## Two-flavor (v)QCD

- All v-hadrons decay immediately to v-pions and the lightest v-baryons
- Two of the three v-pions cannot decay via a Z’
*But the third one can!*

**v*******Q**1**Q**2** ******stable*

**v*******Q**2**Q**1** ******stable*

**v*******Q**1**Q**1** ******Q**2**Q**2** *  *(Z’)***** *  *f f*

*b*

*b*

**v**

*Z’*

- Pseudoscalars: their decays require a helicity flip; branching fractions proportional to fermion masses *m**f**2*

## Long lifetimes

- The v-hadrons decay to standard model particles through a heavy Z’ boson.
**Therefore – no surprise -- these particles may have long lifetimes**

- Notice the very strong dependence on what are essentially free parameters
- LEP constraints are moderate; cosomological constraints weak
- Thus displaced bottom-quark pairs and tau pairs are common in such models, but not required.

## q q  Q Q  :   v-quark production

*q*

*q*

*Q*

* **Q*

*Z’*

***v-quarks***

## Production Rates for v-Quarks

- For a particular model.  Others may differ by
- ~ factor of 10

- ~ 100 events/year

## q q  Q Q  :   v-quark production

*q*

*q*

*Q*

* **Q*

*Z’*

***v-quarks***

## q q  Q Q

*q*

*Q*

* **q*

* **Q*

*Z’*

***v-gluons***

## q q  Q Q

*q*

*q*

*Q*

*Q*

*Z’*

## q q  Q Q

**v**,* ***v**;**v**

- q q  Q Q

*q*

*q*

*Q*

*Q*

**v**,* ***v**;**v**

***v-pions***

- For now, take masses in range 20-350 GeV so that dominant **v** decay is to b’s

*Z’*

## q q  Q Q

*q*

*q*

*Q*

*Q*

***v-pions***

*Z’*

## q q  Q Q

*q*

*q*

*Q*

*Q*

***v-pions***

***The *****v**,* ***v*****are invisible and stable***

*Z’*

## q q  Q Q

*q*

*q*

*Q*

*Q*

***v-pions***

*Z’*

## q q  Q Q

*q*

*q*

*Q*

*Q*

***v-pions***

***But the *****v*****s decay in the detector to bb pairs, or rarely taus***

*Z’*

## How to simulate? Analogy...

- Pythia is designed to reproduce data from 70’s/80’s

## q q  Q Q

## q q  Q Q

***ISR***

## q q  Q Q

***ISR***

***FSR***

## q q  Q Q

***ISR***

***FSR***

***Jet***
***Formation***

## q q  Q Q

***ISR***

***FSR***

***Underlying***
***Event***

***Jet***
***Formation***

## Slide 43

## Slide 44

## Event Display

- This is my own event display -- not ideal or bug-free
- Face on along beampipe –
- Color indicates angle (pseudorapidity)
- Blue – heading forward
- Red – heading backward
- Green/Yellow -- central
- Notes:
- No magnetic field; tracks are straight
- No tracks below 3 GeV are shown
- All photons/neutrals shown starting at calorimeter

**CMS**

## Slide 46

## Top quark pair event

## Long lifetimes

- The v-hadrons decay to standard model particles through a heavy Z’ boson.
**Therefore – no surprise -- these particles may have long lifetimes**

- Notice the very strong dependence on what are essentially free parameters
- LEP constraints are moderate; cosomological constraints weak
- Thus displaced bottom-quark pairs and tau pairs are common in such models, but not required.

## Easier Case – Long-lived Particles

- For light v-pions or heavy Z’, get macroscopic v-pion decay lengths
- Displaced vertices result, possibly well outside beampipe
- b pairs or tau pairs in this model
- Other possible final states in other models
***No standard model background!***
***Significant detector-related challenges!!***
- Tevatron searches very limited
- D0 has search for muon pairs at 5 to 30 cm
- D0 now undertaking search for displaced jets
- CDF planning stages
- LHC studies very limited
- ATLAS undertaking study
- CMS preparing to study
- LHCb – **ideal setting!!!** – undertaking first study

## Can’t reconstruct entire events, but can find vertices, resonances!

***Can’t reconstruct entire events, but can find vertices, resonances!***

## Slide 51

## Slide 52

## Harder Case – All decays prompt

- Events with
- Multiple jets
- Some b-tags
- Possibly taus
- Some missing energy from invisible v-hadrons
- Events fluctuate wildly (despite all being Z’ decays)
- Events cannot be reconstructed
- Kinematic information is scrambled well-beyond repair
- Backgrounds? Not computable
*What clues may assist with identifying this signal?*

## 150 GeV v-pions

## 60 GeV v-pions

## Top quark pairs

## Triggering 

- Should not be a problem in this model

- MET in GeV

- 1000

- Jet  HT in GeV

- 1000

- 2000

- 60 GeV v-pions

## Jet distributions

- Number of jets depends on algorithm, parameters within algorithm
- Two IR-safe algorithms in use
- Cone (multiple variants, some not IR safe)
- kT (nice at e+e- collider, sensitive to UE)
- Studies with cone algorithm reveal some interesting features
- Studies with kT not complete
- All results shown using Pythia hadron-level output;
*no detector resolution effects!*

## Jet-to-Parton (mis)Matching

- For any setting of cone algorithm, jets not well correlated with partons

- Number of partons above 50 GeV

- Number of jets above 50 GeV

- Number of partons above 50 GeV

- Number of jets above 50 GeV

- Top quark pairs

- 60 GeV v-pions

- Midpoint Cone 0.7

## Jet-to-Parton (mis)Matching

- For any setting of cone algorithm, jets not well correlated with partons

- Number of partons above 50 GeV

- Number of jets above 50 GeV

- Number of partons above 50 GeV

- Number of jets above 50 GeV

- Top quark pairs

- 30 GeV v-pions

- Midpoint Cone 0.7

## Jet-to-Parton (mis)Matching

- For any setting of cone algorithm, jets not well correlated with partons

- Number of partons above 50 GeV

- Number of jets above 50 GeV

- Number of partons above 50 GeV

- Number of jets above 50 GeV

- Top quark pairs

- 150 GeV v-pions

- Midpoint Cone 0.7

## Reasons:

- Breakdown of jet–parton relation
- Single boosted v-pion gives one jet –
- two partons merge
- Single slow v-pion often decays to one moderate-pT parton and one soft parton –
- one parton is lost
- Multiple v-pions have correlated momenta –
- their partons may overlap
- All of these reduce the number of partons per jet
- Many final state partons  much FSR, esp. heavy v-pions
- Can bring back a few jets, but relatively small effect

## Invariant Mass of Highest-pT Jet

- 30

- Number of jets

- Invariant mass of jet

- Signal only! No background.

## Invariant mass of two hardest jets

- Top quark pairs

- 30 GeV v-pions

- 150 GeV v-pions

- 60 GeV v-pions

- Invariant mass of highest pT jet

- Invariant mass of 2nd-highest pT jet

## Comments

- Unfair comparison:
- Top quark pairs dominantly near threshold
- Z’ decay provides large energy resource;
- highest-pT v-pions tend to provide a single high pT jet
- Backgrounds are smooth in this variable, except near W and Z mass, but are presumably large
- Must first improve S/B for this to be useful
- B-tagging?
- Taus?
- Other kinematic features?
- Other calorimetric information?

## New methods probably needed

- What do we need?
- To use moderate pT “jets”, if possible
- To use soft hadrons, soft muons, if possible ??!?
- Technique to classify events as QCD-like or not-QCD-like
- What approaches might be available?
- Jet substructure?
- Modified use of existing jet algorithms?
- New algorithms?
- Move away from jets altogether?
- Revisit vertexing/b-tagging ?
- [a “jet” may contain 2, 3,..., 6 b-quarks?!]

## Summary of this preliminary study

- Z’ decays to the v-sector give events with
- Great variability
- Many partons
- Poor jet/parton matching
- Many b’s, some taus
- Missing energy
- Possibly highly-displaced vertices
- Many of these issues apply in other models as well – to be studied
- But let’s now consider other “communicators”
- Higgs
- LSP

## Higgs decays to the v-sector

*g*

*g*

*Q*

* **Q*

***v-quarks***

*h*

*h**v*

- mixing

- w/ K Zurek, May 06

- Higgs mixing in U(1)’ model
- Schabinger + Wells 05

## Higgs decays to the v-sector

*g*

*g*

***v-pions***

*h*

*h**v*

- mixing

- w/ K Zurek, May 06

*b*

*b*

*b*

*b*

- See Dermasek and Gunion 04-06 h aa  bb bb, bb ,  , etc. and much follow up work by many authors

## Higgs decays to the v-sector

*g*

*g*

***v-pions***

*h*

*h**v*

- mixing

- w/ K Zurek, May 06

*b*

*b*

*b*

*b*

**Displaced vertex**

**Displaced vertex**

## A Higgs Decay

*Schematic; not a simulated event!*

## An Overlooked Discovery Channel

- This may be how the Higgs is found!
- Even at small branching fractions, may win at Tevatron -- ***and LHCb!!***
- Branching fraction for light Higgs may be ~ 1
- True for other scalars/pseudoscalars (e.g. A0), increasing Tevatron reach
- Can happen in many models with an approximately conserved global symmetry
- Fox Cheng Weiner, Fall 05 [weakly coupled extended SUSY model]
- [argued would have been ruled out at LEP but did not consider Tevatron]
- JHU group, July 06 [R-parity violating model]
- Also pointed out LHCb connection
- Current status
- at Tevatron, esp D0 (trigger on muons) – search underway
- CDF?
- LHCb (trigger? Perhaps need associated production?) – study in progress
- CMS? Atlas? Trigger issues under study...

- MJS + K. Zurek May 06

## SUSY decays to the v-sector

*g*

*g*

- q

- ~

- q*

- ~

- q

- q

- 

- 

- _

- Two neutral particles: *Missing Momentum transverse to beampipe* (“MET”)

- MJS July 06

## SUSY decays to the v-sector

*g*

*g*

- q

- ~

- q*

- ~

- q

- q

- 

- 

- _

- But if the Standard Model LSP is heavier than the v-sector LSP (LSvP), then...

- Two neutral particles: *Missing Momentum transverse to beampipe* (“MET”)

- MJS July 06

## SUSY decays to the v-sector

*g*

*g*

*Q*

* **Q*

***v-(s)quarks***

- July 06

- q

- ~

- q*

- ~

- q

- q

- 

- 

*Q**

- ~

*Q*

- ~

- _

- _

- But if the Standard Model LSP is heavier than the v-sector LSP (LSvP), then**...!!!**

## SUSY decays to the v-sector

*g*

*g*

- q

- ~

- q*

- ~

- q

- q

- 

- 

- _

***v-pions***

- The lightest
- SUSY v-hadron!

- The lightest
- SUSY v-hadron!

- MJS July 06

## SUSY decays to the v-sector

***The traditional missing energy signal is replaced with multiple soft jets, reduced missing energy, and possibly multiple displaced vertices***

- MJS July 06

*g*

*g*

- q

- ~

- q*

- ~

- q

- q

- 

- 

- _

***v-pions***

- The lightest
- SUSY v-hadron!

- The lightest
- SUSY v-hadron!

## SUSY events?	

- At the present time, I have no idea what these events really look like
- Simulation package can be modified to allow this

## SUSY with Unstable SM LSP

- Long history
- Gauge mediation
- Hidden sectors
- R-parity violation
- RH neutrinos
- As in all such models, the SM LSP need not be electrically neutral and/or colorless
- Implies many possible scenarios
- Example:

## SUSY decays to the v-sector

- MJS July 06

*g*

*g*

- q

- ~

- q*

- ~

- q

- q

- 

- 

- _

***v-pions***

- 

- 

- 

- ~

- 

- 

- 

- 

- ~

- 4 taus in every SUSY event, 2 possibly displaced, plus soft v-hadrons, possibly with displaced decays

- 

## Discovering SUSY?

- Favorable case: displaced vertices
- Displaced vertices from long-lived LSP has long history
- Gauge mediation
- Hidden sectors
- R-parity violation
- RH neutrinos
- Displaced jets as SUSY signal
- Very limited LHC studies
- No Tevatron searches yet
- Here hidden valley offers a new feature,
- The LSP may be long-lived
- The v-hadrons may be long-lived
- Or both!
- Multiple v-hadron production implies complex final state
- Many phenomenological scenarios to prepare for

## Discovering SUSY?

- Sometimes less favorable case: no displaced vertices
- Difficulty depends on nature of LSP decays
- If every event has a “SUSY-tag” signal, may be ok
- If not, MET signal might still be large enough [but challenge]
- If not, then the (possibly soft) v-pion decays must be identified
- More challenging v-phenomenology than Z’ decays:
- Most energetic jets may come from quarks/gluons, not v-pions
- But v-pions may still make hard-enough jets to allow their invt mass to be measured.
*This signal is likely to have escaped notice at Tevatron – perhaps true even in favorable case.*

## Other v-sectors

- I will not discuss other possible communicators here
- Neutrinos
- Loops
- Instead I’d like briefly to consider other v-sectors
- This is much harder, since unknown strong dynamics often plays a role
- Let’s quickly glance at a few possibilities

## Heavier v-quarks?

- Heavy v-quarks may be produced in Z’ decays or SUSY events.
- Meson spectrum like B meson spectrum
- Large m-quark approximations apply
- Most mesons unstable to v-strong decays
- Last vector meson stable against v-strong decays
- Will decay to last pseudoscalar via Z’;
- No helicity suppression!  sometimes muon, electron pairs
- Thus Z’  heavy v-quarks generates
- few v-pions
- possible vector-to-pseudo decays to jets or leptons
- MET plus several rather soft jets, leptons
- But leptons have a kinematic endpoint

*f*

*f*

*Z’*

**M***

**M**

## Only one light v-quark?

**vQCD with one flavor: very different **
- Spectrum not precisely known
- v-omega meson cannot decay to v-hadrons
- The v-omega can decay to any SM fermions
- Including muons, electrons – resonance!
- Possibly a challenge to detect
- Should be possible if a sufficiently pure sample of events can be identified
- Cascade decays may be interesting
- For instance, excited baryon
- light-lepton production in three-body decays – kinematic endpoints
- Simulation package needed –
-  working with Peter Skands
- Better understanding of spectrum, matrix elements needed also, as input to simulation
- Analytic and lattice gauge theory needed

- w/ K. Zurek, April 06

## No light v-quarks?

- Low-energy v-hadrons are        v-glueball states
- Variety of quantum numbers  variety of lifetimes, decay chains
- Decays depend on communicator(s)
- Cascade decays?
- Additional theoretical study required
- Simulation package needed – working w/ P Skands

- w/ K. Zurek, April 06

- Morningstar
- Figure

- Morningstar and Peardon 99

***YM glueball spectrum***

## v-SUSY YM?

- Supersymmetry may be active in the v-sector
- SUSY may be more weakly broken in v-sector than in ours
- Approximate R-symmetry may lead to accidental N=1 SYM in v-sector
- Consequently v-spectrum would have approx degeneracies
- Discover SUSY through v-spectroscopy!
- Other observables too...
- Possibly without ever seeing a SM superpartner
- However, to make such a claim believable requires
- Understanding spectral resolution – not yet known
- Spectrum and decay chains of v-hadrons
- Problem : the spectrum of N=1 SYM unknown beyond lowest multiplet!
- So no reliable simulation package can be written.
*Our poor theoretical understanding of N=1 SYM actually might obstruct discovery of SUSY at the LHC.*

## Other v-Sectors – the Far Future

- The v-sector might contain very interesting dynamics
*Supersymmetric confinement*
*RS/KS throats*
*Seiberg duality*
*Maldacena duality*
*New bulk or brane physics*
*Remnants of SUSY breaking sectors*
- Because LHC may sample two orders of magnitude (10s of GeV – few TeV) can dream of exploring such phenomena
- Admittedly this is somewhat premature
- Not easy to imagine practical observables that would reveal, say, a duality cascade in action
- First, must understand what the LHC can measure – need the simulation packages, expt studies

## Conclusions

- Models with new sectors: abundant, reasonable, and little studied
- Many such models produce light neutral bound states,
- often several,
- possibly with heavier charged states
- Novel multi-parton final states, with large fluctuations, result
- Highest pT jets useful
- Moderate pT jets, soft jets need to be put into play
- Other clues might include
- MET
- Many b’s, taus
- Muon/electron resonances or endpoints
- Highly displaced jet pairs or lepton pairs

## Conclusions

- Signal identification/Background separation a challenge
- Easier if displaced vertices are present
- Clues from kinematics, tagging if not
- Jet/parton matching breaking down
- LHCb may have advantages!
- May affect Higgs physics, SUSY physics, other models
- May make detection easier if displaced vertices
- May impede detection if not
- A number of other remarkable phenomenological signals possible
*Theoretical work needed for predictions, input to simulations, ideas for signal extraction*
*Simulation development needed to allow theoretical and experimental studies, searches*
*Experimental work on several fronts to ensure these different types of signals can all be found.*