New String-Motivated Phenomenological Signals at the Tevatron and LHC

1
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

2
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.

3
Experimental Motivation

• 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 whats 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

4
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 doesnt 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

5
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

6
Hidden Valley Models (w/ K. Zurek)
April 06

• Basic minimal structure

Communicator
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
7
A Conceptual Diagram
Energy
Inaccessibility
8
Hidden Valley Models (w/ K. Zurek)

• Basic minimal structure

Communicator
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
9
Communicators
New Z from U(1)
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
10
Communicators
Higgs Boson Or Bosons
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
11
Communicators
Lightest Standard Model Superpartner
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
12
Communicators
Heavy Sterile Neutrinos
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
13
Communicators
Loops of Particles Charged Under SM and HV
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
14
Communicators

• Note that the communicator for production need
  not be the communicator for the decays

New Z from U(1)
Hidden Valley Gv with v-matter
Standard Model SU(3)xSU(2)xU(1)
Higgs Bosons
15
The Hidden Valley (v-)Sector
Communicator
Hidden Valley QCD-like Theory
Standard Model SU(3)xSU(2)xU(1)
16
The Hidden Valley (v-)Sector
Communicator
Hidden Valley QCD-like Theory With N Colors With
n1 Light Quarks And n2 Heavy Quarks
Standard Model SU(3)xSU(2)xU(1)
17
The Hidden Valley (v-)Sector
Communicator
Hidden Valley Gluons only
Standard Model SU(3)xSU(2)xU(1)
18
The Hidden Valley (v-)Sector
Communicator
Hidden Valley Gluons Plus Adjoint Matter
Standard Model SU(3)xSU(2)xU(1)
19
The Hidden Valley (v-)Sector
Communicator
Hidden Valley KS Throat/RS Model
Standard Model SU(3)xSU(2)xU(1)
20
The Hidden Valley (v-)Sector
Communicator
Hidden Valley Multiple Gauge Groups
Standard Model SU(3)xSU(2)xU(1)
21
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 lt 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

22
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

23
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

New Z from U(1)
Hidden Valley v-QCD with 2 (or 3) light v-quarks
Standard Model SU(3)xSU(2)xU(1)
24
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 Lv
• 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)

25
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!

pv Q1Q2 stable
pv- Q2Q1 stable
pv0 Q1Q1 - Q2Q2 ? (Z) ? f f
b
pv0
Z
b
Pseudoscalars their decays require a helicity
flip branching fractions proportional to fermion
masses mf2
26
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.
27
q q ? Q Q v-quark production
v-quarks
Q
q
Z
q
Q
28
Production Rates for v-Quarks
For a particular model. Others may differ by
factor of 10
100 events/year
29
q q ? Q Q v-quark production
v-quarks
Q
q
Z
q
Q
30
q q ? Q Q
v-gluons
Q
q
Z
q
Q
31
q q ? Q Q
q
Q
Z
q
Q
32
q q ? Q Q
v-pions
pv , pv- pvo
For now, take masses in range 20-350 GeV so that
dominant pvo decay is to bs
q
Q
Z
q
Q
pv , pv- pvo
33
q q ? Q Q
v-pions
q
Q
Z
q
Q
34
q q ? Q Q
v-pions
The pv , pv- are invisible and stable
q
Q
Z
q
Q
35
q q ? Q Q
v-pions
q
Q
Z
q
Q
36
q q ? Q Q
v-pions
But the pvos decay in the detector to bb pairs,
or rarely taus
q
Q
Z
q
Q
37
How to simulate? Analogy
Pythia is designed to reproduce data from
70s/80s
38
q q ? Q Q
39
q q ? Q Q
ISR
40
q q ? Q Q
FSR
ISR
41
q q ? Q Q
Jet Formation
FSR
ISR
42
q q ? Q Q
Jet Formation
FSR
Underlying Event
ISR
43
(No Transcript)
44
(No Transcript)
45
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
46
(No Transcript)
47
Top quark pair event
48
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.
49
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

50
Cant reconstruct entire events, but can find
vertices, resonances!
51
(No Transcript)
52
(No Transcript)
53
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?

54
150 GeV v-pions
55
60 GeV v-pions
56
Top quark pairs
57
Triggering

• Should not be a problem in this model

60 GeV v-pions
MET in GeV
1000
1000
2000
Jet HT in GeV
58
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 ee- 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!

59
Jet-to-Parton (mis)Matching

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

Midpoint Cone 0.7
Number of jets above 50 GeV
Number of jets above 50 GeV
Number of partons above 50 GeV
Number of partons above 50 GeV
Top quark pairs
60 GeV v-pions
60
Jet-to-Parton (mis)Matching

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

Midpoint Cone 0.7
Number of jets above 50 GeV
Number of jets above 50 GeV
Number of partons above 50 GeV
Number of partons above 50 GeV
Top quark pairs
30 GeV v-pions
61
Jet-to-Parton (mis)Matching

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

Midpoint Cone 0.7
Number of jets above 50 GeV
Number of jets above 50 GeV
Number of partons above 50 GeV
Number of partons above 50 GeV
Top quark pairs
150 GeV v-pions
62
Reasons

• Breakdown of jetparton 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

63
Invariant Mass of Highest-pT Jet
Number of jets
Signal only! No background.
30
Invariant mass of jet
64
Invariant mass of two hardest jets
30 GeV v-pions
Top quark pairs
Invariant mass of 2nd-highest pT jet
Invariant mass of highest pT jet
150 GeV v-pions
60 GeV v-pions
65
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?

66
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?!

67
Summary of this preliminary study

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

68
Higgs decays to the v-sector
w/ K Zurek, May 06
Q
g
h
hv
v-quarks
g
Q
mixing
Higgs mixing in U(1) model Schabinger Wells 05
69
Higgs decays to the v-sector
w/ K Zurek, May 06
b
g
h
hv
b
b
g
v-pions
b
mixing

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

70
Higgs decays to the v-sector
Displaced vertex
w/ K Zurek, May 06
b
g
h
hv
b
b
g
v-pions
b
mixing
Displaced vertex
71
A Higgs Decay
Schematic not a simulated event!
72
An Overlooked Discovery Channel
MJS K. Zurek May 06

• 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

73
SUSY decays to the v-sector
MJS July 06
q
c

q
g
Two neutral particles Missing Momentum
transverse to beampipe (MET)

q
g
c
_
q
74
SUSY decays to the v-sector
MJS July 06
q
c

q
g
Two neutral particles Missing Momentum
transverse to beampipe (MET)

q
g
c
_
q
But if the Standard Model LSP is heavier than the
v-sector LSP (LSvP), then
75
SUSY decays to the v-sector
July 06

Q
q
c

q
g
Q
v-(s)quarks
_
Q

q
g
c

_
Q
q
But if the Standard Model LSP is heavier than the
v-sector LSP (LSvP), then!!!
76
SUSY decays to the v-sector
MJS July 06
The lightest SUSY v-hadron!
q
c
v-pions

q
g

q
g
c
_
q
The lightest SUSY v-hadron!
77
SUSY decays to the v-sector
MJS July 06
The lightest SUSY v-hadron!
q
c
v-pions

q
g

q
g
c
_
q
The traditional missing energy signal is replaced
with multiple soft jets, reduced missing energy,
and possibly multiple displaced vertices
The lightest SUSY v-hadron!
78
SUSY events?

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

79
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

80
SUSY decays to the v-sector
MJS July 06
t
t
q

t
c
v-pions

q
c
g

t
c

q
g
c
_
q
t
t
4 taus in every SUSY event, 2 possibly displaced,
plus soft v-hadrons, possibly with displaced
decays
81
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

82
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.

83
Other v-sectors

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

84
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
Z
f
M
M
85
Only one light v-quark?
w/ K. Zurek, April 06

• 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

86
No light v-quarks?
w/ K. Zurek, April 06
Morningstar and Peardon 99

• 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

Morningstar Figure
YM glueball spectrum
87
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 N1
  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 N1 SYM unknown beyond
  lowest multiplet!
• So no reliable simulation package can be written.
• Our poor theoretical understanding of N1 SYM
  actually might obstruct discovery of SUSY at the
  LHC.

88
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

89
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 bs, taus
• Muon/electron resonances or endpoints
• Highly displaced jet pairs or lepton pairs

90
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.