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“Hidden Valleys” and their Novel Signals at Colliders Matthew Strassler University of Washington - hep-ph/0604261,0605193 w/ K Zurek - hep-ph/0607160 -

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Presentation on theme: "“Hidden Valleys” and their Novel Signals at Colliders Matthew Strassler University of Washington - hep-ph/0604261,0605193 w/ K Zurek - hep-ph/0607160 -"— Presentation transcript:

1 “Hidden Valleys” and their Novel Signals at Colliders Matthew Strassler University of Washington - hep-ph/ , w/ K Zurek - hep-ph/ 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 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 Experimental Motivation

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 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

5 Hidden Valleys – Preview

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8 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.

9 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

10 Hidden Valley Models (w/ K. Zurek) Basic minimal structure Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley G v with v-matter April 06

11 A Conceptual Diagram Energy Inaccessibility

12 Hidden Valley Models (w/ K. Zurek) Basic minimal structure Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley G v with v-matter

13 Communicators Standard Model SU(3)xSU(2)xU(1) New Z’ from U(1)’ Hidden Valley G v with v-matter

14 Communicators Standard Model SU(3)xSU(2)xU(1) Higgs Boson Or Bosons Hidden Valley G v with v-matter

15 Communicators Standard Model SU(3)xSU(2)xU(1) Lightest Standard Model Superpartner Hidden Valley G v with v-matter

16 Communicators Standard Model SU(3)xSU(2)xU(1) Heavy Sterile Neutrinos Hidden Valley G v with v-matter

17 Communicators Standard Model SU(3)xSU(2)xU(1) Loops of Particles Charged Under SM and HV Hidden Valley G v with v-matter

18 Note that the communicator for production need not be the communicator for the decays… Standard Model SU(3)xSU(2)xU(1) Hidden Valley G v with v-matter New Z’ from U(1)’ Higgs Bosons Communicators

19 The Hidden Valley (“v”-)Sector Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley QCD-like Theory

20 The Hidden Valley (“v”-)Sector Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley QCD-like Theory With N Colors With n 1 Light Quarks And n 2 Heavy Quarks

21 The Hidden Valley (“v”-)Sector Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley Gluons only

22 The Hidden Valley (“v”-)Sector Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley Gluons Plus Adjoint Matter

23 The Hidden Valley (“v”-)Sector Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley KS Throat/RS Model

24 The Hidden Valley (“v”-)Sector Standard Model SU(3)xSU(2)xU(1) Communicator Hidden Valley Multiple Gauge Groups

25 Many Models, Few Constraints Number of possibilities is huge! Constraints are limited LEP : production rare or absent Precision tests: new sector is SM-neutral, very small effects 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

26 This talk Carry out above program for simplest subset of simplest class General setup Simulation and results Harder case: no long-lived particles Easier case: long-lived (neutral) 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…

27 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

28 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)

29 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v Z’ Pseudoscalars: their decays require a helicity flip; branching fractions proportional to fermion masses m f 2

30 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.

31 q q  Q Q : v-quark production q q Q Q Z’ v-quarks

32 LHC Production Rates for v-Quarks For a particular model. Others may differ by ~ factor of 10 ~ 100 events/year

33 q q  Q Q : v-quark production q q Q Q Z’ v-quarks

34 q q  Q Q q Q q Q Z’ v-gluons

35 q q  Q Q q q Q Q Z’

36  v ,  v  ;  v  q q  Q Q q q Q Q  v ,  v  ;  v  v-pions For now, take masses in range GeV so that dominant  v  decay is to b’s Z’

37 q q  Q Q q q Q Q v-pions Z’

38 q q  Q Q q q Q Q v-pions The  v ,  v  are invisible and stable Z’

39 q q  Q Q q q Q Q v-pions Z’

40 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’

41 How to simulate? Analogy… Pythia is designed to reproduce data from 70’s/80’s

42 q q  Q Q

43 ISR

44 q q  Q Q ISR FSR

45 q q  Q Q ISR FSR Jet Formation

46 q q  Q Q ISR FSR Underlying Event Jet Formation

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49 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

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51 Top quark pair event

52 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.

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 LHC : 150 GeV v-pions

55 LHC : 60 GeV v-pions

56 LHC : Top quark pairs

57 Triggering Should not be a problem in this particular model The Z’ kicks lots of energy sidewise (big HT) Many v-hadrons are invisible (big MET) MET in GeV 1000 Jet HT in GeV GeV v-pions

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 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!

59 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 pairs60 GeV v-pions Midpoint Cone 0.7

60 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 pairs30 GeV v-pions Midpoint Cone 0.7

61 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 pairs150 GeV v-pions Midpoint Cone 0.7

62 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

63 Invariant Mass of Highest-pT Jet 30 Number of jets Invariant mass of jet Signal only! No background.

64 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 2 nd - highest pT jet

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 This is nice to know, but surely not enough to get good S/B What else 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?!] No answers yet…

67 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!! LHC studies very limited ATLAS undertaking study (Seattle/Rome group) CMS preparing to study LHCb – ideal setting!!! – undertaking first studies Tevatron searches very limited D0 has search for muon pairs at 5 to 30 cm D0 now undertaking search for displaced jets [more later] CDF -- planning stages? [I’m hoping to learn the status today!]

68 Tevatron versus LHC Caution: this particular model won’t give highly displaced vertices at Tevatron. In this model Z’ is communicator for production and decay If heavy, no production rate If lighter, no long-lived v-pions unless v-pions very light Strong LEP constraints on very light v-pions with light Z’ No other v-hadrons decay However, in other models, no such restriction Example: FCNC’s can allow for late decay of  v ,  v  Example: if Z’ decays to quarks Q but v-pions are made from quarks Q’ that don’t couple to Z’, then  Q’-Q mixing angles determine v-pion lifetime, or  coupling to a heavier Z’ or Higgs boson can determine lifetime Point being: reasonable to look for such physics at Tevatron, but don’t use this model as benchmark. Typical Signal: missing energy plus 2, 4, 6 jets with definite jet-pair invariant mass.

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

70 LHC : Long-lived v-hadrons

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72 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

73 Higgs decays to the v-sector g g Q Q v-quarks h hvhvhvhv mixing w/ K Zurek, May 06 Higgs mixing in U(1)’ model Schabinger + Wells 05

74 Higgs decays to the v-sector g g v-pions h hvhvhvhv mixing w/ K Zurek, May 06 b b b b See Dermasek and Gunion h  aa  bb bb, bb ,  , etc. and much follow up work by many authors

75 Higgs decays to the v-sector g g v-pions h hvhvhvhv mixing w/ K Zurek, May 06 b b b b Displaced vertex

76 A Higgs Decay Schematic; not a simulated event!

77 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, esp. those lacking WW decays (e.g. CP-odd Higgs A 0 ), increasing Tevatron reach toward 200 GeV! Can happen in many other models with an approx conserved global symmetry MJS & Zurek [weakly-coupled extra real scalar] Fox Cheng Weiner, Fall 05 [weakly-coupled extended-SUSY model] considered LEP but not Tevatron JHU group, July 06 [R-parity violating model with final-state jet trios] Also pointed out LHCb connection I can build models with occasional final state lepton resonances Current status at Tevatron, esp D0 (trigger on muons) – search underway CDF? [I need an update] LHCb (trigger? Perhaps need associated production?) – study in progress CMS? Atlas? Trigger issues under study…

78 The Challenge:

79 Higgs decay (CP-odd, 200 GeV  40 GeV) Andy Haas – D0 can trigger on soft muons from b decays. In the inner tracker D0 can see the primary, secondary, and tertiary vertices! This significantly reduces backgrounds and may allow use of events where only one displaced decay to bb is observed.

80 Higgs decay (CP-odd, 200 GeV  40 GeV) Second decay occurs too far out for track reconstruction – jet without tracks.

81 What’s True for Higgs is True for SUSY

82 SUSY decays to the v-sector g g q ~ q* ~ q q   _ Two neutral particles: Missing Momentum transverse to beampipe (“MET”) MJS July 06

83 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

84 SUSY decays to the v-sector g g Q Q v-(s)quarks q ~ q* ~ q q   Q* ~ Q ~ _ _ But if the Standard Model LSP is heavier than the v-sector LSP (LSvP), then…!!! MJS July 06

85 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

86 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!

87 Comments Production through LSP decay V-pion decay through Higgs boson or heavy Z’ The lightest R-parity-odd v-hadron may be stable, and other v- hadrons may be stable, so some MET signal survives But MET reduced by quite a lot, so SM backgrounds are much larger; need new techniques to find The LSP and/or v-hadrons may give displaced vertices SUSY tag Extra soft jets?!

88 SUSY tag 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:

89 SUSY tag in 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 

90 SUSY events? How can these SUSY events be identified? Displaced vertices? Great – but how best to search for them? SUSY tag? Easy if four taus in every event. No displaced vertices? And no SUSY tag? The v-hadron decay products are much softer than for Z’ case MET may still help; depends on the v-model May need to classify the medium-pT jets as unusual Worry: like SM plus unusual underlying event? This might be very challenging! Needs study. Cannot currently simulate these models, but in the works Same issues afflict models with KK-parity, T-parity – indeed, any new global symmetry

91 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

92 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.

93 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

94 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* M

95 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 Skands, Mrenna Better understanding of spectrum, matrix elements needed also, as input to simulation Analytic and lattice gauge theory needed w/ K. Zurek, April 06

96 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 w/ K. Zurek, April 06 Morningstar Figure Morningstar and Peardon 99 YM glueball spectrum

97 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.

98 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

99 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

100 Conclusions Signal identification/Background separation a challenge Easier if displaced vertices are present If not, clues from kinematics, tagging 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.

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