“Hidden Valleys” and their Novel Signals at Colliders Matthew Strassler University of Washington - hep-ph/0604261,0605193 w/ K Zurek - hep-ph/0607160 - in preparation.
Download ReportTranscript “Hidden Valleys” and their Novel Signals at Colliders Matthew Strassler University of Washington - hep-ph/0604261,0605193 w/ K Zurek - hep-ph/0607160 - in preparation.
“Hidden Valleys” and their Novel Signals at Colliders Matthew Strassler University of Washington - hep-ph/0604261,0605193 w/ K Zurek - hep-ph/0607160 - in preparation Hidden Valleys – Preview 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. 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 Sharp alteration of Higgs decays; Unusual parton clustering Breakdown of jet/parton matching 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) April 06 Basic minimal structure Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter Energy A Conceptual Diagram Inaccessibility Hidden Valley Models (w/ K. Zurek) Basic minimal structure Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter Communicators New Z’ from U(1)’ Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter Communicators Higgs Boson Or Bosons Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter Communicators Lightest Standard Model Superpartner Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter Communicators Heavy Sterile Neutrinos Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter Communicators Loops of Particles Charged Under SM and HV Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gv with v-matter 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 The Hidden Valley (“v”-)Sector Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley QCD-like Theory The Hidden Valley (“v”-)Sector Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley QCD-like Theory With N Colors With n1 Light Quarks And n2 Heavy Quarks The Hidden Valley (“v”-)Sector Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gluons only The Hidden Valley (“v”-)Sector Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley Gluons Plus Adjoint Matter The Hidden Valley (“v”-)Sector Communicator Standard Model SU(3)xSU(2)xU(1) Hidden Valley KS Throat/RS Model The Hidden Valley (“v”-)Sector Communicator Standard Model SU(3)xSU(2)xU(1) 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 is SM-neutral, very small effects Cosmology: few constraints if In general, complexities too extreme for purely analytic calculation Efficient mixing of species One species with lifetime < 1 second to decay to SM 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 Different communicators with simple v-sector Effects on Higgs [more generally, discovering Higgs via highly-displaced vertices] Effect on SUSY Harder case: no long-lived particles Easier case: long-lived (neutral) particles [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 New Z’ from U(1)’ Standard Model SU(3)xSU(2)xU(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 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) 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 pv0 Z’ b b Pseudoscalars: their decays require a helicity flip; branching fractions proportional to fermion masses mf2 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 v-quarks q q Q Z’ Q LHC 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 v-quarks q q Q Z’ Q qqQQ v-gluons q q Q Z’ Q qqQQ q q Z’ Q Q qqQQ v-pions pv+ , pv- ;pvo q Z’ q Q Q For now, take masses in range 20-350 GeV so that dominant pvo decay is to b’s pv+ , pv- ;pvo qqQQ v-pions q q Z’ Q Q qqQQ v-pions The pv+ , pv- are invisible and stable q q Z’ Q Q qqQQ v-pions q q Z’ Q Q qqQQ v-pions q q Z’ Q Q But the pvos decay in the detector to bb pairs, or rarely taus How to simulate? Analogy… Pythia is designed to reproduce data from 70’s/80’s qqQQ qqQQ ISR qqQQ FSR ISR qqQQ ISR Jet Formation FSR qqQQ ISR Jet Formation FSR Underlying Event 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 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. 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? LHC : 150 GeV v-pions LHC : 60 GeV v-pions LHC : Top quark pairs Triggering 60 GeV v-pions MET in GeV Should not be a 1000 problem in this particular model The Z’ kicks lots of energy sidewise (big HT) Many v-hadrons are invisible (big MET) 1000 Jet HT in GeV 2000 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 Top quark pairs Number of jets above 50 GeV Midpoint Cone 0.7 Number of partons above 50 GeV 60 GeV v-pions Number of jets above 50 GeV Jet-to-Parton (mis)Matching For any setting of cone algorithm, jets not well correlated with partons Number of partons above 50 GeV Top quark pairs Number of jets above 50 GeV Midpoint Cone 0.7 Number of partons above 50 GeV 30 GeV v-pions Number of jets above 50 GeV Jet-to-Parton (mis)Matching For any setting of cone algorithm, jets not well correlated with partons Number of partons above 50 GeV Top quark pairs Number of jets above 50 GeV Midpoint Cone 0.7 Number of partons above 50 GeV 150 GeV v-pions Number of jets above 50 GeV Reasons: Breakdown of jet–parton relation Single boosted v-pion gives one jet – Single slow v-pion often decays to one moderate-pT parton and one soft parton – two partons merge 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 Number of jets Signal only! No background. 30 Invariant mass of jet Invariant mass of two hardest jets Top quark pairs 30 GeV v-pions Invariant mass of 2ndhighest pT jet Invariant mass of highest pT jet 150 GeV v-pions 60 GeV v-pions 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… 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!] 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 pv+ , pv- 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. LHC : Long-lived v-hadrons LHC : Long-lived v-hadrons 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 Q g h hv g v-quarks Q mixing Higgs mixing in U(1)’ model Schabinger + Wells 05 w/ K Zurek, May 06 Higgs decays to the v-sector w/ K Zurek, May 06 b g h hv b b g v-pions b mixing Dermasek and Gunion 04-06 h aa bb bb, bb tt, tt tt, etc. and much follow up work by many authors See Higgs decays to the v-sector Displaced vertex g w/ K Zurek, May 06 b h hv b b g v-pions mixing b Displaced vertex A Higgs Decay Schematic; not a simulated event! 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 A0), 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] JHU group, July 06 [R-parity violating model with final-state jet trios] considered LEP but not Tevatron 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… The Challenge: 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. Higgs decay (CP-odd, 200 GeV 40 GeV) Second decay occurs too far out for track reconstruction – jet without tracks. What’s True for Higgs is True for SUSY MJS July 06 SUSY decays to the v-sector q g g c ~ q ~ q* c _ q Two neutral particles: Missing Momentum transverse to beampipe (“MET”) MJS July 06 SUSY decays to the v-sector q g g c ~ q ~ q* c Two neutral particles: Missing Momentum transverse to beampipe (“MET”) _ q But if the Standard Model LSP is heavier than the v-sector LSP (LSvP), then… MJS July 06 SUSY decays to the v-sector ~ q g Q* c ~ q Q v-(s)quarks _ g Q ~ q* c _ q ~ Q But if the Standard Model LSP is heavier than the v-sector LSP (LSvP), then…!!! MJS July 06 SUSY decays to the v-sector q g ~ q g ~ q* _ q c The lightest SUSY v-hadron! v-pions c The lightest SUSY v-hadron! MJS July 06 SUSY decays to the v-sector q g ~ q g ~ q* _ q c The lightest SUSY v-hadron! v-pions c The traditional missing energy signal is replaced with multiple soft jets, reduced missing energy, and possibly multiple displaced vertices The lightest SUSY v-hadron! 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?! 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: MJS July 06 SUSY tag in decays to the v-sector t t q g g ~ q ~ t c c* ~ t ~ q* _ q c* c t 4 taus in every SUSY event, 2 possibly displaced, plus soft v-hadrons, possibly with displaced decays t v-pions 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 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 Z’ M* 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 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 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 No light v-quarks? Low-energy v-hadrons are w/ K. Zurek, April 06 Morningstar and Peardon 99 v-glueball states Variety of quantum numbers variety of lifetimes, decay chains Morningstar Figure Decays depend on communicator(s) Cascade decays? Additional theoretical study required Simulation package needed YM glueball spectrum 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 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.