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Unusual Physics Signatures at the LHC

Unusual Physics Signatures at the LHC. Matt Strassler University of Washington. LHC Physics. Perhaps it will be dull SM Higgs and nothing else Maybe it will be exciting but in an expected way SUSY, even mSUGRA Technicolor, Little Higgs or KK resonances: t’, W’, Z’

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Unusual Physics Signatures at the LHC

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  1. Unusual Physics Signatures at the LHC Matt Strassler University of Washington

  2. LHC Physics • Perhaps it will be dull • SM Higgs and nothing else • Maybe it will be exciting but in an expected way • SUSY, even mSUGRA • Technicolor, Little Higgs or KK resonances: t’, W’, Z’ • Or perhaps it won’t look the way we generally expect • Hadron colliders  need to think about this now! • Talk today: • A variety of ideas, many not fully studied even theoretically • Focus on experimental issues • Intention to be provocative rather than definitive

  3. Objectification of Particle Physics • Standard Model Objects • Electrons (isolated ECAL, track) • Photons (isolated ECAL, no track) • Muons (etc…) • Jets • Untagged • Heavy-flavor-tagged • Hadronic Taus • MET

  4. Beyond-Standard-Model Objects • Beyond the Standard Model • mSUGRA SUSY • Technicolor • Little Higgs • Extra Dimensions all give signals built from Standard Objects… • …appearing in standard combinations, except • Soft objects • Soft jet pairs • Soft leptons, alone or in pairs • Black Holes • High multiplicity • May give leptons/photons/jets democratically Giddings and Thomas; Dimopoulos and Landsberg

  5. Odd Combinations of SM Objects • Higgs Decays • h  X X ; • X  invisible • X  photon photon • X  b pairs, tau pairs • 4 taus (2 boosted pairs ) at the Tevatron • Boosted tau pair: • Boost factor ~ 5  Delta R ~ 0.4 • The isolation criteria cancel • The tracks add •  Zero isolation, even number of tracks Chang, Fox and Weinerhep-ph/0608310 Dermisek and Gunionhep-ph/0502105, … Graham, Pierce and Wackerhep-ph/0605162

  6. Hyperactive Decays • h  X X ; • X  Y Y ; • Y  b pairs, tau pairs • Final states include 8 low pT b’s • Certainly not 8 jets • Hard to find slow B mesons • Is this hopeless? • A speculative suggestion: hep-ph/0511250, Chang, Fox and Weiner

  7. p p  W h ; h  8 b’s Event Simulated Using Pythia The LHC is an asymmetric collider Simplified event display developed by Rome/Seattle ATLAS working group To guide the eye: Tracks in dark blue are from primary vertex Tracks in red are from displaced decays (All tracks shown are truth tracks) h  Y Y Y Y ; Y  b bbar M_h = 130 GeV; M_Y = 20 GeV Track pT > 0.8 GeV

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

  9. Beyond Standard-Model-Objects • Less popular variants of Supersymmetry • GMSB, AMSB, corners of mSUGRA, R-parity violation, etc. • Any superpartner may be the lightest if metastable • Two such particles per event • Stable (on detector time scales) • Charged particles • New “muons” • Colored particles • New hadrons • Tracks with varying charge • Tracks with fractional charge Baer, Drees, Chen, Gunion, Godbole, Tata, Moretti, Cheung, Mrenna, Feng, Randall, Moroi, Ghergetta, Giudice, Wells, Ellwenger, Hugonie, Hesselbach, Franke, Fraas, Hall, Suzuki, Dimopoulos, Dine, Raby, Thomas, Matchev, Ambrosiano, Kribs, Martin, Sarid, Kane, Arkani-Hamed, Dimopoulos, Arvanitaki, A. Pierce, Rajendran, Graham, Wacker …

  10. Beyond Standard-Model Objects • Unstable (on detector time scales)… • Charged particles • Track stubs • Tracks with kinks • Tracks ending in spray • Colored particles • Decaying in flight to jets • Decaying out of time after stopping • Neutral particles • Leptons out of nowhere • Jets out of nowhere • Photons out of nowhere • Observable remnants may not point back toward IP Baer, Drees, Chen, Gunion, Godbole, Tata, Moretti, Cheung, Mrenna, Feng, Randall, Moroi, Ghergetta, Giudice, Wells, Ellwenger, Hugonie, Hesselbach, Franke, Fraas, Hall, Suzuki, Dimopoulos, Dine, Raby, Thomas, Matchev, Ambrosiano, Kribs, Martin, Sarid, Kane, Arkani-Hamed, Dimopoulos, Arvanitaki, A. Pierce, Rajendran, Graham, Wacker …

  11. Higgs Decays to Displaced Vertices h  X X ; X  jet pair/trio or lepton pair/trio with long lifetime • LEP precursor hep-ph/0511250, Chang, Fox and Weiner • Hadron colliders/CMS/ATLAS/LHCb hep-ph/0604261,0605193 : MJS and K. Zurek hep-ph/0607204 : Carpenter, Kaplan and Rhee • D0/CDF: • Very challenging, being searched for now • LHCb • Golden?! • CMS/ATLAS: (UW/Rome ATLAS study) • Triggering very inefficient for X  b pair at level 1 • Work needed on level 2

  12. Higgs Decay to Two Long-Lived Particles Image provided by ATLAS Rome-Seattle working group: Guido Ciapetti Carlo Dionisi Stefano Giagu Daniele DePedis Giuseppe Salamanna Marco Rescigno Lucia Zanello Barbara Mele* Henry Lubatti Matt Strassler* Dan Ventura Laura Bodine Can enough events pass the ATLAS/CMS triggers!? Overlooked Discovery Mode for Higgs? Y 0.6 meters Z D0/CDF are searching… LHCb might win here!

  13. Ok, is that all?

  14. Hidden Valleys ?

  15. Motivation • Many beyond-the-standard-model theories contain new sectors. • Top-down constructions (esp. string theory) • Bottom-up constructions (twin Higgs, folded SUSY) • “Hidden Valley” sectors • Coupling not-too-weakly to our sector • Containing not-too-heavy particles may be observable at Tev/LHC • Experimental urgency • Novel signatures often present • Could hide in Tevatron data • Could pose challenges for LHC triggering/reconstruction

  16. 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)

  17. A Conceptual Diagram Energy Inaccessibility

  18. Hidden Valley Models (w/ K. Zurek) • Basic minimal structure Z’, Higgs, neutralino, sterile neutrinos, loops of charged particles,… Communicator Hidden Valley Gv with v-matter Standard Model SU(3)xSU(2)xU(1) Limited only by your imagination (?)…

  19. q q  Q Q : v-quark production v-quarks Q q Z’ q Q

  20. q q  Q Q v-gluons Q q Z’ q Q

  21. q q  Q Q q Q Z’ q Q

  22. q q  Q Q v-hadrons q Q Z’ q Q

  23. q q  Q Q v-hadrons q Q Z’ q Q

  24. q q  Q Q Some v-hadrons are stable and therefore invisible v-hadrons But some v-hadrons decay in the detector to visible particles, such as bb pairs, tau pairs, etc. q Q Z’ q Q

  25. Simplest Class of Models • N colors and two light v-quarks • 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 • Two v-pions invisible • Third decays visibly, possibly long-lived,to heavy flavor pairs New Z’ from U(1)’ Hidden Valley v-QCD with 2 light v-quarks Standard Model SU(3)xSU(2)xU(1)

  26. 3 TeV Z’ decays to 30 GeV v-pions EM Calorimeter: green TRT: red Silicon/Pixels: not shown V-pions: green dot-dash lines Charged hadrons: solid lines Neutral hadrons: dashed lines Image courtesy of Rome/Seattle ATLAS working group on displaced decays Event Simulated Using Hidden Valley Monte Carlo 0.4 (written by M. Strassler using elements of Pythia) • Probably good L1 trigger efficiency here: • Lots of energy • Lots of missing energy • Muons common • But could L2 throw it all away?

  27. Harder Case – All decays prompt • If decays are late (picosec – nanosec), it’s an experimentalist’s problem • Trigger an issue – ATLAS, LHCb (CMS?) studies • No SM background • Complex detector backgrounds • If decays prompt, it’s a theorist’s challenge • Backgrounds? • What are they? • Not obviously computable… • What clues may assist with identifying this signal?

  28. Event Simulated Using Hidden Valley Monte Carlo 0.4 (written by M. Strassler using elements of Pythia) Z’ decay to v-pions Simplified event display developed by Rome/Seattle ATLAS working group All tracks are Monte-Carlo-truth tracks; no detector simulation ECAL TRT Si Pixels 3 TeV Z’ 50 GeV v-pions Prompt v-pion decays to b-bbar Track pT > 1.0 GeV

  29. Jets, Partons, and Clusters • Large HT, MET – trigger ok • 10 – 1000 events/year at moderate luminosity • The events are unusual in structure • Some v-hadrons are very hard • Some v-hadrons are very soft • The v-hadrons are clustered • Therefore Hadronic Jet  Partonnot true here • (as in certain SM processes) • But Hadron clusters match with Parton clusters! • Hadronic Jets  Partonic Jets to good accuracy • True for cone and kT, various settings/sizes

  30. Jets and b-quarks 1000 Events, Z’ of mass 3 TeV, v-pions of mass 50 GeV Number of events with k partons (mostly b’s) Number of events with n jets, pT>50 GeV k n Midpoint Cone R=0.4 Thus the number of B mesons (~8) greatly exceeds the number of jets (~4).

  31. Event Simulated Using Hidden Valley Monte Carlo 0.4 (written by M. Strassler using elements of Pythia) Z’ decay to v-pions Simplified event display developed by Rome/Seattle ATLAS working group All tracks are Monte-Carlo-truth tracks; no detector simulation ECAL TRT Si Pixels 3 TeV Z’ 50 GeV v-pions Prompt v-pion decays to b-bbar Track pT > 1.0 GeV

  32. Pixels 5 cm Dotted blue lines are B mesons Track pT > 2.5 GeV Multiple vertices may cluster in a single jet

  33. Beyond Tagged and Untagged Jets • Matching between jets and vertices neither one-to-one nor onto. • Characterizing jets as “b-tagged” or “not” is not enough at LHC. • A more global approach to these events seems advisable • After reconstruction, important not to lose the unique features of these events in compressed data storage • Backgrounds are still under study, hard to estimate • Useful observables: number and fraction of tracks w/ nonzero impact parameter

  34. High-Impact-Parameter Tracking t tbar (sqrt-s > 1 TeV) Number of Events with n tracks with 3d IP more than 150 microns Z’  v-pions n Number of Events with fraction x of tracks (pT>2 GeV) with 3d IP more than 150 microns Obviously, for t tbar h, t tbar Z, t tbar b bbar, will be somewhat larger x

  35. Single Jets may be V-Hadrons • Typical hard jet has 2 or more b-quarks in it • Opportunity to discover new particles using jet invariant mass Jet mass All hadronic jets Highest pT hadronic jet Jet mass Jet pT 0.1 x 0.1 calorimeter cells No detector smearing!! Midpoint Cone R=0.4

  36. Collimation of Boosted Object • X  jet pair • Boost ~ 5 – quarks separated by ~ 0.4 • Jets can be analyzed using calorimeter • Boost ~ 20 – quarks separated by ~ 0.1 • Jets overlapping in calorimeter towers • Tracking can help determine parton momenta • Pixel clusters may stand out above noise, UE • 1000s of pixels for each calorimeter tower • Detector-specific studies needed to optimize Cf. Lillie talk Baur talk others… Thanks to K. Agashe, G. Lifshitz, J. Virzi for conversations; Thanks also to S. Ellis

  37. W  quark pair, pT = 1800 GeV Pseudorapidity Pseudorapidity Azimuthal Angle Track pT Red 5-15 GeV Cyan 15-25 GeV Blue 25-40 GeV Violet > 40 GeV Azimuthal Angle One 0.1 x 0.1calorimeter tower

  38. Pseudorapidity W  quark pair, pT = 1800 GeV Track pT Red 5-15 GeV Cyan 15-25 GeV Blue 25-40 GeV Violet > 40 GeV Azimuthal Angle

  39. Boosted W • About 2/3 of hadronic W’s show this effect • Color-singlet • Know what this looks like in the rest frame • Pythia is sufficiently reliable here • For colored particles not (yet) reliable • Radiation at moderate-to-large angles • Cf. 3-jet effect at Tevatron • For quark/gluon-jet substructure, must calibrate on LHC data • Butterworth, Cox and Forshaw hep-ph/0201098 • kT : distinguish W vs. jet + gluon emission statistically • Suggestion: combine tracking and calorimetry to maximize sensitivity

  40. Signal with harder v-hadrons • Z’ can decay to X Y • Y  invisible • X  v-hadrons • V-hadrons from X decay form single fat jet • Jet often has substructure • More pronounced than in Z’  v-hadrons Q q X Z’ Q q Y

  41. Z’  X Y ; X  v-hadrons Track pT Grey < 5 GeV Red 5-10 GeV Cyan 15-25 GeV Blue 25-40 GeV Violet > 40 GeV MET

  42. No pT cut on tracks! Track pT Grey < 5 GeV Red 5-10 GeV Cyan 15-25 GeV Blue 25-40 GeV Violet > 40 GeV

  43. Global Event Structure • Many of these events look unusual • Substructure • Sphericity

  44. Four light flavors with FCNC decays Prompt Decays No Magnetic Field!

  45. Four light flavors with FCNC decays LEGO Plot 3 2 1 0 -1 -2 -3 Prompt Decays No Magnetic Field! Pseudorapidity 0 p 2p Azimuthal Angle

  46. Clandestine Dilepton Resonances • Many v-sectors have narrow spin-one resonances • These can decay to lepton pairs • Decays often prompt • Inclusive search: resonances totally lost in Drell-Yan background • But various techniques can tease them out • vQCD with one light flavor (MJS and Zurek) : v-rho meson • Study: Han, Si, Zurek (special purpose Monte Carlo) • 1 TeV Z’, • 20 GeV resonance • vQCD with two moderately-heavy flavors: triplet of v-rho mesons • Study: Mrenna, Skands, MJS (new version of HV Monte Carlo) • 3 TeV Z’ • 130 GeV resonance

  47. Disclaimer: • PRELIMINARY RESULTS AHEAD

  48. LEGO plot Han, Si, Zurek Trigger on dilepton

  49. “Hemisphere” cluster mass Han, Si, Zurek • Select events based on mass of fat cluster At least 2 isolated leptons At least 3 isolated leptons Cluster Mass (GeV)

  50. Mrenna, Skands, MJS

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