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Search for H eavy S table C harge P articles in CMS

Search for H eavy S table C harge P articles in CMS. Krzysztof Nawrocki on behalf of the CMS Collaboration Soltan Institute for Nuclear Studies (IPJ Warsaw)‏ Physics at LHC Split 28.09.2008. HSCP search in CMS. Outline: Motivation for HSCP searches Methods of the detection:

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Search for H eavy S table C harge P articles in CMS

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  1. Search for Heavy Stable Charge Particles in CMS • Krzysztof Nawrocki • on behalf of the CMS Collaboration • Soltan Institute for Nuclear Studies (IPJ Warsaw)‏ • Physics at LHC • Split 28.09.2008

  2. HSCP search in CMS Outline: • Motivation for HSCP searches • Methods of the detection: • Time Of Flight (TOF) from Drift Tubes (DT)‏ • dE/dx from tracker • Simulation studies • Conclusions

  3. HSCP Phenomenology (1)‏ • Many extensions of the Standard Model predict new charged particles that are: • Heavy: mass > 100 GeV/c2 (in general non-relativistic)‏ • Semi-stable: ctau > few meters (can escape the detector)‏ • Heavy Stable Charged Particles (HSCP) are expected in models with a new conserved or almost conserved global quantum number like SUSY with R-parity or ExtraDim with KK-parity • In general, electrically charged stable states are incompatible with the dark matter problem, and colored particles are strongly constrained. Therefore HSCPs are only semi-stable higher-level states with the lightest one neutral GMSB - NLSP: stau(or slepton), LSP: Gravitino mUED – supressed decay of KK lepton by mass degeneration toLKP: KK-photon

  4. HSCP Phenomenology (2)‏ • More and more models predict HSCPs. CMS should be ready to detect them, e.g.: • GMSB – Gauge Mediated SUSY Breaking => long-lived stau • Extra Dimensions => long-lived KK states • Split SUSY => long-lived gluino (R-hadron)‏ • Other models => 4th generation of leptons • The presence of HSCPs could solve the so-called lithium BBN problem (K. Jedamzik, Phys. Rev. D77, 063524 (2008))‏ • HSCP with colour charge hadronize into charge-flipping R-hadrons:

  5. HSCP: main scenarios' Xsections Lepton Like Split SUSY Gluino’s MSSM Stop’s

  6. How to discover HSCP ? • Measure momentum using track bending in inner tracker/muon system • Measure using: • Time Of Flight in muon systems (TOF)‏ (for HSCP should be delayed wrt the c-speed SM particle)‏ • Energy loss in inner tracker (dE/dx)‏ (for HSCP should be higher then for light SM particles)‏ • Calculate particle's mass = p/c

  7. HSCP Signatures • Lepton-like HSCP • Can penetrate the whole detector • High ionization energy loss (with respect to light SM particles)‏ • Delayed with respect to the c-speed SM particle • R-Hadron-like HSCP • Heavy parton behaves as a spectator • Does not shower in the calorimeters • The charge can change in hadronic interactions with matter while crossing the detector • Neutral R-Hadrons will give no signals in trackers

  8. DT Reco of tracks • DTs are in the barrel only • One station = 3SL (4Layers each)‏ DT cell = 1 cm x 4cm x ~2m • Synchronization works to • build a straight line from • muon hits • 2SL in phi-, 1SL in z-plane • In the outer most station there is no z-SL

  9. TOF Method Muon HSCP : hits are shifted

  10. DT TOF dedicated Reconstruction • Time aware 2D DT Segment Builder • Because default builder tends to take only left or only right hits for off time particles • Estimate of 2D direction and δt by a line fitting method • 1/is related to δt in each SL CMS 1/ • momentum (GeV)‏

  11. dE/dx in tracker • Energy loss depends on velocity of particles • In the interesting region of non-relativistic muons 0.1 < < 0.9 good aproximation: dE/dx ~ 1/2

  12. dE/dx in tracker Silicon Strips: • Average dE/dx (constituent hits distributed according to Landau PDF) of the track is calculated with dedicated estimators • Parameterk to be obtained from the calibration for e.g.: protons k k • Background • Tails from SM particles

  13. HSCP tiggering • Timing issue important => L1/HLT algos not prepared for slow particles which can be reconstructed in different Bxs or fail reco (constraint: Δt<12.5ns <=> β > ~0.6)‏ Two main trigger paths: • Muon HLT path HSCP is self triggering or SM muons present in the event give trigger • MET HLT path more model dependent, but in many models the large MET comes from cascade decays in which HSCP is produced • Final online trigger efficiency is about 70% for lepton-like HSCPs and in the range 40% - 95% for the R-hadron samples

  14. Predictions for CMS using DT 1/fb Integrated luminosity needed for 3 events for the four signal models gluino full circles, stop full squares, KK tau empty circles, stau empty squares Mass distribution with 1/fb for two of the lowest cross section models 300 GeV KK tau 800 GeV stop

  15. Predictions for CMS using dE/dx StandAlone analysis 1/fb 100/pb Mass distribution with 100/pb for 500 GeV stop Integrated luminosity needed for 5sigma discovery for the four signal models gluino full circles, stop full squares, KK tau empty circles, stau empty squares

  16. Combined selections (DT TOF, dE/dx)‏ βDt-1 vs. βTk-1 1fb-1 4.6fb-1 ~ SM Muons t1 500GeV

  17. Conclusions • CMS detector should be ready for the detection of any new signatures of new physics • Non-standard methods improve standard procedures • mGMSB stau and low mass R-Hadron could be discovered with a few hundred pb-1 • 1fb-1 could be enough for gluino masses above 1TeV and for KK tau • Some topics not covered in this talk: • Improved HSCP analyses based on information from other subdetectors are being developed • Cosmic data are being used to verify described algorithms and estimate background

  18. BACKUP

  19. Why HSCP can occur? • Electroweak baryogenesis from MSSM suggests a meta-stable light stop NLSP non-universal squark mass terms are used to arrange a small Δmass (stop-LSP)‏ decay is forbidden ONLY radiative process possible • By breaking electroweak symmetry and SUSY by a compact ExtraDIM one can get LSP stop (with mass range 130-800 GeV)‏ • InSplit SUSY, all SUSY scalar particles have very large masses (>>TeV), while only masses of gaugino and higgsino are around the weak scale (of order TeV) => gluino becomes metastable because it can only decay via virtual squarks

  20. Benchmark HSCP models • Models with lepton-like particles: • UED  Kaluza-Klein di-tau resonance (m=300 GeV)‏ • SUSY GMSB  NLSP stau (m=156, 247 GeV)‏ • Models with hadrons: • MSSM (specific points)  long lived stop (m=[130,800] GeV)‏ • Split SUSY  long lived gluino (m=[200,1500] GeV)‏

  21. Trigger Strategies • Muon trigger : • Useful for most models • Efficiency depends on the HSCP mass and model • Very robust with respect to the PT threshold (can be increased up to ~50 GeV)‏ • Jet / Missing ET : • Useful for certain models (in particular for mGMSB)‏ • Less sensitive to timing/β issues CMS Trigger Efficiency with full simulation Global ~ mGMSB τ1~ 99% ~ UED KK τ1 ~ 80% ~ MSSM t1~ 40% to 70% ~ Split SUSY g ~ 60% to 95%

  22. TOF Method

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