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Searches for GMSB and for High ET Di-lepton Pair Events at the LHC

Searches for GMSB and for High ET Di-lepton Pair Events at the LHC. Daniele del Re Universita’ di Roma “La Sapienza” and INFN Roma. Rencontres de Moriond QCD and High Energy Interactions 8-15 March. Intro and Outline. Two striking signatures to discover new physics at the LHC:

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Searches for GMSB and for High ET Di-lepton Pair Events at the LHC

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  1. Searches for GMSB and for High ET Di-lepton Pair Events at the LHC Daniele del Re Universita’ di Roma “La Sapienza” and INFN Roma Rencontres de Moriond QCD and High Energy Interactions 8-15 March

  2. Intro and Outline • Two striking signatures to discover new physics at the LHC: 1) long lived particles with large masses and low b 2) high-mass resonances decaying to two leptons • Important analyses at beginning of data taking • low luminosity needed for discovery OUTLINE • Very short intro on GMSB and models with TeV resonances decaying in two leptons • ATLAS and CMS results and discovery potential for • GMSB in photons and staus • High-mass resonances in di-electron and di-muon pairs • Focus on • low statistics scenarios and experimental issues at start-up • techniques to get efficiencies/backgrounds from data Daniele del Re (La Sapienza & INFN) - Moriond QCD

  3. GMSB • Gauge Mediated Supersymmetry Breaking. Models for SUSY breaking, alternative to mSUGRA • SUSY breaking transmitted from Hidden sector to visible sector via gauge interactions (“messengers”) • Lightest supersymmetric particle (LSP) is the Gravitino (m≤keV) • light, stable and weakly interacting • possible candidate for Dark Matter • Depending on parameters N(ext)LSP • neutralino • stau • both cases studied in ATLAS and CMS • N(ext)LSP lifetime value connected to parameter L Present limits: Tevatron, L > 80 TeV, m(neutr.,charg.) > 108/195 GeV Daniele del Re (La Sapienza & INFN) - Moriond QCD

  4. GMSB: final states with g’s • If NLSP neutralino 2g in event • Selection • g, isolation, cut on pT(g) • Large MET, Njets > 3 • Main backgrounds • g+jets, W+jets • after cuts: S/B > 10 • If lifetime(c) ≠ 0 non-pointing g • experimentally tough measurement • Lifetime measurement: • transversal (CMS) and longitudinal (ATLAS) cluster shape to get photon direction • time measurement in calorimeter (ATLAS) to close kinematics g jet q q jet … p p q … jet q jet g Daniele del Re (La Sapienza & INFN) - Moriond QCD

  5. GMSB with g’s: Discovery Potential Low statistics for discovery both in pointing (ct=0) and non-pointing scenarios Lifetime measurement feasible but large statistics needed Reconstruction of leptons in the event can be used to extract both neutralino and slepton masses for L=90 TeV L=100fb-1 for L=140 TeV ct (cm) Daniele del Re (La Sapienza & INFN) - Moriond QCD

  6. GMSB with staus Points used by CMS • With a different choice of parameters (e.g. Nm>3) NLSP is the stau • quasi-stable due to the smallness of the coupling constant • One or more staus produced via heavier SUSY particles (as for g final states) • Large stau mass implies low b • Through tracker and muon detectors • ionization in tracker (dE/dx) • time of flight using muon detector • Other models predict heavy stable charged particles: Split SUSY R-hadrons, Kaluza-Klein lepton like particles Arbitrary norm b Daniele del Re (La Sapienza & INFN) - Moriond QCD

  7. Trigger and Timing Issues Bunch crossing Dt - 25ns Bunch crossing Dt- 25ns Due to particle slowness, limited trigger and data acquisition efficiency Detailed studies on systematic effects ongoing • Studying possibility of taking data of the next bunch crossing and setting up ad-hoc triggers Daniele del Re (La Sapienza & INFN) - Moriond QCD

  8. b and Mass Measurements Goal: stau mass 1) b fromtime of flight • both ATLAS and CMS use muon drift tubes • timing information and staggering used to extract delays with respect to muons and calculate b 2) b fromionization (dE/dx) in tracker (CMS) for low b’s TOF and dE/dx tuning on data (CMS): use of Z→mm, cosmics, high ionizing low pT protons tracking Db for 300GeV slepton needed stau track expected muon drift averaged over all layers actual stau drift 500GeV mass charged particles dx MIPs Daniele del Re (La Sapienza & INFN) - Moriond QCD

  9. Discovery Potential btrk-1 btrk-1 Two options proposed by CMS TOF + dE/dx combined • sel. criteria: bTOF<0.8, bDEDX<0.8 and quality requirements on tracking • almost background free measurement ! • at least 3 events to claim discovery Standalone tracker (dE/dx only) • as a cross-check bkg stau bDT-1 bDT-1 TOF + dE/dx combined GMSB stau Stop (split susy) KK tau Daniele del Re (La Sapienza & INFN) - Moriond QCD

  10. High-Mass Resonances: Di-lepton • Many extensions of the Standard Model predict resonances decaying to two leptons and with large masses: • super-string inspired, extra dimensions and GUT theories; • left-Right Symmetric Models; • little Higgs Models • Resonances produced via Drell-Yan process • Stringent limits from precision EW experiments and direct searches • Given the striking signature, di-lepton scan over a wide range of masses represents a priority for experiments, regardless of indirect limits and models. Focus on maximizing • mass resolution: significance decreases as the square root of resolution • background rejection TEVATRON limits ~ 1 TeV Daniele del Re (La Sapienza & INFN) - Moriond QCD

  11. Experimental Issues Analysis strategy: • Two leptons (high pT) • QCD and non leptonic backgrounds reduced with isolation (in a cone around lepton direction): • no additional tracks • no hadronic deposit • no additional electromagnetic deposit • Invariant mass used for signal extraction (likelihood fit) Complications: • charge measurement flipped because of large momentum • not perfect momentum resolution at early data taking, affecting invariant mass measurements Backgrounds: • Irreducible Drell-Yan (but small at very high masses) • Other contributions are almost negligible Daniele del Re (La Sapienza & INFN) - Moriond QCD

  12. Di-muon Analysis New results from CMS Selection criteria: • L1+HLT trigger requirements (single, double muon triggers), e ~ 97-98% • Global reconstruction: tracker + muon detector • Tracks with opposite charge • pT>20GeV efficiency ~ 80% at 2TeV - misidentification < 1% in barrel small background contribution (S/B>20) Efficiencies from data (Z→mm tag and probe) • one m is reconstructed with tight cuts • cut on Z invariant mass • recoiling m probe to measure efficiencies • Small stat. at high pT. Extrapolate at start-up Muon efficiency from data with tag and probe Z→mm method for 100pb-1 Global muon reconstruction Daniele del Re (La Sapienza & INFN) - Moriond QCD

  13. Di-muon: Effect of Misalignment • Checked impact of misalignment on measurement at beginning of data taking • Chambers shifted and rotated randomly (±5mm and ±5mrad) to simulate start-up conditions • Used track based alignment with muons from W in 100pb-1 Results for 100pb-1: • Mass resolution affected • ~doubled compared to perfect alignment • small negative shift • Small impact on background amount Perfect alignment Arbitrary norm With misalignment in 100pb-1 scenario Drell Yan bkg Daniele del Re (La Sapienza & INFN) - Moriond QCD

  14. Di-muon: Discovery Potential • Use of unbinned maximum likelihood fit with both signal and background normalizations floating • Discovery luminosity estimated with likelihood ratio • 1-2 TeV resonances (ZSSM and Zy) discovered with low statistics Z′→mm 1TeV Zy in 100pb-1 ZSSM bkg-only fit Zy sig+bkg fit Daniele del Re (La Sapienza & INFN) - Moriond QCD

  15. Di-electron • Di-electron invariant mass resolution improves with e± momentum • dominated by constant term in em calorimeter for very high E • ATLAS: di-electron better than di-muon • CMS: important saturation effects after ~3TeV • Selection similar to di-muon case (e± trigger and identification,pT, isolation) • Example of potential for Randall-Sundrum scenario (Set A,B,C are three different choices of effective coupling constants) 4TeV KK Z′ Daniele del Re (La Sapienza & INFN) - Moriond QCD

  16. Conclusions • Signatures with long lived particles (both neutral and charged) and di-lepton high-mass resonances, if seen, will represent an undisputable proof of new physics at the LHC • Discoverypossible already at start-up (luminosity<1fb-1) • Presented last updates on this topic from both ATLAS and CMS experiments • Studies performed with a realistic simulation of detector • including uncertainties from data-driven calibrations at beginning of data taking Daniele del Re (La Sapienza & INFN) - Moriond QCD

  17. BACKUP Daniele del Re (La Sapienza & INFN) - Moriond QCD

  18. ATLAS and CMS Detectors A Large Toroidal LHC ApparatuS Compact Muon Solenoid Total weight 7000 t Overall diameter 25 m Barrel toroid length 26 m End-cap end-wall chamber span 46 m Magnetic field 2 Tesla Total weight 12 500 t Overall diameter 15.00 m Overall length 21.6 m Magnetic field 4 Tesla Detector subsystems are designed to measure: energy and momentum of g ,e, m, jets, missing ET up to a few TeV Daniele del Re (La Sapienza & INFN) - Moriond QCD

  19. CMS Detector: Tracker Reconstruct tracks and charged particles momentum • Two different detector types: • Pixel • - 100x150mm2 • - s(r-f)~10mm, s(z)~ 20mm • Silicon strips • - thickness 320-500mm • - pitch 80-500mm • - s(r-f)~10mm, s(z)~ 20mm • About 220 m2 of Si Sensors • 107 Si strips • 6.5∙107 pixels •  A total of O(108) channels!!! Daniele del Re (La Sapienza & INFN) - Moriond QCD

  20. CMS Detector: EM Calorimetry Reconstruct photon and electron energy >75k lead tungstate crystals crystal lenght ~23cm Front face 22x22mm2 PbWO4 30g/MeV X0=0.89cm Daniele del Re (La Sapienza & INFN) - Moriond QCD

  21. CMS Detector: Muon Detector Resistive Plate Chambers RPC Course position, fine timing Barrel 80K channels Endcap 92K channels Reconstruct muons Drift Tubes (DT) 250 Chambers 200K Channels TDC 200μm Resolution Cathod Strip Chambers (CSC) 468 Chambers 240K strips 150μm Resolution CSC Daniele del Re (La Sapienza & INFN) - Moriond QCD

  22. GMSB: some parameters SUSY breaking term Mass of gaugino and scalars of MSSM (ai couplings) vev superfield Daniele del Re (La Sapienza & INFN) - Moriond QCD

  23. GMSB: S and B MET (CMS) Daniele del Re (La Sapienza & INFN) - Moriond QCD

  24. GMSB: ATLAS angular resolution Daniele del Re (La Sapienza & INFN) - Moriond QCD

  25. Long Lived: Standalone Daniele del Re (La Sapienza & INFN) - Moriond QCD

  26. Long Lived: ATLAS b M(GeV) Daniele del Re (La Sapienza & INFN) - Moriond QCD

  27. Di-lepton in CMS KK Z’ Daniele del Re (La Sapienza & INFN) - Moriond QCD

  28. Z’: discriminate models Distinguish • spin-1 Z(1) from spin-2 G: angular distribution of decay products • spin-1 Z(1) from spin-1 Z’ with SM-like couplings: forward-backward asymmetry due to contributions of the higher lying states, interference terms and additional √2 factor in its coupling to SM fermions. The Z(1) can be discriminated for masses up to about 5 TeV with L=300fb-1. 4 TeV resonances 4 TeV Z(1)/g(1) or Z’ or RS Graviton? 1000 2000 3000 4000 1000 2000 3000 4000 100 fb-1 1000 2000 3000 4000 1000 2000 3000 4000 M (GeV) Daniele del Re (La Sapienza & INFN) - Moriond QCD

  29. RS: set A,B,C cross-sections Daniele del Re (La Sapienza & INFN) - Moriond QCD

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