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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.

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Presentation on theme: "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."— Presentation transcript:

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 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD2 Intro and Outline Two striking signatures to discover new physics at the LHC: 1) long lived particles with large masses and low  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

3 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD3 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  Present limits: Tevatron,  > 80 TeV, m(neutr.,charg.) > 108/195 GeV Par.Description  SUSY breaking scale MmMm Messenger mass scale tan  Ratio of Higgs vev NmNm Number of SU(5) messenger multiplets sign(  )  from Higgs sector C grav Sets NLSP lifetime

4 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD4 GMSB: final states with  ’s If NLSP neutralino  2  in event Selection –  isolation, cut on p T (  ) – Large MET, Njets > 3 Main backgrounds –  +jets, W+jets – after cuts: S/B > 10 If lifetime(  ) ≠ 0  non-pointing  –experimentally tough measurement Lifetime measurement: –transversal (CMS) and longitudinal (ATLAS) cluster shape to get photon direction –time measurement in calorimeter (ATLAS) to close kinematics   p p q q q q … … jet

5 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD5 GMSB with  ’s: Discovery Potential Low statistics for discovery both in pointing (c  =0) and non-pointing scenarios for  =140 TeV for  =90 TeV L=100fb -1 Lifetime measurement feasible but large statistics needed Reconstruction of leptons in the event can be used to extract both neutralino and slepton masses c  (cm)

6 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD6 GMSB with staus Points used by CMS  mass NmNm 33  TeV  5080 M m  TeV) Tan  10 sign(  ) 11 C grav 10 4 Arbitrary norm  With a different choice of parameters (e.g. N m >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  final states) Large stau mass implies low  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

7 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD7 Trigger and Timing Issues 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 Bunch crossing  t - 25ns

8 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD8  and Mass Measurements Goal: stau mass 1)  from time of flight both ATLAS and CMS use muon drift tubes timing information and staggering used to extract delays with respect to muons and calculate  2)  from ionization (dE/dx) in tracker (CMS) for low  ’s TOF and dE/dx tuning on data (CMS): use of Z→ , cosmics, high ionizing low p T protons 500GeV mass charged particles MIPs tracking needed averaged over all layers  for 300GeV slepton expected muon drift actual stau drift stau track xx

9 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD9 Discovery Potential Two options proposed by CMS TOF + dE/dx combined sel. criteria:  TOF <0.8,  DEDX <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 GMSB stau Stop (split susy) KK tau bkgstau TOF + dE/dx combined  DT   trk 

10 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD10 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

11 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD11 Experimental Issues Analysis strategy: Two leptons (high p T ) 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

12 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD12 Di-muon Analysis Selection criteria: L1+HLT trigger requirements (single, double muon triggers),  ~ 97-98% Global reconstruction: tracker + muon detector Tracks with opposite charge p T >20GeV  efficiency ~ 80% at 2TeV - misidentification < 1% in barrel  small background contribution (S/B>20) Efficiencies from data (Z→  tag and probe) –one  is reconstructed with tight cuts –cut on Z invariant mass –recoiling  probe to measure efficiencies Small stat. at high p T. Extrapolate at start-up New results from CMS Muon efficiency from data with tag and probe Z→  method for 100pb -1 Global muon reconstruction

13 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD13 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 With misalignment in 100pb -1 scenario Drell Yan bkg Arbitrary norm

14 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD14 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 (Z SSM and Z  ) discovered with low statistics Z SSM ZZ Z′→  1TeV Z  in 100pb -1 sig+bkg fit bkg-only fit Model  /M %  BR(  ) with interference 1TeV1.5TeV2TeV Z SSM fb84fb25fb ZZ fb31fb13fb

15 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD15 Di-electron 4TeV KK Z′ 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,p T, isolation) Example of potential for Randall-Sundrum scenario (Set A,B,C are three different choices of effective coupling constants)

16 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD16 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 Discovery possible 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

17 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD17 BACKUP

18 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD18 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 t Overall diameter m Overall length 21.6 m Magnetic field 4 Tesla Detector subsystems are designed to measure: energy and momentum of ,e, , jets, missing E T up to a few TeV Compact Muon Solenoid A Large Toroidal LHC ApparatuS ATLAS and CMS Detectors

19 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD19 CMS Detector: Tracker Reconstruct tracks and charged particles momentum Two different detector types: Pixel  100x150  m 2  (r-  )~10  m,  (z)~ 20  m Silicon strips  thickness  m  pitch  m  (r-  )~10  m,  (z)~ 20  m About 220 m 2 of Si Sensors  10 7 Si strips  6.5∙10 7 pixels  A total of O(10 8 ) channels!!!

20 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD20 CMS Detector: EM Calorimetry Reconstruct photon and electron energy >75k lead tungstate crystals crystal lenght ~23cm Front face 22x22mm 2 PbWO 4 30  /MeV X 0 =0.89cm

21 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD21 CMS Detector: Muon Detector Reconstruct muons Drift Tubes (DT) 250 Chambers 200K Channels TDC 200μm Resolution Resistive Plate Chambers RPC Course position, fine timing Barrel 80K channels Endcap 92K channels Cathod Strip Chambers (CSC) 468 Chambers 240K strips 150μm Resolution CSC

22 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD22 GMSB: some parameters SUSY breaking term vev superfield Mass of gaugino and scalars of MSSM (  i couplings)

23 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD23 GMSB: S and B MET (CMS)

24 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD24 GMSB: ATLAS angular resolution

25 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD25 Long Lived: Standalone

26 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD26 Long Lived: ATLAS  M(GeV)

27 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD27 Di-lepton in CMS KK Z’

28 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD28 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 TeV Z (1) /  (1) or Z’ or RS Graviton? 4 TeV resonances fb M (GeV)

29 03/10/08Daniele del Re (La Sapienza & INFN) - Moriond QCD29 RS: set A,B,C cross-sections


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