Teruki Kamon For the CMS Collaboration

Transcription

1 Searches at CMS Teruki Kamon For the CMS Collaboration Mitchell Institute for Fundamental Physics and Astronomy Texas A&M University & Department of Physics Kyungpook National University Ninth Particle Physics Phenomenology Workshop (PPP9) National Central University (NCU), Taiwan, June 3 ~ June 6, 2011 June 2011 SUSY Searches at CMS 1 OUTLINE Summary 3 1) Why? Dark Matter and SUSY 2) Where? LHC & CMS Detector 3) How? SUSY Searches Prologue It has been 13.8 B years, since the LHC machine was set up. The machine finally started providing proton-proton collisions at a center-of-mass energy of 7 TeV on March 30, 2010 and became the energy frontier machine to lead discoveries of new particles. The Standard Model (SM) is currently well tested up to ~100 GeV, but is expected to break down in the TeV domain where new physics should occur. This is precisely the domain that we will study at the LHC. 2

2 Dark Matter and SUSY LHC Now CMB ~ seconds annihilation combination Probing 10-7 sec. after Big Bang Teruki Kamon SUSY Searches at CMS 3 LHC at CERN 27 km ring 4

3 Compact Muon Solenoid & PF (see Appendix A) As of May 31 The CMS (21 m x 15 m x 15 m, 12,500 tonnes) is one of two super-fast & super-sensitive detectors, consisting of 15 heavy elements, collecting debris from the collision and converting a visual image for us. Particle Telescope at CERN vs. Hubble Space Telescope in outer space 5 CMS SUSY Searches in 2010 URL: Fully hadronic searches: SUS (arxiv: , PLB698 (2011) 196) & SUS : T SUS : MET + b-jets + T SUS : inclusive MET + 3jets SUS : Inclusive search with Razor variables Searches with leptons: SUS : MET + jets + single lepton SUS (arxiv: ): MET + jets + LS dilepton SUS (arxiv: , JHEP): MET + jets + OS dilepton. SUS : Multileptons SUS & SUS (~200 pb -1 ): MET + jets + Z Searches with photons: SUS (arxiv: , PRL): MET + jets + photons SUS (arxiv: ): MET + photon + lepton 6

4 Missing ET(& Jets) at the LHC Example: SUSY g~ g~, g~ q ~, or q ~ q ~ production will be dominant, followed 0 by their decays (e.g., q ~ q ~ 2 ). Jets R parity conservation Stable lightest supersymmetric particle (LSP) 0 If LSP is the lightest neutralino ( ~ 1 ), it will escape the detector MET ( E T ) 0 ~ 1 = Cold Dark Matter candidate Cosmology Thus, the evidence of SUSY-like new physics will appear in the Jets+MET final states. Cosmology LHC = [Exciting Motivation][Right Place&Timing] MET - inferring new physics (e.g., Dark Matter) /files/SUS pas.pdf 8

5 All hadronic inclusive analysis with key variables: HT = scalar sum of Jet p T (selecting large s-hat production) MHT = negative vector sum of Jet p T Baseline Event selection: HT Trigger 3 jet with p T > 50 GeV & < 2.5 (central production) Veto events with isolated electrons & muons (suppress EWK background) (MHT, Jet1,2,3) > (0.5, 0.5, 0.3) (reduce QCD background) HT > 300 GeV & MHT > 150 GeV baseline selection Final Event Selection: Analysis Strategy High HT (HT > 500 GeV): High eff. for signals with long cascade decay chains High MHT (MHT > 250 GeV): High background rejection 9 Baseline Selection HT > 300 GeV & MHT > 150 GeV An out-of-box comparison of Data vs MC for HT and MHT Baseline selection w/o MHT cut >150 GeV [ LM1] m0 60 GeV, m1/ GeV, tan 10, A 0, 0 0 Baseline selection >300 GeV Major BGs: Invisible Z() + Jets.. Irreducible background Top / W + Jets QCD Jets High MHT High HT Data-driven BG Estimate 10

6 MET / MHT Invisible Z Three different methods using boson+jets were employed to obtain the data-driven estimates of this background (substitute boson with MHT) remove - + W - remove _ - remove Lower statistics than and W Suffer from Br(Z) / Br(Z)=1/6 Similar event topology Higher stat than Z (W+jets rate is about x 2.5 of Z+jets) Similar to Z+jets at large p T (MHT) High stat (no branching ratio) Cross check of different channels: photon + jets provides an accurate prediction (Appendix B) Solely used for limit calculation 11 N Invisible Z 2 1 Z( ) jets data Z( ) jets jets MC Reco FRAG data/mc FRAG : Correct for fragmentation photons based on JETPHOX PUR : Correct for photons from light mesons using shower shape MC ID PUR data N jets data

7 W MET / l MHT W/Top Leptons failing the lepton veto contribute to background. There can be 3 reasons to lose leptons: the lepton is not reconstructed not isolated out of acceptance [Step 1] Start with a control sample of events with exactly one muon and measure the identification and isolation (in)efficiencies from data [Step 2] Scale the control sample according to the measured (in)efficiencies from data 13 [Step 1] Start with a muon+jets sample [Step 2] Replace the muon by tau response template derived from MC [Step 3] Recalculate HT and MHT including this expected energy from tau [Step 4] Correct for muon acceptance W/Top Trigger efficiency, Reco efficiency BR(W )/BR(W)* BR(hadrons) 14

8 Ideal Jet MET / MHT Reality QCD Significant p T imbalance due to Physics effects: semi-leptonic decay of heavy flavor quarks Detector effects: Intrinsic jet energy resolution Dead channels (a significant contribution from ECAL) [Step 0] Jet response and resolution functions using + jets and dijet events Balanced multijet Response functions Smearing 15 QCD: Rebalance + Smearing [Step 1] Rebalance the data events (jets with p T >10GeV)usingjetp T resolutions by maximizing a likelihood (LJets), being subject to constraint MHT = 0 create the pseudo-particle-level QCD events [Step 2] Smear rebalanced jets (p T > 10 GeV) with resolution functions Baseline selection w/o MHT cut Baseline selection MHT >150 GeV MHT HT HT R+S predicts full event kinematics (jet p T and angular distributions) Consistent with Factorization Method (extrapolate two-variable correlation to signal region) 16

9 Results No excess of observed events over expected Standard Model prediction. Setting limits. 17 For Future Excitement MHT [ LM1] m 60 GeV m 0 1/ 2 tan 10, A GeV 0 0 MHT = 693 GeV & HT = 1132 GeV M eff = MHT + HT = 1.83 TeV No b-tagged jet & No isolated lepton Incompatible with W or top mass HT Invisible Z??? 18

10 Within the msugra/cmssm 4 parameters and a sign: m 0, m 1/2, tan, A 0, sign() m 0 : common mass for spin 0 particles at the GUT scale m 1/2 : common mass for spin 1/2 particles at the GUT scale tan 10 tan 10 Gluino masses up to ~700 GeV are excluded. Less sensitive to tan(see Appendix C) Sensitivity greater than ATLAS at high m 0. High HT search region was effective. Sensitivity lower than ATLAS at high m 1/2. Need to look at 2 jet events See Appendix D for Simplified Model (currently only 3 jets) 19 CHALLENGE: All hadronic inclusive search is complete at the same pace as other searches. Summary ROBUST data-driven techniques for all SUSY searches in 36 pb -1 in 2010 GOOD agreement with the SM predictions HOT: ~1 fb -1 /month. Big excitement in 2011 & 2012 Cross-section limits pb, excluding m(gluino) < 700 GeV in the msugra/cmssm plane. [ LM1] m0 60 GeV, m1/ GeV, tan 10, A 0,

11 Personal Remarks 21 Remark 1: MET + Jets + Taus Excluded by 1) a Rare B decay b s 2) b No CDM candidate 3) c Muon magnetic moment Rouzbeh Allahverdi, Bhaskar Dutta, Yudi Santoso arxiv: CDMS II Teruki Kamon Stau - neutralino co-annihilation scenario (e.g., Arnowitt, Dutta, Gurrola, Kamon, Krislock, Toback, PRL100 (2008) ) SUSY Searches at CMS 22

12 Remark 2: B s 23 Remark 3: MET + Jets + W s Bi-Event Subtraction Technique (hep-ph/ ) B. Dutta, T. Kamon, N. Kolev, A. Krislock pp t t j ( W b) ( W b ) j j l j pp W jjjj l BEST: jet mixing from two different events (TTbar, TTbar), (TTbar,W), (W,W) Teruki Kamon SUSY Searches at CMS 24

13 BEST in TTbar & SUSY m jj m bw m jw m jj 25 Remark Summary 4: PPC Interconnection between Particle Physics and Cosmology PPC 2011 at CERN, June PPC 2012 at??? 26

14 Simplified Grand Summary CSI: Supersymmetry at the LHC Collider Scene Investigation LHC keep going! 27 Appendix A: CMS Detector & PF SUSY Searches at CMS 28

15 Particle Flow (PF) Algorithm In this search, all physics objects (jets, leptons, HT, MHT etc) are reconstructed with the PF algorithm. Basic idea: Reconstruct and identify all different types of particles Apply corresponding calibrations The list of particles is given to the jet clustering and missing E T (MET) reconstruction algorithm 29 Charged hadrons ~65% of jet energy Use the high resolution tracker ~1% at 100 GeV Teruki Kamon SUSY Searches at CMS

16 Photons ~25% of jet energy Use high resolution / good granularity ECAL Granularity: 0.02 () Energy resolution: ~2%/E Teruki Kamon SUSY Searches at CMS Neutral hadrons ~10% of jet energy Use HCAL Granularity: 0.1 () Energy resolution: ~100%/E Teruki Kamon SUSY Searches at CMS

17 Particles clustered in jets Jet: Charged hadron (solid) Photon (dashed line) Neutral hadron (dotted line) Teruki Kamon SUSY Searches at CMS PF Jet and MET Performance Jet energy response Calorimeter jet PF jet Jet energy resolution Calorimeter jet PF jet PF algorithm improves the performance of jet and missing E T reconstruction significantly. 34

18 Appendix B: Invisible Z Method using leptonic W samples obs bkg Z 6 N N Z R W W N( Z ) R W l 10 A W l W W bveto Method using leptonic Z samples obs RECO Consistent with photons and with simulation. Z from photon results best precision: therefore solely used for limit calculation W N Z N Z Z Z N( Z ) R R A Z ll Z ll Z Z bkg Baseline selection: 29 Z ee( ) : 3218(12 13 Combined : 1710 Z ( Sim) : ) lepton Z ( Iso where Iso leptopn trig ) 2 RECO trig HLT, 1 (1 35 Appendix C: Large tan Case Low tan vs. High tan trig HLT ) 2 tan 10 tan 50 Less sensitive to tan 36

19 Appendix D: Simplified Model Focus on topology instead of underlying physics model (physics is not understood anyway) Provide ability to characterize data in model-independent and more comprehensive ways Provide intuitive guidance for investigation Allow one to factorize the key elements potentially present in a new signal in order to answer specific questions. Set limit on cross section (.Br) Any model with same topology (parent particle mass, decay chain, duaghters mass) can be easily compared with experimental results. 37 Within Simplified Model m(gluino) m(lsp) m(squark) m(lsp) 38

20 Appendix E: Old Limits on msugra/cmssm 4 parameters and a sign: m0, m1/2, tan, A 0, sign() m 0 : common mass for spin 0 particles at the GUT scale m 1/2 : common mass for spin 1/2 particles at the GUT scale 39