Top Physics at CMS. Intae Yu. Sungkyunkwan University (SKKU), Korea Yonsei University, Sep 12 th, 2013

Transcription

1 Top Physics at CMS Intae Yu Sungkyunkwan University (SKKU), Korea Yonsei University, Sep 12 th, 2013

2 Outline Overview of CMS Operation Korea CMS Group Doing Top Physics at LHC Top Production Top Quark Mass Top and W Polarization, Top Spin Correlations Search for New Physics In Top Quark Events Prospects and Summary Yonsei University, Sep 12th

3 Overview of CMS operation

4 CMS Run Summary Yonsei University, Sep 12th

5 CMS Run Summary (cont.) Yonsei University, Sep 12th

6 CMS Detector Overview η <2.5 : Tracker s / p T»10-4 p T Å η <4.9 : EM Calorimeter / E 0.03/ E η <4.9 : Had Calorimeter / E 1.0/ E 0.05 η <2.6 : Muon spectrometer / pt 0.10 (1TeV muons) Yonsei University, Sep 12th

7 Total weight t Overall diameter 15 m Overall length 28.7 m ECAL 76k scintillating PbWO 4 crystals HCAL Scintillator/brass The CMS Detector Interleaved ~7k ch 3.8T Solenoid 473 Cathode Strip Chambers (CSC) IRON YOKE MUON ENDCAPS 432 Resistive Plate Chambers (RPC) Preshower Si Strips ~16 m 2 ~137k ch Foward Cal Steel + quartz Fibers ~2k ch Pixels & Tracker Pixels (100x150 mm 2 ) ~ 1 m 2 ~66M ch Si Strips ( mm) Yonsei MUON University, BARREL Sep 12th 2013 ~200 m 2 ~9.6M ch 250 Drift Tubes (DT) and 7

8 CMS Detector Operations Excellent performance during run Data taking efficiency : 90.5% for 7 TeV, 93.5% for 8 TeV All components work well (> 97~98%) Yonsei University, Sep 12th

9 9 Operational Status Strips ECAL Endcap HCAL Outer HCAL Endcap muon RPC muon CSC / E 1.0/ E Pixel Tracke r Strip Tracke r Preshower ECAL Barrel 97.1% 97.75% 97.1% % ECAL Endcap s HCAL Barrel 98.54% % HCAL Endcap s HCAL Forwar d Yonsei University, Sep 12th 2013 HCAL Outer Muon DT 99.96% 99.88% 96.88% 99.1 % Muon CSC % Muon RPC 98.2 %

10 Korea CMS Group

11 Overview of Korea CMS Group 8 Institutions (* New Institutions) Chonbuk*, Chonnam, Kangwon, Korea, Kyungbook Nat l, Seoul Nat l*, Sungkyunkwan, U of Seoul Members (2013.9) Professors 13 Postdocs & Research Professors Graduate Students 41 (23 Ph.D. Students) 16 Staff & Technicians 10 Total 80 Yonsei University, Sep 12th

12 Activities of Korea CMS Group Physics Analysis - Top Physics (top cross section subgroup convener) - Search for Exotics (W, Stop, Charged Higgs,..) - W Physics - Heavy Ion Physics Detector & Upgrades - RPC Gap Production - RPC Chamber Production & Test - RPC Commissioning (RPC commissioning coordinator) - Muon Detector Upgrade R&D (GEM detector) Yonsei University, Sep 12th

13 Members Korea CMS Top Group - 5 institutions (Chonnam, Kangwon, Korea, Sungkyunkwan, U. of Seoul) Activities - In 2010, top pair production cross section measurement in dilepton channel - In 2011, top differential cross section in dilepton channel - In 2012, the first measurement of ttbb production in dilepton channel Ongoing analyses - top pair angular correlations - top mass measurement using a new technique Yonsei University, Sep 12th

14 Doing Top Physics at LHC

15 Top Physics at LHC Heaviest Elementary Particle Largest Yukawa Couplings to Higgs Boson Sensitive to New Physics at High Energy Important Background Events to New Physics Searches Yonsei University, Sep 12th

16 Top Physics at LHC Top quark pair production via gluon fusion at LHC energies mostly top b+w (~100%) Top events are classified by the W decay modes as follows: Yonsei University, Sep 12th

17 High P T leptons - typically, P T > 20 GeV/c - well isolated from jets Top Signatures at LHC High Energy Jets - E T > 20 GeV - b-tagged Large Missing Transverse Energy - 20~60 GeV Yonsei University, Sep 12th

18 Challenges at LHC Many pp interactions per beam crossing (high pile-up) - robust reconstruction of leptons, jets, and missing energy required Top quark reconstruction - jets to quarks assignment - kinematical fits - unfolding kinematical distributions Background estimation - data-driven estimation - multijets, W/Z+ jets, Drell-Yan, and etc Control of systematics - most of the measurements limited by systematics Yonsei University, Sep 12th

19 The challenge of 2012: 8 TeV and high pile-up Yonsei University, Sep 12th 2013

20 Top Production

21 Top Quark Pair Production ~7M top pair events produced at CMS during 2011~2012 Predicted cross sections (NNLO+NNLL) Yonsei University, Sep 12th

22 Top Quark Pair Cross Section Consistent with QCD predictions within uncertainties Comparable experimental and theoretical uncertainties (±5%) Yonsei University, Sep 12th

23 Top Quark Pair Cross Sections at Hadron Collider Yonsei University, Sep 12th

24 Top Quark Pair Differential Cross Sections Differential cross section measurements - constrain Monte Carlo predictions - contribute to PDF determinations - sensitive to new physics Data Analysis - detector effects unfolded to compare with predictions - full reconstruction of top quark kinematics - systematic uncertainties dominate Yonsei University, Sep 12th

25 Top Quark Pair Differential Cross Sections Lepton + Jets channel Normalized to 1 Yonsei University, Sep 12th

26 Dilepton channel Normalized to 1 Top Quark Pair Differential Cross Sections Yonsei University, Sep 12th

27 Single Top Production Single top quarks are produced through charged current weak interactions QCD predictions (NLO+NNLL, 7 TeV) The t-channel cross sections are measured at CMS Yonsei University, Sep 12th

28 Single Top Production Multivariate techniques used for optimization of sensitivity Consistent with QCD calculations Measure the CKM matrix element V tb Yonsei University, Sep 12th

29 Top-Antitop Charge Asymmetry QCD predicts an asymmetry for produced via qq annihilation tt - Top quark emitted along the direction of incoming quark (Tevatron) - Top quarks emitted at larger rapidities (LHC) - exchange of new particles modifies the asymmetry forward-backward asymmetry center - forward asymmetry Yonsei University, Sep 12th

30 Top-Antitop Charge Asymmetry Tevatron observed an anomalous charge asymmetry CMS measurements are consistent with QCD predictions - Dilepton: 0.050± Lepton+Jets: 0.004±0.010± SM: ± Yonsei University, Sep 12th

31 Top Pair Associated Production Top pair production associated with a vector boson (W or Z) Measure couplings between t and V Yonsei University, Sep 12th

32 ttbar bbbar Production The first measurement of ttbb production Measure the cross section ratioσ(ttbb)/σ(ttjj) - ratio = 3.6±1.1(stat)±0.9(syst) % Yonsei University, Sep 12th

33 Top Quark Mass

34 Top Quark Mass Top quark decays before hadronization can measure the quark mass accurately m t, m W, m H are related at loop level Challenges - final state topology/event selection - reconstruction of kinematics - detector modeling (especially, jet energy calibration) Yonsei University, Sep 12th

35 Tevatron Measurements Top Mass Measurements at Tevatron mt = ±0.51(stat)±0.71(syst) GeV Yonsei University, Sep 12th

36 Combined CMS Measurements Top Mass Measurements at CMS m t = ±0.37(stat)±0.91(syst) GeV Yonsei University, Sep 12th

37 Top and W Polarization, Top Spin Correlations

38 W Polarization in Top Decays W helicity is sensitive to the V-A coupling Measure the angular distribution between the lepton and the b quark in the rest frame of W NNLO QCD Yonsei University, Sep 12th

39 W Polarization in Top Decays Results consistent with NNLO QCD Limits on the anomalous couplings g L, g R Yonsei University, Sep 12th

40 W Polarization in Single Top Events First measurement in single top events Consistent with the SM and with the measurement in the top pair events Yonsei University, Sep 12th

41 Top Polarization In the SM, the top quark is produced unpolarized Some models predict different top quark polarizations Measure the polar angle of the lepton in the rest frame of the top Yonsei University, Sep 12th

42 Top Spin Correlations The SM predicts correlation of spin of the top and antitop Measure spin correlation coefficient using angular distribution between leptons (Δφ) Sensitive to new physics CMS 7 TeV Measurement A = 0.24±0.02(stat)±0.08(syst) (SM prediction: 0.31) Yonsei University, Sep 12th

43 Search for New Physics In Top Quark Events

44 Search for Resonant ttbar Production Model-independent search for the production of heavy resonances decaying into top quark pairs m Z > 2.04 CL m KK > 1.82 CL Yonsei University, Sep 12th

45 Search for Resonant ttbar Production Model-independent search in dilepton channels m Z > % CL m Z > % CL Yonsei University, Sep 12th

46 4 th Generation Quarks 4 th generation quarks: t, b t bw, b tw : final states (bb + nw) : inclusive searches Backgrounds: top, tw, W decays M(q ) > 685 GeV/c 2 at 95% CL where q = t, b Yonsei University, Sep 12th

47 Prospects and Summary

48 Future Run Plans of LHC Yonsei University, Sep 12th

49 CMS Detector Upgrades Yonsei University, Sep 12th

50 Future Run Plans of LHC 7-8 TeV run (~30 fb -1 ) : 2010 ~ spin/parity of Higgs particle at 3~4σ - search for SUSY and new physics 13/14 TeV run (~ 300 fb -1 ): ~2022 : Phase 1 - measure properties of Higgs particle - search for new physics at higher mass scale High luminosity 13/14 TeV run ( ~3000 fb -1 ): ~ 2032 : Phase 2 - measure Higgs coupling in precision - search for Multi-TeV new physics Yonsei University, Sep 12th

51 Prospects for Top Physics at LHC The LHC will be a top factory - 75 M top events in Phase 1 (~300 fb -1 ) Direct Measurement of the top-yukawa coupling in tth events Precise measurement of asymmetries and polarizations More accurate measurements of the top mass Search for ttbar resonances Top rare decays (FCNC t Zq) and so many interesting topics Yonsei University, Sep 12th

52 Summary LHC successfully completed its 3-year run and delivered about 30 fb -1 of pp collision data. The CMS detector was working well and accumulated about 27 fb -1 between 2010 and Various properties of the top quark are measured precisely. Most measurements are limited by systematic uncertainties There are no evidence beyond the SM in top physics sector More new results using the full data will come out soon. In the next 20 years, the LHC will be a top factory and the properties of the top quark will be measured in precision and the discovery potential for new physics will be fully investigated. Yonsei University, Sep 12th