Top Physics at CMS Intae Yu Sungkyunkwan University (SKKU), Korea Seminar @ Yonsei University, Sep 12 th, 2013
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 Seminar @ Yonsei University, Sep 12th 2013 2
Overview of CMS operation
CMS Run Summary Seminar @ Yonsei University, Sep 12th 2013 4
CMS Run Summary (cont.) Seminar @ Yonsei University, Sep 12th 2013 5
CMS Detector Overview η <2.5 : Tracker s / p T»10-4 p T Å 0.005 η <4.9 : EM Calorimeter / E 0.03/ E 0.003 η <4.9 : Had Calorimeter / E 1.0/ E 0.05 η <2.6 : Muon spectrometer / pt 0.10 (1TeV muons) Seminar @ Yonsei University, Sep 12th 2013 6
Total weight 14000 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 (80-180 mm) Seminar @ Yonsei MUON University, BARREL Sep 12th 2013 ~200 m 2 ~9.6M ch 250 Drift Tubes (DT) and 7
CMS Detector Operations Excellent performance during 2010-2012 run Data taking efficiency : 90.5% for 7 TeV, 93.5% for 8 TeV All components work well (> 97~98%) Seminar @ Yonsei University, Sep 12th 2013 8
9 Operational Status Strips ECAL Endcap HCAL Outer HCAL Endcap muon RPC muon CSC / E 1.0/ E 0.05 0 20 40 60 80 100 Pixel Tracke r Strip Tracke r Preshower ECAL Barrel 97.1% 97.75% 97.1% 99.16 % ECAL Endcap s HCAL Barrel 98.54% 99.92 % HCAL Endcap s HCAL Forwar d Seminar @ Yonsei University, Sep 12th 2013 HCAL Outer Muon DT 99.96% 99.88% 96.88% 99.1 % Muon CSC 97.67 % Muon RPC 98.2 %
Korea CMS Group
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 Seminar @ Yonsei University, Sep 12th 2013 11
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) Seminar @ Yonsei University, Sep 12th 2013 12
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 Seminar @ Yonsei University, Sep 12th 2013 13
Doing Top Physics at LHC
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 Seminar @ Yonsei University, Sep 12th 2013 15
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: Seminar @ Yonsei University, Sep 12th 2013 16
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 Seminar @ Yonsei University, Sep 12th 2013 17
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 Seminar @ Yonsei University, Sep 12th 2013 18
The challenge of 2012: 8 TeV and high pile-up Seminar @ Yonsei University, Sep 12th 2013
Top Production
Top Quark Pair Production ~7M top pair events produced at CMS during 2011~2012 Predicted cross sections (NNLO+NNLL) Seminar @ Yonsei University, Sep 12th 2013 21
Top Quark Pair Cross Section Consistent with QCD predictions within uncertainties Comparable experimental and theoretical uncertainties (±5%) Seminar @ Yonsei University, Sep 12th 2013 22
Top Quark Pair Cross Sections at Hadron Collider Seminar @ Yonsei University, Sep 12th 2013 23
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 Seminar @ Yonsei University, Sep 12th 2013 24
Top Quark Pair Differential Cross Sections Lepton + Jets channel Normalized to 1 Seminar @ Yonsei University, Sep 12th 2013 25
Dilepton channel Normalized to 1 Top Quark Pair Differential Cross Sections Seminar @ Yonsei University, Sep 12th 2013 26
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 Seminar @ Yonsei University, Sep 12th 2013 27
Single Top Production Multivariate techniques used for optimization of sensitivity Consistent with QCD calculations Measure the CKM matrix element V tb Seminar @ Yonsei University, Sep 12th 2013 28
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 Seminar @ Yonsei University, Sep 12th 2013 29
Top-Antitop Charge Asymmetry Tevatron observed an anomalous charge asymmetry CMS measurements are consistent with QCD predictions - Dilepton: 0.050±0.043+0.010-0.039 - Lepton+Jets: 0.004±0.010±0.012 - SM: 0.0115±0.0006 Seminar @ Yonsei University, Sep 12th 2013 30
Top Pair Associated Production Top pair production associated with a vector boson (W or Z) Measure couplings between t and V Seminar @ Yonsei University, Sep 12th 2013 31
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) % Seminar @ Yonsei University, Sep 12th 2013 32
Top Quark Mass
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) Seminar @ Yonsei University, Sep 12th 2013 34
Tevatron Measurements Top Mass Measurements at Tevatron mt = 173.20±0.51(stat)±0.71(syst) GeV Seminar @ Yonsei University, Sep 12th 2013 35
Combined CMS Measurements Top Mass Measurements at CMS m t = 173.44±0.37(stat)±0.91(syst) GeV Seminar @ Yonsei University, Sep 12th 2013 36
Top and W Polarization, Top Spin Correlations
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 Seminar @ Yonsei University, Sep 12th 2013 38
W Polarization in Top Decays Results consistent with NNLO QCD Limits on the anomalous couplings g L, g R Seminar @ Yonsei University, Sep 12th 2013 39
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 Seminar @ Yonsei University, Sep 12th 2013 40
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 Seminar @ Yonsei University, Sep 12th 2013 41
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) Seminar @ Yonsei University, Sep 12th 2013 42
Search for New Physics In Top Quark Events
Search for Resonant ttbar Production Model-independent search for the production of heavy resonances decaying into top quark pairs m Z > 2.04 TeV @95% CL m KK > 1.82 TeV @95% CL Seminar @ Yonsei University, Sep 12th 2013 44
Search for Resonant ttbar Production Model-independent search in dilepton channels m Z > 1.3 TeV @ 95% CL m Z > 1.9 TeV @ 95% CL Seminar @ Yonsei University, Sep 12th 2013 45
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 Seminar @ Yonsei University, Sep 12th 2013 46
Prospects and Summary
Future Run Plans of LHC Seminar @ Yonsei University, Sep 12th 2013 48
CMS Detector Upgrades Seminar @ Yonsei University, Sep 12th 2013 49
Future Run Plans of LHC 7-8 TeV run (~30 fb -1 ) : 2010 ~ 2012 - 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 Seminar @ Yonsei University, Sep 12th 2013 50
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 Seminar @ Yonsei University, Sep 12th 2013 51
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 2012. 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. Seminar @ Yonsei University, Sep 12th 2013 52