top physics at cms - yonsei...

Intae Yu

Sungkyunkwan University (SKKU), Korea

Seminar @ Yonsei University, Sep 12th, 2013

Top Physics at CMS

Seminar @ Yonsei University, Sep 12th 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

Overview of CMS operation


CMS Run Summary


CMS Run Summary (cont.)


CMS Detector Overview

|η|<2.5 : Tracker

|η|<4.9 : EM Calorimeter

|η|<4.9 : Had Calorimeter

|η|<2.6 : Muon spectrometer

s / pT »10-4 pT Å0.005

003.0/03.0E/ E

10.0p/ T (1TeV muons)

05.0/0.1E/ E

Seminar @ Yonsei University, Sep 12th 2013

The CMS Detector

3.8T Solenoid

ECAL 76k scintillating

PbWO4 crystals

HCAL Scintillator/brass

Interleaved ~7k ch

• Pixels (100x150 mm2)

~ 1 m2 ~66M ch

•Si Strips (80-180 mm)

~200 m2 ~9.6M ch

Pixels & Tracker

MUON BARREL 250 Drift Tubes (DT) and

480 Resistive Plate Chambers (RPC)

473 Cathode Strip Chambers

(CSC)

432 Resistive Plate Chambers

(RPC)

MUON ENDCAPS

Total weight 14000 t

Overall diameter 15 m

Overall length 28.7 m

IRON YOKE

Preshower

Si Strips ~16 m2

~137k ch

Foward Cal

Steel + quartz

Fibers ~2k ch

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%)


9

05.0/0.1E/ E

Operational Status

0 20 40 60 80 100

muon CSC

muon RPC

HCAL Endcap

HCAL Outer

ECAL Endcap

Strips

Pixel Tracke

r

Strip Tracke

r

Preshower ECAL Barrel

ECAL Endcap

s

HCAL Barrel

HCAL Endcap

s

HCAL Forwar

d

HCAL Outer

Muon DT

Muon CSC

Muon RPC

97.1% 97.75% 97.1% 99.16%

98.54% 99.92%

99.96% 99.88% 96.88% 99.1%

97.67%

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

16

Graduate Students 41 (23 Ph.D. Students)

Staff & Technicians 10

Total 80


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)


Korea CMS Top Group • Members

- 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

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


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:


Top Signatures at LHC

• High PT leptons

- typically, PT > 20 GeV/c

- well isolated from jets

• High Energy Jets

- ET > 20 GeV

- b-tagged

• Large Missing Transverse Energy

- 20~60 GeV


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


The challenge of 2012: 8 TeV and high pile-up

Top Production


Top Quark Pair Production

• ~7M top pair events produced at CMS during 2011~2012

• Predicted cross sections (NNLO+NNLL)


Top Quark Pair Cross Section

• Consistent with QCD predictions within uncertainties

• Comparable experimental and theoretical uncertainties (±5%)


Top Quark Pair Cross Sections at Hadron Collider


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



• Lepton + Jets channel

• Normalized to 1



• Dilepton channel

• Normalized to 1


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


Single Top Production

• Multivariate techniques used for optimization of sensitivity

• Consistent with QCD calculations

• Measure the CKM matrix element Vtb


Top-Antitop Charge Asymmetry

• QCD predicts an asymmetry for produced via annihilation

- Top quark emitted along the direction of incoming quark (Tevatron)

- Top quarks emitted at larger rapidities (LHC)

- exchange of new particles modifies the asymmetry

tt qq

forward-backward asymmetry center - forward asymmetry


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


Top Pair Associated Production

• Top pair production associated with a vector boson (W or Z)

• Measure couplings between t and V


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) %

Top Quark Mass


Top Quark Mass

• Top quark decays before hadronization

→ can measure the quark mass accurately

• mt, mW, mH are related at loop level

• Challenges

- final state topology/event selection

- reconstruction of kinematics

- detector modeling (especially, jet energy calibration)


Top Mass Measurements at Tevatron

• Tevatron Measurements

mt = 173.20±0.51(stat)±0.71(syst) GeV


Top Mass Measurements at CMS

• Combined CMS Measurements

mt = 173.44±0.37(stat)±0.91(syst) GeV

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


W Polarization in Top Decays

• Results consistent with NNLO QCD

• Limits on the anomalous couplings gL, gR


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


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


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)

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 mZ’ > 2.04 TeV @95% CL

mKK > 1.82 TeV @95% CL


Search for Resonant ttbar Production

• Model-independent search in dilepton channels

mZ’ > 1.9 TeV @ 95% CL mZ’ > 1.3 TeV @ 95% CL


4th Generation Quarks

• 4th generation quarks: t’, b’

• t’ → bW, b’→ tW : final states (bb + nW) : inclusive searches

• Backgrounds: top, tW, W decays

• M(q’) > 685 GeV/c2 at 95% CL where q’= t’, b’

Prospects and Summary


Future Run Plans of LHC


CMS Detector Upgrades


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


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


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.

top physics at cms - yonsei...

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