tW 共振态 b *在 LHC/CMS 上的寻找

tW 共振态 b* 在 LHC/CMS 上的寻找孟祥伟

Guoming Chen, Xiangwei Meng, Sarmad Shaheen, Huaqiao Zhang and Shihai Zhu IHEP,CAS

粒子天体中心 . 高能物理研究所中国科学院

中国物理学会高能物理分会第 9 届全国会员代表大会暨学术年会武汉 . 湖北 4 月 18-22 日 .2014 年

2014-04-20 1第 9 届全国会员代表大会暨学术年会 20,04, 2014

Contents Introduction

Data Strategy and methods

preSelection Background estimation Selection optimization Systematic uncertainties Limit setting

Search results

Summary


Introduction Single top quark signature sensitive to many models of new physics

b* framework Excite quark/lepton could reveal the substructure of SM fundamental particles Composite 3rd generation quark model allows FCNC/SM coupling

Previous searches mostly exploit the coupling between excited and u/d

Recent search by ATLAS using full 7 TeV data, set lower limit to ~1TeV with 4.7/fbPhys. Lett. B 721 (2013) 171-189

Aim at full 8TeV 2012 data at CMS Sharing the same selection and background modeling as other tW analysis


Single b* theory b* predicted by composite 3’rd generation model J. Nutter, R. Schwienhorst, D. Walker, J.-H. Yu, Phys. Rev. D 86 (2012) 094006, arXiv:1207.5179 [hep-ph] generated coupling to a gloun and a b quark decay could be bg, bZ, bH or tW purely left-handed, purely right-handed, or vector like with equal couplings to both left and

right-handed parts


Leading-order Feynman diagram for single-b∗-quark production and decay to Wt

Data and MC samples 2012 data: 8TeV 19.8/fb Muon/Electron data Stream

MC samples b* samples MadGraph5+pythia Other backgrounds: official production

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process generator Cross section [pb]

tW Powheg+pythia 22.2 (NNLL)Single top t-channel Powheg+pythia 87.1(NNLL)Single top s-channel Powheg+pythia 5.55(NNLL)ttbar MadGraph+Pythia 245.8(NNLL)W+jets MadGraph+Pythia 36257.2(LO)Z+jets MadGraph+Pythia 3503.71(NNLO

)WW Pythia 57.110(LO)WZ Pythia 32.316(LO)ZZ Pythia 8.255(LO)QCD(EM enriched, 20<pT<30 GeV) Pythia 2914860(LO)QCD(EM enriched, 30<pT<80 GeV) Pythia 3866200(LO)QCD(EM enriched, 80<pT<170 GeV) Pythia 183294.9(LO)QCD(EM enriched, 170<pT<250 GeV) Pythia 4586.5 (LO)QCD(Mu enriched, Pt>20GeV) Pythia 134680(LO)

Dedicated b*tWlepton+jet, left-/right-handed b*full simulation, central produced

第 9 届全国会员代表大会暨学术年会 20,04, 2014

Object definition/Event Selection Electron

MVA Id, Pt>30GeV, |eta| < 2.4 && not in 1.4442<|eta|<1.5660, leptonsRhoCorrectedRelIso<0.1

Muon PF/global Muon, Pt>26GeV,|eta|<2.1 leptonDeltaCorrectedRelIso<0.1Delta R(muon,jet)>0.3

Jet: PF AK5 jets, Pt>40 GeV, B-tagged Jet: CSVT jets MET: unclustered MET

CMS Single Top Group definition

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Preselection high Pt trigger Chain

Muon: HLT_IsoMu24_eta2p1_v13/ HLT_Ele27_WP80_v* Primary vertex, Good Run, data cleaning etc. Exactly one electron or muon: Veto additional loose leptons Select only 3 Jets, one b-tagged

Optimized with central jets of |eta|<2.4 Preselection + lepton Pt>130 GeV


QCD enriched control region

QCD from these plots are demonstrate onlyfrom MC simulation predictions, limited by MC statistics

Anti-isolation control region: QCD purity ~99%Electron: RhoCorrectedRelIso > 0.3Muon: DeltaCorrectedRelIso > 0.3

Electron Channel Muon Channel


QCD background Fitting

QCD Data Driven WeightMuon+3J1T : (2227 ± 240) / 33731 Electron+3J1T: (3143 ± 298) / 46291

Muon ChannelQCD = 2227

Electron ChannelQCD = 3143

Fit methods: p0*MC + p1*QCD, MC: MC simulation of single top, ttbar, W, Z, dibosonQCD: data QCD enriched control region

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region contaminated for uncertainties Muon+3J1T : ± 130 / 33731 Electron+3J1T: ± 53 / 46291


Data Driven W+Jets estimation

W+Jets Data Driven WeightMuon+3J1T : (8724 ± 545) / 4598 Electron+3J1T : (9211 ± 478) / 3956

Fit methods: p0*MC + p1*Wjets + QCDQCD: from DataW+Jets: MC sampleMC: MC samples of single top, ttbar, Z, diboson

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Muon ChannelW+jets = 8724

Electron ChannelW+jets = 9211

MC to model the shape of W+jets, other detector systematics like JES/JER/Btag/mis-Tag/leptonSF etc also considered as the uncertainties that impact W+jets shape modeling


Data driven Estimation CheckFor QCD estimation, we use W+jets from MC predictionNow fixed this W+jets to data driven value and redo QCD

estimation as cross check

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Electron ChannelQCD = 2299

Muon ChannelQCD = 3304

Changes on QCD estimation within the fitting uncertaintiesScale factors on other MCs are very close to 1


Selection Optimization Methodology

Optimize the cuts on jet pT, leading jet pT, MET, transverse W mass and MET

1. Change cut on jet pT, redo the whole analysis to find the best EXPECTED limit on the 1300 GeV b*

2. Fix jet pT to the value that find above, redo step1 with other variables and fix to the optimized cut

3. After optimized on all variables, loop again to the first optimized variable and so, until the optimization does not change the cut

This lead to the final selection Preselection (jet |eta|<2.4) + lepton Pt > 130 GeV


Events Yield

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Statistical uncertainties only


Data/MC at final Selection

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MET

Electron Channel

Muon Channel


Systematic Uncertainties I Theory modeling (both Acceptance and

Shape) Q2: Dedicated samples with Factorization

and Renormalization scale vitiate a factor 4 or ¼6-8% impact on the acceptance

Top Mass: Dedicated sample with top mass variant +-1 GeV2-4% impact on the acceptance

Matching: Dedicated sample with MLE matching threshold changed13% on ttbar

PDF: Use CT10 Error PDF to evaluate both acceptance and shape unc. 4-12%, on the backgrounds, 17-58% on

the signal

Bkg Normalization Acceptance only

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sample Q2 Top Mass

Matching PDF

ttbar Y Y Y YtW N Y N YT-channel Y Y N YS-channel N N N YW+jets N N N YZ+jets N N N YWW/WZ/ZZ N N N Y

QCD N N N Yb* N N N Y


Systematic Uncertainties II Detector effects

Lepton Scale factors ID/Trigger/Isolation

B-tagging Mis-tagging JES/JER Pile-Up

Luminosity: 2.6%, Acceptance only

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Theory modeling Theory: >~10%

Bkg Normalization ~10%-30%

Detector effects JES: 1-5% B-tag: 2-4% Others: <1%

Luminosity: 2.6%


following recipes from Top group recommendation, including both acceptance and shape uncertainties

Limit Setting

Tool: Theta Method: Asymptotic CLs limits

Cross-checked by Bayesian limits within Theta Likelihood function


Fitting variable: b* mass

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Electron channel

Muon channel

b* mass


Limit results

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With Linear assumption for the theory cross-section

Exp:Obv:

Left-handed

right-handed

Vector Like


Systematics Impact on limit Remove one systematic each time to see the change of

expected limits Biggest impact comes from PDF (11GeV) , all background

normalization(7GeV), JES(4GeV)

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Unc. removed Exp. Limit Unc. removed Exp. Limit--- 951 Mis-tag 951JES 955 Pile-Up 952JER 951 Matching 952lepSFID 951 PDF 962lepSFIso 951 Q2 952lepSFTrig 949 Top Mass 949B-tag 951 Normalization 958Lumi 951


Summary and Outlook

b* searched on full 8 TeV data CMS with tW Lepton+Jets channel Data driven QCD and W+Jets estimation Systematic uncertainties

No tW resonance bump found, Limit setting for left-,right-handed and vector like b* b* below 950GeV excluded at 95% CL (purely left-handed

couplings) the systematics impact checked

Will combine results from dilepton channel and full hadronic channel


THANKS!

2014-04-20 第 9 届全国会员代表大会暨学术年会 20,04, 2014 21

tW 共振态 b *在 LHC/CMS 上的寻找

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