James Howarth on behalf of the ATLAS Collaboration The University of Manchester

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Spin Correlations, Polarisation and Charge Asymmetries in Top Quark Pairs. James Howarth on behalf of the ATLAS Collaboration The University of Manchester. Top Quark Properties. l +. Decay W Polarisation , Colour Flow, Branching Ratios, | V tb |. ν. The Top Quark - PowerPoint PPT Presentation

Transcript of James Howarth on behalf of the ATLAS Collaboration The University of Manchester

Z->ee Tag and Probe tracking efficiency study

Spin Correlations, Polarisation and Charge Asymmetries in Top Quark Pairs James Howarthon behalf of the ATLAS CollaborationThe University of Manchester

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1Top Quark Properties2ttl+W+W-dubbPropertiesMass, Mass difference, Width, Charge, Spin, Polarisation, Spin correlation, AsymmetriesProductionCross section, generator studies, rare couplingsDecayW Polarisation, Colour Flow, Branching Ratios, |Vtb|The Top Quark

Very heavy (Mtop =173 GeV) Narrow width short lifetime (10-25s) Decays before hadronisation Bare quark (almost)

Dilepton Events3

Dilepton Events: 2 Leptons (opposite sign, isolated, trigger match) At least 2 Jets ET > 60 GeV (ee/) HT > 130 GeV (e) HT = Scalar sum of all lepton & jet pT mll > 15 GeV and veto 81 GeV < mlll < 101 GeV (ee/) Optional b-tagging (70% efficiency working point)

l+ l-lbbttW+W-miss Single Lepton4u d l-lbbttW+W-Single Lepton Events: 1 Lepton (isolated, trig match) At least 4 Jets with at least 1 b-tag(e + jets) ET > 20 GeV ET + mT > 30 GeV( + jets) ET > 35 (30) GeV mT > 25 (30) GeV

mT =

miss miss miss WWWSpin Correlation and Polarisation5Introduction Spin Variables6 Polarisation (P) and Spin Correlation (A) closely related.

Greg Mahlon, 3rd International Workshop on Top Quark Physics, Bruges, May 2010Introduction Spin Variables7 Polarisation (P) and Spin Correlation (A) closely related.

cos(i/j) Angle between a decay particle from the top and some chosen spin quantisation axis in top rest frame.

Top Helicity is a well known example.

Introduction Spin Variables8

Polarisation (P) and Spin Correlation (A) closely related.

Spin CorrelationSpin Correlation&

Introduction Spin Variables9 Polarisation (P) and Spin Correlation (A) closely related.

Looking at the double differential distribution requires full tt reconstruction.

between two spin analysers in lab frame is also sensitive to spin correlations.

Does not require tt reconstruction and sensitive to gluon gluon fusion.

Precision test of the SM.

Ideal variable for LHC!

Introduction Spin Variables10

Polarisation (P) and Spin Correlation (A) closely related.

Polarisation

Introduction Spin Variables11

Polarisation (P) and Spin Correlation (A) closely related.

leptond ui/j (LO)1.001.00-0.31i/j (NLO)1.000.93-0.31

Leptons and down type jets are the best analysers Hard to distinguish u type jets from d type jetsF. Hubaut, E. Monnier, P. Pralavorio, K. Smolek, V. Simak, Eur.Phys.J. C44S2 (2005) 13-33Results12Observation of Spin Correlation13

AHELICITY : 0.40 0.04 (stat) +0.08/-0.07 (syst)SM Prediction: 0.31 2.1 fb-1 7 TeV Perform likelihood fit with templates A=SM and A=0 and extract fSM.

fSM = 1.30 0.14 (stat.) +0.27/-0.22 (syst.)

Extrapolate AHELICITY = fSM * PredHELICITY

Exclude the A = 0 case with 5.1

First Observation of Spin Correlation in tt!

Consistent with hypothesis of spin Phys. Rev. Lett: Volume 108 Issue 21(Prediciton) W. Bernreuther and Z. G. Si, Nucl. Phys. B 837, 90(2010)Top Quark Polarisation14

4.7 fb-1 7 TeV

P : -0.060 0.018 (stat) +0.046/-0.064 (syst) Template fit similar to Spin Correlation, hypotheses P = +1 and P = -1 Dominant Systematic comes from jet reconstruction, jet resolution and signal modeling. All results consistent with SM.ATLAS-CONF-2012-133EventsCharge Asymmetry15Introduction Charge Asymmetry16

|yl|=|yl+|-|yl-|: Doesnt Require Reconstruction |yt|=|yt+|-|yt-|: Easier to compare

ACAsymmetry measurements at the LHC and Tevatron:

yAFB Small Asymmetry expected at Tevatron (~5%) Large deviation seen (~15%) LHC tt is pp collider and charge symmetric. Asymmetry observable but expected to be very small

16Single Lepton Charge Asymmetry171.04 fb-1 7 TeVEur. Phys. J. C (2012) 72:2039: http://arxiv.org/abs/1203.4211 Events reconstructed using Kinematic Likelihood Fitter (KL) Rapidity distributions unfolded to parton level.

Inclusive and differential measurements in [email protected] (inclusive) Prediction AC = 0.006 0.002

AC = -0.019 0.028 (stat.) 0.024 (syst) inclusiveAC = -0.052 0.070 (stat.) 0.054 (syst) mtt > 450 GeVAC = -0.008 0.035 (stat.) 0.032 (syst) mtt < 450 GeVhighlowSingle Lepton Charge Asymmetry18Eur. Phys. J. C (2012) 72:2039: http://arxiv.org/abs/1203.4211

INCLUSIVEmtt > 450 GeVNote: Does not include most recent results from all collidersAC = -0.019 0.028 (stat.) 0.024 (syst) inclusiveAC = -0.052 0.070 (stat.) 0.054 (syst) mtt > 450 GeVAC = -0.008 0.035 (stat.) 0.032 (syst) mtt < 450 GeVhighlowD0Dilepton Charge Asymmetry19

4.7 fb-1 7 TeV Asymmetry measured at parton level

Background subtracted data corrected for detector acceptance.

Measured both lepton and top asymmetry.

Results consistent with SM (predictions from [email protected]).COMB WITH L+JETS RESULT

ATLAS-CONF-2012-57

Current ATLAS Asymmetry Results20 Current Status of the 7 TeV Asymmetry measurements at ATLAS Everything consistent with SMACATLAS (combined)ATLAS (dilep)ATLAS (single lepton)predictiontt + HF 21NEW!

tt + HF (HF = bb, cc, b, c) Flavour coming from gluon splitting or proton main irreducible background to ttH Many BSM models also predict additional HF in tt events.

At least 3 b-tagged jetsAt least 2 b-tagged jets Many experimental uncertainties cancel in ratio Cross sections measured in fiducial region (with a factor to correct for detector acceptance) Correction factor is 0.093 0.004(stat.) in HF, 0.129 0.001(stat.) in tt + jHeavy Flavor Ratiott + HF 224.7 fb-1 7 TeVNEW!

RHF = [7.1 1.3 (stat.) +5.3/-2.0 (syst.)] %RHF (LO) = [3.4 1.1 (syst.)] %RHF (NLO) = [5.2 1.7 (syst.)] % perform a binned maximum likelihood fit to extract fid (tt + HF) fid (tt + j) taken from observed yield in data. Use the displaced vertex mass in bins of b-tag purity (improves LF-c jet discrimination).To be submitted to Physical Review D

Dominant systematic is flavor compositionSummary and Outlook23 LHC delivering precision measurements.

First observation of non vanishing Spin correlations, measurements on Polarisation and Charge Asymmetry.

7 TeV Analyses for ATLAS Top Properties almost completed (one or two more to look forward to)

Start to see 8 TeV properties results soon!

Charge Asymmetry results so far statistics limited.

Long Shutdown 1 will be a very exciting time for top properties and plenty to look forward to with 13 TeV!Backup24References25Spin Correlations: TEVATRON vs. LHC, Greg Mahlon, 3rd International Workshop on Top Quark Physics, Bruges, May 2010https://agenda.irmp.ucl.ac.be/conferenceTimeTable.py?confId=538#20100530ttbar asymmetries in the SM, Germn Rodrigo, LHC Workshop From Charge Asymmetry to the Boosted Regime 02-04 May 2012https://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=175916Top Charge Asymmetry at ATLAS, Kerim Suruliz, LHC Workshop From Charge Asymmetry to the Boosted Regime 02-04 May 2012https://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=175916

FiguresPapersATLAS sensitivity to top quark and W boson polarization in tt events, F. Hubaut, E. Monnier, P. Pralavorio, K. Smolek, V. Simak, Eur.Phys.J. C44S2 (2005) 13-33http://arxiv.org/abs/hep-ex/0508061

Distributions and correlations for top quark pair production and decay at the Tevatron and LHCW. Bernreuther and Z. G. Si, Nucl. Phys. B 837, 90(2010), and private communication. Systematics: Dilep Charge Asymm26

tt + HF b tag purity27

High PurityMedium Purity

Low PurityAsymmetries Cartoon28http://cds.cern.ch/record/1493476/files/TOP-12-010-pas.pdfCMS DileptonCMS l+jetshttp://cds.cern.ch/record/1458955/files/plb.717.129.pdfhttp://cds.cern.ch/record/1453785/files/ATLAS-CONF-2012-057.pdfATLAS Dilep + CombinationATLAS l + jetshttp://link.springer.com/article/10.1140%2Fepjc%2Fs10052-012-2039-5Introduction Spin Variables29

leptond ui/j (LO)1.001.00-0.31i/j (NLO)1.000.97-0.32 Polarisation (P) and Spin Correlation (A) closely related.

Double Differential DistributionP = 0, A = SM[a]

Physics Objects at ATLAS30JETS: Anti-kT jets (R=0.4) Corrected to EM Scale || < 2.5, ET > 25 GeV 75% tracks point to vertex B-Tagged using Neural Net based tagger, eff 70%.

MUONS: Muon Spectrometer track combined with Inner Detector track Isolated from other objects|| < 2.5 PT > 20 GeVELECTRONS: Central energy deposit combined with Inner Detector track Isolated from other objects |cluster| < 2.47, 1.37 < |cluster | < 1.52 ET > 25 GeV

MISSING TRANSVERSE ENERGY: Sum of transverse energies of all reconstructed physics objects. Accounts for unassociated calorimeter cells. ?Event Model - Backgrounds 31leptonFakes (mismeasured leptons) Data Driven Matrix Method

Single Top: [email protected] + HERWIG & JIMMY Dilepton Wt channel only.Drell-Yan: ee, , ALPGEN + HERWIG & JIMMY Z + (0-5 jets inclusive)

W + jets: ALPGEN + HERWIG & JIMMY W + (0-5 jets inclusive)

DiBoson: HERWIG (ALPGEN) & JIMMY WW, WZ and ZZ