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Top physics within CMS-France

This article discusses the main activities in top physics within the CMS-France community, including calibration, trigger development, b-tagging activities, ttbar production, and top mass/properties measurements. It also highlights the responsibilities within top-CMS and the detector performance in terms of triggers and efficiency.

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Top physics within CMS-France

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  1. Top physics within CMS-France Jeremy Andrea On behalf of the CMS-top-France community IPHC : J.L.Agram, J.Andrea, A.Aubin, C.Beluffi, D.Bloch, M.Cardaci, E.Chabert, C.Collard, E.Conte, C.Ferro, B.Fuks, D.Gelé, A.C.Lebihan, P.VanHove IPNL : R.Chierici, S.Beauceron, E. Bouvier, S.Brochet, A.L. Pequegnot, S.Perries, V.Sordini, P.Verdier

  2. Introduction • Top-CMS France, mainly 2 institutes : IPN(Lyon) and IPHC(Strasbourg). • Main activities in top physics : • Calibration: • Development of triggers (IPNL) • (b) JEC (IPNL) • B-tagging activities and ttbar events (IPHC) • Ttbar production : • Ttbar cross-section measurements in dilepton and tau+jets (IPHC) • Search for ttbar resonances in the lepton+jets (IPNL) • Top mass/properties: • Ttbar spin correlation (IPHC) • Ttbar charge asymmetry (IPHC) • Future analyses : • Top mass with J/Psi (IPNL), • Search for ttbar H (IPHC) • Search for New Physics with effective models (IPHC). • Responsibilities within top-CMS: • 1 Top convener (2011-2012), TopLHCWG coordinator (since 2013) R.Chierici. • 2 Sub-conveners top-dilepton (2010) D.Gelé, top mass/properties (2011-2012) J.Andrea. • 1 Top-Trigger contact person (since 2012) S.Beauceron

  3. Detector performance and top physics

  4. Level 1 trigger (hardware): single lepton: 22 GeV for ECal, 16 GeV for muons double lepton: 13/7 GeV for ECal, 10/3.5 GeV for muons, Muon 12/ECal 7 GeV Multijet: QuadJet 36 GeV High Level Trigger (HLT):Based on cross triggers depending on the final states. Single Top: e/μ+1 PFjet Btag with PT > 30GeV rate ~ 4Hz Ttbar Semi-leptonic: e/μ +3 PFJet with PT>45,35,25 GeV  rate ~ 7Hz Ttbar Di-leptonic: ee/μμ/eμ with PT~15/7 GeV  rate ~ 4Hz Ttbar full hadronic: QuadJet PT>45 GeV  rate ~150 Hz (Parked) Top with Tau: no triggers specific anymore in 2012, could use Higgs/Standard Model physics ones. Very high efficiencies for Top physics along the year (>95%), preparing strategy for 2015 and beyond. Top Triggers S.Beauceron L1xHLT Efficiency

  5. Input to top physics :JEC with γ+jet • Residual corrections to apply to the data, extracted from the absolute response (as a function of pT) of jets inγ/Z+jet events. • Since 2011, responsibility of the photon+jet analysis (Sébastien Brochet, Viola Sordini) • Same final state is exploited to perform preliminary studies on the dependence of the jet flavor in the response (Elvire Bouvier, Sébastien Brochet, Anne-Laure Pequegnot, Viola Sordini) Evaluated from MC Jet pT [GeV]

  6. B-tagging activities J.Andrea, A.Aubin, C.Beluffi, D.Bloch, E.Chabert, C.Collard, D.Gelé, P. VanHove • High level of involvement of the IPHC in the b-tagging. • Calibration activities : • Validation/commissioning of b-tagging algorithms using data : multi-jets and ttbar-dilepton events. • B-tagging efficiencies and mistag-rates measurements from data : multi-jets and ttbar events (see next slide). • Development/studies of b-taggers : • B-taggers at HLT level. • Setting-up a super-combined tagger (combining taggers outputs with a MVA). • B-tagging at the high pT regime : b-tagging in boosted tops, for boosted b-jets. ttbar MC arXiv 1211.4462 Multijet data arXiv 1211.4462

  7. Measurement of b-tagging efficiency With top dilepton events E.Chabert, C.collard, D.Gele + top dilepton team 7 TeV 7 TeV

  8. ttbar production

  9. Ttbar cross section in the dilepton channel @7TeV Collaboration IPHC, IFCA/Oviedo JHEP 11 (2012) 065 • Luminosity : 2.3 fb-1 • Event selection : • Dilepton trigger. • 2 high pT (20 GeV) leptons with opposite charges in the acceptance of the tracker. • mll>20 GeV (ee, μμ, eμ channels) and |mll-mZ|> 15 GeV (ee, μμ channels) . • MET > 40 GeV for ee, μμ channels, no MET cut for the eμ channel. • ≥2 jets with pT>30 GeV and |η|<2.5. ≥1b-tagged jets (Combined Secondary Vertex). • Background determinationfrom data : DY events (Routin, Mll fit) and events with at least on fake lepton (Matrix Method). • Analysis strategy : • Cross section is measured from a profile likelihood ratio using the Njets vs NBjets distribution. • Complementary measurement : simple counting analysis. Top dilepton team : J.Andrea, C.Cardaci, E.Chabert, C.Collard, D.Gelé Cross section measurements. (5%) Most precise measurement at the LHC

  10. Dilepton channel at 8 TeV Collaboration IFCA/Oviedo/Desy, IPHC • Luminosity : 2.4 fb-1. • Events selection, backgrounds determination and selection efficiencies as the 7 TeV measurement. • Different fake lepton estimation : using like-sign lepton selection. • Counting experiment. • Main systematics : • Luminosity, JES, lepton efficiency. Combined cross section measurement. (7%) CMS PAS TOP-12-007

  11. Ttbar cross section in the tau+jets channel @7TeV D.Bloch, C.Ferro, A.C. Lebihan TOP-11-004, arXiv:1301.5755v1 • Luminosity : 3.9 fb-1, 7TeV • Event selection : • Tau+jets trigger : 4 jets and an additional hadronic tau (overlapping with a jet). • 3 jets with pT > 45 GeV + 1 jets with pT>20 GeV and |η|<2.4. • 1 isolated HPS tau with pT > 45 and |η|<2.3 • No additional leptons + MET > 20 GeV. • At least 1 b-tagged jet (jet-probability tagger). • Backgrounds from data : multi-jet background determined by inverting the b-tagging selection. • Analysis strategy based on a Neural-Network output : HT, Aplanarity, q|η|, MET, Δφ(tau-MET), M(tau-jets), χ2 of the kin. fit. • Cross section determined from a template fit on the NN output.

  12. CMS combinations @7TeV CMS PAS TOP-11-024 J.Andrea, D.Gelé, R.Chierici • CMS combination using 0.8-1.1 fb-1. • Combination done using a binned maximum likelihood (TOP-11-003). Gain 21% of stat. and 11% of syst. uncertainty compared to the l+jets channel. • Our contribution : combination cross-checked with a Best Linear Unbiased Estimator (BLUE) method : agree within 1%, 3% less precise.

  13. Search for resonances decaying into ttbar • Search for new physics in resonances decaying to ttbar. • Study of semileptonic (mu, e) events, full reconstruction of the ttbar invariant mass (the longitudinal part of the neutrino momentum being constrained, starting from MET, thanks to the knowledge of the W mass) • Two analyses optimized separately to explore both the low mass (standard reconstruction tools) and high mass (boosted objects, non isolated leptons, W and top tagging in jets) regimes. • IPNL takes care of the low mass analysis (Sébastien Brochet, Stéphane Perries, Viola Sordini). Most recent public document on 2011 data JHEP 12 (2012) 015 setting upper limits on the new physics resonance production cross section. IPNL : same involvement for the 2012 data analysis. A public document, showing improved performances, should be released soon (being finalized). Mtt<1TeV

  14. Top properties

  15. Top mass Collaboration Brown U. (main authors) IPHC (secondary) • Measurement of the top mass in the dilepton channel. • Contributions from IPHC : event selection, efficiencies and determination of backgrounds from data. • The top mass is measured using the AMWT method. • Kinematic of ttbar events are reconstructed assuming a top mass. • The best solution is determined through the calculation of a weight. • The kinematics is solved scanning on the top mass. • The most probable top mass is measured using a likelihood profile technique (top mass distribution). J.Andrea+dilepton team Eur. Phys. J. C72 (2012) 2202 World average (Tevatron) :173.2 ±0.9 GeV

  16. Ttbar spin correlation (1) CMS PAS TOP-12-004 Collaboration with Aachen/UCSB(D)/FNAL • Tops decay : spin information transferred to the top decay products. • Study spin correlation : probe the production of ttbar events, search for new physics. • Measurement of spin correlation strength, performed by fitting the Δφ(l-l) distribution. • Knowing the strength of the spin correlation in MC, the measurement done by fitting the fraction of events with spin correlation. • Results Ahel = 0.24±0.02(stat.)±0.08(syst.) • To be compared to theoretical calculation Atheo=0.31±0.03(Bernreuther&al.). • Paper in preparation. J.Andrea+dilepton team

  17. Ttbar charge asymmetry CMS PAS TOP-12-010 M.Cardaci+dilepton team • Measurement of the ttbar charge asymmetry : search for deviation w.r.t the SM predictions (excess at Tevatron on the fwd-bckw asymmetry). • Event selection and backgrounds determination from TOP-11-005. • Requires a complete kinematic reconstruction (AMWT) and an unfolding procedure. • Charge asymmetry also measured as a function of mtt, |y|tt and pT,tt. Compatible with SM. • From theory : Ac = 0.0115±0.006

  18. Future (BSM)Top activities

  19. Top mass using J/psi E. Bouvier, R.Chierici, V. Sordini, P. Verdier • Top mass measurement using lepton+jets events with a b-jets containing a J/Psi. • Signature : 1 isolated lepton, 4 jets, and two opposite-sign electrons or muons compatible with J/Psi candidates. • Main advantages : • Invariant mass of the 3 leptons correlated with the top mass, • Almost not affected by systematics on JES and b-tagging . • But low statistic. • Plan : Prepare the analysis for the re-start of data taking (13 TeV?) with high luminosity, when this analysis may become competitive with the direct reconstruction ones.

  20. ttbarH A.C.Lebihan, J.Andrea (+2 master1) • Search for ttbarH in the 3-lepton channel, sensitive to H→WW, H→ττ, H→ZZ. • Positive and negative aspects : • +++ Good statistic (especially for a higgs mass of 125 GeV…), sensitive to different higgs decays, • --- significant background contribution (ttbar, ttbar+V, WZ+jets), no real sensitivity on the Higgs mass. • Long term analysis : study 8 TeV data and prepare for the 13 TeV collisions.

  21. ANR-BATS • ANR BATS@LHC : search for new physics in the top sector using bottom-up approach and effective theory. • Signatures investigated • from the pheno point of view first, • the relevance/sensitivity of the NP is studied using fastsimulation, • finally measurements with the CMS data are performed. • Close collaboration between theorists/phenomenologists and experimentalists. • Signatures investigated (so far) : • Production of ttbar+MET events, exp. measurement ongoing (exp. PhD student, A.Aubin), • Single top+MET : monotop, pheno ongoing, exp. PhD starting in September, • Anomalous gqt and Zqt couplings in single-top : search for tZ events, finalizing pheno. study and exp. measurement. • BSM contributions to ttbar spin correlation, finalizing exp. measurement (collaboration with W. Bernreuther). Contributors : J.L.Agram, J.Andrea, A.Aubin, E.Chabert, C.Collard, E.Conte, B.Fuks, D.Gelé

  22. Two examples • Production of a single-top quarks with missing transverse energy : monotop. • Phenomenology done at parton level for the hadronic channel. • With FastSimulation : hadronic and leptonic channels under study. • Production of a single top-quark in association with a Z boson : • Probe anomalous gluons (gtq) and Z (Ztq) couplings. • Complementary channel to gq→t and ttbar→WbZq. • Phenomenology in the 3 leptons channel, including FastSimulation. • Experimental analysis ongoing, results expected for LHCP. Phys. Rev. D 84, 074025 (2011) J.Andrea, E.Conte, B.Fuks preliminary J.L.Agram, J.Andrea, E.Conte, B.Fuks, D.Gelé

  23. Conclusions • High expertise and visibility of the French labs in the CMS-top community. • Wide range of activities : calibration for/with top quarks, studies of the top-quarks production and properties. • Orientations for the next years : precise measurements with original methods, Higgs and BSM searches. • Despite a limited manpower, the CMS-top French community was able to perform many analyses, with a real impact on the field. • Expertise gained with 7/8 TeV data will allow us to perform (hopefully) more nice measurements with the 13 TeV data.

  24. Backups

  25. (1) (2) (3) (6) (5) (4) Le détecteur CMS • De forme cylindrique centré sur l’axe du faisceau. Dimensions : diamètre de 15 m, longueur de 22 mètres (12500 tonnes). • Composé d’une partie centrale et de deux bouchons. • (1)Trajectographe au silicium. • (2)Calorimètreélectromagnétique (ECAL) au tungstate de plomb. • (3)Calorimètre hadronique (HCAL) : plaques de cuivre et scintillateurs plastiques. • (4)Solénoïde supraconducteur : 4 T. • (5)Chambres à muons. • (6) Structure de soutien et de retour des boucles de champ.

  26. Dilepton channel at CMS (1) arXiv:1208.2671 • Luminosity : 2.3 fb-1 • Event selection : • Dilepton trigger : ET(electrons) > 8-17 GeV, pT(muons) > 7-17 GeV. • 2 reconstructed, isolated and identified leptons with opposite charges, pT>20 GeV and |η|<2.5 for electrons (2.1 for muons). • mll>20 GeV (ee, μμ, eμ channels) and |mll-mZ|> 15 GeV (ee, μμ channels) . • MET > 40 GeV for ee, μμ channels, no MET cut for the eμ channel. • ≥2 jets with pT>30 GeV and |η|<2.5. • ≥1b-tagged jets (Combined Secondary Vertex). • Selection efficiency • Dilepton trigger efficiency estimated using an independent sample triggered by the MET. • Lepton selection efficiencies estimated from Z→ll events. • MET selections estimated from the eμ channel.

  27. Dilepton channel at CMS (2) arXiv:1208.2671 • Cross section is measured from a profile likelihood ratio using the Njets vs NBjets distribution. • Complementary measurement : simple counting analysis. • Background determination : • Z→ll in the ee and μμ channels : using the expected ratio of events outside and inside the Z mass cut. Ratio taken from simulation but corrected using control region in data. • Z→ττ→eμ from a template fit of the mll distribution. • Fake-lepton backgrounds (dominated by tt l+jets) estimated using an extended Matrix Method. • Other backgrounds (single top, diboson) estimated from simulation.

  28. Dilepton channel at CMS (3) Counting experiment arXiv:1208.2671 • With higher luminosity, lower statistical uncertainty and better control of systematics. • More precise luminosity calculation using pixel. • Main uncertainties : • Luminosity, JES, W Branching ratio, Cross section measurements. • Combination done with the likelihood fit (with σtt as a single parameter), a Best Linear Unbiased Estimate (BLUE, Nucl.Instrim.Meth. A270 (1988) 110 ) method for the counting analysis. • Combination dominated by the eμ channel (more statistic, less backgrounds, no MET selection). • Very good agreement with the counting analysis. • Top mass dependence : (5%) Top mass uncertainty at WA : 1.4 pb

  29. Systematic Tau+jets

  30. ttbar cross section at 8 TeV • Very similar di-lepton measurement at 8 TeV. • Combination of the CMS 8 TeV measurements, using a BLUE method. • Combination dominated by the dilepton measurement. Combined cross section measurement. • Ratio of the 8TeV (combination) and 7TeV cross sections (dilepton at 2.3 fb-1). • Some systematic uncertainties cancel out (signal modeling and some detector effects). • Ratio found to be 1.41±0.10.

  31. LHC Combination @7TeV • ATLAS+CMS combined cross section measurements. • Total correlations between the measurements : 30%. • Combined tt cross section uncertainty becomes 5.8% (around 10 pb) => gain about 7% w.r.t. the most precise measurement. Combined cross section measurement Better results are expected with new measurements : more statistics, better lumi. systematic.

  32. Ttbar spin correlation (1) Collaboration with UCSD/UCSD/FNAL CMS PAS TOP-12-004 • Tops decay before their hadronization : spin information transferred to the top decay products. • Study spin correlation : probe the production of ttbar events, search for new physics. • Measurement of spin correlation through the spin correlation strength parameter A. • Sensitive variables : differential cosθ1cosθ2 cross section, Δφ(l+-lepton-).

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