Flavour changing neutral currents and Higgs interactions in top quark production and decay Gr´ egory Hammad on behalf of the ATLAS and CMS collaborations Mons University, Belgium ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 1 / 24
FCN interactions in the top quark sector tqX interactions with q = u , c and X = γ, Z , g , H , ? Standard Model No FCN interaction at tree level Higher order processes suppressed by the GIM mechanism Ex: B ( t → qZ ) = O ( 10 − 14 ) Beyond the Standard Model Various models (SUSY, ED, etc...) predict higher branching ratios Up to O ( 10 − 4 ) Signs of FCN interactions at a measurable rate at the LHC � Evidence for new physics ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 2 / 24
FCN interactions in the top quark sector Theoretical (Optimistic) upper limits on branching ratios / Process SM 2HDM MSSM R SUSY RS t → c γ 4 . 6 × 10 − 14 ∼ 10 − 6 2 × 10 − 6 1 × 10 − 6 ∼ 10 − 9 t → cZ 1 . 0 × 10 − 14 ∼ 10 − 7 2 × 10 − 6 3 × 10 − 5 ∼ 10 − 5 t → cg 4 . 6 × 10 − 12 ∼ 10 − 4 8 × 10 − 5 2 × 10 − 4 ∼ 10 − 9 3 . 0 × 10 − 15 ∼ 10 − 3 ∼ 10 − 5 ∼ 10 − 6 ∼ 10 − 9 t → cH Similar values for t → uX except for t → uH (lower values). [J. A. Aguilar-Saavedra, Acta Phys. Pol. B 35 (2004)] Effective field theory approach describes effects of new physics at a high energy scale Λ allows to parametrize anomalous couplings in a model-independent way ◮ suitable for model-independent searches for new physics! ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 3 / 24
ATLAS and CMS experiments at the LHC A very successful Physics Run I Proton run ended on Dec. 2012. Recorded luminosity: > 21 fb − 1 (93 % ) A major discovery: Brout-Englert-Higgs boson First observations of rare processes: B s → µµ , tW , t ¯ t + V , etc. p s = 8 TeV CMS Integrated Luminosity, pp, 2012, Data included from 2012-04-04 22:37 to 2012-12-16 20:49 UTC 25 25 Total Integrated Luminosity ( fb ¡ 1 ) LHC Delivered: 23.30 fb ¡ 1 CMS Recorded: 21.79 fb ¡ 1 20 20 15 15 10 10 5 5 0 0 y n l g p t v c a u u u e c o e M J J A S O N D 1 1 1 1 1 1 1 1 Date (UTC) ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 4 / 24
Outlines 1. Search for FCN couplings in top quark pair events: L ( fb − 1 ) 7 TeV � Exp. U.L. on BR (95 % C.L.) References 2.1 fb − 1 JHEP 09 (2012) 139 ATLAS 0.73 % tqZ 5 fb − 1 Phys. Lett. B718 (2013) 1252 1 CMS 0.21 % 8 TeV 19.7 fb − 1 CMS-PAS-TOP-12-037 2 tqZ CMS 0.07 % 20.3 fb − 1 ATLAS-CONF-2013-081 3 ATLAS 0.79 % tqH 19.5 fb − 1 CMS-PAS-SUS-13-002 4 CMS 1.28 % 2. Search for FCN couplings in single top quark events: L ( fb − 1 ) � 7 TeV Exp. U.L. on BR (95 % C.L.) 5 fb − 1 tqZ, q=u/c CMS 0.51/11.4 % { CMS-PAS-TOP-12-021 5 fb − 1 CMS 0.56/7.12 % 5 fb − 1 tqg, q=u/c CMS 0.036/0.034 % CMS-TOP-14-007 5 fb − 1 Phys. Lett. B712 (2012) 351-369 1 ATLAS 0.0057/0.027 % L ( fb − 1 ) � 8 TeV Exp. U.L. on BR (95 % C.L.) 14.2 fb − 1 tqg, q=u/c ATLAS 0.0031/0.016 % ATLAS-CONF-2013-063 19.1 fb − 1 tq γ , q=u/c CMS 0.016/0.182 % CMS-PAS-TOP-14-003 1 Superseded. Not presented. Listed for completeness. 2 7+8 TeV data combination: ArXiv:1312.4194, accepted by PRL. 3 ArXiv:1403.6293, accepted by JHEP 4 ArXiv:1404.5801, submitted to PRD ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 5 / 24
Search for FCN couplings in top quark pair events JHEP 09 (2012) 139: tqZ coupling, 2 . 1 fb − 1 @7TeV Event selection Tri-lepton final state 3 isolated leptons (3ID) OR 2 isolated leptons + 1 iso. track (2ID+TL) / E T > 20 GeV at least 2 jets p T > 25 GeV / c ≥ 1 b-tagged jet (2ID+TL) Event reconstruction lepton and jet combination: Events / 10 GeV Events / 10 GeV 8 ATLAS ATLAS data data 12 t t → WbZq signal ∫ ∫ t t → WbZq signal 7 -1 t t W/Z -1 � 2 � 2 L dt = 2.1 fb L dt = 2.1 fb � � fakes mreco mreco − mt j 2 l 3 ν − mt t t (SM) 10 6 j 1 l 1 l 2 t t W/Z χ 2 = Z+jets 3ID 2ID + TL + + dibosons σ 2 σ 2 dibosons 5 8 bkg. uncertainty t t bkg. uncertainty 4 � 2 � 2 � � 6 mreco mreco l 3 ν − mw − mz l 1 l 2 3 + 4 σ 2 σ 2 2 w z 2 1 select event if reco. masses 0 0 140 160 180 200 220 140 160 180 200 220 compatible with m top / m w / m z m [GeV] m [GeV] llq llq ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 6 / 24
Search for FCN couplings in top quark pair events JHEP 09 (2012) 139: tqZ coupling, 2 . 1 fb − 1 @7TeV Background estimation No fake lepton: VZ backgrounds, estimated using simulations ≥ 1 fake lepton: ◮ 1 fake lepton (3ID): Z +jets background ⋆ extrapolated from a control region with exactly 1 Z-candidate (2 OSSF leptons) ◮ 1 fake lepton (2ID+TL): fake TL background ⋆ jet-faking-TL rate (vs. jet p T , N vtx ) from γ +jets data sample ◮ ≥ 2 fake leptons (3ID): multi-jet and W+jets backgrounds ⋆ extrapolated from number of same-sign events ( l + l + l + or l − l − l − ) 95% CL. upper limits on B ( t → qZ ) channel observed ( − 1 σ ) expected (+1 σ ) 3ID 0.81% 0.63% 0.95% 1.4% 2ID+TL 3.2% 2.15% 3.31% 4.9% Combination 0.73% 0.61% 0.93% 1.4% ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 7 / 24
Search for FCN couplings in top quark pair events CMS-PAS-TOP-12-037: tqZ coupling, 19 . 7 fb − 1 @8TeV Tri-lepton final state Event selection 2 isolated leptons, p T > 20 GeV / c | m ll − m Z | < 12 GeV / c 2 exactly 1 additional isolated lepton / E T > 30 GeV at least 2 jets p T > 30 GeV / c exactly 1 b-tagged jet Background estimation Dominant background processes: VZ , t ¯ t and t ¯ t + V , with V = W , Z Method based on the number of b-tagged jets observed in data: N 0 b − jet ∼ N VZ N tot 1 1 1 = α 0 α 1 α 2 N 1 b − jet ∼ N signal N 1 b − tagged jet β 0 β 1 β 2 N 2 b − jets ∼ N t ¯ N 2 b − tagged jets t + X with α i , β i = f ( ǫ btag , ǫ mistag ) ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 8 / 24
Search for FCN couplings in top quark pair events CMS-PAS-TOP-12-037: tqZ coupling, 19 . 7 fb − 1 @8TeV Event reconstruction and limit settings Top quark candidate reconstruction: ◮ jet combination maximizing ∆ φ ( Zj , Wb ) Event yields in 50 x 70 GeV mass windows: N Est . bckgd . = 3 . 1 ± 0 . 8 ( stat . ) ± 0 . 8 ( syst . ) Dominant systematic uncertainties: ◮ b-tagging efficiency ◮ top quark candidate mass acceptance ◮ jet energy scale and resolution Exclusion limits at 95% CL. B ( t → qZ ) < 0.06% (8 TeV data) B ( t → qZ ) < 0.05% (7+8 TeV data) ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 9 / 24
Search for FCN couplings in top quark pair events ATLAS-CONF-2013-081: tqH coupling, 5 + 20 fb − 1 @7+8TeV Event selection g ¯ t 2 iso. photons E T > 40 / 30 GeV γ g H m γγ ∈ [ 100 , 160 ] GeV / c 2 Further event classification according to W γ g t decay: W → jj or W → l ν Events / 10 GeV Events / 5 GeV ∫ 22 ∫ ATLAS Preliminary ATLAS Preliminary 60 -1 √ -1 √ b L dt = 20.3 fb , s = 8 TeV L dt = 20.3 fb , s = 8 TeV 20 Data Data Signal, Br = 10% 18 Signal, Br = 10% 50 j Sherpa j Sherpa γ γ γ γ 16 Hadronic selection: 40 14 12 30 10 ≥ 4 jets, p T > 25 GeV / c 8 20 6 4 10 ≥ 1 b-tagged jet 2 0 0 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 m [GeV] m [GeV] γ γ j jjj Leptonic selection: Events / 10 GeV Events / 10 GeV ∫ ∫ ATLAS Preliminary ATLAS Preliminary -1 -1 √ L dt = 20.3 fb , √ s = 8 TeV L dt = 20.3 fb , s = 8 TeV 25 ≥ 2 jets, p T > 25 GeV / c Data Data 10 Signal, Br = 10% Signal, Br = 10% γ γ j Sherpa γ γ j Sherpa 20 8 m W T > 30 GeV / c 2 15 6 10 4 Event selected if reco. masses 5 2 compatible with m top 0 0 0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500 m [GeV] m [GeV] γ γ ν j l j ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 10 / 24
Search for FCN couplings in top quark pair events ATLAS-CONF-2013-081: tqH coupling, 5 + 20 fb − 1 @7+8TeV Statistical analysis Systematic uncertainties Hadronic selection: template fit to m γγ Photon identification ◮ template from simulation Jet energy scale ◮ compared to data in m γγ side-band regions Effect of ISR/FSR Leptonic selection: counting experiment modelling on signal ◮ signal region: m γγ ∈ [ 123 , 129 ] acceptance ◮ bckd. estimated from side band regions ATLAS Preliminary 9 Events / 1 GeV Events / 4 GeV Data 2011+2012 ATLAS Preliminary Hadronic selection 14 Hadronic selection Sig+SM Higgs (126.8 GeV)+Bkg fit 8 ∫ Data SM Higgs+Bkg -1 √ L dt = 20.3 fb , s = 8 TeV 12 7 nd ∫ γ γ j Sherpa Bkg (2 order polynomial) -1 √ L dt = 4.7 fb , s = 7 TeV ∫ 6 10 -1 √ L dt = 20.3 fb , s = 8 TeV ∫ -1 5 √ L dt = 4.7 fb , s = 7 TeV 8 4 6 3 4 2 2 1 0 0 100 110 120 130 140 150 160 100 110 120 130 140 150 160 m [GeV] m [GeV] γ γ γ γ � Exclusion limits (95 % C. L.): B ( t → cH ) < 0 . 79 % → λ 2 tuH + λ 2 tcH < 0 . 17 ghammad@cern.ch (Umons) Search for FCNC/H in the top sector 27/05/2014 11 / 24
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