University of Science Technology of China USTC WZg

University of Science & Technology of China (USTC) W/Z+g Measurement @ ATLAS Presented by Zhengguo Zhao, on behalf of Liang HAN University of Science & Technology of China (USTC) On behalf of ATLAS Collaboration ICHEP 2012 Melbourne, Australia

University of Science & Technology of China (USTC) Physics Motivations • Di-Boson production cross-sections are sensitive to the coupling of the triple gauge-boson vertices (TGCs) ‣ Provide direct test of SM predictions ‣ WWγ and WWZ vertices are predicted and have been measured ‣ ZZγ, ZγZ, Zγγ and ZZZ vertices are forbidden • The presence of new physics could: ‣ Give anomalous Triple Gauge Couplings (a. TGC) ‣ Modify cross-sections and/or kinematic distributions • Backgrounds to the searches of Higgs and new physics 2012/07/03 hanl@ICHEP 2012 2

University of Science & Technology of China (USTC) Motivation of W , Z Ø W(ln)/Z(ll)+ ll g production measurement: s-channel TGC gluon/quark fragmentation FSR ISR: t/u-channel Ø Searching anomalous triple gauge couplings (a. TGC): l W magnetic dipole and electric quadrupole moment WW a. TGC: Dk , l l Prior-LHC results + D 0, 4. 2 fb-1 W , PRL 107(2011)241803 2012/07/03 l ZZg/Zgg prohibited by SM Z a. TGC: h 3/4 ZZ a. TGC: hz 3/4 + CDF, 5 fb-1 Z , PRL 107(2011)051802 + D 0, 6. 2 fb-1 Z , PRD 85(2012)052001 hanl@ICHEP 2012 3

University of Science & Technology of China (USTC) Background • Z/W+jets: photon from the jet (mainly π0→γγ) → data driven method • Diboson backgrounds: ZZ, WW, WZ → MC • Top background → MC • γ+jets: fake lepton from jet and mis-measured ETmiss (Wγ analysis only) → data driven method 2012/07/03 hanl@ICHEP 2012 4

University of Science & Technology of China (USTC) Event Selection Ø ATLAS 7 Te. V 1 fb-1 (35 pb-1) l Lepton : data: ü ATLAS 35 pb-1 result as JHEP 1109, 072 ü ATLAS 1. 02 fb-1 result as ar. Xiv: 1205. 2531 + e/m p. T>25 Ge. V, detector fiducial | | coverage; isolated in calorimeter; + Tight electron identification l W/Z events : MET>25 Ge. V, MT(ln)>40 Ge. V; M(ll)>40 Ge. V l Photon : + p. T>15 Ge. V, + | |< 1. 37 or 1. 52 <| |< 2. 37 + Isolated in calorimeter + Tight photon identification + FSR suppression d. R(l, g)>0. 7 + Simulation corrected to Z llg data l Jet : p. T>30 Ge. V, | |<4. 4, d. R(j, /lepton)>0. 6 Inclusive (>=0 jet) vs. Exclusive (==0 jet) 2012/07/03 hanl@ICHEP 2012 5

University of Science & Technology of China (USTC) W(ln)+ control plot • Electroweak background derived from simulation • Dominant background, W+jet has to be estimated from data 2012/07/03 hanl@ICHEP 2012 6

University of Science & Technology of China (USTC) W/Z+jet background Ø Data driven: 2 D sideband jet “ g” background estimation: l Photon Identification: based on calorimeter shower-shape l Photon Isolation: 2012/07/03 hanl@ICHEP 2012 7

University of Science & Technology of China (USTC) Jet+ background in Wg Ø Date-driven jet “ e/m” estimation: 1) jet+ : real ; non-isolated letpon from heavy b/c decay; 2) Control region : MET<20 Ge. V to extract faked “e/m” isolation shape W(en) : MET vs. isolation 2 -d sideband 2012/07/03 hanl@ICHEP 2012 8

University of Science & Technology of China (USTC) Signal event yield Ø Photon ET spectrum: W(ln)g inclusive Z(ll)g inclusive * Signal distribution normalized to the number of extracted data 2012/07/03 hanl@ICHEP 2012 9

University of Science & Technology of China (USTC) Ø Number of jet distribution: W(ln)g : p. T( )>100 Ge. V Z(ll)g : p. T( )>60 Ge. V p. T( )>100 Ge. V p. T( )>60 Ge. V Inclusive (>=0 jet) vs. Exclusive (==0 jet) 2012/07/03 hanl@ICHEP 2012 10

University of Science & Technology of China (USTC) Cross section measurement • CWg (CZg): Correction factor reconstruction efficiency with fiducial selection requirements (trigger, rec. PID, event selection) • Awg ( AZg): acceptances with geometrical and kinematic constraints of fiducial cross section at particle level • L: Integrated luminosity: 1. 024 fb-1± 3. 8% • Unfold detection efficiency: - Systematic d. C~ 10 %, dominated by photon identification & jet energy scale - Correction factor CW (Z ) ~ 40 - 60% 2012/07/03 hanl@ICHEP 2012 11

University of Science & Technology of China (USTC) Ø Unfold for detector acceptance : + Extend detector fiducial to a uniform lepton | | coverage l Estimated from + Theoretical uncertainty on acceptance Alpgen/Sherpa d. Theo. ~ 1 -3% Ø Compare to SM prediction: l Compared against MCFM (ISR + FSR + QCD NLO) 2012/07/03 hanl@ICHEP 2012 12

University of Science & Technology of China (USTC) Differential cross sections 1) Photon l l p. T>15, 60, 100 Ge. V; 2) Inclusive (≥ 0 jet) vs. Exclusive (=0 jet) The Exclusive measurements are consistent with MCFM predictions (SM NLO) The W Inclusive are higher than MCFM, especially in high p. T( ) region high order effects (NNLO and beyond) 2012/07/03 hanl@ICHEP 2012 13

University of Science & Technology of China (USTC) Anomalous couplings + a. TGC h. V 3/4 : ZVg electric dipole / magnetic quadrupole transition moment + non-zero a. TGC will result in increasing of W/Z+ cross section, especially in high photon p. T region Z a. TGC: h 3/4 ZZ a. TGC: hz 3/4 h 30=0. 05 2012/07/03 hanl@ICHEP 2012 14

University of Science & Technology of China (USTC) Ø Extract ZVg a. TGC: + Exclusive ET(g)>60 Ge. V measurement against a. TGC hypotheses + Bayesian probability with nuisance parameters to set limits 2012/07/03 hanl@ICHEP 2012 15

University of Science & Technology of China (USTC) Ø Extract WWg a. TGC: Exclusive ET(g)>100 Ge. V measurement against a. TGC WW a. TGC hypotheses : Dk , l WW a. TGC: Dk , l Dk =0. 4 2012/07/03 hanl@ICHEP 2012 16

University of Science & Technology of China (USTC) Summary l The differential cross section W(ln)g/Z(ll)g measured @ 1 fb-1 7 Te. V ATLAS: Ø Exclusive (=0 jet) measurement is consistent with SM NLO Ø High order effect (NNLO and beyond) is observed in Wγ inclusive (≥ 0 jet) data, especially in high photon p. T( )>60 Ge. V region l Limits on anomalous TGC couplings derived from high photon p. T spectrum Ø WW a. TGC results better than the existing Tevatron limits 2012/07/03 hanl@ICHEP 2012 17

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University of Science & Technology of China (USTC) Signal event yield Ø W(ln)g : l Dominate background as W+jet(“ ”), +jet (“e”), Z(ll) Ø Z(ll)g : l Dominate background as Z+jet 2012/07/03 hanl@ICHEP 2012 21

University of Science & Technology of China (USTC) Ø ISR/FSR vs. p. T( ) cut: ISR: M(ll ) > MZ FSR: M(ll ) ≤ MZ ISR p. T( )>15 Ge. V FSR High photon p. T cut to suppress FSR as Z : p. T( )>15, 60 Ge. V; W : p. T( )>15, 60, 100 Ge. V 2012/07/03 hanl@ICHEP 2012 22