Top Quark physics with ATLAS @ LHC LPNHE, Paris, 24th March 2011 Francesco Spanò Columbia University francesco.spano@cern.ch
Outline •Why top quark? • The LHC is back: a top factory at work Data results: hot • The ATLAS detector : a top observer off the press! •Measuring top quark production (and mass) Most recent: approved 48 hours ago. Oldest ~ 1 •Towards new physics with top quark week . Disclaimer: wide field, concentrate on selected topics Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 2
Why Top (quark)? Masses of known fundamental particles Most massive constituen t of matter 200 M Top ~ M Gold Atom M top ~ electroweak symmetry breaking scale 150 Decay and strong production rate are tests of standard model 100 July 2010 photon/gluon neutrinos LEP2 and Tevatron (prel.) electron up LEP1 and SLD 80.5 down 50 strange 68 % CL muon charm m W [ GeV ] tau bottomW 0 80.4 Z top Various scenarios with direct/indirect coupling to new physics: 80.3 !" m H [ GeV ] from extra dimensions to new strong forces 114 300 1000 150 175 200 q m t [ GeV ] t q t G µ ν Z � Background to possible new physics (Higgs, SUSY) q q ¯ ¯ ¯ ¯ t t Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 3
LHC : a Top producer counter-rotating high intensity proton bunches colliding with 3.5 TeV/beam (E CM =7 TeV) in 27 Km tunnel eventually: E CM =14TeV (7 TeV per beam, design value) 2011 22nd March: Break 2010 record 2010: peak lumi ~2.5 ⋅ 10 32 cm -2 s -1 •peak instantaneous luminosity: 2.1 ⋅ 10 32 Plans: cm -2 s - 1 peak lumi:~0.5 to 1 ⋅ 10 33 cm -2 s -1 •delivered integrated ∫ Ldt between 1 and 3 fb -1 luminosity ~50 pb -1 Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 4
Top quark (pair) production @ E CM = 7 TeV LHC proton-proton collisions gluon fusion qq annihilation ~70% ~30% total xsec =165 +11-11 pb @ 14 TeV : qq~10%, gg ~90% top is also singly produced, but focus on dominant pair production Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 5
Top @ LHC: in the context tt cross section LHC14 Rate at L= √ s( TeV) xsec (pb) 10 33 cm -2 s - 1 ~7 1.96 (pp) 7 (pp) ~165 0.2Hz LHC7 14 (pp) ~900 0.9Hz Theory uncertainty: ~ 8 to 6% at Tevatron, 6 to 4% at LHC for ∫ Ldt =1 fb -1 @ 7TeV, expect 16*10 4 events Tevatron: 9.4 fb -1 on tape, expect ~ 6.6*10 4 events Top Quark with ATLAS @ LHC fracesco.spano@cern.ch LPHNE Seminar - 24th March 2011 6
Top signatures l, q (e,mu)+jets • High P T jets ℓ ν ~32.4% ν , q’ Tau to (e,mu)+jets • b-jets qq ~67.6% Fully hadronic W Had tau • 1 to 2 high P T leptons Di-lepton (e,mu) W + b • Missing energy Di-lepton (tau) b t t p p tt decays t t di-lepton 1.6% b had tau (e, μ ) 4.9% W W + +jets +jets 29.6% 13.5% b ν , q’ 4.7% - all jets l, q bkgs_tt: W/Z(+jets), single lep tau 45.7% top, QCD, Di-bosons +jets Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 7
ATLAS : a Top observer 3 trigger levels for event 44m size selection matters phi Muon spectrometer p theta p Inner detector 25 m EM Calorimeters Hadronic Calorimeters η = pseudorapidity =-ln (tan(theta/2)) Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 8
ATLAS : a Top observer..... → � �������� Jet Muon ������ Missing Energy Top events are �������� real commissioning tool: full ��������������� detector at ���������������� electron ��������������� play Muon �������������� �������������� Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 9
...with excellent data taking performance For top analyses using 35 pb -1 2010 - expect ~5700 tt events Luminosity uncertainty ~ 3.4% 2011 Already collected ~ a few pb -1 Data sample for first top paper~3 pb -1 Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 10
Ingredients I : leptons Entries / 1 GeV ∫ 1600 1600 1600 -1 Data 2010 ( s = 7 TeV) L dt = 36 pb → Z ee 1400 1400 1400 ATLAS Preliminary * | η cluster | ∉ [1.37,1,52] •Electrons QCD 1200 1200 1200 ‣ tight definition using shower 1000 1000 1000 shape variables, track quality, track-cluster matching, E/p, 800 800 800 transition radiation ATLAS-CONF-2011-041 600 600 600 ‣ isolated 400 400 400 ‣ central *: | η cluster |<2.4, p T >20 GeV 200 200 200 ‣ remove close-by duplicate jets 0 0 0 70 75 80 85 90 95 100105110115 70 75 80 85 90 95 100105110115 70 75 80 85 90 95 100105110115 m [GeV] ee 1600 Entries / 1 GeV ATLAS Preliminary Data 2010 ( s = 7 TeV) Z 1400 ! µ µ •Muons " -1 L= 33 pb 1200 ‣ combined fitted track 1000 ATLAS-CONF-2011-041 ‣ isolated 800 ‣ central | η track |<2.5, p T >20 GeV 600 ‣ suppress heavy flavour decays : 400 no muon within DR< 0.4 of a jet 200 scale factors to correct small data/MC mismatch 0 70 75 80 85 90 95 100105 110115 Top Quark with ATLAS @ LHC fracesco.spano@cern.ch LPHNE Seminar - 24th March 2011 11 m [GeV] µ µ
Ingredient: jets •set of colour-less particles “remembering” momentum/colour flow from parton interaction Simulated QCD di-jet MeV FCal1C ! sin Cluster 5 10 " | # |tan significant ( E cell / 0.05 4 10 exp_noise cell ) 0 energy deposits 3 10 in calorimeters -0.05 2 10 -0.05 0 0.05 |tan | cos # " ! clusters → jet with anti-k T algorithm (R=0.4) (Cacciari,Salam, Soyez,2008) “hard stuff clusters with nearest phi neighbour” eta Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 12
Ingredients II : jets (in the making) ATLAS colllisions 2010 0.8 <E/P> Extensive validation of simulation in test- ATLAS-CONF-2011-028 (0.6<| |<1.1) ! -1 beam data → good collision data description Data 2010. L=866 b µ 0.7 Pythia ATLAS MC10 systematic uncertainty 0.6 ATLAS test beam 2004 0.5 NIMA 621 (2010) 134 0.85 MC 0.4 0.8 Data beam 0.75 0.3 ATLAS Preliminary /E Comb η pion =0.55 0.7 MC/DATA E 0.65 1.1 0.6 1 [%] 6 4 Comb 2 2% ± 0 E –2 0.9 ∆ –4 2 2 2 20 30 40 50 60 10 2 10 3 10 × × 1 10 E [GeV] p[GeV] p[GeV] beam Linearity within ~2% Data/MC within 2% for p<10 GeV single pion response for known single isolated charged hadron beam energy response vs track momentum Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 13
Ingredients II : jets (scale) ATLAS-CONF-2011-053 0.18 • Calibrate jet energy scale with Fractional JES systematic uncertainty Anti-k R =0.6, EM+JES, 0.3 | | < 0.8, Data 2010 + Monte Carlo QCD jets ≤ η t 0.16 ( η ,p T ) dependent weight from ALPGEN + Herwig + Jimmy Noise Thresholds 0.14 PYTHIA Perugia2010 JES calibration non-closure simulated “true” jet Single particle (calorimeter) Additional dead material 0.12 kinematics Total JES uncertainty 0.1 ATLAS Preliminary 0.08 • Scale uncertainty: range 0.06 between 2% to 8% in p T and η 0.04 0.02 0 2 2 3 20 30 40 10 2 10 10 •Contributions from × jet [GeV] p T ‣ Physics models for generation 1.14 Data / MC ATLAS-CONF-2011-053 and hadronization 1.12 Multi-jet ATLAS Preliminary 1.1 Track-jet ‣ Calorimeter response: collision 1.08 -jet direct balance γ -jet MPF 1.06 γ single particle data, test beam 1.04 ‣ Detector simulation 1.02 1 0.98 0.96 •Validation in control samples 0.94 0.92 JES uncertainty anti-k R =0.6, EM+JES t 0.9 3 2 10 10 jet p [GeV] Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 14 T
Ingredients III: missing transverse energy (E Tmiss ) Events / 1 GeV ATLAS Preliminary 6 6 10 10 ATLAS-CONF-2010-057 • Negative vector sum of Data 2010 s = 7 TeV 5 5 10 10 ! -1 Ldt=0.34 nb ‣ energy in calorimeter cells , 4 4 10 10 | |<4.5 " projected in transverse plane Data 3 3 10 10 MC MinBias associated with high pt RefFinal 2 2 10 10 object 10 10 ‣ muon momentum 1 1 ‣ dead material loss 0 0 10 10 20 20 30 30 40 40 50 50 60 60 projected in transverse plane miss E [GeV] T 10 Resolution [GeV] 9 Data: fit 0.49 E ! T 8 MC Minbias: fit 0.51 E ! • Cells are calibrated according T 7 LCW to association to high p T object 6 (electron, photon,tau, jet, muon) ATLAS-CONF-2010-057 miss 5 y ,E 4 miss x E 3 • Remove overlapping calo cells Data 2010 s = 7 TeV 2 involving jets and electrons " -1 ATLAS Preliminary Ldt=0.34 nb 1 | |<4.5 # 0 0 50 100 150 200 250 300 E [GeV] ! T Top Quark with ATLAS @ LHC francesco.spano@cern.ch LPHNE Seminar -24th March 2011 15
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