Measurement of the W-mass with the ATLAS detector

Transcription

1 Measurement of the W-mass with the ALAS detector Oleh Kivernyk CEA/Irfu/SPP July, 0 Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

2 Motivation Relation between M W and α EM, G F, sin θ M W = πα EM GF ( M W /M Z )( r) Radiative corrections r depend on m t as m t and on M H as log M H oday the r is known up to δm SM,theory W = MeV Precise knowledge of M W, m t and M H provides a test of the SM Comparison of measured and predicted M W provides sensitivity to the new physics Corrections from squark loops can increase the predicted M W by 0 00MeV World average: M W = 80.8 ± 0.0MeV Most precise measurement at the evatron Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

3 Strategy of W-mass measurement W leptonic decay is used W lν, l = e, µ Basic objects: lepton(l) and hadronic recoil(u) Goal: Select events with lepton of high p l and small hadronic recoil minimize Bkgs In presence of a neutrino we cannot compute invariant mass mass M W of W lν(cannot estimate longitudinal p ν z ) Measure the Jacobian peak of transverse distribution Use observables sensitive to M W : template fit method Lepton transverse momentum ransvese mass m W = p l t pν ( cos φ lν) Neutrino transverse momentum p l E ν = p ν, p ν = ( p l + u) p µ : Inner Detector p e : EM calorimeter+id u = cluster E: calo Z ll used for the calibration:m ll = M Z, u = p ll Apply the same strategy for M Z extraction verify calibration Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

4 emplate fit method he p l, mw miss and E distributions are computed with MC for different M W Each template is compared to data he value which maximizes binned likelihood agreement is prefered M W Sharper the Jacobian peak better precision of M W : Expected stat. sensitivity: δm W 7MeV (p l ), δm W MeV (m W ) Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

5 W-mass at the LHC Main differences between evatron and LHC: Higher pile-up recoil calibration pp instead of p p larger theor. unc. Assymetric production of W + and W charge dependent analysis W + from u d + u s + u b +... W from dū + d c + sū +... Different polarization p l spectra Higher statistics at the LHC: W eν 6M events W µν 8.7M events Z µµ.m events Z ee 0.6M events Source at CDF Expected at Measurement which (MeV) LHC(MeV) provides constraints Lepton calibration 7 8 Z ll invariant mass peak Recoil calibration 6 7 p Z, E in Z µµ Statistics 7 emplate fit method Backgrounds Multijet background otal experimental Physics BD Z-rapidity, W-asymmetry,W-polarization otal 9 BD Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

6 Lepton Calibration Precise lepton calibration is needed for precise M W measurement Muon momentum calibration performed on J/ψ µµ and Z µµ resonance peaks from data Electron momentum calibration performed on Z ee decays Systematics to M W : 7.MeV for p µ, 7.8MeV for mw 9MeV for p e, 9.MeV for mw avg Da/Mc: 90.70/90.76 rms Da/Mc:.09/.0 χ /n dof = 90.6/ Data Z µµ Z ττ W lν top WW/WZ/ZZ QCD jets Data / MC [GeV] m µµ Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 6 /

7 Recoil Calibration Recoil u = vector sum of all calo clusters excluding cones around the signal lepton and replaced by another cone (same η, different φ) Recoil is affected by emission of quarks or gluons(isr) or photons(isr/fsr) Z µµ is used to model the recoil E miss and m W are derived quantities Correction performed for W +, W for different pile-up bins Recoil calibration: ) Equalize Pile-up in Data and MC ) MC to Data correction of E ) Residual correction to the hadronic recoil in ( E cor, pv ) plane 0 avg Da/Mc: 7.86/7.8 rms Da/Mc:.0/.8 χ /n dof =.6/ Z µµ Data Z µµ Z ττ W lν top WW/WZ/ZZ QCD jets Systematics 7MeV Data / MC u [GeV] Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 7 /

8 Recoil Calibration: control plots Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 8 /

9 Z-mass fits avg Da/Mc:.08/.0 rms Da/Mc:.66/.667 χ /n dof =./ Data Z µµ Z ττ W lν top WW/WZ/ZZ QCD jets pµ m Z (µ+) Data / MC p [GeV] l W-like transverse mass m l+ : - Reconstructed from recoil and l+ - Similarly defined m l Calibration is verified with M Z template fit method of p l and ml M Z value compatible within σ with the PDG value Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 9 /

10 Backgrounds in muon channel he following backgrounds are fully simulated with MC: W τν, Z µµ, Z ττ, top and dibosons decays Another background comes from jets. Sources: ) b/c-quarks decay semileptonically ) punch-trough hadrons ) pions and kaons decaying in flight within tracking system Difficult to get good prediction of multijet background from MC Data-driven techniques are used he main goal: estimate the multijet fraction and shape of the distribution Needed for W-mass template fit method Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

11 Method Method uses regions in phase space: - Signal Region(described above) and corresponding Jet Control Region - Fit Region and corresponding Jet Control Region Iso Multijet Control Region Multijet Control Region CR FR Jets Find Fit Region with isolated electrons where jet fraction is big Respective jet control regions: same cuts but anti-isolated electrons Determine Jet bkg shape (subtract EW) Fit Jets+EW to Data and find CR FR is normalization of Jet bkg CR FR Jets Scale Jet bkg distribution from CR Jets. with Jets CR FR. Recalculate jet fraction in SR as N Jets /N Data Fit Region(FR) find CR FR Jets mw < 60GeV m W Signal Region > 60GeV Region Muon isolation p tracks /p muon in cone 0. - Iso < 0. signal dominated events - 0. < Iso < 0. Jets enriched events Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

12 Method example for m W Relaxed m W, pw muons anti-isolated background muons jet-enriched data W µν W τν Z ll top WW/WZ/ZZ W [GeV] m Fit Region: p W relaxed, 0GeV mw 60GeV Determine jet background distribution in respective Multijet Control Region. Subtract predicted EW contamination (according to cross-sections) Amount of EW contamination: % Data/MC 7 Data ( s = 7 ev) Fit result W lν + ew + tt 6 QCD Fit: 0GeV m W GeV Information from fit: QCD: 0. +/ % χ/ndf: -nan / Apply pure jet distribution H Jets to Fit Region assuming their shape is the same Fit H Data = Jets CR FR H Jets + K EW H EW using RooFit and find Jets CR FR = 0. Plot corresponds to m W, pw relaxed. Here EW distribution additionally scaled by N Data N Jets N EW m W [GeV] Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

13 Method example for m W muons anti-isolated bkg muons jet-enriched data W µν W τν Z ll top WW/WZ/ZZ W [GeV] m Signal Region: p W < 0GeV, mw > 60GeV Determine jet background distribution in respective Multijet Control Region. Subtract predicted EW contamination (according to cross-sections) Amount of EW contamination: % Data / MC 6 avg Da/Mc: 79.8/79.86 rms Da/Mc:.66/. χ /n dof = 6.6/ 60 Data W µν W τν Z ll top WW/WZ/ZZ QCD jets Signal Region mw [GeV] W [GeV] m Scale pure jet distribution by CR FR Jets = 0. Jet fraction in Signal Region is frac = N Jets N Data = CR FR Jets N Data Iso NSR Data = 0.% Control Plot m W in Signal Region with 0.% of data driven Jet bkg Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

14 Jets ISO ISO D correction of m W MtW_vs_muISO ptw, mtw, met relaxed Jet bkg anti-iso MtW_vs_muISO ISO ISO linear extrapolation m W m W [GeV] [GeV ] Jet bkg distribution in ISO can differ from real Jet distribution in ISO region Correct Jet bkg shape: Plot (Iso,m W ) in 0. < Iso < 0. region mu_iso ptw, mtw, met relaxed MtW_vs_muISO Iso Iso Fit each slice of m W by line.. m 0.0 W [GeV] Extrapolate the line from ISO to ISO Produce (Iso,m W ) in Iso < 0. according to m W [GeV] extrapolated lines m W [GeV] Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 / g GeV < m W QCD from 0.<Iso<0. extrapolated QCD mtw, ptw, met relaxed < GeV

15 Jets ISO ISO D correction of m W Corrected Jet bkg shape provides better agreement in Jet+EW to Data fit Method works for different kinematical distributions 7 Data ( s = 7 ev) Fit result 6 W lν + ew + tt QCD Information from fit: QCD: 0.9 +/- 0.00% (6) χ/ndf: 700. / 79 CR FR QCD = 0.6 mu_iso g MtW_vs_muISO QCD from 0.<Iso<0. extrapolated QCD ptw, mtw, met relaxed m W [GeV] m W [GeV] m W [GeV] Information from fit: 7 Data ( s = 7 ev) 6 Fit result W lν + ew + tt QCD QCD: 0. +/- 0.00% (6) χ/ndf:.6 / 79 CR FR QCD = 0. Before correction After correction mtw, ptw, met relaxed mtw, ptw, met relaxed Data/MC mw [GeV] 0.9 Data/MC mw [GeV] W [GeV] m W [GeV] m Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /

16 Other discriminative distributions 7 6 Data ( s = 7 ev) Fit result W lν + ew + tt QCD Information from fit: QCD: 0.0 +/- 0.00% (687) χ/ndf: / 99 CR FR QCD = 0.8 d Data ( s = 7 ev) Fit result W lν + ew + tt QCD Information from fit: QCD: 0.6 +/- 0.00% (0) χ/ndf: 78. / 89 CR FR QCD = 0. p l /mw Data/MC Data/MC ptw, mtw relaxed µ d 0 [mm] 7 Data ( s = 7 ev) Fit result W lν + ew + tt 6 QCD Information from fit: QCD: 0.9 +/- 0.00% (68) χ/ndf: 7. / 99 CR FR QCD = 0.6 hr E miss [GeV] 0.9 E miss E miss [GeV] hr Data/MC pl.0 mw 0.9 ptw, mtw, met relaxed pl mw Muons coming from b/c quark decays are non-prompt d 0 tails Jets dominated Peak at 0. of ptl/mtw corresponds to φ(l, ν) = π. Angle between l and ν can be any for Jet events Jet misidentified as lepton+mismeasurement of jet p E miss peaked at lower value Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 6 /

17 Jet bkg fit of m W : e/µ comparison(mw and pw relaxed) Relaxed m W, pw jet-enriched data W µν muons anti-isolated W τν Z ll top WW/WZ/ZZ Relaxed m W, pw electrons EtIso=0, PtIso=0 jet-enriched data W eν W τν Z ll top WW/WZ/ZZ background muons background electrons few % W [GeV] m W [GeV] m 7 Data ( s = 7 ev) Fit result 6 W lν + ew + tt QCD Information from fit: QCD: 0. +/- 0.00% (068) χ/ndf: -nan / 79 K QCD = Data ( s = 7 ev) Fit result 6 W lν + ew + tt QCD Information from fit: QCD: 0. +/- 0.00% (8) χ/ndf: -nan / 9 K QCD = 0. Data/MC Fit: 0GeV m W 60GeV W m [GeV] 0.9 no QCD correction W m [GeV] Oleh Kivernyk (CEA/Irfu/SPP) m W [GeV] m W [GeV] Measurement of the W-mass with the ALAS detector July, 0 7 / Data/MC 0.9 ISO ISO correction needed

18 Variable and Fit Regions he following variables and corresponding Fit Regions are used: Variables m W p W p µ /mw d 0 d 0 /σ(d 0 ) d 0 d 0 /σ(d 0 ) Fit Regions p W relaxed, fit 0 < mw < 60GeV m W relaxed, fit 0 < pw < 0GeV m W and pw relaxed, fit < pµ /mw < m W and pw relaxed, fit d 0 > 0. mm m W and pw relaxed, fit d 0/σ(d 0 ) > fit d 0 > 0. mm in Signal Region fit d 0 /σ(d 0 ) > in Signal Region Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 8 /

19 Results variable W + W W W (combined p l bins) d 0 (signal region) d 0 /σ(d 0 ) (signal region) m W (relaxed selection) p W (relaxed selection) d 0 (relaxed selection) d 0 /σ(d 0 ) (relaxed selection) ± ± ± ± 0.0 Amount of jet background in Signal Region is found to be between 0.7% and 0.7% η range Inclusive W ± 0.7 ± ± ± ± 0.0 W ± ± ± ± 0.0 W 0. ± ± ± ± 0.0 able: Measured multijet background fraction as a function of muon pseudorapidity (coarse binning). Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 9 /

20 MW uncertainty from multijet fraction PseudoData: EW+top+QCD(0.%) emplates: EW+top+QCD( %) Jet bkg taken from Data MC normalized to cross-sections Uncertainty= Max(MwBias) Min(MwBias) Results: p l m W.8 MeV 6. MeV hmtw MwBias, MeV fqcd in emplates fqcd = 0.% in PSD hptl QCD fraction [%] hptl Fit: 0 p l 60GeV MwBias, MeV 6 0 fqcd in emplates fqcd = 0.% in PSD χ M W = 8099 MeV bias = 0.06 MeV M W = 6.0 MeV Fit: 60 m W GeV QCD fraction [%] ( ) [MeV] Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 0 /

21 Conclusions Simplified table. Numbers below apply to p l fit and are preliminary Channel Statistics Calibration Efficiencies Recoil Background otal exp. Electron 7MeV 8MeV 9MeV 7MeV MeV 6MeV Muon 7MeV 8MeV MeV 7MeV MeV MeV Combined.MeV We are finalizing the background uncertainty and PDF uncertainty estimates which are the last steps before a complete result Oleh Kivernyk (CEA/Irfu/SPP) Measurement of the W-mass with the ALAS detector July, 0 /