W and Z production in the forward region with the LHCb experiment - PowerPoint PPT Presentation

W and Z production in the forward region with the LHCb experiment Philip Ilten on behalf of the LHCb Collaboration University College Dublin July 25, 2011 PANIC11, MIT Ilten (UCD) Forward EW at LHCb July 25, 2011 1 / 19

Outline Outline ❼ Introduction ❼ LHCb ❼ Motivation ❼ Selection and Backgrounds ❼ Z → µµ ❼ W → ν µ µ ❼ Z → ττ ( µ, e ) and ( µ, µ ) ❼ Efficiencies ❼ Results ❼ Conclusion Ilten (UCD) Forward EW at LHCb July 25, 2011 2 / 19

Introduction : LHCb LHCb ❼ 2010 dataset ❼ 37 . 7 pb − 1 ❼ 2011 dataset ❼ 210 pb − 1 (processed) ❼ 389 pb − 1 (recorded) ❼ tracker, ECAL, HCAL, muon ❼ designed for B decays chambers (common) ❼ forward arm spectrometer ❼ Cherenkov detectors (unique) ❼ 1 . 9 ≤ η ≤ 2 . 5 (common) ❼ 2 . 5 < η ≤ 4 . 9 (unique) ❼ p T > 10 GeV muon trigger Ilten (UCD) Forward EW at LHCb July 25, 2011 3 / 19

Introduction : Motivation Asymmetry and PDF’s ❼ W ± asymmetry at high η ❼ new constraints on PDF’s at low x and high Q Ilten (UCD) Forward EW at LHCb July 25, 2011 4 / 19

Introduction : Motivation PDF Uncertainty � � σ ( x, Q 2 ) = f i ( x i , Q 2 ) f j ( x j , Q 2 ) � �� � i,j ≈ 1 − 8% σ ( x i , x j , Q 2 ) × ˆ d x i d x j � �� � ≈ 1% ❼ W/Z boson y < 2 PDF uncertainty ≈ 1% ❼ W/Z boson y ≈ 5 PDF uncertainty ≈ 6 − 8% ❼ partonic σ uncertainty ≈ 1% at NNLO ❼ measure σ Z → µµ and σ W → ν µ µ , can be used to constrain PDF’s Ilten (UCD) Forward EW at LHCb July 25, 2011 5 / 19

Selection and Backgrounds : Z → µµ Z → µµ (LHCb-CONF-2011-039) ❼ trigger on single muon ❼ p µ T > 10 GeV ❼ heavy flavor background ❼ b ¯ ❼ reconstruct two muons b and c ¯ c events with µµ ❼ track quality final state ❼ p µ ❼ impact parameter cut and T > 20 GeV estimate efficiency from ❼ 2 . 0 < η µ < 4 . 5 simulation ❼ 60 ≤ M µµ ≤ 120 ❼ 4 . 3 ± 1 . 7 events ❼ N Z tot = 1966 ❼ Z → ττ background ❼ estimated from simulation ❼ 0 . 61 ± 0 . 04 events ❼ generic QCD background ❼ calculated from same sign events ❼ N Z bkg = 4 . 9 ± 2 . 0 Ilten (UCD) Forward EW at LHCb July 25, 2011 6 / 19

Selection and Backgrounds : W → ν µ µ W → ν µ µ (LHCb-CONF-2011-039) ❼ electroweak ❼ trigger on single muon ❼ p µ ❼ shapes from MC T > 10 GeV ❼ normalization from observed ❼ reconstruct one muon rates in data ❼ track quality ❼ heavy flavor ❼ p µ T > 20 GeV ❼ shape from anti-cut on IP ❼ 2 . 0 < η µ < 4 . 5 ❼ no other muons with p T > 5 ❼ normalization from simulation GeV ❼ IP µ < 40 µ m ❼ π/K punch-through E ECAL + E HCAL ❼ shape from anti-cut on E/p µ µ < 0 . 04 ❼ p µ ❼ � p tracks ,γ ❼ normalization from data < 2 GeV within T ❼ π/K decay ∆ R < 0 . 5 ❼ shape from events with other ❼ N W + = 15608 tot triggers ❼ N W − = 12301 ❼ normalization from fit tot Ilten (UCD) Forward EW at LHCb July 25, 2011 7 / 19

Selection and Backgrounds : W → ν µ µ W → ν µ µ Ilten (UCD) Forward EW at LHCb July 25, 2011 8 / 19

Selection and Backgrounds : W → ν µ µ W → ν µ µ Ilten (UCD) Forward EW at LHCb July 25, 2011 9 / 19

Selection and Backgrounds : Z → ττ → µe Z → ττ → µe (LHCb-CONF-2011-041) ❼ electroweak background ❼ WW , W , and γ ∗ /Z events ❼ trigger on single muon ❼ calculated from simulation ❼ p µ T > 10 GeV ❼ 3 ± 1 . 2 events ❼ reconstruct one muon and ❼ QCD background electron ❼ calculated from data ❼ p µ T > 20 GeV ❼ 9 . 5 ± 3 events ❼ p e T > 5 GeV ❼ 2 . 0 < η µ,e < 4 . 5 20 ❼ acoplanarity LHCb 18 Preliminary s = 7 TeV, L = 247 pb -1 16 ❼ ∆ φ µ,e > 2 . 7 14 ❼ isolation asymmetry 12 10 − P p track � � p µ,e 8 ❼ min > 0 . 8 T T + P p track p µ,e 6 T T 4 ❼ N Z tot = 81 2 0 50 100 m [GeV] e µ Ilten (UCD) Forward EW at LHCb July 25, 2011 10 / 19

Selection and Backgrounds : Z → ττ → µµ Z → ττ → µµ (LHCb-CONF-2011-041) ❼ electroweak background ❼ trigger on single muon ❼ normalized from data ❼ p µ T > 10 GeV ❼ 5 . 5 ± 1 . 8 events ❼ reconstruct two muons ❼ QCD background ❼ p µ 1 T > 20 GeV ❼ calculated from data ❼ p µ 2 T > 5 GeV ❼ 1 . 6 ± 1 . 3 events ❼ 2 . 0 < η µ < 4 . 5 ❼ acoplanarity, ∆ φ µ > 2 . 7 ❼ p T asymmetry, p µ 1 T − p µ 2 T > 0 . 2 p µ 1 T + p µ 2 T ❼ lifetime, IP µ 1+ µ 2 > 4 σ IP � p µ 1 ,µ 2 − P p track � ❼ min T T > 0 . 8 + P p track p µ 1 ,µ 2 T T ❼ M µµ < 80 ❼ N Z tot = 33 Ilten (UCD) Forward EW at LHCb July 25, 2011 11 / 19

Efficiencies : Z → µµ , W → ν µ µ Z → µµ , W → ν µ µ ǫ = Aǫ trigger ǫ track ǫ id ǫ selection ❼ ǫ trigger ❼ trigger on single high p T muon ❼ separate into µ + , µ − , and µ + µ − triggered ❼ ǫ track ❼ use Z → µµ sample ❼ muon firing trigger is tag ❼ probe is muon stub, look for associated track ❼ ǫ id ❼ use Z → µµ sample ❼ muon firing trigger is tag ❼ probe is track, look for associated muon stub ❼ A and ǫ Z selection defined as 1 ❼ ǫ W selection from Z → µµ sample Ilten (UCD) Forward EW at LHCb July 25, 2011 12 / 19

Efficiencies : Z → ττ Z → ττ ǫ = Aǫ trigger ǫ µ track ǫ µ track ǫ ℓ id ǫ ℓ id ǫ selection ❼ ǫ trigger from tag-and-probe method using the Z → µµ sample ❼ ǫ µ track from tag-and-probe method using the Z → µµ sample track from MC scaled by ǫ µ track (data) /ǫ µ ❼ ǫ e track (MC) ❼ ǫ µ id from tag-and-probe method using the Z → µµ sample ❼ ǫ e id from tag-and-probe method using the Z → ee sample ❼ ǫ selection from MC with systematics from MC data comparison ❼ A from MC using Pythia 8 and Herwig++ Ilten (UCD) Forward EW at LHCb July 25, 2011 13 / 19

Results : Cross Sections Definition and Uncertainties σ ( Z → ℓℓ, W → ν µ µ ) = N tot − N bkg ǫ L ❼ 2 . 0 < η ℓ < 4 . 5, p ℓ T > 20 GeV, 60 < M ℓℓ < 120 GeV ❼ cross sections corrected for FSR with HORACE uncertainty [%] σ W + σ W − σ Z → µµ σ Z → ττ → µe σ Z → ττ → µµ background ± 1 . 6 ± 1 . 6 ± 0 . 4 ± 5 ± 9 template ± 1 . 9 ± 1 . 7 −− −− −− efficiency ± 2 . 0 ± 1 . 8 ± 5 . 1 ± 5 ± 5 FSR ± 0 . 2 ± 0 . 2 ± 0 . 3 −− −− systematic ± 3 . 5 ± 3 . 2 ± 5 . 1 ± 7 ± 11 ± 3 . 5 ± 3 . 5 ± 3 . 5 ± 3 . 5 ± 3 . 5 luminosity statistical ± 0 . 9 ± 1 . 1 ± 2 . 1 ± 12 ± 17 Ilten (UCD) Forward EW at LHCb July 25, 2011 14 / 19

Results : Cross Sections Cross Sections Ilten (UCD) Forward EW at LHCb July 25, 2011 15 / 19

Results : Differential Cross Sections Z → µµ Ilten (UCD) Forward EW at LHCb July 25, 2011 16 / 19

Results : Differential Cross Sections W → ν µ µ Ilten (UCD) Forward EW at LHCb July 25, 2011 17 / 19

Results : PDF Improvement PDF Improvement ❼ M. Ubiali, Assessment of the impact of LHC W lepton asymmetry data on PDF fits, 04/05/11, Working Group on Electroweak precision measurements at LHC ❼ using only 16 . 5 pb − 1 of data from initial 2010 run Ilten (UCD) Forward EW at LHCb July 25, 2011 18 / 19

Conclusion Conclusion ❼ W → ν µ µ and Z → µµ cross section measurements in good agreement with NNLO theory ❼ expected asymmetry observed ❼ initial cross section measurements already begin to restrict PDF’s ❼ initial Z → ττ analysis presented, further work on additional channels underway Ilten (UCD) Forward EW at LHCb July 25, 2011 19 / 19