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

• n 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 → νµµ 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 designed for B decays ❼ forward arm spectrometer

❼ 1.9 ≤ η ≤ 2.5 (common) ❼ 2.5 < η ≤ 4.9 (unique)

❼ tracker, ECAL, HCAL, muon

chambers (common)

❼ Cherenkov detectors (unique) ❼ pT > 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, Q2) =

• i,j
• fi(xi, Q2)fj(xj, Q2)
• ≈1−8%

× ˆ σ(xi, xj, Q2)

• ≈1%

dxi dxj

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 σZ→µµ and σW→νµµ,

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 pµ

T > 10 GeV

❼ reconstruct two muons

❼ track quality ❼ pµ

T > 20 GeV

❼ 2.0 < ηµ < 4.5 ❼ 60 ≤ Mµµ ≤ 120

❼ NZ

tot = 1966

❼ heavy flavor background

❼ b¯

b and c¯ c events with µµ final state

❼ impact parameter cut and

estimate efficiency from simulation

❼ 4.3 ± 1.7 events

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 NZ

bkg = 4.9 ± 2.0

Ilten (UCD) Forward EW at LHCb July 25, 2011 6 / 19

Selection and Backgrounds : W → νµµ

W → νµµ (LHCb-CONF-2011-039)

❼ trigger on single muon

❼ pµ

T > 10 GeV

❼ reconstruct one muon

❼ track quality ❼ pµ

T > 20 GeV

❼ 2.0 < ηµ < 4.5 ❼ no other muons with pT > 5

GeV

❼ IPµ < 40 µm ❼

EECAL

µ

+EHCAL

µ

pµ

< 0.04

❼ ptracks,γ

T

< 2 GeV within ∆R < 0.5 ❼ NW +

tot

= 15608

❼ NW −

tot

= 12301

❼ electroweak

❼ shapes from MC ❼ normalization from observed

rates in data ❼ heavy flavor

❼ shape from anti-cut on IP ❼ normalization from

simulation ❼ π/K punch-through

❼ shape from anti-cut on E/p ❼ normalization from data

❼ π/K decay

❼ shape from events with other

triggers

❼ normalization from fit

Ilten (UCD) Forward EW at LHCb July 25, 2011 7 / 19

Selection and Backgrounds : W → νµµ

W → νµµ

Ilten (UCD) Forward EW at LHCb July 25, 2011 8 / 19

Selection and Backgrounds : W → νµµ

W → νµµ

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 trigger on single muon

❼ pµ

T > 10 GeV

❼ reconstruct one muon and

electron

❼ pµ

T > 20 GeV

❼ pe

T > 5 GeV

❼ 2.0 < ηµ,e < 4.5

❼ acoplanarity

❼ ∆φµ,e > 2.7

❼ isolation asymmetry

❼ min

• pµ,e

T

−P ptrack

T

pµ,e

T

+P ptrack

T

• > 0.8

❼ NZ

tot = 81

❼ electroweak background

❼ WW, W, and γ∗/Z events ❼ calculated from simulation ❼ 3 ± 1.2 events

❼ QCD background

❼ calculated from data ❼ 9.5 ± 3 events

[GeV]

e µ

m

50 100 2 4 6 8 10 12 14 16 18 20 Preliminary LHCb

• 1

= 7 TeV, L = 247 pb s

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 trigger on single muon

❼ pµ

T > 10 GeV

❼ reconstruct two muons

❼ pµ1

T > 20 GeV

❼ pµ2

T > 5 GeV

❼ 2.0 < ηµ < 4.5

❼ acoplanarity, ∆φµ > 2.7 ❼ pT asymmetry, pµ1

T −pµ2 T

pµ1

T +pµ2 T

> 0.2

❼ lifetime, IPµ1+µ2

σIP

> 4

❼ min

pµ1,µ2

T

−P ptrack

T

pµ1,µ2

T

+P ptrack

T

• > 0.8

❼ Mµµ < 80 ❼ NZ

tot = 33

❼ electroweak background

❼ normalized from data ❼ 5.5 ± 1.8 events

❼ QCD background

❼ calculated from data ❼ 1.6 ± 1.3 events

Ilten (UCD) Forward EW at LHCb July 25, 2011 11 / 19

Efficiencies : Z → µµ, W → νµµ

Z → µµ, W → νµµ

ǫ = Aǫtriggerǫtrackǫidǫselection

❼ ǫtrigger

❼ trigger on single high pT muon ❼ separate into µ+, µ−, and µ+µ− triggered

❼ ǫtrack

❼ use Z → µµ sample ❼ muon firing trigger is tag ❼ probe is muon stub, look for associated track

❼ ǫid

❼ use Z → µµ sample ❼ muon firing trigger is tag ❼ probe is track, look for associated muon stub

❼ A and ǫZ

selection defined as 1

❼ ǫW

selection from Z → µµ sample

Ilten (UCD) Forward EW at LHCb July 25, 2011 12 / 19

Efficiencies : Z → ττ

Z → ττ

ǫ = Aǫtriggerǫµ

trackǫℓ trackǫµ idǫℓ idǫselection

❼ ǫtrigger from tag-and-probe method using the Z → µµ sample ❼ ǫµ

track from tag-and-probe method using the Z → µµ sample

❼ ǫe

track from MC scaled by ǫµ track(data)/ǫµ track(MC)

❼ ǫµ

id from tag-and-probe method using the Z → µµ sample

❼ ǫe

id from tag-and-probe method using the Z → ee sample

❼ ǫselection 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 → νµµ) = Ntot − Nbkg ǫL

❼ 2.0 < ηℓ < 4.5, pℓ

T > 20 GeV, 60 < Mℓℓ < 120 GeV

❼ cross sections corrected for FSR with HORACE

uncertainty [%] σW + σW − σZ→µµ σZ→ττ→µe σZ→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 luminosity ±3.5 ±3.5 ±3.5 ±3.5 ±3.5 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 → νµµ

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 → νµµ 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