Precision electroweak measurements: LHCb. Tara Shears, On behalf of the LHCb collaboration. Overview W, Z production Measurement definitions. 1. Introduction 2. Crosssections 3. Outlook 4. Conclusions. Introduction Crosssections: Z, W, ratios Outlook: PDF sensitivity, A FB
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W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Introduction
Crosssections: Z, W, ratios
Outlook: PDF sensitivity, AFB
Conclusions
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Interaction point
300mrad
Beam
Beam
Vertex detector
Tracking
Calo
Muon
Fully instrumented within 1.9 ≤ ≤ 4.9
Trigger: p > 3 GeV, pt > 0.5 GeV, m > 2.5 GeV
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
2010:
37.7 pb1 data recorded
16.5 ± 1.7 pb1 used
2011:
hope for 12 fb1 of data
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
17% (16%) of W+ (W) within LHCb acceptance
8% of Z within LHCb acceptance
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
X, Q2 explored by previous experimental data
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Crosssections known to NNLO
PDF uncertainty dominates
Known to ~1% at y ~1.52, 68% at y~5
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Cancel or highlight PDF uncertainties with ratios
R+ tests dV/uV ratio
AW tests difference between uV and dV
RWZ almost insensitive to PDFs
LHCb
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
PDFs have large uncertainty at low x
(Maria, yesterday)
W, Z production
Measurement definitions
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Definition of measured crosssections:
(as function of Z rapidity)
(as function of muon pseudorapidity)
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Z selection
Z background estimation
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
Data, simulation
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
W selection
W background estimation
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
(data driven, using Z events)
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Fit muon pT spectrum in data to expected shapes
for signal and background,
extract Nbkg+, Nbkg
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
Nbkg+ = 2194 ± 150
Nbkg = 1654 ± 150

+
Z (fixed with sim)
t (fixed and scaled to W)
QCD: fit fraction. (shape from data)
W+/: fit fraction (shape from MC)
Perform fit in bins for differential results
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Measurements made in kinematic acceptance
AZ, AW = 1
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Determine from data (Z sample)
Tag: 1 identified muon having fired single muon trigger
Probe: 1 identified muon
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary

+
Efficiency is flat in , pT.
No evidence for charge bias
eW=72 1%
eZ=86 1%
pT
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Efficiency flat in , pT
Two regions considered in
LHCb preliminary
(+,  different average efficiency due to different distribution)
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Determine from data (Z sample)
Tag: 1 identified muon
Probe:1 identified track
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
data
simulation
truth level
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Found before:
Z: (simulation) 1.00
W: (data driven, using Z events) 55.0 1.0%
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Z crosssection
LHCb preliminary MCFM NLO+MSTW08
16.5 pb1s=7 TeV
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
W crosssection, asymmetry
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Predicted W asymmetry vs. W and lepton rapidity
(courtesy J. Stirling)
NZ, Nbkg
NW, Nbkg
Efficiencies
Results
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
LHCb preliminary
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Outlook:
PDF sensitivity studies
AFB
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
From global fits, PDFs described by a set of orthogonal eigenvectors,
which have a ‘central’ value e0, and ‘uncertainties’ ei.
(where δi is #sigmas along ei)
Prediction using central value
Deviations from central value according to eigenvector uncertainty
Current knowledge of PDFs mapped out by sampling δi from unit multinomial distribution.
Perform pseudoexperiments, generating LHC data and fitting for δi, to see how eigenvector knowledge improves.
See: F. De Lorenzi, DIS2010; R. McNulty, ICHEP2010.
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Uncertainty on PDF with 0.1fb1 of LHCb data Uncertainty on PDF without LHCb data
105 104 103 102 101 1
105 104 103 102 101 1
105 104 103 102 101 1
7 TeV
105 104 103 102 101 1
105 104 103 102 101 1
Modest improvement with small amount of data
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Uncertainty on PDF with 0.1fb1 of LHCb data Uncertainty on PDF without LHCb data
7 TeV
Similar sensitivity. Ability to distinguish models
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Uncertainty on PDF with 1fb1 of LHCb data Uncertainty on PDF without LHCb data
14 TeV
More data and higher energy lead to larger improvements (~30%).
Uncertainty on PDF with 0.1fb1 of LHCb data Uncertainty on PDF without LHCb data
105 104 103 102 101 1
105 104 103 102 101 1
105 104 103 102 101 1
105 104 103 102 101 1
105 104 103 102 101 1
Uncertainty on PDF with 0.1fb1 of LHCb data Uncertainty on PDF without LHCb data
Similar improvements to MSTW, CTEQ and Alekhin PDFs.
Sensitivity exists to distinguish between models.
20%
20%
20%
10%
10%
10%
106 105 104 103 102 101 1
106 105 104 103 102 101 1
106 105 104 103 102 101 1
20%
20%
10%
10%
106 105 104 103 102 101 1
106 105 104 103 102 101 1
Significant improvements possible with modest amount of data
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
AFB sensitive to sin2W
Asymmetry at LHC larger than at LEP (leptonic)
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Pythia: generator study
94% correct
LHCb
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
Statistical errors only:
Note: Very preliminary study:
1 fb1implies 4% statistical precision on AFB
implies 0.15% statistical precision on sin2W (cf. 0.07% world average)
Studies ongoing:
PDF uncertainties (estimated at 0.04%)
Needs theoretical prediction of comparable precision
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
… and other channels
e.g. Zee
AFB
1. Introduction
2. Crosssections
3. Outlook
4. Conclusions
… and other channels
e.g. Z
2. Crosssections
3. Outlook
4. Conclusions