LHCb: Xmas 2010

Tara Shears,On behalf of the LHCb group

1. Introduction2. Electroweak physics3. Other work4. Conclusions

Xmas09 and 2010LHCb overviewLHCb kinematic planeMotivation of ewk measurements

Introduction

Electroweak: Z, W, ratios

Other work: other Z channels, exclusive dimuons, AFB

Conclusions

Data: looking forward to studying high momentum muons with LHCb.

W, Z, DY selection studies estimate a statistical precision < 1% with ~100 pb-1 of data (2010).

Systematic errors dominated by luminosity uncertainty.Systematic errors for low mass DY need to be studied.Exclusive J/psi have similar yield.

Plan: by end 2010First paper on W, Z productionWork towards paper on low mass DY productionWork towards another on exclusive states.Plus continue rest of group programme.

1. Introduction2. Status of studies3. Reach with 100 pb-1

4. Conclusions

XMAS09 - reminder

Achievements/ hardware plans:

VELO operations

VELO replacement build

Upgrade plans (more build)

Thanks to all the workshop & downstairs crew.

Physics:

VELO performance and trackingThemis, David, Kurt, Karol, Abdi, James, Emma, Henry

ElectroweakTara, Themis, Kurt, Karol, Stephanie, Emma, Myfanwy, Henry

B physicsThemis, David, James

Why?

W/Z provide high p track samples:Tracking performance, track stability, errors, ipExtends ewk: W, tau etc.

Optimal tracking needed for B physics

Ewk / B can be extended in NP searches in future.Long lived massive particlesBoson + heavy flavour

BsDsDs

+ tracking work to optimise lifetime distribution

Plots courtesy of James

High pT tracking studiesErrors, ghosts, preselection, efficiency

Muon studiesTrigger, identification, backgrounds

Electron studiesTrigger, identification, backgrounds

Theory studiesProduction studies:

Z, W, Z, ZeeZ + jet*, *eepppp+ (luminosity), excl. J/, '

PDF sensitivity studies Underlying event studiesAFB

*(Liverpool contributions)

Electroweak working group+ MSTW/NNPDF collaboration (PDFs)+ Stirling/Harland-Lang/Khoze (exclusives)+ LHC ewk WG (Mangano et al)

1. Introduction2. Cross-sections3. Other work4. Conclusions

OverviewLHCb kinematic regionPredictions of W, Z productionMeasurement definitions

Beam Beam

MuonCalo

Interaction point

Tracking

Vertex detector

300mrad

Fully instrumented within 1.9 ≤ ≤ 4.9Trigger: p > 3 GeV, pt > 0.5 GeV, m > 2.5 GeV

1. Introduction2. Cross-sections3. Other work4. Conclusions

OverviewW, Z productionMeasurement definitions

2010: 37.7 pb-1 data recorded16.5 ± 1.7 pb-1 used

2011: hope for 1-2 fb-1 of data

1. Introduction2. Cross-sections3. Other work4. Conclusions

OverviewW, Z productionMeasurement definitions

8% of Z within LHCb acceptance

17% (16%) of W+ (W-) within LHCb acceptance

1. Introduction2. Cross-sections3. Other work4. Conclusions

Overview

W, Z productionMeasurement definitions

1. Introduction2. Cross-sections3. Other work4. Conclusions

Overview

W, Z productionMeasurement definitions

X, Q2 explored by previous experimental data

1. Introduction2. Cross-sections3. Other work4. Conclusions

Overview

W, Z productionMeasurement definitions

X, Q2 explored byLHCb.Z, W: x of 10-4, 10-1

(low mass * 10-6)

1. Introduction2. Cross-sections3. Other work4. Conclusions

Overview

W, Z productionMeasurement definitions

Cross-sections known to NNLOPDF uncertainty dominatesKnown to ~1% at y ~1.5-2, 6-8% at y~5

1. Introduction2. Cross-sections3. Other work4. Conclusions

Overview

W, Z productionMeasurement definitions

Cancel or highlight PDF uncertainties with ratiosR+ tests dV/uV ratioAW tests difference between uV and dV

RWZ almost insensitive to PDFs

LHCb

1. Introduction2. Cross-sections3. Other work4. Conclusions

Overview

W, Z productionMeasurement definitions

€

σ(Z→ μμ : 2 <η μ < 4.5,PTμ > 20GeV ,81< Mμμ <101GeV )

€

σ(W → μν : 2 <η μ < 4.5,PTμ > 20GeV )

1. Introduction2. Cross-sections3. Other work4. Conclusions

OverviewW, Z production

Measurement definitions

Definition of measured cross-sections:

(as function of Z rapidity)

(as function of muon pseudorapidity)

€

σ Z→μμ (Δy) =N tot

Z −NbkgZ

εZL

Z selection

Z background estimation

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Trigger:Single , pT > 10 GeV

Muon:Good track quality (σp/p, 2 probability) pT> 20 GeV 2.0 < < 4.5

Z: 81 < m() < 101 GeV

Z =1.00 (by definition to compare with theory)

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

NZ = 833

Backgrounds:Z ( ~ 0.2 )Heavy flavour ( ~ 1)K/ ( < 0.03)Nbkg = 1.2 ± 1.2

LHCb preliminary

Data, simulation

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

W selection

W background estimation€

σW→μν (Δη ) =N tot

W −NbkgW

εWL

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Trigger:Single , pT > 10 GeV

Muon: Good track quality (σp/p, 2 probability)pT > 20 GeV 2.0 < < 4.5Impact parameter significance < 2pT in R=(2+2)=0.5 cone around

< 2 GeV

Rest of event: Mass < 20 GeVpT < 10 GeV

W= 55.0 1.0%

(data driven, using Z events)

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

LHCb preliminary

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

NW+ = 7624 NW - = 5732

Background sources:Z (1 in acceptance)Z W Hadronic events

Data SimulationData + simulation

Fit muon pT spectrum in data to expected shapesfor signal and background,extract Nbkg+, Nbkg-

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Nbkg+ = 2194 ± 150

Nbkg- = 1654 ± 150

Z (fixed with sim) (fixed and scaled to W)QCD: fit fraction. (shape from data)W+/-: fit fraction (shape from MC)

LHCb preliminary

+-

Perform fit in bins for differential results

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Measurements made in kinematic acceptance

AZ, AW = 1

€

Z = AZεZtrigεZ

trackεZmuonεZ

selection

€

W = AWεWtrigεW

trackεWmuonεW

selection

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Determine from data (Z sample)

Tag: 1 identified muon having fired single muon trigger

Probe: 1 identified muon

€

Z = AZεZtrigεZ

trackεZmuonεZ

selection

€

W = AWεWtrigεW

trackεWmuonεW

selection

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Efficiency is flat in , pT.

No evidence for charge bias

W =72 1%

Z =86 1%

LHCb preliminary - +

pT

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

LHCb preliminary

€

Z = AZεZtrigεZ

trackεZmuonεZ

selection

€

W = AWεWtrigεW

trackεWmuonεW

selection

Determine from data (Z sample)

Tag: 1 identified muon

Probe: 1 muon stub + TT hit

(TT not used in tracking)

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Efficiency flat in , pT

Two regions considered in

W+= 73 3%

W -= 78 3%

Z = 83 3%LHCb preliminary

(+, - different average efficiency due to different distribution)

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

€

Z = AZεZtrigεZ

trackεZmuonεZ

selection

€

W = AWεWtrigεW

trackεWmuonεW

selection

Determine from data (Z sample)

Tag: 1 identified muon

Probe:1 identified track

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

Efficiency flat in , pT

No evidence of charge bias

W = 98.2 0.5%

Z = 96.5 0.7%LHCb preliminary

datasimulationtruth level

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

€

Z = AZεZtrigεZ

trackεZmuonεZ

selection

€

W = AWεWtrigεW

trackεWmuonεW

selection

Found before:Z: (simulation) 1.00W: (data driven, using Z events) 55.0 1.0%

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

EfficienciesResults

LHCb preliminary MCFM NLO+MSTW08 16.5 pb-1 s=7 TeV

Z cross-section

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

Efficiencies

Results

W cross-section, asymmetry

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

Efficiencies

Results

LHCb preliminary

1. Introduction

2. Cross-sections3. Other work4. Conclusions

NZ, Nbkg

NW, Nbkg

Efficiencies

Results

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channelsExclusive AFB

Other work (briefly):

Other Z decay channels

Exclusive

AFB

… and other channelse.g. Zee

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channelsExclusive AFB

… and other channelse.g. Z

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channelsExclusive AFB

Exclusive production

Two muons: dca<0.15 mm; M>1 GeV; PT < 0.9 GeV; SPD multiplicity<5; 0 extra tracks.

Exclusive = no charged+neutral activity 1.9<<4.9No charged tracks -4<<-2

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channels

Exclusive AFB

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channels

Exclusive AFB

€

AFB0, f =

3

4A f uAu + dAd + sAs( )

€

A f =2gVf gAfgVf2 + gAf

2

AFB sensitive to sin2W

Uncertainties from :Forward (quark) directionPDF knowledge of sea

LHCb: predominately valence - sea collisionsss contribution reduced

Pythia: generator study

LHCb

94% correct

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channelsExclusive AFB

Statistical errors only:

1 fb-1 implies 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

1. Introduction2. Cross-sections

3. Other work4. Conclusions

Other Z decay channelsExclusive AFB

1. Introduction2. Cross-sections3. Oher work

4. Conclusions

2010:Good year for electroweak physicsTested electroweak sector to 6% at LHCFirst signs of exclusive dimuons

2011:Papers comingMore stringent tests of the SMPDF constraintsFirst AFB measurementFirst B measurementsTracking work allows extension to taus, B and beyond.