W and Z production in the forward region with LHCb
W&Z production with LHCb Tara Shears, University of Liverpool 1. Introduction 2. W→µ, Z→µµ LHCb 3. Other channels Motivation 4. Outlook Dataset 5. Conclusions
• Introduction • W→µν, Z→µµ production measurements • Measurements in other Z decay channels • Outlook • Conclusions
W&Z production with LHCb Tara Shears, University of Liverpool 2 1. Introduction 2. W→µ, Z→µµ LHCb 3. Other channels Motivation 4. Outlook Dataset 5. Conclusions
Interaction point 300mrad
Beam Beam
Vertex detector Tracking Calo Muon
Fully instrumented within 1.9 ≤ η ≤ 4.9
Trigger: pµ > 3 GeV, pTµ > 0.5 GeV, mµµ > 2.5 GeV W&Z production with LHCb Tara Shears, University of Liverpool 3 1. Introduction LHCb 2. W→µ, Z→µµ 3. Other channels Motivation 4. Outlook Dataset 5. Conclusions
LHCb
8% of Z within 17% (16%) of W+ LHCb acceptance (W-) within LHCb acceptance
W&Z production with LHCb Tara Shears, University of Liverpool 4 1. Introduction LHCb 2. W→µ, Z→µµ 3. Other channels Motivation 4. Outlook Dataset 5. Conclusions
X, Q2 explored by previous experimental data
W&Z production with LHCb Tara Shears, University of Liverpool 5 1. Introduction LHCb 2. W→µ, Z→µµ 3. Other channels Motivation 4. Outlook Dataset 5. Conclusions
Cross-sections known to NNLO PDF uncertainty dominates.
W,Z: Known to ~2% at y ~1.5-2, 6-8% at y~5
Forward measurements can test SM, and provide data to constrain partons. LHCb
W&Z production with LHCb Tara Shears, University of Liverpool 6
1. Introduction LHCb 2. W→µ, Z→µµ 3. Other channels Motivation 4. Outlook Dataset 5. Conclusions
2010: 37.7 pb-1 data recorded
2011: ~1.1 fb-1 recorded
(note: low average no. of interactions in 2010, 2011 due to luminosity levelling)
W&Z production with LHCb Tara Shears, University of Liverpool 7 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
Definition of measured cross-sections:
σ(Z → µµ : 2 < ηµ < 4.5,PTµ > 20GeV,60 < Mµµ <120GeV)
(as function of Z rapidity, Z PT)
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σ(W → µν : 2 < ηµ < 4.5,PTµ > 20GeV) (as function of muon pseudorapidity)
€ LHCb-CONF-2011-039
W&Z production with LHCb Tara Shears, University of Liverpool 8 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
Trigger:
Single µ, pT > 10 GeV
Muon: Good track quality
pT> 20 GeV 2.0 < η < 4.5 Z: 60 < M(µµ) < 120 GeV 1966 candidates Backgrounds: Z→ττ 0.6 ± 0.2 Heavy flavour: 4.3 ± 3 Mis-id: 1 ± 1
W&Z production with LHCb Tara Shears, University of Liverpool 9 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
Trigger:
Single µ, pT > 10 GeV
Muon: Good track quality
pT > 20 GeV 2.0 < η < 4.5 Unbiased impact parameter < 40 µm 2 2 Σ(pT +E(γ)) in R=√(Δη +Δφ )=0.5 cone around µ < 2 GeV E/p < 0.04
No other µ with PT > 5 GeV
Efficiency 45%-80% Estimated using Z data η dependent
W&Z production with LHCb Tara Shears, University of Liverpool 10 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
NW+ = 15 608 NW - = 12 301 Fit muon pT spectrum in data to expected shapes Background sources: for signal and background,
Z→ µµ (1 µ in acceptance) extract Nbkg+, Nbkg- γ*→ µµ Z→ ττ W→ τ ν Punch-through Heavy flavour Decay in flight Purity: Data ~80% (W+) Simulation ~78% (W-) Data + simulation
W&Z production with LHCb Tara Shears, University of Liverpool 11 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
µ+ µ-
W&Z production with LHCb Tara Shears, University of Liverpool 12 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
track muon trig selection εZ = AZεZ εZ εZ εZ track muon trig selection εW = AWεW εW εW εW
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€ AW (AZ) from MC, consistent with 1.0.
W&Z production with LHCb Tara Shears, University of Liverpool 13 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
track muon trig selection εZ = AZεZ εZ εZ εZ track muon trig selection εW = AWεW εW εW εW
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Determine from data (Z events) Bin efficiencies in lepton η, calculate for each event. Tag: 1 identified muon ε(W+,W-) ~ 79% ε(Z) ~ 81.5% Probe: 1 muon stub + TT hit
W&Z production with LHCb Tara Shears, University of Liverpool 14 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
track muon trig selection εZ = AZεZ εZ εZ εZ track muon trig selection εW = AWεW εW εW εW
€ €
Determine from data (Z events) Bin efficiencies in lepton η, calculate for each event. Tag: 1 identified muon ε(W+,W-) ~ 99% ε(Z) ~ 98% Probe: 1 track
W&Z production with LHCb Tara Shears, University of Liverpool 15 1. Introduction Z selection 2. W→µ, Z→µµ W selection 3. Other channels Efficiencies 4. Outlook Systematic errors 5. Conclusions Results
track muon trig selection εZ = AZεZ εZ εZ εZ track muon trig selection εW = AWεW εW εW εW
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€ Determine from data (Z events) Bin efficiencies in lepton η, calculate for each event. Tag: 1 identified muon having fired the ε(W+,W-) ~ 80% single muon trigger ε(Z) ~ 95% ε(mult) ~ 95% Probe: 1 identified muon
+ Hit multiplicity threshold: estimate from data.
W&Z production with LHCb Tara Shears, University of Liverpool 16 1. Introduction Z selection 2. W→µ, Z→µµ W selection Efficiencies 3. Other channels 4. Outlook Systematic errors 5. Conclusions Results
Δσ(W+) [%] Δσ(W-) [%] Δσ(Z) [%] Background ± 1.6 ± 1.6 ± 0.4 Shape (fit) ± 1.9 ± 1.7 n/a Efficiency ± 2.0 ± 1.8 ± 5.1 FSR ± 0.2 ± 0.2 ± 0.3 correction Sys. error ± 3.5 ± 3.2 ± 5.1 Luminosity ± 3.5 ± 3.5 ± 3.5 Stat. error ± 0.9 ± 1.1 ± 2.1
W&Z production with LHCb Tara Shears, University of Liverpool 17 1. Introduction Z selection 2. W→µ, Z→µµ W selection Efficiencies 3. Other channels Systematic errors 4. Outlook 5. Conclusions Results
W&Z production with LHCb Tara Shears, University of Liverpool 18 1. Introduction Z selection 2. W→µ, Z→µµ W selection Efficiencies 3. Other channels Systematic errors 4. Outlook 5. Conclusions Results
W&Z production with LHCb Tara Shears, University of Liverpool 19 1. Introduction Z selection 2. W→µ, Z→µµ W selection Efficiencies 3. Other channels Systematic errors 4. Outlook 5. Conclusions Results
W&Z production with LHCb Tara Shears, University of Liverpool 20 1. Introduction Z selection 2. W→µ, Z→µµ W selection Efficiencies 3. Other channels Systematic errors 4. Outlook 5. Conclusions Results
W&Z production with LHCb Tara Shears, University of Liverpool 21 1. Introduction Z selection 2. W→µ, Z→µµ W selection Efficiencies 3. Other channels Systematic errors 4. Outlook 5. Conclusions Results
W&Z production with LHCb Tara Shears, University of Liverpool 22 1. Introduction 2. W , Z →µ →µµ Z 3. Other channels → ττ Z → ee 4. Outlook 5. Conclusions
Other measurements:
Z → ττ 247 pb-1 (eµ, µµ) (81, 33 cands.)
LHCb-CONF-2011-041
W&Z production with LHCb Tara Shears, University of Liverpool 23 1. Introduction 2. W , Z →µ →µµ Z 3. Other channels → ττ Z → ee 4. Outlook 5. Conclusions
LHCb-CONF-2011-041
W&Z production with LHCb Tara Shears, University of Liverpool 24 1. Introduction 2. W , Z →µ →µµ Z → ττ 3. Other channels Z → ee 4. Outlook 5. Conclusions
Data s=7 TeV 600 LHCb Z/γ * → e+e- MC
Events preliminary 500 Background (e±e±) Z → ee 400 -1 900 pb 300 21526 cands. 200
100
0 40 60 80 100 120 M(e+e-) /GeV
LHCb-CONF-2012-011
W&Z production with LHCb Tara Shears, University of Liverpool 25 1. Introduction 2. W , Z →µ →µµ Z → ττ 3. Other channels Z → ee 4. Outlook 5. Conclusions
80 LHCb 2011 Preliminary, s = 7 TeV [pb]
Z 70 Datastat MSTW08
/dy Data ABKM09 60 tot ee JR09 → Z 50 NNPDF21 σ
d HERA15 40 CTEQ6M (NLO) 30
20 pe > 20 GeV/c 10 T 2 60 < Mee < 120 GeV/c 0 2 2.5 3 3.5 4 4.5 yZ LHCb-CONF-2012-011
W&Z production with LHCb Tara Shears, University of Liverpool 26 1. Introduction 2. W→µ, Z→µµ 3. Other channels 4. Outlook 5. Conclusions
Outlook:
• Comparisons to NNLO (MSTW, ABKM, JR09, HERA, NNPDF), NLO (CTEQ) • Improved understanding of W backgrounds, purity
• W charge asymmetry with PT>20, >25, >30 GeV • Differential W+ and W- distributions (wrt muon η) • Full correlation matrix available, publication forthcoming. (DIS)
• 2011 data to add for W→µ, Z→µµ. Z PT to be published separately. • More decay channels and data to add for Z→ττ • Lower mass Drell-Yan measurements (DIS)
W&Z production with LHCb Tara Shears, University of Liverpool 27 1. Introduction 2. W→µ, Z→µµ 3. Other channels 4. Outlook 5. Conclusions
Measurements of W, Z production in the forward region presented
W→µν, Z→µµ: In agreement with NNLO predictions Data-driven method, publication soon. Precision will improve with 2011 data
Other Z decay modes: Electron, tau final states measured Production in agreement with NNLO predictions.
W&Z production with LHCb Tara Shears, University of Liverpool 28 Backup
W&Z production with LHCb Tara Shears, University of Liverpool 29
Z→ττ
Final states considered: eµ, µµ
µ: 2 < ηµ < 4.5 E/p < 0.2
e: 2 < ηe < 4.5 EECAL/p > 0.1, EHCAL/p < 0.05 EPRS> 0.05 GeV
W&Z production with LHCb Tara Shears, University of Liverpool 30
Z→ττ
Trigger:
Single µ, pT > 10 GeV
µ Muon: PT > 20 GeV
e Electron: PT > 5 GeV
Z: Δφ (eµ) > 2.7 radians Isolation I > 0.8.
81 candidates Backgrounds: QCD: 9.5 ± 3 EWK: 3 ± 1.2 W&Z production with LHCb Tara Shears, University of Liverpool 31
Z→ττ
Trigger:
Single µ, pT > 10 GeV
µ1 Muon: PT > 20 GeV, µ2 PT > 5 GeV.
Z : I > 0.8 Δφ(µµ) > 2.7 radians IPsum significance > 4 APT > 0.2
33 candidates Backgrounds: QCD: 1.6 ± 1.3 EWK: 5.5 ± 1.8 W&Z production with LHCb Tara Shears, University of Liverpool 32
Z→ττ
track track muon electron trig selection ε = A εµ εe ε ε ε ε
A (MC) εtrig (data): tag-and-probe Z→µµ track € ε µ (data): tag-and-probe Z→µµ track track ε e (MC) scaled to ε µ µ ε (data): tag-and-probe Z→µµ e ε (data): tag-and-probe Z→ee sel ε (MC): systematic from MC/data comparison in Z→µµ events.
W&Z production with LHCb Tara Shears, University of Liverpool 33
Z→ττ
Δσ(eµ) [%] Δσ(µµ) [%] Background ± 5 ± 7 Efficiency ± 8 ± 9 Acceptance ± 5 ± 2 Sys. error ± 10 ± 11 Luminosity ± 3.5 ± 3.5 Stat. error ± 12 ± 17
W&Z production with LHCb Tara Shears, University of Liverpool 34