Electroweak physics, QCD and jets in the forward region Nicola - - PowerPoint PPT Presentation

SLIDE 1

Electroweak physics, QCD and jets in the forward region

Nicola Chiapolini

• n behalf of the LHCb collaboration

Epiphany Conference, 7.-9. January 2013

SLIDE 2

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 2 / 33

1

Introduction

2

pp → Z → ℓ+ℓ−

3

pp → Z → µ+µ− + Jets

4

pp → W → µ ν

5

Low Mass Drell-Yan

6

Conclusion

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Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 3 / 33

Further (QCD) Topics

Measurement of the forward energy flow in pp collisions at √s = 7 TeV with the LHCb experiment

(arXiv:1212.4755 [hep-ex])

Measurement of charged particle multiplicities in pp collisions at √s = 7 TeV in the forward region

(Eur. Phys. J. C 72 (2012) 1947)

Measurement of the inclusive φ cross-section in pp collisions at √s = 7 TeV

(Phys. Lett. B 703 (2011) 267-273)

Measurement of V 0 production ratios in pp collisions at √s = 0.9 and 7 TeV

(J. High Energy Phys. 08 (2011) 034)

Prompt K0

S production

in pp collisions at √s = 0.9 TeV

(Phys. Lett. B 693 (2010) 69-80)

SLIDE 4

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 4 / 33

The LHCb Detector

Muon System Calorimeters RICH detectors Vertex detector Tracking stations

Beam Beam

Interaction Point

Forward spectrometer, fully instrumented in 2 < η < 5 Trigger threshold: Mµµ > 2.5 GeV /c2

SLIDE 5

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 5 / 33

Data Taking

Data Recorded

Year L ECM 2010 37 pb−1 7.0 TeV 2011 1.1 fb−1 7.0 TeV 2012 2.1 fb−1 8.0 TeV Average number of interactions constant in all 3 years (1.5)

SLIDE 6

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 6 / 33

Cross-Section Measurements

scattering process at LHC

parton parton scattering described by perturbative QCD needs parton distribution functions parton distribution functions determined from measurements

a b p

A

pB fa/A fb/B X

σAB→X =

• dxadxb · fa/Afb/B · ˆ

σab→X parton distribution function parton parton scattering

SLIDE 7

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 7 / 33

Electroweak Measurements at LHCb

xa,b = M

√s · e±η fraction of proton momentum carried by parton

Q2 = M2 4-momentum transfered LHCb probes two distinct regions in x/Q2 plane unique region at low x down to x = 8 · 10−6

Q2 (GeV2)

10

1

10

2

10

3

10

4

10

5

10 10

• 1

10 10

• 1

10

• 2

10

• 3

10

• 4

10

• 5

10

• 6

10

• 7

x

LHCb

10

6

GPDs 2 < y < 5 |y| < 2.5

Measured by previous experiments Unexplored

ps = 7 TeV W, Z

(5 GeV)

SLIDE 8

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 8 / 33

pp → Z → ℓ+ℓ−

SLIDE 9

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 9 / 33

Z → µ+µ−

(JHEP 2012, 6 (2012), 58)

Data

2010 dataset L = 37 pb−1 60 < Mℓℓ < 120 GeV /c2 2 < ηℓ < 4.5 pT > 20 GeV /c

]

2

Dimuon invariant mass [GeV/c

60 80 100 120

)

2

Events / (2 GeV/c

50 100 150 200 250 300 350 400 450 LHCb

• Nr. of Candidates

1966 Purity 99.7 %

SLIDE 10

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 10 / 33

Z → e+e−

(arXiv:1212.4620 [hep-ex])

Data

2011 dataset L = 945 pb−1

Challenges

Energy measurement

saturation in calo bremsstrahlung

QCD background

use same-sign data

]

2

c ) [GeV/

• e

+

(e M

40 60 80 100 120

)

2

c Events / (2 GeV/

200 400 600 800 1000 1200

Data Signal Background

LHCb

• Nr. of Candidates

21 420 Purity 95.5 %

SLIDE 11

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 11 / 33

Z → τ+τ−

(arXiv:1210.6289 [hep-ex])

Data

2011 dataset L = 1 fb−1

Challenges

partial reconstruction

• f different final states

many backgrounds

µ µ

Mµµ [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 5 10 15 20 25 30 35 40 Data Z → ττ QCD EWK t¯ t → µµ WW → µµ Z → µµ LHCb √s = 7 TeV

e µ

Meµ [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 5 10 15 20 25 30 35 40 Data Z → ττ QCD EWK t¯ t → eµ WW → eµ LHCb √s = 7 TeV

e h

Meh [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 5 10 15 20 25 30 Data Z → ττ QCD EWK t¯ t → eh WW → eh Z → ee LHCb √s = 7 TeV

µ e

Mµe [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 10 20 30 40 50 60 70 80 Data Z → ττ QCD EWK t¯ t → µe WW → µe LHCb √s = 7 TeV

µ h

Mµh [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 5 10 15 20 25 30 35 Data Z → ττ QCD EWK t¯ t → µh WW → µh Z → µµ LHCb √s = 7 TeV

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Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 12 / 33

Z → τ+τ−: Two Examples

(arXiv:1210.6289 [hep-ex])

Z → τ+τ− → µ+µ−

Mµµ [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 5 10 15 20 25 30 35 40 Data Z → ττ QCD EWK t¯ t → µµ WW → µµ Z → µµ LHCb √s = 7 TeV

• Nr. of Candidates

124 Purity 75 % Z → τ+τ− → µh

Mµh [GeV /c2] 20 40 60 80 100 120 Events / (5 GeV /c2) 5 10 15 20 25 30 35 Data Z → ττ QCD EWK t¯ t → µh WW → µh Z → µµ LHCb √s = 7 TeV

• Nr. of Candidates

189 Purity 78 % Total Nr. of Candidates 990

SLIDE 13

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 13 / 33

Common Considerations

All events triggered by single muon or single electron trigger Most efficiencies determined from data (tag & probe) Magnitude of most uncertainties dominated by statistics

(most important for Z → µ+µ−)

Uncertainties [%]

Z → µ+µ− Z → e+e− Z → τ+τ−

(combined)

Statistic 2.2 1.1 4.9 Systematic 4.3 2.6 3.9 Luminosity 3.5 3.5 3.5

SLIDE 14

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 14 / 33

Differential Production Cross Sections

(JHEP 2012, 6 (2012), 58; arXiv:1212.4620 [hep-ex])

pp → Z → µ+µ−

Z

y 2 2.5 3 3.5 4 4.5 [pb]

Z

/dy

µ µ → Z

σ d 10 20 30 40 50 60 70 80

= 7 TeV s LHCb,

stat

Data MSTW08

tot

Data ABKM09 JR09 NNPDF21 HERA15 CTEQ6M (NLO)

2

< 120 GeV/c

µ µ

60 < M < 4.5

µ

η 2.0 < > 20 GeV/c

µ T

p

pp → Z → e+e−

Z

y

2 2.5 3 3.5 4 4.5

[pb]

Z

y /d σ d

10 20 30 40 50 60 70 80

Data (stat.) Data (tot.) MSTW08 NNPDF21 CTEQ (CT10)

LHCb (a)

Compared to NNLO predictions (DYNNLO)

SLIDE 15

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 15 / 33

e+e− Angular Result

(arXiv:1212.4620 [hep-ex])

* φ

• 1

10 1

* [pb] φ /d σ d

• 1

10 1 10

2

10

3

10

Data (stat.) Data (tot.) MSTW08 NNPDF21 CTEQ (CT10)

LHCb (b)

φ∗ ≡ tan

• π−|∆φ|

2

• cosh
• ∆η

2

• ≈ pT

Mc

Fixed Order (no soft gluons)

* φ

• 1

10 1

Prediction / data

0.4 0.6 0.8 1 1.2 1.4

Data (stat.) Data (tot.) MSTW08 NNPDF21 CTEQ (CT10)

LHCb ( a )

Resummation / Parton Shower

* φ

• 1

10 1

Prediction / data

0.4 0.6 0.8 1 1.2 1.4

Data (stat.) Data (tot.) Resbos Powheg + PS LHCb Pythia6

LHCb (b)

SLIDE 16

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 16 / 33

Results: τ+τ−

(arXiv:1210.6289 [hep-ex])

τµτµ τµτe τeτµ τµτh τeτh ττ µµ σpp→Z→ℓℓ [pb] 55 60 65 70 75 80 85 90 LHCb √s = 7 TeV Dynnlo MSTW08 @NNLO pT > 20 GeV /c 2.0 < η < 4.5 60 < M < 120 GeV /c2

SLIDE 17

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 17 / 33

pp → Z → µ+µ− + Jets

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Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 18 / 33

Z → µ+µ− + Jets

(LHCb-CONF-2012-016)

Data

2011 dataset L = 1 fb−1 Z → µ+µ− selection

Challenges

jet reconstruction energy scale and resolution

η

2 3 4 5

φ

• 3
• 2
• 1

1 2 3

[GeV/c]

T

p

10 20 30 40 50 60 70 80

= 7 TeV Data s

Preliminary LHCb

Reconstructed Z Decay Muons Jet

(example of signal candidate)

SLIDE 19

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 19 / 33

The Jets

(LHCb-CONF-2012-016)

Definition

anti-kT clustering algorithm radius parameter R = 0.5

Selection

pT(jet) > 10 GeV /c 2.0 < ηjet < 4.5 jet isolated from µ (R = 0.4)

Energy Calibration (dominant systematic uncertainty)

(Z, Jet) φ Δ

1 2 3

Event Rate

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

2011 Data = 7 TeV Data s

Preliminary LHCb

(Z)

T

(Jet) / p

T

p

0.5 1 1.5 2

Event Rate

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

2011 Data Simulation

= 7 TeV Data s

Preliminary LHCb

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Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 20 / 33

Normalized Z + Jet

(LHCb-CONF-2012-016)

measurement at hadron level predictions at parton level (order α2

S)

Jet Multiplicity

1 2 >2

) (Z σ + n Jets) (Z σ

• 2

10

• 1

10 1

= 7 TeV s

preliminary LHCb

Z + Jet Z LHCb 0.229 ± 0.006 (stat) ± 0.009 (syst) Theory 0.212+0.006

−0.009 (PDF) ± 0.016 (scale)

SLIDE 21

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 21 / 33

pp → W → µ ν

SLIDE 22

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 22 / 33

W → µ ν

(JHEP 2012, 6 (2012), 58)

Data

2010 dataset L = 37 pb−1 2 < ηµ < 4.5 pT > 20 GeV /c

Challenges

selection efficiencies

from data using Z → µ+µ− events with one µ removed

backgrounds

IP [mm] 0.1 0.2 0.3 0.4 0.5 Event probability

• 4

10

• 3

10

• 2

10

• 1

10 1 LHCb

Pseudo-W (Data) (Simulation) ν µ → W (Simulation) µ X → b b (Simulation) µ X → c c

SLIDE 23

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 23 / 33

Purity from Template Fit

(JHEP 2012, 6 (2012), 58)

[GeV/c]

µ T

p Events / (1 GeV/c) 100 200 300 400 500 600 700 800 20 30 40 50 60 70 20 30 40 50 60 70 LHCb (a) < 4.5

µ

η 2.0 <

+

µ

• µ

Data ν µ → π K/ Fit µ µ → Z ν µ → W τ τ → & Z ν τ → W Heavy Flavour

Shape Normalisation W → µ ν simulation fit K/π decay in flight data fit γ∗/Z → µ+µ− simulation fixed W → τ ν, Z → τ+τ− simulation fixed Heavy Flavour data fixed

Cand. Purity [%] W+ 14660 78.8 W− 11618 78.4

SLIDE 24

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 24 / 33

Production Cross Section and Ratios

(JHEP 2012, 6 (2012), 58)

= 7 TeV s LHCb,

stat

Data

tot

Data MSTW08 NNPDF21 ABKM09 HERA15 JR09 CTEQ6M (NLO) > 20 GeV/c

µ T

p < 4.5

µ

η 2.0 <

2

< 120 GeV/c

µ µ

Z: 60 < m 65 70 75 80 85 90

[pb]

µ µ → Z

σ

700 750 800 850 900 950

[pb]

ν

+

µ →

+

W

σ

550 600 650 700 750

[pb]

ν

• µ

→

• W

σ

1.1 1.2 1.3 1.4 1.5

ν

• µ

→

• W

σ

ν

+

µ →

+

W

σ

16 17 18 19 20 21 22 23

µ µ → Z

σ

ν

• µ

→

• W

σ +

ν

+

µ →

+

W

σ

9 10 11 12

µ µ → Z

σ

ν

+

µ →

+

W

σ

7 7.5 8 8.5 9 9.5 10

µ µ → Z

σ

ν

• µ

→

• W

σ

Compared to NNLO predictions (DYNNLO) σZ σW+ σW−

σW+ σW− σW++σW− σZ σW+ σZ σW− σZ

SLIDE 25

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 25 / 33

Differential W Cross Section

(JHEP 2012, 6 (2012), 58)

µ

η 2 2.5 3 3.5 4 4.5 [pb]

µ

η /d

ν µ → W

σ d 100 200 300 400 500 600 700 800

= 7 TeV s LHCb,

ν

+

µ →

+

W stat

Data MSTW08

ν

+

µ →

+

W tot

Data ABKM09

ν

• µ

→

• W

stat

Data JR09

ν

• µ

→

• W

tot

Data NNPDF21 HERA15 CTEQ6M (NLO)

> 20 GeV/c

µ T

p

As expected W− production higher than W+ in forward region

SLIDE 26

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 26 / 33

Lepton Charge Asymmetry

(JHEP 2012, 6 (2012), 58)

Aµ = σW+→µ+ν − σW−→µ−ν σW+→µ+ν + σW−→µ−ν

µ

η 1 2 3 4

µ

A

• 0.6
• 0.4
• 0.2

0.2 0.4 0.6

= 7 TeV s LHCb,

stat

Data MSTW08

tot

Data ABKM09 JR09 NNPDF21 HERA15 CTEQ6M (NLO)

> 20 GeV/c

µ T

p

Precise measurement in good agreement with predictions

SLIDE 27

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 27 / 33

LHC Combination

(ATLAS-CONF-2011-129)

 η  0.5 1 1.5 2 2.5 3 3.5 4 Lepton charge asymmetry

• 0.3
• 0.2
• 0.1

0.1 0.2 0.3

• 1

) 35 pb ν l → ATLAS (extrapolated data, W

• 1

) 36 pb ν µ → CMS (W

• 1

) 36 pb ν µ → LHCb (W MSTW08 prediction (MC@NLO, 90% C.L.) CTEQ66 prediction (MC@NLO, 90% C.L.) HERA1.0 prediction (MC@NLO, 90% C.L.)

ATLAS+CMS+LHCb Preliminary =7 TeV s > 20 GeV

l T

p

SLIDE 28

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 28 / 33

Low Mass Drell-Yan

SLIDE 29

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 29 / 33

pp → γ∗/Z → µ+µ−

(LHCb-CONF-2012-013)

Data

2010 dataset L = 37 pb−1 2 < ηµ < 4.5 pT > 3 GeV /c

Challenges

5 < Mµµ < 120 GeV /c2 different backgrounds muon isolation = PT

µ−in Jet

PT

full Jet

SLIDE 30

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 30 / 33

Mass Bins

(LHCb-CONF-2012-013)

Minimum muon isolation

0.5 1

Events

200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

2.0 < y < 4.5

2

7.0 < M < 9.0 GeV/c

Minimum muon isolation

0.5 1

Events

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

LHCb preliminary 2010 data Drell-Yan Upsilon Heavy Flavour Hadron mis-id

2.0 < y < 4.5

2

5.0 < M < 7.0 GeV/c

Minimum muon isolation

0.5 1

Events

100 200 300 400 500 600 700 800 900

2.0 < y < 4.5

2

60.0 < M < 120 GeV/c Minimum muon isolation

0.5 1

Events

100 200 300 400 500 600 700 800

2.0 < y < 4.5

2

10.5 < M < 12.5 GeV/c

Minimum muon isolation

0.5 1

Events

100 200 300 400 500

2.0 < y < 4.5

2

12.5 < M < 15.0 GeV/c

Minimum muon isolation

0.5 1

Events

50 100 150 200 250 300 350 400 450

2.0 < y < 4.5

2

15.0 < M < 20.0 GeV/c

Minimum muon isolation

0.5 1

Events

50 100 150 200 250 300

2.0 < y < 4.5

2

20.0 < M < 30.0 GeV/c

Minimum muon isolation

0.5 1

Events

20 40 60 80 100 120

2.0 < y < 4.5

2

30.0 < M < 40.0 GeV/c

Minimum muon isolation

0.5 1

Events

10 20 30 40 50 60 70 80

2.0 < y < 4.5

2

40.0 < M < 60.0 GeV/c

SLIDE 31

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 31 / 33

Result

(LHCb-CONF-2012-013)

)]

2

[pb/(GeV/c

µ µ

/dM

µ µ → * γ

σ d

1 10

2

10

= 7 TeV s LHCb Preliminary,

stat

Data

tot

Data LO PYTHIA (CTEQ5L) NLO FEWZ (MSTW08) NLO DYNNLO (MSTW08)

< 4.5

µ

η 2.0 < > 10 GeV/c

µ

p > 3 (15) GeV/c

µ T

p ]

2

Dimuon invariant mass [GeV/c

10

2

10

Theory/Data

0.5 1 1.5

Also differential measurements in 5 dimuon rapidity-bins (for Mµµ in 10.5 - 20 GeV /c2 and 20 - 40 GeV /c2)

Theory/Data

SLIDE 32

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 32 / 33

Summary & Outlook

Summary

LHCb: Unique kinematic range down to x = 8 · 10−6 W/Z production at LHCb in agreement with NNLO predictions Ratio W+/W− cross section: 1.7 % uncertainty Measurement of low mass Drell-Yan production First measurements of Z + jet production

Outlook

update remaining analyses with 2011 dataset(L = 1.1 fb−1) analyze 2012 dataset (L = 2.1 fb−1 at 8 TeV) W and Z production in association with b and c jets

SLIDE 33

Introduction pp → Z → ℓ+ℓ− pp → Z → µ+µ− + Jets pp → W → µ ν Low Mass Drell-Yan Conclusion 33 / 33

Thank you for your attention

SLIDE 34

1 / 33

Systematic Uncertainties: Z + Jets

(LHCb-CONF-2012-016)

n Jets 1 2 ≥ 3 Bin-to-Bin Migration 0.2 1.0 2.9 9.7 GEC and Trigger 0.3 0.9 1.5 3.8 µ ID 0.2 0.6 0.9 1.4 µ Tracking 0.5 1.3 4.0 3.6 Jet E Correction 1.0 2.6 7.0 11.0 Jet E Resolution 0.1 0.6 1.7 3.6 Jet ID 0.3 0.8 1.6 2.9 Total 1.2 3.4 9.1 16 All numbers in %

SLIDE 35

2 / 33

Systematic Uncertainties: W → µ ν

(JHEP 2012, 6 (2012), 58)

Source ∆σZ→µ+µ− ∆σW+→µ+ν ∆σW−→µ−ν Signal purity 0.1 1.2 0.9 Template shape – 0.9 1.0 Efficiencies 4.3 2.2 2.0 Additional selection – 1.8 1.7 FSR correction 0.02 0.01 0.02 Total 4.3 3.2 2.9 Luminosity 3.5 3.5 3.5 All numbers in %