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

Electroweak physics, QCD and jets in the forward region Nicola Chiapolini on behalf of the LHCb collaboration Epiphany Conference, 7.-9. January 2013

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 2 / 33 Introduction 1 pp → Z → ℓ + ℓ − 2 pp → Z → µ + µ − + Jets 3 4 pp → W → µ ν 5 Low Mass Drell-Yan Conclusion 6

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction 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 K 0 S production in pp collisions at √ s = 0 . 9 TeV (Phys. Lett. B 693 (2010) 69-80)

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 4 / 33 The LHCb Detector Muon System Calorimeters RICH detectors Interaction Point Beam Beam Vertex detector Tracking stations Forward spectrometer, fully instrumented in 2 < η < 5 / c 2 Trigger threshold: M µµ > 2 . 5 GeV

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 5 / 33 Data Taking Data Recorded Year E CM L 37 pb − 1 2010 7.0 TeV 1.1 fb − 1 2011 7.0 TeV 2.1 fb − 1 2012 8.0 TeV Average number of interactions constant in all 3 years (1.5)

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 6 / 33 Cross-Section Measurements f a/A scattering process at LHC p A a parton parton scattering X described by perturbative QCD b needs parton distribution functions p B f b/B parton distribution functions determined from measurements � σ AB → X = dx a dx b · f a / A f b / B · ˆ σ ab → X parton distribution function parton parton scattering

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 7 / 33 Electroweak Measurements at LHCb √ s · e ± η fraction of proton momentum carried by parton x a , b = M Q 2 = M 2 4-momentum transfered 6 10 LHCb 2 < y < 5 5 Measured by previous 10 GPDs |y| < 2.5 p s = 7 TeV 4 10 experiments W, Z Unexplored LHCb probes two distinct 3 10 Q 2 (GeV 2 ) regions in x / Q 2 plane 2 10 unique region at low x 1 (5 GeV) 10 down to x = 8 · 10 − 6 0 10 -1 10 -7 -6 -5 -4 -3 -2 -1 0 10 10 10 10 10 10 10 10 x

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

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 9 / 33 Z → µ + µ − (JHEP 2012, 6 (2012), 58) ) 2 450 Events / (2 GeV/c LHCb 400 350 300 Data 250 2010 dataset 200 L = 37 pb − 1 150 100 / c 2 60 < M ℓℓ < 120 GeV 50 0 2 < η ℓ < 4 . 5 60 80 100 120 2 Dimuon invariant mass [GeV/c ] p T > 20 GeV / c Nr. of Candidates 1966 Purity 99 . 7 %

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 10 / 33 Z → e + e − (arXiv:1212.4620 [hep-ex]) ) 2 c 1200 LHCb Events / (2 GeV/ Data Data Signal 1000 Background 2011 dataset 800 L = 945 pb − 1 600 400 Challenges 200 Energy measurement 0 saturation in calo 40 60 80 100 120 bremsstrahlung + - 2 M (e e ) [GeV/ c ] QCD background Nr. of Candidates 21 420 use same-sign data Purity 95 . 5 %

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 11 / 33 Z → τ + τ − (arXiv:1210.6289 [hep-ex]) µ e µ µ 40 80 Data Data /c 2 ) /c 2 ) Z → ττ Z → ττ 35 70 Events / (5 GeV Events / (5 GeV QCD QCD 30 EWK EWK LHCb 60 √ s = 7 TeV t ¯ t → µµ t ¯ t → µe 25 50 WW → µµ WW → µe Z → µµ 20 40 15 LHCb 30 √ s = 7 TeV 10 20 Data 5 10 0 0 20 40 60 80 100 120 20 40 60 80 100 120 2011 dataset M µµ [GeV /c 2 ] M µe [GeV /c 2 ] e µ µ h L = 1 fb − 1 40 Data Data /c 2 ) /c 2 ) Z → ττ 35 Z → ττ 35 Events / (5 GeV Events / (5 GeV QCD QCD 30 30 EWK EWK t ¯ t → eµ t ¯ t → µh Challenges 25 25 WW → eµ WW → µh Z → µµ 20 20 15 LHCb 15 LHCb partial reconstruction √ s = 7 TeV √ s = 7 TeV 10 10 5 5 of different final states 0 0 20 40 60 80 100 120 20 40 60 80 100 120 M eµ [GeV /c 2 ] M µh [GeV /c 2 ] many backgrounds e h 30 Data /c 2 ) Z → ττ Events / (5 GeV 25 QCD EWK t ¯ 20 t → eh WW → eh Z → ee 15 LHCb 10 √ s = 7 TeV 5 0 20 40 60 80 100 120 /c 2 ] M eh [GeV

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction 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 − Z → τ + τ − → µ h 40 Data /c 2 ) Data /c 2 ) Z → ττ 35 35 Z → ττ Events / (5 GeV QCD Events / (5 GeV QCD 30 EWK 30 LHCb EWK t ¯ √ s = 7 TeV t → µµ t ¯ t → µh 25 25 WW → µµ WW → µh Z → µµ 20 Z → µµ 20 15 15 LHCb √ s = 7 TeV 10 10 5 5 0 0 20 40 60 80 100 120 20 40 60 80 100 120 /c 2 ] M µµ [GeV M µh [GeV /c 2 ] Nr. of Candidates 189 Nr. of Candidates 124 Purity 78 % Purity 75 % Total Nr. of Candidates 990

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction 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

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction 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 → e + e − 80 [pb] pp → Z → µ + µ − (a) 70 LHCb 80 Z [pb] y LHCb, s = 7 TeV /d 60 70 Data MSTW08 Z stat /dy σ Data ABKM09 tot 60 d 50 µ µ JR09 → 50 NNPDF21 Z σ 40 HERA15 d 40 CTEQ6M (NLO) 30 30 Data (stat.) 20 Data (tot.) µ p > 20 GeV/c 20 T η µ 10 2.0 < < 4.5 MSTW08 2 60 < M < 120 GeV/c µ µ 10 0 NNPDF21 2 2.5 3 3.5 4 4.5 CTEQ (CT10) y Z 0 2 2.5 3 3.5 4 4.5 y Z Compared to NNLO predictions (DYNNLO)

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 15 / 33 e + e − Angular Result (arXiv:1212.4620 [hep-ex]) Fixed Order (no soft gluons) * [pb] 3 10 Prediction / data (b) LHCb 1.4 ( a ) LHCb 1.2 φ 2 10 /d 1 σ 0.8 d Data (stat.) Data (tot.) 10 0.6 MSTW08 Data (stat.) NNPDF21 CTEQ (CT10) 0.4 Data (tot.) -1 10 1 φ * MSTW08 1 NNPDF21 Resummation / Parton Shower CTEQ (CT10) Prediction / data -1 1.4 10 (b) LHCb -1 10 1 1.2 φ * 1 � � π −| ∆ φ | 0.8 tan Data (stat.) ≈ p T Data (tot.) 2 φ ∗ ≡ 0.6 Resbos Powheg + PS � � Mc ∆ η LHCb Pythia6 cosh 0.4 2 -1 10 1 φ *

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 16 / 33 Results: τ + τ − (arXiv:1210.6289 [hep-ex]) p T > 20 GeV /c LHCb 2 . 0 < η < 4 . 5 Dynnlo √ s = 7 TeV 60 < M < 120 GeV /c 2 MSTW08 @NNLO τ µ τ µ τ µ τ e τ e τ µ τ µ τ h τ e τ h ττ µµ 55 60 65 70 75 80 85 90 σ pp → Z → ℓℓ [pb]

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

pp → Z → µ + µ − + Jets pp → Z → ℓ + ℓ − Introduction pp → W → µ ν Low Mass Drell-Yan Conclusion 18 / 33 Z → µ + µ − + Jets (LHCb-CONF-2012-016) LHCb Reconstructed Z Decay Muons Preliminary Jet Data s = 7 TeV Data 2011 dataset [GeV/c] 80 L = 1 fb − 1 70 60 Z → µ + µ − selection 50 T 40 p 30 20 5 10 Challenges 4 0 3 η 2 3 1 jet reconstruction 0 -1 -2 -3 2 φ energy scale and resolution (example of signal candidate)