Electroweak Measurements at LHCb!

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1 Electroweak Measurements at LHCb! Simone Bifani University of Birmingham (UK) on behalf of the LHCb collaboration LHCb workshop on quantum interference effects, QCD measurements and generator tuning CERN, 2th - 22nd October 214

2 Outline Introduction Analyses» W µν» Z ll (l = µ, e, τ)#» Z µµ in pa Prospects Summary Simone Bifani 2

LHCb A Forward Spectrometer Designed to look at CP violation in B decays @ LHC Fully

3 LHCb A Forward Spectrometer Designed to look at CP violation in B LHC Fully instrumented within 2. < η < mrad Beam mrad Beam JINST 3 (28) S85 Simone Bifani 3

4 LHCb A Forward Spectrometer Overlap with ATLAS & CMS 2. < η < 2.5 Complementary range 2.5 < η < 5. η# in LHCb 17%(16%) of W + (W - ) within LHCb 8% of Z within LHCb Simone Bifani 4

5 Datasets Analyses based on 211(213) pp(pa) data samples at 7(5) TeV 212 pp data at 8 TeV are currently being analysed» L 211 ~1 fb -1» L 213 ~1.6 nb -1 Due to luminosity levelling, same running conditions throughout fills EW trigger thresholds unchanged during years Simone Bifani 5

W & Z Production and PDFs LHCb s forward acceptance provides very interesting possibilities to study the proton Parton Density Functions Take large-x from one proton and a small-x from the other

6 W & Z Production and PDFs LHCb s forward acceptance provides very interesting possibilities to study the proton Parton Density Functions Take large-x from one proton and a small-x from the other probe two distinct regions in the (x, Q2) space» W and Z (x of -4 and -1)» Low-mass Drell-Yan (x down to -6) Simone Bifani ATLAS/CMS LHCb CDF/D W&Z HERA Fixed Target Q2 [GeV2] Can probe the low-x, high-q2 region inaccessible to other experiments LHC 7 TeV Kinematics 9 5 W&Z γ* γ* 1 7 y =6 6 y =4 5 y =2 4 M x1,2 = p e±y s y = y =2 3 y =4 2 y =6 1 x Q2 = M 2 6

7 W & Z Production at LHCb arxiv: LHCb-CONF LHCb has measured the W and Z production cross-section at 7 TeV using several final states Pull Events per 1 GeV/c LHCb µ + Purity ~77% 2. < η < 4.5 Data Fit W µν K/π µ ν Electroweak Heavy flavour p [GeV/c] W µν# T - µ ) 2 Events / (1 GeV/c Z µµ# LHCb preliminary Data Purity >99% Dimuon invariant mass [GeV/c 2 ] 211 Z->µµ analysis with much reduced systematic uncertainty currently under review Simone Bifani 7

8 W & Z Production at LHCb JHEP 2 (213) 6 JHEP 1 (213) 111 LHCb has measured the W and Z production cross-section at 7 TeV using several final states Events / (2 GeV/c 2 ) Z ee LHCb M (e Data Signal Background Purity ~95% + e - ) [GeV/c 2 ] Events / (5 GeV/c 2 ) Events / (5 GeV/c 2 ) 8 Data 7 Z æ QCD 6 EWK t t æ µe 5 WW æ µe LHCb Ô s =7TeV M µe [GeV/c 2 ] M µh [GeV/c 2 ] Events / (5 GeV/c 2 ) 4 Data 35 Z æ QCD 3 EWK t t æ eµ 25 WW æ eµ 2 Z ττ# Purity 6-7% Data Z æ QCD EWK t t æ µh WW æ µh Z æ µµ LHCb Ô s =7TeV Events / (5 GeV/c 2 ) 15 5 LHCb Ô s =7TeV M eµ [GeV/c 2 ] Data Z æ QCD EWK t t æ eh WW æ eh Z æ ee LHCb Ô s =7TeV M eh [GeV/c 2 ] Simone Bifani 8

9 Results W µν arxiv: Fiducial volume: p T,µ > 2 GeV/c, 2. < η µ < 4.5 LHCb, Data stat Data tot s = 7 TeV MSTW8 NNPDF23 CT ABM12 HERA15 JR p > 2 GeV/c T 2. < η < 4.5 σ W + µ + ν [pb] [pb] ν - µ - σ W LHCb, Data s = 7 TeV Data stat Data tot MSTW8 NNPDF23 CT ABM12 HERA15 JR9 syst p > 2 GeV/c T 2. < η < 4.5 L ~37 pb % CL ellipse area σ - W µ - ν σ W + µ + ν σ W - µ - ν [pb].8% precision! σ W + µ + ν [pb] Results in general agreement with NNLO predictions Main systematics: template fit, reconstruction efficiencies Luminosity uncertainty down to 1.7% Simone Bifani 9

10 Results W µν arxiv: dσ W µν /dη [pb] Theory/Data 8 LHCb, s = 7 TeV p T > 2 GeV/c Datastat Data Data Data tot stat tot + (W ) (W + ) - (W ) - (W ) MSTW8 NNPDF23 CT ABM12 HERA15 JR η dσ W µν /dη [pb] s = 7 TeV LHCb (211 extrapolated) W LHCb (211 extrapolated) W + ATLAS (2) W µ + ν - ATLAS (2) W µ - ν µ + ν µ - ν p T M T E miss > 2 GeV/c > 4 GeV/c > 25 GeV 2 η Good agreement with NNLO Good agreement with ATLAS (after η adapting to ATLAS cuts) Simone Bifani

11 Results W µν arxiv: Lepton charge asymmetry Aµ LHCb, Data Data s = 7 TeV stat tot MSTW8 NNPDF23 CT ABM12 HERA15 JR9 A l p T > 25 GeV/c Theory-Data p T > 2 GeV/c η s = 7 TeV LHCb (211 extrapolated) W µν CMS (211) W µν η Good agreement with NNLO Good agreement with CMS (after adapting to CMS cuts) Simone Bifani 11

12 Results Z ll LHCb-CONF Fiducial volume: p T,l > 2 GeV/c, 2. < η l < 4.5, 6 < M ll < 12 GeV/c 2 LHCb Preliminary Z µµ LHCb preliminary (75.4 ±.3 stat ± 1.9 syst ± 2.6 lumi ) pb Z ee (76. ±.8 stat ± 2. syst ± 2.6 lumi ) pb Z ττ NNLO(MSTW8) (71.4 ± 3.5 stat ± 2.8 syst ± 2.5 lumi ) pb ( PDF ±.4 T heory) pb σ(z ll) [pb] Results agree with each other and NNLO predictions Measurements limited by statistics (ττ) or luminosity (ee, µµ) Main systematics: reconstruction (µµ), tracking efficiency (ee), backgrounds and efficiency (ττ) Simone Bifani 12

13 Results Z ll LHCb-CONF Graph dσ/dy [pb] 7 LHCb preliminary Data (stat) Data (tot) MSTW8 (NNLO) CT (NNLO) NNPDF23 (NNLO) ABM11 (NNLO) dσ/dy [pb] 7 LHCb preliminary Data (stat) Data (tot) Z ee Z boson rapidity Z boson rapidity Good agreement with NNLO Good agreement between µµ and ee final states Good agreement with ATLAS (after adapting to ATLAS cuts) dσ/dy [pb] LHCb 211 preliminary, Z µµ extrapolated LHCb 211, Z ee extrapolated ATLAS 2, Z µµ, Z ee y(z) Simone Bifani 13

14 Results Z ll LHCb-CONF dσ/dφ* [pb] 3 LHCb preliminary Data (stat) Data (tot) NNLO - MSTW8 ResBos Powheg + PS φ* prediction/data LHCb preliminary Data (stat) Data (tot) NNLO - MSTW8 ResBos Powheg + PS φ* = tan (( )/2) cosh ( /2) p T m Z NNLO fails to describe φ* Bett er agreement when compared to ResBos and POWHEG dσ/dφ* [pb] 3 LHCb preliminary Graph -1 1 Data (stat) Data (tot) Z ee φ* Simone Bifani 14

15 Z µµ in pa! LHCb-PAPER Sensitive to npdf in a region where there is no experimental input Candidates / (2 GeV/c 2 ) LHCb ppb s pn forward = 5 TeV LHCb ppb s pn = 5 TeV [nb] σ Z µ + µ LHCb stat. LHCb syst. + lumi. LHCb ppb s pn = 5 TeV FEWZ NNLO + MSTW8 FEWZ NNLO + MSTW8 + EPS9 (NLO) m [GeV/c 2 µ + µ ] forward backward Forward (pa): σ(z µµ) = ( stat ± 1.1 syst ) pb Backward (Ap): σ(z µµ) = ( stat ± 1. syst ) pb Simone Bifani 15

16 Impact on PDFs LHCb Impication Workshop Simone Bifani 16

17 Prospects Updates with 8 TeV data for all analyses Perform inclusive, differential and associated measurements with Run-II 13(14) TeV Measurement of event properties, multiplicities and multiplicity ratios in Z events with identified particles (p, pbar, K ±, Lambda->pπ, K S ->ππ, maybe ρ and φ) What should we measure with higher priority that would be an important input for MC tuning? Simone Bifani 17

Summary LHCb probes a unique region in η and low p T reach at LHC and can provide important inputs to PDFs in the forward region W and Z production cross-sections

18 Summary LHCb probes a unique region in η and low p T reach at LHC and can provide important inputs to PDFs in the forward region W and Z production cross-sections measured by using a variety of final states Results consistent with theoretical predictions calculated at NNLO Many other measurements expected soon! Simone Bifani 18

19 Backup

W & Z Production and PDFs Theoretical predictions» Partonic cross-sections known at NNLO to few %» PDF uncertainty dominates at large rapidities (1% for y<2, 6-8% at y~5) Experimental measurements»

20 W & Z Production and PDFs Theoretical predictions» Partonic cross-sections known at NNLO to few %» PDF uncertainty dominates at large rapidities (1% for y<2, 6-8% at y~5) Experimental measurements» Muon modes provide clean signature and easily reconstructible final states» Electron and tau modes provide complementary measurements and test lepton universality Cross-section LHCb can constrain PDFs Simone Bifani 2

21 W & Z Production and PDFs Cancel or highlight PDF uncertainties with ratios» A µ = (dσ W+ - dσ W- ) / (dσ W+ + dσ W- ) tests u V and d V difference A µ# R W#» R W = dσ W+ / dσ W- tests d V /u V ratio» R WZ = dσ W / dσ Z almost insensitive to PDFs precise test of SM Many systematic errors cancel Simone Bifani 21

22 W µν! Single muon trigger: p T > GeV/c 1 reconstructed & isolated muon» p T > 2 GeV/c» 2. < η < 4.5» Cone p T (R=.5) < 2 GeV/c» Extra muon veto (p T > 2 GeV/c)» Impact parameter < 4 µm» E / pc < 4% Backgrounds» Z/γ* µµ (MC)» W τν and Z ττ (MC)» Heavy flavour (Data)» K/π decay in flight (Data) N Candidates = 147k + 116k - Purity ~ 79% + 78% - Events per 1 GeV/c Pull LHCb L ~37 pb -1 (2) µ + 2. < η < 4.5 Data Fit W µν K/π µ ν Electroweak Heavy flavour p [GeV/c] Template fit in 5 η bins W and Z muon p T spectrum at NNLO Simone Bifani 22 T - µ

23 W µν! Specific cuts implemented to reduce each background component Z/γ* µµ» Veto on 2 nd muon with p T > 2 GeV/c W τν, Z ττ and Heavy flavour» Impact parameter < 4 µm K/π punchthrough» E / pc <.4 Largest residual backgrounds» Decays in flight of K/π» Z µµ events with one muon outside the acceptance IP [mm] Simone Bifani 23 Events per.2 mm Events per LHCb Data Fit Pseudo- W (data) W τν (simulation) bb+cc Xµ (simulation) LHCb Data Fit Pseudo-W (data) Hadrons (data) / pc E calo

24 Z µµ! Single muon trigger: p T > GeV/c 2 reconstructed muons» p T > 2 GeV/c» 2. < η < 4.5» 6 < M µµ < 12 GeV/c 2 Backgrounds» Heavy flavour (Data)» K/π mis-id (Data)» Z ττ (MC)» tt - (MC)» WW (MC) ) 2 Events / (1 GeV/c LHCb preliminary Data L ~1 fb -1 (211) N Candidates = Purity > 99% Dimuon invariant mass [GeV/c 2 ] Simone Bifani 24

25 Z ee! Single electron trigger: p T > 15 GeV/c 2 reconstructed electrons» p T > 2 GeV/c» 2. < η < 4.5» E ECal / pc >.1» E HCal / pc <.5» M ee > 4 GeV/c 2 Backgrounds» K/π mis-id (Data)» Heavy flavour (Data)» Z ττ (MC)» tt - (MC) Events / (2 GeV/c 2 ) LHCb L ~945 pb -1 (211) Data Signal Background N Candidates = 2142 Purity ~95% M (e + e - ) [GeV/c 2 ] Mass peak distorted by bremsstrahlung Simone Bifani 25

26 Z ττ! Single lepton trigger: p T,µ(e) > (15) GeV/c 5 final states: µµ, µe, eµ, µh, eh» p T,1 > 2 GeV/c, p T,2 > GeV/c» 2. < η l < 4.5, 2.25 < η h < 3.75» M 12 > 2 GeV/c 2 Backgrounds» QCD (Data)» EW (Data)» tt (MC)» WW (MC)» Z ll (MC) M µµ [GeV/c 2 ] N Candidates = 99 Purity ~6-7% Simone Bifani 26 Events / (5 GeV/c 2 ) Events / (5 GeV/c 2 ) L ~1 fb -1 (211) 4 Data LHCb Ô s =7TeV Z æ QCD EWK t t æ µµ WW æ µµ Z æ µµ 8 Data 7 Z æ QCD 6 EWK t t æ µe 5 WW æ µe LHCb Ô s =7TeV M µe [GeV/c 2 ]

27 Cross-Section The cross-section for boson production can be expressed as BR= 1 R L N Candidates A " T rigger " Tracking " P articleid " Selection f FSR Measurements performed in the forward region (2.<η<4.5) for leptons with p T >2 GeV/c: Acceptance = 1 for Z µµ and W µν, but obtained from MC for Z ee and Z ττ Efficiencies determined mostly from data and cross checked with simulation FSR correction evaluated using HERWIG++ and PHOTOS+PYTHIA Simone Bifani 27

trajectory from muon stub and minimal tracking information Particle ID

28 Reconstruction Efficiencies Trigger» Tag: triggered muon#» Probe: offline identified muon Tracking Tracking» Tag: identified muon track» Probe: trajectory from muon stub and minimal tracking information Particle ID Particle ID» Tag: identified muon#» Probe: reconstructed track Simone Bifani 28

29 W µν Simone Bifani 29

30 Z ll Simone Bifani 3

31 Z ττ! Simone Bifani 31

32 Z µµ in pa Simone Bifani 32

33 Z µµ in pa Candidates / (2 GeV/c 2 ) LHCb ppb s pn forward = 5 TeV LHCb Preliminary ppb = 5 TeV s pn Candidates / (2 GeV/c 2 ) LHCb ppb s pn backward = 5 TeV LHCb Preliminary ppb = 5 TeV s pn m [GeV/c 2 µ + µ ] m [GeV/c 2 µ + µ ] Candidates / (.2) LHCb Preliminary ppb = 5 TeV s pn forward Candidates / (.2) LHCb Preliminary ppb = 5 TeV s pn backward y Z,lab y Z,lab y' y' Simone Bifani 33

34 References Simone Bifani 34

PDF Studies at LHCb! Simone Bifani. On behalf of the LHCb collaboration. University of Birmingham (UK)

PDF Studies at LHCb! Simone Bifani University of Birmingham (UK) On behalf of the LHCb collaboration MENU 213 Rome 3th September - 4th October 213 Outline Introduction Analyses» Z/γ* ll, l =, e, τ#» W