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

Transcription

1 PDF Studies at LHCb! Simone Bifani University of Birmingham (UK) On behalf of the LHCb collaboration MENU 213 Rome 3th September - 4th October 213

2 Outline Introduction Analyses» Z/γ* ll, l =, e, τ#» W ν#» Z/γ* +jet Summary and Outlook Simone Bifani MENU 213 2

3 LHCb A Forward Spectrometer Designed to look at CP violation in B LHC Fully instrumented within 2. < η < 5.» : overlap with ATLAS & CMS» : complementary range 25 mrad 1 mrad Beam Beam Simone Bifani MENU 213 3

4 Analyses based on 21/211 data samples at 7 TeV» L 21 ~37 pb -1» L 211 ~1 fb -1 Datasets Due to luminosity levelling, same running conditions throughout fills and throughout year EW trigger thresholds unchanged between 21, 211 and 212 Simone Bifani MENU 213 4

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 probe two distinct regions in the (x, Q 2 ) space ATLAS/CMS LHCb CDF/D W&Z HERA Fixed Target LHC 7 TeV Kinematics Can probe the low-x, high-q 2 region inaccessible to other experiments» W and Z (x of 1-4 and 1-1 )» Low-mass Drell-Yan (x down to 1-6 ) Q 2 [GeV 2 ] W&Z γ* γ* y =6 y =4 y =2 y = y =2 y =4 y = x x 1,2 = M p s e ±y Q 2 = M 2 Simone Bifani MENU 213 5

6 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 MENU 213 6

7 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 and W ν, 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 MENU 213 7

8 Z/γ*! LHCb-CONF Preliminary L ~1 fb -1 (211) Single muon trigger: p T > 1 GeV/c 2 reconstructed muons» p T > 2 GeV/c» 2. < η < 4.5» 6 < M < 12 GeV/c 2 Backgrounds» Heavy flavour (Data)» K/π mis-id (Data)» Z ττ (MC) -» tt (MC)» WW (MC) N Candidates = Purity > 99% ) 2 Events / (1 GeV/c LHCb preliminary Data Z/γ* Dimuon invariant mass [GeV/c ] 2 Simone Bifani MENU 213 8

9 Z/γ* ee! LHCb-PAPER arxiv: L ~945 pb -1 (211) 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) N Candidates = 2142 Purity ~ 95% Events / (2 GeV/c 2 ) LHCb e - ) [GeV/c 2 ] Simone Bifani MENU M (e Data Signal Background Mass peak distorted by bremsstrahlung +

10 Z/γ* ττ! LHCb-PAPER arxiv: L ~1 fb -1 (211) Single lepton trigger:» p T,(e) > 1(15) GeV/c 5 final states:, e, e, h, eh» p T,1 > 2 GeV/c, p T,2 > 1 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) Simone Bifani MENU 213 1

11 Z/γ* ττ! LHCb-PAPER arxiv: Events / (5 GeV/c 2 ) 4 Data LHCb Ô s =7TeV Z æ QCD EWK t t æ WW æ Z æ Events / (5 GeV/c 2 ) 8 Data 7 Z æ QCD 6 EWK t t æ e 5 WW æ e LHCb Ô s =7TeV Events / (5 GeV/c 2 ) 4 Data 35 Z æ QCD 3 EWK t t æ e 25 WW æ e LHCb Ô s =7TeV M [GeV/c 2 ] M e [GeV/c 2 ] M e [GeV/c 2 ] N Candidates = 99 Events / (5 GeV/c 2 ) Data Z æ QCD EWK t t æ h WW æ h Z æ LHCb Ô s =7TeV Events / (5 GeV/c 2 ) Data Z æ QCD EWK t t æ eh WW æ eh Z æ ee LHCb Ô s =7TeV Purity ~6-7% M h [GeV/c 2 ] M eh [GeV/c 2 ] Simone Bifani MENU

12 Results Z/γ* ll LHCb-CONF Preliminary Fiducial volume: p T,l > 2 GeV/c, 2. < η l < 4.5, 6 < M ll < 12 GeV/c 2 LHCb Preliminary Z 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 NNLO Measurements limited by statistics (ττ) or luminosity (ee, ) Main systematics: reconstruction (), tracking efficiency (ee), backgrounds and efficiency (ττ) Simone Bifani MENU

13 Results Z/γ* ll LHCb-CONF Preliminary dσ/dy [pb] 7 LHCb preliminary Data (stat) 6 Data Data (tot) (tot) MSTW8 NNLO - MSTW8 (NNLO) 5 ResBos CT1 Powheg (NNLO) + PS 4 NNPDF23 (NNLO) ABM11 (NNLO) Z boson rapidity dσ/dy [pb] 7 LHCb preliminary Graph Data (stat) Data (tot) Z ee Z boson rapidity Good agreement with NNLO Good agreement between and ee final states Good agreement with ATLAS (after adapting to ATLAS cuts) dσ/dy [pb] LHCb 211 preliminary, Z extrapolated LHCb 211, Z ee extrapolated ATLAS 21, Z, Z ee y(z) Simone Bifani MENU

14 Results Z/γ* ll LHCb-CONF Preliminary dσ/dφ* [pb] 3 1 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 1 LHCb preliminary Graph Data (stat) Data (tot) Z ee φ* Simone Bifani MENU

15 W L ~37 pb-1 (21) LHCb-PAPER arxiv: ν! Single muon trigger: pt > 1 GeV/c ν# 1 reconstructed & isolated muon» pt > 2 GeV/c» 2. < η < 4.5» Cone pt (R=.5) < 2 GeV/c W+ + (charged & neutral information) Backgrounds» Z/γ*» W τν and Z ττ» Heavy flavour» K/π punchthrough» K/π decay in flight Simone Bifani R (MC) (MC) (Data) (Data) (Data) R= MENU 213 p

16 W ν! LHCb-PAPER arxiv: Specific cuts implemented to reduce each background component Z/γ*» Veto on 2 nd muon with p T > 2 GeV/c W τν, Z ττ and Heavy flavour» Impact parameter < 4 m K/π punchthrough» E / pc <.4 Largest residual backgrounds» Decays in flight of K/π» Z events with one muon outside the acceptance IP [mm] Simone Bifani MENU Event probability Event probability LHCb LHCb Pseudo-W (Data) W ν (Simulation) bb X (Simulation) cc X (Simulation) Pseudo-W (Data) W ν (Simulation) Hadrons (Data) E / pc

17 W ν LHCb-PAPER arxiv: Fit positive and negative muon p T spectra in data to expected shapes for signal and backgrounds in 5 η bins Events / (1 GeV/c) LHCb + (a) < η < 4.5 p [GeV/c] Data K/π ν Fit Z W ν T - W τν & Z ττ Heavy Flavour Signal and decay in flight templates free to vary; remaining backgrounds fixed N + Candidates = 1466 N - Candidates = Purity + ~ 79% Purity - ~ 78% W and Z muon p T spectrum at NNLO Simone Bifani MENU

18 Results W ν LHCb-PAPER arxiv: Fiducial volume: p T,l > 2 GeV/c, 2. < η l < 4.5 (831 ± 9 stat ± 27 syst ± 29 lumi ) pb (656 ± 8 stat ± 19 syst ± 23 lumi ) pb 1.27 ±.2 stat ±.1 syst Results in general agreement with NNLO predictions Main systematics: background templates, efficiencies (statistical in nature) Simone Bifani MENU

19 l Results W ν LHCb-PAPER LHCb-CONF [pb] dσ W ν/dη 8 LHCb, s = 7 TeV p T > 2 GeV/c + W + ν stat + W + ν tot - - W ν stat - - W ν tot Data Data Data Data MSTW8 ABKM9 JR9 NNPDF21 HERA15 CTEQ6M (NLO) η [pb] dσ/dη LHCb 21, W ν - LHCb 21, W ν + ATLAS 21, W ν - ATLAS 21, W ν extrapolated extrapolated η l Good agreement with NNLO Good agreement with ATLAS (after adapting to ATLAS cuts) Simone Bifani MENU

20 Results W ν LHCb-PAPER LHCb-CONF A LHCb, Datastat Datatot s = 7 TeV MSTW8 ABKM9 JR9 NNPDF21 HERA15 CTEQ6M (NLO) p T > 2 GeV/c η Lepton charge asymmetry l p T LHCb 21, W ν CMS 21, W ν CMS 21, W eν > 25 GeV/c l eta Good agreement with NNLO Good agreement with CMS (after adapting to CMS cuts) Simone Bifani MENU 213 2

21 Z/γ* +jet! LHCb-CONF Preliminary L ~1 fb -1 (211) Same trigger & selection as Z Jet reconstruction» Particle Flow: tracks, calorimeter clusters, Vs» Anti-k t algorithm (R=.5)» Jet ID: veto on isolated particles, require tracks from primary vertex» Jet Energy Correction from MC Jet requirements» p T > 1 GeV/c» 2. < η < 4.5» ΔR(jet, ) >.4 Event Rate [GeV/c] T p LHCb Preliminary s = 7 TeV Data 3 LHCb preliminary s = 7 TeV 2 Inclusive Z Inclusive Z + Jet Reconstructed Z Decay Muons Jet 1 φ M() [GeV] 2 3 η 4 5 Simone Bifani MENU

22 Results Z/γ* +jet! LHCb-CONF Preliminary Number of Candidates LHCb preliminary s = 7 TeV Data Simulation Number of Candidates LHCb preliminary s = 7 TeV Data Simulation p (Jet) [GeV] T η(jet) Simulation well describes the data JEC is validate on data 1 st step for jet measurements at LHCb Event Rate LHCb Preliminary s = 7 TeV Data p 211 Data Simulation T (Jet) / p (Z) T Simone Bifani MENU

23 Results Z/γ* +jet! LHCb-CONF Preliminary + n Jets) σ(z ) σ (Z LHCb preliminary s = 7 TeV ] -1 ) [GeV / σ(z LHCb preliminary s = 7 TeV -2 1 dσ (Z +Jet) d pt (Z ) >2 Jet Multiplicity p (Z T o ) [GeV] Z!+jet Z! Data :.229 ±.6 stat ±.9 syst Theory : PDF ±.12 scale Simone Bifani MENU

24 Summary and Outlook LHCb probes a unique region in η and low p T reach at LHC Z and W production cross-sections measured at 7 TeV in the forward region by using different final states Results consistent with theoretical predictions calculated at NNLO using recent parameterisation of the PDFs Upcoming updates with full 211 and 212 data sets for all analyses Z/γ* +jet paper coming out soon Low mass Drell-Yan: LHCb-CONF Simone Bifani MENU

25 Backup

26 LHCb A Forward Spectrometer Complementary η range to ATLAS & CMS» Overlap for cross check 2. < η < 2.5» Unique to LHCb 2.5 < η < 5. η# in LHCb 17%(16%) of W + (W - ) within LHCb 8% of Z within LHCb Simone Bifani MENU

27 W & Z Production and PDFs Cancel or highlight PDF uncertainties with ratios» A = (dσ W+ - dσ W- ) / (dσ W+ + dσ W- ) tests u V and d V difference A # 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 MENU

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 MENU

29 Z/γ* ll Simone Bifani MENU

30 Z/γ*! Simone Bifani MENU 213 3

31 Z/γ* ee! Simone Bifani MENU

32 Z/γ* ττ! Simone Bifani MENU

33 Z/γ* ττ! Simone Bifani MENU

34 W ν Event probability LHCb Pseudo-W (Data) W ν (Simulation) IP > 8 m (Data) Event probability LHCb Pseudo-W (Data) W ν (Simulation) IP > 8 m (Data) [GeV/c] pcone T [GeV] cone E T Simone Bifani MENU

35 W ν Fit positive and negative muon p T spectra in data to expected shapes for signal and backgrounds in 5 η bins Events / (1 GeV/c) LHCb + - (b) < η < 2.5 p [GeV/c] T Events / (1 GeV/c) LHCb (c) < η < 3. p [GeV/c] T 22 2 LHCb (d) < η < 3.5 p [GeV/c] Events / (1 GeV/c) T Events / (1 GeV/c) LHCb + (e) - Events / (1 GeV/c) LHCb + (f) < η < 4. p [GeV/c] T < η < 4.5 p [GeV/c] W and Z muon p T spectrum at NNLO Simone Bifani MENU T

36 W ν Simone Bifani MENU

37 Z/γ* +jet! Simone Bifani MENU

38 Z/γ* +jet! Jet Efficiency LHCb simulation s = 7 TeV Jet Efficiency LHCb simulation s = 7 TeV.4.2 p p jet T jet T > 5 GeV > 15 GeV <η <5. jet 2.<η <4.5 jet jet η jet p T (GeV) Simone Bifani MENU

39 References Simone Bifani MENU

40 Low Mass DY! LHCb-CONF Preliminary L ~37 pb -1 (21) Dimuon trigger: p T > 2.5 GeV/c 2 reconstructed muons» p > 1 GeV/c» p T > 3(15) GeV/c (M > 4 GeV/c 2 )» 2. < η < 4.5» 5 < M < 12 GeV/c 2 Backgrounds» Heavy flavour (Data)» K/π mis-id (Data)» Υ (MC) Fit muon isolation spectrum in data to expected shapes for signal and backgrounds in 9 M bins isolation = p T /p-jet T Purity varies from ~7% (at low mass) to ~1% Simone Bifani MENU 213 4

41 Results Low Mass DY LHCb-CONF Preliminary )] 2 [pb/(gev/c dσ γ* /dm Theory/Data 2 1 LHCb Preliminary, s = 7 TeV p > 1 GeV/c p > 3 (15) GeV/c T 2. < η < 4.5 Data stat Data tot LO PYTHIA (CTEQ5L) NLO FEWZ (MSTW8) NLO DYNNLO (MSTW8) 2 2 ] 1 Dimuon invariant mass [GeV/c [pb] γ* dσ γ* /dy p p T > 1 GeV/c > 3 GeV/c 1.5 < M < 2 GeV/c 2 LHCb Preliminary, Data stat Data tot s = 7 TeV LO PYTHIA (CTEQ5L) NLO FEWZ (MSTW8) NLO FEWZ (NNPDF2) NLO FEWZ (CTEQ66) Dimuon rapidity Main systematic at low mass comes from the fit PYTHIA predictions agree in shape but too low in normalisation Reasonable agreement with NLO predictions where calculations are available Simone Bifani MENU

42 Low Mass DY! Events Events Events 22 LHCb preliminary 2 21 data < M < 7. GeV/c Drell-Yan Upsilon Heavy Flavour Hadron mis-id 2. < y < Minimum muon isolation.5 1 Minimum muon isolation < M < 15. GeV/c 2 3. < M < 4. GeV/c 2. < y < < y < Minimum muon isolation Events Events Events 2 7. < M < 9. GeV/c 2. < y < Minimum muon isolation < M < 2. GeV/c 2. < y < Minimum muon isolation < M < 6. GeV/c 2. < y < Minimum muon isolation Events Events Events < M < 12.5 GeV/c.5 1 Minimum muon isolation < M < 3. GeV/c 2 6. < M < 12 GeV/c 2. < y < < y < Minimum muon isolation 2. < y < Minimum muon isolation Simone Bifani MENU

43 Low Mass DY! Simone Bifani MENU