Status of the LHCb experiment and minimum bias physics

Transcription

1 Status of the LHCb experiment and minimum bias physics Sebastian Bachman Heidelberg University on behalf of the LHCb collaboration 6/19/2010 Sebastian Bachmann 1

2 Beauty and Charm at the LHC LHC is a factory for B- and D-mesons: With 1fb -1 for 2010/2011 run we expect ~ 2.5 x B-Mesons ~ 4 x D-Mesons s=7tev Today ~15nb -1 recorded 86,5% of delivered luminosity recorded with all detectors in nominal state for data taking. 6/19/2010 Sebastian Bachmann 2

3 Where we are Physics reach vs. #minimum bias events light mesons strangeness open charm + J/ψ # of recorded MB events needed to observe 100 events of the process X beauty We are here 6/19/2010 Sebastian Bachmann 3

4 A first glimpse of beauty Clear excess of J/ψ candidates for large positive proper times B 0 D + π - + B + D 0 π + 6/19/2010 Sebastian Bachmann 4

5 W µν candidate Charge = +1 η = 2.65 p T = 39.2 GeV/c 6/19/2010 Sebastian Bachmann 5

6 This conference: this talk M.Charles (this session) J.van Tilburg (tomorrow session) 6/19/2010 Sebastian Bachmann 6

7 Key ingredients for LHCb B s D s (K K π ) π π + ( ) B s 0 D s µm K + K - 47µm L = 7mm 144 µm π - 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification 3. High statistics: Efficient trigger for hadronic and leptonic final state 6/19/2010 Sebastian Bachmann 7

8 LHCb detector Vertex locator (VELO) Tracking system ECAL + HCAL RICH detectors for particle ID Muon system 6/19/2010 Sebastian Bachmann 8

9 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolutio Particle identification 3. High statistics: Efficient trigger Vertex resolution: Vertex locator (VELO): 21 sensors, r phi geometry moved in when beam stable approaches beam at 8mm Vertex resolution in X & Y Vertex resolution in Z 6/19/2010 Sebastian Bachmann 9

10 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification 3. High statistics: Efficient trigger Tracking performance: Tracking system magnet with Bdl = 4Tm tracking station made of Si sensors before magnet 3 tracking stations behind magnet with Si sensors (inner region) and straw tube detectors (outer region) σ = 4.8 MeV/c 2 6/19/2010 Sebastian Bachmann 10

11 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification 3. High statistics: Efficient trigger Tracking efficiency: Strategy: Determine ε from MC Use data for validation 1. Select K s from long track + VeloCalo track 2. Check if tracks are found in tracking stations 3. Determine efficiency from # tracks ε = # tracks (VELO + IT/OT+CALO) (VELO + CALO) Limitations of method: VELO tracking eff. is not probed Restrictive phase-space, i.e. K S decay products phase space 6/19/2010 Sebastian Bachmann 11

12 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification (RICH) 3. High statistics: Efficient trigger θ C (mrad) e μ π K p Aerogel θ C max 242 mrad Silica Aerogel n= GeV/c RICH1 C 4 F 10 gas n= Up to ~70 GeV/c RICH2 CF 4 gas n= Beyond ~100 GeV/c 50 0 π C 4 F 10 gas CF 4 gas Momentum (GeV/c) K 53 mrad 32 mrad without RICH with RICH Φ KK? 6/19/2010 Sebastian Bachmann 12

13 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification 3. High statistics: Efficient trigger Photon reconstruction: π 0 γγ σ = 7.2 MeVC PID with muon system: Calibration: J/Ψ μ + μ - (tag & probe): η π + π γ 6/19/2010 Sebastian Bachmann 13 Physics at LHC, Hamburg

14 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification 3. High statistics: Efficient trigger 2010 run: o reduced luminosity allows to use lower cuts improved efficiencies o good opportunity for charm physics. o special micro-bias trigger. 40 MHz 1 MHz 30 khz 2 khz L0 e, γ ECAL Alley L0 had Had. Alley L0 μ Muon Alley Global reconstruction Inclusive selections: topological, μ, μ+track, μμ, D X, Φ Exclusive selections Storage: Event size 40kB Level-0 High-pt signals in calorimeter & muon Systems. HLT1 Confirm L0 signals by matching L0 candidates to tracks. HLT2 Full detector information available. HLT2 does full reconstruction and loose selection of B- and D-candidates. 6/19/2010 Sebastian Bachmann 14

15 Minimum bias physics First - Production measurements, e.g. strange, charm, bottom. - Multiplicities of charged particles - Particle/Antiparticle asymmetries This talk: Strangeness production, i.e. - K s s=900gev (2009 data) - Measurement of Λ/Λ ratio at s=900 GeV and s=7 TeV (2010 data) Motivation: o Strange quarks are no valence quarks excellent test field for fragmentation models o Particle/Antiparticle ratios help to understand 1. which partons are carriers of the baryon number, 2. the baryon number flow in inelastic hadronic collisions. 6/19/2010 Sebastian Bachmann 15

16 LHCb covers unique range in rapidity (2-5) and p t (down to 200MeV) P t [GeV] 6/19/2010 Sebastian Bachmann 16 y

17 6/19/2010 Sebastian Bachmann 17 Prompt K s production: Analysis idea y p y p y p Ldt y p N dy dp y p d t t reco t trig t K t t K s s Δ Δ = ), ( ), ( ), ( ), ( 2 ε ε σ Measure σ K s in bins of p t and y: on K s (pt, y) and Ldt from data. o ε reco (pt, y) and ε trig (pt, y) from MC + data driven validation

18 Event selection: Long vs. downstream tracks Two approaches for event selection: Particles reconstructed in Velo, TT and main tracker: Pro: better resolution Con: less statistics (most K s decay outside VELO, VELO half Particles reconstructed in TT and main tracker: Pro: better statistics Con: worse resolution 6/19/2010 Sebastian Bachmann 18

19 Event selection: Downstream tracks: 2009 data, beam-beam LHCb preliminary DD Long tracks: 2009 data, beam-beam LHCb preliminary LL 2009 data, beam-gas LHCb preliminary DD DD LL Mass resolution ~ 9.3 ~ 4.0 (MeV/c 2 ) Total yield in beam-beam 4864 ± ± 36 Total yield in beam-gas 56 ± ± 6 o Take most precise result for each bin in p t and y o Signal extraction from fit, sideband subtraction used for study of systematics o Beam gas interactions reduced by cuts on vertex region and statistically subtracted 6/19/2010 Sebastian Bachmann 19

20 Luminosity is given by: Luminosity measurement N n i n i i= π σ x, i σ y, (some refinement needed, e.g. crossing angle due to LHCb dipole magnet, differences in transverse size, beams not head-on on ) L = Idea: 1. Get beam currents from machine measurements (BCT). 2. Use Velo to measure beam size, positions and angles in beam-gas. f i Measured luminosity in data sample: L int (2009) = 6.8 ± 1.0 μb 1 Dominant systematic uncertainities: Currents: 12% Width: 5% Positions: 3% Angles: 1% 6/19/2010 Sebastian Bachmann 20

21 Trigger efficiency Trigger efficiency measured on data Use two uncorrelated classes of events: - trigger on Signal (TOS) - trigger independent of signal (TIS) TOS TIS&TOS TIS ε TOS trig ( p t, y) = N TIS N N TIS TOS ε TIS trig ( p t, y) = N TIS N N TOS TOS no measurement in bins of (p t, y) due to lack of statistics use trigger emulation of MC and crosscheck with data in 1D projections. 6/19/2010 Sebastian Bachmann 21

22 Results for prompt K s production s=900gev o Statistical error ~10% (dependent on bin) o Main systematic uncertainties: - luminosity (15%) - data/mc agreement (10%) - fit stability (4%) - stability of selection cuts (4%) - trigger (2,5%) 6/19/2010 Sebastian Bachmann 22

23 Predictions for Λ/Λ ratio LHCb LHCb taken from 6/19/2010 Sebastian Bachmann 23

24 Event selection Event selection similar to K s analysis, but using only long tracks. Armenteros-Podolansky variable used for selection of Λ and Λ. No PID used. Pointing of Λ s to primary vertex required. Data for both magnet polarities analysed seperately consistent results Selected events: 0.9 TeV field up data 0.9 TeV field down data 7 TeV field up data Λ Λ TeV field down data 6/19/2010 Sebastian Bachmann 24

25 Invariant mass for Λ and Λ σ = 2.3MeV σ = 2.3MeV Λ Λ σ = 2.5MeV σ = 2.6MeV Λ Λ 6/19/2010 Sebastian Bachmann 25

26 p T and pseudorapidity 6/19/2010 Sebastian Bachmann 26

27 Efficiency corrected ratios for prompt Λ s Numbers corrected for non-prompt Λ s coming from Ξ s. No correction for diffraction Perugia tunes do not include diffraction, LHCb tune includes diffraction. Plots include both statistical and systematic error. Field up and down results were averaged. Systematic uncertainties: Re-weighting of p t -distributions to match data (2%) difference in proton/anti-proton cross section ~10% below 10GeV, reproduced by MC (effect reduced by kinematic selection) contribution to systematic error 2% 6/19/2010 Sebastian Bachmann 27

28 Conclusion LHCb had an excellent start into the LHC era By and by the landscape of the SM re-appears: Many signals from strange, charm and bottom, as well as W-production seen by LHCb. LHCb is able to extend measurements on minimum bias physics to lower p t and higher values of y. Deviations from PYTHIA predictions observed in some kinematic regions: -K s and Λ spectrum tend to be harder than predicted -prompt Λ/Λ ratio tends to be lower at s=900gev, fair agreement at s=7tev valuable input for tuning of MC s Other results on minimum bias physics expected soon: - p/anti-p ratio - meson/baryon ratios, i.e. a measurement of the (Λ + Λ )/K s -ratio - multiplicities of charged particles 6/19/2010 Sebastian Bachmann 28

29 Backup 6/19/2010 Sebastian Bachmann 29

30 Reality check: s and Ldt in All LHCb simulation studies until recently assumed E cm =14 TeV & annual event yields of 2 fb 1. How do parameter values of run affect the physics reach? Beam Energy LHCb physics reach is not seriously compromised Compare expected cross section by at de scoped design energy parameters with 3.5 of TeV run σ [mb] bb x 0.44 cc x 0.57 Pythia 6.4 Small penalty in statistical precision (but all MC predictions shown today assume, for historical reasons, bb cross section of 500 μb at 14 TeV conservative?) Luminosity LHCb design luminosity is 2 x cm 2 s 1 will be in this regime in 2011! Lower luminosities of 2010 allows for lower trigger thresholds see later 6/19/2010 Sebastian Bachmann 30

31 LHCb Operation Instantaneous Luminosity Optimization scans Integrated Luminosity VELO powering/closure Cumulative Run Inefficiency 6/19/2010 Physics Sebastian at LHC, Bachmann Hamburg

32 A fully reconstructed B J/ B J/ψK + 6/19/2010 Sebastian Bachmann 32

33 B J/ J/ψK + : Zoom into vertex region y vertical [mm] N.B.: All observables far from cut values defined before data- taking Tracksfromprimaryvertex (PV), refittedthrough PV Primaryvertex B + m + B decayvertex K + J/ψ m - x horizontal [mm] 6/19/2010 Sebastian Bachmann 33

34 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Momentum measurement: s p /p~0.5% Outer Tracker 24 layer Straws s hit ~200mm Trigger Tracker Inner Tracker 4 layers Si: ~200 mm pitch 6/19/2010 Sebastian Bachmann 34

35 1. Measure proper time: Excellent vertex resolution 2. Background reduction: Robust tracking + very good mass resolution Particle identification (RICH) 3. High statistics: Efficient trigger Silica Aerogel n= GeV/c RICH1 C 4 F 10 gas n= Up to ~70 GeV/c RICH2 CF 4 gas n= Beyond ~100 GeV/c θ C (mrad) e μ π K π p Aerogel C 4 F 10 gas CF 4 gas Momentum (GeV/c) K θ C max 242 mrad 53 mrad 32 mrad 6/19/2010 Sebastian Bachmann 35

36 PID with RICH 6/19/2010 Sebastian Bachmann 36 LHC 2010, Hamburg, Physics Germany at LHC, LHCb Hamburg PID XING

37 Feynman x F 6/19/2010 Sebastian Bachmann 37