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Status of the LHCb experiment and minimum bias physics

Status of the LHCb experiment and minimum bias physics. Sebastian Bachman Heidelberg University on behalf of the LHCb collaboration. 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 10 11 B-Mesons

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Status of the LHCb experiment and minimum bias physics

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  1. Status of the LHCb experiment and minimum bias physics Sebastian Bachman Heidelberg University on behalf of the LHCb collaboration Sebastian Bachmann

  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 1011 B-Mesons ~ 4 x 1012 D-Mesons √s=7TeV 86,5% of delivered luminosity recorded with all detectors in nominal state for data taking. Today ~15nb-1recorded Sebastian Bachmann

  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… Sebastian Bachmann

  4. A first glimpse of beauty Clear excess of J/ψ candidates for large positive proper times B0  D+p- + B+D0p+ Sebastian Bachmann

  5. Wµn candidate Charge = +1 η = 2.65 pT = 39.2 GeV/c Sebastian Bachmann

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

  7. Key ingredients for LHCb p+ 440 µm ( ) Bs0 K+ Ds- K- 144 µm p- 47µm Bs  Ds(K K p ) p • Measure proper time: •  Excellent vertex resolution • Background reduction: •  Robust tracking • + very good mass resolution •  Particle identification • 3. High statistics: •  Efficient trigger for hadronic and leptonic final state Sebastian Bachmann

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

  9. Measure proper time: •  Excellent vertex resolution • 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 Sebastian Bachmann

  10. Tracking performance: • Measure proper time: •  Excellent vertex resolution • Background reduction: •  Robust tracking • + very good mass • resolution •  Particle identification • 3. High statistics: •  Efficient trigger • 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) s = 4.8 MeV/c2 Sebastian Bachmann

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

  12. Measure proper time: •  Excellent vertex resolution • Background reduction: •  Robust tracking • + very good mass • resolution •  Particle identification (RICH) • 3. High statistics: •  Efficient trigger RICH2 RICH1 C4F10 gas n=1.0014 Up to ~70 GeV/c CF4 gas n=1.0005 Beyond ~100 GeV/c Silica Aerogel n=1.03 1-10 GeV/c with RICH without RICH F →KK ? Sebastian Bachmann 12

  13. Measure proper time: •  Excellent vertex resolution • Background reduction: •  Robust tracking • + very good mass • resolution •  Particle identification • 3. High statistics: •  Efficient trigger Photon reconstruction: p0gg s = 7.2 MeVC PID with muon system: Calibration: J/Ψ→μ+μ- (tag & probe): hp+p-g Sebastian Bachmann Physics at LHC, Hamburg 2010 13

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

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

  16. Acceptance@LHCb LHCb covers unique range in rapidity (2-5) and pt (down to 200MeV) Pt[GeV] y Sebastian Bachmann

  17. Prompt Ks production:Analysis idea Measure σKs in bins of pt and y: • NKs(pt, y) and ∫Ldt from data. • εreco(pt, y) and εtrig (pt, y) from MC • + data driven validation Sebastian Bachmann

  18. Event selection: Long vs. downstream tracks Two approaches for event selection: Particles reconstructed in TT and main tracker: Pro: better statistics Con: worse resolution Particles reconstructed in Velo, TT and main tracker: Pro: better resolution Con: less statistics (most Ks decay outside VELO, VELO half open @900GeV) Sebastian Bachmann

  19. Event selection: Long tracks: Downstream tracks: 2009 data, beam-beam LHCb preliminary 2009 data, beam-beam LHCb preliminary DD LL 2009 data, beam-gas LHCb preliminary DD • Take most precise result for • each bin in pt and y • Signal extraction from fit, • sideband subtraction used • for study of systematics • Beam gas interactions reduced • by cuts on vertex region and • statistically subtracted Sebastian Bachmann

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

  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 TIS&TOS • no measurement in bins of (pt, y) due to lack of statistics  use trigger emulation of MC and crosscheck with data in 1D projections. Sebastian Bachmann

  22. Results for prompt Ks production • Statistical error ~10% (dependent on bin) • Main systematic uncertainties: • - luminosity (15%) • - data/MC agreement (10%) • - fit stability (4%) • - stability of selection cuts (4%) • - trigger (2,5%) √s=900Gev Sebastian Bachmann

  23. Predictions for Λ/Λ ratio LHCb LHCb taken from http://home.fnal.gov/~skands/leshouches-plots/ Sebastian Bachmann

  24. Event selection • Event selection similar to Ks 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: Sebastian Bachmann

  25. Invariant mass for Λ and Λ σ = 2.3MeV σ = 2.3MeV Λ Λ σ = 2.6MeV σ = 2.5MeV Λ Λ Sebastian Bachmann

  26. pT and pseudorapidity Sebastian Bachmann

  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 pt-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% Sebastian Bachmann

  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 pt and higher values of y.  Deviations from PYTHIA predictions observed in some kinematic regions: - Ks and Λspectrum 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 )/Ks-ratio - multiplicities of charged particles Sebastian Bachmann

  29. Backup Sebastian Bachmann

  30. Reality check: s and  Ldt in 2010-11 cc bb σ [mb] Pythia 6.4 x 0.57 x 0.44 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 ?) All LHCb simulation studies until recently assumed Ecm=14 TeV & annual event yields of 2 fb-1. How do parameter values of 2010-11 run affect the physics reach? Beam Energy LHCb physics reach is not seriously compromised by de-scoped parameters of 2010-11 run Compare expected cross-section at design energy with 3.5 TeV Luminosity LHCb design luminosity is 2 x 1032 cm-2s-1 – will be in this regime in 2011 ! Lower luminosities of 2010 allows for lower trigger thresholds – see later Sebastian Bachmann

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

  32. A fully reconstructed BJ/ψK+ Sebastian Bachmann

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

  34. OuterTracker Momentum measurement: 24 layer Straws shit~200mm • Measure proper time: •  Excellent vertex resolution • Background reduction: •  Robust tracking • + very good mass • resolution sp/p~0.5% TriggerTracker InnerTracker 4 layers Si: ~200 mm pitch Sebastian Bachmann

  35. Measure proper time: •  Excellent vertex resolution • Background reduction: •  Robust tracking • + very good mass • resolution •  Particle identification (RICH) • 3. High statistics: •  Efficient trigger RICH2 RICH1 C4F10 gas n=1.0014 Up to ~70 GeV/c CF4 gas n=1.0005 Beyond ~100 GeV/c Silica Aerogel n=1.03 1-10 GeV/c Sebastian Bachmann 35

  36. PID with RICH Sebastian Bachmann LHC 2010, Hamburg, Germany LHCb PID - XING 36 Physics at LHC, Hamburg 2010 36

  37. Feynman xF Sebastian Bachmann

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