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First Results from the LHCb Experiment

Antonio Pellegrino on behalf of the LHCb Collaboration, HESI 2010, Kyoto, 12-08-2010. First Results from the LHCb Experiment. Outline: introduction (our goal) LHCb mission and key measurements first data (where we are, LHC start-up) LHCb performance first results

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First Results from the LHCb Experiment

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  1. Antonio Pellegrino on behalf of the LHCb Collaboration, HESI 2010, Kyoto, 12-08-2010 First Results from the LHCb Experiment Outline: • introduction (our goal) • LHCb mission and key measurements • first data (where we are, LHC start-up) • LHCb performance • first results • prospects for future measurements (where we are going)

  2. LHCb Mission • The LHCb mission is to search for New Physics (NP) • Mainly search of possible corrections to the Standard Model (SM) picture of flavor • Actually a hugely successful part of the electroweak (EW) sector of the SM! • 2008 Nobel prize to Kobayashi and Maskawa! • LHCb key measurements described in detail in arXiv:0912.4179v2 [hep-ex] • typical LHCbphysicists “expert” of standard electro-weak model • QCD mainly perceived as a “theoretical” uncertainty to overcome to get to the new physics!?

  3. LHCb Key Measurements • CKM angle  • improve tree-level determination • compare with virtual-loop-level determination • CP violation in Bs decays • Rare decay B0s  µµ • Lorentz structure • Scattering angular distribution B0  K0 µµ • Time evolution of B0s   new particles contributions (strength, phase, Lorentz structure) to loop diagrams in Flavor-Changing Neutral Currents (FCNC)

  4. Potentia et Actus • LHCb key measurements require ~1,00010,000 pb-1 LHC still “ramping up” • ~0.1 pb-1 per fill (~15 hours) • expect O(103 pb-1) by 2011 Last update: August 9 Integrated lumi (nb-1) Days since Jan 1st 2010 • not yet results on key measurements • 2011 “annus mirabilis” for B0s  µµ and B0s  J/yf

  5. First results I will focus on: • First results on particle production • J/ cross section(s) • (pp  bbX) cross sections • extrapolation from inclusive J/ • extrapolation from b  D0X • open-charm cross sections • Ks cross section • /, p/p, /Ks production ratios _ _ • first fully reconstructed B decays and prospects for 2010-2011 • CP violation studies with charm (D+K+K-+) • CP violation in Bs  J/  • rare decay B0s  µµ • angular distribution B0  K0 µµ

  6. The LHCb Detector LHCb is a forward spectrometer b-hadrons predominantly produced in the forward cone

  7. Where it is

  8. The LHCb Cavern Proton beam Shielding wall(against radiation)‏ Cavern ~100m below surface Electronics + CPU farm Detectors can be moved away from beam-line for access Offset interaction point (to make best use of existing cavern)‏ Proton beam

  9. B-Physics Experiment in a nutshell 1. vertex resolution • identify B and D hadrons • resolve fast oscillations 2. momentum resolution • separate topologicallysimilar final states ~1 cm Btag K- 4. muon, electron and photon ID • for various other interesting final states • to tag B flavor 5. highly selective trigger • to reduce rate to acceptable level • based on muons, electrons, high pT hadrons, large IP tracks 3. K/ separation • separate topologicallysimilar final states • tag B flavor Example: Bs Ds K Antonio Pellegrino

  10. LHCb Detector (Overview) VELO: Vertex Locator (around IP) ; TT, T1, T2, T3: Tracking stations RICH 1-2: Ring Imaging Cherenkov (PID) ; M1–M5: Muon stations ECAL, HCAL: Calorimeters Dipole magnet VELO proton beam proton beam collision point ~1 cm Crucial for B physics: – polyvalent trigger (incl. hadrons) – excellent particle ID – excellent tracking/vertexing (m, ) B Antonio Pellegrino

  11. Detector Performance Intermezzo follow a few slides on sub-components of the LHCb detector • main focus will be on performance • main message will be • things work largely as expected • even if we may not always have the “ultimate” performance • no limitation for any measurement

  12. LHCb Detector Slide Show (1) • contains the pp-collision point • precise determination of primary and secondary vertices (B lifetime) 21 silicon -strip stations • r-φ geometry • pitch= 40-100 μm ~1 cm B Antonio Pellegrino

  13. X resolution Y resolution Vertexing • excellent hit resolution • cluster finding efficiency 99.7% • module and sensor alignment better than 5 m • VELO is opened during injection ! • Fill-to-fill variation of alignment < 5 m ~20m IP resolution at high pT expected to improve with better material description pp vertex resolution e.g. with 25 tracks ~15m in X,Y and ~90m in Z

  14. LHCb Detector Slide Show (2) • charged particle momentum determination • TT before magnet, Inner and Outer Tracker after magnet Antonio Pellegrino

  15. LHCb Preliminary LHCb Preliminary LHCb Preliminary Residual (mm) Residual (mm) Tracking IT TT OT Hit resolutions close to expected • IT : 54 m • TT : 55 m • OT : 250 m expected to improve with better alignment

  16. Invariant Mass Resolution At present already good mass resolution (will be improved) D0→ K (data) = 9 MeV (MC) = 7 MeV Ks→  (data) = 3.3 MeV (MC) = 2.6 MeV L~100 nb-1 J/ →  (data) = 16 MeV (MC) = 12 MeV  →  (data) = 52 MeV

  17. LHCb Detector Slide Show (3) • Particle IDentification; kaon-pion separation Antonio Pellegrino

  18. Particle Identification LHCb Data (Preliminary) Kaon Ring 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 lnL(K-)>0 RICH2 RICH1 p/K/p separation in 2–100 GeV/c range • two gaseous and one aerogel radiator

  19. LHCb Detector Slide Show (4) • muon tracking • trigger (at 40MHz) Antonio Pellegrino

  20. Muon system Muon Identification J/ Tracking system µ tag (2S) J/ µ probe High -ID efficiency • P() = (2.350.04)% [Ks] • P(p) = (0.210.05)% [p] • P(K) = (1.670.06)% [KK]

  21. LHCb Detector Slide Show (5) • particle identification; electron, photon, hadron • trigger (at 40MHz) Antonio Pellegrino

  22. The LHCb Trigger 40 MHz LHC clock [CPU farm] [hardware] ~30 MHz crossings L0 trigger max. 1 MHz L0 trigger max. 2 kHz ~10 MHz visible inelastic in LHCb LHCb has a trigger system “dedicated” to B Physics • “efficiently” select decays with various final states (, e, , K, , …) • triggering is a challenge • ~1/100 events with bb • B decays of interest branching fractions ~10-3 (or lower) _ Meeting this challenge is one of the main objectives of LHCb operation!

  23. Present Trigger Strategy For bulk of running foreseen this year, with luminosities up to ~1030 cm-2 s-1, we can relax many of our trigger cuts 2010 approach Apply very low pt cuts – main purpose of L0 is now to seed HLT1 regions of interest Reduce requirements on track impact parameter w.r.t. nominal settings Not needed at all initially, then introduce with rather loose suppression requirements Boost trigger efficiencies for hadronic decays of promptly produced D’s  Golden opportunity for charm physics studies! Total efficiencies for hadronic B decays ~70% and for leptonic decay modes >90%.

  24. Trigger Performance The LHCb trigger concept works! • full trigger operational • efficiencies as expected • at low lumi, running with relaxed thresholds and quickly adapting to conditions more challenging than nominal nominal running conditions trig = [NMC(J/) triggered] / [NMC(J/) reconstructed]

  25. Day 1 at s = 7 TeV pp collision at 3.5+3.5 TeV, March 30, 2010 Event display, top view

  26. LHCb Operation LHCb operation proceeds very reliably and efficiently • ~92% data taking efficiency Integrated lumi (nb-1) Days since Jan 1st 2010

  27. First results I will focus on: • First results on particle production • J/ cross section(s) • (pp  bbX) cross sections • extrapolation from inclusive J/ • extrapolation from b  D0X • open-charm cross sections • Ks cross section • /, p/p, /Ks production ratios _ _ • first fully reconstructed B decays and prospects for 2010-2011 • CP violation studies with charm (D+K+K-+) • CP violation in Bs  J/  • rare decay B0s  µµ • angular distribution B0  K0 µµ

  28. J/ Production • intrinsically interesting (J/ production mechanisms) • b  J/ X of crucial importance in the LHCb core program Measurement strategy: BR(J/ µ+µ-) = (5.930.06)% • measured J/’s through their J/ µ+µ- decay mode • N(J/) = N(J/ µ+µ-) / BR(J/ µ+µ-) • separate contribution from b-decays from the “prompt” one (directly in a pp collision or from decay of heavier (2S), c,etc.) • use pseudo proper time • measured total cross section and d/dpT • present measurement coverage (limited by statistics) • yJ/ψ (2.5,4.0) and pTJ/ψ< 10 GeV

  29. J/ Selection • Trigger • L0 : MUON with pT > 0.48GeV • HLT : (pT)single-µ>1.3GeV M(µ+µ-)>2700MeV/c2 • Offline • 2 µ’s with good vertex • pT > 0.7 GeV • select events through µ+µ- invariant-mass window • N(J/ µ+µ-) = 287273 Fit to data/background yielded: • S/B = 1.3 • Mean = (3088 ± 0.4) MeV/c2 • σ = (15.0 ± 0.4) MeV/c2

  30. Separate b-Decays Contribution µ+ tz = [z / pz(J/)] M(J/) Pseudo-proper time PV displacement of the di-µ vertex along the beam line z z µ- • Prompt J/’s zero pseudo-proper time • J/’s from b-decays  exponentially decaying tz distribution • due to the lifetime of the parent B-hadrons maximum-likelihood fit to the (unbinned) tz distribution  J/’s from b-decays

  31. J/’s from b Decays max.-likelihood fit to tz • N(prompt) = 252774 • N(from b decays) = 31624 fJ/(from b) = (11.10.8)%

  32. Acceptance and Efficiency to complete cross section extraction  = ACCEPTANCE  TRIGGER  RECONSTRUCTION [NMC(J/) with both µ’s in LHCb] / [NMC(J/) generated] [NMC(J/) triggered] / [NMC(J/) reconstructed] [NMC(J/) reconstructed] / [NMC(J/) in acceptance] Limited by statistics In the analysis phase space : TOT  4070%

  33. J/ Cross Section(s) • For yJ/ψ  (2.5,4) and pTJ/ψ < 10 GeV/c • σ(J/ inclusive) = (7.65 ± 0.19 ± 1.10 ) μb • σ(J/ from b decays) = (0.81 ± 0.06 ± 0.13) μb +0.87 -1.27 • For yJ/ψ  (2.5,4) • dσ/dpT(J/ inclusive) Dominant systematic errors • trig. and tracking eff. (~9%) • luminosity meas. (~10%) However, measurement still dominated by statistics • now increasing ~0.1pb-1 / fill • bin in y and extend pT range • full angular analysis

  34. Prospects for J/ Cross Section(s) Measurement still dominated by statistics • now increasing ~0.1pb-1 / fill • bin in y and extend pT range • e.g with ~50pb-1, 5 bins in y and 10 in pT up to 12 GeV/c with ~10% accuracy • extend analysis to (2S) effects of J/ spin configuration not discussed here • with increasing statistics, angular analysis  polarization

  35. Extrapolation to bb Cross Section _ • if one extrapolates • (J/ from b decays)  (Hb X) any b- or b-hadron in LHCb acceptance 2<<6 For Hb(2,6), ½ (pp  Hb X) = (84.5  6.3  15.6) b Extrapolation with PYTHIA 6.4 • assume LEP b-hadrons production fractions • with further extrapolation to full angular acceptance _ (pp  bbX) = (319  24  59) b • compare with extrapolation from B  D0  X …

  36. First results I will focus on: • First results on particle production • J/ cross section(s) • (pp  bbX) cross sections • extrapolation from inclusive J/ • extrapolation from b  D0X • open-charm cross sections • Ks cross section • /, p/p, /Ks production ratios _ _ • first fully reconstructed B decays and prospects for 2010-2011 • CP violation studies with charm (D+K+K-+) • CP violation in Bs  J/  • rare decay B0s  µµ • angular distribution B0  K0 µµ

  37. Extrapolation to bb Cross Section From PDG • b in B/B0/Bs0/b-baryon admixture  D0 l+l X • BR = 6.82%  0.35% • (production fractions from Heavy Flavor Averaging Group) _ _ Measurement strategy • measure right-sign D0 - pair originating at a common vertex different from the pp interaction vertex _ • separate D0’s from b-decays from “prompt” ones (directly in a pp collision or from decay of heavier states) • use impact parameter of D0’s wrt pp vertex • … extrapolation to (pp  bbX) from to B  D0  X …

  38. D0 Selection Measured D0’s through their K- + decay mode • N(D0) = N(D0  K- +) / BR(D0  K- +) • BR(D0  K- +) = (3.91  0.05)% Reject background and mass combinations • require minimum pT • pT and pKT > 0.3 GeV • K- and + from same vertex • K-,+ vertex not the same as pp ~3 nb-1

  39. D0‘s from b-Decays If D0 comes from a b-decay, then K-+ has a large impact parameter (IP) with respect to the pp vertex Use IP to separate D0‘s from a b-decay from “prompt” ones (produced in pp collision directly or from decay of heavier states) K- D0 PV Prompt + b IP ~3 nb-1 X From b-decay

  40. D0 from b-Decays • require  in final state • require common D0 vertex • require right sign combination D0- and D0+ • combine M(K) window with large IP(D0) requirement • yield from unbinned log-likelihood fit simultaneously to M(K) and ln(IP) _ 0.1 pb-1 0.1 pb-1 Right Sign Wrong Sign from B 0.1 pb-1 0.1 pb-1 1540 ± 45 events with D0 from b-decay prompt

  41. Extrapolation to bb Cross Section cross section defined as efficiency (acceptance, trigger, reconstruction) d/d in 4 bins of pseudo-rapidity in the LHCb acceptance 2<<6 •  = -ln(/2), with  determined from the pp and D0 vertices • dominating systematic uncertainties from luminosity and tracking • extrapolate to (pp  Hb X) (PYTHIA 6.4, LEP b-hadrons production fractions) Total in 2<<6 : ½(ppHb X) = (74.95.312.8) b Further extrapolation to full : ½(ppHb X) = (2822048) b From J/ incl. : (3192459) b Theory MCFM : 332 b Theory NFMR : 254 b

  42. First results I will focus on: • First results on particle production • J/ cross section(s) • (pp  bbX) cross sections • extrapolation from inclusive J/ • extrapolation from b  D0X • open-charm cross sections • Ks cross section • /, p/p, /Ks production ratios _ _ • first fully reconstructed B decays and prospects for 2010-2011 • CP violation studies with charm (D+K+K-+) • CP violation in Bs  J/  • rare decay B0s  µµ • angular distribution B0  K0 µµ

  43. Open Charm • forward D-meson production intrinsically interesting • mixing and CP violation (e.g. lifetime difference between D0KK and D0K) • rare decays D0+- • necessary step for the understanding of B-meson decays measurements of D*, D0, D, Ds production cross sections ongoing Prompt From secondary • impact parameter key tool to separate “prompt” D,Ds production Ds L~124 nb-1 D+ L~2 nb-1 (D+)/(Ds) = 2.32 ± 0.27 ± 0.26 PDG 2008: f(cD+)/f(cDs) = 3.08±0.70 Huge yield of D0KK with O(100 pb-1)

  44. First results I will focus on: • First results on particle production • J/ cross section(s) • (pp  bbX) cross sections • extrapolation from inclusive J/ • extrapolation from b  D0X • open-charm cross sections • Ks cross section • /, p/p, /Ks production ratios • first fully reconstructed B decays and prospects for 2010-2011 • CP violation studies with charm (D+K+K-+) • CP violation in Bs  J/  • rare decay B0s  µµ • angular distribution B0  K0 µµ

  45. B-meson Decays analysis of fully reconstructed B-decays advancing by the day • integrated luminosity growing “exponentially” • event yields in line with MC expectations • good mass resolution Nsignal= 36.6  5.5  = (36.56.3) MeV L~230 nb-1 First signal in charmed B decays combining: • B0D+p- and B+D0p+ BK Nsignal = 22.9±5.3 = 12.0±2.5 MeV Nsignal= 9.5  1.4  = (33.78.6) MeV L~13 nb-1 L~230 nb-1 B  D BsKK Expect soon Bs Ds- and Cabibbo-suppressed BDK

  46. B+  J/ K+ Event Display Y (mm) • M(J/ψK) = 5326.7±10.9 MeV/c2 • p(J/ψK) = 62.7 GeV/c • pT (J/ψK) = 10.48 GeV/c • L = 2.03 mm • cos() = 0.9999 X (mm)

  47. B  J/ K Analysis analysis of BJ/K+ and BJ/K*0 rapidly advancing • good momentum resolution • proper-time resolution not yet final, but good enough to extract signal • unbinned log-likelihood fit to (M,t | t) • event yields in line with MC expectations L~230 nb-1 L~230 nb-1 t>0.3 ps t>0.3 ps BJ/K*0 BJ/K+

  48. First results I will focus on: • First results on particle production • J/ cross section(s) • (pp  bbX) cross sections • extrapolation from inclusive J/ • extrapolation from b  D0X • open-charm cross sections • Ks cross section • /, p/p, /Ks production ratios _ _ • first fully reconstructed B decays and prospects for 2010-2011 • CP violation studies with charm (D+K+K-+) • CP violation in Bs  J/  • rare decay B0s  µµ • angular distribution B0  K0 µµ

  49. Bs  J/  Event Display First reconstructed Bs  J/  decays: • M(μμ) = 3072 MeV/c2 • M(KK) = 1020 MeV/c2 • M(μμKK) = 5343 MeV/c2 • 2vtx / nDOF = 0.8 • t/σ(t) = 78 (L = 20 mm!) • cos() = 0.9999998 L~230 nb-1 main lines of analysis analogous to BJ/K t>0.3 ps in line with expected yield

  50. Prospects for Bs  J/  BsJ/  one of the key measurements that will be pursued in 2010/2011 sJ/ψ= -2S is very small and precisely predicted in the standard model • Very sensitive to NP !!! Based on the fact that: • ~50k events / fb-1 consistent with number of BsJ/seen in data • proper-time resolution <st> = 0.038 ps • at present is ~1.6 worse in data • Tagging performance eD2 = 6.2% • to be tested with more data 2010/2011 run promises exciting results on the sJ/ measurement!!

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