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J/ ψ Production at the LHC

J/ ψ Production at the LHC. Giulia Manca (University of Cagliari and INFN , Italy). 7 th Workshop on B Physics Orsay, France 4 th –5 th October 2010. Outline. Motivation Cern and the LHC The experiments J/ y production and results Conclusions and outlook. CERN and the LHC.

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J/ ψ Production at the LHC

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  1. J/ψ Production at the LHC Giulia Manca (University of Cagliari and INFN , Italy) 7th Workshop on B Physics Orsay, France 4th–5th October 2010

  2. Outline • Motivation • Cern and the LHC • The experiments • J/y production and results • Conclusions and outlook Giulia Manca

  3. CERN and the LHC • pp collider : NOW : • @ √s = 7 TeV • L ≈ 1-2·1031 cm-2 s-1 p p NOMINAL (2011) : √s =14 TeV L = 2·1032 cm-2 s-1 (LHCb specific) Giulia Manca

  4. The four LHC Detectors p p Giulia Manca

  5. Rapidity Range Giulia Manca

  6. Luminosity • LHC running well, all experiments have an efficiency ≈90% • Already more than 3 pb-1 on tape • These analyses : L ≈ 9-100 nb-1 Goals : • 1 pb-1 (August 2010) • 100 pb-1 (end of 2010) • 1 fb-1 (end of 2011) ✓ Mar 2010 May 2010 July 2010 Giulia Manca

  7. Motivations • The production mechanism in pp collisions still unclear • Several models around : • Color singlet and color octet mechanisms (NRQCD) describe the pT spectrum and cross section of the J/y as measured by Tevatron, but not the polarization (and has other failures) • Other models such as color evaporation model, kt factorization, soft color interaction model cannot describe the data either • New data from LHC experiments will help to resolve this issue J/y cross section crucial milestone in understanding detector and first step to B cross section measurement Giulia Manca

  8. J/y Production y J Giulia Manca

  9. J/y Production y J Giulia Manca

  10. J/y Production at pp Prompt J/y at LHC LHCb MC samples (unpolarised J/ψ) LO color singlet+color octet Pythia 6.4 √s=7 TeV 10<q<400 mrad √s=10 TeV J.Lee, H.S. Chung hep-ph/0412158 BR(J/ψ)≈6% Giulia Manca

  11. J/y Acceptance CMS LHCb CMS ALICE ATLAS Total Acceptance≈20% ATLAS Acceptance 85% -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 y of J/y LHCb ATLAS Total Acceptance≈13% LHCb Acceptance 85% Total Acceptance≈2-8% ATLAS Acceptance 80% Giulia Manca

  12. J/y→mm mass distribution CMS Data Observed ALICE |y|<1.4 • J/y rate ≈300/nb-1 target: s=70 MeV/c2 (half in ee channel) With high purity muons: s=29 MeV/c2 LHCb 2.5<y<4, pT<10 GeV/c N = 2872 ± 73 σ = 15.0 MeV/c2 s=70 MeV/c2 ATLAS Most recent plots s~13 MeV/c2 Giulia Manca

  13. Inclusive cross section measurements ALICE CMS ATLAS LHCb 2.5<y<4 Giulia Manca

  14. Cross section measurements Giulia Manca

  15. J/y proper time/decay lenght tz=Δz/pz *MJ/ψ • tz used to separate J/y prompt from J/y from B CMS LHCb ATLAS Giulia Manca

  16. Non prompt J/y Giulia Manca

  17. Influence of J/y Polarisation J/y – lab virtual flight direction • Detector acceptance as a function of helicity angle cosq MC with no polarisation:LHCb Example: helicity frame J/y rest frame Both mu <300 mrad • acceptance generates an artificial polarisation large influence of polarisation on measurement • First step: Treat polarisation as systematic error; present results in three different polarisation scenarios Giulia Manca

  18. Different polarisation scenarios CMS CMS LHCb ATLAS Up to 20% Giulia Manca

  19. Integrated cross section measurements * Extrapolating to the LHCb acceptance using Pythia 6.4 Giulia Manca

  20. Conclusions and Outlook • LHC is in great shape and all experiments are taking data with high efficiency • All the analysis tools are in place and start to deliver physics results • J/ψ events clearly reconstructed • Crucial standard candle for detector understanding as well as cross check of luminosity • Cross section measurements probe of non-relativistic QCD theories • Results in four experiments compatible. Publications expected by the end of the year (with 2-5 pb-1). • Polarisation measurement next. Giulia Manca

  21. Back-up Giulia Manca

  22. Inclusive cross section measurements • Extrapolations with PYTHIA 6.4 (LEP hadronization fractions assumed) • ½ production cross section for b or b in LHCb acceptance • Total bb production cross section An independent σ( bb) measurement by LHCb with resultsin excellent agreement. Averaging: LEP b hadronization fractions 88.3±4.5±13.0 TeVatron b hadronization fractions 333±17±49 Giulia Manca

  23. J/y→ee mass distribution Giulia Manca

  24. J/y proper time/decay lenght Data Observed • tz used to separate J/y prompt from J/y from B Giulia Manca

  25. The LHCb detector h=2.5 Muon System • Angular acceptance :10<q<300 mrad RICH Detectors Vertex Locator VELO h=7 p p pp collision Point Tracking System Calorimeters • Performance numbers relevant to quarkonium analyses: • Charged tracks Dp/p = 0.35 % - 0.55%, s(m)=10-25 MeV/c2 • ECAL s(E)/E= 10% (E/GeV)-1/2 1 % • Muon ID: e(mm) = 97%, mis-ID rate (pm) = 1-3 % • Vertexing: proper time resolution 30-50 fs • Trigger: dominantly software possibility to reverse field polarity to check for detector asymmetries Giulia Manca

  26. LHCb Trigger Measure muon trigger efficiencies using trigger lines not involving muons L0 x HLT1 Efficiency J/ψ->mm Giulia Manca

  27. Muon Reconstruction Efficiency Muon system J/ψ used to measure the Muon reconstruction efficiency Tracking system µ tag J/ µ probe ε() = 97.3 ± 1.2 % P of muon (MeV/c) Giulia Manca

  28. Muon mis-identification LHCb 2010 preliminary LHCb 2010 preliminary p→μ dominated by combinatorics in muon stations π→μ dominated by decays in flight π μ misID This plots shows the probability to misidentify a pion from Ks and a proton from Lambda as a muon as a function of momentum. Giulia Manca

  29. Primary Vertex resolution Giulia Manca

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