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Observation of double charm production at LHCb

Observation of double charm production at LHCb. Vanya Belyaev On behalf of LHCb Collaboration. LHCb-PAPER-2012-003 (in preparation). Outline. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios

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Observation of double charm production at LHCb

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  1. Observation of double charm production at LHCb Vanya Belyaev On behalf of LHCb Collaboration LHCb-PAPER-2012-003(in preparation)

  2. Outline 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  3. Heavy quark production in pp(gg)-collisions LHCis LgC • Open beauty & open charm : • “well known” • The measurements are in a reasonable agreement with state-of-artpQCD calculations • Charmonium& bottomonium: • few open questions and puzzles • Polarization? • Color Singlet/CS vsColor Octet/CO • Recently very good progress with theory NLLO* • Double (charm)onia • Test for COvsCS • 2×J/y is measured by NA3 in 1982 [PLB 114 457,PLB 158, 85] LHCb in 2011 [PLB 707 52] • LHCb measurement is in excellent agreement with pQCD calculations for gg → 2×J/y sLHCb = 5.1 ±1.0± 1.1 nb sgg = 4 nb Vanya Belyaev

  4. How to get 2xCharm? A.Berezhnoyet al., Phys Rev D57 4385 (1998) S.P.Baranov.Phys Rev D73 074021 (2000) J.-P.Lansberg. Eur.Phys.J. C61 693 (2009) • pQCD matrix elements gg → 2×J/y and toJ/y and • Agrees well for 2×J/y • Intrinsic Charm: • Charm from (badly known) charm PDF • Lack of predictive power • Double Parton Scattering • Simple paradigm with raising popularity Vanya Belyaev

  5. Double Parton Scattering 240k documents Vanya Belyaev

  6. DPS: simple paradigm Two independent scattering processes Relations through (unknown) 2PDFs Assume factorization of 2PDFs (Can’t be true for all x,Q2) Easy to make predictions! And the predictions are easy to test Universal (energy and process independent) factor CDF, F.Abeet al., PDR 56 3811 (1997) scatters Vanya Belyaev

  7. 2×Charm as proton probe • Intrinsic Charm Model: • we are testing/constraining (badly known) charm PDFs – typical uncertainties ×2 • Double Parton Scattering • Provide 2PDFs • Measure seff – universal proton property Vanya Belyaev

  8. 2×Charm @ LHCb C = D0, D+, Ds, Lc 2<yJ/y,C<4 3<<12 GeV/c < 12 GeV/c • We want to measure • and CC • As bonus • Dominated by the regular • More information useful from correlations • Gluon splitting , flavour creation, etc. • Similar to CDF’2k+6 • In total 25 possible modes: (1 J/yJ/y) + 4 J/yC + 10 CC 10 Vanya Belyaev

  9. Predictions for LHCb sgg A.Berezhnoyet al., Phys Rev D57 4385 (1998) S.P.Baranov.Phys Rev D73 074021 (2000) J.-P.Lansberg. Eur.Phys.J. C61 693 (2009) sDPS based on LHCb measurements of sJ/y [EPJ C71 1645] sC [LHCb-CONF-2010-013] C.H.Kom, A.Kulesza & J.W.Stirling, Phys.Rev.Lett, 107 082002 (2011) S.P.Baranov, A.M.Snigirev and N.P.Zotov, Phys.Lett. B705 116 (2011) A.Novoselov, arXiv:1105.62076 M.Luszczak, R.Maciula, A.Szczurek, arXiv:1111.3255 S = 0.1mb sIC based on Alekhin’s PDFs S.Alekhin, PRD68 014002 Vanya Belyaev

  10. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  11. How to measure 2×Charm? • Need excellent detector: • Track reconstruction and momentum resolution • Hadron identification • Muon identification • Vertex/lifetime/impact parameter resolution • Efficient trigger for muonsand hadrons • Need high statistics… Natural choice: LHCb at LHC Vanya Belyaev

  12. LHCb: beauty detector General purpose universal detector in forward region pp-collisions 2<h<5 4% of solid angle 40% of heavy quarks Vanya Belyaev

  13. VELO 42×2silicon strip planes r-f geometry 40-100 mm pitch 7mm away from the beam Vanya Belyaev

  14. Tracking system Two silicon stations upstream magnet Dipole magnet 4Tm Three stations downstream magnet Inner: silicon Outer: Straw tubes Momentum resolution: 0.4-0.6% J/y mass resolution 13 MeV/c2 Vanya Belyaev

  15. Hadron ID Two RICH detectors Good p/K separation up to ~100 GeV/c Vanya Belyaev

  16. Calorimeter system Scintillating Pad Detector/SPD Preshower Detector Electromagnetic Shashlik Calorimeter Hadron Tile Calorimeter Important to trigger hadronic final states Vanya Belyaev

  17. Muon system 4(+1) stations MWPC 0.7% p→mmisID Vanya Belyaev

  18. Trigger 10 MHz 1 MHz DAQ records information needed for off-line trigger matching, allowing determination of trigger efficiency directly from data 50 kHz 3kHz L0 hardware • high-pTm, 2m, h, e±,g Software Hlt1 • Reconstruct m, 2m,h • cut on IP, pT, mass Software Hlt2 • Full reconstruction of J/y • Full reconstruction of open charm hadrons Vanya Belyaev

  19. Lumi’2k+11 1.1fb-1recorded at√s=7TeV This analysis: 355 pb-1 Unlike Big Brothers LHCb runs at lower instantaneous luminosity: up to 3.5×1032 Low pileup: 1.4 pp/BX Many thanks to LHC machine team! Vanya Belyaev

  20. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  21. Analysis strategy 2<y<4 3<<12 GeV/c < 12 GeV/c • Determine the model independent cross-sections in LHCbfiducial volume • Reconstruct prompt charm hadrons: J/y→m+m- D0→K-p+, D+→K-p+p+, Ds→ (K+K-)fp+, Lc→ p+K-p+ • Take care about background and keep track on efficiency determination • Use sPlot technique for background subtraction • Use per-event efficiency correction • Extract efficiencies from data (when possible) Vanya Belyaev

  22. Event Selection J/y two muons in common PV vertex Open charm hadrons m- K- p+ D0 m+ Vanya Belyaev

  23. Event Selection J/yСtwo charm with common vertex 2×Open charm hadrons K- K- m- p+ p+ D0 D0 D0 m+ Vanya Belyaev

  24. Charm hadron reconstruction ”3s mantra” - Daughter particles do not point to PV (>3s) - Mother particle does point to PV (<3s) - Mother particle has non-zero lifetime (except J/y) - The decay structure is self-consistent • Start from good quality tracks • Apply positive PID m,K,p,p • Vertex quality cuts • PV & decay consistency • ct cut for open charm hadrons • As similar as possible (a bit tighter for Lc) Vanya Belyaev

  25. Charm hadrons D+→K-p+p+ D0→K-p+ LHCb Preliminary J/y→m+m- 66M 33M Ds→K-K+p+ Lc→p+K-p+ 3.6M 0.6M 50M Vanya Belyaev

  26. 2×Charm • Require both hadrons consistent with the same PV – the only one cut c2fit(C1C2)/ndf < 5 • By construction: 100% efficiency for signal: • c2fit(C1C2) = c2fit(C1)+c2fit(C2) • c2fit(C1)/ndf < 5 & c2fit(C2)/ndf < 5 • Remove particles from different PV (pileup) • Apply trigger matching: J/yC require the event is triggered by J/y CCand : either of open charm hadrons triggers event Vanya Belyaev

  27. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  28. J/yC2D-mass spectra Clear signals! LHCb Preliminary J/yD0 J/yD+ J/yDs J/yLc Vanya Belyaev

  29. D0C2D-mass spectra Clear signals! LHCb Preliminary D0D0 D0D+ D0Ds D0Lc Vanya Belyaev

  30. D+C2D-mass spectra LHCb Preliminary D+D+ D+Ds D+Lc Not enough statistics (yet) for DsDs, DsLc & LcLc Vanya Belyaev

  31. 2D-mass spectra LHCb Preliminary D0D- Vanya Belyaev

  32. 2D-mass spectra Signal Extraction • 2D- unbinned maximum likelihood fit Signal J/y: double-sided Crystal Ball Open Charm: «Bukin» Background: exponential Extensive goodness-of-fit tests Cross-check (binned) fit-in-slices Significance LHCb Preliminary D+D- Vanya Belyaev

  33. Yields & Significances >5s 4 J/yC 6 CC 7 Yield Significance Goodness-of-fit[%] Vanya Belyaev

  34. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  35. Per-event efficiencies: as much as possible from data MC DATA Diff etot = eacc&rec&sel×epid×etrg×e*track eacc&rec&sel = e1acc&rec&sel×e2acc&rec&sel epid = PeK× Pep×Pep [ ×e2m,J/y ] e*track = Pe*track etrg(J/yC) = etrg(J/y) etrg(CC,) = 1 - ( 1 – e1trg ) ( 1 – e2trg) Vanya Belyaev

  36. Efficiencies II • eiacc&rec&sel from (single charm) Monte Carlo Simulation • As function of pT & y for D0, D+, Ds, Lc • As function of pT,y & cosq*for J/y • eK,epand epfrom DATA using L0→p+p-and D*+→(D0→K-p+) p+ • As function of p&hand #Tracks • e2m,J/yfrom DATA, using inclusive J/y peak • As function of J/y pT&y • etrg(J/y) &eitrgfrom DATA using inclusive J/y, D0, D+, Ds+, Lc+ • As function of pT&y • e*track from detailed DATA/MC comparison • As function of track pT&h Vanya Belyaev

  37. Cross-section The price: The inflation of “statistical” error Need good control over efficiency! • Use sWeight/sPlot technique: • Each event i has weightwi from sWeight • Probability event to be signal • This weight is corrected by 1/eTOT Vanya Belyaev

  38. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  39. Systematic uncertainties • Dominant: • hadron track reconstruction uncertainty related to hadron interactions in detector: • 2% per hadron track • For modes with Lc and Ds large uncertainties due to uncertainties in branching fractions • cancelled in ratios • Uncertainties related to signal extraction and efficiency corrections are small (1-3-5%) Vanya Belyaev

  40. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  41. J/yC cross-sections and ratios LHCb Preliminary Using LHCb measurements for sJ/y [EPJ C71, 1645] and sC [LHCb-CONF-2010-013] LHCb Preliminary Vanya Belyaev

  42. CC & cross-sections LHCb Preliminary Vanya Belyaev

  43. Cross-sections & ratios seff from Tevatron gg→ Vanya Belyaev

  44. 2×Charm LHCb Detector & Data sample Event Selection 2×Charm signals Efficiency corrections Systematics Cross-sections & ratios Properties of 2×Charm events Conclusions Vanya Belyaev

  45. Properties of J/yC,CC& events J/yC & CC pQCDsome correlations DPS the production is essentially uncorrelated Gluon splitting, flavour creation flavour excitation, etc… • Background subtracted & efficiency corrected distributions: pT(C1), pT(C2) Df and Dy m(C1,C2) Vanya Belyaev

  46. J/yCpT-spectra Similar to Different from gg→J/y ● J/yD0 ■ J/yD+ ▲ J/yDs ▼ J/yLc ○ gg→J/y ● J/yD0 ■ J/yD+ ▲ J/yDs ▼ J/yLc Dashed colored: single C Vanya Belyaev

  47. CCpT-spectra Spectra are flavour independent ● D0D0 ■ D0D+ ■ D+D+ ▲ D+Ds Vanya Belyaev

  48. pT-spectra Spectra are flavour independent ● ■ D0D- ▲ ▼ ■ D+D- ▲ ▼ Vanya Belyaev

  49. pT-slopes: 3<pT< 12 GeV/c Fit with exponential • “Similar” within each category • C from J/yC is similar to single C • J/y from J/yC is very different from single J/y • CC and are similar and both are very different from single C Vanya Belyaev

  50. J/yCDfand Dy ● J/yD0 ■ J/yD+ ▲ J/yDs ● J/yD0 ■ J/yD+ ▲ J/yDs Support for non-correlated production Vanya Belyaev

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