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Double Parton Scattering measurements at LHCb

Double Parton Scattering measurements at LHCb. Vanya Belyaev ( ITEP/Moscow , Russia) On behalf of LHCb Collaboration. Outline. DPS measurements LHCb detector and data set Double charm analysis and discussion Z 0 + jets analysis Conclusions. LHCb DPS measurements.

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Double Parton Scattering measurements at LHCb

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  1. Double Parton Scattering measurements at LHCb Vanya Belyaev ( ITEP/Moscow, Russia) On behalf of LHCb Collaboration

  2. Outline DPS measurements LHCb detector and data set Double charm analysis and discussion Z0+jets analysis Conclusions Vanya Belyaev, LHCb DPS measurements

  3. LHCb DPS measurements • Observation of J/y pair production in pp collisions at √s=7TeVPhys. Lett. B 707 (2012) 52 • Observation of double charm production involving open charm in ppcollisions at √s=7 TeV JHEP 06 (2012) 141 • Measurement of jet production in Z0/g*→m+m-events at LHCb in √s=7TeVpp collisions LHCb-CONF-2012-016 Not direct DPS measurements, but measurements that are interesting to discuss in context of DPS Vanya Belyaev, LHCb DPS measurements

  4. Double Parton Scattering 287k documents Vanya Belyaev, LHCb DPS measurements

  5. 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, LHCb DPS measurements

  6. How totest DPS ? EJPC 71(2011) 1645 Dedicated talk by Patrick Spradlin Forward production studies at LHCb arXiv:1204.1620 CERN-LHCb-PAPER-2012-041 CERN-LHCb-CONF-2011-015 • For two species A and B one need to measure associative production s(A+B) as well as their inclusive productions s(A), s(B) • DPS contribution follows from identity: • Look for the correlations: pT spectra, Df & Dy correlations, mass spectra, polarization effects, …. ? • Inclusive production is well measured at LHCb for many species J/y Z0 Open charm: D0, D+, Ds, Lc jets and many-many others: y’, Y(nS), W±, cc, cb, B-hadrons, ... Today 26 pairs: 2×J/y (1)J/y+open charm (4) 2×open charm (6+10) Z0+jets (1) Vanya Belyaev, LHCb DPS measurements

  7. LHCb experiment Vanya Belyaev, LHCb DPS measurements

  8. 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, LHCb DPS measurements

  9. VELO 42×2silicon strip planes r-f geometry 40-100 mm pitch 7mm away from the beam Vanya Belyaev, LHCb DPS measurements

  10. 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 resoluton13 MeV/c2 Vanya Belyaev, LHCb DPS measurements

  11. Hadron ID Two RICH detectors Good p/K separation up to ~100 GeV/c Vanya Belyaev, LHCb DPS measurements

  12. Calorimeter system Scintillating Pad Detector/SPD Preshower Detector Electromagnetic Shashlik Calorimeter Hadron Tile Calorimeter Important to trigger hadronic final states Vanya Belyaev, LHCb DPS measurements

  13. Muon system 4(+1) stations MWPC 0.7% p→mmisID Vanya Belyaev, LHCb DPS measurements

  14. LHCb in numbers • Data taking efficiency > 90% • Working channels > 99% • Integrated Luminosity: 2k+10 37pb-1 2k+11 1fb-1 2k+12 >2fb-1 (not a final word yet) • Trigger efficiency : • for dimuon final states ~ 90% • for multihadron final states ~ 30% Vanya Belyaev, LHCb DPS measurements

  15. Inclusive signals • Start from well reconstructed tracks • Utilize powerful particle ID: • muons from J/y, Z0→m+m-decays [MUON] • charged kaons, pions and protons from from open charm [RICH] D0→K-p+, D+→K-p+p+, Ds→K-K+p+, Lc→pK-p+ • Exploit the excellent vertex and momentum resolution: • Good quality common vertex • Narrow mass-peaks Vanya Belyaev, LHCb DPS measurements

  16. Dimuons: J/y and Z0 • Yields @ 7 TeV 1.5×108/fb-1 • Yields @ 7 TeV 5.5×104/fb-1 arXiv:1204.1620 JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements

  17. Open charm signals JHEP 06(2012) 141 N(D0) ≈ 2×108/fb-1 N(D+) ≈1×108/fb-1 N(Ds) ≈ 1×107/fb-1 N(Lc) ≈2×106/fb-1 Vanya Belyaev, LHCb DPS measurements

  18. Event Selection J/yСtwo charm with common vertex 2×Open charm hadrons K- K- m- p+ p+ D0 D0 D0 m+ Vanya Belyaev, LHCb DPS measurements

  19. Make a common vertex and refit signal signal background background JHEP 06(2012) 141 • Global c2/ndf from consistency refit: • Remove pileup, cascade and background Vanya Belyaev, LHCb DPS measurements

  20. Signal extraction 2×J/y : fit one mm-mass in bins of another mm-pair mass • 141±19 events • significance exceed 6s • ~30 years after NA3(fixed target) PLB 114 (1982) 457 PLB 158 (1985) 85 pPt: 13 J/yJ/y pPt: 16±4 J/yJ/y PLB707(2011) 52 Vanya Belyaev, LHCb DPS measurements

  21. Signal extraction J/yD+ J/yD0 J/yLc J/yDs JHEP 06(2012) 141 J/y + open charm clear signals for all four modes Significances > 7s Vanya Belyaev, LHCb DPS measurements

  22. (open charm)2 D0 & open charm D+ & open charm D+Ds D0D0 D0D+ D+D+ D+Lc D0Lc D0Ds For all cases significance > 5s, 2.5 sigma D+Lc+ JHEP 06(2012) 141 JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements

  23. Open charm + open anti-charm D0 & open anti-charm D+ & open anti-charm D+D- D0D- For all cases significance > 8s JHEP 06(2012) 141 JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements

  24. Cross-sections JHEP 06(2012) 141 • Use per-event efficiency, mainly from DATA: trigger, particle ID, background etc. • Major systematic: tracking (reducible) Br(Lc), Br(Ds), …. Vanya Belyaev, LHCb DPS measurements

  25. Cross-sections JHEP 06(2012) 141 Major systematic: tracking (reducible) and Br(Lc), Br(Ds), …. Major systematic: tracking (reducible) and Br(Lc), Br(Ds), …. Vanya Belyaev, LHCb DPS measurements

  26. Cross-sections 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) JHEP 06(2012) 141 Vanya Belyaev, LHCb DPS measurements

  27. Event Properties:pT J/y + open charm: Vanya Belyaev, LHCb DPS measurements

  28. Slope parameter for pT-spectra • Fit pT-spectra with exponential function: ~ exp (b×pT) • DPS: expected similarity between inclusive and • Expected to be similar between J/yC and CC • No reason to be the same for J/yC and inclusive • Expected to be similar between and inclusive Vanya Belyaev, LHCb DPS measurements

  29. Df & Dy correlations No evident correlations Vanya Belyaev, LHCb DPS measurements

  30. Df & Dy correlations Clear correlations! Vanya Belyaev, LHCb DPS measurements

  31. Compare with CDF’2k+6 http://www-cdf.fnal.gov/physics/new/bottom/060921.blessed-double-charm-corr/ CDF: azimuthal correlations for D(0,+) D*- Large gluon splitting contribution Very different kinematical region Vanya Belyaev, LHCb DPS measurements

  32. Mass distributions The same shape for m>7 GeV/c2 Vanya Belyaev, LHCb DPS measurements

  33. Z0&jets • Good test of pQCD • Sensitive to PDF for small x and large Q2 • Poorly constrained by existing measurements … and also possible contribution from DPS Vanya Belyaev, LHCb DPS measurements

  34. Z0&jets • 2k+11 data set: 1fb-1 Jet reconstruction • Particle Flow: tracks, V0, g, p0 and unmatched HCAL clusters • Anti-kT algorithm, R = 0.5 CERN-LHCb-CONF-2012-016 Vanya Belyaev, LHCb DPS measurements

  35. Jet distributions pT> 10 GeV/c clean-up 2<h<4.5 CERN-LHCb-CONF-2012-016 Vanya Belyaev, LHCb DPS measurements

  36. s(Z0+jets)/s(Z0) • Jet multiplicity Fraction on jet events: DATA: 0.229 ±0.06 ±0.09 FEWZ/MSTW08 0.212 ±0.009±0.016 Vanya Belyaev, LHCb DPS measurements

  37. DPS @ LHCb summary • Processes, sensitive to DPS, and their properties have been studied at LHCb with 2k+10 and (part of) 2k+11 data • 2×J/y is in good agreement both with SPS/pQCD and DPS • J/y+Cstrongly disagree with SPS/pQCD, supports DPS dominance (and well consistent with see charm quark contributions) • DPS is only partially supported by (open charm)2: if DPS dominates seff would be factor 2-3 larger • The pattern of pT-distributions is difficult to interpret if only one mechanism dominates • Z0+jetsis nicely consistent with SPS picture Still more data to analyse (including √s=8 TeV) … and more processes to study Vanya Belyaev, LHCb DPS measurements

  38. Thanks to Anatoly Likhoded for inspiring efforts and stimulating discussions Antoni Szczurek for useful discussions on DPS Jean-Philippe Lansberg for the great help with MadOnia MPI@LHC organizers for the invitation and all of you for your kind attention Vanya Belyaev, LHCb DPS measurements

  39. BACK UP Vanya Belyaev, LHCb DPS measurements

  40. 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, LHCb DPS measurements

  41. 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, LHCb DPS measurements

  42. Predictions for LHCb 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) 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 Vanya Belyaev, LHCb DPS measurements

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

  44. 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, LHCb DPS measurements

  45. Comparison with models pQCD ()/MadOnia, DPS, Pythia, IC • pQCD is off by the factor ~20 • Support for (factorization) DPS • excellent agreement for J/yC • factor ~3 off for CC • general support for “uncorrelated” production • Pythia fails to reproduce all the cross-section ratios and spectra. • IC agrees on cross-section, but lack of well-defined predictions on spectra, correlations, … Vanya Belyaev, LHCb DPS measurements

  46. Theory: double charm at LHCb PYTHIA State-of-art pQCD Ff Vanya Belyaev, LHCb DPS measurements

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