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Introduction

Status and perspectives in pp and pA -collisions in LHCb for photoproduction and diffractive processes. Patrick Robbe on behalf of LHCb, LAL Orsay, 2 Dec 2013, SaporeGravis Workshop, Nantes (France). Introduction. LHCb Detector

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Introduction

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  1. Status and perspectives in pp and pA-collisions in LHCb for photoproduction and diffractive processes Patrick Robbe on behalf of LHCb, LAL Orsay, 2 Dec 2013, SaporeGravis Workshop, Nantes (France)

  2. Introduction • LHCb Detector • Analysis techniques for Central Exclusive Production at LHCb • J/y and y(2S) cross-sections • cc cross-sections • Future prospects

  3. LHCb Detector JINST 3 (2008) S08005 • Single arm spectrometer • Fullyinstrumented in 2 < h < 5 • Backwardtrack reconstruction in -4 < h < -1.5

  4. LHCb Detector • Vertex Locator: • 42 siliconstrip detectors surrounding interaction region • Detectors upstream of interaction point allowing reconstruction of backwardtracks • Scintillating Pad Detector (SPD): • Scintillator plane parallel to beam axis • Segmentedtransversally in square cells • Providesmeasurement of global trackmultiplicity in events (usedat the hardware trigger)

  5. Diffractive studies at LHCb • Main resultsconcerning Central Exclusive Production (CEP), made possible thanks to: • Detector coverage up to highrapidities (h=5) • Low pile-up: large fraction (21% of luminosity) of eventswith a single interaction used for simplicity • Flexible trigger: • Hardware level: muon detectors and calorimeters • Software level: full event information to performanalysis-likeselections • Excellent particle identification, momentum and vertex resolution • Can detectlowmomentumparticles, and reconstruct hadrons down to almostpT=0.

  6. Central exclusive di-muon • Elasticprocess, protons are intact and fly in the beam-pipe • Exchange of colour-lessobjects (photon, pomeron) Di-photon fusion Di-pomeron fusion g-pomeron fusion LPAIR STARLight SuperCHIC Generators: [A.G. Shamov, V.I. Telnov, NIM A494 (2002) 51] [S.R. Klein and J. Nystrand, PRL 92 (2004) 142003] [L.A. Harland-Lang, V.A. Khoze, M.G. Ryskin, W.J. Stirling, EPJC 65 (2010) 433] • Process signature: isolated muons in acceptance + rapidity gap • 36pb-1 of 2010 data (7 TeV) [JPhysG 40 (2013) 045001] and 930pb-1 of 2011 data (7 TeV) [NEW: LHCb-PAPER-2013-059]

  7. J/y and y(2S) selection • Hardware trigger: • 1 muon withpT>400 MeV, or dimuonwitheachpT>80 MeV • Number of SPD hits < 20 • Software trigger: • Dimuonwith mass > 2.9 GeV, or with mass < 1 GeV and pT < 900 MeV and distance of closestapproach < 150 mm. • Offline: • Twoidentified muons in 2<h<4.5 • No photons, no otherforwardtracks: Dy=3.5 • No backwardtracks: Dy=1.7 • Dimuon mass in 65 MeV mass window of the J/y and y(2S) masses.

  8. Event Display

  9. Backward tracks veto JPhysG 40 (2013) 045001 All events passing trigger Afterbackwardtrack veto

  10. Invariant masses LHCb-PAPER-2013-059 • Fit invariant mass spectra: • Signal: Crystall Ball function, 55985 J/y and 1565 y(2S) • Exponential for combinatorial background • Background contaminationin signal windows: • (0.8±0.1)% for J/y • (17.0±0.3)% for y(2S)

  11. Feed-down • J/yfromy(2S) decays: • Suppressed by the 2 trackrequirement • ResidualestimatedwithSuperCHICgenerator: (2.5±0.2)% of J/y come fromy(2S). • J/yfromccdecays: (gundetected) • Suppressed by the requirement of no photon • ResidualestimatedwithSuperCHICgenerator: (7.6±0.9)% of J/y come fromcc. • y(2S) from X(3872) decays: (gundetected): • Estimated: (2.0±2.0)% LHCb-PAPER-2013-059

  12. Inelastic contamination • Largest background frominelastic production with extra particlesoutside of LHCb • EstimatedusingpT2shapesmeasuredat HERA, to distinguish « exclusive » and « inelastic » components • Feed-down pT2shapestakenfrom data • Combinatorial background shapestaken in mass sidebands.

  13. Inelastic contamination LHCb-PAPER-2013-059 • Purity of sample in exclusivelyproduced: • J/y: (59.2±1.2)% • y(2S): (52±7)%

  14. Systematic Uncertainties LHCb-PAPER-2013-059

  15. Results (J/y and y(2S)) • Cross-section x branching fraction in 2<hm+,m-<4.5: 6.5 LHCb-PAPER-2013-059

  16. Cross-sections (J/y and y(2S)) LHCb-PAPER-2013-059 J/y y(2S) Predictionsfrom Jones, Martin, Ryskin and Teubner [arXiv: 1307.7099]

  17. Cross-sections (J/y and y(2S)) LHCb-PAPER-2013-059 y(2S) J/y Saturation modelsfrom Gay Ducati, Griep, Machado [arXiv: 1305.4611] and Motyka and Watt [PRD78 014023]

  18. Results (J/y ds/dy) • To compare with HERA measurements, the differential cross-section iscalculated in 10 rapiditybins and reweighted by photon flux: • Two solutions for W in eachrapidity bin • Possible deviationfrom power law, whichcanbeexplained by higherordereffects and saturation effects. LHCb-PAPER-2013-059

  19. cc production • Selection: (36pb-1 of 2010 data – 7 TeV) • Dimuon + gwith ET>200 MeV in ECAL, • No extra track: 194 events • Background: • Inelastic: samemethod as J/y • Feed-down fromy(2S) estimatedfromSTARLight • Total purity: (39±13)% • Results LHCb-CONF-2011-022

  20. Future prospects • With di-muon: • More data available for the ccanalysis • Measurements of Y(nS) • 8 TeV data set to beexploited • Hadronic final states to reconstructother hadrons: • open charm, • cc➝hh. • pA/Ap data recorded in 2013 to beanalyzed • 25 ns bunchspacing in 2015 willmeanlower pile-up and higher usable integratedluminosity

  21. Conclusions • J/y, y(2S) and cc central exclusive production measuredat LHCb • Improvedresultswithlargerstatistics are imminent • New ideas for further analyses: active area within LHCb.

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