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PROTON-PROTON PHYSICS WITH ALICE

PROTON-PROTON PHYSICS WITH ALICE . Outline Introduction & ALICE description p-p results Conclusions . Ermanno Vercellin Università and INFN Torino, Italy On behalf of the ALICE collaboration. INTRODUCTION . CERN LHC & experiments. 06/02/2009. L.H.C. 2. ALICE and pp collisions.

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PROTON-PROTON PHYSICS WITH ALICE

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  1. PROTON-PROTON PHYSICS WITH ALICE • Outline • Introduction & ALICE description • p-p results • Conclusions Ermanno Vercellin Università and INFN Torino, Italy On behalf of the ALICE collaboration

  2. INTRODUCTION CERN LHC & experiments 06/02/2009 L.H.C. 2

  3. ALICE and pp collisions • Heavy-ions  main focus [ talk by G. Feofilov] ALICE is a general-purpose heavy-ion experiment designed to measure all the known observables related to the expected QGP formation in a high-multiplicity environment • pp collisons  relevant part of ALICE programme [ this talk] • necessary baseline: to compare with heavy-ion data, e.g. the nuclear modification factor RAA • Intrinsic interest: Global event features,production mechanisms, tuning of MC generators, heavy flavors (N.B. in pp collisions at LHC energies particle multiplicities can be comparable to those of heavy-ion collisions at lower c.m. energies )

  4. ALICE main features • Experiment designed for Heavy Ion collisions at LHC • Very robust tracking • high-granularity detectors with many space points per track, very low material budget (~11% X0 for r < 2.5 m and ||<0.9) and moderate magnetic field (0.5 T) • PID over a very large ptrange • Hadrons (barrel), leptons (barrel + muon spectrometer) and photons (barrel) • Very low pT cutoff (~0.1 GeV/c for pions) • Excellent vertexing (6 layers of Si) for charm & beauty

  5. Size: 16 x 26 meters Weight: 10,000 tons Detectors:18 Russian contribution

  6. (charged particles) ALICE Acceptance • central barrel -0.9 < h < 0.9 • 2 p tracking, PID (ITS, TPC, TRD, TOF) • single arm RICH (HMPID) • single arm em. calo (PHOS) • jet calorimeter • forward muon arm -4.0 < h<-2.5 • absorber, 3 Tm dipole magnet10 tracking + 4 trigger chambers • multiplicity -3.4 < h< 5.1 • including photon counting in PMD • trigger & timingdets • 6 Zero Degree Calorimeters • T0: ring of quartz window PMT's • V0: ring of scint. Paddles µ arm

  7. ALICE Collaboration > 1000 Members from both NP and HEP communities 33 Countries 116 Institutes~ 150MCHF capital cost (+ ‘free’ magnet) History 1990-1996: Design 1992-2002: R&D 2000-2010: Construction 2002-2007: Installation 2008 -> : Commissioning 3 TP addenda along the way: 1996: muon spectrometer 1999: TRD 2006 : EMCAL

  8. ALICE Physics Results for pp Collisions Diffractive processes

  9. ALICE pp results discussed in this talk • Inclusive production • Charged particle multiplicity, dNch/d, dNch/dpt • Identified particle production • Yields and pT spectra: /K/p, 0/, vector mesons, multi-strange • Correlations • HBT correlations • Heavy flavours • Charmonium • Open charm, open beauty

  10. Relative increase in dNch/dh ALICE CMS dNch/dh versus √s dNch/dh versus√s Inelastic Nch ≥ 1 in |h|<1 NonSingleDiffractive all Inelastic fits ~ s0.1 - dNch/dh well described by power law (√s)0.2 • increase with energy significantly stronger in data than MC’s • Alice & CMS agree to within 1 s (< 3%)

  11. Multiplicity distributions ALICE, Eur. Phys. J. C (2010) 68: 345–354 • Multiplicity distributions in pp collisions measured at 0.9, 2.36 and 7 TeV : • Not well reproduced by most of the event-generators (pre-LHC tunes) • Reasonably well reproduced by single negative binomial fits

  12. Charged particles: pt spectra ALICE (0.9 TeV): Phys. Lett. B 693 (2010) 53-68

  13. Charged Particles: Mean ptvs. Multiplicity Phys. Lett. B 693 (2010) 53-68 • Increase of the mean transverse momentum with multiplicity • The effect is predicted (qualitatively) by event generators

  14. Identifiedparticles: , K, p spectra (I) 7 TeV spectra: ALICE Preliminary 900 GeV spectra: Eur. Phys. J C 71 (2011) Different techniques used Minimum pT= 0.1 / 0.2 / 0.3 GeV/c for /K/p (small extrapolation for yields and <pT> calculation) MC models:poor description of data 900 GeV spectra: http://arxiv.org/abs/1101.4110  EPJ C …

  15. Identified particles: 0spectra

  16.  at midrapidity: data-MC comparison Yellow band: data systematics Good agreement with PYTHIA D6T up to 2 GeV/c, good agreement with PHOJET for higher pT

  17. Identified particles: Multi-strange hadrons W-  L0 + K+  p + p- + K+ Antiparticle/particle ratios, measured in wide pT range, are compatible with 1 MC’s (PYTHIA tunes Perugia-0and Z2) underpredict yields, particularly for the 

  18. Bose-Einstein correlations of identical pions • Study space-time characteristics of particle production (homogeneity region) by measuring HBT radii (long, side, out): • vs. pair transverse momentum kT • vs. event multiplicity Nch (high multiplicity pp ≈ peripheral Pb-Pb) • vs. center-of-mass energy √s http://arxiv.org/abs/1101.3665, submitted to Physical Review D

  19. Radii obtained with identical pions At fixed kT: radii at different √s scale with dNch/d; At fixed (high) multiplicity:  radii falling with kT suggests collective behavior/ hydrodynamical phase

  20. Heavy Flavors • Heavy-Flavor production in pp collisions: • A tool to test pQCD calculations • A reference for heavy-ion collisions • Energy loss in a deconfined medium  suppression of high-pt heavy flavors • Studied in ALICE by three different methods: • In the central barrel (|h|<0.8) • Hadronic decays of D mesons • Electrons from semi-electronic decay of H.F. • In the muon spectrometer (2.5 < h< 4.0) • Muons from semi-muonic decay of H.F. • ALICE pp data taking and analysis:

  21. D-mesons (“hadronic charm”) Channels studied • D0 K π (K π π π) • D+ K π π • Ds K K π • D*  D0π • Λc K p π • Selection strategy: • - Displaced vertex (ITS) • (Impact parameter of the tracks, angle between • meson flight line and particle momentum) • - Particle identification (TPC + TOF) • (p/p/K identification)

  22. D meson cross-sections pp collisions, 7 TeV pp collisions, 2.76 TeV  pQCD (FONLL) driven feed-down subtraction for the moment.  data well described by pQCD predictions (FONLL and GM-VFNS) FONLL: Cacciari et al., private comm. GM-VFNS: Kniehl et al., private comm.

  23. HF muons at forward rapidity B + D μ± + X • Muon spectrometer (tracking + trigger), ITS (Vertexing) • Remove hadrons and low pt secondary muons by requiring a muon trigger signal plus a cut on the DCA ✴Subtract decay muons by subtracting MC dN/dpt normalized to data at low pt ✴ pt and pseudo-rapidity distributions well described by pQCD (FONLL) calculations

  24. Quarkonia • J/y studies in ALICE: inclusive production down to pt=0 • In the central barrel : J/ye+e-, |y|<0.9 • In the forward muon spectrometer : J/ym+m- , 2.5<y<4 • Triggers: • minimum bias (MB): -3.7<h<5.1 • muon (m-tri): MB & -4.0<hm<-2.5 • p-p analyses: • at 7 TeV, L=16 nb-1 (m-tri) and 3.9 nb-1(MB) • at 2.76 TeV, L=20 nb-1 (m-tri) 1.1 nb-1(MB); ALICE coll., arXiv:1105.0380v1 (2011)

  25. sJ/yand pt-y distributions ALICE coll., arXiv:1105.0380v1 (2011)

  26. J/yin high multiplicity pp events J/y yield in multiplicity bin (|h|<1.6) over the yield per inelastic pp collision) multiplcity of each bin normalized to the average inelastic pp multiplicity Relative J/y yield vs. relative multiplicity Approximately linear increase of J/y yield with charged particle density.

  27. Conclusions • Rich proton-proton physics programme developed by ALICE (0.9, 2.36, 2.76 and 7 TeVc.m. energies) • Several observables measured, including: • Inclusive production: charged particles up to 100 GeV/c; , K, p, 0, , hyperons, , , resonances up to 5-10 GeV/c • HBT correlations • Heavy flavours: J/ and D-meson cross-sections • Extensive comparison with pQCD and MC models • pp baseline for Pb-Pb studies (√sNN=2.76 TeV) established

  28. Backup slides

  29. Underlying event studies At low pt steep increase of multiplicity - diffractive events are present . At high pt multiplicity saturates  independence of the bulk particle production from the hard scale.

  30. Diffraction dissociation ALICE has 1-arm and 2-arm triggers allowing one to extract Single and Double Diffraction cross-sections Gotsman et al., arXiv:1010.5323, EPJ. C74, 1553 (2011) Kaidalov et al., arXiv:0909.5156, EPJ. C67, 397 (2010) Ostapchenko, arXiv:1010.1869, PR D83 114018 (2011) Khoze et al., EPJ. C60 249 (2009), C71 1617 (2011)

  31. Central Trigger Detectors V0C -3.7 < |h| < -1.7array of 32 scintillator tiles V0A2.8 < |h| < 5.1array of 32 scintillator tiles, < 1ns time resolution SPD Layer 1 |h| < 2.0 Silicon pixel detectors, 3.2M Channels SPD Layer 2 |h| < 1.4 Silicon pixel detectors 6.5 M Channels

  32. ALICE momentum resolution • combined TPC-ITS • momentum resolution: • σ(pT)/pT = 20% at pT = 100 GeV/c L. Ramello for the ALICE Collaboration PLHC 2011 - Perugia, June 6-11, 2011

  33. ALICE P.ID. Performance L. Ramello for the ALICE Collaboration PLHC 2011 - Perugia, June 6-11, 2011

  34. Identifiedparticles: , K, p spectra (II) Modest increase of <pT> with √s  harder spectra Integrated (and pT differential) particle ratios ~ independent of energy between 0.9 and 7 TeV

  35. Identified particles: Vector mesons f results: via m+m- decay in the forward muon spectrometer and via K+K- in the central barrel  (2.5<y<4, 1<pT<5 GeV/c) = 0.940±0.084(stat.)±0.095(syst.) mb

  36. Heavy-flavor electrons B + D  e± + X B (tagging) e± + X Tracking (ITS, TPC), electron ID (TPC, TOF, TRD, EMCal), Vertexing (ITS) ✴ Subtracted cocktail of electron background (measured π0spectrum + mt-scaling + pQCD direct photons.) ✴ Good agreement with FONLL b+c ✴ Consistent with the prompt charm measurement from D mesons ✴ Select electrons from displaced vertexes ✴ B-tagged electron spectrum agrees with FONLL

  37. Charm cross section vs √sNN ✴ Extrapolation down to pt=0 and full rapidity using FONLL ✴Good agreement with ATLAS and LHCb measurements ✴ Measurements show a consistent behavior vs MNR (NLO) with √s

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