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ALICE – Highlights di fisica e prospettive 2012 e oltre

ALICE – Highlights di fisica e prospettive 2012 e oltre. Present : first precision results in PbPb collisions at the LHC “Next” future: p- Pb ( Pb -p) 2012  cold nuclear matter First shutdown (2013-2014)LHC towards design energy

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ALICE – Highlights di fisica e prospettive 2012 e oltre

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  1. ALICE – Highlights di fisica eprospettive 2012 e oltre • Present: first precision results in PbPbcollisions at the LHC • “Next” future: p-Pb (Pb-p) 2012  cold nuclear matter • First shutdown (2013-2014)LHC towards design energy • “Intermediate” future (2015-2017)  Pb-Pb (other systems ?) at • sNN for nuclear collisions > 4 TeV (5.5 TeV design energy) • Integrated luminosity  x102 b-1 • Second shutdown (2018)  detector upgrades installation • 2019 onwards  Pb-Pb at 50 kHz collision rate, • ALICE goal Lint ~10 nb-1 E. Scomparin (INFN Torino) Meeting referees – 9 maggio 2012

  2. Papers from 2010 runs • Scientific production in terms of published papers very good • pp collisions: 14 published papers + 4 on arXiv • PbPb collisions: 8 published papers + 3 on arXiv • …plus 11 ready and circulating in the Collaboration • …plus many more in preparation • Strong participation of Italian groups in the analysis/publication • process : at least 1 Italian physicist in the Paper Committee for • ~50% of the papers • Let’s now focus on PbPb collisions and review the main results…

  3. Focus on Pb-Pb • Results from 2010 PbPb data for all the observables: • Global event features (energy density) • Collective expansion (flow) • Strangeness and chemical composition (chemical freeze-out) • Parton energy loss in the medium • Light flavours • Heavy flavours • Quarkonia dissociation/regeneration (deconfinement) • in the medium • Main advantage of ALICE with respect to other LHC experiments: • Excellent tracking in a very high multiplicity environment • Particle identification over a large range of transverse momenta • (down to very low pTthanks to the low material budget) Important also for upgrade-related considerations

  4. Charged multiplicity – Energy density PRL106 (2011) 032301 PRL105 (2010) 252301 • dNch/d = 1584  76 • (dNch/d)/(Npart/2) = 8.3  0.4 • ≈ 2.1 x central AuAuat √sNN=0.2 TeV • ≈ 1.9 x pp (NSD) at √s=2.36 TeV • Stronger rise with √s in AA w.r.t. pp • Stronger rise with √s in AA w.r.t. log extrapolation from lower energies • Very similar centrality dependence at LHC & RHIC, after scaling RHIC results (x 2.1) to the multiplicity of central collisions at the LHC

  5. System size • Spatial extent of the particle emitting source extracted from interferometry of identical bosons • Two-particle momentum correlations in 3 orthogonal directions -> HBT radii (Rlong, Rside, Rout) • Size: twice w.r.t. RHIC • Lifetime: 40% higher w.r.t. RHIC ALICE: PLB696 (2011) 328 ALICE: PLB696 (2011) 328

  6. Identified hadrons and radial flow Centrality STAR pp √s=200 GeV Blast-wave fit parameters • Common blast-wave fit to , K and p • Strong radial flow: b≈0.66 for most central collisions, 10% higher than at RHIC • Freeze-out temperature below 100 MeV • Combined analysis (ITS, TPC and TOF) • Significant change in mean pT between √sNN=200 GeV and 2.76 TeV harder spectra • For the same dN/dhhigher mean pT than at RHIC

  7. Hadrochemistry • Relative abundances of hadron species can be described by statistical distributions (Tch, B) A.Andronic et al., Nucl.Phys.A772(2006) • Description still not satisfactory • at LHC energy • Low Tch suggested by p spectra, but • excluded by  and  • If p excluded, Tch =164 MeV •  Tch (LHC) ~ Tch(RHIC) ~ Tc J.Cleymans et al., Phys.Rev.C73(2006)034905

  8. Elliptic flow • v2 (LHC) ~ 1.3 v2 (RHIC) (pTintegrated) • Increase consistent with increased radial expansion (higher pT) • System at LHC energy still behaves as a near-perfect fluid, not gas!

  9. Identified particle v2 • Elliptic flow mass dependence due to large radial flow • Magnitude and mass splitting predicted by viscous hydro • in all centrality bins • Observation of v2 scaling with the number of constituent quarks • not as good as at RHIC

  10. Charged hadron RAA Related to parton energy loss, in the BDMPS approach • RAA(pT) for charged particles : larger suppression wrt RHIC • Suppression increases with increasing centrality • Minimum for pT~ 6-7 GeV/c in all centrality classes • RAAincreases in the region pT>10 GeV/c • Hint of flattening above 30 GeV/c • Model comparison

  11. Identified particle RAA • Mesons vs baryons: different RAA at intermediate pT • Related to baryon enhancement (coalescence), • observed e.g. in /K ratio • At high pT(>8-10 GeV/c)RAA universality for light-flavour hadrons • For hadrons containing heavy quarks, smaller suppression expected: • dead cone effect, gluon radiation • suppressed for <mq/Eq

  12. Open charm in ALICE • Analysis strategy • Invariant mass analysis of fully reconstructed decay topologies displaced from the primary vertex • Feed down from B (10-15 % after cuts) subtracted using FONLL • Plus in PbPb hypothesis on RAA of D from B K p arXiv:1203.2160

  13. D-meson RAA • pp reference from measured D0, D+ and D* pT differential cross-sections at 7 TeV scaled to 2.76 TeV with FONLL arXiv:1203.2160 • Suppression of prompt D mesons in central (0-20%) PbPb collisions by a factor 3-4 for pT>5 GeV/c • Little shadowing at high pT suppression comes from hot matter • Similar suppression for D mesons and pions • Maybe a hint of RAAD > RAAπ at low pT

  14. J/ suppression peripheral central • Inclusive J/y RAA • pp reference from pp data set at 2.76 TeV • Contribution from B feed-down not subtracted (very small effect) • J/y are suppressed with respect to pp collisions • J/y RAAalmost independent of centrality arXiv:1202.1383

  15. J/: comparison with RHIC arXiv:1202.1383 ALICE, LHC, forward rapidity PHENIX, RHIC, mid-rapidity PHENIX, RHIC, forward rapidity • Less suppression than at RHIC at forward rapidity: • RAA(ALICE) > RAA(PHENIX, 1.2<y<2.2) • Similar suppression as at RHIC at midrapidity (not for central!) • RAA(ALICE) ≈ RAA(PHENIX, |y|<0.35) • Caveat:cold nuclear matter effects different at RHIC and LHC needs pPb running

  16. e.m. dissociation • Measure e.m. dissociation cross section in Pb-Pb via neutron • emission at very forward angles (ZDC) 1n 2n 3n … in good agreement with model predictions (RELDIS) arXiv:1203.2436

  17. Event background fluctuationsand jet reconstruction • Low-ptcomponent of jets important for the measurement • of medium modifications (jet quenching) • Not accessible to ATLAS/CMS • Region to region background • fluctuations  main source of jet • momentum uncertainty, affect jet • structure observables JHEP 03(2012) 053 • For a pT=0.15 GeV/ccut-off •  fluct=10.98  0.01 GeV/c • (R=0.4, 0-10% central PbPb) • fluctdecreases to 4.82 GeV for • pT,min = 2 GeV/c • (reduced region to region fluctuations) • Asymmetric shape of fluctuations • have a large impact on the • jet yield up to 100 GeV/c

  18. A pp new result: J/ polarization • ALICE focusses on pp results mainly as reference for PbPb • On hard probes usually no competition with other LHC • experiments due to smaller luminosity in ALICE • Some notable exceptions, too  J/ polarization • (first LHC results on this issue, arXiv:1111.1630) • Important measurement to discriminate among the different • theoretical models of J/ production • Long-standing puzzle with CDF results • J/ polarization measured via anisotropies in the angular • distributionsof J/ decay products • (polarization parameters    ) >0  transverse polarization, <0  longitudinal polarization

  19. J/ polarization results ALICE Coll., arXiv:1111.1630, accepted by PRL M.Butenschoen, A.Kniehl, arXiv:1201.3862 • First result: almost no polarization for the J/ • First theoretical calculation (NLO NRQCD) compared to data: • promising result, reasonable agreement with theory

  20. Data analysis in 2012: 2011 Pb-Pb data • 2011 Pb-Pb data very successful • Smooth running, much higher luminosity  >10 times more • statistics (centrality and rare triggers) compared to 2010 • New, exciting results expected soon! A couple of performance plots Triggering on EMCAL Total 2011 statistics  40000 J/

  21. Data analysis in 2012: first 2011 Pb-Pbresults soon • Analysis is progressing fast: first results from 2011 Pb-Pb run • will be released at the end of May (Hard Probes 2012, Cagliari) Confidential: still to be released! Confidential: still to be released! • Examples: new results on differential RAA and elliptic flow for J/ • Another example: D0 and D+ elliptic flow

  22. Analysis prospects for 2012-2013 • Analysis effort on 2011 PbPb data will continue during 2012 • and (at least) half 2013 (complete analysis, submit papers) • We are also expecting very important results from 2012 pPb run • essential to distinguish hot/cold nuclear matter effects on • QGP-related observables • essential to evaluate initial state effects (partonshadowing), • very poorly known at LHC energy (only extrapolations by now) • An example from RHIC: • back-to-back angular • correlations • Only by looking at d-Au • the observed effect can be • ascribed to final state • effects

  23. Analysis efforts after 2013 (before upgrade) • Data analysis for p-Pb/Pb-p collisions (plus more involved • analysis on Pb2011 data) expected to last at least to the • end of 2014 • 2015: physics in the new high-energy range • Precise running conditions still not known: for Pb-Pb running • a higher luminosity and c.m.s. energies > 4 TeVper nucleon pair • are expected • Physics prospects for ALICE • pp physics topics accessible to the experiment • Pb-Pb collision studies very relevant for QGP physics • (excitation functions) • In addition: larger luminosity higher pTreach • Examples • J/ physics: final determination of regeneration vs screening • Heavy flavor correlations, jet tagging

  24. Upgrade planning • Strong detector/physics efforts in view of the LHC upgrade • Upgrade experiment to be able to run with 50 kHz Pb-Pb • collision rates, several nb-1 per run (2 MHz proton-proton) • Various new detectors being proposed • (stregthen ALICE uniqueness at LHC) • ITS: B/D separation, heavy baryons, • low-mass dielectrons • MFT: b-tagging for low pt J/psi and • low-mass di-muons at forward y • VHMPID: New high momentum PID • capabilities • FOCAL: Low-x physics with identified g/p0 • ITS upgrade presented to LHCC (March 20) • Technical details on detector developments to be discussed in • other presentations  shortly review physics aspects, • in particular on hard and electromagnetic probes

  25. ITS upgrade • Current problems to be overcome • charmdifficult for pt0 (background is too large); • resolution not sufficient for charmed baryons • (Lcct=1/2 D0=1/5 D+); • physics results on Lcimpossible in Pb-Pbcollisions (only hints of a signal), difficult in pp (only high pt) • Lbimpossible in Pb-Pb collisions (insufficient statistics and resolution) • B/D separation difficult, especially at low pt (e PID + vertexing)

  26. ITS upgrade • D-meson detection: factor 5 improvement in S/B • Assuming ~ 109 central events Significance >100 in all pt bins • c-baryon detection • Assuming ~ 1.7 x 1010 central • events (10 nb-1) in 0-20% •  Significance: • 7 for 2<pt<4 GeV/c • >50 for 6<pt<8 GeV/c

  27. ITS upgrade Estimate of statistical uncertainties for RAADfromb/RAADfromc Estimate of statistical uncertainties for /D0 ratio, 0-20%

  28. MUON upgrade - MFT • Low-mass dileptonphysics • practically still untouched at • LHC energy • Excellent thermometer of the • medium (see NA60, PHENIX, STAR) • Modification of  spectral function • Thermal dileptons  mass resolution: very strong improvement Bck rejection

  29. HMPID upgrade - VHMPID • PID in jets, for p, , K • in 5<pT<25 GeV/c • Identify strange particle • and baryon components • in jet fragmentation •  strongly affected by • the medium! PID performance at pT= 20 GeV/c

  30. Conclusions • After an already excellent start in 2010, with plenty of pp results, • focus in 2011 on the analysis of the first Pb-Pb run • First complete set of results at the LHC available • Medium with >3 times higher energy density than at RHIC • Soft observables • Smooth evolution of global event characteristics from RHIC to • LHC energies  better constraints for existing models • Hard probes: novelties, surprises, challenges for theory • Strong suppression of high pT hadrons (factor 7 at pT=7 GeV/c) • Light and heavy quarks RAAsimilar • J/ is less suppressed than at lower energies • 2012-2014: fully “booked” by the analysis of 2011 (Pb-Pb) and • 2012 (pPb) runs • 2015-2017: high-energy “campaign”, more physics ahead • 2019-202x: physics with upgraded ALICE set-up (pp, PbPb, ArAr)

  31. Backup

  32. 2010 data taking: detector configuration • ITS, TPC, TOF, HMPID, MUON, V0, To, FMD, PMD, ZDC (100%) • TRD (7/18) • EMCAL (4/10) • PHOS (3/5) • HLT (60%)

  33. Identified particle spectra Open symbols: ppbar Close symbols: pp

  34. More on strangeness Inverse slope increases with mass s do not follow this trend (limited statistics?) <pT> has almost no increase over a factor 36 in √s (ISRLHC)

  35. Still on HBT radii Increase with multiplicity both in p-p and A-A, but different features

  36. Analysis strategy • Require muon trigger signal to remove hadrons and low pt secondary muons • Remove residual decay muons by subtracting MC dN/dpt normalized to data at low pt • Alternative method: use muon distance-of-closest-approach to primary vertex • What is left are muons from charm and beauty • Apply efficiency corrections 36

  37. D meson reconstruction Analysis strategy: invariant-mass analysis of fully-reconstructed topologies originating from displaced vertices Build pairs/triplets/quadruplets of tracks with correct combination of charge signs and large impact parameters Particle identification from TPC and TOF to reject background (at low pt) Calculate the vertex (DCA point) of the decay tracks Require good pointing of reconstructed D momentum to the primary vertex • D0 K-π+ • D+ K-π+π+ • D*+ D0π+ • D0 K-π+π+π- • Ds K-K+π+ • Λc +  pK-π+ 37

  38. D0 K-p+ Signals from 108 events 7 pt bins in the range 1<pt<12 GeV/c Selection based mainly on cosine of pointing angle and product of track impact parameters (d0Kd0p) 38

  39. PID (ITS, TPC, TOF)

  40. MonteCarlo scoreboard

  41. Centrality vs models

  42. High pTelliptic flow Due to path length dependence of parton energy loss

  43. RAA – comparison with models

  44. Introduction • ALICE (A Large Heavy-Ion Collision Experiment): the dedicated heavy-ion experiment at the LHC • Main focus on Pb-Pb collisions  QGPstudies From the problem…. …to the solution • p-p collisionsstudied too (luminosity limited to a few 1030 cm-2s-1) • Reference for heavy-ion collision studies • Genuine p-p physics

  45. Size: 16 x 26 meters Weight: 10,000 tons Detectors:18

  46. ALICE: specific features • ALICE peculiarities among the LHC experiments • Focus on PID investigate chemical composition of the hot matter • Push acceptance down to pT=0 (low material budget, low B) •  many QGP-related features become more evident at low pT • Sustain very high hadronic multiplicities (up to dNch/d~8103)

  47. PID performance: selected plots ITS Silicon Drift/Strip dE/dx TPC dE/dx Ω ΛΚ TOF

  48. Analyzed data samples 2010 2011 • Triggers • MB: based on VZERO • (A and C) and SPD • SINGLE MUON: forward muon in coincidence with MB trigger

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