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ALICE physics

ALICE physics. Guy Pai ć Instituto de Ciencias Nucleares UNAM Mexico. The aim. The energy density reached in heavy ion collisions at LHC is large according to the predictions of QCD theory of strong interactions, nuclear matter will go through a QGP (Quark Gluon Plasma) phase

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ALICE physics

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  1. ALICE physics Guy Paić Instituto de Ciencias Nucleares UNAM Mexico

  2. The aim • The energy density reached in heavy ion collisions at LHC is large • according to the predictions of QCD theory of strong interactions, nuclear matter will go through a QGP (Quark Gluon Plasma) phase • state of deconfined partons (in a large volume). • the question at LHC is not actually to put in evidence the QGP but rather to study its properties and hadronisation. Guy Paic LISHEP- ALICE physics

  3. The aim cont’d • observe phenomena that are very difficult to explain from a hadronic perspective but have a simple qualitative explanation based on quarks and gluons. • make quantitative predictions for the emission of various kinds of “hard” radiation from the quark gluon plasma. Guy Paic LISHEP- ALICE physics

  4. QCD potential: • in dense and hot matter • screening of color charges • potential vanishes for large distance scales • deconfinement of quarks ! • in vacuum • linear increase with distance • strong attractive force • quark confinement • in hadrons • baryons (qqq) and • mesons (qq) QCD phase transition Guy Paic LISHEP- ALICE physics

  5. Dynamics of a collision After S. Bass • before the collision – coherent field configuration the clouds of gluons and quarks represented by the QCD approximation of A x structure functions of nucleons • The QCD fields persist after the nuclear valence quark pancakes collide – the interaction lasts for ~ 30 fm/c =10-22 s • Hadronization! The fields hadronize in a way that is not well understood • The dense final state debris further interact as it expands Guy Paic LISHEP- ALICE physics

  6. Change of perspective • SPS - evidence for collective phenomena in Nucleus- nucleus collisions • many interesting signals telltale of phase transition • not much hard processes • Dynamics of a collision • first inkling of new processes (hard) at RHIC more to be seen at LHC • dominance of minijets • dominance of gluon-gluon interactions • importance of parton shadowing • parton saturation phenomena • high initial temperatures • jet quenching Guy Paic LISHEP- ALICE physics

  7. Two main classes • Soft physics – low pt (<3 GeV/c) • Hard probes Guy Paic LISHEP- ALICE physics

  8. p L p K f e jet m g QGP Au Au Time evolution time g e  Expansion  distance Guy Paic LISHEP- ALICE physics

  9. Soft physics Guy Paic LISHEP- ALICE physics

  10. 1 Soft Physics in Pb-Pb and pp Event characterization Centrality selection Global observables Chemical composition Hadronisation mechanisms Bulk properties: soft hadrons + interplay hard–soft Identified particle spectra (wide pT range) Expansion dynamics Space-time structure Radial, anisotropic flow Momentum correlations Event by event physics Fluctuations Guy Paic LISHEP- ALICE physics

  11. Pseudorapidity distributions at ALICE and Atlas Guy Paic LISHEP- ALICE physics

  12. 3 Global event characterization in Pb-Pb Centrality determination brec(fm) sb ~ 1fm Event by event determination of the centrality Zero degree hadronic calorimeters (ZDC) + electromagnetic calorimeters (ZEM) EZDC , EZEM Nspec Npart impact parameter (b) bgen (fm) Correlations between ZDC and ZEM EZDC (TeV) Events reconstructed generated sNpart ~15 Guy Paic LISHEP- ALICE physics Npart EZEM (GeV) Npart

  13. Global event properties in Pb-Pb 4 Generated Tracklets Multiplicity distribution (dNch/dh) in Pb-Pb Energy density Silicon Pixel Detector (SPD) : -1.6 < h < +1.6 + Forward Multiplicity Detector (FMD): h -5, +3.5 (dN/dh)|h|<0.5 dN/dh % centrality (Npart) Fraction of particles produced in hard processes Generated Tracklets (dN/dh)|h|<0.5 1 central Hijing event Guy Paic LISHEP- ALICE physics Npart

  14. Identified particle spectra in Pb-Pb and pp 5 Excitation functions of bulk observables for identified hadrons New regime at LHC: strong influence of hard processes Chemical composition Equilibrium vs non equilibrium stat. models ? Jet propagation vs thermalization ? Interplay between hard and soft processes at intermediate pT Rcp: central over peripheral yields/<Nbin> Baryon/meson ratio Elliptic flow RHIC Parton recombination + fragmentation ? or soft (hydro -> flow) + quenching ? or … ? Production mechanisms for different hadron species also in pp Guy Paic LISHEP- ALICE physics

  15. Identified particle spectra 6 Particle reconstruction and identification capabilities: unique to ALICE Global tracking (ITS-TPC-TRD) + dE/dx (low pT + relativ. rise), TOF, HMPID, PHOS, … Invariant mass, topological reconstruction Acceptance / efficiency / reconstruction rate (e) / contamination pT range (PID or stat. limits) for 107 central Pb-Pb and 109 min. bias pp For ~ 20 particle species for -1 < y < +1 and -4 < y < +2.5 p, K, p: 0.1- 0.15 50 GeV Weak or strong decaying particles: until 10-15 GeV Mid-rapidity p PID in the relativistic rise K p Pb-Pb Pb-Pb Guy Paic LISHEP- ALICE physics pT (GeV/c)

  16. Topological identification of strange particles 7 Statistical limit : pT ~11 - 13 GeV for K+, K-, K0s, L, 7 - 10 GeV for X, W Secondary vertex and cascade finding pT dependent cuts -> optimize efficiency over the whole pT range Pb-Pb central L 300 Hijing events Reconst. rates: X: 0.1/event W: 0.01/event pT: 1 7-10 GeV 13 recons. L/event 11-12 GeV About the same pT limit for 109 pp Identification of K+, K- via their kink topology K mn 6x104 pp collisions X pp collisions Guy Paic LISHEP- ALICE physics Limit of combined PID

  17. Resonances (r, f, K*, …) 8 Time difference between chemical and kinetic freeze-out In medium modifications of mass, width, comparison between hadronic and leptonic channels partial chiral symmetry restoration Invariant mass reconstruction, background subtracted (like-sign method) mass resolutions ~ 1.5 - 3 MeV and pT stat. limits from 8 (r) to 15 GeV (f,K*) r0(770)p+p- 106central Pb-Pb K*(892)0 K p 15000 central Pb-Pb Mass resolution ~ 2-3 MeV Invariant mass (GeV/c2) Generated & reconstructed f for 107 central Pb-Pb Mass resolution ~ 1.2 MeV f (1020) K+K- Guy Paic LISHEP- ALICE physics

  18. Anisotropic Flow 9 y x py px Hydro limit (full local thermalization) at RHIC ? More likely at LHC ? V2, V4, ... Relation between V2 and higher harmonics (V4, V6, …) to test perfect liquid % viscous fluid At LHC: more sensitivity to the QGP Flow of identified hadrons -> partonic d’s of freedom ? RHIC Initial conditions CGC + hydro (until T ~ 170 MeV) i.e., contribution of the QGP + hadronic cascade At LHC, contribution from QGP much larger than at RHIC Guy Paic LISHEP- ALICE physics

  19. Hard Probes

  20. The yields of hard probes give rather direct information about the initial state of the collision PDFs the environment they have to traverse on there way out(QGP). Rescattering Energy loss Color screening A, pA and pp necessary and compulsory to be able to interpret the results Open flavor Heavy quarks produced copiously at LHC 120 ccbar et 5 bbbar per central Pb-Pb, event produced at (~1/2 mQ ~0.1 fm/c compared to τQGP ~10 fm/c) Should test: pQCD Test the medium thru energy loss of partons (jet quenching) test the color screening of quarkonia. Guy Paic LISHEP- ALICE physics

  21. gluon radiation Parton energy loss • High energy partons, resulting from a initial hard scattering, will create a high energy collimated spray of particles → jets • Partons traveling through a dense colour medium are expected to lose energy via medium induced gluon radiation, “jet quenching”, and the magnitude of the energy loss depends on the gluon density of the medium • Total jet energy is conserved, but “quenching” changes the jet structure and fragmentation function Measurement of the parton fragmentation products reveals information about the QCD medium Guy Paic LISHEP- ALICE physics

  22. |y| < 0.5 4 108 central PbPb collisions/month 6 105 events Jet rates at LHC Copious production: Several jets per central PbPb collisions for ET > 20 GeV However, for measuring the jet fragmentation function close to z = 1, >104 jets are needed. In addition you want to bin, i.e. perform studies relative to reaction plane to map out L dependence. Guy Paic LISHEP- ALICE physics

  23. gluon radiation nucl-ex/0406012 PRL91, 072304 (2003) ● PHENIX (π0) 1/NtriggerdN/d() x5 Results from RHIC Evidence for partonic energy loss in heavy ion collisions High-pT suppression in central AuAu collisions High-pT hadrons of recoiling jet suppressed in AuAu but not in dAu Guy Paic LISHEP- ALICE physics

  24. Eskola et al., hep-ph/0406319 Full jet reconstruction Leading Particle Leading particle becomes fragile as a probe • Surface emission: • Small sensitivity of RAA to medium properties. • For increasing in medium path length L, the momentum of the leading particle is less and less correlated with the original parton 4-momentum. Reconstructed Jet Ideally, the analysis of reconstructed jets will allow us to measure the original parton 4-momentum and the jet structure. → Study the properties of the medium through modifications of the jet structure: • Decrease of particles with high z, increase of particles with low z • Broadening of the momentum distribution perpendicular to jet axis Guy Paic LISHEP- ALICE physics

  25. 100 Jet rates at the LHC 20 100 200 2 pt (GeV) 100K/year 100/event 1/event • Huge jet statistics from ET ~10 GeV to ET~100 GeV • Jets with ET > 50 GeV will allow full reconstruction of hadronic jets, even in the underlying heavy-ion environment. • Multijet production per event extends to ~ 20 GeV Guy Paic LISHEP- ALICE physics

  26. C. Loizides 50 GeV jet 100 GeV 50 – 100 GeV jets in Pb–Pb At large enough jet energy – jet clearly visible But still large fluctuation in underlying energy η–φ lego plot with Δη 0.08 Δφ 0.25 Central Pb–Pb event (HIJING simulation) with 100 GeV di-jet (PYTHIA simulation) Guy Paic LISHEP- ALICE physics

  27. D mesons quenching reduced Ratio D/hadrons (or D/p0) enhanced and sensitive to medium properties Heavy Quarks – dead cone • Heavy quarks with momenta < 20–30 GeV/cv << c • Gluon radiation is suppressed at angles < mQ/EQ “dead-cone” effect • Due to destructive interference • Contributes to the harder fragmentation of heavy quarks • Yu.L.Dokshitzer and D.E.Kharzeev: dead cone implies lower energy loss Q Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [arXiv:hep-ph/0106202]. Guy Paic LISHEP- ALICE physics

  28. Detection strategy for D0 K-p+ • Weak decay with mean proper length ct = 124 mm • Impact Parameter (distance of closest approach of a track to the primary vertex) of the decay products d0 ~ 100 mm • STRATEGY: invariant mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices • Measurement of Impact Parameters • Measurement of Momenta • Particle identification to tag the two decay products Guy Paic LISHEP- ALICE physics

  29. Hadroniccharm Combine ALICE tracking + secondary vertex finding capabilities (sd0~60mm@1GeV/c pT) + large acceptance PID to detect processes as D0K-+ ~1 in acceptance / central event ~0.001/central event accepted after rec. and all cuts Results for 107 PbPb ev. (~ 1/2 a run) significance vs pT S/B+S ~ 37 S/B+S ~ 8 for 1<pT<2 GeV/c (~12 if K ID required) Guy Paic LISHEP- ALICE physics

  30. Low pt (< 6–7 GeV/c) Nuclear shadowing + kt broadening + ? thermal charm ? ‘High’ pt (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) Sensitivity on RAA for D0 mesons A.Dainese nucl-ex/0311004 Guy Paic LISHEP- ALICE physics

  31. vacuum 1 0.8 medium 0.6 0.4 R Et = 50 GeV 0.2 0 r(R) 1 0.8 0.6 0.4 Et = 100 GeV 0.2 0 0 0.8 0.2 0.4 0.6 1 R=√(Dh2+Df2) Jet quenching • Excellent jet reconstruction… but challenging to measure medium modification of its shape… • Et=100 GeV (reduced average jet energy fraction inside R): • Radiated energy ~20% • R=0.3 DE/E=3% • EtUE ~ 100 GeV Medium induced redistribution of jet energy occurs inside cone C.A. Salgado, U.A. Wiedemann hep-ph/0310079 Guy Paic LISHEP- ALICE physics

  32. 1 10-2 vacuum medium z pjet 10-4 kt 0 0.5 1 z z=pt/ pjet Fragmentation functions Guy Paic LISHEP- ALICE physics

  33. The quarkonia physics Guy Paic LISHEP- ALICE physics

  34. Acceptance for quarkonia measurements • ALICE can measure J/ down to pt = 0 (unique @ the LHC) • ALICE-muon can measure J/ &  at large y Guy Paic LISHEP- ALICE physics

  35. CMS  ~ 80 MeV ALICE dielectrons ALICE dimuons background level 1 = 2 HIJING evts with dNch/d = 6000 @  = 0 each mass resolution(  100 MeV @ M ~ 10 GeV is needed to separate the  sub-states) ATLAS  > 120 MeV • ALICE (& CMS) can measure the  sub-states • warning: ≠ simulation frameworks & inputs Guy Paic LISHEP- ALICE physics ATLAS CERN/LHCC/2004-009, CMS NOTE 2000-060 (updated)

  36. 0 < b < 3 fm 0 < b < 3 fm 0 < b < 3 fm 1. 2. 3. Extract  signals • get invariant mass cocktail for all centrality & pt bins • subtract non-correlated dimuons (assuming a perfect event-mixing subtraction) • fit invariant mass spectra with 3 modified Landau convoluted with Gaussian & exponential for background Guy Paic LISHEP- ALICE physics

  37. Centrality dependence of ’/  • statistics : one month PbPb • nuclear absorption not in • interest to combine pt dependence of the ratio • systematic errors underway Guy Paic LISHEP- ALICE physics

  38. 1 month of dielectrons in the central barrel Guy Paic LISHEP- ALICE physics

  39. W detection in ALICE (Z.Conesa del Vale) • W LO production process is: • NLO processes contribute just ~ 13% to the total cross section • LO dominant contribution (~ 80%) comes from udbar for W+,dubar for W- • detection? • Via their leptonic decay: • Where? ATLAS strategy is to measure m at |h| < 2.4 and e at |h| < 2.5 CMS will be able to measure m spectra for |h| < 2.4 ALICE can measure e for |h| < 0.9 and m for – 4.0 < h < – 2.5 for – 4.0 < h < - 2.5 ALICE is the only LHC Experiment able to measure W boson production Frixione & Mangano, hep-ph/0405130 Martin, et al, hep-ph/9907231 Guy Paic LISHEP- ALICE physics

  40. Some estimations for pp and PbPb nominal runs at LHC Point 2... pp @ 14 TeV  627.000 ’s generated from W decay in the ALICE IP   337.000 at Pt (30,50) GeV/c  88.800 ’sgenerated from W decay in the Muon Spectrometer Acceptance   51.000 at Pt (30,50) GeV/c PbPb @ 5.5 TeV, Min Bias  142.000 ’s generated from W decay in the ALICE IP   77.000 at Pt (30,50) GeV/c  15.500 ’s generated from W decay in the Muon Spectrometer Acceptance   7.800 at Pt (30,50) GeV/c W at LHC Single Muons at LHC Guy Paic LISHEP- ALICE physics

  41. The first three minutes…. Guy Paic LISHEP- ALICE physics

  42. Beam characteristics (LHC-OP-BCP-0001 rev 1.) • The highest possible beam energy will be achieved soon, however, with a small number of bunches, and low intensity • Beam conditions will be ideal for ALICE pp physics – TPC drift time ~80ms – no or small pile-up – L= 1x1029cm-2s-1 corresponds to 1 inel event in 160ms later 936 75 1.3x1032 Only 3 minutes to collect sample of 104 events… Guy Paic LISHEP- ALICE physics

  43. Motivation for pp study • First insight in pp collisions in new energy domain (s  14 TeV), study of evolution of soft hadronic physics • Cosmic ray interactions show `knee’ in 10151016 eV region and `ankle’ in 10181019 eV region • s  14 TeV corresponds to 1017 eV in lab frame • Contribution to knowledge of underlying minimum bias (background) pp events for other LHC physics programmes (Higgs search, B-physics, etc.) • Provide pp data as a reference for study of other collision systems (p-A, A-A) • Low multiplicity data to commission and calibrate various components of ALICE Guy Paic LISHEP- ALICE physics

  44. Pseudorapidity density dN/dη pT spectrum of charged particles CDF: Phys. Rev. D41, 2330 (1990) 30000 events at √s=1.8TeV 9400 events at √s=640TeV CDF: Phys. Rev. Lett. 61, 1819 (1988) 55700 events at √s=1.8TeV Multiplicity distribution Mean pT vs multiplicity UA5: Z. Phys 43, 357 (1989) 6839 events at √s=900GeV 4256 events at √s=200GeV CDF: Phys. Rev. D65,72005(2002) 3.3M events at 1.8TeV 2.6M events at 630GeV • It only takes a handful of events to measure a few important global event properties (dN/dh, ds/dpT, etc.) – after LHC start-up, with few tens of thousand events we will do: Claus Jorgensen GOING BACK TO WRITE THE FIRST PAPER! Guy Paic LISHEP- ALICE physics

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