1 / 35

Latest Physics News from ALICE Experiment Mar. 2011

Update on ALICE Technologies, PbPb Collisions, Physics Results, and Data Samples. Insights on Heavy Ions and pp Physics. Impact of Monte Carlo Tuning and QCD Studies. Significant findings for QGP at LHC.

gloriawoods
Download Presentation

Latest Physics News from ALICE Experiment Mar. 2011

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. News from alice • ALICE Experiment • News from pp collisions • Physics Results from PbPb Pasquale Di Nezza LNF, Mar 2011

  2. ALICE Technologies:18 Tracking: 7 PID: 6 Calo. : 5 Trigger, Nch:11 Collaboration: > 1000 Members>100 Institutes > 30 countries Detector: Size: 16 x 26 meters Weight: 10,000 tons 2

  3. Ready for Data EMCal, the LNF baby!

  4. pp Physics in ALICE • Core Business is Heavy Ions • Physics with pp • collect ‘comparison data’ for heavy ion program • many signals measured ‘relative’ to pp • comprehensive study of MB@LHC • tuning of Monte Carlo (background to BSM) • soft & semi-hard QCD • very complementary to other LHC expts • address specific issues of QCD • very high multiplicity pp events • dNch/dh comparable to HI => mini-plasma ?

  5. Data Samples LHC performed exceedingly well: - increasing pp L by 105 in 2010 (L > 2x1032) - delivering > 8 mb-1 Pb in 4 weeks (L > 2x1025, ~ 1/20 Lmax)

  6. Physics exploitation of ALICE started for good ! submitted to EPJC 28 Nov 2009 Recorded all of 280 events • It took: • 20 years to built ALICE • 40 minutes to take the first data • 1 hour to get the prel. result (±10%) • 2 days for the final result • and 3 days to agree on the Authorlist 6

  7. BE enhancement vs qINV unlike sign p+p- high Nch, kT high multiplicity high momentum (Phojet) baseline low multiplicity low momentum kT Bose Einstein Correlations • QM enhancement of identical Bosons at small momentum difference • ‘enhancement’ rel. to phase-space and any non-BE correlations (‘baseline’) • non-BE correlations important at high √(s) (‘minijets’) • less so at RHIC, but definitely at FNAL/LHC ! Important Message: At LHC, even MB events show signs of pQCD ! We may not always be able to rely on common wisdom & analysis techniques which were correct at lower energies

  8. Source Radius vs pair momentum Using different Baselines Source Radius vs Multiplicity HBT @ 900 GeV Results: • Radius increases with Nch, comparable to ISR, RHIC, TeV • much smaller <kT> dependence than at FNAL dependence usually interpreted as sign of ‘flow’ in heavy ions sign. systematic uncertainty from ‘baseline’ shape • neglecting non-BE correlations (‘flat baseline’) can cause kT dependence (at high √ s)!

  9. |h| < 1 L/K0SRatio 900 GeV |y| < 0.75 • very good agreement between STAR (200 GeV) and ALICE (900 GeV) • very different from CDF (630/1800) and UA1 (630) for pT > 1.5 GeV - UA1(630) and CDF(630) don’t agree either … to be further investigated (different triggers, acceptance, feed-down correction ?)

  10. string junction M M M B B B p/p Ratio • Can one stop a proton ‘on its track’ at LHC ? • where does the conserved baryon number reappear after the pp collision ? • fragmentation function f(z) of baryon number • Di-quark qq: z2 => a = -1, small Δy • single q: √z =>a = 0.5, medium Δy • no valence q:a = ??; large Δy ?? Veneziano: a ≈ 0.5 others: a ≈ 1(pQCD estimates, s(p-pbar annihilation), ‘odderon’) a ≈ 1 => f(y) = constant, pbar/p approaches 1 very slowly (< 0.95 at LHC) d u za ~ e –aΔ y =e –(1-α)Δ y (Δy »1) α = intercept of relevant Regge trajectory Δy = ybeam – ybaryon = ‘rapidity loss’ u B.Z. Kopeliovich, Sov. J. Nucl. Phys. 45, 1078 (1987); G.C. Rossi and G. Veneziano, Nucl. Phys. B123, (1977) 507 u d SJ u

  11. p/p vs pT p/p vs √s 900 GeV |y|<0.5 QGSM aSJ = 0.9 enhanced stopping MC’s HIJING/B, Perugia-soft 7 TeV |y|<0.5 0.9 TeV: p/p = 0.957±0.006(stat) ±0.014(syst) 7 TeV: p/p = 0.990±0.006(stat) ±0.014(syst) p/p Ratio @ LHC standard Pythia Results: • you can’t stop a proton on its track (at least not at LHC) • ‘string junction’ picture: aSJ ≈ 0.5 (G.V. was right !) • little room for any additional diagrams which transport baryon number over large rapidity gaps

  12. Much more to come... S*→ L p K*→ K p X → L p W → L K < 2% of statistics at 7 TeV

  13. Charm at 7 TeV D0→ K p p p D0→ K p D+→ Kpp Lc→ pKp Ds+→ Φπ→ KKp D*→ D0p

  14. J/Y→ m+m- , e+e- at 7 TeV <pT2> vs √ s <pT> vs √ s J/Y → m+m- Prel. Results: • agreement ALICE/LHCb • <pT>&<pT>2 follow √s trend • energy dependence ~ pQCD

  15. ‘Little Bang’The first 3 weeks …

  16. Events A Single Event • Properties of average events instead of average event properties

  17. Anti-Nuclei ~ 2 M Pb-Pb Min Bias events

  18. Role of LHC after RHIC/SPS • Search for the ‘QGP’ is essentially over • Discovery of QGP is well under way (with fantastic results & surprises at RHIC) • Measuring QGP parameters has just begun • 1) Quantitative differences • significantly different state of QGP in terms of energy density, lifetime, volume • large rate for ‘hard probes’ : jets, heavy quark states (b,c,U,J/Y ),… • 2) Test & validate the HI ‘Standard Model’ (< 10 years old !)QGP = very strongly interacting (almost) perfect liquid • Test predictions/extrapolations from RHIC to LHC • examples: flow (‘soft’) Quarkonia suppression (‘hard’) • 3) ‘Precision’ measurements of QGP parameters • Quantitative and systematic study of the new state of matter • Equation-of-Statef(e,p,T), viscosityh (flow), transport coefficientq (jet quenching), Debye screening mass (Quarkonia suppression), … • Confront data with Theory and Models: • standard tools: Lattice QCD, pQCD, Thermo- and Hydrodynamics, … • new tools: AdS/CFT (‘duality’), Classical QFT (‘Colour Glass Condensate’) • 4) Surprises ? • we are dealing with QCD in the strong coupling limit ! > 10 year program where are we after 3 weeks ? ^

  19. pQCD shadowing saturation pp extrapolations Who gets it right and why ? • Multiplicity and Energy density e: • dNch/dh (@5%) ~ 1600 ± 76 (syst)  8.3 per participant pair • somewhat on high side of expectations • growth with √s faster in AA than pp (√s dependent ‘nuclear amplification’) • Energy density ≈ 3 x RHIC (fixed t) • lower limit, likely t0(LHC) < t0(RHIC)

  20. Saturation Models HIJING DPMJET Who gets it right and why ? • dNch/dh as a function of centrality (norm. to ‘overlap volume’ ~ Nparticipants) • soft process dNch/dh~ number of scattered nucleons (strings, participants, …) • ‘nuclear amplification’ should be energy independent • (very) hard processes dNch/dh~ number of nucleon-nucleon collisions • getting more important with √s & with centrality • DPMJET MC • gets it right for the wrong reason • HIJING MC • strong centr. dependentgluon shadowing • Others • saturation models: Color Glass Condensate,‘geometrical scaling’ fromHERA/ photonuclear react. Important constraint for models sensitive to details of saturation

  21. LHC ~ RHIC !!

  22. Bits and Pieces ... • Centrality determination with Glauber fits: • very tight correlation of several centrality measures (different acceptance/detectors) • 1/√N is a small number at LHC ! • very robust results fitting centrality between 30% and 90% of total cross section • Glauber fit Nch ~ f * Npart + (1-f) * Ncoll visible better than Nch ~ (Npart)a • NpartGlauber fit = Npart from pure nuclear geometry (slicing in impact paramet b) ZDC – V0 Trigger scintillators V0A: 2.8 < h < 5.1 V0C: -2.5 < h < -3.7 TPC tracks – V0

  23. DE Fragmentation function f(z) Jet Quenching • Jet quenching:jet E -> jet E’ (=E-DE) + soft gluons (DE) modified jet fragmentation function via matter induced gluon radiation/scattering => QGP properties • how much energy is lost ? (measures e.g. q^) • very difficult question, may depend on jet cone R, pt-cutoff, .. • how is it lost ? (e.g. multiple soft or few hard gluons ?) • look at soft part of f(z), pt < 2-5 GeV • ‘response of QGP’ (shock waves, Mach cones ??) • properties of bulk matter around jet, pt ~ 1 GeV Atlas • Both Atlas and CMS see very striking effects • in the dijet-imbalance for central events ! • Atlas paper: http://arxiv.org/abs/1011.6182 • Cacciari et al: http://arxiv.org/abs/1101.2878

  24. Jets in ALICE (TPC) we see qualitatively a similar effect quantitative analysis is ongoing small acceptance (statistics), => need full 2010 data try to include low pt (study pt-cut off dependence of imbalance) 10-20% peripheral 168 GeV 192 GeV Dh Df 0-10% central 102 GeV 47 GeV Df Dh Charged Jets bin size: 0.1x0.1

  25. Data driven Interpolation 900 GeV & 7 TeV or using NLO for change in shape 7 TeV * NLO (2.76 TeV)/NLO(7 TeV) Including CDF data 0.9 TeV * NLO (2.76 TeV)/NLO(0.9 TeV) Jet Quenching as seen by pt spectra • Suppression of high pt particles ( ~ leading jet fragments) • Minimum RAA ~ 1.5 – 2 x smaller than at RHIC • Rising with pt ! (ambiguous at RHIC !) • accuracy limited by pp reference => need pp at 2.76 TeV ! RAA = 1 for (very) hard QCD processes in absence of nuclear modifications

  26. Associated pTt Δf Trigger High pT Particle Correlations ‘near’ side ‘away’ side UE Trigger Particle Trigger Particle: highest pT particle in event (pTt) Associate Particle: all the others (pTa)

  27. q q Star@RHIC pT,trig 8-15 GeV Jet Quenching seen by High pT Correlations • classic ‘jet quenching signal’ • away side correlation in central Pb-Pb washed out up to pT,trig > 10 GeV PT associated 2 – 6 GeV ‘near’ side ‘away’ side Df Df Df

  28. pp Pb PbPb peripheral pp 7 TeV CMS pp 7 TeV ‘near side ridge’ PbPb central PbPb central Jet Quenching (?) seen via Multiparticle Correlations • ‘Autocorrelation’: d2Nch/dDhdDf (signal)/d2Nch/dDhdDf (mixed events) • ‘near side ridge’: • - striking effect, not really understood • response of QGP to jet quenching ? • initial state gluon radiation ? • ???

  29. Z Reaction plane Y X f Pz Py Px Nch yield Testing the HI ‘Standard Model’ • Elliptic Flow: one of the most anticipated answers from LHC • experimental observation: particles are distributed with azimuthally anisotropy around the scattering plane • Are we sure Hydro interpretation is correct ? Elliptic Flow v2asinterpreted by Hydrodynamics Pressure gradient converts spatial anisotropy → momentum anisotropy → particle yield anisotropy

  30. LHC ? Testing the HI ‘Standard Model’ • Hydro seems to work very well for first time at RHIC • LHC prediction: modest rise (Depending on EoS, viscosity, speed of sound, dNch/dh, ..) • (‘better than ideal is impossible’) • experimental trend & scaling predicts large increase of flow • (‘RHIC = Hydro is just a chance coincidence’) BNL Press release, April 18, 2005: Data = ideal Hydro "Perfect" Liquid New state of matter more remarkable than predicted – raising many new questions (scaled) Flow

  31. STAR at RHIC ALICE +30% RHIC ALICE First Elliptic Flow Measurement at LHC • v2 as function of pt • practically no change with energy ! • extends towards larger centrality/higher pt ? • v2 integrated over pt • 30% increase from RHIC • <pt> increases with √s • pQCD powerlaw tail ? • Hydro predicts increased ‘radial flow’ • very characteristic pt and mass dependence; to be confirmed !

  32. Testing the HI ‘Standard Model’ • Hydro passed the first test ! • many more tests of Hydro and the HI-SM to come…. LHC ! CERN Press release, November 26, 2010: ‘confirms that the much hotter plasma produced at the LHC behaves as a very low viscosity liquid (a perfect fluid)..’ Disclaimer: very rough guesstimate, assuming geometry not to change between RHIC and LHC

  33. Strangeness in Pb-Pb

  34. Charm in Pb-Pb • ‘Jet quenching’ with heavy quarks: • Energy loss depends on • color charge (quark/gluon) • mass (light/heavy quarks)

  35. Conclusions and Perspectives 2010 has been a memorable year for ALICE ! • Excellent performance of the detector, data analysis has smoothly and quickly delivered the first physics results • 13 physics papers published so far, many more in the pipeline • 2011 LHC run about to start • pp (short) run at √s=2.76 TeV  Essential as a reference for heavy-ion results • Long pp run at √s = 7 TeV, 1 month of PbPb at √s=2.76 TeV/N

More Related