1 / 41

Latest Results from the LHC: Heavy-Ion Physics

Latest Results from the LHC: Heavy-Ion Physics. Jan Fiete Grosse-Oetringhaus CERN 2nd August 2011, CERN. Contents. I would like to give credit to many EPS speakers from which I took slides, in particular Federico Antinori. Introduction Selection of recent heavy-ion physics results on

bandele
Download Presentation

Latest Results from the LHC: Heavy-Ion Physics

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. Latest Results from the LHC: Heavy-Ion Physics Jan Fiete Grosse-OetringhausCERN 2nd August 2011, CERN

  2. Contents I would like to give credit to many EPS speakers from which I took slides, in particular Federico Antinori Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Introduction • Selection of recent heavy-ion physics results on • Particle multiplicity • Correlations • Identified particles • High pT suppression • Heavy flavours • Quarkonia • Jets

  3. Introduction Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  4. Ultrarelativistic A-A Collisions • Basic idea: compress large amount of energy in a very small volume Produce a “fireball” of hot matter • Temperature: O(1012 K) • ~ 105 times T at centre of Sun • ~ T of universe about 10 µs after the Big Bang • How does matter behave under such extreme conditions? • Study the fireball properties • QCD predicts state of deconfined quarks and gluons (Quark-Gluon Plasma) • LHC can accelerate ions (up to Pb) up to ÖsNN = 5.5 TeV Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  5. Geometry of a Pb-Pb Collision Central collisions Smallimpact parameter b High number ofparticipants high multiplicity Peripheral collisions Largeimpact parameter b Low number ofparticipants low multiplicity For example: sum of the amplitudes in the ALICE V0 scintillators Reproduced by Glauber model fit Random relative position of nuclei in transverse plane Woods-Saxon distribution inside nucleus Deviation at very low amplitude expected due to non-nuclear (electromagnetic) processes b peripheral central Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  6. Multiplicity Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  7. Particle Multiplicity • For the 5% most central collisions: • 1584 ± 80 (syst) charged particles per unit of η (|η|<0.5) • 2 dNch/dη / <Npart> = 8.3 ± 0.4 (syst) • 2.2 x central Au+Au (√sNN=0.2 TeV) 1.9 x pp (NSD) (√sNN=2.36 TeV) • log extrapolationfails (finally!) ALICE: PRL105 (2010) 252301 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  8. Centrality Dependence ALICE: PRL 106 (2011) 032301 Helena Santos - ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Model comparisons • DPMJET (with string fusion) • HIJING 2.0 (no quenching) • Centrality-dependent gluon shadowing • Tuned to multiplicity in 0-5% • Saturation models (sometimes too much?) • Very similar centrality dependence at LHC & RHIC • Once corrected for difference in absolute values

  9. Correlations Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  10. Azimuthal Asymmetry • Why is it important? • Non-central collisions are asymmetric in azimuth • Transfer of this asymmetry to momentum space provides a measure of the strength of collective phenomena • Large mean free path • Particles stream out isotropically, no memory of the asymmetry • Extreme: ideal gas (infinite mean free path) • Small mean free path • Larger density gradient  larger pressure gradient  larger momentum • Extreme: ideal liquid (zero mean free path, hydrodynamic limit) •  Quantified by second coefficient (v2) of Fourier expansion of azimuthal distribution Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  11. Elliptic Flow v2 v2 still large at the LHC System still behaves very close to ideal liquid (low viscosity) v2(pT) very similar at LHC and RHIC  Similar hydrodynamical behaviour? ALICE: PRL 105 (2010) 252302 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  12. Closer Look at v2 • v2 as function of h • Evolution with h consistent with RHIC PHOBOS, 200 GeV CMS: PAS HIN-10-002 PHOBOS: PRC72,051901 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  13. Structures in (Δη,Δφ) Near-side jet peak Two shoulders on away side (at 120 and 240) called “Mach cone” Long-range structure in η on near side called “Ridge” Helena Santos – ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  14. Fluctuations and v3 Matt Luzum (QM 2011) v2 v3 v3/RP ALICE: PRL 107 (2011) 032301 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • “Ideal” shape of participants’ overlap is elliptic, then • No odd harmonics expected • Participants’ plane coincides with reaction plane • Fluctuations in initial conditions • Participants' plane  reaction plane • v3 (“triangular”) harmonic appears [B Alver & G Roland, PRC81 (2010) 054905] • Indeed v3 0 measured! • v3 has weaker centrality dependence than v2 • When calculated w.r.t. reaction plane, v3 vanishes • as expected, if due to fluctuations…

  15. Long η-range Correlations ? Andrew Adare – ALICE (QM2011) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • “Ultra-central” events: dramatic shape evolution in a very narrow centrality range • Double-hump structure on away-side appears on 1% most central • Visible without v2 subtraction! • First five harmonics describe shape at 10-3 level • “Ridge” and “Mach cone” • Explanations based on medium response to propagating partons were proposed at RHIC • Fourier analysis at LHC suggests natural alternative explanation in terms of hydrodynamic response to initial state fluctuations

  16. Identified Particles Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  17. pT Spectra and Hydrodynamics • Identified particle spectra modified by radial flow • Comparison to hydrodynamical predictions • (calculations by C Shen et al.: arXiv:1105.3226 [nucl-th]) • OK for π and K, but p seem to “misbehave” (less yield, flatter spectrum) p: feed-down corrected Roberto Preghenella - ALICE Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  18. v2 and Hydrodynamics Raimond Snellings ALICE (QM2010) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Comparison of identified particles v2(pT) with hydro prediction • (calculation by C Shen et al.: arXiv:1105.3226 [nucl-th])  again, protons are off…  what’s going on with the protons?

  19. High pT Suppression Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  20. Nuclear Modification Factor (RAA) • RAA: particle yield in AA relative to pp scaled with number of binary nucleon-nucleon collisions • Without modification RAA = 1 • RAA(pT) for charged particles in 0-5% centrality range • Minimum (~ 0.14) for pT ~ 6-7 GeV/c • Then slow increase at high pT • Still significant suppression at pT ~ 100 GeV/c • Essential quantitative constraint for parton energy loss models Yen-Jie Lee – CMS CMS-PAS-HIN-10-005 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  21. Suppression vs Event Plane • Assess path-length dependent quenching • Significant effect, even at 20 GeV • Further constraints to energy-loss models  Path-length dependence of energy loss Alexandru Dobrin – ALICE (QM2011) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  22. Jet-Yield Modification Factor IAA • Near-side of central events slightly enhanced IAA ~ 1.2  medium effects also visible for near-side • Away-side of central events suppressed: IAA ~ 0.6  expected from in-medium energy loss • Peripheral events consistent with unity JFGO - ALICE (QM 2011) Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  23. Heavy Flavours Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  24. c and b Quenching at LHC • Study RAA of charm and beauty mesons and compare to light mesons • Parton mass and colour charge dependence of energy loss • Substantial suppression of heavy flavour production at LHC • Beauty suppressed too Diego Stocco – ALICE Catherine Silvestre – CMS [compilation: Andrea Dainese] Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  25. D vs π • Quarks expected to couple weaker than gluons • Colour factor (and other effects) • E.g. at pT ~ 8 GeV, factor ~ 2 less suppression expected for D than for light hadrons in BDMPS-ADSW • Charm suppression similar to pion suppression • Hint of RAAD > RAAπ at low pT? • To be continued with higher statistics… N Armesto et al., PRD 71 (2005) 054027 Diego Stocco – ALICE Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  26. Quarkonia Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  27. Quarkonia Suppression Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus Quark-Gluon Plasma "signature" proposed in the 80’s[T Matsui & H Satz, Phys. Lett. B 178 (1986) 416] In the plasma phase the interaction potential is expected to be screened beyond the Debye length λD (analogous to e.m. Debye screening) ccbar and bbbar pairs with radius > λD will not bind  production suppressed Critical "melting" temperature for J/ψ, ψ', , ', '' etc.

  28. Quarkonia at LHC Catherine Silvestre – CMS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  29. J/ψ at LHC: Forward y, Low pT • In 2.5 < y < 4 at LHC • Less suppression than at RHIC in 1.2 < y < 2.2 • as suppressed as at RHIC in |y| < 0.35 • pA reference needed for quantitative conclusions LHC: 2.5 < y < 4, pT > 0 (ALICE) RHIC: 1.2 < y < 2.2, pT > 0 (PHENIX) RHIC: |y| < 0.35. pT > 0 (PHENIX) Livio Bianchi – ALICE Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  30. LHC: |y| < 2.4, pT > 6.5 GeV/c prompt J/ψ (CMS)more suppressed than RHIC: |y| < 1. pT > 5 GeV/c inclusive J/ψ(STAR) LHC |y| < 2.5, pT > 3 GeV/c (ATLAS) J/ψ at LHC: Central y, High pT RCP PLB 697 (2011) 294 Catherine Silvestre – CMS Helena Santos – ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  31. (2S+3S) Suppression Yield of (2S+3S) relative to (1S) in Pb-Pb compared to pp Yen-Jie Lee – CMS arXiv:1105.4894 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  32. Jets Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  33. Di-jet Imbalance • Pb-Pb events with large di-jet imbalance observed by ATLAS & CMS  recoiling jet strongly quenched! Frank Ma - CMS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  34. Di-jet Asymmetry AJ Enhancement of asymmetric di-jets with increasing centrality measured w.r.t. pp & HIJING + PYTHIA AJ Helena Santos - ATLAS ATLAS: PRL105 (2010) 252303 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  35. Jet Nuclear Modification Factor RCP Suppression of jet production In central Pb-Pb w.r.t. binary-scaled peripheral Weak centrality dependence Helena Santos - ATLAS Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  36. Di-jet Decorrelation in Δφ pT,1 > 120 GeV/c pT,2 > 50 GeV/c e.g.: Frank Ma – CMS CMS: arXiv:1102.1957 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus • Although significant energy loss (large AJ), no visible angular decorrelation in Δφ w.r.t. pp collisions • Quenched jets still back-to-back

  37. Quenched Energy • Measurement of missing pT w.r.t. leading jet direction • Di-jet momentum difference balanced by low pT particles (spread far out of jet cone) Yen-Jie Lee – CMS Frank Ma – CMS CMS: arXiv:1102.1957 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  38. Conclusions • Heavy-ion collisions at LHC have entered a new regime with abundant hard probes and powerful detectors • Exciting results from first short (low L) run • Comprehensive explanation of ridge and Mach cone • Anomalies in proton yields & momentum distributions • Heavy-flavour suppression challenges energy-loss models • Strong jet quenching balanced by soft particles • Precision measurements will constrain dynamics and transport properties of the medium Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  39. Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  40. Backup Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

  41. QCD Phase Diagram ~ 10 ms after Big Bang LHC Early Universe RHIC Quark-Gluon Plasma Tc ~ 170 MeV SPS AGS Hadron gas Temperature Nuclear Neutron Star matter ~ 5 - 10 nuclear r Baryon density ec ~ 1 GeV/fm3 Latest Results from the LHC: Heavy-Ion Physics - Jan Fiete Grosse-Oetringhaus

More Related