1 / 24

Heavy Ions at the LHC Theoretical issues

Heavy Ions at the LHC Theoretical issues. Super-hot QCD matter What have we learned from RHIC & SPS What is different at the LHC ? Goals of HI experiments at the LHC. LHC2003 Workshop Fermilab April 30 – May 3, 2003. initial. LHC. state. RHIC. LHC. QCD phase diagram.

yestin
Download Presentation

Heavy Ions at the LHC Theoretical issues

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. Heavy Ions at the LHCTheoretical issues • Super-hot QCD matter • What have we learned from RHIC & SPS • What is different at the LHC ? • Goals of HI experiments at the LHC LHC2003 WorkshopFermilab April 30 – May 3, 2003

  2. initial LHC state RHIC LHC QCD phase diagram

  3. QGP = quark-gluon plasma Hadron gas From hadrons to QGP QCD equation of state from lattice QCD

  4. Signatures of a QCD phase change • Effects of “latent heat” in (E,T) relation • Enhancement of s-quark production • Bulk hadronization • Disappearance of light hadrons (ρ0) • Thermal l+l- and g radiation • Dissolution of Ψ, Ybound states • Large energy loss of fast partons (jet quenching) • Net charge and baryon number fluctuations • Collective vacuum excitations (DCC)

  5. T E Additional energy is used up to liberate new degrees of freedom (color!) in transition region Thermodynamics near Tc

  6. RHIC SPS AGS Hadrons at the boiling point ? Plateau is an indicator of latent heat of phase transformation.

  7. Mass (MeV) NA57 data (sss) (qss) (qqs) Flavor Strangeness enhancement… …probes chiral symmetry restoration and deconfinement

  8. High-energy parton loses energy by rescattering in dense, hot medium. q q q q g Jet Quenching Radiative energy loss can be described as medium effect on parton fragmentation:

  9. Phenix preliminary Scaled p0 yield in Au+Au vs. p+p collisions Peripheral Central

  10. Central Peripheral p /p ratio HIGH-ENERGY PHYSICS:Wayward Particles Collide With Physicists' Expectations Charles Seife EAST LANSING --At a meeting here last week, resear-chers announced results that, so far, nobody can explain. By slamming gold atoms together at nearly the speed of light, the physicists hoped to make gold nuclei melt into a novel phase of matter called a quark-gluon plasma. But al-though the experiment produced encoura-ging evidence that they had succeeded, it also left them struggling to account for the behavior of the particles that shoot away from the tremen-dously energetic smashups.

  11. y Coordinate space: initial asymmetry Momentum space: final asymmetry px x Azimuthal anisotropy v2 Indicates early equilibration (< 1 fm/c) Semiperipheral collision py Collective flow behavior extends to higher pT for baryons (p,L) than mesons (p,K)

  12. Fragmentation Recombination Quark recombination ?

  13. Quark distribution function at “freeze-out” Recombination vs. Fragmentation For a thermal distribution: Recombination: Fragmentation… …never competes with recombination for an exponential spectrum: … but wins out at large pT, where the spectrum is a power law ~ (pT)-b

  14. R.J. Fries, BM, C. Nonaka, S.A. Bass (PRL in print) pQCD spectrum shifted by 2.2 GeV Teff = 350 MeV fitted to spectrum Model fit to hadron spectrum Also explains p/p+ ratio ≥ 1 below 5 GeV/c !

  15. P. Sorensen (UCLA – STAR) Does v2 reflect parton flow? Recombination model suggests that hadronic flow reflects partonic flow (n = number of valence quarks): Provides measurement of partonic v2 !

  16. What’s different (better) at the LHC ? • Higher energy density e0 at earlier time t0. • Jet physics can be probed to pT > 100 GeV. • b, c quarks are plentiful, good probes. • Increased lifetime of QGP phase (10-15 fm/c)  Initial state effects less important. • QGP more dominant over final-state hadron interactions. Much larger “dynamic range” compared to RHIC

  17. ~ 1/Q2 Parton saturation at small x l  0.5 After “liberation”, partons equilibrate and screen color force

  18. LHC LHC RHIC RHIC ECM dependence of dN/dy, dE/dy NLO pQCD with geometric parton saturation (Eskola et al. - EKRT) Probably overestimate of growth of dN/dy, dE/dy with ECM

  19. Thews et al. Karsch et al. Quo vadis - J/Y ? Vqq is screened at scale (gT)-1  heavy quark bound states dissolve above some Td. But deconfined c-quarks can recombine at hadronization and form new J/Y. J/Y suppression ? J/Y enhancement ?

  20. Jet quenching at the LHC I. Vitev, M. Gyulassy, PRL 89 (2002) 252301

  21. R.J. Fries et al. (unpublished) br = 0.85 includesparton energy loss br = 0.75 br = 0,65 Hadron production at the LHC

  22. q g g Photon tagged jets High-energy photon defines energy of the jet, but remains unaffected by the hot medium. Parton energy loss is measured by the suppression of the fragmentation function D(z) near z1 .

  23. q + g q + g q + q g + g g q g Measuring the density Backscattering probes the plasma density and initial parton spectrum R.J. Fries, BM, D.K. Srivastava, PRL 90 (2003) 132301

  24. Summary • SPS: First glimpse (“evidence”) of the QGP • RHIC: Discovery of the QGP ?! • LHC: (Quantitative) exploration of the QGP facilitated by plentiful hard probes ! • Specific questions: • How does dE/dx depend on energy density? • How is the fragmentation function modified? • Are c and b quarks thermalized? • Gluon saturation in nuclei at small x • Higher twist effects

More Related