Marzia Rosati mrosati@iastate.edu Iowa State University Charmonium in Heavy Ion Collisions Marzia Rosati mrosati@iastate.edu Iowa State University Beijing, China October 11, 2004

Outline Why Heavy Ion Collisions? QCD and the QGP Phase Transition Quarkonium in Media Measurements at the SPS New Quarkonium Measurements at RHIC Future Prospects at RHIC and LHC

QCD Lagrangian The interaction between quarks and gluons can be described by as the coupling “constant” NP HEP non perturbative at long range/low energy asymptotic freedom at short range / high energy

QCD Missing Mass Puzzle The mass terms one inserts into the QCD Lagrangian have ~nothing to do with the observed hadron masses Each quark has the mass of about 1% of a proton or neutron (!) md ~ 7 MeV mu ~ 4 MeV The origin of the rest (~98%) of the mass is of dynamical origin: it is due to the interactions. Non-perturbative Vacuum q

Gluon field fluctuations QCD and Confinenement Non-perturbative Vacuum q Gluons carry the color charge  gluons can emit gluons! qq pairs, gluon loops fill space, “normal vacuum” is not empty!! Possible correlations between loops  vacuum “superconducting” QCD color field excluded from vacuum  quarks must stay outside of vacuum and inside hadrons q Gluon field fluctuations

Lattice QCD calculations Teraflop-scale computers simulate equilibrium QCD Predict phase transition: hadrons quark/gluon (QUARK GLUON PLASMA) (F. Karsch, hep-lat/0106019)

Where to study the QGP Phase Transition? Big Bang Only one chance… Lattice QCD Neutron stars Heavy Ion Colliders

What are we doing in Heavy Ion Collisions? Why? Collide heavy nuclei at the highest possible energies Au+Au Collisions in URQMD Model Why? create Quark Gluon Plasma (QGP) as transient state in heavy ion collisions to study QCD confinement of quarks to hadrons How hadrons get their masses

Charmonium as a Probe of QGP Matsui and Satz predicted J/y production suppression in Quark Gluon Plasma because of color screening

QCD Potential in vacuum: Coulomb potential Confinement in vacuum: linear increase with distance, strong attractive force confinement of quarks to hadrons in dense and hot matter screening of color charges (similar to Debye screening in dense atomic matter) potential vanishes for large distance deconfinement of quarks  QGP

Successive Melting of Charmonium rD = mD-1 Debye screening radius when m> miD, state i is no longer bound state mD (GeV) TD eD y’ 0.3 <Tc <ec melts first c 0.35 Tc ec melts 2nd J/y 0.70 1.2Tc 2ec smallest, hard to screen

Quarkonium in QGP Hadrons with radii greater than ~lD will be dissolved Study quarkonium bound states

Screening by the QGP

Heavy Ion Collisions b is large b is small In a glancing blow or “peripheral” collision, not much of excitement happens. b is large In a head on or “central” collision, there is a lot of energy transferred – forming a QGP? b is small Impact parameter cannot be measured directly. So experiments have to use a measured quantity as a proxy for impact parameter: multiplicity, total transverse energy, etc…

QGP Search with Quarkonium Peripheral Collision: Large impact paramater Central Collision: Small impact parameter

Production of J/y Use J/y and y’ beams to test energy density of matter: J/y, y’ matter box ?? medium in box: A) vacuum no absorption B) confined low energy density absorption of y’ C) deconfined high energy density absorption of J/y and y’ vary energy density  search for threshold behavior in J/y and y’ absorption

Heavy-Ion Accelerators 1 2 3 4 Colliding Nuclei Hard Collisions Parton Cascade Hadron Gas & Freeze-out

The NA50 experiment A closed-geometry muon spectrometer, like many other charmonium experiments.

NA50 Measurement Physics: Experiment: Analysis: Look at J/Y via decay to m+m- Experiment: Absorb “all” hadrons before they make muons! Analysis: Form spectrum of Remove “combinatoric background” by subtracting (suitably scaled) like-sign mass spectrum Absorber Calorimeter Spectrometer Incident Beam Target(s) m+ m-

NA50 in Practice Fits to the mass spectrum are simultaneous fit to: Background Open charm J/Y Y’ Drell-Yan Absolute yields of J/Y are (were) scaled by that of “Drell-Yan Yield Scales like A*B No final state interactions

The Plot That Got Everyone Excited Suppression pattern vs. L is different for Pb-Pb What is L? “the mean length of the path of the (cc) system through nuclear matter of mean density r0” A way to combine different beams, targets and energies “Anomalous J/Y suppression in Pb-Pb interactions at 158 GeV/c per nucleon”, Phys. Lett. B410, 337 (1997).

J/y and y’ Cross Section versus L M.C. Abreu et al., Phys.Lett. B450 (1999) 456 NA50 anomalous absorption of J/y in Pb-Pb anomalous absorption of y’ in Pb-Pb and S-U

Detailed study of “Normal Nuclear Suppression” NA50: J/Y and Y’ from p-Be, Al, Cu, Ag, W, Pb G. Borges, " New Results on J/psi and psiprime nuclear absorption in p-A and S-U collisions at the CERN/SPS "

NA50 more recently

NA38/50 Summary Plot cc suppression J/y suppression ? Measured / Expected J/y suppression ?

The story is not so simple! MATSUI-SATZ: Rplasma screening < Rquarkonium : SUPPRESSION NA50: Anomalous Suppression ALTERNATIVES: Dense hadronic medium, comovers NEW LATTICE RESULTS: Jpsi survives beyond Tc

Percolation Model: geometrical transition H. Satz, M. Nardi In Central collisions nucleons undergo several interactions and, since each collision establishes a string, we will obtain a spaghetti like of intertwined overlapping QCD strings. Deconfinement is expected when there is enough internetting between nucleons. Deconfinement is a function of string size (QCD) and deconfinement string density hep-ph 9805247

Dual Parton Model: A. Capella Na50 J/y suppression can be reproduced by DPM with absorption by comovers. The number of comovers in Capella model is proportional to number of participants and also to number of collisions. A. Capella, D. Sousa, nucl-th/0303055

Multiple ccbar pairs in high energy AA Collisions

Statistical coalescence model A.P.Kostyuk, M.I. Gorenstein, H. Stocker, W. Greiner, Phys. Lett B 531, 195-202

New Lattice Results (I) S. Datta, F. Karsch, P. Petreczky, I. Wetzorke, Phys. Rev. D69:094507 (2004)

New Lattice Results (II) M. Asakawa and T. Hatsuda, Phys. Rev. Lett: 012001 (2004)

Question is Still Open J/Y in Heavy Ion Collisions is Normal Nuclear Production (pA) scaled up PLUS Hot hadron gas, comovers QGP/dense matter modifications to production: Debye screening, Enhancement in coalescence models, balancing of D+D↔J/Y+X

Charm Production at SPS and RHIC Increased cross section will make production at RHIC 40-50 times than at SPS.

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