How To See the Quark-Gluon Plasma Matthew Wysocki University of Colorado at Boulder July 22 Hot Quarks 2004 And Now For Something Completely Different…

How To See the Quark-Gluon PlasmaMatthew WysockiUniversity of Colorado at BoulderJuly 22Hot Quarks 2004And Now For Something Completely Different

How to see the QGP - Matt Wysocki

7/22/2004How to see the QGP - Matt Wysocki

The Quark-Gluon PlasmaThe quark-gluon plasma is a hot, dense state of matter in which partons have become deconfined (within the region of the plasma) from the normal hadronic state.

Characterized by high energy density (e > few GeV/fm^3) and high temperature (T > 100-200 MeV) or baryon density (n > 0.72/fm^3) relative to normal nuclear matter.



Signature RequiredQ: How can we tell the difference between states of matter?A: We need a signature to check!Proposed signatures include:Dilepton productionPhoton productionHanbury-Brown-Twiss EffectStrange matter contentJ/Y suppression



Debye ScreeningThe charge of one particle is cancelled (screened) by the surrounding charges.

Debye Screening Radius (lD): The distance at which the effective charge is reduced by 1/e.

Originally defined for electromagnetic plasma, later extended to plasma of color charges.These quarks effectively cannot see each other!



Charmonium and the J/YCharmonia ( ) is represented fairly well (at T0) by the potential:

T=0

StateMass (GeV)Charmonia states as given in the Particle Data Bookh c2.98J/Y3.1c c3.4-3.5Y3.7-4.4



J/Y in the QGPMatsui & Satz (Phys. Lett. B178 (1986) 416):In the QGP the screening radius could become smaller than the J/Y radius, effectively screening the quarks from each other!

T=0T=200aeff0.520.200.41 fm1.07 fm0.59 fmFrom Introduction to High-Energy Heavy-Ion Collisions, C.Y. Wong 1994



Bam! J/Y Suppression!In a QGP at T > Tc, we should see less J/Ys than we would expect without the plasma (J/Y suppression).



The villain of our story:Dilepton BackgroundsRHICenergies*Dileptons from open charm decay were not examined by Matsui & Satz



The hero fights back:Background SubtractionDimuon invariant mass plot from PHENIX Run4Signal after background subtraction.*Slide courtesy of David Silvermyr



Whoa there, cowboyJ/Y suppression from other sources:Nuclear absorptionShadowing

J/Y enhancement!Recombination

More recent lattice calculations show J/Ys remaining bound as high as 1.5Tc . (Petreczky et al, hep-lat/0309012)A lot has happened since Matsui & Satz:



NA50: Keeping it real



Cliffs NotesIn the quark-gluon plasma, the J/Y bound state will be suppressed.

How hot? How much?

High-energy heavy ion collisions (such as those at RHIC and soon the LHC) offer the best chance of observing this effect, and hence evidence of the QGP.



FinMany thanks to the Hot Quarks Organizing Committee for putting this workshop together!


How To See the Quark-Gluon Plasma Matthew Wysocki University of Colorado at Boulder July 22 Hot Quarks 2004 And Now For Something Completely Different…

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