Progress in QCD Pheno for RHIC?

Awesome. I love it when people do good old-fashioned straight-up QCD Pheno. RHIC sees tons of cool effects where the theory just can’t cut the muster, so I get really excited when someone hits QCD head-on, instead of doing something easier, or unfalsifiable.

So I just read this paper this morning, which basically extends DGLAP parton showering to include iteractions with Quark Gluon Plasma. This is pretty cool, as that it seems to qualitatively reproduce some of R_AA supressions. Sad thing is they neglect the reaction of the medium, so I doubt this will describe the mach cone, which is one of my favorite things out of RHIC. Can’t have it all, I guess.

In case you’re wondering, RHIC is a versatile collider on Long Island, which collides combinations of protons, deuterons, copper ions, and gold ions. The goal is to study lots of processes, but most significantly to create really hot, dense conditions where we may be able to observe a phase transition in QCD to something called the quark-gluon plasma. Maybe we already have seen it, but the theory is wicked hard, and no one is certain whether there’s really a phase transition or not. Whatever they are making, the “medium” is hot, dense, and is pretty much in thermal equilibrium as its expanding. They also know that it smears hadronic information, but electromagnetic stuff passes through unscattered. The hadronic smearing I’m talking about seen in the R_AA plots, which are ratios of stuff from gold-gold and proton-proton collisions. The basic idea is, there’s a hard scatter in pp or AuAu which are essentially the same, the energy has to pass through the medium in AuAu, and the distributions are really different. You can read more here from the STAR collaboration. The mach cone thing I mentioned is a hunch that people are seeing something analogous to a sonic boom as partons traverse the medium. This is fantastic, because if you can measure a mach cone, you can measure a speed of “sound.” If you can find a place where the speed of “sound” suddenly changes, thats pretty good evidence for a phase transition, which is the name of the game. Heres some slides of a talk I saw at DIS last year. Its a good introduction and overview to RHIC.


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