[Triumf-seminars] TRIUMF Seminar today at 13:00

[TRIUMF Seminars]

Date/Time: Tue 2013-11-12 at 13:00

Location:  Theory Room         

Speaker:   Francesco d'Eramo (UC Berkeley)

Title:     Transverse Momentum Broadening: weak vs. strong coupling

Abstract: Transverse momentum broadening of an energetic parton propagating through a quark-gluon plasma is described P(k_\perp), defined as the probability that after propagating through the medium for a distance L the parton has acquired transverse momentum k_\perp. In this talk I will first review how to formulate the problem within the Effective Field Theory framework, and I will show how P(k_\perp) can be expressed in terms of the expectation value of two transversely separated light-like path-ordered Wilson lines of gluon fields from the medium. The nature of the medium does not enter this calculation, and any of its property becomes relevant only when one seeks to evaluate the expectation value. I will then present the calculation of P(k_\perp) for a weakly-coupled quark gluon plasma, where this expectation value can be evaluated by using perturbation theory. I will compare the result at weak coupling to expectations from holographic calculations that assume a plasma that is strongly coupled at all length scales. The shape of P(k_\perp) at modest k_\perp may not be very different in weakly coupled and strongly coupled plasmas, but at large enough k_\perp it must be parametrically larger in a weakly coupled plasma than in a strongly coupled plasma. This means that by looking for rare (but not exponentially rare) large-angle deflections of the jet resulting from a parton produced initially back-to-back with a hard photon, experimentalists can find the weakly coupled short-distance quark and gluon quasiparticles within the strongly coupled liquid quark-gluon plasma produced in heavy ion collisions, much as Rutherford found nuclei within atoms or Friedman, Kendall and Taylor found quarks within nucleons.



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