Probing nuclear matter with jet conversions

Abstract

We discuss the flavor of leading jet partons as a valuable probe of nuclear matter. We point out that the coupling of jets to nuclear matter naturally leads to an alteration of jet chemistry even at high transverse momentum p T . In particular, quantum chromodynamics (QCD) jets coupling to a chemically equilibrated quark gluon plasma in nuclear collisions will lead to hadron ratios at high transverse momentum p T that can differ significantly from their counterparts in p+p collisions. Flavor measurements could complement energy loss as a way to study interactions of hard QCD jets with nuclear matter. Roughly speaking they probe the inverse mean free path 1/λ while energy loss probes the average squared momentum transfer µ 2 /λ. We present some estimates for the rate of jet conversions in a consistent Fokker-Planck framework and their impact on future high-p T identified hadron measurements at RHIC and LHC. We also suggest some novel observables to test flavor effects.

Deviation from quark number scaling of the anisotropy parameterv2of pions, kaons, and protons inAu+Aucollisions atAdare1, Afanasiev2, Aidala3 et al. 2012Phys. Rev. C827490View full textAdd to dashboardCite

“…This indicates that a simple interplay between recombination and jet energy loss is not enough to explain the v 2 and R AA of pions and protons in Au + Au collisions in this p T region. Additional considerations may include the nonAbelian nature of jet energy loss [53], the quark versus gluon fragmentation production of pions and protons [54][55][56], and jet chemistry effects such as enhanced parton splitting [57] and jet conversion [58]. Detailed model calculations that take all of these effects into account are not yet available, and it is an open question whether doing so is enough for an adequate interpretation of the p T v 2 and R AA of pions and protons.…”

Evaluating results from the Relativistic Heavy Ion Collider with perturbative QCD and hydrodynamics

“…In Ref. [137] the authors predicted a factor 2 increase in the R AA of kaons vs pions which seems to bee seen in preliminary STAR data [140].…”

“…A heavy ion environment not only redistributes energies of energetic particles, it can also lead to significant changes in the relative abundances of hadrons. This can either happen through profound changes in the way hadronization works in high multiplicity environments [135], see also the discussion on quark recombination in the next section, or through the exchange of particles with the quark gluon plasma which leads to a phenomenon termed jet conversion [136,137,138,139]. Jet conversions would increase the number of protons and kaons relative to pions in nuclear collisions vs p + p collisions.…”

Energy Loss and Flavor Dynamics from Single Particle Measurements in PHENIX

“…In Reference [1], a novel measurement, the so-called "double ratio," is proposed as an observable to test for jet flavor conversion. The fragmentation functions of protons, indeed all baryons, have larger gluon contributions than those of pions, or mesons in general.…”

“…By this, we mean elastic scattering processes in which the leading parton of the jet changes flavor or type. The two dominant modes of this are 1) annihilation and its inverse reaction gluon fusion,q + q ↔ g + g, and 2) Compton scattering, q + g ↔ g + q, wherein the momenta between the quark and gluon are exchanged and the particle with the higher momentum has consequently changed type [1].…”