STAR HardProbes PWG

[Tristan Protzman <tlp220 AT lehigh.edu>]

Hi all, 

I would like to propose two abstracts for Quark Matter 23.  One is an extension of the jet v2 measurement I showed at Hard Probes expanding into the O+O running, and the other is a new topic, looking for the polarization of lambdas around a jet axis from the thermalization of jet energy loss.  I recognize this second analysis is still very new, the plan would be to reassess the status of the analysis closer to May 1st to decide if we want to proceed with it.  Additionally, it is not determined between Rosi and I who would be showing which result.

Cheers,

Tristan

Jet $v_2$ in medium sized systems at STAR

Hard partonic scatterings early in the evolution of AA collisions, known as jets, experience the full evolution of the quark-gluon plasma (QGP). As they traverse through the QGP, they lose energy through jet quenching processes. In semi-central events, a non-uniform QGP is produced, shown in measurements of collective behavior such as elliptical flow. Thus the mean in-plane and out-of-plane path lengths differ. This fact can be used to constrain the average path length for jets traversing the QGP, as those which travel in the direction of the event plane should experience less path-length dependent quenching than those which travel perpendicular to it. This suppression manifests in an excess of yield in-plane relative to out-of-plane, quantified by jet $v_2$. This is of particular interest in small systems, where signs of the onset of QGP formation are being searched for.

In this work, jet $v_2$ will be presented in $\sqrt{s_{NN}}=200\hbox{ GeV}$ Ru+Ru & Zr+Zr at multiple jet resolution parameters as well as $\sqrt{s_{NN}}=200\hbox{ GeV}$ O+O collisions. Through the comparison of these systems with larger Pb+Pb systems and smaller p+Pb systems, competing effects and biases can be investigated.

$\Lambda$ polarization from quenched jets at STAR

As high-momentum jets traverse through the quark-gluon plasma (QGP), they will interact and lose energy to the medium through jet quenching processes. This energy loss may thermalize into the medium, forming vortical structures around the axis. To search for experimental evidence of these structures, the polarization of $\Lambda$ baryons around a jet axis is measured using the ring observable, which measures the polarization relative to the plane formed by the jet axis and the $\Lambda$ baryon. An observation of such a signal serves as evidence that the lost energy from quenched jets is thermalized into the medium. In this presentation, work in the direction of measuring this signal will be presented in Au+Au collisions at STAR.