Studies of jet quenching in O+O collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV by STAR

TL;DR

The study addresses whether jet-quenching signatures appear in O+O collisions at $\sqrt{s_{\rm NN}}=200$ GeV and how they depend on system size. It analyzes high-$p_T$ charged hadrons, inclusive jets, and semi-inclusive $h$+jet using observables $R_{\rm AA}$, $R_{\rm CP}$, and $I_{\rm CP}$, with event-mixing for background and iterative Bayesian unfolding to correct detector effects; centrality is tied to Glauber modeling. The results show $R_{\rm AA}$ for charged hadrons is near unity at high $p_T$, while $R_{\rm CP}$ and $I_{\rm CP}$ are below unity, and recoil $I_{\rm CP}$ decreases with increasing $N_{\rm part}$; isobar comparisons indicate consistent suppression trends but baselines differ, complicating interpretation. The findings provide constraints on jet quenching in intermediate system sizes, informing CNM versus QGP interpretations and motivating future p+p references, theory benchmarks, and LHC O+O results.

Abstract

Jet quenching is a well-established probe of the QGP in large collision systems such as Au+Au and Pb+Pb, but is absent in smaller p+A collisions despite the presence of collectivity. This makes it important to study its dependence on system size. O+O collisions offer an ideal opportunity, bridging the gap between small and large systems. In these proceedings, we present the measurements of the following observables related to jet quenching: inclusive charged hadron $R_{\rm AA}$ and $R_{\rm CP}$ at high transverse momentum ($p_{\rm T}$), inclusive jet $R_{\rm CP}$, and semi-inclusive hadron+jet $I_{\rm CP}$, using O+O collisions data collected with the STAR detector in 2021 at $\sqrt{s_{\rm NN}} = 200$ GeV. For jet measurements, combinatorial background is subtracted based on the event mixing technique, while background fluctuations and detector effects are corrected via unfolding. Inclusive charged hadron and jet $R_{\rm CP}$ and h+jet $I_{\rm CP}$ are found to be below unity, indicating suppression relative to peripheral events.

Figures (4)

• Figure 1: Inclusive charged hadron $R_{\rm AA}$ as a function of $p_{\rm T}$ in different centrality classes of O+O collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. Vertical bars and boxes around data points display statistical and systematic uncertainties, respectively.
• Figure 2: Inclusive charged hadron (left) and jet (right) $R_{\mathrm{CP}}$ as a function of $p_{\mathrm{T}}$ in different centrality classes of O+O collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV. Vertical bars and boxes around data points display statistical and systematic uncertainties, respectively.
• Figure 3: Recoil jet $I_{\mathrm{CP}}$ as a function of $p_{\mathrm{T,jet}}^{\mathrm{ch}}$ for two jet radii of $R=0.2$ (left) and 0.5 (right) in different centrality classes of O+O collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. Vertical bars and boxes around data points display statistical and systematic uncertainties, respectively.
• Figure 4: Recoil jet yields of O+O and Ru+Ru / Zr+Zr isobar collisions at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV, integrated for $p_{\mathrm{T,jet}}^{\mathrm{ch}} > 5$ GeV/$c$, as a function of the number of participating nucleons ($N_{\text{part}}$), from peripheral to central (left to right).