Selection bias effects on high-$p_\mathrm{T}$ yield and correlation measurements in Oxygen+Oxygen collisions

TL;DR

The paper assesses how centrality-selection biases influence measurements of high-$p_\mathrm{T}$ yields and correlations in intermediate-sized Oxygen+Oxygen collisions at RHIC and the LHC. Using Hijing and Angantyr MC generators, it quantifies bias factors across centrality definitions ($N_\mathrm{ch}$ and $\Sigma E_\mathrm{T}$) and observables (hadron yields, jet yields, and hadron-triggered recoil-jet correlations), disentangling multiplicity effects from direct jet contributions. Key findings show sizable biases (up to 20–30%) for yields that depend on energy, centrality, and kinematics, with a stronger bias at the LHC and a weaker dependence for correlation observables, which remain close to unity. The results offer practical guidance for experimental design and interpretation of O+O jet-quenching measurements, highlighting the importance of centrality definition choice and the potential value of correlation-based observables to mitigate bias.

Abstract

Oxygen+Oxygen (O+O) collisions at RHIC and the LHC offer a unique experimental opportunity to observe the onset of jet quenching in intermediate relativistic collision systems. As with the smaller proton-nucleus or larger nucleus-nucleus systems, measurements of centrality-selected high-$p_\mathrm{T}$ processes in O+O collisions are expected to be sensitive to selection bias effects, which will be necessary to quantify or mitigate before a definitive conclusion on the presence of jet quenching. Using two Monte Carlo heavy-ion event generators, we provide a survey of centrality bias effects on high-$p_\mathrm{T}$ yield and correlation measurements. Some highlights of our findings include that (1) bias factors for the accessible kinematic range at RHIC show a non-trivial $p_\mathrm{T}$ dependence, compared to a negligible one at the LHC given the smaller accessible Bjorken-$x$ range, (2) centrality definitions based on multiplicity are less sensitive to bias effects than those based on the transverse energy, (3) the Angantyr generator gives qualitatively similar but larger-magnitude bias factors than HIJING, and (4) correlation measurements have a much smaller sensitivity to bias effects than do yield measurements. The findings here are intended to guide the experimental design and interpretation of O+O jet quenching and other hard-process measurements.

Figures (12)

• Figure 1: $N_\mathrm{coll}$ distributions in centrality-selected O+O events in the Angantyr heavy-ion event generator. Results are shown for RHIC with a forward charged-particle multiplicity-based definition, $N_\mathrm{ch}$.
• Figure 2: Centrality bias factors for charged-hadron yield measurements as a function of $p_\mathrm{T}$ in O+O collisions at RHIC, determined in Angantyr, using the $N_\mathrm{ch}$-based centrality definition. The different colors represent different selected centrality intervals.
• Figure 3: Centrality bias factors for charged-jet yield measurements as a function of $p_\mathrm{T}$ in O+O collisions at RHIC, determined in Angantyr, using the $N_\mathrm{ch}$-based centrality definition. The different colors represent different selected centrality intervals.
• Figure 4: Centrality bias factors for charged-hadron yield measurements as a function of $p_\mathrm{T}$ in O+O collisions at RHIC, determined in Hijing, using the $N_\mathrm{ch}$-based centrality definition. The different colors represent different selected centrality intervals.
• Figure 5: Centrality bias factors for charged-hadron yield measurements as a function of $p_\mathrm{T}$ in O+O collisions at RHIC, determined in Angantyr, using the $\Sigma{E}_{T}$-based centrality definition. The different colors represent different selected centrality intervals.