ZYAM and $\bf v_2$: Underestimating jet yields from dihadron azimuth correlations

TL;DR

This paper critically examines the ZYAM method and elliptic flow measurements in dihadron azimuth correlations, revealing that both are overestimated, which leads to significant underestimation of jet yields and misinterpretation of jet-related phenomena in nuclear collisions.

Contribution

The study demonstrates that the ZYAM background subtraction method and conventional $v_2^2$ measurements are invalid, causing underestimation of jet yields in heavy-ion collisions.

Findings

ZYAM overestimates the background offset.

Conventional $v_2^2$ measurements overestimate elliptic flow.

Jet yields in central collisions are substantially underestimated.

Abstract

Dihadron azimuth correlations can provide combinatoric access to jet structure in nuclear collisions. To isolate true jet yields a background must be subtracted, including a constant offset and a contribution from "elliptic flow" (azimuth quadrupole measured by $v^2_2$). The principle of "zero yield at minimum" (ZYAM) has been introduced to determine the constant offset. Independent measurements determine $v_2^2$. This analysis demonstrates that the ZYAM concept is invalid (offset typically overestimated) and $v_2^2$ is also overestimated by conventional measurements. Jet yields are thus substantially underestimated in more-central A-A collisions, and the "away-side" azimuth peak (back-to-back jet correlations) is strongly distorted, leading to incorrect inference of "Mach shocks."