This paper presents the first measurement of the angle between different jet axes (denoted as Delta R-axis) in Pb-Pb collisions. The measurement is carried out in the 0-10% most-central events at root s(NN) = 5.02 TeV. Jets are assembled by clustering charged particles at midrapidity using the anti-kT algorithm with resolution parameters R = 0.2 and 0.4 and transverse momenta in the intervals 40 < p(T)(ch jet) < 140 GeV/c and 80 < p(T)(ch jet) < 140 GeV/c, respectively. Measurements at these low transverse momenta enhance the sensitivity to quark-gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP suggests that the observed narrowing of the Pb-Pb distribution relative to pp can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements disfavor intrajet p(T) broadening as implemented in a simple model calculation with the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism for energy loss in the QGP. The comparison of Pb-Pb and pp collisions shows sensitivity to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.
Measurement of the angle between jet axes in Pb-Pb collisions at sqrt(sNN) = 5.02 TeV
La Rocca, P.;Rasa, M.;
2026-01-01
Abstract
This paper presents the first measurement of the angle between different jet axes (denoted as Delta R-axis) in Pb-Pb collisions. The measurement is carried out in the 0-10% most-central events at root s(NN) = 5.02 TeV. Jets are assembled by clustering charged particles at midrapidity using the anti-kT algorithm with resolution parameters R = 0.2 and 0.4 and transverse momenta in the intervals 40 < p(T)(ch jet) < 140 GeV/c and 80 < p(T)(ch jet) < 140 GeV/c, respectively. Measurements at these low transverse momenta enhance the sensitivity to quark-gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP suggests that the observed narrowing of the Pb-Pb distribution relative to pp can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements disfavor intrajet p(T) broadening as implemented in a simple model calculation with the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism for energy loss in the QGP. The comparison of Pb-Pb and pp collisions shows sensitivity to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.


