Jet hadrochemistry as a characteristics of jet quenching

TL;DR

This paper proposes jet hadrochemistry as a novel observable of jet quenching in heavy-ion collisions. It establishes a vacuum baseline using MLLA+LPHD for intrajet spectra and introduces a simple medium-modification model that enhances parton splitting, predicting softer jet distributions and increased heavy-hadron content within jets. It then embeds jets into a high-multiplicity underlying event modeled by recombination and fragmentation, and shows that jet hadrochemistry signals—especially enhanced K/pi and p/pi ratios—persist above the background, quantified by a jet modification factor J_AA. The work provides a baseline framework for interpreting hadrochemical changes in LHC Pb-Pb data and offers a concrete observable to probe the microscopic mechanisms of parton energy loss and medium response.

Abstract

Jets produced in nucleus-nucleus collisions at the LHC are expected to be strongly modified due to the interaction of the parton shower with the dense QCD matter. Here, we point out that jet quenching can leave signatures not only in the longitudinal and transverse jet energy and multiplicity distributions, but also in the hadrochemical composition of the jet fragments. In particular, we show that even in the absence of medium effects at or after hadronization, the medium-modification of the parton shower can result in significant changes in jet hadrochemistry. We discuss how jet hadrochemistry can be studied within the high-multiplicity environment of nucleus-nucleus collisions at the LHC.

Figures (7)

• Figure 1: Sketch of an entirely gluonic parton shower in the large $N_c$ limit, where gluons are represented as pairs of $q\bar{q}$ fermion lines, and quarks as single lines. (a) Fragmentation of the gluon in the vacuum. (b) Interaction of the gluon with a target quark in the medium via a single gluon exchange. This interaction changes the color flow and may affect hadronization, see text.
• Figure 2: Two examples for the comparison of the MLLA+LPHD formalism with data on single inclusive spectra inside a jet as a function of the logarithm of the hadron momentum fraction $\xi$. a) The distribution (\ref{['2.4']}) of charged pions ($\pi^++\pi^-$), kaons ($K^++K^-$) and (anti)-protons ($p+\bar{p}$) in a jet of energy $E_{\rm jet} = 14.5$ GeV, compared to TPC data on $e^+e^-$ collisions Aihara:1983ic. The MLLA parameters are $\Lambda = 155$ MeV and $K_{ \rm LPHD} = 1.22$. b) The MLLA+LPHD distribution of all charged hadrons in a jet of energy $E_{\rm jet} = 108$ GeV for various opening angles $\Theta_c$, compared to CDF data from $p\bar{p}$ collisions Acosta:2002gg. The MLLA parameters are $\Lambda = Q_0 = 235$ MeV, $K_{ \rm LPHD} = 0.555$.
• Figure 3: Medium modification of the single inclusive spectra inside a jet as a function of the logarithm of the hadron momentum fraction $\xi$ for $f_{\rm med} = 1$. a) Distributions of all charged particles in the jet of energy $E_{\rm jet} = 108$ GeV for various opening angles $\Theta_c$. b) Expected modification of the pion, kaon and proton spectra in the jet of energy $E_{\rm jet} = 14.5$ GeV and opening angle $\Theta_c = \pi/2$.
• Figure 4: Results of the MLLA+LPHD formalism for $K^{\pm}/\pi^{\pm}$ and $p(\bar{p})/\pi^{\pm}$ ratios in jets with energies $E_{\rm jet} =$ 50, 100 and 200 GeV. The jet opening angle is $\Theta_c = 0.28$ and medium-induced changes are calculated for $f_{\rm med} = 1$.
• Figure 5: Identified transverse momentum spectra within a cone of opening angle $\Theta_c=0.28$ for pions, kaons and protons.