The measurement of the transverse-momentum fraction ($z^{ \rm ch}$) carried by prompt and non-prompt J/$\psi$ in charged-particle jets in proton--proton collisions with a center-of-mass energy $\sqrt{ s}= 13$ TeV is reported by the ALICE Collaboration at the CERN Large Hadron Collider. The measurement is based on a Transition Radiation Detector triggered data sample corresponding to an integrated luminosity of $\mathcal{ L} = 1.63\pm0.03$ pb$^{ -1}$. Inclusive J/$\psi$ mesons with transverse momentum ($p_{ \rm T}$) above 1 GeV/$c$ are reconstructed at midrapidity through the electron--positron decay channel. The prompt and non-prompt J/$\psi$ contributions are separated using the secondary vertices from beauty-hadron decays. Jets are reconstructed from J/$\psi$-meson candidates and charged particles using the anti-$k_{ \rm T}$ algorithm with jet resolution parameter $R = 0.4$ in the pseudorapidity range $|\eta_{ \text{ jet}}| < 0.5$. The distribution of the charged-particle jet $p_{ \rm T}$ fraction carried by the prompt and non-prompt J/$\psi$ mesons, $z^{ \rm ch}$, is measured in the range $0.3 < z^{ \rm ch} \leq 1.0$ for the jet-$ p_{ \rm T}$ range $7 < p_{ \rm T}^{ \rm jet} < 15$ GeV/$c$. The measured $z^{ \rm ch}$ distributions for prompt and non-prompt J/$\psi$ are compared to pQCD calculations and PYTHIA 8 simulations. Prompt and non-prompt J/$\psi$ production within charged-particle jets are found to be qualitatively well reproduced by PYTHIA 8 for $z^{ \rm ch}<0.9$, however, as $z^{ \rm ch}$ approaches one, the simulations overshoot the measured data, indicating an overestimation of the fraction of isolated J/$\psi$. This observed tension between data and simulations in the highest $z^{ \rm ch}$ bins reflects the challenge of simulating hadronization of low-momentum jets.
Categories: hep-ex nucl-ex