Measurement of the charged-particle-jet transverse-momentum fraction carried by prompt and non-prompt J/$ψ$ mesons in pp collisions at $\sqrt{s}=13$ TeV

Abstract

The measurement of the transverse-momentum fraction ($z^{\rm ch}$) carried by prompt and non-prompt J/$ψ$ 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/$ψ$ 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/$ψ$ contributions are separated using the secondary vertices from beauty-hadron decays. Jets are reconstructed from J/$ψ$-meson candidates and charged particles using the anti-$k_{\rm T}$ algorithm with jet resolution parameter $R = 0.4$ in the pseudorapidity range $|η_{\text{jet}}| < 0.5$. The distribution of the charged-particle jet $p_{\rm T}$ fraction carried by the prompt and non-prompt J/$ψ$ 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/$ψ$ are compared to pQCD calculations and PYTHIA 8 simulations. Prompt and non-prompt J/$ψ$ 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/$ψ$. This observed tension between data and simulations in the highest $z^{\rm ch}$ bins reflects the challenge of simulating hadronization of low-momentum jets.

Figures (5)

• Figure 1: Invariant-mass (left) and pseudo-proper decay-length (right) distributions for $\text{J}/\psi$ candidates, measured in charged-particle jets with $7<p_{\rm T}^{\text{ch jet}}\xspace<15$ GeemV/$c$, with superimposed projections of the maximum-likelihood fit for the intervals $0.4 < z^{\rm{ch}}\xspace < 0.5$ and $0.90 < z^{\rm{ch}}\xspace < 0.95$ in the top and bottom panels, respectively. The pseudo-proper decay-length distributions are shown for $\text{J}/\psi$ candidates reconstructed in the invariant-mass range $2.92 < m_{\rm e^+e^-}\xspace < 3.16$ GeemV/$c^2$ for display purposes only.
• Figure 2: $\text{J}/\psi$ acceptance and reconstruction efficiency (red cross), TRD trigger efficiency (blue box), and total efficiency (black point) as a function of transverse momentum.
• Figure 3: Detector-response matrix for jets containing a non-prompt $\text{J}/\psi$ meson, representing the bin-migration probability as a function of the jet $p_{\rm T}^{\text{ch jet}}$ and $z^{\rm{ch}}$. The $y$ axis represents the true $z^{\rm{ch}}$ in bins of true $p_{\rm T}^{\text{ch jet}}$, and the $x$ axis shows the measured $z^{\rm{ch}}$ in bins of measured $p_{\rm T}^{\text{ch jet}}$.
• Figure 4: Fully corrected, normalized prompt (left) and non-prompt (right) $\text{J}/\psi$ transverse-momentum fraction ($z^{\rm{ch}}$) measured in jets with $7<p_{\rm T}^{\text{ch jet}}\xspace < 15$ GeemV/$c$ for $p_{\rm T}^{\text{J}/\psi}\xspace > 1$ GeemV/$c$ in pp collisions at $\sqrt{s}~=~13$ TeemV. Measurements are compared to PYTHIA 8.311 calculations obtained using the Monash 2013 tune Skands:2014pea, where $\text{J}/\psi$ are produced directly in parton--parton scatterings (black dotted line) and as a part of a parton shower (green dashed line) Cooke:2023ldt. The prompt-$\text{J}/\psi$ distribution is compared to a model calculation from Zhang and Xing Zhang:2024owrKang:2017yde (cyan box). The error bars represent statistical uncertainties, while the boxes around the data points represent the total systematic uncertainty.
• Figure 5: Comparison of the measured prompt $\text{J}/\psi$ transverse-momentum fraction ($z^{\rm{ch}}$) measured in charged-particle jets with $7<p_{\rm T}^{\text{ch jet}}\xspace < 15$ GeemV/$c$ for $p_{\rm T}^{\text{J}/\psi}\xspace > 1$ GeemV/$c$ in pp collisions at $\sqrt{s}~=~13$ TeemV (red point) with the prompt-$\text{J}/\psi$ transverse-momentum fraction ($z$) measured in full jets with $30<p_{\rm T}^{\text{jet}}\xspace < 40$ GeemV/$c$ for $p_{\rm T}^{\text{J}/\psi}\xspace > 6.5$ GeemV/$c$ in pp collisions at $\sqrt{s}~=~5.02$ TeemV reported by CMS (blue box) CMS:2021puf. The error bars represent statistical uncertainties, while the boxes around the data points represent the total systematic uncertainty.