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${{J}/\psi }$ and ${{D}} ^0$ production in $\sqrt{s_{\scriptscriptstyle \text {NN}}} =68.5 \text {GeV} $ PbNe collisions

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Abstract

The first measurement of $J/\psi$ and $D^0$ production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of $J/\psi$ and $D^0$ mesons is studied with a beam of lead ions with an energy of 2.5 TeV per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\rm NN}}$ = 68.5 GeV. The $J/\psi/D^0$ production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from $p$Ne collisions at the same energy and show no difference in the observed $J/\psi$ suppresion trend when comparing $p$Ne and PbNe peripheral collisions with PbNe central collisions.

Figures and captions

Mass distributions of (left) $ { J \mskip -3mu/\mskip -2mu\psi } \rightarrow \mu ^- \mu ^+ $ and (right) $ D ^0 \rightarrow K ^\mp \pi ^\pm $ candidates. The data are overlaid with the fit function.

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Ratios of $ { J \mskip -3mu/\mskip -2mu\psi }$ to $ D ^0$ cross-sections as a function of (left) $y^\star$ and (right) transverse momentum. The error bars represent uncertainties that are uncorrelated bin-to-bin while the boxes represent the correlated uncertainties.

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Left: $ { J \mskip -3mu/\mskip -2mu\psi }$ / $ D ^0$ cross-section ratio as a function of $AB$, the product of the beam ($A$) and target ($B$) atomic mass numbers; the error bars represent the quadratic sum of statistical and systematic uncertainties. Right: $ { J \mskip -3mu/\mskip -2mu\psi }$ / $ D ^0$ cross-section ratio as a function of $ N_{\mathrm{coll}}$ ; the error bars represent the quadratic sum of statistical and uncorrelated systematic uncertainties while the boxes correspond to the correlated systematic uncertainty. The red and black points correspond to $ p\text{Ne}$ [22] and PbNe collisions, respectively.

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Animated gif made out of all figures.

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Tables and captions

Summary of the systematic uncertainties affecting the $ { J \mskip -3mu/\mskip -2mu\psi }$ / $ D ^0$ production ratio. Those that are correlated between bins affect all measurements by the same relative amount. Ranges denote the minimum and the maximum values among the $y$, $ p_{\mathrm{T}}$ or hit multiplicity bins.

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The mapping from intervals of the hit multiplicity to intervals of $ N_{\mathrm{coll}}$ ; $\langle N_{\mathrm{coll}}\rangle$ and RMS( $ N_{\mathrm{coll}}$ ) correspond to the $ N_{\mathrm{coll}}$ distribution mean and root mean square values respectively.

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Created on 23 March 2024.