First Measurement of Charm Production in its Fixed-Target Configuration at the LHC

Information

LHCb-PAPER-2018-023
CERN-EP-2018-266
arXiv:1810.07907 [PDF]

(Submitted on 18 Oct 2018)
Phys. Rev. Lett. 122 (2019) 132002
Inspire 1699199

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Abstract

The first measurement of heavy-flavour production by the LHCb experiment in its fixed-target mode is presented. The production of $J/\psi$ and $D^0$ mesons is studied with beams of protons of different energies colliding with gaseous targets of helium and argon with nucleon-nucleon centre-of-mass energies of $\sqrt{s_{NN}} = 86.6 $ and $ 110.4$ ${\rm GeV}$, respectively. The $J/\psi$ and $D^0$ (including charge conjugate) production cross sections in $p{\rm He}$ collisions in the rapidity range $[2,4.6]$ are found to be $\sigma_{J/\psi} = 652 \pm 33$ (stat) $\pm 42$ (syst) nb$/$nucleon and $\sigma_{D^0} = 80.8 \pm 2.4$ (stat) $\pm 6.3$ (syst) $\mu$b$/$nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-$x$ region.

Figures and captions

Mass distributions, fitted by an extended unbinned maximum-likelihood in $\sqrt{s_{\scriptscriptstyle\rm NN}} =86.6\mathrm{ Ge V} $ $ p\text{He}$ collisions; $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \to\mu ^- \mu ^+ $ (left); $ D ^0 \to K ^- \pi ^+ $ (right). The dashed blue line corresponds to the combinatorial background, the red line to the signal and the solid blue line to the sum of the two.	Fig1a.pdf [17 KiB] HiDef png [198 KiB] Thumbnail [165 KiB] *.C file
	Fig1b.pdf [18 KiB] HiDef png [214 KiB] Thumbnail [184 KiB] *.C file
Left: $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ cross-section measurements as a function of the center-of-mass energy. Experimental data, represented by black points, are taken from Ref. [39]. The band corresponds to a fit based on NLO NRQCD calculations [39]. Right: $c\overline{c}$ cross-section measurements as a function of the center-of-mass energy. Experimental data, represented by black points, are taken from Ref. [40]. The yellow band corresponds to NLO pQCD calculations [41]. Red points correspond to the $ p\text{He}$ results from the present analysis.	Fig2a.pdf [21 KiB] HiDef png [708 KiB] Thumbnail [160 KiB] *.C file
	Fig2b.pdf [21 KiB] HiDef png [1 MiB] Thumbnail [175 KiB] *.C file
Differential $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production cross sections for (top) $ p\text{He}$ and differential $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ yields for (bottom) $ p\text{Ar}$ collisions, as a function of (left) center-of-mass rapidity $y^*$ and (right) transverse momentum $ p_{\mathrm{T}} $. The data points mark the bin centers. The quadratic sum of statistical and uncorrelated systematic uncertainties are indicated by the vertical black lines. The correlated systematic uncertainties are indicated by the grey area. Theoretical predictions are described in the text. The lower panel of each plot shows the ratio of data to HELAC-ONIA $pp$ predictions.	Fig3a.pdf [16 KiB] HiDef png [424 KiB] Thumbnail [276 KiB] *.C file
	Fig3b.pdf [16 KiB] HiDef png [361 KiB] Thumbnail [249 KiB] *.C file
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Differential $ D ^0$ production cross sections for (top) $ p\text{He}$ and differential $ D ^0$ yields for (bottom) $ p\text{Ar}$ collisions, as a function of (left) center-of-mass rapidity $y^*$ and (right) transverse momentum $ p_{\mathrm{T}} $. The data points mark the bin centers. The quadratic sum of statistical and uncorrelated systematic uncertainties are indicated by the vertical black lines. The correlated systematic uncertainties are indicated by the gray area. Theoretical predictions are described in the text. The lower panel of each plot shows the ratio of data to HELAC-ONIA $pp$ predictions.	Fig4a.pdf [16 KiB] HiDef png [353 KiB] Thumbnail [232 KiB] *.C file
	Fig4b.pdf [16 KiB] HiDef png [281 KiB] Thumbnail [214 KiB] *.C file
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Animated gif made out of all figures.	PAPER-2018-023.gif Thumbnail

Tables and captions

Systematic and statistical uncertainties on the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $ D ^0$ yields in $\%$. Systematic uncertainties correlated between bins affect all measurements by the same relative amount. Ranges denote the minimum and the maximum values among the $y$ or $ p_{\mathrm{T}}$ bins.

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Supplementary Material [file]

Supplementary material full pdf	Supple[..].pdf [206 KiB]
This ZIP file contains supplemetary material for the publication LHCb-PAPER-2018-023. The files are: Supplementary.pdf : An overview of the extra figures .pdf, .png, .eps .C : The figures in variuous formats	Fig5a.pdf [15 KiB] HiDef png [169 KiB] Thumbnail [154 KiB] *C file
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