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Prompt $\Lambda^+_c$ production in $p\mathrm{Pb}$ collisions at $\sqrt{s_{NN}} = 5.02$ TeV

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Abstract

The production of $\Lambda^+_c$ baryons produced directly at the interacting point is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of $1.58\mathrm{nb}^{-1}$ recorded at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV. Measurements of the differential cross-section and the forward-backward production ratio are reported for $\Lambda^+_c$ baryons with transverse momenta in the range $2<p_{T}<10$GeV/$c$ and rapidities in the ranges $1.5<y^*<4.0$ and $-4.5<y^*<-2.5$ in the nucleon-nucleon centre-of-mass system. The ratio of cross-sections of $\Lambda^+_c$ baryons and $D^0$ mesons is also reported. The results are compared with next-to-leading order calculations that use nuclear parton distribution functions.

Figures and captions

Distributions of the invariant mass, $m( p K ^- \pi ^+ )$, in the range $2< p_{\mathrm{ T}} <10 {\mathrm{\,GeV\!/}c} $ for (a) the forward data sample with $1.5<y^*<4.0$ and (b) the backward data sample with $-4.5<y^*<-2.5$. The red dotted line is the inclusive $\Lambda ^+_ c $ candidates, the grey shaded area is the combinatorial background and the blue solid line is the sum of the two.

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Distributions of $\log_{10}\chi^2_{\text{IP}} (\Lambda ^+_ c ) $ in the range $2< p_{\mathrm{ T}} <10 {\mathrm{\,GeV\!/}c} $ with the fit results overlaid for (a) the forward data sample with $1.5<y^*<4.0$, and (b) the backward data sample with $-4.5<y^*<-2.5$. The solid blue curve is the sum. The red dotted line is the prompt component, the green is the $\Lambda ^+_ c \mathrm{\text{-}from\text{-}} b $ component and the grey shaded area denotes the combinatorial background.

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Double-differential cross-section of prompt $\Lambda ^+_ c $ baryons in $ p\mathrm{Pb} $ collisions in the (a) forward and (b) backward collision samples. The uncertainty represents the quadratic sum of the statistical and the systematic uncertainties.

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Differential cross-section of prompt $\Lambda ^+_ c $ baryons in $ p\mathrm{Pb} $ collisions as a function of (a) $ p_{\mathrm{ T}} $ and (b) $y^{*}$ in the forward and backward samples. The forward and backward differential cross-sections $\mathrm{d}\sigma/\mathrm{d} p_{\mathrm{ T}} $ in the common rapidity region $2.5<|y^*|<4.0$ are scaled by 0.1 to improve the visibility. The uncertainty represents the quadratic sum of the statistical and the systematic uncertainties.

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(a) Forward-backward production ratios $R_\mathrm{FB}$ as a function of $ p_{\mathrm{ T}} $ integrated over $2.5<|y^*|<4.0$ for $ p_{\mathrm{ T}} $ less than $7 {\mathrm{\,GeV\!/}c} $ and $2.5<|y^*|<3.5$ for $ p_{\mathrm{ T}} $ greater than $7 {\mathrm{\,GeV\!/}c} $, and (b) $R_\mathrm{FB}$ as a function of $y^*$ integrated over $2< p_{\mathrm{ T}} <10 {\mathrm{\,GeV\!/}c} $. The uncertainty represents the quadratic sum of the statistical and the systematic uncertainties.

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The cross-section ratio $ R_{\Lambda ^+_ c / D ^0 }$ between $\Lambda ^+_ c $ baryons and $ D ^0$ mesons as a function of $ p_{\mathrm{ T}} $ integrated over four different rapidity regions. The uncertainty represents the sum in quadrature of the statistical and the systematic uncertainties. The coloured curves represent HELAC-Onia calculations with nPDF EPS09LO/NLO and nCTEQ15.

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The cross-section ratio $ R_{\Lambda ^+_ c / D ^0 }$ between $\Lambda ^+_ c $ baryons and $ D ^0$ mesons as a function of $y^*$ integrated over $2< p_{\mathrm{ T}} <10 {\mathrm{\,GeV\!/}c} $. The uncertainty represents the sum in quadrature of the statistical and the systematic uncertainties. The coloured curves show HELAC-Onia calculations incorporating nPDFs EPS09LO/NLO and nCTEQ15.

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Tables and captions

Systematic and statistical uncertainties for the differential cross-sections. The ranges indicate the variation over the ($ p_{\mathrm{ T}} , y^*$) bins.

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Measured differential cross-section (in $\mathrm{ \,mb} /( {\mathrm{\,GeV\!/}c} )$) of prompt $\Lambda ^+_ c $ baryons as a function of $ p_{\mathrm{ T}} $ in $ p\mathrm{Pb} $ forward and backward data in different rapidity regions. The right column shows the results for $ p_{\mathrm{ T}} > 7 {\mathrm{\,GeV\!/}c} $ and $2.5<|y^*|<3.5$, which are used to compute the $ R_\mathrm{FB} $ values at $ p_{\mathrm{ T}} > 7 {\mathrm{\,GeV\!/}c} $. The first uncertainties are statistical and the second are systematic.

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Differential cross-section (in $\mathrm{ \,mb} $) for prompt $\Lambda ^+_ c $ baryons as a function of $|y^{*}|$ in $ p\mathrm{Pb} $ forward and backward data. The first uncertainties are statistical and the second are systematic.

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Forward-backward prompt $\Lambda ^+_ c $ production ratio $ R_\mathrm{FB} $ as a function of $ p_{\mathrm{ T}} $ in the common range $2.5<|y^*|<4.0$. The first uncertainty is statistical and the second is systematic.

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$ R_\mathrm{FB} $ ratio as a function of $|y^*|$ in the range $2< p_{\mathrm{ T}} <10 {\mathrm{\,GeV\!/}c} $. The first uncertainty is statistical and the second is systematic.

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Production ratio $ R_{\Lambda ^+_ c / D ^0 } $ as a function of $ p_{\mathrm{ T}} $ in the forward and backward rapidity regions. The first uncertainty is statistical and the second is systematic.

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Production ratio $ R_{\Lambda ^+_ c / D ^0 } $ as a function of $y^*$ for $2< p_{\mathrm{ T}} <10 {\mathrm{\,GeV\!/}c} $. The first uncertainty is statistical and the second is systematic.

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.