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Prompt charm production in $pp$ collisions at $\sqrt{s}$ = 7 TeV

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Abstract

Charm production at the LHC in pp collisions at sqrt(s)=7 TeV is studied with the LHCb detector. The decays D0 -> K- pi+, D+ -> K- pi+ pi+, D*+ -> D0(K- pi+) pi+, D_s+ -> phi(K- K+) pi+, Lambda_c+ -> p K- pi+, and their charge conjugates are analysed in a data set corresponding to an integrated luminosity of 15 nb^{-1}. Differential cross-sections dsigma/dp_T are measured for prompt production of the five charmed hadron species in bins of transverse momentum and rapidity in the region 0 < p_T < 8 GeV/c and 2.0 < y < 4.5. Theoretical predictions are compared to the measured differential cross-sections. The integrated cross-sections of the charm hadrons are computed in the above p_T-y range, and their ratios are reported. A combination of the five integrated cross-section measurements gives sigma(c\bar{c})_{p_T < 8 GeV/c, 2.0 < y < 4.5} = 1419 +/- 12 (stat) +/- 116 (syst) +/- 65 (frag) microbarn, where the uncertainties are statistical, systematic, and due to the fragmentation functions.

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Mass and $\log_{10}(\mathrm{IP} \,\chi^2 )$ distributions for selected $ D ^0 \!\rightarrow K ^- \pi ^+ $ and $ D ^+ \!\rightarrow K ^- \pi ^+ \pi ^+ $ candidates showing \subref{fig:Dz:m:m} the masses of the $ D ^0$ candidates, \subref{fig:Dz:m:ip} the $\log_{10}(\mathrm{IP} \,\chi^2 )$ distribution of $ D ^0$ candidates for a mass window of $\pm 16 {\mathrm{\,MeV\!/}c^2} $ (approximately $\pm 2\sigma$) around the fitted $m( K ^- \pi ^+ )$ peak, \subref{fig:Dp:m:m} the masses of the $ D ^+$ candidates, and \subref{fig:Dp:m:ip} the $\log_{10}(\mathrm{IP} \,\chi^2 )$ distribution of $ D ^+$ candidates for a mass window of $\pm 11 {\mathrm{\,MeV\!/}c^2} $ (approximately $\pm 2\sigma$) around the fitted $m( K ^- \pi ^+ \pi ^+ )$ peak. Projections of likelihood fits to the full data samples are shown with components as indicated in the legends. \label{fig:Dp:m}

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Mass and $\log_{10}(\mathrm{IP} \,\chi^2 )$ distributions for selected $ D ^{*+} \!\rightarrow D ^0 ( K ^- \pi ^+ ) \pi ^+ $ candidates showing \subref{fig:Dstarp:m:mkpi} the masses of the $ D ^0$ candidates for a window of $\pm 1.6 {\mathrm{\,MeV\!/}c^2} $ (approximately $\pm 2\sigma$) around the fitted $\Delta m $ peak, \subref{fig:Dstarp:m:delm} the differences between the $ D ^{*+}$ and $ D ^0$ candidate masses for a mass window of $\pm 16 {\mathrm{\,MeV\!/}c^2} $ (approximately $\pm 2\sigma$) around the fitted $m( K ^- \pi ^+ )$ peak, and \subref{fig:Dstarp:m:ip} the $\log_{10}(\mathrm{IP} \,\chi^2 )$ distribution of the $ D ^0$ candidate for a mass signal box of $\pm 16 {\mathrm{\,MeV\!/}c^2} $ around the fitted $m( K ^- \pi ^+ )$ peak and $\pm 1.6 {\mathrm{\,MeV\!/}c^2} $ around the fitted $\Delta m $ peak. Projections of a likelihood fit to the full data sample are shown with components as indicated in the legend. The ` $ D ^0$ backgrounds' component is the sum of the secondary, prompt random slow pion, and secondary random slow pion backgrounds.

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Mass and $\log_{10}(\mathrm{IP} \,\chi^2 )$ distributions for selected $ D ^+_ s \!\rightarrow \phi ( K ^- K ^+ ) \pi ^+ $ and $\Lambda _ c ^+ \!\rightarrow p K ^- \pi ^+ $ candidates showing \subref{fig:Ds:m:m} the masses of the $ D ^+_ s $ candidates, \subref{fig:Ds:m:ip} the $\log_{10}(\mathrm{IP} \,\chi^2 )$ distribution of $ D ^+_ s $ candidates for a mass window of $\pm 8 {\mathrm{\,MeV\!/}c^2} $ (approximately $\pm 2\sigma$) around the fitted $m(\phi ( K ^- K ^+ )\pi ^+ )$ peak, \subref{fig:Lcp:m:m} the masses of the $\Lambda _ c ^+$ candidates, and \subref{fig:Lcp:m:ip} the $\log_{10}(\mathrm{IP} \,\chi^2 )$ distribution of $\Lambda _ c ^+$ candidates for a mass window of $\pm 12 {\mathrm{\,MeV\!/}c^2} $ (approximately $\pm 2\sigma$) around the fitted $m( p K ^- \pi ^+ )$ peak. Projections of likelihood fits to the full data samples are shown with components as indicated in the legends. \label{fig:Lcp:m}

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Differential cross-sections for \subref{fig:lhcb:Dz:a} $ D ^0$ , \subref{fig:lhcb:Dp:b} $ D ^+$ , \subref{fig:lhcb:dstar:a} $ D ^{*+}$ , and \subref{fig:lhcb:Dsp:b} $ D ^+_ s $ meson production compared to theoretical predictions. The cross-sections for different $y$ regions are shown as functions of $p_{\rm T}$ . The $y$ ranges are shown as separate curves and associated sets of points scaled by factors $10^{-m}$, where the exponent $m$ is shown on the plot with the $y$ range. The error bars associated with the data points show the sum in quadrature of the statistical and total systematic uncertainty. The shaded regions show the range of theoretical uncertainties for the GMVFNS prediction. \label{fig:lhcb:Dp} \label{fig:lhcb:dstar} \label{fig:lhcb:Dsp}

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Differential cross-sections for $\Lambda _ c ^+$ baryon production compared to the theoretical prediction from the GMVFNS scheme. The error bars associated with the data points show the sum in quadrature of the statistical and total systematic uncertainty. The shaded region shows the range of theoretical uncertainty for the theoretical prediction.

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Tables and captions

Overview of systematic uncertainties and their values, expressed as relative fractions of the cross-section measurements in percent (%). Uncertainties that are computed bin-by-bin are expressed as ranges giving the minimum to maximum values of the bin uncertainties. The correlated and uncorrelated uncertainties are shown as discussed in the text.

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Open charm production cross-sections in the kinematic range $ 0 < p_{\rm T} < 8 {\mathrm{\,GeV\!/}c} $ and $ 2.0 < y < 4.5$ . The computation of the extrapolation factors is described in the text. The first uncertainty is statistical, the second is systematic, and the third is the contribution from the extrapolation factor.

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Correlation matrix of the uncertainties of the integrated open charm production cross-sections in the kinematic range $ 0 < p_{\rm T} < 8 {\mathrm{\,GeV\!/}c} $ and $ 2.0 < y < 4.5$ . The first column restates measured values of the integrated cross-sections .

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Cross-section ratios for open charm production in the kinematic range $ 0 < p_{\rm T} < 8 {\mathrm{\,GeV\!/}c} $ and $ 2.0 < y < 4.5$ . The numbers in the table are the ratios of the respective row/column.

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Bin-integrated production cross-sections in $ {\rm \,\upmu b}$ for prompt $\Lambda _ c ^+$ $+$ c.c. baryons in bins of $y$ integrated over the range $2 < p_{\rm T} < 8 {\mathrm{\,GeV\!/}c} $. The first uncertainty is statistical, and the second is the total systematic.

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Differential production cross-sections , $\mathrm{d}\hspace{-0.1em}\sigma/\mathrm{d} p_{\rm T} $ , in $ {\rm \,\upmu b} /( {\mathrm{GeV\!/}c} )$ for prompt $\Lambda _ c ^+$ $+$ c.c. baryons in bins of $ p_{\rm T} $ integrated over the rapidity range $ 2.0 < y < 4.5$ . The first uncertainty is statistical, and the second is the total systematic.

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Supplementary Material [file]

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2012-041. The files are: LHCb-PAPER-2012-041-Supplementary.pdf : Description of and results from cross-check analyses. Table_*_XSec.hepdata.txt : Flat text files of the tables of differential cross-sections in LHCb-PAPER-2012-041. These are formatted to ease importing the measurements into the Reactions Database of the Durham HepData Project.

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Created on 11 December 2018.Citation count from INSPIRE on 11 December 2018.