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Measurement of $J/\psi$ production in $pp$ collisions at $\sqrt{s}$ = 7 TeV

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Abstract

The production of J/psi mesons in proton-proton collisions at sqrt(s)=7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/psi production is measured as a function of the J/psi transverse momentum pT and rapidity y in the fiducial region 0<pT<14 GeV/c and 2.0<y<4.5. The differential cross-section and fraction of J/psi from b-hadron decays are also measured in the same pT and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2pb-1. The measured cross-sections integrated over the fiducial region are 10.52 +/- 0.04 +/- 1.40 +1.64/-2.20 mub for prompt J/psi production and 1.14 +/- 0.01 +/- 0.16 mub for J/psi from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/psi production cross-section is obtained assuming no J/psi polarisation and the third error indicates the acceptance uncertainty due to this assumption.

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Dimuon mass distribution ({\it left}) and $t_z$ distribution ({\it right}), with fit results superimposed, for one bin ($3 < p_{\rm T} <4\,\,\mathrm{GeV}\mskip -2mu/\mskip -1mu c$,\,$2.5<y<3.0$). On the mass distribution, the {\it solid red line} is the total fit function, where the signal is described by a Crystal Ball function, and the {\it dashed blue line} represents the exponential background function. On the $t_z$ distribution, the {\it solid red line} is the total fit function described in the text, the {\it green dashed line} is the $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ contribution, the {\it single-hatched area} is the background component and the {\it cross-hatched area} is the tail contribution.

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Total $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ efficiency, as a function of $ p_{\rm T}$ in bins of $y$ assuming that $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ are produced unpolarised. The efficiency is seen to drop somewhat at the edges of the acceptance.

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Differential production cross-section for prompt $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ as a function of $ p_{\rm T}$ in bins of $y$ , assuming that $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ are produced unpolarised. The errors are the quadratic sums of the statistical and systematic uncertainties.

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Differential production cross-section for $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ as a function of $ p_{\rm T}$ in bins of $y$. The errors are the quadratic sums of the statistical and systematic uncertainties.

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Differential production cross-section for $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ as a function of $ p_{\rm T}$ in bins of $y$, assuming full transverse ({\it left}) or full longitudinal ({\it right}) $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ polarisation. The errors are the quadratic sums of the statistical and systematic uncertainties.

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Differential production cross-section as a function of $y$ integrated over $ p_{\rm T}$ , for unpolarised $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ ({\it left}) and $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ ({\it right}). The errors are the quadratic sums of the statistical and systematic uncertainties.

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Fraction of $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ as a function of $ p_{\rm T}$ , in bins of $y$.

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Comparison of the LHCb results for the differential prompt $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ production for unpolarised $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ ({\it circles with error bars}) with: ({\it top, left}) {\it direct} $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ production as predicted by LO and NLO NRQCD; ({\it top, right}) {\it direct} $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ production as predicted by NLO and NNLO$\star$ CSM; ({\it bottom, left}) {\it prompt} $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ production as predicted by NLO NRQCD; ({\it bottom, right}) {\it prompt} $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ production as predicted by NLO CEM. A more detailed description of the models and their references is given in the text.

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Comparison of the LHCb results for the differential $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ production for unpolarised $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ ({\it circles with error bars}) with $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ production as predicted by FONLL ({\it hatched orange uncertainty band}). A more detailed description of the model and its references is given in the text.

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Animated gif made out of all figures.

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Tables and captions

Summary of systematic uncertainties.

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Mean $ p_{\rm T}$ and RMS for $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ (assumed unpolarised) and $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ . The first uncertainty is statistical, the second systematic and the third for $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ the uncertainty due to the unknown polarisation.

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$\frac{{\rm d}\sigma}{{\rm d}y}$ in nb for $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ (assumed unpolarised) and $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ , integrated over $ p_{\rm T}$ . The first uncertainty is statistical, the second is the component of the systematic uncertainty that is uncorrelated between bins and the third is the correlated component.

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$\frac{{\rm d}^2\sigma}{{\rm d}p_{\rm T}{\rm d}y}$ in nb/( $\,\mathrm{GeV}\mskip -2mu/\mskip -1mu c$ ) for prompt $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ in bins of the $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ transverse momentum and rapidity, assuming no polarisation. The first error is statistical, the second is the component of the systematic uncertainty that is uncorrelated between bins and the third is the correlated component.

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$\frac{{\rm d}^2\sigma}{{\rm d}p_{\rm T}{\rm d}y}$ in nb/( $\,\mathrm{GeV}\mskip -2mu/\mskip -1mu c$ ) for $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ in bins of the $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ transverse momentum and rapidity. The first error is statistical, the second is the component of the systematic uncertainty that is uncorrelated between bins and the third is the correlated component.

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$\frac{{\rm d}^2\sigma}{{\rm d}p_{\rm T}{\rm d}y}$ in nb/( $\,\mathrm{GeV}\mskip -2mu/\mskip -1mu c$ ) for prompt $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ in bins of the $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ transverse momentum and rapidity, assuming fully transversely polarised $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ . The first error is statistical, the second is the component of the systematic uncertainty that is uncorrelated between bins and the third is the correlated component.

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$\frac{{\rm d}^2\sigma}{{\rm d}p_{\rm T}{\rm d}y}$ in nb/( $\,\mathrm{GeV}\mskip -2mu/\mskip -1mu c$ ) for prompt $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ in bins of the $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ transverse momentum and rapidity, assuming fully longitudinally polarised $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ . The first error is statistical, the second is the component of the systematic uncertainty that is uncorrelated between bins and the third is the correlated component.

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Fraction of $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu \mathrm{from} b$ (in %) in bins of the $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ transverse momentum and rapidity. The first uncertainty is statistical, the second systematic (uncorrelated between bins) and the third is the uncertainty due to the unknown polarisation of the $\mathrm{prompt} J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ ; the central values are for unpolarised $ J\mskip -2.5mu/\mskip -1mu\psi\mskip 1mu$ .

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