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Measurement of $\Upsilon$ production in $pp$ collisions at $\sqrt{s}=2.76$ TeV

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Abstract

The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons decaying into the dimuon final state is studied with the LHCb detector using a data sample corresponding to an integrated luminosity of 3.3 pb^{-1} collected in proton-proton collisions at a centre-of-mass energy of sqrt{s}=2.76 TeV. The differential production cross-sections times dimuon branching fractions are measured as functions of the Upsilon transverse momentum and rapidity, over the ranges p_T<15 GeV/c and 2.0<y<4.5. The total cross-sections in this kinematic region, assuming unpolarised production, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S) -> mu+mu-) = 1.111 +/- 0.043 +/- 0.044 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S) -> mu+mu-) = 0.264 +/- 0.023 +/- 0.011 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S) -> mu+mu-) = 0.159 +/- 0.020 +/- 0.007 nb, where the first uncertainty is statistical and the second systematic.

Figures and captions

Invariant mass distribution of selected $\Upsilon \rightarrow \mu ^+\mu ^- $ candidates with $ p_{\rm T} <15 {\mathrm{ Ge V /}c} $ and $2.0<y<4.5$. The result of the fit described in the text is illustrated with a red solid line, while the signal and background components are shown with magenta dotted and blue dashed lines, respectively. The three peaks correspond to the $\Upsilon(1\mathrm{S}) $, $\Upsilon(2\mathrm{S}) $ and $\Upsilon(3\mathrm{S}) $ mesons (from left to right).

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Differential cross-sections for $\Upsilon(1\mathrm{S})$ , $\Upsilon(2\mathrm{S})$ and $\Upsilon(3\mathrm{S})$ mesons times dimuon branching fractions as functions of $p_{\rm T}$ (left) and $y$ (right). The inner error bars indicate the statistical uncertainty, while the outer error bars indicate the sum of statistical and systematic uncertainties in quadrature. The next-to-leading order non-relativistic QCD predictions [18] are shown by the solid yellow band.

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Ratios of the $\Upsilon(2\mathrm{S}) $ to $\Upsilon(1\mathrm{S}) $ and $\Upsilon(3\mathrm{S}) $ to $\Upsilon(1\mathrm{S}) $ cross-sections times dimuon branching fractions as functions of $p_{\rm T}$ and $y$. The error bars indicate the total uncertainties of the results obtained by adding statistical and systematic uncertainties in quadrature.

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Animated gif made out of all figures.

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Tables and captions

Relative systematic uncertainties (in $\%$) affecting the \Upsilon production cross-section measurements in the full kinematic region. The total uncertainties are obtained by adding the individual effects in quadrature.

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Cross-sections for $\Upsilon(1\mathrm{S})$ , $\Upsilon(2\mathrm{S})$ and $\Upsilon(3\mathrm{S})$ mesons times dimuon branching fractions (in $\rm nb$ ) in bins of $p_{\rm T}$ and $y$ without normalisation to the bin sizes. The first uncertainty is statistical and the second is systematic.

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Ratios of the $\Upsilon(2\mathrm{S}) $ to $\Upsilon(1\mathrm{S}) $ and $\Upsilon(3\mathrm{S}) $ to $\Upsilon(1\mathrm{S}) $ cross-sections times dimuon branching fractions as functions of $p_{\rm T}$ and $y$. The first uncertainty is statistical and the second is systematic.

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Created on 26 April 2024.