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

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Abstract

The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons in proton-proton collisions at the centre-of-mass energy of sqrt(s)=7 TeV is studied with the LHCb detector. The analysis is based on a data sample of 25 pb-1 collected at the Large Hadron Collider. The Upsilon mesons are reconstructed in the decay mode Upsilon -> mu+ mu- and the signal yields are extracted from a fit to the mu+ mu- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the Upsilon transverse momentum pT and rapidity y, over the range pT < 15 GeV/c and 2.0 < y < 4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S)->mu+ mu-) = 2.29 {\pm} 0.01 {\pm} 0.10 -0.37 +0.19 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S)->mu+ mu-) = 0.562 {\pm} 0.007 {\pm} 0.023 -0.092 +0.048 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S)->mu+ mu-) = 0.283 {\pm} 0.005 {\pm} 0.012 -0.048 +0.025 nb, where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three Upsilon states.

Figures and captions

Invariant mass distribution of the selected $\varUpsilon\rightarrow \mu^+\mu^-$ candidates in the range $ p_{\rm T} <15 {\mathrm{\,GeV\!/}c} $ and $2.0<y<4.5$. The three peaks correspond to the $\varUpsilon(1S)$, $\varUpsilon(2S)$ and $\varUpsilon(3S)$ signals (from left to right). The superimposed curves are the result of the fit as described in the text.

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Total efficiency $\varepsilon$ of the $\varUpsilon(1S)$ as a function of (a) the $\varUpsilon(1S)$ transverse momentum and (b) rapidity, estimated using the Monte Carlo simulation, for three different $\varUpsilon(1S)$ polarisation scenarios, indicated by the parameter $\alpha$ described in the text.

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Double differential ${\varUpsilon\rightarrow \mu^+\mu^-}$ cross-sections times dimuon branching fractions as a function of $p_{\rm T}$ in bins of rapidity for (a) the $\varUpsilon(1S)$, (b) the $\varUpsilon(2S)$ and (c) the $\varUpsilon(3S)$. The error bars correspond to the total uncertainty for each bin.

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Differential $\varUpsilon(1S)\rightarrow\mu^+\mu^-$ production cross-section times dimuon branching fraction as a function of $p_{\rm T}$ integrated over $y$ in the range 2.0--4.5, compared with the predictions from (a) the NNLO* CSM [29] for direct production, and (b) the NLO NRQCD [31] and CEM [14]. The error bars on the data correspond to the total uncertainties for each bin, while the bands indicate the uncertainty on the theory prediction.

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Differential (a) $\varUpsilon(2S)\rightarrow\mu^+\mu^-$ and (b) $\varUpsilon(3S)\rightarrow\mu^+\mu^-$ production cross-sections times dimuon branching fractions as a function of $p_{\rm T}$ integrated over $y$ in the range 2.0--4.5, compared with the predictions from the NNLO* CSM for direct production [29]. The error bars on the data correspond to the total uncertainties for each bin, while the bands indicate the uncertainty on the theory prediction.

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Differential cross-sections of $\varUpsilon(1S),\varUpsilon(2S)$ and $\varUpsilon(3S)$ times dimuon branching fractions as a function of (a) $ p_{\rm T} $ integrated over $y$ and (b) $y$ integrated over $ p_{\rm T} $. The error bars on the data correspond to the total uncertainties for each bin.

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Ratios of $\varUpsilon(2S)\rightarrow\mu^+\mu^-$ and $\varUpsilon(3S)\rightarrow\mu^+\mu^-$ with respect to $\varUpsilon(1S)\rightarrow\mu^+\mu^-$ as a function of $ p_{\rm T} $ of the $\varUpsilon$ in the range $2.0<y<4.5$, assuming no polarisation. The error bars on the data correspond to the total uncertainties for each bin except for that due to the unknown polarisation, which ranges between 15% and 26% as listed in Table 5.

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Animated gif made out of all figures.

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Tables and captions

Summary of the relative systematic uncertainties on the cross-section measurements. Ranges indicate variations depending on the ($ p_{\rm T} ,y$) bin and the $\varUpsilon$ state. All uncertainties are fully correlated among the bins.

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Double differential cross-section $\varUpsilon(1S)\rightarrow\mu^+\mu^-$ as a function of rapidity and transverse momentum, in pb/( $ {\mathrm{\,GeV\!/}c}$ ). The first uncertainty is statistical, the second is systematic, and the third is due to the unknown polarisation of the $\varUpsilon(1S)$.

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Double differential cross-section $\varUpsilon(2S)\rightarrow\mu^+\mu^-$ as a function of rapidity and transverse momentum, in pb/( $ {\mathrm{\,GeV\!/}c}$ ). The first uncertainty is statistical, the second is systematic, and the third is due to the unknown polarisation of the $\varUpsilon(2S)$. Regions where the number of events was not sufficient to perform a measurement are indicated with a dash.

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Double differential cross-section $\varUpsilon(3S)\rightarrow\mu^+\mu^-$ as a function of rapidity and transverse momentum, in pb/( $ {\mathrm{\,GeV\!/}c}$ ). The first uncertainty is statistical, the second is systematic, and the third is due to the unknown polarisation of the $\varUpsilon(3S)$. Regions where the number of events was not sufficient to perform a measurement are indicated with a dash.

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Ratios of cross-sections $\varUpsilon(2S)\rightarrow\mu^+\mu^-$ and $\varUpsilon(3S)\rightarrow\mu^+\mu^-$ with respect to {$\varUpsilon(1S)\rightarrow\mu^+\mu^-$} as a function of $ p_{\rm T} $ in the range $2.0<y<4.5$, assuming no polarisation. The first uncertainty is statistical, the second is systematic and the third is due to the unknown polarisation of the three states.

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