Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at sqrt(s) = 7 TeV

The ALICE experiment at the LHC has studied $\jpsi$ production at mid-rapidity in pp collisions at $\sqrt{s} = 7$ TeV through its electron pair decay on a data sample corresponding to an integrated luminosity $L_{\rm {int}}$ = 5.6nb$^{-1}$. The fraction of $\jpsi$ from the decay of long-lived beauty hadrons was determined for $\jpsi$ candidates with transverse momentum $\pt$ > 1.3 GeV/$c$ and rapidity |$y$| < 0.9. The cross section for prompt $\jpsi$ mesons, i.e. directly produced $\jpsi$ and prompt decays of heavier charmonium states such as the $\psi$(2S) and $\chi_c$ resonances, is $\sigma_{{\rm {prompt}} \; \jpsi}$ ($\pt$ > 1.3 GeV/$c$, |y| < 0.9) = 8.3 $\pm$ 0.8 (stat.) $\pm$ 1.1 (syst.)$^{+1.5}_{-1.4}$ (syst. pol.) $\mu$b. The cross section for the production of b-hadrons decaying to $\jpsi$ with $\pt$ > 1.3 GeV/$c$ and |y|< 0.9 is $\sigma_{\jpsi \leftarrow {\rm {h_B}}} = 1.46 \pm 0.38$ (stat.) $^{+0.26}_{-0.32}$ (syst.) $\mu$b. The results are compared to QCD model predictions. The shape of the $\pt$ and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the ${\rm {b\bar{b}}}$ pair total cross section and d$\sigma/$d$y$ at mid-rapidity.

Figures

Figure 1

Invariant mass (left panel) and pseudoproper decay length (right panel) distributions of opposite sign electron pairs for $|y_{\rm J/\psi}|< 0.9$ and $p_{\rm t}^{\rm J/\psi} > 1.3$ GeV/$c$ with superimposed projections of the maximum likelihood fit. The latter distribution is limited to the $\jpsi$ candidates under the mass peak, i.e. for $2.92 < m_{\rm e^+ e^-} < 3.16$ GeV/$c^2$, for display purposes only. The $\chi^2$ values of these projections are reported for both distributions.
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Figure 2

Invariant mass (left panels) and pseudoproper decay length (right panels) distributions in different $\pt$ bins with superimposed projections of the maximum likelihood fit. The $\chi^2$ values of these projections are also reported for all distributions.
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Figure 3

The fraction of $\jpsi$ from the decay of b-hadrons as a function of $\pt$ of $\jpsi$ compared with results from ATLAS and CMS in pp collisions at $\sqrt{s}$ =7 TeV.
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Figure 4

$\frac{{\rm d}\sigma_{\rm prompt \; J/\psi}}{{\rm d}p_{\rm t}{\rm d}y}$ as a function of $\pt$ compared to results from ATLAS and CMS at mid-rapidity (left panel) and to theoretical calculations (right panel). The error bars represent the quadratic sum of the statistical and systematic uncertainties.
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Figure 5

$\frac{{\rm d}\sigma_{\rm prompt \; J/\psi}}{{\rm d}y}$ as a function of $y$ The error bars represent the quadratic sum of the statistical and systematic errors, while the systematic uncertainties on luminosity and branching ratio are shown as boxes around the data points. The symbols are plotted at the center of each bin The CMS value was obtained by integrating the published d$^{2}\sigma_{\rm prompt \; J/\psi }$/d$\pt$d$y$ data measured for $1.6< \left| y \right|< 2.4$. The results obtained by LHCb and CMS are reflected with respect to $y = 0$ (open symbols).
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Figure 6

$\frac{{\rm d}\sigma_{{\rm J}/\psi \; {\rm {from}} \; {\rm B}}}{{\rm d}y}$ as a function of $y$. The error bars represent the quadratic sum of the statistical and systematic errors, while the systematic uncertainties on luminosity and branching ratio are shown as boxes. The systematic uncertainties on the extrapolation to $\pt$ = 0 are indicated by the slashed areas. The CMS values were obtained by integrating the published d$^{2}\sigma_{{\rm J}/\psi \; {\rm {from}} \; {\rm B}}$ /d$\pt$d$y$ data measured for $1.2 < \left| y \right|< 1.6$ and $1.6 < \left| y \right|< 2.4$. The results obtained in the forward region by LHCb are reflected with respect to $y = 0$ (open symbols). The FONLL calculation (and its uncertainty) is represented by solid (dashed) lines.
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Figure 7

d$\sigma_{\rm b \bar{b}}$/d$y$ at mid rapidity as a function of $\sqrt{s}$ in pp (PHENIX[47] and ALICE results) and ${\rm p\bar{p}}$ (UA1 [16] and CDF [17] results) collisions. The FONLL calculation [41][42] (and its uncertainty) is represented by solid (dashed) lines.
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