Beauty production in pp collisions at $\sqrt{s}$ = 2.76 TeV measured via semi-electronic decays

The ALICE collaboration at the LHC reports measurement of the inclusive production cross section of electrons from semi-leptonic decays of beauty hadrons with rapidity $|y|< 0.8$ and transverse momentum $1< p_{\mathrm{T}}< 10$ GeV/$c$, in pp collisions at $\sqrt{s} = $ 2.76 TeV. Electrons not originating from semi-electronic decay of beauty hadrons are suppressed using the impact parameter of the corresponding tracks. The production cross section of beauty decay electrons is compared to the result obtained with an alternative method which uses the distribution of the azimuthal angle between heavy-flavour decay electrons and charged hadrons. Perturbative QCD calculations agree with the measured cross section within the experimental and theoretical uncertainties. The integrated visible cross section, $\sigma_{\mathrm{b} \rightarrow \mathrm{e}} = 3.47\pm0.40(\mathrm{stat})^{+1.12}_{-1.33}(\mathrm{sys})\pm0.07(\mathrm{norm}) \mu$b, was extrapolated to full phase space using Fixed Order plus Next-to-Leading Log (FONLL) predictions to obtain the total b$\bar{\mathrm{b}}$ production cross section, $\sigma_{\mathrm{b\bar{b}}} = 130\pm15.1(\mathrm{stat})^{+42.1}_{-49.8}(\mathrm{sys})^{+3.4}_{-3.1}(\mathrm{extr})\pm2.5(\mathrm{norm})\pm4.4(\mathrm{BR}) \mu$b.

Figures

Figure 1

(a) Transverse impact parameter ($d_{0}$) distributions of electrons from beauty and charm hadron decays, light hadron decays, and photon conversions obtained with PYTHIA 6 simulations in the electron $\pt$ range 1 $< \pt < $ 6 GeV/$c$, along with the measured distribution of conversion electrons. The distributions are normalized to the same integrated yield. (b) Ratios of the measured and simulated $d_{0}$ distributions of conversion electrons in the ranges 1 $< \pt < $ 6 GeV/$c$.
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Figure 2

Raw spectrum of electrons from the impact parameter analysis (open circles) compared to background sources (from charm hadron decays, photon conversions, Dalitz decays, and hadron contamination) as a function of $\pt$. The background sources originating from light flavour hadrons were obtained using a MC simulation and re-weighted according to the $\pi^{0}$ $\pt$ spectrum measured with ALICE . The charm hadron decay background was estimated using the charm hadron spectra measured with ALICE . The raw yield after background sources are subtracted is also shown (filled circles). The error bars represent the statistical uncertainties.
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Figure 3

The azimuthal correlation between heavy-flavour decay electrons and charged hadrons, scaled by the number of electrons is shown for (a) the MB events in the $p^{\mathrm{e}}_{\mathrm{T}}$ range 1.5 to 2.5 GeV/$c$ and (b) the EMCal events in the $p^{\mathrm{e}}_{\mathrm{T}}$ range 4.5 to 6.0 GeV/$c$. The diamonds represent the MC distribution for electrons from charm hadron decays, squares are the MC distribution for electrons from beauty hadron decays. The line is the MC fit (Eq. \ref{eq:fit}) to the data points (circles).
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Figure 4

(a) Relative beauty contribution to the heavy-flavour electron yield; measured from the azimuthal correlations between heavy-flavour decay electrons and charged hadrons (black circles) compared to that from the method based on the track impact parameter (red squares). The green dashed, red dotted, and blue dot-dashed lines represent the FONLL , $k_{\rm T}$-factorization , and GM-VFNS predictions, respectively. (b) The \pt -differential inclusive production cross section of electrons from beauty hadron decays obtained using the impact parameter method (red squares) and the e-h correlation (black circles) method. For both panels, the error bars (boxes) represent the statistical (systematic) uncertainties. The notation $\rm b (\rightarrow \rm c) \rightarrow \rm e$ is used to indicate that the relative beauty contribution includes those electrons which originate directly from beauty hadron decays and those which originate from charm hadron decays, where the charm hadron is the decay product of a beauty hadron.
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Figure 5

(a) $\pt$-differential inclusive production cross section of electrons from beauty hadron decays. The green dashed, red dotted, and blue dot-dashed lines represent the FONLL , $k_{\rm T}$-factorization , and GM-VFNS uncertainty range, respectively. (b)-(d) Ratios of the data and the central prediction of pQCD calculations for electrons from beauty hadron decays. For all panels, the error bars (boxes) represent the statistical (systematic) uncertainties
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Figure 6

Inclusive beauty production cross section per rapidity unit measured at mid-rapidity as a function of center of mass energy in pp collisions (PHENIX and ALICE results) and p$\bar{\mathrm{p}}$ collisions (UA1 and CDF results) along with the the comparison to FONLL calculations. Error bars represent the statistical and systematic uncertainties added in quadrature. The FONLL calculation was performed for the five experimental rapidity ranges and center of mass energies shown in the figure, and these points are drawn as a curve.
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