Measurement of electrons from heavy-flavour hadron decays in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

The production of electrons from heavy-flavour hadron decays was measured as a function of transverse momentum ($p_{\rm T}$) in minimum-bias p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV with ALICE at the LHC. The measurement covers the $p_{\rm T}$ interval $0.5<~p_{\rm T}<~12$ GeV/$c$ and the rapidity range $-1.06 <~ y_{\rm cms} <~ 0.14$ in the centre-of-mass reference frame. The contribution of electrons from background sources was subtracted using an invariant mass approach. The nuclear modification factor $R_{\rm pPb}$ was calculated by comparing the $p_{\rm T}$-differential invariant cross section in p-Pb collisions to a pp reference at the same centre-of-mass energy, which was obtained by interpolating measurements at $\sqrt{s}= 2.76$ TeV and $\sqrt{s} =7$ TeV. The $R_{\rm pPb}$ is consistent with unity within uncertainties of about 25%, which become larger for $p_{\rm T}$ below 1 GeV/$c$. The measurement shows that heavy-flavour production is consistent with binary scaling, so that a suppression in the high-$p_{\rm T}$ yield in Pb-Pb collisions has to be attributed to effects induced by the hot medium produced in the final state. The data in p-Pb collisions are described by recent model calculations that include cold nuclear matter effects.

Figures

Figure 1

(a): Measured d$E/$d$x$ in the TPC as function of momentum $p$ expressed as a deviation from the expected energy loss of electrons, normalised by the energy-loss resolution ($\sigma_{\rm TPC}$) after eID with TOF. The solid lines indicate the $n_{\sigma}^{TPC}$ selection criteria for the TPC and TOF eID strategy. (b): $E/p$ distribution of electrons ($-1 < n_{\sigma}^{TPC} < 3$) and hadrons ($n_{\sigma}^{TPC} < -3.5$) in the transverse momentum interval $6 < \pt < 8$ GeV/$c$. The $E/p$ distribution of hadrons was normalised to that of electrons in the lower $E/p$ range (0.4-0.6), where hadrons dominate. The solid lines indicate the applied electron selection criteria.
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Figure 2

Invariant mass distributions of unlike-sign and like-sign electron pairs for the inclusive electron $\pt$ interval $0.5 < \pt < 0.6$ GeV/$c$. The difference between the distributions yields the photonic contribution.
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Figure 3

The $\pt$-differential invariant cross section of electrons from heavy-flavour hadron decays in minimum-bias p-Pb collisions at $\snn$ = 5.02 TeV, comparing the results of the eID strategies in the two transition regions at 2.5 and 6 GeV/$c$. The centre values are slightly shifted along the $\pt$-axis in the transition regions for better visibility. The results agree within 1%. Details on the eID strategies can be found in the text.
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Figure 4

The $\pt$-differential invariant cross section of electrons from heavy-flavour hadron decays in minimum-bias p-Pb collisions at $\snn$ = 5.02 TeV. The pp reference obtained via the interpolation method is shown, not scaled by $A$, for comparison. The statistical uncertainties are indicated for both spectra by error bars, the systematic uncertainties are shown as boxes.
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Figure 5

Nuclear modification factor $\RpPb$ of electrons from heavy-flavour hadron decays as a function of transverse momentum for minimum-bias p-Pb collisions at $\snn$ = 5.02 TeV, compared with theoretical models, as described in the text. The vertical bars represent the statistical uncertainties, and the boxes indicate the systematic uncertainties. The systematic uncertainty from the normalisation, common to all points, is shown as a filled box at high $\pt$
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