Measurements of $e^{+}{e}^{-}$ pairs from open heavy flavor in $p+p$ and $d+A$ collisions at $\sqrt{s_{\mathit{\text{NN}}}}=200$ GeV

We report a measurement of $e^{+}{e}^{-}$ pairs from semileptonic heavy-flavor decays in $p+p$ collisions at $\sqrt{s_{{}_{\mathit{\text{NN}}}}}=200$ GeV. The $e^{+}{e}^{-}$ pair yield from $b\overline{b}$ and $c\overline{c}$ is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and $p_T$. We used three different event generators, pythia, mc@nlo, and powheg, to simulate the $e^{+}{e}^{-}$ spectra from $c\overline{c}$ and $b\overline{b}$ production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to $4\pi$, significant differences are observed for the total cross section. These difference are less pronounced for $b\overline{b}$ than for $c\overline{c}$. The same model dependence was observed in already published $d+A$ data. The $p+p$ data are also directly compared with $d+A$ data in mass and $p_T$, and within the statistical accuracy no nuclear modification is seen.

Figure 1

Relative acceptance correction $\alpha$ defined as the ratio of $B_{+-}^{\mathrm{comb}}$ to $B_{\pm \pm }^{\mathrm{comb}}$ as defined in Eq. (1). This correction approaches 1 at high mass.

Figure 2

Unlike-sign foreground $N_{+-}$ spectrum overlaid with like-sign foreground spectrum after being corrected by the relative acceptance correction $\alpha$ [see Fig. 1 and Eq. (1)].

Figure 3

Compilation of meson production in $p+p$ collisions at $\sqrt{s_{\mathit{\text{NN}}}}=200$ GeV. The data shown above are taken from the following sources: ${\pi }^0\to \gamma \gamma$ [16, 28], $({\pi }^{+}+{\pi }^{-})/2$ [29], $\eta \to \gamma \gamma$ [30, 31], $\eta \to {\pi }^0{\pi }^{+}{\pi }^{-}$ [31], $\omega \to e^{+}{e}^{-}$ [32], $\omega \to {\pi }^0{\pi }^{+}{\pi }^{-}$ [32], $\omega \to {\pi }^0\gamma$ [32], $\varphi \to K^{+}{K}^{-}$ [33], $\varphi \to e^{+}{e}^{-}$ [32], $J\psi \to e^{+}{e}^{-}$ [34, 35], ${\psi }^{\prime }\to e^{+}{e}^{-}$ [35]. The data are compared to the parametrization based on $m_T$ scaling used in exodus.

Figure 4

Inclusive $e^{+}{e}^{-}$ pair yield from $p+p$ collisions as a function of mass. The data are compared to our model of expected sources. The inset shows in detail the mass range up to 4.5 GeV/$c^2$. In the lower panel, the ratio of data to expected sources is shown with systematic uncertainties.

Figure 5

Double differential $e^{+}{e}^{-}$ pair yield from semileptonic decays of heavy flavor in inelastic $p+p$ collisions. Shown are mass projections in slices of $p_T$. The $p_T$ intervals are indicated in each panel. Systematic uncertainties are shown as boxes, downward pointing arrows indicate upper limits at 90% CL.

Figure 6

Double differential $e^{+}{e}^{-}$ pair yield from semileptonic decays of heavy flavor as simulated by pythia, mc@nlo, and powheg. Shown are mass projections in slices of $p_T$. The $p_T$ intervals are indicated in each panel.

Figure 7

Double differential $e^{+}{e}^{-}$ pair yield from heavy-flavor decays fitted to simulated distributions from pythia. The simulation is fitted to data in the mass region between $1.15<m_{e^{+}{e}^{-}}<2.4\text{GeV}/c^2$ and $4.1<m_{e^{+}{e}^{-}}<8.0\text{GeV}/c^2$.

Figure 8

Double differential $e^{+}{e}^{-}$ pair yield from heavy-flavor decays fitted to simulated distributions from mc@nlo.

The simulation is fitted to data in the mass region between $1.15<m_{e^{+}{e}^{-}}<2.4\text{GeV}/c^2$ and $4.1<m_{e^{+}{e}^{-}}<8.0\text{GeV}/c^2$.

Figure 9

Double differential $e^{+}{e}^{-}$ pair yield from heavy-flavor decays fitted to simulated distributions from powheg. The simulation is fitted to data in the mass region between $1.15<m_{e^{+}{e}^{-}}<2.4\text{GeV}/c^2$ and $4.1<m_{e^{+}{e}^{-}}<8.0\text{GeV}/c^2$.

Figure 10

The top panel compares the mass dependence of $e^{+}{e}^{-}$ pair yield with pythia, mc@nlo, and powheg calculations. The bottom panel shows the comparison for the $p_T$ dependence. The blue region shown in the top panel is not used in the fitting and is excluded in the $p_T$ projection.

Figure 11

Comparison of the $\mathrm{\Delta }\varphi$ distribution from data to the different MC generators. The leftmost column shows the comparison to pythia, the middle column to mc@nlo, and the rightmost column shows the comparison to powheg. Each row corresponds to the $p_T$ interval indicated in the leftmost column. The solid line corresponds to the total HF contribution, dashed line represents $c\overline{c}$, dotted line represents $b\overline{b}$, and the big dashed line shows DY contribution for a given generator. The normalization of different contributions is explained in the text. The negative yield for the simulations results from the like-sign subtraction performed in simulations similar to data analysis.

Figure 12

Comparison of the invariant $e^{+}{e}^{-}$ yield from $c\overline{c}$ and $b\overline{b}$ for $p+p$ collisions determined using pythia (solid line), mc@nlo (dotted line), and powheg (dashed line) and normalized using the extracted cross sections.

Figure 13

The extracted cross sections of $c\overline{c}$ and $b\overline{b}$ in $p+p$ and $d+\mathrm{Au}$ collisions. The $d+\mathrm{Au}$ cross section has been scaled down by $N_{\mathrm{coll}}$ to represent the equivalent nucleon-nucleon cross section.

Figure 14

The nuclear modification factor $R_{d\mathrm{Au}}$ of $c\overline{c}$ and $b\overline{b}$ pairs constructed using the cross sections. The $d+\mathrm{Au}$ cross sections are scaled down by $N_{\mathrm{coll}} =7.6\pm 0.4$.

Figure 15

Comparison of mass spectrum of $e^{+}{e}^{-}$ pairs from heavy flavor in $p+p$ and $d+\mathrm{Au}$ collisions. The $d+\mathrm{Au}$ data shown are from [13]. The $p+p$ yield has been scaled by $N_{\mathrm{coll}} =7.6\pm 0.4$ for MB $d+\mathrm{Au}$ collisions.

Figure 16

Comparison of transverse momentum spectrum of $e^{+}{e}^{-}$ pairs in $p+p$ and $d+\mathrm{Au}$ collisions. The $d+\mathrm{Au}$ data shown are from [13]. The $p+p$ yield has been scaled by $N_{\mathrm{coll}} =7.6\pm 0.4$ for MB $d+\mathrm{Au}$ collisions.