Open Charm Yields in $d+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$

Midrapidity open charm spectra from direct reconstruction of $D^0(\overline{D^0})\to K^{\mp }{\pi }^{\pm }$ in $d+\mathrm{A}\mathrm{u}$ collisions and indirect electron-positron measurements via charm semileptonic decays in $p+p$ and $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ are reported. The $D^0(\overline{D^0})$ spectrum covers a transverse momentum ($p_T$) range of $0.1<p_T<3\mathrm{G}\mathrm{e}\mathrm{V}/c$, whereas the electron spectra cover a range of $1<p_T<4\mathrm{G}\mathrm{e}\mathrm{V}/c$. The electron spectra show approximate binary collision scaling between $p+p$ and $d+\mathrm{A}\mathrm{u}$ collisions. From these two independent analyses, the differential cross section per nucleon-nucleon binary interaction at midrapidity for open charm production from $d+\mathrm{A}\mathrm{u}$ collisions at BNL RHIC is $d{\sigma }_{c\overline{c}}^{NN}/dy=0.30\pm 0.04(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 0.09(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\mathrm{m}\mathrm{b}$. The results are compared to theoretical calculations. Implications for charmonium results in $A+A$ collisions are discussed.

Figure 1

(a) Invariant mass distributions of kaon-pion pairs from $d+\mathrm{A}\mathrm{u}$ collisions. The solid circles depict the signal after mixed-event background subtraction, the open circles after subtraction of the residual background using a linear parametrization. (b) $dE/dx$ in the TPC versus particle momentum ($p$) with a TOF cut of $|1/\beta -1|\le 0.03$. Inset: projection on the $dE/dx$ axis for particle momenta $1<p<1.5\mathrm{G}\mathrm{e}\mathrm{V}/c$.

Figure 2

Upper panels: Electron distributions from $p+p$ (left) and $d+\mathrm{A}\mathrm{u}$ (right) collisions. Solid and open symbols depict electrons/positrons [$(e^{+}+e^{-})/2$] identified via a combination of TOF and $dE/dx$ and electrons ($e^{-}$) identified via $dE/dx$ alone. The total photonic backgrounds are shown as solid lines. Dashed lines depict the various contributing sources. The fractions were derived from simulations. Bottom panels: The ratio of inclusive electrons to the total backgrounds. The gray band represents the systematic uncertainty in each panel.

Figure 3

Reconstructed $D^0$ (solid squares) $p_T$ distributions from $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. Nonphotonic electron $p_T$ distributions from $p+p$ collisions (triangles) and $d+\mathrm{A}\mathrm{u}$ collisions (circles). Solid and dashed lines are the fit results from both $D^0$ and electron spectra in $d+\mathrm{A}\mathrm{u}$ collisions. The dotted line is scaled down by a factor of $N_{\mathrm{b}\mathrm{i}\mathrm{n}}=7.5\pm 0.4$ [20] from $d+\mathrm{A}\mathrm{u}$ to $p+p$ collisions. The dot-dashed line depicts a PYTHIA calculation [27].

Figure 4

Total $c\overline{c}$ cross section per nucleon-nucleon collision versus the collision energy ($\sqrt{s_{NN}}$). The dashed line depicts a PYTHIA calculation [27]. The solid and dot-dashed lines depict two NLO PQCD calculations with the Martin-Roberts-Sterling-Thorne highest order set, $m_c=1.2\mathrm{G}\mathrm{e}\mathrm{V}/c^2$, ${\mu }_F=2m_c$, ${\mu }_R=m_c$, and $2m_c$, respectively [18].