Measurement of the Prompt $D^0$ Nuclear Modification Factor in $p\text{−}\mathrm{Pb}$ Collisions at $\sqrt{s_{NN}}=8.16\mathrm{TeV}$

The production of prompt $D^0$ mesons in proton-lead collisions in both the forward and backward rapidity regions at a center-of-mass energy per nucleon pair of $\sqrt{s_{NN}}=8.16\mathrm{TeV}$ is measured by the LHCb experiment. The nuclear modification factor of prompt $D^0$ mesons is determined as a function of the transverse momentum $p_T$, and the rapidity in the nucleon-nucleon center-of-mass frame $y^{*}$. In the forward rapidity region, significantly suppressed production with respect to $pp$ collisions is measured, which provides significant constraints on models of nuclear parton distributions and hadron production down to the very low Bjorken-$x$ region of $\sim {10}^{-5}$. In the backward rapidity region, a suppression with a significance of 2.0–3.8 standard deviations compared to parton distribution functions in a nuclear environment expectations is found in the kinematic region of $p_T>6\mathrm{GeV}/c$ and $-3.25<y^{*}<-2.5$, corresponding to $x\sim 0.01$.

Figure 1

Nuclear modification factor as a function of $p_T$ in different $y^{*}$ intervals for prompt $D^0$ mesons in the (top) forward and (bottom) backward regions. The error bars show the statistical uncertainties and the boxes show the systematic uncertainties. The LHCb results at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ [14] and theoretical calculations at $\sqrt{s_{NN}}=8.16\mathrm{TeV}$ from Refs. [9, 61, 62, 63, 64] are also shown. For LHCb results at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$, the error bars show the quadric sum of statistical and systematic uncertainties.

Figure 2

Nuclear modification factor as a function of $x_{\exp }$ in different $Q_{\exp }^2$ intervals for prompt $D^0$ mesons for LHCb results at $\sqrt{s_{NN}}=8.16\mathrm{TeV}$ and $\sqrt{s_{NN}}=5.02$ [14] and the ALICE result at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ [22]. Theoretical calculations at $\sqrt{s_{NN}}=8.16\mathrm{TeV}$ from Refs. [61, 62] are also shown. The horizontal error bars account for the maximum and minimum $x_{\exp }$ values for a given $(p_T,y^{*})$ interval and the vertical error bars show the quadric sum of statistical and systematic uncertainties.