Open charm tomography of cold nuclear matter

TL;DR

This work develops a LO perturbative QCD framework to quantify open charm production and charm-triggered di-hadron correlations in proton-nucleus collisions, incorporating nuclear-enhanced high-twist power corrections and a cold-nuclear-matter energy-loss mechanism. It shows that single inclusive $D$ meson production is dominated by charm scattering on light partons, while the away-side jet composition is strongly shaped by the heavy-quark fragmentation function, producing a characteristic heavy-flavor hump in di-hadron spectra. The coherent final-state interactions lead to $A^{1/3}$-enhanced suppression via a kinematic shift in parton momentum fractions, with the heavy-quark mass reducing the effect; energy loss further suppresses yields with a distinct $p_T$ dependence, helping reconcile theory with forward-rapidity data. Overall, the results establish a baseline for using open charm as a tomography tool of cold nuclear matter and set the stage for heavy-quark studies at RHIC and the LHC.

Abstract

We study the relative contribution of partonic sub-processes to D meson production and D meson-triggered inclusive di-hadrons to lowest order in perturbative QCD. While gluon fusion dominates the creation of large angle DD-bar pairs, charm on light parton scattering determines the yield of single inclusive D mesons. The distinctly different non-perturbative fragmentation of c quarks into D mesons versus the fragmentation of quarks and gluons into light hadrons results in a strong transverse momentum dependence of anticharm content of the away-side charm-triggered jet. In p+A reactions, we calculate and resum the coherent nuclear-enhanced power corrections from the final state partonic scattering in the medium. We find that single and double inclusive open charm production can be suppressed as much as the yield of neutral pions from dynamical high-twist shadowing. Effects of energy loss in p+A collisions are also investigated phenomenologically and may lead to significantly weaker transverse momentum dependence of the nuclear attenuation.

Figures (21)

• Figure 1: Schematic representation of the initial- and final-state elastic, inelastic and coherent multiple parton scattering that give the nuclear $A^{n/3}$-enhanced corrections similar to Eq. (\ref{['series']}) for proton-nucleus collisions in the nuclear rest frame.
• Figure 2: Cross section for $D^0$ and $D^+$ charm meson production to LO in perturbative QCD at $\sqrt{s}=1.96$ TeV. Three approximately equivalent pairs of a phenomenological $K$-factor and the $D$ meson fragmentation parameter $r$ are shown.
• Figure 3: The cross section for $D^0 + D^+$ charm meson production to LO in perturbative QCD at $\sqrt{s}=200$ GeV in $p+p$ collisions at RHIC with $K_{NLO} = 2 - 3$ and $r = 0.2$. The differential cross section is shown in four rapidity bins: $y=0, \, 1.25, \, 2.5$ and $3.75$.
• Figure 4: Fractional contribution of partonic sub-processes ($i$) to moderate and high $p_{T_1}$$D^0 + D^+$ meson production in $\sqrt{s} = 200$ GeV $p+p$ collisions at rapidities $y =0,\, 1.25, \, 2.5$ and $3.75$. We considered (1) $cg \rightarrow cg$ (solid line), (2) $cq(\bar{q}) \rightarrow cq(\bar{q})$ (dashed line), (3) $gg \rightarrow c\bar{c}$ (dot-dashed line), (4) $q\bar{q} \rightarrow c\bar{c}$ (double dot-dashed line) and (5) $c\bar{c} \rightarrow c\bar{c}$ (dotted line). Note the dominance (except at the highest values of $p_{T_1}$) of the $cg \rightarrow cg$ channel.
• Figure 5: Contribution of light hadrons and anticharm mesons to the fractional production cross section for $p_{T_1} = 5$ GeV $D^0+D^+$ meson-triggered away-side correlations for $y_1 = y_2 = 0$. The insert illustrates the difference in the fragmentation of light quarks and gluons into hadrons versus that for the $c$ quark into charm mesons. Three different values for the non-perturbative fragmentation parameter $r = 0.1,\, 0.2$ and $0.4$ were used.