Heavy quark pair production in high energy pA collisions: Open heavy flavors

TL;DR

Open heavy flavor production in high-energy pA collisions is explored within the Color Glass Condensate framework to probe small-$x$ gluon saturation in the nucleus. The authors deploy rcBK-evolved unintegrated gluon distributions, compare with McLerran–Venugopalan initial conditions, and compute D and B meson spectra, nuclear modification factors, and azimuthal correlations across RHIC and LHC energies. Results show pronounced suppression at low $p_T$ and forward rapidity at the LHC, with saturation-induced modifications to heavy-quark pair correlations, thereby establishing a CGC-based baseline for initial-state effects in heavy-ion collisions. These findings aid in disentangling cold-nuclear matter effects from hot-medium dynamics in AA collisions and guide interpretation of heavy-flavor observables in high-energy nuclear physics.

Abstract

We study open heavy flavor meson production in proton-nucleus (pA) collisions at RHIC and LHC energies within the Color Glass Condensate framework. We use the unintegrated gluon distribution at small Bjorken's x in the proton obtained by solving the Balitsky-Kovchegov equation with running coupling correction and constrained by global fitting of HERA data. We change the initial saturation scale of the gluon distribution for the heavy nucleus. The gluon distribution with McLerran-Venugopalan model initial condition is also used for comparison. We present transverse momentum spectra of single D and B productions in pA collisions, and the so-called nuclear modification factor. The azimuthal angle correlation of open heavy flavor meson pair is also computed to study the modification due to the gluon saturation in the heavy nucleus at the LHC.

Figures (10)

• Figure 1: $x_1$ (black) and $x_2$ (red) coverages of $D^0$ production at mid and forward rapidities, for fixed $p_\perp = 2$ GeV at $\sqrt{s}=200$ GeV (a), and for fixed $p_\perp = 2$ (b) and 10 GeV (c) at $\sqrt{s}=5.02$ TeV. $x_{1,2}$ coverages of $B^0$ production are shown in (d) for fixed $p_\perp = 2$ at $\sqrt{s}=5.02$ TeV.
• Figure 2: (a) Differential cross-section of $D$ (rescaled as $D^0/f_{c\to D^0}$ and $D^{*+}/f_{c\to D^{*+}}$) vs transverse momentum $p_\perp$ for rapidity range $|y|<1.0$ in pp collisions at $\sqrt{s}=200$ GeV, computed with Eq. (\ref{['eq:open-cross-section-LN']}) with uGD sets MV (gray band) and g1118 (double-hatched). The upper (lower) curve of the band corresponds to the result with $m_c=1.2$ (1.5) GeV. The data is taken from Ref. open_charm_xsection-STAR. (b) Differential cross-section of $D^0$ vs transverse momentum $p_\perp$ at $|y|<0.5$ in pp collisions at $\sqrt{s}=5.02$ TeV. The ALICE data is taken from Ref. ALICE:2011aa.
• Figure 3: (a) Differential cross-section of $B^0$ vs transverse momentum $p_\perp$ for rapidity range $2 < y < 4.5$ in pp collisions at $\sqrt{s}=5.02$ TeV, computed with Eq. (\ref{['eq:open-cross-section-LN']}) with uGD sets MV (gray band) and g1118 (double-hatched). The upper (lower) curve of the band corresponds to the result with $m_b=4.5$ (4.8) GeV. (b) Differential cross-section of $B^0$ vs $y$ in the range $0<p_\perp<40$ GeV in pp collisions at $\sqrt{s}=5.02$ TeV. The notation of the curve is the same as in (a). The LHCb data is taken from Ref. LHCb:B1.
• Figure 4: Transverse momentum spectrum of $D^0$ multiplicity per event in pA collisions, computed with Eq. (\ref{['eq:open-cross-section-LN']}) with uGD sets MV (gray) and g1118 (double-hatch), in rapidity range $|y|<1.0$ at $\sqrt{s}=200$ GeV (a) and in $-1.0<y<0.0$ at $\sqrt{s}=5.02$ GeV (b). The upper (lower) curve of the band corresponds to the result with $m_c=1.2$ (1.5) GeV. dAu data is taken from open_charm_yields-STAR.
• Figure 5: (a) Nuclear modification factor $R_\text{pA}$ of $D$ production vs $p_\perp$ computed with Eq. (\ref{['eq:def-RpA']}) with uGD set g1118 with $m_c=1.5$ GeV in the rapidity range $|y|<1.0$ at $\sqrt{s}=200$ GeV. (b) $R_\text{pA}(p_\perp)$ of $B$ production with $m_b=4.8$ GeV.