Collectivity of heavy mesons in proton-nucleus collisions

Using a model based on the color glass condensate framework and the dilute-dense factorization, we systematically study the azimuthal angular correlations between a heavy flavor meson and a light reference particle in proton-nucleus collisions. The obtained second-harmonic coefficients (also known as the elliptic flows) for $J/\psi$ and $D^0$ agree with recent experimental data from the LHC. We also provide predictions for the elliptic flows of $\mathrm{\Upsilon }$ and $B$ mesons, which can be measured in the near future at the LHC. This work can shed light on the physical origin of the collectivity phenomenon in the collisions of small systems.

Figure 1

An example of Feynman diagrams that contribute to the differential spectrum of heavy quark pair production accompanied by a spectator quark. The transverse coordinates of partons are illustrated in the diagrams. This diagram shows the interference contribution before and after the splitting of the heavy quark pair. The total contribution also includes the squares of the above individual amplitudes.

Figure 2

Elliptic flow of heavy quarkonium in the $g\to \mathcal{Q}\overline{\mathcal{Q}}+q$ channel compared with the experimental data from the CMS Collaboration [10].

Figure 3

Elliptic flows of heavy quarkonia with a quark or a gluon as the reference particle.

Figure 4

Differential cross section for $B$ mesons computed in our model and compared with experimental data from the CDF Collaboration [87] in $p\overline{p}$ collisions. Note that we use smaller values of $Q_s^2$ due to the consideration of smaller target size and lower collision energy and $S_{\perp }=12\mathrm{mb}$ for a proton target.

Figure 5

Elliptic flow of open heavy mesons in the $g\to \mathcal{Q}\overline{\mathcal{Q}}+q$ channel compared with the experimental data from the CMS Collaboration [11, 12]. In the numerical calculation, the same set of values for parameters has been adopted as in the quarkonia case—namely, $B_p=6{\mathrm{GeV}}^{-2}$, $\mathrm{\Delta }=0.5\mathrm{GeV}$, and $Q_s^2=5{\mathrm{GeV}}^2$.

Figure 6

Elliptic flows of open heavy mesons in the $g\to \mathcal{Q}\overline{\mathcal{Q}}+q$ channel calculated with different fragmentation functions.

Figure 7

Elliptic flows of open heavy mesons in the $g\to \mathcal{Q}\overline{\mathcal{Q}}+q$ and $g\to \mathcal{Q}\overline{\mathcal{Q}}+g$ channels.