Coherent photoproduction of vector mesons in ultraperipheral heavy ion collisions: Update for run 2 at the CERN Large Hadron Collider

We make predictions for the cross sections of coherent photoproduction of $\rho ,\varphi ,J/\psi ,\psi \left(2S\right)$, and $\mathrm{{\rm Y}}\left(1S\right)$ mesons in Pb-Pb ultraperipheral collisions (UPCs) at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ in the kinematics of run 2 at the Large Hadron Collider extending the approaches successfully describing the available Pb-Pb UPC data at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. Our results illustrate the important roles of hadronic fluctuations of the photon and inelastic nuclear shadowing in photoproduction of light vector mesons on nuclei and the large leading twist nuclear gluon shadowing in photoproduction of quarkonia on nuclei. We show that the ratio of $\psi \left(2S\right)$ and $J/\psi$ photoproduction cross sections in Pb-Pb UPCs is largely determined by the ratio of these cross sections on the proton. We also argue that UPCs with electromagnetic excitations of the colliding ions followed by the forward neutron emission allows one to significantly increase the range of photon energies accessed in vector meson photoproduction on nuclei.

Figure 1

The $\gamma p\to \varphi p$ cross section as a function of $W_{\gamma p}$. The fixed-target [35, 36] and HERA [37, 38] data vs the DL model [34].

Figure 2

The $d{\sigma }_{\mathrm{Pb}\mathrm{Pb}\to \rho \mathrm{Pb}\mathrm{Pb}}\left(y\right)/dy$ cross section as a function of the $\rho$-meson rapidity $y$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. Predictions of the combination of the modified VMD and GG models (mVMD-GGM) are shown for the four considered reaction channels. The solid curves correspond to the calculation using the nominal value of ${\omega }_{\sigma }^{\rho }$; the shaded areas show the theoretical uncertainty in modeling of this quantity. The dashed curves labeled “one side” show the contribution of the first term in Eq. (1).

Figure 3

The $d{\sigma }_{\mathrm{Pb}\mathrm{Pb}\to \varphi \mathrm{Pb}\mathrm{Pb}}\left(y\right)/dy$ cross section as a function of the $\varphi$-meson rapidity $y$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. For notation, see Fig. 2.

Figure 4

The $d{\sigma }_{\mathrm{Pb}\mathrm{Pb}\to J/\psi \mathrm{Pb}\mathrm{Pb}}\left(y\right)/dy$ cross section as a function of the $J/\psi$ rapidity $y$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$: predictions of LO pQCD with the gluon shadowing ratio $R_g(x,{\mu }^2)$ of the leading twist nuclear shadowing model. The shaded areas span the range of predictions corresponding to the upper and lower limits on $R_g(x,{\mu }^2)$.

Figure 5

The $d{\sigma }_{\mathrm{Pb}\mathrm{Pb}\to J/\psi \mathrm{Pb}\mathrm{Pb}}\left(y\right)/dy$ cross section as a function of the $J/\psi$ rapidity $y$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$: predictions of LO pQCD with the EPS09 gluon shadowing ratio $R_g(x,{\mu }^2)$. The shaded areas show the uncertainties of $R_g(x,{\mu }^2)$. The dashed curves labeled “one side” show the contribution of the first term in Eq. (1).

Figure 6

The $d{\sigma }_{\mathrm{Pb}\mathrm{Pb}\to \psi \left(2S\right)\mathrm{Pb}\mathrm{Pb}}\left(y\right)/dy$ cross section as a function of the $\psi \left(2S\right)$ rapidity $y$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. See Fig. 4 for notations.

Figure 7

The ${\sigma }_{\gamma p\to \mathrm{{\rm Y}}p}\left(W_{\gamma p}\right)$ cross section as a function of $W_{\gamma p}$. The high-energy ZEUS Collaboration [52, 53, 54], the H1 Collaboration [55] and the LHCb Collaboration [13] data are compared to pQCD predictions of Eq. (9) using the leading-order (CTEQ6L) and next-to-leading order (CTEQ6M) gluon distributions of the proton.

Figure 8

The $d{\sigma }_{\mathrm{Pb}\mathrm{Pb}\to \mathrm{{\rm Y}}\left(1S\right)\mathrm{Pb}\mathrm{Pb}}\left(y\right)/dy$ cross section as a function of the $\mathrm{{\rm Y}}$ rapidity $y$ at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$: NLO pQCD calculations with $R_g(x,{\mu }^2)$ given by the leading twist nuclear shadowing model (red band labeled LTA) and the EPS09 fit (blue solid curve with the band); the shaded bands indicate uncertainties of the respective predictions. The dashed curve labeled one side is the contribution of the first term in Eq. (1).