Incoherent diffractive photoproduction of $J/\psi$ and $\mathrm{{\rm Y}}$ on heavy nuclei in the color dipole approach

We calculate cross sections and transverse momentum distributions for the incoherent diffractive production of vector mesons $J/\psi$ and $\mathrm{{\rm Y}}$ on heavy nuclei. In distinction to coherent diffraction, the nucleus is allowed to break up, but except for the vector meson no new particles are produced in the reaction. Within the color dipole approach, we derive the multiple scattering expansion of the incoherent diffractive cross section as an expansion over quasielastic scatterings of the color dipole. We also compare our results to the measurement of the ALICE Collaboration for incoherent $J/\psi$ production at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ and show predictions at $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. We also briefly discuss a possible contribution to $J/\psi$ production in peripheral collisions in the $70–90\%$ centrality class.

Figure 1

(a) Coherent photoproduction of a vector meson in which the nucleus stays in its ground state. (b) An example diagram for incoherent diffractive production, in which the nucleus breaks up.

Figure 2

Incoherent diffractive cross section for $\gamma A\to J/\psi X$ for $A={}^{208}\mathrm{Pb}$ at (a) $W=30\mathrm{GeV}$ and (b) $W=100\mathrm{GeV}$. Shown are the contributions from 1 to 5 scatterings. Here $-t\equiv {\mathbf{\Delta }}^2$.

Figure 3

Incoherent diffractive cross section for $\gamma A\to J/\psi X$ for $A={}^{65}\mathrm{Cu}$ at (a) $W=30\mathrm{GeV}$ and (b) $W=100\mathrm{GeV}$. Shown are the contributions from 1 to 5 scatterings.

Figure 4

Incoherent diffractive cross section for $\gamma A\to \mathrm{{\rm Y}}X$ for $A={}^{208}\mathrm{Pb}$ at (a) $W=30\mathrm{GeV}$ and (b) $W=100\mathrm{GeV}$. Shown are the contributions from 1 to 2 (a) and 3 (b) scatterings.

Figure 5

Incoherent diffractive cross section for $\gamma A\to \mathrm{{\rm Y}}X$ for $A={}^{65}\mathrm{Cu}$ at (a) $W=30\mathrm{GeV}$ and (b) $W=100\mathrm{GeV}$. Shown are the contributions from 1 to 2 (a) and 3 (b) scatterings.

Figure 6

An enlargement of the region of very low $t$ of the incoherent cross section. The solid line shows the forward dip, while the dashed line is the single scattering term of the large-$t$ limit.

Figure 7

The nuclear suppression ratio (3.12) for $\gamma A\to VX$ on lead as a function of $x=m_V^2/W^2$ for $V=\mathrm{{\rm Y}}$ (upper lines) and $V=J/\psi$ (lower lines). The dashed lines refer to dipole cross section fit I, while the solid lines show the result for fit II.

Figure 8

Incoherent diffractive cross section for $\gamma A\to J/\psi X$ as a function of rapidity $y$ of the $J/\psi$. Solid lines include correction of Eq. (3.18) for real part and skewedness; dashed lines do not include real part/skewedness correction. (a) $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$, data point from ALICE (Ref. [40]); (b)$\sqrt{s_{\mathrm{NN}}}=5.02\mathrm{TeV}$.