Absorption of 1$P$-wave heavy charmonium $χ_{c1}(1P)$ in nuclei

Abstract

We study the inclusive heavy charmonium $χ_{c1}(1P)$ photoproduction from nuclei near the kinematic threshold within the collision model, based on the nuclear spectral function, for incoherent direct photon--nucleon charmonium creation processes. The model accounts for the final $χ_{c1}(1P)$ absorption in nuclear medium, target nucleon binding and Fermi motion. We calculate the absolute and relative excitation functions on $^{12}$C and $^{184}$W target nuclei at near-threshold photon beam energies of 8.25--16.0 GeV, the absolute momentum differential cross sections and ratios of them for its production off these target nuclei at laboratory polar angles of 0$^{\circ}$--10$^{\circ}$ and for photon energy of 13 GeV as well as the A-dependences of the transparency ratios for the $χ_{c1}(1P)$ at photon energy of 13 GeV within the different scenarios for its absorption cross section in nuclei. We demonstrate that the absolute and relative observables considered reveal distinct sensitivity to these scenarios. Therefore, they might be useful for the determination of this cross section from the comparison of them with the experimental data from the future experiments at the upgraded up to 22 GeV CEBAF facility, which is of crucial importance in understanding of charmonium production and suppression in high-energy heavy--ion collisions in a search for the quark-gluon plasma.

Figures (10)

• Figure 1: (Color online.) Total cross sections for the reactions ${\gamma}p \to {\chi_{c1}(1P)}p$, ${\gamma}p \to {J/\psi}p$ and ${\gamma}p \to {\psi(2S)}p$ as functions of the laboratory energy $E_{\gamma}$ of the photon--proton collisions in the kinematic range accessible at the upgraded up to 22 GeV JLab facility [83--85]. Solid, dashed, dotted and dashed-dotted curves represent calculations performed using Eqs. (7), (9), (10) and (12), respectively. The arrows indicates the threshold energies of 8.21, 10.08 and 10.93 GeV for $J/\psi$, $\chi_{c1}(1P)$ and $\psi(2S)$ photoproduction on a free target proton at rest.
• Figure 2: (Color online.) The fractions of $J/\psi$ mesons arising from radiative decays of the two $\chi_{c1}(1P)$, $\chi_{c2}(1P)$ states ($F(\chi_c)$) and hadronic decays of the $\psi(2S)$ mesons ($F(\psi'))$ produced, respectively, in the direct reactions ${\gamma}p \to {\chi_{c1,c2}(1P)}p$ and ${\gamma}p \to {\psi(2S)}p$ with respect to the total $J/\psi$ yield originating from these decays and from the process ${\gamma}p \to {J/\psi}p$ as well as their sum, $F(\chi_c)+F(\psi')$, as functions of the incident photon energy $E_{\gamma}$. The left and right panels represent calculations performed using, correspondingly, Eqs. (10) and (12) for the total cross section of the ${\gamma}p \to {\psi(2S)}p$ reaction.
• Figure 3: (Color online.) Excitation function for production of $\chi_{c1}(1P)$ mesons off $^{12}$C from the direct reactions (1), (2) proceeding on an off-shell target nucleons and on a free ones being at rest. The curves are calculations for $\sigma_{\chi_{c}N}=$ 3.5, 7, 14 and 20 mb. The arrow indicates the threshold energy for the $\chi_{c1}(1P)$ photoproduction on a free nucleon.
• Figure 4: (Color online.) The same as in Fig. 3, but for the $^{184}$W target nucleus.
• Figure 5: (Color online.) Momentum differential cross sections for the production of $\chi_{c1}(1P)$ mesons from the direct processes (1), (2) in the laboratory polar angular range of 0$^{\circ}$--10$^{\circ}$ in the interaction of photons having energy of $E_{\gamma}=$ 13 GeV with $^{12}$C (left) and $^{184}$W (right) nuclei, calculated for different values of the absorption cross section $\sigma_{\chi_{c}N}$ indicated in the inset.