Exclusive photoproduction of excited quarkonia in ultraperipheral collisions

Abstract

In this paper, we discuss the exclusive photoproduction of ground and excited states of ψð1S; 2SÞ and ϒð1S; 2SÞ in ultraperipheral collisions (UPCs). Using the potential model in order to obtain the vector meson wave function, we find a good agreement of our calculations with data from the LHC and HERA colliders for J=ψð1S; 2SÞ and ϒð1SÞ in γp collisions. We extend the calculations to the nuclear target case applying them to AA UPCs with the use of the shadowing and finite coherence length effects fitted to the data. Our results are compared to the recent LHC data, in both incoherent (J=Ψð1SÞ at 2.76 TeV) and coherent (J=Ψð1SÞ at 2.76 and 5.02 TeV) processes. We also show the corresponding predictions for the excited states, in the hope that future measurements could provide more detailed information about the vector meson wave functions and nuclear effects.

Ultra-peripheral nuclear collisions as a source of heavy quarkonia

“…(3.1) and (3.4) in Ref. [49]). This cannot lead to a correct and proper inclusion of the finite-CL effects in calculations and, consequently, cannot provide a correct predictions for nuclear production cross sections in regions of large positive resp.…”

“…For the 2S-radially excited quarkonia the onset of the finite-l c effects, generated by the Green function formalism, is significantly different from VDM, especially in the incoherent case, as a direct consequence of the nodal structure of their wave functions. Such the node effect is stronger for ψ (2S) compared to Υ (2S) state leading thus to much complicated non-monotonic behaviour of the factor F inc (s) towards small values of s. On the other hand, a stronger energy dependence from the region of small Q Q transverse separations below the node position compared to large Q Q dipole sizes above the node position causes a weakening of the node effect with the energy resulting thus in a gradual convergence of factors F inc V (s) to values of F inc V (s) towards large s. Note that authors in the recent paper [49] used the above presented Glauber approximation for calculations of F coh and F inc repeating only our previous studies [27][28][29]50]. As we have already mentioned above, such an approximation cannot be applied properly for the photo-and electro-production of heavy quarkonia off nuclei.…”

“…However, it is unclear whether these effects have been incorporated properly in Ref. [49] since the nucleon amplitude presented there depends also on a derivative of σ q q and the corresponding explanation of adaptability of spin effects to nuclear targets is missing.…”

Photon induced processes: from ultraperipheral to semicentral heavy ion collisions

“…This however is not a complete review of the available literature, nor can we, due to space limitations, provide extensive discussions of the merits and shortcomings of different approaches. For applications of the color dipole approach to UPCs, some of them extending to light vector mesons and excited states, we refer the reader to [40][41][42][43][44][45][46][47][48][49][50][51][52]. The momentum space formulation, k ⊥factorization, which is equivalent to the dipole approach was used in [53], where also qqg-states were included.…”

“…The ALICE data however suggest, that around x ∼ 10 −3 , gluon shadowing effects may be important. Recently a reasonable description including gluon shadowing from a DGLAP fit of nuclear partons has been obtained in [45].…”