Abstract
We study sub-threshold heavy quarkonium (J/ψ and ϒ) photo-productions in γA collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the γp threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for J/ψ and ϒ. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China.
Highlights
Nucleon-nucleon short range correlation (SRC) describes an important aspect of the nuclear structure and has been a subject of intensive studies in the last few decades, see, for example, Refs. [1,2,3,4,5,6]
We find that the Υ cross section near threshold is about 10−3 ∼ 10−2 nb, and this is further reduced to 10−5 nb around the region Wγp 9.7 GeV where the SRC contribution starts to dominate
We have provided a detailed derivation of the sub-threshold heavy quarkonium production cross section in γA collisions
Summary
Nucleon-nucleon short range correlation (SRC) describes an important aspect of the nuclear structure and has been a subject of intensive studies in the last few decades, see, for example, Refs. [1,2,3,4,5,6]. In a recent paper by two of us [23], it was suggested that heavy flavor production in deep inelastic scattering (DIS) can provide a gluonic probe for the SRC contribution and further test the above mentioned universality This can be achieved by measuring the charm-structure function in eA collisions, and at the same time, one can measure the so-called sub-threshold heavy flavor production in γA collisions. In a recent experimental effort [31], the sub-threshold J/ψ production in γA collisions has been investigated at JLab with a low incoming photon energy (around 5.7GeV in the rest frame of the nuclear target). A number of experiments have already been approved to carry out J/ψ production in various photo-nuclear experiments We expect that these experiments will measure J/ψ production in the sub-threshold region, and provide an important test of the SRC universality.
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