Session RC: Mini-Symposium: Probing nucleons and nuclei in ultra-peripheral collisions and with vector mesons I

Probing the high-energy nuclear initial state and nuclear quantum fluctuations using ultra-peripheral heavy-ion collisions with the CMS detector

The CERN Large Hadron Collider serves as a photon-nucleus, photon-proton and photon-photon collider at unprecedented energies. In particular, the study of vector meson and dijet photoproduction has resulted in new information on nuclear effects beyond the ordinary nuclear parton distribution functions. In this talk, we will discuss recent results on ultra-peripheral heavy-ion collisions using the CMS detector. Particular attention will be given to recent studies that shed light on the high-energy nuclear initial state and nuclear quantum fluctuation, and how the studies of UPCs are paving the way for an exciting program at electron-nucleus colliders.   

Coherent phenomena in nuclear high-energy scattering from UPCs to EIC

Studying coherent phenomena in the interaction of high-energy probes with nuclei is essential for understanding high-energy QCD in both the soft and hard regime. Measurements of coherent production of vector mesons in ultraperipheral collisions (UPCs) of heavy nuclei have established the presence of large shadowing effects in both the soft ($\rho$ production) and hard ($J/\psi$ production) regime. We explore the possibility of studying the same effects in coherent electroproduction of vector mesons on light nuclei ($A \leq 4$) at the Electron-Ion Collider (EIC). The controlled virtuality in electroproduction provides insight into the scale dependence of coherent effects; the use of light nuclei allows one to separate multiple scattering effects involving two, three and more nucleons. Our analysis uses two- and three-body nuclear form factors calculated using realistic $A = 3, 4$ nuclear wave functions. We discuss the complementarity between the two types of measurements and the possibility of a combined analysis.   

Exploring QCD in ultraperipheral collisions with production of leading J/psi meson

We review several possibilities for probing QCD dynamics in ultraperipheral heavy ion collision with $J/\psi $ production. We argue that rapidity gap events in $\gamma p$ and $\gamma A$ scattering allow to study the BFKL dynamics, as well as dynamics of propagation of small dipoles through nuclei. At the same time coherent and quasielastic $J/\psi$ production in $\gamma A$ scattering provide a unique information about gluon shadowing at small x and moderate virtualities.   

Photoproduction of {\$}J/$\backslash $psi{\$}-mesons off deuteron in d$+$Au Ultra-Peripheral Collisions using the STAR detector

Nuclear dynamics at short distances among nucleons is one of the most outstanding phenomena in nuclear physics. Understanding the role of QCD in generating nuclear forces is important for uncovering the underlying physics of Short-Range Correlations (SRCs). In recent years, SRCs have been observed from light to heavy nuclei using fixed target experiments at Jefferson lab via high energy electron-nucleus scattering. It has been recently suggested that the exclusive {\$}J/$\backslash $psi{\$} production of electron-deuteron scattering at the Electron-Ion Collider (EIC) would provide new insights into the SRCs, in particular from the aspect of the underlying quark-gluon dynamics. In the absence of electron-nucleus data from an EIC, data from deuteron-gold (d$+$Au) ultra-peripheral collisions (UPCs) recorded by the STAR detector at the Relativistic Heavy Ion Collider can be used as a proxy to test various techniques and hypotheses. The coherent and incoherent cross sections of {\$}J/$\backslash $psi{\$} photoproduction in d$+$Au UPC events are measured, and the implications of the results will be discussed. The reported results will be a first-time measurement of {\$}J/$\backslash $psi{\$}-meson photoproducton off deuteron in high energy collisions.