Photon induced processes: from ultraperipheral to semicentral heavy ion collisions

Abstract

We present an overview of processes induced by the coherent Weizsäcker-Williams (WW) photon cloud in heavy ion collisions. Due to the rather broad energy spectrum of photons a large variety of physics topics can be addressed. At the low-energy side, there are the electromagnetic dissociation processes. We discuss the few-neutron production via giant dipole resonance excitation. A typical high energy photonuclear process that has attracted much attention is the diffractive photoproduction of vector mesons. We review the color dipole approach to coherent and incoherent diffractive photoproduction of $$J/\psi $$ J / ψ mesons. Finally we turn to peripheral and semicentral collisions and discuss the role of WW photons in the production of very low-$$P_T$$ P T dileptons.

Coherent Photoproduction of Low- p T Charmonium in Peripheral Heavy Ion Collisions within the Color Dipole Model

“…The peripheral collisions of heavy ions at RHIC and LHC give an opportunity to explore high-energy nuclear physics with beams of quasi-real photons [10][11][12][13][14]. The J/ψ can also be produced via the strong electromagnetic fields generated by heavy ions, e.g., photon-nucleus coherent or incoherent interactions, in peripheral heavy ion collisions [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Recently, a significant excess of J/ψ yield at very low transverse momenta has been observed by the ALICE collaboration in peripheral hadronic Pb-Pb collisions with ffiffiffiffiffiffiffi s NN p = 2:76 TeV at forward rapidity [30], and by the STAR collaboration in hadronic Au-Au collisions with ffiffiffiffiffiffiffi s NN p = 200 GeV and U-U collisions with ffiffiffiffiffiffiffi s NN p = 193 GeV at midrapidity [31,32], that cannot be explained within the hadronic J/ψ production modified by the cold and hot medium effects.…”

The reggeometric pomeron and exclusive production of $J/ψ$ and $ψ(2S)$ in ultraperipheral collisions at the LHC

“…Vector meson production in ultra-peripheral collisions (UPC) were studied in a number of papers (see comprehensive reviews in Refs. [6,7,8,9]). Ultra-peripheral vector meson production was studied, both experimentally and theoretically in proton-proton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions at the LHC energies and below.…”

Exclusive dilepton production via timelike Compton scattering in heavy ion collisions

“…One interesting process is the electron-nucleus collision, which is planned to be investigated at the Electron Ion Collider (EIC) [4] and at the Large Hadron-Electron Collider (LHeC) [5]. Photonuclear reactions can be also studied in ultraperipheral heavy ion collisions [6,7] and it would be timely to analyze TCS in electromagnetic processes for large impact parameter proton-nucleus and nucleus-nucleus collisions.…”