Conveners
Parallel Session T09: Ultra-peripheral collisions: I
- Dariusz Miskowiec (GSI Darmstadt)
Parallel Session T09: Ultra-peripheral collisions: II
- George Stephans (Massachusetts Inst. of Technology (US))
Ultraperipheral lead-lead collisions at $\sqrt{s_{_{\mathrm{NN}}}} =$ 5.02 TeV produce very large photon fluxes that provide the conditions to study photon-photon fusion processes in phase space regions inaccessible with proton-proton data. Measurements of light-by-light (LbyL) scattering and lepton pair photoproduction in ultraperipheral PbPb collisions will be presented with data collected...
Photon-photon and photonuclear reactions are induced by the strong electromagnetic field generated by ultrarelativistic heavy-ion collisions. These processes have been extensively studied in ultra-peripheral collisions with impact parameters larger than twice the nuclear radius. Since a few years, both the photoproduction of the J/$\psi$ vector meson and the production of dileptons via...
Measurements of quarkonia production in peripheral and ultra-peripheral heavy-ion collisions are sensitive to photon-photon and photon-nucleus interactions, the partonic structure of nuclei, and the mechanisms of vector-meson production. LHCb has studied both coherent and incoherent production of $J/\psi$ mesons in peripheral and ultra-peripheral collisions using PbPb data at forward rapidity...
Relativistic heavy-ion beams are accompanied by a large flux of equivalent photons, giving rise to a set of photon-induced processes. These can lead to photon-photon interactions in ultraperipheral collisions. This talk presents a series of measurements of such processes performed by the ATLAS Collaboration. New measurements of exclusive dilepton production (electron, muon, or tau pairs) are...
Ultra-strong electromagnetic field can generate a large flux of quasi-real photons arising from the Lorentz-contraction and the large electric charge (Z) of heavy nuclei colliding at ultra-relativistic speeds. These ultra-strong fields can be studied through dileptons ($e^{+}e^{-}$ and $\mu^{+}\mu^{-}$) and vector mesons ($J/\psi$) produced via photon-photon and photonuclear processes,...
With a unique geometry covering the forward rapidity region, the LHCb detector provides unprecedented kinematic coverage at low Bjorken-$x$ down to $x \sim 10^{-5}$ or lower. The excellent momentum resolution, vertex reconstruction and particle identification allow precision measurements down to very low hadron transverse momentum. In this contribution, we present the latest studies of the...
The diffractive photoproduction of $\rm{J/\psi}$ vector mesons is studied at the LHC with the ALICE detector in p--Pb and Pb--Pb ultra-peripheral collisions (UPCs), where the Pb ions act as powerful sources of quasi-real photons.
In this talk, the first measurement at the LHC of dissociative photoproduction of $\rm{J/\psi}$ off protons is presented; this process is sensitive to quantum...
The exclusive photoproduction of vector mesons provides a unique opportunity to constrain the gluon distribution function within protons and nuclei. Measuring vector mesons of various masses over a wide range of rapidity and as a function of transverse momentum provides important information on the evolution of the gluon distribution within nuclei. A variety of measurements, including the...
This talk reports the observation of $\tau$-lepton pair production in ultraperipheral lead-lead collisions and a measurements of for the $\tau$-lepton anomalous magnetic moment, $a_{\tau}$. The dataset corresponds to an integrated luminosity of 1.44/nb of Pb+Pb collisions at 5.02 TeV recorded by the ATLAS experiment in 2018.
We discuss the sensitivity of the process in ultraperipheral Pb+Pb collisions on the anomalous magnetic ($a_\tau$) and electric ($d_\tau$) moments of $\tau$ lepton at LHC energies. We derive the corresponding cross sections by folding the elementary cross section with the heavy-ion photon fluxes and considering semi-leptonic decays of both $\tau$ leptons in the fiducial volume of ATLAS and CMS...
Coherent exclusive J/Psi photoproduction in ultraperipheral heavy-ion collisions (UPCs) at the LHC, Pb+Pb $\rightarrow$ Pb+J/Psi +Pb, has traditionally been suggested as an efficient probe of nuclear gluon distributions. While in the leading order pQCD this is so, we show that the situation changes rather dramatically at NLO. We present the first NLO study of this process in heavy-ion...
