We discuss the physics of large impact parameter interactions at the LHC: ultraperipheral collisions (UPCs). The dominant processes in UPCs are photon–nucleon (nucleus) interactions. The current LHC ...detector configurations can explore hard phenomena at small
x
with nuclei and nucleons at photon–nucleon center-of-mass energies above 1 TeV, extending the
x
range of HERA by a factor of ten. In particular, it will be possible to probe diffractive and inclusive parton densities in nuclei using several processes. The interaction of small dipoles with protons and nuclei can be investigated in elastic and quasi-elastic
J
/
ψ
and
Υ
production as well as in high
t
ρ
0
production accompanied by a rapidity gap. Several of these phenomena provide clean signatures of the onset of the new high gluon density QCD regime. The LHC is in the kinematic range where nonlinear effects are several times larger than those at HERA. Two-photon processes in UPCs are also studied. In addition, while UPCs play a role in limiting the maximum beam luminosity, they can also be used as a luminosity monitor by measuring mutual electromagnetic dissociation of the beam nuclei. We also review similar studies at HERA and RHIC as well as describe the potential use of the LHC detectors for UPC measurements.
As predicted by theory and confirmed by measurements, one, two or three neutrons are emitted frequently in ultraperipheral collisions (UPCs) of heavy relativistic nuclei, in particular,
Pb. The ...exchange of low-energy Weizsäcker–Williams photons dominates in such interactions. This leads to the excitation and decay of Giant Dipole Resonances (GDR) in colliding nuclei below the proton emission threshold. Less is known about the electromagnetic dissociation of
208
Pb induced by energetic photons leading to violent fragmentation of
208
Pb. The UPCs of lead nuclei at the LHC were modeled with Relativistic ELectromagnetic Dissociation (RELDIS) model to evaluate the contribution of photonuclear reactions in the domain of quasideuteron absorption and at higher photon energies. It was demonstrated that due to the presence of a single heavy residue in the final state mostly accompanied by free protons and neutrons, the cross sections of the production of specific elements can be well approximated by the proton emission cross sections, which can be measured in the ALICE experiment at the LHC.
Electromagnetic interactions of high-energy nuclei in ultraperipheral collisions are considered. Such collisions, which take place without any overlap of nuclear densities, can be considered as ...irradiation of nuclei by intense photon beams with a broad energy spectrum. This leads to several unusual phenomena, such as mutual electromagnetic excitation of nuclei, including exotic double and triple excitations of giant resonances, and multifragmentation of nuclei. The RELDIS model is presented, which describes fragmentation of nuclei and meson production by equivalent photons. It is shown that the RHIC and LHC colliders provide unique opportunities to study electromagnetic interactions of ultrarelativistic nuclei. The cross sections calculated by the RELDIS model are used in the method of monitoring the LHC luminosity on the basis of neutron emission rates, as well as to simulate interactions of beam nuclei with LHC construction elements.
The electromagnetic dissociation of ultrarelativistic nuclei has a substantial impact on the lifetime of beams in the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC), and ...secondary nuclei produced upon this dissociation may have an adverse effect on collider components. At the same time, the detection of neutrons originating from the electromagnetic dissociation process makes it possible to monitor the luminosity of colliders. In order to calculate the total and partial cross sections for the electromagnetic dissociation process by the Weizsäcker–Williams method, one needs reliable photonuclear reaction models preliminarily tested via a comparison of the results that they produce with available experimental data. Since the commissioning of the LHC, attention has been given primarily to
Pb–
Pb collisions. A run involving
Xe nuclei was also performed. In contrast to the case of
Pb nuclei, for which the photonuclear reaction and electromagnetic dissociation cross sections have been measured at various laboratories, there are no data for
Xe. By employing the experimental–theoretical method, the (
), (
), (
), and (
, abs) cross sections for the
Xe nucleus are evaluated on the basis of available data for the neighboring nucleus of
I and the combined photonuclear reaction model (CPNRM). It is found that the results of CPNRM calculations performed for
Xe at photon energies up to 40 MeV by employing the TENDL-2017 library compiled by means of the TALYS code are close to one another and are in fairly good agreement with data obtained at the Saclay laboratory for
I. These new evaluated data, the TENDL-2017 library, and approximations of the total photoabsorption cross sections above the pion production threshold are used to calculate the electromagnetic dissociation cross section for
Xe at the LHC and at the FCC-hh collider being designed. The results of these calculations are compared with their counterparts obtained on the basis of the RELDIS model.
The abrasion–ablation model is implemented in the form of the computer code Abrasion–Ablation Monte Carlo for Colliders (AAMCC) and applied to collisions of relativistic nuclei at the collider NICA ...now under construction. The total number of free nucleons, the fraction of free nucleons in the total volume of spectator matter, and their
n
/
p
ratio are calculated as functions of the impact parameter in
197
Au–
197
Au collisions at NICA. Correlations are calculated between the total volumes of spectator matter, as well as between the numbers of spectator nucleons from each of the colliding nuclei. The obtained results can be used to improve the method of centrality determination in nucleus–nucleus collisions by registering spectator nucleons and to estimate the impact of heavy spectator fragments on NICA components, including superconducting magnets.
The production of heavy secondary nuclei in
197
Au–
197
Au collisions at NICA and in
129
Xe–
129
Xe and
208
Pb–
208
Pb collisions at the LHC is calculated by means of Glauber Monte Carlo model ...connected with nuclear de-excitation models from Geant4 toolkit. The production of secondary nuclei in ultraperipheral heavy-ion collisions is additionally simulated with the RELDIS model, which predicts the dominance of neutron emission in the electromagnetic interactions of the considered nuclei. As found, Te, I and Au, Hg, Tl nuclei are frequently produced, respectively, in decays of
129
Xe and
208
Pb excited electromagnetically at the LHC. In contrast, mostly gold isotopes are produced in ultraperipheral collisions at NICA. A possible impact of secondary nuclei on collider components is discussed.
The detection of spectator nucleons emitted forward in the beam direction in experiments on the study of nucleus—nucleus interactions using forward Zero Degree Calorimeters (ZDCs) allows the ...determination of the event centrality and the detection of the nucleons from electromagnetic dissociation (EMD). In this paper, we propose a simple combinatorial model for calculating the energy releases in the ZDC, taking into account the calorimeter acceptance and efficiency. Using this model, the effect of the limited acceptance and nucleon detection efficiency on the spectral shape in the ZDC and the possibility of measuring the yield of a certain number of nucleons from the EMD is studied at LHC energies.
—
In central collisions of heavy relativistic nuclei spectator matter is represented by noninteracting nucleons from the nuclear periphery. In the context of the AAMCC model based on the Glauber ...Monte Carlo model to determine the volume of spectator matter and the models of the decay of excited spectator matter from the Geant4 toolkit, it is shown that the yields of a certain number of neutrons in central collisions of
208
Pb nuclei are sensitive to the presence of the neutron skin. When the neutron skin is considered in the calculations using various parameterizations of the excitation energy of spectator matter, an increase in the yield of spectator neutrons is especially noticeable in the events without the emission of spectator protons. The proposed new method for studying the neutron skin in relativistic nucleus–nucleus collisions by means of zero degree calorimeters complements the known methods used at significantly lower collision energies. It can be implemented at existing experimental facilities.
The properties of spectator matter created in
197
Au–
197
Au and
208
Pb–
208
Pb collisions with energies typical for the NICA accelerator complex were studied with the Abrasion–Ablation Monte Carlo ...for Colliders (AAMCC) model. We review predictions made with AAMCC for several characteristics of spectator matter and compare them with available data. The sum of squares of spectator charges per spectator nucleon is proposed as an additional indicator of collision centrality in BM@N and MPD experiments at NICA. The forward-backward asymmetry of free spectator nucleons is calculated and compared to the asymmetry of the total volume of spectator matter. The sensitivity of calculated yields of spectator neutrons in central
208
Pb‒
208
Pb collisions to the presence of neutron skin in
208
Pb is demonstrated.
The cross sections of forward emission of one, two and three neutrons by 158A GeV 115In nuclei in collisions with Al, Cu, Sn and Pb targets are reported. The measurements were performed in the ...framework of the ALICE–LUMI experiment at the SPS facility at CERN. Various corrections accounting for the absorption of beam nuclei and produced neutrons in target material and surrounding air were introduced. The corrected cross section data are compared with the predictions of the RELDIS model for electromagnetic fragmentation of 115In in ultraperipheral collisions, as well as with the results of the abrasion–ablation model for neutron emission in hadronic interactions. The measured neutron emission cross sections well agree with the RELDIS results, with the exception of In–Al collisions where the measured cross sections are larger compared to RELDIS. This is attributed to a relatively large contribution of hadronic fragmentation of In on Al target with respect to electromagnetic fragmentation, in contrast to similar measurements performed earlier with 30A GeV 208Pb colliding with Al.
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