Ultra-peripheral collisions (UPCs) have been a significant source of study at RHIC and the LHC. In these collisions, the two colliding nuclei interact electromagnetically, via two-photon or ...photonuclear interactions, but not hadronically; they effectively miss each other. Photonuclear interactions produce vector meson states or more general photonuclear final states, while two-photon interactions can produce lepton or meson pairs, or single mesons. In these interactions, the collision geometry plays a major role. We present a program, STARlight, that calculates the cross-sections for a variety of UPC final states and also creates, via Monte Carlo simulation, events for use in determining detector efficiency.
Program Title : STARlight (v2.2)
Program Files doi : http://dx.doi.org/10.17632/xjpf4rxtbj.1
Licensing provisions : GNU GPLv3
Programming Language : C++
External Routines : PYTHIA 8.2 and DPMJET 3.0 are needed for some final states.
Nature of problem : The cross-section for ultra-peripheral collisions is obtained by integrating the photon fluxes in transverse impact parameter space, subject to the requirement (which is also impact parameter dependent) that the colliding nuclei do not interact hadronically. The program is a two step process. First, it calculates the cross-sections for the reaction of interest, as a function of W (photon–Pomeron or two-photon center of mass energy), Y (final state rapidity) and pT (final state transverse momentum). Second, STARlight generates Monte Carlo events which can be used to determine cross-sections within specific kinematic constraints or for studies of detector efficiencies. The second step includes the decay of any unstable particles produced in the reaction, with appropriate consideration of particle spins and parity. It outputs these events in ASCII format.
Solution method : The program generates a two dimensional look-up table of the production cross-section as a function of final state rapidity and mass. The dimensions of the table are selectable, allowing the user to choose the desired accuracy. For certain final states, a second two-dimensional look-up table, giving the transverse momentum distribution, as a function of rapidity, is also used. With these look-up tables, the program generates final states. Particle decays and the final angular distributions are calculated for each event.
Restrictions : The program is focused on ultra-relativistic collisions at Brookhaven’s RHIC (Relativistic Heavy Ion Collider) and CERN’s LHC (Large Hadron Collider), with final states that are visible in a central detector. At lower energies (i.e., at the CERN SPS), caution should be exercised because STARlight does not account for the longitudinal momentum transfer to the nucleus; this is larger at low beam energies.
References: http://starlight.hepforge.org and references in this article.
In collisions between heavy ions at ultra-relativistic energies the participating protons lose energy, which is converted into new particles. As the protons slow down, they emit bremsstrahlung ...radiation. The yield and angular distribution of the emitted radiation are sensitive probes of how much energy the incoming protons have lost. In this paper, the spectrum of bremsstrahlung radiation is calculated for different stopping scenarios, and the results are compared with the expected yield of photons from hadronic interactions.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
3.
PHYSICS OF ULTRA-PERIPHERAL NUCLEAR COLLISIONS Bertulani, Carlos A.; Klein, Spencer R.; Nystrand, Joakim
Annual review of nuclear and particle science,
12/2005, Letnik:
55, Številka:
1
Journal Article
Recenzirano
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▪ Abstract Moving highly-charged ions carry strong electromagnetic fields that act as a beam of photons. In collisions at large impact parameters, hadronic interactions are not possible, and the ...ions interact through photon-ion and photon-photon collisions known as ultra-peripheral collisions (UPCs). Hadron colliders like the Relativistic Heavy Ion Collider (RHIC), the Tevatron, and the Large Hadron Collider (LHC) produce photonuclear and two-photon interactions at luminosities and energies beyond that accessible elsewhere; the LHC will reach a γp energy ten times that of the Hadron-Electron Ring Accelerator (HERA). Reactions as diverse as the production of anti-hydrogen, photoproduction of the ρ
0
, transmutation of lead into bismuth, and excitation of collective nuclear resonances have already been studied. At the LHC, UPCs can study many types of new physics processes.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We discuss the photoproduction of Upsilon and J/psi at high energy pp, pp, and heavy ion colliders. We predict large rates in pp interactions at the Fermilab Tevatron and in pp and heavy ion ...interactions at the CERN Large Hadron Collider. The J/psi is also produced copiously at the Relativistic Heavy Ion Collider. These reactions can be used to study the gluon distribution in protons and heavy nuclei. We also show that the different CP symmetries of the initial states lead to large differences in the transverse momentum spectra of mesons produced in pp vs pp collisions.
Vector mesons are copiously produced in ultra-peripheral nucleus–nucleus collisions. In these collisions, the nuclei are separated by impact parameters larger than the sum of the nuclear radii, and ...the interaction is mediated by the electromagnetic field. The interaction effectively corresponds to a photonuclear interaction between a photon, generated from the electromagnetic field of one of the nuclei, and the target nucleus. The ALICE Collaboration has previously published results on exclusive J/ψ photoproduction at mid and forward rapidities in Pb–Pb collisions. The cross section for this process is a particularly good measure of the nuclear gluon distribution. In this talk, the latest results on exclusive production of light and heavy vector mesons from ALICE in Pb–Pb collisions will be presented.
Vector mesons are produced copiously in peripheral relativistic heavy-ion collisions. Virtual photons from one ion can fluctuate into quark-antiquark pairs and scatter from the second ion, emerging ...as vector mesons. The emitter and target are indistinguishable, so emission from the two ions will interfere. Vector mesons have negative parity so the interference is destructive, reducing the production of mesons with small transverse momentum. The mesons are short lived, and decay before emission from the two ions can overlap. However, the decay-product wave functions overlap and interfere since they are produced in an entangled state, providing an example of the Einstein-Podolsky-Rosen paradox.
Vector meson photoproduction in UPCs with FoCal Bylinkin, A; Nystrand, J; Tapia Takaki, D
Journal of physics. G, Nuclear and particle physics,
05/2023, Letnik:
50, Številka:
5
Journal Article
Recenzirano
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Abstract
We discuss the physics prospects of photon-induced measurements using the high-granularity FoCal detector to be installed at the ALICE experiment, covering the pseudorapidity interval 3.4 ≤
...η
≤ 5.8. This new detector, scheduled to be in operation from Run 4, will explore the small Bjorken-
x
physics region in an unprecedented way. In this region the gluon ,saturation phenomenon is expected to be dominant. Combined with the rest of the ALICE subdetectors, including the zero degree calorimenters, FoCal will serve to reconstruct in a model-independent way the measured photoproduction cross sections for vectors mesons in a wide range of photon-target energies, down to
x
values of about 7 × 10
−6
and 2 × 10
−6
in ultra-peripheral photon–proton and photon–lead collisions, respectively.
This paper deals with so-called Ultra-Peripheral Collisions (UPCs) of heavy ionsC.A. Bertulani, S.R. Klein and J. Nystrand, Ann. Rev. Nucl. Part. Sci. 55 (2005) 271; G. Baur, K. Hencken, D. ...Trautmann, S. Sadovsky and Y. Kharlov, Phys. Rept. 364 (2002) 359. These can be defined as collisions in which no hadronic interactions occur because of the large spatial separation between the projectile and target. The interactions are instead mediated by the electromagnetic field. Two types of ultra-peripheral collisions can be distinguished: purely electro-magnetic interactions (two-photon interactions) and photonuclear interactions, in which a photon from the projectile interacts with the hadronic component of the target.
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