STARlight

STARlight is a computer simulation (Monte Carlo) event generator program to simulate ultra-peripheral collisions among relativistic nuclei.[1][2] It simulates both photonuclear and two-photon interactions. It can simulate multiple interactions among a single ion pair, such as vector meson photoproduction accompanied by mutual Coulomb excitation.

These reactions are currently the primary method of studying photo-nuclear and two-photon interactions.

## History

STARlight was initially written in the late 1990s, in FORTRAN.[3] After a period of expansion to include additional final states, etc. it was recoded into C++ in the early 2000s. The code is now hosted on the Hepforge code repository.[4]

## Reactions simulated

* Two-photon production of lepton pairs
* Two-photon production of single mesons
* Photonproduction of vector mesons
* Generalized photoproduction (via an interface to DPMJet)

STARlight has been used by both STAR and PHENIX, at RHIC, and at the ALICE, CMS, ATLAS and LHC-b experiment at the Large Hadron Collider, for simulations of ultra-peripheral collisions.

STARlight is designed to handle complex reactions involving multiple photon exchange between a single ion pair. These reactions are important at heavy ion colliders, because, with the large nuclear charges, the probability of multi-photon interactions in near grazing collisions (impact parameter b just slightly above twice the nuclear radius) is large. STARlight does this by calculating cross-sections in an impact-parameter dependent formalism.[5][6]

One of its major successes was the successful prediction of the cross-sections for ρ0 photoproduction at both RHIC[7] and the LHC.[8] It also accurately predicted the cross-section for e+e− pair production at RHIC[9] and the LHC,[10] using lowest order quantum electrodynamics. The latter reaction is important because it shows that there are no large higher order corrections, as could be expected because of the large nuclear charge. In both of the RHIC results, the presence of neutrons in downstream zero-degree calorimeters was used in the trigger, selecting events with impact parameters less than about 40 fermi; these events were then searched for photoproduced ρ0.

A detailed description of the code is available.[11]

## References

1. ↑ * Relativistic Heavy Ion Physics without Nuclear Contact, C.A. Bertulani and G. Baur, Physics Today, March 1994, pg. 22.
2. ↑ Bertulani, Carlos A.; Klein, Spencer R.; Nystrand, Joakim (2005). "Physics of ultra-peripheral relativistic nuclear collisions". Annual Review of Nuclear and Particle Science 55 (1): 271–310. doi:10.1146/annurev.nucl.55.090704.151526. ISSN 0163-8998.
3. ↑ J. Nystrand and S. Klein, arXiv:nucl-ex/9811007
4. ↑ "Starlight – Hepforge". https://starlight.hepforge.org/.
5. ↑ Baltz, Anthony J.; Klein, Spencer R.; Nystrand, Joakim (2002-06-14). "Coherent Vector-Meson Photoproduction with Nuclear Breakup in Relativistic Heavy-Ion Collisions". Physical Review Letters 89 (1). doi:10.1103/physrevlett.89.012301. ISSN 0031-9007. PMID 12097035. Bibcode: 2002PhRvL..89a2301B.
6. ↑ Baltz, Anthony J.; Gorbunov, Yuri; Klein, Spencer R.; Nystrand, Joakim (2009-10-07). "Two-photon interactions with nuclear breakup in relativistic heavy ion collisions". Physical Review C (American Physical Society (APS)) 80 (4). doi:10.1103/physrevc.80.044902. ISSN 0556-2813. Bibcode: 2009PhRvC..80d4902B. https://digital.library.unt.edu/ark:/67531/metadc1014781/.
7. ↑ Abelev, B. I.; Aggarwal, M. M.; Ahammed, Z.; Anderson, B. D.; Arkhipkin, D. et al. (2008-03-31). "ρ0 photoproduction in ultraperipheral relativistic heavy ion collisions at sNN=200 GeV". Physical Review C (American Physical Society (APS)) 77 (3): 034910. doi:10.1103/physrevc.77.034910. ISSN 0556-2813.
8. ↑ Adam, J.; Adamová, D.; Aggarwal, M. M.; Aglieri Rinella, G.; Agnello, M. et al. (2015). "Coherent ρ0 photoproduction in ultra-peripheral Pb-Pb collisions at sNN=2.76 TeV". Journal of High Energy Physics (Springer Science and Business Media LLC) 2015 (9): 95. doi:10.1007/jhep09(2015)095. ISSN 1029-8479.
9. ↑ Adams, J.; Aggarwal, M. M.; Ahammed, Z.; Amonett, J.; Anderson, B. D. et al. (2004-09-28). "Production of e+e− pairs accompanied by nuclear dissociation in ultraperipheral heavy-ion collisions". Physical Review C (American Physical Society (APS)) 70 (3): 031902(R). doi:10.1103/physrevc.70.031902. ISSN 0556-2813.
10. ↑ Abbas, E.; Abelev, B.; Adam, J.; Adamová, D.; Adare, A. M. et al. (2013). "Charmonium and e + e − pair photoproduction at mid-rapidity in ultra-peripheral Pb–Pb collisions at sNN=2.76 TeV". The European Physical Journal C (Springer Science and Business Media LLC) 73 (11): 2617. doi:10.1140/epjc/s10052-013-2617-1. ISSN 1434-6044. PMID 25814847.
11. ↑ Klein, Spencer R.; Nystrand, Joakim; Seger, Janet; Gorbunov, Yuri; Butterworth, Joey (2017). "STARlight: A Monte Carlo simulation program for ultra-peripheral collisions of relativistic ions". Computer Physics Communications 212: 258–268. doi:10.1016/j.cpc.2016.10.016. ISSN 0010-4655. Bibcode: 2017CoPhC.212..258K.

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