Electron-positron production in ultra-peripheral heavy-ion collisions with the STAR experiment

Thesis/Dissertation · Wed Jan 01 00:00:00 EST 2003

DOI:https://doi.org/10.2172/817249· OSTI ID:817249

Morozov, Vladimir Borisovitch ^[1]

---

1. Univ. of California, Berkeley, CA (United States)

This thesis presents a measurement of the cross-section of the purely electromagnetic production of e⁺e^- pairs accompanied by mutual nuclear Coulomb excitation AuAu → Au*Au* + e⁺e^-, in ultra-peripheral gold-gold collisions at RHIC at the center-of-mass collision energy of √S_NN = 200 GeV per nucleon. These reactions were selected by detecting neutron emission by the excited gold ions in the Zero Degree Calorimeters. The charged tracks in the e⁺e^- events were reconstructed with the STAR Time Projection Chamber. The detector acceptance limits the kinematical range of the observed e⁺e^- pairs; therefore the measured cross-section is extrapolated to 4π with the use of Monte Carlo simulations. We have developed a Monte Carlo simulation for ultra-peripheral e⁺e^- production at RHIC based on the Equivalent Photon Approximation, the lowest-order QED e⁺e^- production cross-section by two real photons and the assumption that the mutual nuclear excitations and the e⁺e^- production are independent (EPA model). We compare our experimental results to two models: the EPA model and a model based on full QED calculation of the e⁺e^- production, taking the photon virtuality into account. The measured differential cross-section dσ/dM_inv (M_inv - e⁺e^- invariant mass) agrees well with both theoretical models. The measured differential cross-section dσ/dp $$tot\atop{\perp}$$ (p$$tot\atop{\perp}$$- e⁺e^- total transverse momentum) favors the full QED calculation over the EPA model.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 817249
• Report Number(s): LBNL-53583; R&D Project: NRNC; TRN: US0305181
• Resource Relation: Other Information: TH: Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); PBD: 1 Aug 2003
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
74 ATOMIC AND MOLECULAR PHYSICS
CALORIMETERS
COULOMB EXCITATION
DIFFERENTIAL CROSS SECTIONS
EQUIVALENT-PHOTON APPROXIMATION
GOLD IONS
NEUTRON EMISSION
PHOTONS
PRODUCTION
SIMULATION
TIME PROJECTION CHAMBERS
TRANSVERSE MOMENTUM
US EPA