p{sup 0} photoproduction in ultraperipheral relativistic heavy ion collisions at {radical}{ovr s}{sub NN} = 200 GeV.

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Phys. Rev. C

DOI:https://doi.org/10.1103/PhysRevC.77.034910· OSTI ID:964252

Abelev, B I; Aggarwal, M M; Ahammed, Z; Anderson, B D; Arkhipkin, D; Krueger, K; Spinka, H M; Underwood, D G

Photoproduction reactions occur when the electromagnetic field of a relativistic heavy ion interacts with another heavy ion. The STAR Collaboration presents a measurement of {rho}{sup 0} and direct {pi}{sup +}{pi}{sup -} photoproduction in ultraperipheral relativistic heavy ion collisions at {radical}s{sub NN} = 200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross section of {sigma} (AuAu {yields} Au{sup +}Au{sup +} {rho}{sup 0}) = 530 {+-} 19(stat.) {+-} 57(syst.) mb, in accord with theoretical calculations based on a Glauber approach, but considerably below the predictions of a color dipole model. The {rho}{sup p} transverse momentum spectrum (p{sub T}{sup 2}) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus; we find {sigma}{sub inc}/{sigma}{sub coh} = 0.29 {+-} 0.03(stat.) {+-} 0.08(syst.). The ratio of direct {pi}{sup +}{pi}{sup -} to {rho}{sup 0} production is comparable to that observed in {gamma}{sub p} collisions at HERA and appears to be independent of photon energy. Finally, the measured {rho}{sup 0} spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: SC; NSF; Swiss NSF
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 964252
• Report Number(s): ANL-HEP-PR-09-84
• Journal Information: Phys. Rev. C, Journal Name: Phys. Rev. C Journal Issue: 2008 Vol. 77; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
74 ATOMIC AND MOLECULAR PHYSICS
COLOR
COULOMB EXCITATION
CROSS SECTIONS
DIPOLES
ELECTROMAGNETIC FIELDS
HEAVY IONS
HELICITY
ION COLLISIONS
MATRIX ELEMENTS
PHOTONS
PHOTOPRODUCTION
S CHANNEL
SPIN
TARGETS
TRANSVERSE MOMENTUM