Naslov
Rho(0) photoproduction in ultraperipheral relativistic heavy ion collisions at root s(NN)=200 GeV

Autori
Abelev, B.I. ; ... ; Planinić, Mirko ; ... ; Poljak, Nikola ; et al. (the STAR Collaboration)

Izvornik
Physical Review C (0556-2813) 77 (2008), 3; 034910-1

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
photoproduction relativistic heavy ion collisions; time projection chamber; vector-meson production; diffractive production; proton scattering; complex nuclei; photon; Hera; colliders; energies; physics

Sažetak
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^0 and direct pi^+pi^- photoproduction in ultra-peripheral relativistic heavy ion collisions at sqrt(s_{; ; ; NN}; ; ; )=200 GeV. We observe both exclusive photoproduction and photoproduction accompanied by mutual Coulomb excitation. We find a coherent cross-section of sigma(AuAu) -> Au^*Au^*rho^0 = 530 pm 19 (stat.) pm 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^0 transverse momentum spectrum (p_{; ; ; T}; ; ; ^2) is fit by a double exponential curve including both coherent and incoherent coupling to the target nucleus ; we find sigma_{; ; ; inc}; ; ; /sigma_{; ; ; coh}; ; ; = 0.29 pm 0.03 (stat.) pm 0.08 (syst.). The ratio of direct pi^+pi^- to rho^0 production is comparable to that observed in gamma p collisions at HERA, and appears to be independent of photon energy. Finally, the measured rho^0 spin helicity matrix elements agree within errors with the expected s-channel helicity conservation.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

Napomena
Art. no. 034910.

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