Study of photon dissociation in diffractive photoproduction at HERA

Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W approximate to 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is gamma p --> XN, where X is the diffractively dissociated photon system of mass M-X and N is either a proton or a nucleonic system with mass M-N < 2 GeV. The cross section for this process in the interval 3 < M-X < 24 GeV relative to the total photoproduction cross section was measured to be sigma(D)(partial)/sigma(tot) = 6.2 +/- 0.2(stat) +/- 1.4(syst)%. After extrapolating this result to the mass interval of m(phi)(2) < M-X(2) < 0.05W(2) and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, gamma p --> Xp, is found to be sigma(SD)/sigma(tot) = 13.3 +/- 0.5(stat) +/- 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < M-X < 24 GeV can be described by the triple pomeron (IP IP IP) diagram with an effective pomeron intercept of alpha(IP)(0) = 1.12 +/- 0.04(stat) +/- 0.08(syst). The cross section for photon dissociation in the range 3 < Mr < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < Mr < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (IP IP IR term, its contribution to the diffractive cross section in the interval 3 < Mr < 24 GeV is estimated to be f(IP IP IR) = 26 +/- 3(stat) +/- 12(syst)%. RI Bashkirov, Vladimir/A-4818-2008; De Pasquale, Salvatore/B-9165-2008; Lancaster, Mark/C-1693-2008; Doyle, Anthony/C-5889-2009; Gladilin, Leonid/B-5226-2011; Golubkov, Yury/E-1643-2012

Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W approximate to 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is gamma p --> XN, where X is the diffractively dissociated photon system of mass M-X and N is either a proton or a nucleonic system with mass M-N < 2 GeV. The cross section for this process in the interval 3 < M-X < 24 GeV relative to the total photoproduction cross section was measured to be sigma(D)(partial)/sigma(tot) = 6.2 +/- 0.2(stat) +/- 1.4(syst)%. After extrapolating this result to the mass interval of m(phi)(2) < M-X(2) < 0.05W(2) and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, gamma p --> Xp, is found to be sigma(SD)/sigma(tot) = 13.3 +/- 0.5(stat) +/- 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < M-X < 24 GeV can be described by the triple pomeron (IP IP IP) diagram with an effective pomeron intercept of alpha(IP)(0) = 1.12 +/- 0.04(stat) +/- 0.08(syst). The cross section for photon dissociation in the range 3 < Mr < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < Mr < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (IP IP IR term, its contribution to the diffractive cross section in the interval 3 < Mr < 24 GeV is estimated to be f(IP IP IR) = 26 +/- 3(stat) +/- 12(syst)%.