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Measurement of elastic J / psi photoproduction at HERA

The ZEUS collaboration Breitweg, J. ; Derrick, M. ; Krakauer, D. ; et al.

Z.Phys.C 75 (1997) 215-228, 1997.

Inspire Record 442537 DOI 10.17182/hepdata.44626

The reaction gamma p -> J/Psi p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/Psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q^2 of 5*10^{-5} GeV^2. The photoproduction cross section, sigma_{gamma p -> J/Psi p}, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter $\delta$ in the form sigma_{gamma p -> J/Psi p} \propto W^{\delta} yields the value \delta = 0.92 \pm 0.14 \pm 0.10. The differential cross section dsigma/d|t| is presented over the range |t| < 1.0 GeV^2 where t is the square of the four-momentum exchanged at the proton vertex. d\sigma/d|t| falls exponentially with a slope parameter of 4.6 \pm 0.4 (+0.4-0.6) GeV^{-2}. The measured decay angular distributions are consistent with s-channel helicity conservation.

9 data tables

Table 1

Data from the electron channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.

Table 2

Data from the muon channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.

Table 3

Data from the electron channel. Second systematic error is that attributed to the uncertainty in the modelof proton dissociation used for background subtraction.

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Measurement of the cross-section for production of two isolated prompt photons in anti-p p collisions at s**(1/2) = 1.8-TeV

The CDF collaboration Abe, F. ; Albrow, Michael G. ; Amidei, Dante E. ; et al.

Phys.Rev.Lett. 70 (1993) 2232-2236, 1993.

Inspire Record 343802 DOI 10.17182/hepdata.19755

We present measurements from events with two isolated prompt photons in p¯p collisions at √s =1.8 TeV. The differential cross section, measured as a function of transverse momentum (PT) of each photon, is about 3 times what next-to-leading-order QCD calculations predict. The cross section for photons with PT in the range 10–19 GeV is 86±27(stat)−23+32(syst) pb. We also study the correlation between the two photons in both azimuthal angle and PT. The magnitude of the vector sum of the transverse momenta of both photons, KT=‖PT1+PT2‖, has a mean value of 〈KT〉=5.1±1.1 GeV.

5 data tables

Table 1

No description provided.

Table 2

No description provided.

Table 3

Vector sum of the photons transvserse momenta.. Errors contain both statistics and systematics.. Data read from plots.