Article

# Measurement of inelastic J / psi photoproduction at HERA

• ##### W.B. Schmidke
01/1997; DOI: 10.1007/s002880050583
Source: OAI

ABSTRACT We present a measurement of the inelastic, non diffractive J/$\psi$ photoproduction cross section in the reaction $e^{+} p \rightarrow e^{+} \mbox{J}/\psi X$ with the ZEUS detector at HERA. The J/$\psi$ was identified using both the $\mu^{+}\mu^{-}$ and $e^{+}e^{-}$ decay channels and events were selected within the range $0.4 ($0.5) for the muon (electron) decay mode, where $z$ is the fraction of the photon energy carried by the J/$\psi$ in the proton rest frame. The cross section, the $p^2_T$ and the $z$ distributions, after having subtracted the contributions from resolved photon and diffractive proton dissociative processes, are given for the photon-proton centre of mass energy range $50 GeV;$p^2_T$is the square of the J/$\psi$transverse momentum with respect to the incoming proton beam direction. In the kinematic range$0.4 and $p^2_T > 1$ GeV$^2$, NLO calculations of the photon-gluon fusion process based on the colour-singlet model are in good agreement with the data. The predictions of a specific leading order colour-octet model, as formulated to describe the CDF data on J/$\psi$ hadroproduction, are not consistent with the data.

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• ##### Article: Investigation of the Balitsky-Fadin-Kuraev-Lipatov dynamics of gluon distributions in the inelastic production of J/ψ mesons at the HERA collider
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ABSTRACT: The inelastic photo-and electroproduction of J/ψ mesons at the HERA collider are considered within the semihard (k T -factorization) QCD approach and the color-singlet model. The total, differential, and double-differential cross sections for the inelastic production of J/ψ mesons are investigated versus the Pomeron intercept Δ, which is the basic parameter of low-x physics; also studied here is the spin alignment parameter α versus the square of the transverse momentum, p ψT 2 , and the variable z. The theoretical results obtained in the present study are compared with the latest experimental data of the H1 and ZEUS Collaborations. It is shown that experimental investigations of the polarization properties of J/ψ mesons at the HERA collider for Q 2<1 GeV2 may provide an additional test of the Balitsky-Fadin-Kuraev-Lipatov dynamics of gluon distributions.
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