A measurement of elastic deeply virtual Compton scattering gamma* p -> gamma p using e^+ p and e^- p collision data recorded with the H1 detector at HERA is presented. The analysed data sample corresponds to an integrated luminosity of 306 pb^-1, almost equally shared between both beam charges. The cross section is measured as a function of the virtuality Q^2 of the exchanged photon and the centre-of-mass energy W of the gamma* p system in the kinematic domain 6.5 < Q^2 < 80 GeV^2, 30 < W < 140 GeV and |t| < 1 GeV^2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q^2 and W values and exponential t-slope parameters are derived. Using e^+ p and e^- p data samples, a beam charge asymmetry is extracted for the first time in the low Bjorken x kinematic domain. The observed asymmetry is attributed to the interference between Bethe-Heitler and deeply virtual Compton scattering processes. Experimental results are discussed in the context of two different models, one based on generalised parton distributions and one based on the dipole approach.
The DVCS cross section as a function of Q**2.
The DVCS cross section as a function of W.
The DVCS cross section as a function of W for three different Q**2 regions.
The STAR collaboration at RHIC presents measurements of \Jpsi$\to{e^+e^-}$ at mid-rapidity and high transverse momentum ($p_T>5$ GeV/$c$) in \pp and central \cucu collisions at \sNN = 200 GeV. The inclusive \Jpsi production cross section for \cucu collisions is found to be consistent at high $p_T$ with the binary collision-scaled cross section for \pp collisions, in contrast to previous measurements at lower $p_T$, where a suppression of \Jpsi production is observed relative to the expectation from binary scaling. Azimuthal correlations of $J/\psi$ with charged hadrons in \pp collisions provide an estimate of the contribution of $B$-meson decays to \Jpsi production of $13% \pm 5%$.
J/psi differential production cross section in sqrt(s).
J/psi transverse momentum distribution in sqrt(s).
J/psi transverse momentum distribution in sqrt(s).
We have studied the diffractive dissociation into di-jets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t_{min} approaches 0) we find that when the per-nucleus cross-section for this process is parameterized as $ \sigma = \sigma_0 A^{\alpha} $, $ \alpha $ has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.
Cross sections is fitted to A**POWER.
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