Direct Photon Production In Pp Collisions Research Articles

Single transverse spin asymmetries.

Using generalized factorization theorems, we calculate the leading single transverse spin asymmetry for high transverse-momentum direct-photon production in pp collisions, in terms of partonic matrix elements. The leading contribution comes from a ``twist-3'' parton distribution, involving the correlation between quark fields and the gluonic field strength. With simple assumptions for this matrix element, the asymmetry increases with ${\mathit{x}}_{\mathit{F}}$, naturally giving effects of 10% or more at large ${\mathit{x}}_{\mathit{F}}$.

Direct photon production beyond leading log approximation—q+q→γ+q+q contribution

Theq+q→γ+q+q contribution (for incoming quarks of equal and different flavours) to the next-to-leading correction for the direct photon production inpp collisions is calculated, analyzed in terms of double moments and compared with the data. The dimensional regularization method is used and the final state Bremsstrahlung infinities are regularized by an angular cut-off. The correction is found to be 30–40% of the Born contribution providing a better description of the data.

High-p T direct photon production inpp collisions

Direct photon and neutral-pion production have been measured inpp collisions at the CERN ISR for 30<\(\sqrt s \)<63 GeV and transverse momenta up to 12 GeV/c. The direct photon signal relative to neutral-pion production increases withpT and shows little\(\sqrt s \)-dependence. Results are reported from a variety of running conditions, and details are given on the method of analysis and on the evaluation of systematic errors for the inclusive cross-section of single-photon and neutral-pion production.