Conference paper
Hard exclusive electroproduction of resonant and non-resonant pion pairs at HERMES
Alexander Borissov (on behalf of the HERMES collaboration)
; Department of Physics and Astronomy, University of Glasgow, Glasgow, G128QQ, United Kingdom
Abstract
A selection of recent HERMES results is presented on the hard exclusive electroproduction of resonant and non-resonant π +π − pairs. The ratio of ρ 0 electroproduction cross sections per nucleon on 14N as compared to that on 1H, known as the nuclear transparency, was found to increase (decrease) with increasing coherence length for coherent (incoherent) ρ 0 electroproduction. For a fixed coherence length, a rise of the nuclear transparency with Q2 is observed for both coherent and incoherent ρ 0 production, which is in agreement with theoretical calculations that include the effect of color transparency. The first-order intensity density for exclusive electroproduction of π +π − pairs has been studied as a function of the invariant mass Mππ in the range 0.3 < Mπ+π− < 1.5 GeV. The derived quantities show a dependence of the π +π − invariant mass, which can be understood as due to the interference between pion pairs in relative P-wave (isovector channel) and S,D-waves (isoscalar channel) states.
Keywords
resonant and non-resonant π+π− pairs; cross sections; hard exclusive electroproduction; generalized parton distributions
Hrčak ID:
305901
URI
Publication date:
1.6.2004.
Visits: 366 *