/ Experiment-HEP hep-ex/0406052

Hard exclusive electroproduction of pi+ pi- pairs

Airapetian, A. ; Akopov, N. ; Akopov, Z. ; Amarian, M. ; Ammosov, V.V. ; Andrus, A. ; Aschenauer, E.C. ; Augustyniak, W. ; Avakian, R. ; Avetissian, A. ; Avetissian, E. ; Bailey, P. ; Balin, D. ; Baturin, V. ; Beckmann, M. ; Belostotski, S. ; Bernreuther, S. ; Bianchi, N. ; Blok, H.P. ; Bottcher, H. ; Borissov, A. ; Borysenko, A. ; Bouwhuis, M. ; Brack, J. ; Brull, A.

Published in: Phys.Lett.
Year: 2004
Vol.: B599
Page No: 212-222
Pages: 9

Abstract: Hard exclusive electroproduction of $\pi^+\pi^-$ pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments $<P_1>$ and $<P_3>$ of the angular distributions of $\pi^+$ mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the $\pi^+\pi^-$ invariant mass can be understood as being due to the interference between relative $P$-wave (isovector) and $S,D$-wave (isoscalar) states of the two pions. % The increase in magnitude of $<P_1>$ as Bjorken $x$ increases is interpreted in the framework of Generalized Parton Distributions as an enhancement of flavour {non-singlet} $q\bar{q}$ exchange for larger values of $x$, which leads to a sizable admixture of isoscalar and isovector pion pairs. % In addition, the interference between {$P$-wave} and {$D$-wave} states separately for transverse and longitudinal pion pairs has been studied. The data indicate that at {$\la Q^2 \ra = 3$ GeV$^2$} higher twist effects can be as large as the leading-twist longitudinal component

Total numbers of views: 1530
Numbers of unique views: 612
e-proceeding