Hard Exclusive Electroproduction of $\pi^+\pi^$ Pairs
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 centerofmass 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 {nonsinglet} $q\bar{q}$ 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 leadingtwist longitudinal component
 Publication:

arXiv eprints
 Pub Date:
 June 2004
 DOI:
 10.48550/arXiv.hepex/0406052
 arXiv:
 arXiv:hepex/0406052
 Bibcode:
 2004hep.ex....6052T
 Keywords:

 High Energy Physics  Experiment
 EPrint:
 Phys.Lett.B599:212222,2004