Hard Exclusive Electroproduction of π+π- Pairs at Hermes
Abstract
Hard exclusive electroproduction of π+π- pairs on hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments < P 2 > and < P 3 > of the angular distributions of π+ mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the π+π- 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 > and < P 3 > as Bjorken x increases is interpreted in the framework of Generalized Parton Distributions as an enhancement of flavour non-singlet qbar 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 in the f2(1270) region at < { Q}2 ; > = 3 {GeV}{2} , higher-twist effects can be as large as the leading-twist longitudinal component.
- Publication:
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SPIN 2004
- Pub Date:
- August 2005
- DOI:
- Bibcode:
- 2005spph.conf..429F