2004/06/30 by The HERMES Collaboration, Н. Акопов, A. Airapetian +98 · 1 citation
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paper · pdf · doi:10.1016/j.physletb.2004.08.059
published as Phys.Lett.B599:212-222,2004
arxiv created 2004/07/22 · openalex publication_date 2004/09/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Hard exclusive electroproduction of π+π− pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments 〈P1〉 and 〈P3〉 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 〈P1〉 as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet qq¯ 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 〈Q2〉=3GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.