Abstract

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〉=3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.

Highlights

  • G due to the interference between relative P -wave and S, D-wave states of the two pions

  • Our understanding of quark–gluon dynamics can be extended considerably by measurements sensitive to the generalized parton distributions (GPD) [1,2,3], which describe the dynamical correlations between partons with different momenta

  • Hard exclusive electroproduction of π+π− pairs is sensitive to the interference between isospin I = 1 and I = 0 channels, and provides a new constraint on certain combinations of GPDs

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Summary

VU Research Portal

Link to publication in VU Research Portal citation for published version (APA) Airapetian, A., Blok, H. H. A., Laziev, A., van der Nat, P. B., Vogt, M., Volmer, J., & Smit, G. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights

HERMES Collaboration
Legendre moment of order n is given by
Pn exclusive
Findings
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