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  • Hard exclusive electroprodu...
    Amarian, M.; Ammosov, V.V.; Andrus, A.; Avakian, R.; Avetissian, A.; Balin, D.; Baturin, V.; Beckmann, M.; Blok, H.P.; Böttcher, H.; Borissov, A.; Bouwhuis, M.; Brack, J.; Bryzgalov, V.; Capitani, G.P.; Dalpiaz, P.F.; De Leo, R.; De Sanctis, E.; Düren, M.; Ehrenfried, M.; Ellinghaus, F.; Elschenbroich, U.; Fantoni, A.; Fechtchenko, A.; Frullani, S.; Gapienko, G.; Gapienko, V.; Garibaldi, F.; Garrow, K.; Grebeniouk, O.; Greeniaus, L.G.; Gregor, I.M.; Hartig, M.; Hasch, D.; Heesbeen, D.; Henoch, M.; Hesselink, W.H.A.; Hoek, M.; Holler, Y.; Iarygin, G.; Izotov, A.; Jackson, H.E.; Jgoun, A.; Kaiser, R.; Kinney, E.; Kisselev, A.; Kopytin, M.; Korotkov, V.; Laziev, A.; Lenisa, P.; Liebing, P.; Lorenzon, W.; Ma, B.-Q.; Makins, N.C.R.; Mao, Y.; Marianski, B.; Marukyan, H.; Mikloukho, O.; Miller, C.A.; Miyachi, Y.; Nappi, E.; Naryshkin, Y.; Nass, A.; Negodaev, M.; Nowak, W.-D.; Oganessyan, K.; Reggiani, D.; Riedl, C.; Rosner, G.; Rubacek, L.; Sanjiev, I.; Schnell, G.; Schüler, K.P.; Seitz, B.; Shutov, V.; Statera, M.; Steffens, E.; Steijger, J.J.M.; Stenzel, H.; Stewart, J.; Stinzing, F.; Tanaka, H.; Taroian, S.; Tchuiko, B.; Terkulov, A.; Tkabladze, A.; Trzcinski, A.; Vandenbroucke, A.; van der Nat, P.; van der Steenhoven, G.; Vetterli, M.C.; Vogel, C.; Vogt, M.; Volmer, J.; Weiskopf, C.; Wendland, J.; Ye, Y.; Ye, Z.; Yen, S.; Zihlmann, B.

    Physics letters. B, 10/2004, Letnik: 599, Številka: 3-4
    Journal Article

    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.