Partonic structure of π and ρ mesons from data on hard exclusive production of two pions off nucleon
نویسندگان
چکیده
We fitted the ππ mass distribution in the range 0.5 ≤ M ππ ≤ 1.1 GeV measured in hard exclusive positron-proton reactions at HERA by the form dictated by QCD at leading twist level. Extracted parameters are related to valence quark distribution in the pion, and to the pion and ρ meson distribution amplitudes. We obtain, for the first time, a measurement of the second Gegenbauer coefficient of the ρ meson distribution amplitude: a (ρ) 2 = −0.10 ± 0.20 for a photon virtuality of Q 2 = 21.2 GeV 2 .
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