Measurement of Angular Distributions and R = σ L / σ T in Diffractive Electroproduction of ρ 0 Mesons
نویسندگان
چکیده
Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the ρ(770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q < 4 GeV and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the Hermes spectrometer, using a longitudinally polarized positron beam and a He gas target internal to the HERA e storage ring. The event sample combines ρ mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the ρ → ππ decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q.
منابع مشابه
Diffractive electroproduction of ρ meson excitations
We use perturbative QCD and parton-hadron duality to estimate the cross sections for the diffractive electroproduction of ρ ′ (1 −) and ρ(3 −) resonances which occur in the 1.3– 1.8 GeV mass interval. We present the cross sections and the ratios σ L /σ T as a function of Q 2. We compare the predictions with those for the diffractive electroproduction of ρ mesons. We show how such diffractive el...
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