Measurement of the spin-density matrix elements in exclusive electroproduction of ρ0 mesons at HERA

Measurement of the spin-density matrix elements in exclusive electroproduction of ρ0 mesons at HERA

Exclusive electroproduction of ρ0 mesons has been measured using the ZEUS detector at HERA in two Q2 ranges, 0.25 < Q2 < 0.85 GeV2 and 3 < Q2 < 30 GeV2. The low-Q2 data span the range 20 < W < 90 GeV; the high-Q2 data cover the 40 < W < 120 GeV...

Podrobná bibliografie
Hlavní autoři:	Breitweg, J, Chekanov, S, Derrick, M, Krakauer, D, Magill, S, Musgrave, B, Pellegrino, A, Repond, J, Stanek, R, Yoshida, R, Mattingly, M, Abbiendi, G, Anselmo, F, Antonioli, P, Bari, G, Basile, M, Bellagamba, L, Boscherini, D, Bruni, A, Bruni, G, Cara Romeo, G, Castellini, G, Cifarelli, L, Cindolo, F, Contin, A
Médium:	Journal article
Jazyk:	English
Vydáno:	2000

Popis
Shrnutí:	Exclusive electroproduction of ρ0 mesons has been measured using the ZEUS detector at HERA in two Q2 ranges, 0.25 < Q2 < 0.85 GeV2 and 3 < Q2 < 30 GeV2. The low-Q2 data span the range 20 < W < 90 GeV; the high-Q2 data cover the 40 < W < 120 GeV interval. Both samples extend up to four-momentum transfers of \|t\| = 0.6 GeV2. The distribution in the azimuthal angle between the positron scattering plane and the ρ0 production plane shows a small but significant violation of s-channel helicity conservation, corresponding to the production of longitudinally polarised (i.e. helicity zero) ρ0 mesons from transverse photons. Measurements of the 15 combinations of spin-density matrix elements which completely define the angular distributions are presented and discussed.