2019 Impact factor 4.389
Particles and Fields
Eur. Phys. J. C 12, 393-410
DOI 10.1007/s100529900246

Measurement of the spin-density matrix elements
in exclusive electroproduction of $\rho^0$ mesons at HERA

The ZEUS Collaboration

J. Breitweg - et al.

Argonne National Laboratory, Argonne, IL, USA

Received: 30 July 1999 / Revised version: 20 September 1999 / Published online: 8 December 1999

Exclusive electroproduction of $\rho^0$ mesons has been measured using the ZEUS detector at HERA in two Q2 ranges, 0.25<Q2<0.85 GeV2and 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 $\rho^0$production plane shows a small but significant violation of s-channel helicity conservation, corresponding to the production of longitudinally polarised (i.e. helicity zero) $\rho^0$ mesons from transverse photons. Measurements of the 15 combinations of spin-density matrix elements which completely define the angular distributions are presented and discussed.

Copyright Springer-Verlag 2000