A Measurement of the t dependence of the helicity structure of diffractive rho meson electroproduction at HERA

The helicity structure of the diffractive electroproduction of ρ mesons, e + p → e + ρ + Y , is studied in a previously unexplored region of large four-momentum transfer squared at the proton vertex, t : 0< t ′<3 GeV 2 , where t ′=| t |−| t | min . The data used are collected with the H1 detector at HERA in the kinematic domain 2.5< Q 2 <60 GeV 2 , 40< W <120 GeV. No t dependence of the r 04 00 spin density matrix element is found. A significant t dependent helicity non-conservation from the virtual photon to the ρ meson is observed for the spin density matrix element combinations r 5 00 +2 r 5 11 and r 1 00 +2 r 1 11 . These t dependences are consistently described by a perturbative QCD model based on the exchange of two gluons.

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20 pages, 4 figures, 1 table Report-no: DESY 02-027

positron p: colliding beams
momentum transfer: high
rho(770): electroproduction
diffraction
helicity: amplitude analysis
spin: density matrix
momentum transfer dependence
quantum chromodynamics: perturbation theory
exchange: two-gluon
H1

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