A polarization relation and the measurement of the longitudinal response in pseudoscalar meson electroproduction off the nucleon

Abstract

For pseudoscalar meson electroproduction off the nucleon in parallel kinematics a relation between three polarization observables is derived. It is shown that, without Rosenbluth separation, a measurement of the longitudinal strength can be achieved through three different ways. They are discussed with preliminary MAMI data for the p( e, e ′ p)π 0 reaction in the energy range of the ∆(1232) resonance.

Measurement of the Recoil Polarization in thep(e→,e′Pospischil1, Bartsch2, Baumann3 et al. 2001Phys. Rev. Lett.Self Cite890140View full textAdd to dashboardCite

“…Equations (5) and (7) show that, in the pp 0 channel, g CMR Re͕S ‫ء‬ 11 M 11 ͖͞jM 11 j 2 can be determined through either P x or the polarization ratio P x ͞P z [16]. Furthermore, the ratio R L ͞R T of longitudinal to transverse response is model-independently accessible without Rosenbluth separation [18].…”

“…The ratio R L ͞R T of longitudinal to transverse response can be obtained in various ways from the so-called reduced polarizations (RPs) x x,y,z [18,27]. However, the The dashed, dot-dashed, full, and dotted curves correspond to CMR 0%, 23.2%, 26.4%, 29.6%, respectively.…”

“…Despite the nonlinear error propagation in R L ͞R T ͑x z ͒, the probability is only a few percent that this discrepancy has purely statistical origin. As a consequence, the consistency relation between the transverse and the longitudinal RPs derived in [18] seems to be violated. This presently prohibits a reliable extraction of R L ͞R T but stresses the importance of a simultaneous measurement of all polarization components with further improved accuracy.…”

Recoil polarization measurements for neutral pion electroproduction atQ2=1(GeV/c)2near t

“…Alternatively, often the most efficient method for extracting the x dependence of response functions for a particular (W, Q 2 ) bin is to perform a two-dimensional fit of the (x, φ) dependencies of the appropriate observable, cross section or polarization, with the aid of the Legendre expansion. This type of analysis can be used to extrapolate response functions to parallel or antiparallel kinematics where interesting symmetry relations have been developed but where the experimental acceptance vanishes [34,35].…”

Photo- and electro-excitation of the Δ-resonance at MAMI

“…According to ref. [46] this can be achieved in three different ways, using either -only the longitudinal component, χ z (cf. also [49]), -the quadratic sum of the transverse components, χ …”