The ratio of the electric and magnetic form factors of the proton G(E(p))/G(M(p)), which is an image of its charge and magnetization distributions, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic e(-->)p---> e(-->)p reaction. The new data presented span the range 3.5< Q(2)< 5.6 GeV(2) and are well described by a linear Q(2) fit. Also, the ratio sqrt[Q(2)] F(2(p))/F(1(p)) reaches a constant value above Q(2) = 2 GeV(2).

Precise measurements of the proton electromagnetic form factor ratio R = µpG p E /G p M using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of R with momentum transfer Q 2 for Q 2 1 GeV 2 , in strong disagreement with previous extractions of R from cross section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab's Hall A measured R at four Q 2 values in the range 3.5 GeV 2 ≤ Q 2 ≤ 5.6 GeV 2 . A possible discrepancy between the originally published GEp-II results and more recent measurements at higher Q 2 motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for R, improving the consistency of the polarization transfer data in the high-Q 2 region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis. * Corresponding author: puckett@jlab.org 2

This is a repository copy of Large underground, liquid based detectors for astro-particle physics in Europe: scientific case and prospects.

We measured angular distributions of recoil-polarization response functions for neutral pion electroproduction for W 1:23 GeV at Q 2 1:0 GeV=c 2 , obtaining 14 separated response functions plus 2 Rosenbluth combinations; of these, 12 have been observed for the first time. Dynamical models do not describe quantities governed by imaginary parts of interference products well, indicating the need for adjusting magnitudes and phases for nonresonant amplitudes. We performed a nearly model-independent multipole analysis and obtained values for Re S 1 =M 1 ÿ 6:84 0:15 % and Re E 1 =M 1 ÿ 2:91 0:19 % that are distinctly different from those from the traditional Legendre analysis based upon M 1 dominance and ' 1 truncation. DOI: 10.1103/PhysRevLett.95.102001 PACS numbers: 14.20.Gk, 13.60.Le, 13.40.Gp, 13.88.+e Insight into QCD-inspired models of hadron structure can be obtained by studying the properties of the nucleon and its low-lying excited states using electromagnetic reactions with modest spacelike four-momentum transfer, Q 2 . In the very simplest models, quark-quark interactions with SU(6) spin-flavor symmetry suggest that the dominant configuration for the nucleon consists of three quarks in an S state with orbital and total angular momenta L 0 and PRL 95, 102001 (2005) P H Y S I C A L