I. Sitnik

Final analysis of proton form factor ratio data at Q2 = 4.0, 4.8, and 5.6 GeV2

Precise measurements of the proton electromagnetic form factor ratio R = mu(p)G(E)(p)/G(M)(p) 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) greater than or similar to 1 GeV2, 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 Labs Hall A measured R at four Q(2) values in the range 3.5 GeV2 <= Q(2) <= 5.6 GeV2. 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. (Less)

Search for η-mesic nuclei in a recoil-free transfer reaction

We have studied the reaction p+{sup 27}Al {yields} {sup 3}He+p+{pi}{sup -}+X at recoil-free kinematics. An {eta} meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear {eta} states exist. The decay of such a state through the N*(1535) resonance would lead to a proton-{pi}{sup -} pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of {approx_equal}0.5 nb is found.

High resolution study of the Λp final state interaction in the reaction p+p→K++(Λp)

The reaction pp ! K + + (�p) was measured at Tp = 1.953 GeV and � = 0 ◦ with a high missing mass resolution in order to study thep final state interaction. The large final state enhancement near thep threshold can be described using the stan- dard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously thep invariant mass spectrum and the total cross section data of the freep scattering.

Cross section and tensor analysing power of the dd→ηα reaction near threshold

The angular distributions of the unpolarised differential cross section and tensor analysing power A xx A x x of the d → d → α η reaction have been measured at an excess energy of 16.6 MeV. The ambiguities in the partial-wave description of these data are made explicit by using the invariant amplitude decomposition. This allows the magnitude of the s -wave amplitude to be extracted and compared with results published at lower energies. In this way, firmer bounds could be obtained on the scattering length of the ηα system. The results do not, however, unambiguously prove the existence of a quasi-bound ηα state.

Upper limits for a narrow resonance in the reaction p + p to K^++ (Lambda p)

The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and \Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. Narrow S = -1 resonances predicted by bag model calculations are not visible in the missing mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV/c^2.

Detailed comparison of the pp→π+pn and pp→π+d reactions at 951 MeV

The positively charged pions produced in proton–proton collisions at a beam momentum of 1640 MeV/c were measured in the forward direction with a high resolution magnetic spectrograph. The missing mass distribution shows the bound state (deuteron) clearly separated from the pn continuum. Despite the very good resolution, there is no evidence for any significant

Analyzing powers for the inclusive reaction of deuterons on carbon at energies between 0.175 and 1.6 GeV

Abstract The results of a new calibration of the polarimeter POMME for energies between 0.175 and 1.6 GeV, using the polarized deuteron beam of the Laboratoire National Saturne, are reported. The present calibration, together with previous ones, gives a complete set of vector analyzing powers in the energy range 0.175–1.8 GeV. The vector analyzing powers are fitted as a function of energy and scattering angle, with empirical formulae. Two sets of parameters are given, one for deuteron energies between 0.175 and 0.575 GeV, and the other in an energy range between 0.7 and 1.8 GeV.

Experimental study of the p + 6Li → η + 7Be reaction 11.3 MeV above threshold

The cross section for the reaction

Precision measurements of the pp ->pi(+)pn and pp ->pi(+)d reactions: Importance of long-range and tensor force effects

p+^6\text{Li}\to\eta+^7\text{Be}

Three-nucleon interaction dynamics studied via the deuteron-proton breakup

was measured at an excess energy of 11.28 MeV above threshold by detecting the recoiling