Measurement of the longitudinal spin-dependent neutron-proton total cross-section difference ΔσL(np) between 500 and 800 MeV

Abstract

A measurement of AuL(np), the difference between neutron-proton total cross sections for pure longitudinal spin states, is described. Data were taken at LAMPF for five neutron beam kinetic energies: 484, 568, 634, 720, and 788 MeV. The statistical errors are in the range 0.64-1.35 mb. Various sources of systematic effects were investigated and are described. Overall systematic errors are estimated to be on the order of 0.5 mb and include an estimate for the uncertainty in the neutron beam polarization. The AUL results are consistent with previous results from PSI and Saclay. These data, when combined with other results and fitted to a Breit-Wigner curve, are consistent with an elastic 1=0 resonance with mass 2214 i 15 (stat) f 6 (syst) MeV and width 75 i 21 f 12 MeV. TNow at 127 Eastgate, Los Alamos, New Mexico 87544. derstanding of the NN interaction a t energies below pion production threshold (about 300 MeV), which is the region of "conventional" nuclear physics, where elastic scattering dominates. The d a t a for both proton-proton (pp) and neutron-proton (np) scattering are fairly copious a t these energies and are generally self-consistent. From a theoretical point of view, quantitative success has been achieved in describing this process in terms of potentials based on field-theoretic formalism involving meson exchange. Among these are the Paris [I], Bonn 121, and Argonne [3] potentials. A review of this work has been given by Machleidt [4]. Other theoretical studies include Skyrme [5,6] and quark [7,8] models. T h e current status of these models has been reviewed by Vinh Mau [9].At energies u p t o about 1 GeV, where pion production and excitation of the A(1232) resonance are possible, the situation is not so well understood, however.

Sensitivity of the COSY dibaryon candidate tonpelastic scattering measurements

“…The pole fit displays a rapid energy variation which would require a fine energy binning and measurements spanning the width of the COSY dibaryon. [26,27] shown as blue filled circles, PSI data [28] shown as black open circles, PPA data [29] shown as magenta open triangles, BNL data [30] shown as green filled triangles, and JINR data [31] shown as red open sqares], ∆σT (middle panel) [PSI data [32] shown as black open circles and SACLAY data [33][34][35] shown as magenta crosses], and ∆σL (right panel) [PSI data [32] shown as black open circles, LAMPF data [36] shown as blue filled circles, Saclay data [33] shown as magenta crosses, and JINR data [31,37] shown as red open squares]. Notation for SAID curves as in Fig.…”

“…is not sufficiently precise to clearly distinguish between these alternatives. Improved measurements of this quantity, with uncertainties comparable to the LAMPF [36] measurements, of order of ∆σ L ∼ 10% would greatly improve this comparison.…”

Updated analysis ofNNelastic scattering data to 1.6 GeV

“…A detailed study of np polarization quantities was carried out at Saclay, producing data for P [25], [26]; A yy [27]; A zz [28]; A zx [29]; A t , N 0nkk , D 0s"0k , R t , N 0nsk , D, and D t [39]. Total np cross sections in pure spin states were also measured [6], [8], [30], [32], [37], [40].…”

Nucleon-nucleon elastic scattering analysis to 2.5 GeV

“…A few total cross sections in pure spin states between 4 and 16 MeV were produced by TUNL [58] and Charles University at Prague [59,60]. Recently, the final LAMPF ∆σ L measurements between 480 and 790 MeV were also published [61]. In addition, some new ∆σ L measurements above 1190 MeV were made at JINR (Dubna) [62].…”