Recent results from the deuteron charge–exchange on hydrogen programme at ANKE/COSY

Abstract

A good understanding of the Nucleon-Nucleon interaction (N N) remains one of the most important goals of nuclear and hadronic physics. Apart from their intrinsic importance for the study of nuclear forces, N N data are necessary ingredients in the modelling of meson production and other nuclear reactions at intermediate energies. Experiments at COSY, using a polarised deuteron beam and/or target, can lead to significant improvements in the np database by studying the quasi-free reaction on the neutron in the deuteron-dp → {pp}n. At low excitation energies of the final pp system, typically Epp < 3 MeV, the spin observables are directly related to the spin-dependent parts of the neutron-proton charge-exchange amplitudes. Measurement of the deuteron-proton spin-correlations allows one also to fix the relative phases of these amplitudes in addition to their overall magnitudes. Recent results of this study at ANKE/COSY are presented, including preliminary data on dp → {pp}∆ 0 .

Neutron-proton scattering in the context of thed*(2380) resonance

“…Though this energy is somewhat below the one used here, the analyzing powers in pd scattering have been observed [15,16] to be only weakly dependent on the beam energy. This is supported by very recent data obtained at COSY-ANKE [17] at T d = 2.27 GeV. As a result we obtain beam polarizations of P z = 0.67(2), P zz = 0.65(2) for "up" and P z = -0.45(2), P zz = 0.17(2) for "down".…”

The neutron-proton charge-exchange amplitudes measured in the dp → ppn reaction

“…But, in the 2006 data, the maximum tensor polarisation dropped to ≈ 55% of the ideal, with little change in the vector polarisation. The difference has been ascribed to the changed efficiencies of the units in the COSY deuterium ion source [21]. For the high |P zz | modes in Table 1 The vector analysing power of the dp → {pp} s n reaction is predicted to vanish in the 1 S 0 limit [6] and this was confirmed at 1.17 GeV in our earlier work [10].…”

“…During the course of the polarised measurements, various configurations of the ion source were used and the beam polarisation had to be determined separately for each state. Several methods to fix the relative luminosities C n of a state with respect to the unpolarised mode are possible at ANKE [21]. The one provided by the dp → p sp X reaction is preferable because the number of single-track events is enormous for all beam energies.…”

The legacy of the experimental hadron physics programme at COSY

“…Extra evidence in support of the dibaryon hypothesis was found from the WASA measurements of the analyzing power in neutron-proton elastic scattering [84,85], which led to a revision of the SAID [65] I = 0 amplitude analysis. There had already been indications from dp → {pp} s n measurements at ANKE [86] that the existing SAID np solution was defective at high energies. Far more measurements are needed in neutronproton elastic scattering above 1 GeV to give definitive solutions.…”

“…2.27 GeV, and detected the recoil proton in coincidence with the spectator proton. The values of the vector and tensor polarizations of the beam were determined using deuteron-proton elastic scattering that had been measured at ANKE [86]. The methodology was also checked by studying in parallel the analyzing power in pp quasi-elastic scattering.…”