Excitation of the Delta(1232) isobar in deuteron charge exchange on hydrogen at 1.6, 1.8, and 2.3 GeV

TL;DR

This study investigates the excitation of the Delta(1232) isobar in deuteron charge exchange reactions at energies of 1.6, 1.8, and 2.3 GeV, providing insights into the underlying mechanisms and comparing experimental data with theoretical models.

Contribution

The paper presents new measurements of differential cross sections and tensor analyzing powers in deuteron charge exchange, extending understanding of Delta isobar excitation at higher energies.

Findings

High Mx unpolarized cross section matches direct Delta excitation models.

Low Mx cross section is underestimated by current models.

Angular dependence of tensor analyzing power differences is reproduced by pion exchange models.

Abstract

The charge-exchange break-up of polarised deuterons pol{d}p -> {pp}n, where the final {pp} diproton system has a very low excitation energy and hence is mainly in the 1S0 state, is a powerful tool to probe the spin-flip terms in the proton-neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Delta(1232) isobar in the pol{d}p -> {pp}X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A_{xx} and A_{yy}, have been extracted in terms of the momentum transfer to the diproton or the invariant mass Mx of the unobserved system X. The unpolarised cross section in the high Mx region is well described in a model that includes only direct excitation of the Delta isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low Mx, even when Delta excitation in the projectile deuteron is included in the calculation. Furthermore, direct Delta production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.