Polarisation in the (d, 2p) reaction at intermediate energies

Abstract

Deuteron tensor polarisations t 2 i are considered in A(d, 2p)A' reactions on hydrogen and nuclei for deuteron kinetic energies 100 to 2000 MeV. In those parts of phase space where the di-proton singlet or triplet final state dominates, both t 20 and t 22 should in general be quite large. Hence the reaction may be used as an efficient and convenient analyser of deuteron tensor polarisations. An interesting specific case is when the di-proton is enhanced by the virtual d ∗ 1S 0 state near threshold for then the polarisation of the deuteron governs the quantum numbers exchanged with the nucleus. Measurements of σ, t 20 and t 22 in inclusive and exclusive (d, d ∗) reactions on J p = 0 + target nuclei may be used to find the spin dependence of nuclear cross sections as functions of momentum transfer. For inclusive processes, t 20 and t 22 should be large as for hydrogen, but with two qualitative differences: (i) pion exchange should be enhanced because of the shadowing of short-range exchanges, (ii) the peak of t 22 moves to a smaller angle because of the shadowing. Excitation of specific final nuclear states by ΔS = 1 transitions is considered. Tensor polarisations are distinctively different for J = L + 1, L and L− l final states, and are useful tools for separating and identifying 0 −, 1 − and 2 − giant excitations. A connection is drawn with the spin-transfer process d( p , n )2 p which is used at meson factories to make polarised neutron beams. The neutron spectrum is estimated and a large variation of the polarisation transfer is found over it. A convenient formalism is given for handling spin effects involving the deuteron D-state in all the above reactions.