Beam-target double spin asymmetries in the reaction γd → π0d near threshold and the role of D-wave component of the deuteron wave function

Abstract

We investigate coherent π 0-photoproduction on the deuteron near threshold with special emphasis on beam-target double spin asymmetries. We present results for the spin asymmetries T c 1M (M = 0, 1) for circular polarized photons and vector polarized deuterons, T c 2M (M = 1, 2) for circular polarized photons and tensor polarized deuterons, T l 1M (M = 0, ±1) for longitudinal polarized photons and vector polarized deuterons, and T l 2M (M = 0, ±1, ±2) for longitudinal polarized photons and tensor polarized deuterons in the γ d → π 0 d reaction near threshold. We also discuss the sensitivity of the estimated results to the D-wave component of the deuteron wave function. The unitary isobar MAID-2007 model is used for the elementary γ N → πN amplitude. This model is parameterized in terms of invariant amplitudes and allows one to give a more reliable description of the threshold region. The realistic and high-precision Bonn NN potential (full model) is used for the deuteron wave function. We have found that the D-wave component of the deuteron wave function has a little effect on the T c 1M (M = 0, 1) and T l 2M (M = 0, 1, 2) spin asymmetries. On the contrary, we have obtained a significant role of the D-wave component on the spin asymmetries T c 2M (M = 1, 2), T l 1M (M = 0, ±1), and T l 2M (M = −1, −2).

Uncertainties in theoretical predictions for γd → π 0d observables near threshold due to the use of different elementary amplitudes

“…As discussed in Refs. [31,38], the vector asymmetries T l 1M are considerably small for π 0 production near threshold. Figure 8 displays also that the difference between the results for T l 10 and T l 1−1 asymmetries using χMAID-2013 model and both DMT-2001 and MAID-2007 increases with increasing photon lab-energy, which indicates that these spin asymmetries are very sensitive the choice of the elementary γN → πN amplitude.…”

“…So far, many studies have been carried out dealing with the reaction γd → π 0 d in the photon energy region from π-threshold up to 1 GeV in order to obtain information on π 0 -photoproduction off free neutrons [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. In spite of all these great theoretical efforts, a good description of the experimental data has not been yet found [3,4,6,7].…”