Width-Fluctuation Effects in (n, n′γ) Reactions

Abstract

The effects of level-width fluctuations in (n,n'y) reactions have been studied for several nuclei. Moldauer has developed a formulation for describing width-fluctuation effects in neutron inelastic scattering. 7-ray angular distributions and cross sections in (n,n'y) reactions with Mg 24 , Al 27 , Si 28 , Ar 40 , Fe 56 , and Pb 208 have been calculated on the basis of Satchler's theory, with the inclusion of width-fluctuation corrections based on Moldauer's formulation. It is found that in the region of threshold or in the cases where only a single level is excited, the inclusion of width-fluctuation effects reduces the cross sections by as much as 45%. The reduction in cross sections is smaller in the cases where several levels are excited. However, in all cases, the agreement between the experimental and calculated cross sections is significantly improved with the inclusion of width-fluctuation corrections. The shape and anisotropy of the 7 distributions are not significantly altered by the width-fluctuation corrections.

Moments of nucleon’s parton distribution for the sea and valence quarks from lattice QCD

“…We can sum over the insertion time to gain more statistics [56,57,58,60]. There are various methods by which the summation is performed [47,60,66,72]. All these methods, except in [60], considered summation over insertion time up to or beyond sink time.…”

“…calculations are performed by using a stochastic noise estimator, the signals for the current loop are always noisy. We can reduce the errors by making good use of some of the discrete symmetries, specifically parity, γ 5 hermiticity, and charge-γ 5 hermiticity (CH transformation) [45,46,47,61].…”

“…So, for O 4i which is odd in parity, one can explicitly consider the odd combination of the nucleon propagators in Table I, and similarly, the even combinations forÕ 44 andÕ 4ii , to reduce noise. According to the CH theorem [45,46,47], the path integral for O in QCD is either real or imaginary (except in the case with chemical potential). It can be shown from Tables I and II that if we combine the CH transformation of the nucleon propagators (with the appropriate combination or parity) and the loop, the three-point functions transform to the positive complex conjugate of themselves on the link U for all the three D.I.…”

“…As illustrated above, one can exclude the real part of the nucleon propagator and the real part of the loop for O 4i operator which contributes to noise with finite number of noise vectors. The utilization of γ 5 hermiticity and CH theorem has been shown to reduce noise effectively in the loop calculation of the quark angular momentum [47]. Similar procedures can be applied to the other two operators.…”

Dynamical coupled-channel approaches on a momentum lattice

“…The masses of meson and baryon ground states could be determined at the few percent level [11] and close to physical pion masses. With regard to excited hadrons, signals of a rich spectrum could be found recently [12,13,14,15,16] in calculations with pion masses ≥ 300 MeV or in the quenched approximation. Of course, those excited states will be able to decay on the lattice, once the employed pion mass approaches the physical value.…”