NUCLEON NUCLEUS WEAK SCATTERING WITHIN A SINGLE PARTICLE MODEL

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NUCLEON NUCLEUS WEAK SCATTERING WITHIN A SINGLE PARTICLE MODEL

Y. Avishai

To cite this version:

Y. Avishai. NUCLEON NUCLEUS WEAK SCATTERING WITHIN A SINGLE PARTICLE MODEL. Journal de Physique Colloques, 1984, 45 (C3), pp.C3-75-C3-76. �10.1051/jphyscol:1984314�.

�jpa-00224028�

JOURNAL DE PHYSIQUE

Colloque C 3 , supplement au n ° 3 , Tome 45, m a r s 1984 page C3-75

NUCLEON NUCLEUS WEAK SCATTERING WITHIN A SINGLE PARTICLE MODEL

Y. Avishai

Centre de Recherches Nucleaires et Universite Louis Pasteur de Strasbourg, Groupe de Physique Nucleaire Theorique, B.P. 20CR

67037 Strasbourg Cedex, France

Résumé - On discute la diffusion faible d'un nucléon sur le noyau dans un mo- dèle où l'interaction faible a une forme à un corps (suggérée par Michel) directement reliée aux paramètres de l'interaction N-N faible. Des résultats

-.40 numériques sont présentés pour la diffusion n+ Ca»

Abstract - We discuss weak scattering of nucleon on nucleus in which the weak interaction has a single particle form (suggested by Michel) which is directly related to the parameters of the weak NN interaction. Numerical re- sults are presented for n+ Ca scattering.

After the neutron spin-rotation experiment at ILL, a lot of theoretical work has been done which focused mainly on the enhancement effects due to neutron resonances.

However, neutron resonance is a complex many particle phenomena, and thus it is impossible to relate the evaluated results with the fundamental weak NN interaction parameters. One way out of this dead end is to concentrate (both in experiment and in theory) on light nuclei. Another way, which we suggest here is to construct crude but realistic models for weak neutron nucleus scattering which are simple enough

and are directly related to the weak NN interaction parameters. Such models will not follow the fine details at the resonant energy but can serve as a reference result over wide energy, angle and mass ranges. Such a model has recently been sug- gested by the author (P.R. C28 (1983) 656) based on strong and weak nucleon-nucleus optical potential suggested by Michel. The weak potential is obtained by folding the NN weak interaction (whose non-relativistic form is taken from DDH-Ann. Phys.

124 (1980) 449) over the target density. The scattering amplitude for N+A scattering is then deduced from a two body Hamiltonian H=T+V+G'0.{p,p(r)} where V is the strong optical potential p(r) is the target nucleon density and C,p are spin and momentum of the projectile. The weak coupling constant G' is written as G'=AT +B where T =1 (-1) for neutron (proton) projectile and A,B are linear combination of

all the weak NN interaction parameters f's and h's.

•+ 4 0

As an example we have computed the spin rotation angle for n+ Ca with the result d<j>/dz= -2.72 x 10 Rad/cm and the asymmetries in the total (A) and differential —fi

(l(9)J cross sections which we show in the figure together with the pertinent cross- sections. In both calculations the " best value " of the weak parameters suggested by DDH is adopted. The vanishing of 1(8) at 180° is a consequence of T invariance as implied in the { } term in the Hamiltonian. Thus, if experiment finds I(180")^0 it implies P and T (hence CP) violation which is one of the puzzles raised by QCD.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984314

JOURNAL DE PHYSIQUE

E=7,9I MeV

cos 8 cos 8

FIG. 1. Results for n + 4 0 ~ a at 2 < E 4 8 hleV. On the right side, the asymmetry I ( @ ) as a function of cos@,,,.

Also indicated is the asymmetry A. On the left side are the calculated differential and total cross sections.

A Careful look a t t h e f i g u r e r e v e a l s an i n t e r e s t i n g f e a t u r e which may have important

experimental consequences : As a f u n c t i o n of energy, t h e asymmetry i n t h e t o t a l

c r o s s - s e c t i o n A changes s i g n a t E = 3.00 Rev. However, t h i s i s not due t o small

asymmetry i n t h e d i f f e r e n t i a l e l a s t i c c r o s s - s e c t i o n I ( 0 ) . I n f a c t , f o r 8>90° t h e r e

i s a l a r g e a n g u l a r domain a t which 11(0) 1 ^{/ ] A \ >>} 1. Hence, i f experimental s e t t i n g

i s p o s s i b l e , it appears t h a t sometimes measuring I ( 8 ) and n o t A can save a subs-

t a n t i a l amount of beam time.