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SPIN PHYSICS IN THE d(e,e’p)n REACTION
A. Korchin, Yu. Mel’Nik, A. Shebeko
To cite this version:
A. Korchin, Yu. Mel’Nik, A. Shebeko. SPIN PHYSICS IN THE d(e,e’p)n REACTION. Journal de Physique Colloques, 1990, 51 (C6), pp.C6-499-C6-502. �10.1051/jphyscol:1990660�. �jpa-00230930�
COLLOQUE DE PHYSIQUE
Colloque C6, supplement au n022, Tome 51, 15 novembre 1990
SPIN PHYSICS IN THE d(e,elp)n REACTION
A.Yu. KORCHIN, Yu.P. MELINIK and A.V. SHEBEKO
Kharkov Institute of Physics and Technology, Ukrainian Academy of Sciences, 310108, Kharkov, U.S. S. R.
R6ame'-On examine la ddpendance de la polarisation des protons dans -actions d(e,e'F)n et d(3,elmn de la choix du modele du courant dlectromagndtique du deuton et des effets de llinteraction de llbtat final, On discute la possibilit6 de la sdparation de la contribution de la fonction structurale longitudinale-transversale h la polarisa- tion dans Is re'action d(e,eljii)n. On dtaient faites les calculs de cet observable dans d(3,es9n dans lea conditions cinbmatiques dtexperi- ment,rtSalisb dans MIT.
Abstract- Dependences of the proton polarization in d(e ,e 'nn and a m ) n reactions on the choice of the electromagnetic
(a)
deuteroncurrent and final-state interaction(FS1) effects are investi ated.
Separation of the longitudinal-tranwerse structure ArnctionTsF) for this observable in the d(e,elp" )n reaction is di~cussed. Calculations of the proton polarLzation in the d(8,e1r )n reaction have been carried out for the NIT kinematfcs,
In view of the constmction of CW electron accelesators,polarization phenom- ena in EM interactions with atomic nuclei attract a constantly increasing interest. The corresponding polarjtzation observables(e.g.,nucleon polariz- ation, target asymmetries)contain much richer information on the reaction mechanism and nuclear structure than that attainable with unpolarized particles, These observables,being dependent on interference terms of vari- ous reaction amplitudes,can be very sensitive to the contributions of sub- nuolear degrees of freedom(e.g.,meson exchange currents(MEC)) and effects of the PSI. Here we demonstrate this by calculating the proton polarization in the d(e ,e8p)n reaction, Therefore, the investigation of the polarization versus the proton emission angle at various relative energies of the p-n pair can give an additional information on the p-n interaction. To attain a deeper understanding of the role of meson exchange effects in the simplest nuclear sysdem,we put special emphasis on a certain consistency of the MEC models with the M-N interaction models. To this end,we have used the one- boson exchange models with modified meson-nucleon vertices/l,2/.
2-STUDY OF PROTON POLARIZATION IN d(e,elp)n FOR THE MII E X P E R ~ N I The transverse (P;),longitudinal (P;) and normal. (Py) components of the proton polarization in the de,e 'an reaction with longitudinally polarized electrons for coplanar kinematics can be written as
0 P, -- 0 , f ~ 2 t c + C f + d ~ 7 + @ ~ ~ s + ~ ~ ~ k 3 3 ~ P%vz
( 2 )where
6
is the d(e ,e *p)n cross section with unpolarized partf ohs, S\ is the incident electron hzlicity,R is the recoil factor,-We have chosen the ortho- normal basis: B, .r q/q, ?Ty = Tx"kl//f
X?/ and nx x%,,assuming that* nx and
5 ,
form the reaction plane,%(Et)
is the momentum of the incident (scattered electrod,a
=H -zl.
The SF andL '
depend on the bilinear combinations of the reaction amplitudes(see/3/for details).Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990660
C6-500 COLLOQUE DE PHYSIQUE
The r e s u l t s of our c a l c u l a t i o n s f o r the blIT I ( I I I ) kinematics /4/ a r e shown i n Fig. l
Fig.?- The angular dependence of p o l a r i z a t i o n observables f o r the MIT I ( l e f t ) and MIT I I I ( r J i g h t ) kinematics/4/. The curves calculated with* =l are:dashed-in the plane wave Born approximation, s o l i d (dash-dotted)- taking i n t o account the FSI f o r the MEC/2/ with the u t - f parameter
h E 4m, (without MEC)
,
where m i s the x i o n mass,8
(e?
i s the angle between the outgoing proton momentum and q i n the 1ab.frame ( t h e centre- of-mass frame).A s seen from the f i g u r e s , f o r p a r a l l e l kinematics (
0 =
00) t h e FSI and blIEC c o n t r i b u t i o n s t o the proton p o l a r i z a t i o n a r e small. The same i s t r u e n e a r6
lim = 90° a s the r e c o i l neutron has the momentumX==%
The PSI influence on the components P; and P: becomes s i g n i f i c a n t a t i n t e m e d i a t e ~ v a l u e s . The component Py i s equal t o zero without the PSI. A s t o the MEC e f f e c t s , t h e i r contributions t o the p o l a r i z a t i o n under these kinematic conditions a r e comparatively small.So,the proton p o l a r i z a t i o n has the values a c c e s s i b l e f o r the planned measurements.
3-SEPARATION OF THE LONGITUDINAL-TKANSVERSE SF FOR THE PROTON POLARIZATION IN THE d ( e , e l S In REA-
The proton p o l a r i z a t i o n i n the d ( e ,e )n r e a c t i o n with unpolarized i n i t i a l p a r t i c l e s f o r coplanar kinematics determined by (2).
In p a r a l l e l kinematics (protons detected a l o n g T ) , t h e r e i s only one SF which survives / 3 / . It depends on the i n t e r f e r e n c e between the l o n g i t u d i n a l and transverse com onents of the deuteron EM current. The dependence oA
XI
on the angle8
between the momentum of the outgoing proton and q can be obtained by measuring the azimuthal ( l e f t - r i g h t ) asymmetry of the Pproton p o l a r i z a t i o n - -
0 (4=03Py
(#=U) -td(4=x)Py(@=slc)
LT= 2 = ' , R f m
where t h e azimuthal angle f$ equals 180° (0°) i f l i e s on the r i g h t ( 3
( l e f t ) of $
.
PO u r c a l c u l a t i o n s Tor the i n i t i a l e l e c t r o n energy E, = 1 GeV have shown
that (i) in the left wing of the quasi-free peak (QFP) with the scattered electron energy E; =827 MeV,
ee
= 50°,0
= 0°, q = 788 MeV/c, the n-p relative energy in the c.m.frame ~ ~ ' ~ * = 1 3 . 2 MeV,the kinetic proton energy in the lab frame T =131.8 MeV, the recoil neutron momentum nP]m
a 273 MeV/c and the d36 cross section P6
= 0.015
nbe~ev-' the proton polarization is P = -38%;(ii) in the right wing of the QFP with E; a 830 Mev, @,=l 100,
0
=00,p
-
233 MeV/c, E:;~*= 155 MeV, Tp =l28 MeV, kn -275 MeV/c andd
=1.4
nb*M~V-' sr-2 ,we get P a -1 2%.
Pig.2- The angular dependence of
X I
in the left(1eft-part) and right (right-part)wings of the &FP. The curves have been calculated taking into account the PSI: solid(dotted) for the MEC/2/ withA
=4m,(A
=DO),
dash-dotted-without the MEC.
As seen from the figures 2,the SF is essentially sensitive to the MEC model.
This fact can be used to verify our understanding of the mecha~sms of deuteron electrodisintegration.
$-DEPENDENCE OF PROTON POLARIZATIOIT IN d(e,e'r )n AND d(Z,e )n ON THE NEmRON ELECTRIC FORBiI FACTOR(Fl+'),
The proton polarization
p
in the d(e ,et$ )n reaction with unpolarized initial particles for coplanar kinematics has the only component Py perpendicular to the ecattering plane (cf. sec.3).It is induced by the FSI in the n-p system. Ous calculations (Korchin, Me1 'nik and Shebeko, to be published) Tor the energy transf era corresponding to the region between the deuteron electrodisintegration threshold and the quasi-free peak in the d 2 6 cross sections in the inclusive d(e,et)
reaction have shown an appreciable sensitivity of Py to the model of G.: Our results at the incident(scattered)electron energy E, 1 GeV (E' 4 2 7 MeV), the electron scattering angle
6,
=50°, q, = 788 MeV/c and E C.&13.2 Mev are displayed in the left part of Fig. 3. The right part of Pig.3 nP corresponds to the MIT kfnematics /4/. As it is seen from Fig.3, the
observable P; depends on the choice of G; at proton emission angles
0
close to the limiting angle8
lim =90°(parallel kinematics for recoil neutrons).COLLOQUE DE PHYSIQUE
Fig. 3- Proton p o l a r i z a t i o n components v e r s u s t h e G; model. The curves have been c a l c u l a t e d f o r MEC /2/ w i t h
/\
=4m, :solid-with G; /S/ ,dashed-with ~$0.Besides, we f i n d h e r e a r a t h e r weak s e n s i t i v i t y of P& t o t h e FSI and MEC e f f e c t s . Y e t , t h e e x t r a c t i o n of a r e l i a b l e information on G; under t h e s e kinematic c o n d i t i o n s w i l l be a complicated problem.
I n f a c t , i n this c a s e P& t a k e s t o o s m a l l v a l u e s ( a few p e r c e n t ) and t h e outgoing p r o t o n energy becomes t o o IOW.
I n o u r opinion,of g r e a t i n t e r e s t i s t h e s t u d y of t h e a n g u l a r dependences s i m i l a r t o t h e one shown i n Fig.3,where t h e component P, undergoes q u a l i t a t i v e changes on r e p l a c i n g :G = 0 by 0: /5/. !I!herefore,precise measurements of t h e component P, may h e l p t o s e e a d i f f e r e n c e between v a r i o u s models f o r t h e n e u t r o n e l e c t r i c FP.
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M e l t n i k Yu.P. and m e k o A.V.,
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