STUDY OF THE 3-NUCLEON SYSTEM:
P.
d+p BREAKUP MEASUREMENTS AT Ed = 80 MeV
Schwandt, C.C. Foster, W.W. Jacobs, H.O. Meyer, E.J. Stephenson, and J. Yang
Indiana University Cyclotron F a c i l i t y , Bloomington, Indiana 47405
R.E. Brown and N. Jarmie
Los Alamos National Laboratory, Los Alamos, New Mexico 87545
W.T.H. van Oers
University of Manitoba, Winnipeg, Manitoba R3T 2N2
Studies of t h e proton-deuteron i n t e r a c t i o n a r e of
t h e ki a r e t h e c.m.
rpomenta of t h e f i n a l - s t a t e
fundamental i n t e r e s t s i n c e the 3-nucleon system i s the
nucleons.
simplest many-body system i n which one can t e s t
( - 8 , ~ - @ ) of the d e t e c t e d protons under t h e f i x e d SCRE
" r e a l i s t i c " e f f e c t i v e (i.e.,
condition, t h e observables a r e measured a s a function
medium-modified) o f f - s h e l l
By varying t h e l a b o r a t o r y angles (8, @) and
NN f o r c e s , and one which ( i n p r i n c i p l e ) i s e x a c t l y
of the angle a of r o t a t i o n of t h e c.m.
c a l c u l a b l e using Faddeev theory.
t r i a n g l e ( v e r t i c e s kl,k2,k3) about an a x i s
s t u d i e s t o a new, higher-energy
Extension of these
regime of s e v e r a l t e n s
momentum
perpendicular t o t h e i n c i d e n t deuteron momentum
This SCRE kinematic
of MeV nucleon l a b energy w i l l allow us t o t e s t t h e
[ s p e c i f i c a l l y , a = c(-kd,kn)].
q u a l i t y of the assumed " r e a l i s t i c " NN i n t e r a c t i o n
c o n f i g u r a t i o n i s of i n t e r e s t because it i s believed t o
( p a r t i c u l a r l y the parameterization of t h e tensor f o r c e )
sample most e f f e c t i v e l y t h e I=1/2, Spp=O amplitude of
a s well a s t h e various computational approaches t o t h e
t h e 3-nucleon f i n a l s t a t e which, i n t u r n , should be
Faddeev c a l c u l a t i o n s (e.g.,
most s e n s i t i v e t o d e t a i l s of t h e assumed NN i n t e r a c t i o n
separable-interaction
r e p r e s e n t a t i o n s f o r a l l p a r t i a l waves vs. p e r t u r b a t i o n
a t s h o r t range i n a Faddeev c a l c u l a t i o n of t h i s breakup
treatment of higher p a r t i a l waves).
process.
At t h e same time,
Experimentally, of course, f o r a given a one
measurement a t higher e n e r g i e s of t h e t e n s o r
o b t a i n s d i s t r i b u t i o n s of t h e observables along t h e
p o l a r i z a t i o n e f f e c t s i n t h e breakup r e a c t i o n d+p+ptp+n
whole kinematic energy locus (Epl vs. Ep2 ), not j u s t
i n p a r t i c u l a r i s experimentally advantageous because of
a t t h e SCRE point (Epl = Ep2).
t h e l a r g e s i z e predicted f o r these e f f e c t s , i n c o n t r a s t
t o the s i t u a t i o n a t low energies.
t h e newly-developed r o t a t i n g d e t e c t o r platform system
With these motivations, preliminary measurements
of the tensor analyzing power
Ayy
The preliminary experiment was c a r r i e d out using
were made f o r t h e
i n the IUCP y-cave.1
Two symmetric AE-E d e t e c t o r
telescopes c o n s i s t i n g of 0.5 mu S i
+
LO mn hyper-pure
kinematically complete d+p breakup r e a c t i o n a t Ed = 80
Ge d e t e c t o r s i n LN2 c r y o s t a t s were used i n conjunction
MeV i n which t h e outgoing protons were detected i n
with CH2 t a r g e t s (-10 mg/cm2) and t h e tensor-polarized
coincidence a t four non-coplanar symmetric angle p a i r s
deuteron beam.
( 8,@).
These measurements a r e p a r t of an ongoing
experimental program a t IUCF t o determine p r i m a r i l y t h e
t e n s o r observables
&
and
Ayy
i n a very s p e c i f i c
Unfortunately, t h e use of hydrocarbon
t a r g e t s caused a s e r i o u s and unforeseen problem i n t h e
August run:
t h e much larger-than-estimated
continuum protons from
y i e l d of
*C gave r i s e t o unacceptably
breakup geometry , namely t h a t
high a c c i d e n t a l coincidence y i e l d s a t t h e planned beam
corresponding t o t h e symmetric constant r e l a t i v e energy
i n t e n s i t y , f o r c i n g us t o acquire d a t a a t considerably
(SCRE) condition Ik11-lk21 =1k31, <(ki,kj )-120'
reduced beam c u r r e n t s (- 5nA, i n s t e a d of t h e 25nA
non-coplanar
where
anticipated).
Consequently, both t h e q u a n t i t y and
r
q u a l i t y of t h e d a t a obtained i n t h e a v a i l a b l e beam time
suffered:
d a t a were obtained a t only 4 angles (a =
75O, 120°, 142" and 150") and the s t a t i s t i c a l e r r o r of
t h e %y measurements ( t y p i c a l l y 20.1) was about twice
what i s needed i n order f o r the d a t a t o provide a
meaningful t e s t of t h e o r e t i c a l c a l c u l a t i o n s .
Partial
S (MeV)
r e s u l t s e x t r a c t e d from these measurements a r e presented
i n Figs.
1 and 2.
I n Fig.
1, t h e Ayy r e s u l t s f o r t h e
\ .
0'
&
SCRE point on t h e kinematic locus a r e shown i n
\
\
0
/
----e0
comparison with a Faddeev c a l c u l a t i o n by Stolk and
~ j o n(dash-dot
~
curve).
.c
The agreement i s remarkably
good but hardly c o n s t i t u t e s a v e r i f i c a t i o n of t h e
theory.
A,
The s o l i d curve i s a s i m i l a r c a l c u l a t i o n of
s t i l l t o be measured.
Figure 2 d i s p l a y s t h e
r e l a t i v e - e n e r g y d i s t r i b u t i o n s of the a=150°
73
measurements along t h e kinematic locus on e i t h e r s i d e
Figure 2.
Preliminary experimental r e s u l t s f o r
d3a/dQ2dE12 ( i n mb/sr2+4e~) and vector and tensor
analyzing powers Ay, +y a s f u n c t i o n of a r c l e n g t h
S(MeV) along t h e kinematic locus f o r a=150°. The
smooth curves drawn through t h e p o i n t s a r e only meant
t o emphasize t h e expected symmetry c h a r a c t e r of t h e
d a t a about t h e SCRE point 510.
of the SCRE point ( o r i g i n of a r c l e n g t h S).
Measurements with 3 p o l a r i z a t i o n s t a t e s of t h e deuteron
beam (unpolarized, +tensor-vector,
-tensorvector)
allowed determination of t h e v e c t o r analyzing power
+
(with l a r g e r u n c e r t a i n t i e s , owing t o t h e small v e c t o r
beam p o l a r i z a t i o n ) and t h e t r i p l e d i f f e r e n t i a l c r o s s
s e c t i o n d 3 a / d ~ , d ~ 2 d ~i 1n 2a d d i t i o n t o An.
symmetric c h a r a c t e r of d3a and An
behavior of
+ about
The
and antisymmetric
t h e SCRE point (required by
fundamental r e a c t i o n symmetry c o n s i d e r a t i o n s ) i s
Figure 1. Preliminary experimental r e s u l t s f o r t h e
t e n s o r parameter Ayy a t t h e SCRE point on t h e kinematic
l o c i corresponding t o a=75O, 120°, 142O, and 150". The
curves a r e p r e d i c t i o n s of Faddeev c a l c u l a t i o n s i n t h e
v a r i a t i o n a l approach of Stolk and Tjon.
r e a d i l y apparent ( t h e dashed curves a r e intended t o
p r e j u d i c e t h e eye towards t h i s conclusion).
These
r e s u l t s give us confidence t h a t t h e sources of
systematic errors are sufficiently under control to
permit us to obtain more and better data (with the
desired precision of f0.05 in Ayy and
& for data bins
Meanwhile, additional Faddeev calculations for this
reaction are underway using the Doleschall
separable-interaction code3 at the Los Alamos National
of about 4 MeV relative energy) with improved
Laboratory.
experimental techniques, principally involving the use
these calculations with those of the older, Stolk and
of an elemental hydrogen target in the form of a
Tjon variational-method calculations2 (shown in Fig. 1)
high-pressure and/or LN-cooled gas cell.
will determine the optimum quantity and precision of
In a 13-shift
Comparison of predicted observables from
Variation of the NN tensor
run requested for April, 1983, we propose to measure
the data to be measured.
(1) Ayy at about 6 non-coplanar angle pairs (8,@)
force parametrization in particular will be explored in
covering the range in rotation angle a of the momentum
future calculations in the Doleschall approach since
triangle between 45' and 150' and (2) Ax, at perhaps 3
one expects the tensor analyzing powers in the d+p
non-coplanar angle pairs corresponding to a-45',
breakup reaction to be sensitive to details of this
and 135'.
90'
Since the spin quantization axis for the
force.
IUCF polarized beams is vertical in the lab, the An
1) see p. 210 of this report.
and
4,measurements
involve orthogonal experimental
configurations in the sense of horizontal and vertical
scattering planes, respectively.
2) C. Stolk and J.A. Tjon, Nucl. Phys. A295, 394
(1978).
3) P. Doleschall, Nucl. Phys. A220, 491 (1974); ibid.
A201, 264 (1973).
-