This work was supported by the National Science Foundation Grant NSF PHY 78-22774 A02 & A03 and by Indiana Universit

Bacher, A.D.

Carey, T.A.

Miller, D.W.

Moss, J.M.

Nann, H.

Olmer, C.

Schwandt, P.

Stephenson, E.J.

English

IUScholarWorks

R. Comfort et al., Phys. Rev. g, 2147 (1980). 2) J.R. Comfort, R.E. Segel 
Miller, to be published. 
Figure 2 Anal zing powers for 
the 1'C(d,p')r2C reaction at 
120 Mev (solid points) and 200 
Mev (open points). States are 
labelled by Ex(Jn;T). The 
curves are DWBA calculations 
at 120 MeV. 
G.L. Moake, and D.W. 
POLARIZATION AND SPIN-FLIP IN PROTON INELASTIC SCATTERING 
T.A. Carey and J.M. Moss 
Los Alamos National Laboratory, Los Alamos, New Mexico 87545 
A.D. Bacher, D.W. Miller, H. Nann, C. Olmer, P. Schwandt, and E.J. Stephenson 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
This report summarizes the first year's progress 
in a program which has as its general aim the detailed 
investigation of the spin-flip probability in proton 
inelastic scattering. To achieve this goal we have 
developed a flexible experimental system which permits 
concurrent measurement of all four partial differential 
cross sections aij (i,j = +,-) for scattering polarized 
protons from initial spin state i to final spin state 
j. With them we can then construct the total 
differential cross section, a (= aft + a+ + a+ + 
a--), the analyzing power, A (aA = aft + a+ - a+ - 
a,) the final-state polarization, P (aP = a++ - a+ + 
a+ - a,) and the spin-flip probability, S (as = a+ + 
a+). Whereas A is primarily sensitive to the average 
nucleon- nucleus spin-orbit field, S has been shown to 
be primarily dependent on the central and tensor 
spin-dependent terms of the effective nucleon-nucleon 
interaction1). In proton scattering these interactions 
can lead to spin transfer accompanied by a flipping of 
the spin of the scattered particle. Of fundamental 
importance is the prediction that spin transfer 
generally leads to a large (near unity) value for S, 
and, conversely, in the absence of spin transfer the 
1 D O  
value obtained for s is small (5 0.1 at small momentum OD8 
transfer)2). Thus measurements of S tend to OD6 
complement those for A and should help to elucidate the S (0) 
relative effects of the various spin-dependent OD4 
interactions that can connect the ground and excited 
states of nuclei. Indeed, our hope is that information 
on these observables will provide particularly o D o  
stringent tests of the DWIA which, although generally 
successful, has suffered some notable failures in 
predicting a and A for certain states strongly 
excited by -150 MeV protons. 
An experimental determination of S for a 
particular excitation requires the scattering of a 
polarized beam from the target of interest followed by 
a precision measurement of the final-state polarization 
of the corresponding inelastically scattered particles. 
For this purpose, we have developed a polarimeter for 
use in the focal plane of the QDDM spectrograph whose 
design and operation is described in some detail in a 
later section of this report (Part 2: Technical Status 
of the Laboratory--Experimental Facilities 
Development). 
In October 1980 we used this system to make the 
first measurements of S in the (p,p') reaction at 
intermediate energies. Spin-flip data were obtained 
for 150 MeV incident protons exciting the 12.71 MeV 
(I+, T=O) , 15 .ll MeV (I+, T=1) and 16 .ll MeV (2+, T=1) 
states of 12C. The results of a preliminary reduction 
of these data are displayed in Figure 1. 
The aim of this first set of experiments was to 
provide some initial basis for an investigation into 
Figure 1. Angular distributions measured so far for 
the spin-f lip probability in 12~(p,p'). The solid 
(dashed) curves are DWIA predictions for the 
Cohen-Kurath (Dubach-Haxton) wave functions and the 
latest Love-Franey effective interaction for -150 MeV 
protons .6) The dash-dot curve represents a 
coupled-channels calculation employing collective-model 
form factors. 
the sensitivities of S as an observable. Towards this 
end we are currently performing a series of calcula- 
tions employing both the DWIA and the coupled-channels 
methods. Although these studies are still in their 
earliest phase we can make the following tentative 
observations (keeping in mind that a detailed 
comparison between theory and experiment must await 
further measurements and a consistent reduction of the 
data as a whole with a more systematic and quantitative 
approach to the estimation of uncertainties than has 
been used so far): 
(i) 12.71 MeV (I+, T=O) state -- The differential cross 
section and analyzing power for excitation of 
this state at IUCF energies have to date been very 
poorly described in the DWIA~). Speculation has 
held that this may be due to deficiencies in the IA 
effective interaction, contributions from multistep 
channels or a combination of these and other 
problems. Our surprising result is that S is 
large over the range where OCm = 8'-36' with 
an angular distribution which is rather well 
described by the DWIA. Furthermore, coupled 
channels calculations show that a purely 
two-step inelastic excitation of this state 
proceeding through the 4.44 MeV (2+, T=O) 
state yields S-0. The resolution of this apparent 
conflict is not presently obvious, and any 
clues which the new observable S may be provi- 
ding about the excitation of this state will 
probably become clear only after more system- 
matics have been gathered for AT=O unnatural 
parity transitions. 
(ii) 15.11 MeV (I+, T=1) state ---Inelastic scattering 
to this state has recently attracted 
considerable interest as a potential test for the 
presence of precritical fluctuations in the nuclear 
pionic field. These effects are expected to 
be most prominent at a momentum transfer (near 
2-3 %c) for which both a and A measurements with 
120-800 MeV protons are not particularly well 
described by a simple excitation mode139 4). We 
find that S for (p,pl) transitions to this state 
is consistently large and is in qualitative 
agreement with DWIA predictions employing the 
Cohen-Kurath wave functions. However, given the 
sparseness of the current data it is obvious 
that we need additional measurements for 
OCm>25' before any conclusions can be drawn 
concerning the importance of the minor 
differences between the Cohen-Kurath and the 
Dubach-Haxton wave functions which are so 
crucial to the interpretation of the corresponding 
(e ,el ) cross sections5). 
In the meantime, calculations for the 
low momentum-transfer region have shown a 
remarkable sensitivity to the tensor component of 
the IA interaction. With reduced 
uncertainties for forward angle data one 
should be able to literally choose the "best" 
tensor interaction from the families which 
(iii) are currently available for -150 MeV protons. 
16.11 MeV (2+, T=l) state ---Both AS=O and AS=l 
transfer are allowed in the excitation of 
this state. Since only the AS=l amplitude 
produces substantial spin-flip, measurements 
of S should be quite sensitive to the 
AS=l/AS=O ratio predicted by any assumed wave 
functions. We have found S to be large 
(-0.45) near the peak of the cross section for the 
excitation of this state; this constitutes the 
first direct evidence for the importance of 
AS=l transfer in this natural-parity transition. 
This result is in good agreement with DWIA 
calculations using Cohen-Kurath wave functions 
while p-shell wave functions, which admit no AS=1 
strength, produce substantial disagreement with the 
data. 
In conclusion, the goal of this program is the 
exploration of the spin-flip probability as an 
additional probe of nuclear structure and reaction 
mechanisms in (p,p'). Since this is the first such 
endeavor at interufediate energies we will in the future 
seek to broaden our data base in terms of the types of 
excitations studied. Strong and weak transitions 
involving both AT=O and AT=1 transfer for relatively 
pure proton and neutron promotions to both low and high 
spin states (particularly stretched configurations) 
need to be probed at a variety of momentum transfers. 
Also, we hope to investigate the prediction that 
intermediate-energy spin-flip measurements can be used 
to elucidate the AJfO contributions to elastic 
contained in the transverse form factors derived from 
elastic electron scattering. Finally, we will consider 
the potential utility that a broad-range, 
second-generation focal-plane polarimeter might have in 
searches for new magnetic modes of excitation which lie 
in a background of more strongly excited electric 
multipoles. 
1) J.M. Moss, W.D. Cornelius and D.R. Brown, Phys. 
Lett. e, 154 (1977); Phys. Lett. G, 87 (1977); 
Phys. Rev. Lett. 41, 930 (1978). 
2) W.D. Cornelius, J.M. Moss and T. Yamaya, Phys. Rev. 
C (in press). 
3) J.R. Comfort et al., Phys. Rev. g, 2147 (1980); 
J.R. Comfort et al., Contribution 2.54 to the Fifth 
International Symposium on Polarization Phenomena in 
Nuclear Physics, Santa Fe, August 11-15, 1980; R.E. 
Segel et al., preprint. 
4) M. Haji-Saeid et al., Phys. Rev. Lett. 45, 880 
(1980); C. Glashausser, private communication. 
5) J. Dubach and W.C. Haxton, Phys. Rev. Lett. 9, 1453 
(1978). 
6) M. Franey, private communication. 
scattering from odd mass nuclides. This should yield 
information on the diagonal matrix elements of the 
spin-dependent operators which is complementary to that 
135 MeV PROTON SCATTERING FROM 3C 
S.F. Collins, B.M. Spicer, G.G. Shute and V.C. Officer 
University of Melbourne, Parkville, Victoria, Australia 3052 
D.W. Devins, D.L. Friesel and W.P. Jones 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
Spectra from the scattering of 135 MeV protons Peak areas have been extracted using the code 
from 13c have been measured at angles from 8" to 80" in GENFIT~) at IUCF and GAUSSFIT2 at Melbourne. The 
the laboratory, using the QDDM spectrograph. Four target used had a thickness of 9.5 mg/cm2 and was 
momentum bites were used at each angle, covering the isotopically enriched to 92% 13c. Angular 
region from 0 to 24 MeV in excitation. A preliminary distributions from the impurity 12~(p,p') reaction for 
report on the spectra in the 2 higher energy bites was. the prominent states agreed well with those measured 
given in last year's report .I) previously by this group. Runs on different targets 


Polarization and Spin-Flip in Proton Inelastic Scattering

https://scholarworks.iu.edu/dspace/bitstream/2022/2790/1/iucf_1980_18-21.pdf

Polarization and Spin-Flip in Proton Inelastic Scattering

Abstract

Similar works

Full text

Available Versions

IUScholarWorks