This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Aziz, S.M.

Bacher, A.D.

Bland, L.C.

Emery, G.T.

Huber, G.M.

Jacobs, W.W.

Korkmaz, E.

Nann, H.

Park, P.W.

Templon, J.A.

Walden, P.L.

English

IUScholarWorks

lines, which were calculated with a coupling constant 
45% larger than that used for the solid lines. Medium 
modifications of the xNN coupling constant are implied 
by sdme interpretations of the EMC effect. 
We feel that we have, at last, a reliable code 
that includes the most important physics of the (p,~) 
reaction in the near-threshold region. In addition to 
investigating the questions mentioned above, we hope to 
apply the model in the near future to the (p,n') 
reaction (for which only the two-nucleon mechanism 
contributes) and to other (P,~+) reactions, and to 
extend the model to higher energies for interpretation 
of TRIUMF and future Cooler experiments. Finally, it 
is planned to document the code and to make it as user 
friendly as possible, so that it will be useful to the 
scientific community. at large. 
1) Z. Grossman, F. Lenz and M.P. Locher, Ann. Phys. 
(N.Y.), 348 (1974). 
2) J.S. Conte, IUCF Scientific and Technical 
Report, p. 28 (1985). 
3) F. Soga et al., Phys. Rev. C 22, 1348 (1980). 
4) F. Soga et al., Phys. Rev. C 24, 570 (1981). 
5) B.A. Brown et al., private communication. 
6) J.J. Kehayias et al., Phys. Rev. C 33, 725 
(1986). 
STUDY OF HIGH-SPIN STATES AND THNE-QUASIPARTICLE (p,~) TRANSITIONS ON LIGHT TARGETS 
S.M. Aziz, A.D. Bacher, L.C. Bland, G.T. Emery, W.W. Jacobs, E. Korkmaz, H. Nann, P.W. Park and J.A. Templon 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
P.L. Walden 
TRIUMF, Vancouver, B.C., Canada V6T 2A3 
G.M. Huber 
University of Regina Regina, Saskatchewan, Canada S4S OA2 
(p,n) reactions necessarily involve large momentum in particular from the analyzing powers and 
transfer, typically greater than 500 MeVIc. An intensity ratids observed by Jacobs et al. ,l in 
important part of the reaction operator has the effect l2 9 1 4 ~ ( p  ,n-) ground-state transitions, especially 
on the target of creating a hole and inserting two from the strong population of 1912- and 1512- states by 
nucleons, thus creating three- (or one-) quasiparticle Vigdor et ale2 in 48~a(p,~') and reactions on 
states relative to the target. The amount of momentum neighboring targets, and the correspondence of the 
transfer for each of the three nucleon states involved latter with the model calculations of Brown, Scholten, 
is about the same as in the inelastic scattering regime and ~ o k i . ~  
where high-spin states are selectively excited, so it (P ,n+) reactions should also strongly populate 
is not strange that there is a tendency for high-spin two-particle, one-hole states of high spin through 
states to be strong in (p,~) reactions. The most similar mechanisms. The largest elementary cross 
striking experimental evidence for the three-quasi- section for pion production is pppn (T=O), so the 
particle mechanism comes from the (p,~') reaction strongest (p,n+) transitions should proceed through 
these channels in the nucleus with AT = 112. Because 
the (P,n+) reaction may be a way to excite unknown or 
poorly known high-spin three-quasiparticle states, 
we have studied (p,n+) with targets of 160, 
14N, and 15N. 
The basic transition we hoped to identify is 
(p312)-1 (d51212, coupled to large angular momentum 
(i312-, 11/2-, 912-, etc.). These final states can be 
reached by M4 excitation from the ground state of 170, 
but cannot be reached by two-particle transfer from 
15N. It was also important to study the transitions 
(P1/2)-1(d5/2)2, which can be reached by E3 inelastic 
scattering and by two-particle transfer from 15N. 
The three reactions 160(p,n+), 14~(p,n+), and 
15~(P,n+) were studied with polarized 200 MeV protons, 
using the QQSP spectrometer at IUCF. The targets were 
in the form of V2O5, v14N, v15N, and V for subtraction. 
12~(p,n+) was used for energy calibration. 
Figure 1 shows the 160(p,n+)170 spectrum at 50". 
Above the ground and 0.87 MeV one-quasiparticle states, 
there are states at 5.24 and 7.76 MeV. These are 
912- and 1112- states of the (d51212 
Channel 
Figure 1. l60(;,rr+) spectrum at Ep=200 MeV and 
= 50". The excitation energies of some final 
states are indicated. 
configuration. The same states are seen in 15~(a,d)4 
and 15~(3~e,p),5 and the 1112- state in (e,e'16 and 
(n,nt) .7 The cross section of the 1112- state is 
relatively featureless except for an exponential 
decline of the cross section (Fig. 2-a) and an Ay (8) 
reaches about -0.8 near 60". At higher excitation 
there are strong states at 15.8 and 17.1 MeV. Their 
energies are determined to about 0.05 MeV, and they 
agree with values found in (n ,n and (e, e'18 for M4 
transitions. As seen in Figs. 2b and 2c, their cross 
sections decrease by a factor of about 10 in going from 
30" to 70" and are almost flat after that; their 
analyzing powers are consistent with being zero or 
slightly negative. 
With 14N as the target, we start with two 
quasiparticles and can reach in 15N three-hole, 
two-particle states relative to 160. If the three 
holes are all in the p1/2 orbital the maximum spin is 
1112 (for T = 112). 1112- and 912- states are seen in 
(a,d) at 13.00 and 11.94 M ~ v . ~  If one of the holes is 
in p3/2 the maximum spin is 1512; these states are not 
known at present. 
Figure 3 shows the spectrum of 14~(p,n+)15~ at 
50'. Many states are populated, especially between 5 
and 14 MeV. Most of these states are identified in 
other reactions, particuarly (a ,dl4 and (n ,n ' ) . At 
high excitation there is a new state at 21.5 MeV. The 
cross section and Ay of this state are similar to those 
of the 15.8 and 17.1 MeV states in 170. 
When the target is 15N, we can reach two-particle, 
two-hole states in 16N. The strongest- transitions 
(pp+pn(T=O)) leading to (p112)-2 will have a maximum 
spin of 5. The (a,d) work has identified a 5+ state at 
5.75 MeV. If one of the holes is in ~312, the maximum 
spin is 7. Little is known about such high-spin 
isovector states in the mass 16 spectrum. 
In the 15~(p,x+)16~ spectrum (Fig. 4) the MeV, whose cross sections also fall rapidly from 30° to 
ground-state quartet is strongly populated, a 5+ 70°, with zero or slightly negative Ay. 
state is seen at 5.75 MeV, and the 4' state known from It is tempting to associate the strong, 
charge-exchange worklo is seen at 6.17 Mev. In high-excitation transitions (15.8 and 17.1 MeV in 170, 
addition there are strong new states at 14.15 and 16.0 21.5 MeV in 15N, 14.15 and 16.1 MeV in 1 6 ~ )  with those 
ANGLE ANGLE ANGLE 
(0) ( b) ( c )  
Figure 2. Preliminary do/dQ and A angular distributions for the 160(p,x+) transitions to 
170 states at: a) Ex = 7.76 MeV, b) Ex = 15.8 MeV and c) E x =  17.1 MeV. 
Channel Channel 
A 
Figure 4. 15~(p,n+) spectrum at Ep = 200 MeV and 
Figure 3. '%(;,x+) spectrum at Ep = 200 MeV and eIab = 50'. Some 16N states are labeled by their 
elab = 50'. Some final states are labeled by their excitation energies. The peak marked by an arrow 
excitation energies. is the 170 state (15.8 MeV). 
seen recently (21.4 MeV in 13c and 23.2 MeV in 14c) by 
Korkmaz et al.ll which have similar angular 
distributions of cross section and Ay. It is also 
tempting to associate them with the expected (p312)-1 
(d512)2 transitions, since those in 170 match the 
excitation of the M4 transitions observed in inelastic 
scattering. If the latter identification were to hold, 
however we would have to understand why the cross 
section distributions are so different for these states 
compared to the 1112' state in 170. 
1) W.W. Jacobs et al., Phys. Rev. Lett. 49, 855 
(1982). 
2) S.E. Vigdor et al., Phys. Rev. Lett. 2, 1314 
(1982). 
3) B.A. Brown et al., Phys. Rev. Lett. 51, 1952 
(1983). 
4) C.C. Lu, Phys. Rev. 186, 1086 (1969). 
5) M.C. Lemaire et al., Phys. Rev. C 2, 328 (1972). 
6) J.C. Kim, et al., Nucl. Phys. A297, 301 (1978). 
7) C.L. Blilie et al., Phys. Rev. C 30, 1989 (1984). 
8) D.J. Manley et al., Phys. Rev. C 34, 1214 (1986). 
9) S.J. Seestrom-Morris, in Spin Excitations in Nuclei 
(Plenum, New York, 1984), p.291. 
10) G.A. Needham et al., Nucl. Phys. A385, 349 (1982). 
11) E. Korkmaz et al., Phys. Rev. Lett. 58, 104 (1987). 
i- 
~(~,n+) CONTINUUM ANALYZING POWERS AND QUASI-FREE EXPECTATIONS 
E. Korkmaz, L.C. Bland, W.W. Jacobs, T.G. ~hrowe.,t S.E. Vigdor 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
M.C. Green 
Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 
P.L. Jolivette 
Department of Physics, Hope College, Holland, Michigan 49423 
J.D. Brown 
Department of Physics, Princeton University, Princeton, New Jersey 08544 
We have seen considerable evidence accumulated in collision vs. one ocurring inside a nucleus.8 We have 
recent years that pion production reactions on nuclei recently studied (;,nr ) reactions on ,13c targets, 
A(p,n)A+l are dominated by a two-nucleon mechanism with results bearing on two separate aspects of free 
i- 
(TNM), i.e., by NN + NNn processes ocurring within the NN + NNn processes that are reasonably well established 
nuclear medium.l-7 While the arguments made in near threshold: the analyzing power behavior and the 
conjunction with these studies do depend on the isospin dependence of the amplitudes. We focus on the 
explicit participation of two nucleons (one from the striking results of the former in this contribution, 
target nucleus), they do not require treating pion which has been the subject of a recent publication.9 
production as a quasifree NN i- NNn process. Indeed, IT+ and n- continuum analyzing powers at several 
one might expect a priori quite different off-shell values of a,>, and for various targets are displayed 
behavior for pion production in a free two-nucleon in Fig 1. The negative going shape of Ay(0) for 
64  


Study of High-Spin States and Three-Quasiparticle (p,π) Transitions on Light Targets

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Study of High-Spin States and Three-Quasiparticle (p,π) Transitions on Light Targets

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