This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit

Bent, R.D.

Debevec, P.T.

Green, M.C.

Marrs, R.E.

Pile, P.H.

Pollock, R.E.

English

IUScholarWorks

CHARGED-PION PRODUCTION I N  PROTON-NUCLEUS COLLISIONS NEAR THRESHOLD 
R.D. Bent, P.H. P i l e ,  R.E. Pollock, P.T. ~ebevec ,*  R.E. Marrs and M.C. Green 
Measurements of pion production u t i l i z i n g  the Table 1. Summary of (p ,r+) Reactions Measured 
with the  QDDM Magnetic Spectrograph 
QDDM magnetic spectrometer have continued. The em- 
Final 
phasis t h i s  year has been on angular d i s t r ibu t ion  Excitation 
Energy Tp (lab) 0,(lab) 
and exc i t a t ion  function measurements i n  the  near Target React ions (MeV) (MeV) (Deg) 
threshold region. The aim of t h i s  work is t o  deter-  6 ~ i  (P,,+) 0 175 25 -+ 87 
0.48 25, 45 
mine the  dependence of the  cross sect ions  on momentum l o B  (P 9 ,+I 0 152 25 
t r ans fe r  q and outgoing pion momentum kT over a broad 
region i n  the  q vs k, plane so  t h a t  s t r ingen t  t e s t s  
of various react ion models can be made. 
Table I summarizes the  (p, IT+) measurements 
t h a t  have been made. The 9 0 ~ r  and 2 0 8 ~ b ( p , ~ + )  r e s u l t s  
175 25, 45 
a re  the f i r s t  reported1) measurements of charged-pion 3.08 166 25, 45 
175 25 
production near threshold i n  proton co l l i s ions  with I60 (P , ,+) 0 166 25 -+ 155 
heavy nuclei .  The angular d i s t r ibu t ions  obtained a t  28~ i  (p ,r+) 0 160 25 -t 155 
1.27 160 25 -+ 155 
160 MeV a r e  shown i n  Fig. 1. The 1°B and 4 0 ~ a  r e s u l t s  2.03 160 25 -+ 155 
3.62 160 25 -+ 155 
include the  f i r s t  measurements a t  0, = zero degrees. 4 0 ~ a  ( p , ~ + )  0 148 25 -+ 155 
These measurements were made by placing a beam s top 152 25 154 0 -+ 155 
ins ide  the  spectrograph and determining the  in tegrated 
beam current from the  a c t i v i t y  induced i n  a t h i n  alumi- 
164 25 
90zr ( P , ~ + )  0 154 25 
num f o i l  placed behind the  target .  The extent  t o  160 25 -t 155 
164 25 
which the  data  can be explained by the  one-nucleon 2 0 8 ~ b  (p, n+) 0 160 25 -+ 155 
0.78 
model is being invest igated using the  distorted-wave 160 25, 40, 55 1.41 156 25 
codes of Keating and wi l ls2)  and Tsangarides and 
Negative pions from the  react ion 2 6 ~ g ( p ,  IT-) 2 7 ~ i  *university of I l l i n o i s  
(g.s.) were observed a t  160 MeV bombarding energy. 1 )  R.D. Bent, P.T. Debevec, P.H. P i l e ,  R.E. 
Pollock, R.E. Marrs and M.C. Green, Phys. 
The cross  sec t ion  a t  = 25 degrees was about 50 Rev. Lett .  40, 495 (1978). 
times lower than the  theore t i ca l  value calculated by 2) M. P. Keating and J . G .  W i l l s  , Phys. Rev. 9, 
1336 (1973). 
Kisslinger and ~ i l l e r 4 )  f o r  the  A* exchange and 
two-step proton charge exchange mechanisms. 
3) M. Tsangarides and J . G .  W i l l s ,  Priv.  Comm. 
(1977). 
4) L.S. Kisslinger and G.A. Miller, Nucl. Phys. 
A254, 493 (19 75) .  
-
Figure 1 
INVESTIGATION OF (p , a') REACTIONS NEAR THRESHOLD 
G.T. Emery, A.D. Bacher, P.T. Debevec, W.W. Jacobs, S.E. Vigdor, P.A. ~ u i n , *  
K. ~otow,** D.A. ~ e n k i n s , * *  and P.L. ~oberson** 
It has  been t h a t  t h e  t o t a l  c ross  *univers i ty  of Wisconsin, Madison, Wisconsin 53706 
sec t ion  f o r  (p , IT-) r eac t ions  should e x h i b i t  reso- **virginia Polytechnic I n s t i t u t e  and S t a t e  Univer- 
s i t y ,  Blacksburg, Virg in ia  24061 
nances s l i g h t l y  below threshold ,  corresponding 
1) G.T. Emery, Phys. Le t t .  60B (1976) 351. 
t o  d i r e c t  production of t he  a' i n  bound pionic-  
2) D.M. Lee, R. C. Minehart, S. E. Sobottka, and 
atom s t a t e s .  Observation of such resonances would K.O.H. Ziock, Nucl. Phys. A197 (1972) 106; 
B. Bassal leck,  W.-D. Klotz,  F. Takeutchi, 
al low inves t iga t ion  of 1s-s ta te  p rope r t i e s  of and H. U l l r i ch ,  Phys. Rev. C16 (1977) 1526. 
p ion ic  atoms t h a t  a r e  not  pos s ib l e  t o  study by 
stopped-pion techniques.  The most prominent 
i d e n t i f i e d  s igna tu re  of a' capture  on n u c l e i  is  
co r r e l a t ed  two-nucleon emission, l s2  but  observa- 
t i o n  of t h e  resonance i n  t h i s  channel is made 
d i f f i c u l t  by a s soc i a t ed  background problems. 
We have made i n i t i a l  background measurements 
of neutron s i n g l e s  counting r a t e s  from a t h i n  
carbon t a r g e t ,  employing a newly-constructed 
thin-walled s c a t t e r i n g  chamber i n  t he  low inten- 
s i t y  a rea .  The r e s u l t s  of t he se  measurements 
suggest  t h a t  t h e  resonance might be marginally 
observable above t h e  acc iden ta l  neutron-neutron 
coincidence background i f  a l a r g e  number of neu- 
t ron  de t ec to r s  were s i t u a t e d  c lo se  t o  t h e  t a r g e t .  
Perhaps a more promising approach is t o  look f o r  
neutron-proton coincidences,  where background 
is  l e s s  of a problem but  t he  branching r a t i o  i n  
T' capture  is smaller. Measurements of t he  back- 
ground neutron-neutron and neutron-proton coin- 
cidence r a t e s  a r e  planned i n  a f u r t h e r  e f f o r t  t o  
determine t h e  f e a s i b i l i t y  of t h i s  experiment. 


Charged-Pion Production in Proton-Nucleus Collisions Near Threshold

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Charged-Pion Production in Proton-Nucleus Collisions Near Threshold

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