This work was supported by National Science Foundation Grants PHY 76-84033A01, PHY 78-22774, and Indiana Universit

Bent, R.D.

Green, M.C.

Jacobs, W.W.

Marrs, R.E.

Meyer, H.O.

Pile, P.H.

Pollock, R.E.

Sjoreen, T.P.

Soga, F.

English

IUScholarWorks

MEASUREMENT OF CHARGED PION YIELDS FROM NUCLEI 
I N  ( p , ~ + )  REACTIONS VERY NEAR THRESHOLD 
P.H. P i l e ,  R.E. Pollock,  T.P. Sjoreen,  W.W. Jacobs,  M.C. Green, 
F. Soga, R.D. Bent, H.O.  Meyer, and R.E. Marrs 
The D 5  Pion ~ ~ e c t r o r n e t e r l ' ~ ) . h a s  been used t o  mea- become a 100 um A l  absorber followed by a 5 o r  10  m i l  
s u re  d i f f e r e n t i a l  c ros s  s ec t ions  and analyzing powers p l a s t i c  s c i n t i l l a t o r  g iv ing  AE and t iming information 
of t he  (p,n+) r eac t ion  on var ious  nuc l e i .  The measure- followed by a 5 mm (100 mm2) s i l i c o n  stopping de t ec to r .  
ments include se l ec t ed  exci ted  s t a t e s  i n  t h e  f i n a l  A l a r g e  a r ea  (450 mm2) s i l i c o n  ve to  de t ec to r  i s  a t  t h e  
nucle i .  r e a r  of t h e  s t ack .  Background l e v e l s  below 1 nb / s r  
The DD Spectrometer is schematical ly shown i n  have been achieved f o r  i t s  f u l l  170 + 1500 range. This 
Figure 1 and i t s  s o l i d  angle vs.  rho i n  Figure 2. The background l e v e l  is achievable a t  t he  most forward 
s o l i d  angle shown was measured with a 100 m2 de tec to r  angles only wi th  t h e  use of a  condi t ion  t h a t  t he  muon 
a t  t he  non-dispersed f o c a l  poin t  and has a maximum decay be observed i n  t h e  5 mm stopping de t ec to r .  This 
(3.5 msr) which equals  t h e  geometric s o l i d  angle  of condi t ion  is  a l s o  appl ied  t o  exc i t ed  s t a t e  spec t r a  i n  
t he  device.  The s tandard  de t ec to r  configut-ation has order  t o  e l iminate  high energy t a i l s  on the  energy 
Horizontal Slits 
Detector 
Figure I .  Schematic drawing o f  the  DD spectrometer 
and detector stack. 
I I I I I I  I l l  I  * 
SZ v s  p D 5  
- 
- .g.--n--4-- n-+. . - 
- 
,$' 6.4 - 
#&' . \ 2, - 
+-n. 
- 4- - 
0 1.4 MeV Alphas - 
A 7.7 MeV Pions (Arbitrary Normalization) 
- - 
- - 
I 1 1 1 1 1 1 I I  1 
Figure 2. The radius o f  curvature f p )  us. sol id  angle 
(Q) of  the  DD with a 100 m2 stopping detector. 
peaks due t o  t he  muon decay. 
A summary of t h e  da t a  obtained with t he  DD spec- 
trometer  is  shown i n  Table I. The 4 0 ~ a ,  9 0 ~ r ,  ~ O B ,  and 
160 da ta  a r e  p a r t  of Ref. 1. The 4 0 ~ a  nd ~ O B  d a t a  
obtained with unpolarized protons is included i n  an 
a r t i c l e  which has been submitted t o  Phys. Rev. L e t t e r s .  
An example of a  spectrum obtained with t h e  DZ is 
shown i n  Figure 3 .  The pion labora tory  ene rg i e s  range 
from 4.4 t o  12.8 MeV. The muon peak r e s u l t s  from 
pions which a r e  stopped i n  t h e  t a r g e t  and subsequently 
12 C (P ,  7r+)13c 
T, = 160.0 MeV 
8,= 35 Deg Lab 
20 40 60 80 100 120 140 160 180 200 
CHANNEL NUMBER 
Figure 3. A 12clp,r+) spectrum taken a t  a 35 degree 
laboratory angle and a 160 MeV proton energy. 
Table I. 
React ion  T, (MeV) Remarks 
2 0 8 ~ b ( p , n + ) 2 0 9 ~ b  149 One angle  on ly  (0-4 MeV) 
9 0 ~ r ( p , n + )  9 1 ~ r  144 Angular d i s t r i b u t i o n s  (0-2 MeV) 
4 0 ~ a  (p , ~ - r + ) ~ l c a  140, 144 Angular d i s t r i b u t i o n s  (0-2 MeV) 
3 0 ~ i  (p ,n+) 3 1~ i  14 9  One ang l e  on ly  (0-4 MeV) 
2 8 ~ i ( p , ~ + ) 2 9 ~ i  149 Angular d i s t r i b u t i o n s  (0-5 MeV) 
160 (P, T+) 70 155 Angular d i s t r i b u t i o n s  (g . s . ) 
3~ (p,  n+) 14c 151 Angular d i s t r i b u t i o n s  (0-5 MeV) 
12c (p, ~r+)  13c 156, 160 Angular d i s t r i b u t i o n s  (0-5 MeV) 
Two angular  d i s t r i b u t i o n s  and a  8, = 
25 deg ( l ab )  e x c i t a t i o n  func t i on  
l o g  (p ,+) l l ~  145-155 Angular d i s t r i b u t i o n s  (0-5 MeV) 
4 8 ~ a ( p , ~ + ) 4 9 ~ a  149 Angular d i s t r i b u t i o n s  (0-5 MeV) 
1°B (G,n+) ' 'B 154 P o l a r i z a t i o n  asymmetry (0-4 MeV) 
12c ($, n+) 13c 156,  159 P o l a r i z a t i o n  asymmetry (0-4 MeV) 
4 0 ~ a ( $ , n + ) 4 1 ~ a  14 7 P o l a r i z a t i o n  asymmetry (0-4 MeV) 
13 v = CgBs. T, (CM ) = 9.3 MeV 
13 T (CM)=7.6 MeV A = C3.09.e" a 
( C M ) = 9 . 8 M e V  
Figure 4.  Differential cross sections for the (p,n+) Figure 5. A (8) vs . 8, for the (8, n') reaction t o  
reaction t o  three different final states. three different final states. 
decay i n t o  4.1 MeV muons. Only two DD magnetic f i e l d  
s e t t i n g s  were requi red  t o  generate t h i s  spectrum. The 
r e so lu t ion  is approximately 300 keV fwhm and is p r i -  
mari ly due t o  t h e  6.5 degree ho r i zon ta l  acceptance of 
t he  DS, the  energy r e so lu t ion  of t h e  proton beam and 
s t r agg l ing  of  t h e  pion i n  t he  A 1  absorber and p l a s t i c  
s c i n t i l l a t o r .  
In  Figure 4 t h r e e  prel iminary angular  d i s t r i b u -  
t i ons  a r e  shown f o r  t he  (p,n+) r eac t ion  t o  t he  ground 
s t a t e s  of 4 9 ~ a ( 3 / 2 - )  and 13c(1/2-) and t h e  3.09 MeV 
(1/2+) s t a t e  i n  13c. The 13c angular  d i s t r i b u t i o n s  
were measured3) e a r l i e r  a t  Uppsala a t  a  185 MeV proton 
energy and d i sp l ay  shapes very s i m i l a r  t o  those  i n  
Figure 4. The 4 8 ~ a  ( ~ , I T + ) ~ ~ C ~ ~ .  . angular  d i s t r i b u t i o n  
r ep re sen t s ,  t o  our knowledge, t h e  f i r s t  pion production 
da t a  a v a i l a b l e  on t h i s  t a r g e t  and does not  d i sp l ay  
s t rdng f ea tu re s  a s  does t he  4 0 ~ a ( p , s + )  reac t ion  t o  
t h e  4 1 ~ a  ground s t a t e .  
Po la r i za t ion  asymmetry measurements have been 
made f o r  seven d i f f e r e n t  f i n a l  s t a t e s  i n  l l B ,  13c and 
4 1 ~ a .  A l l  of t h e  s t a t e s  observed exhib i ted  a substan- 
t i a l  negat ive  asymmetry i n  t h e  range -0.4 t o  -0.8, 
confirming t h e  behavior f i r s t  observed4) a t  TRIUMF a t  
energies  much f u r t h e r  above threshold  f o r  f i n a l  s t a t e s  
i n  9 ~ e  and 13c. Figure 5 shows prel iminary asymmetry 
measurements f o r  pion production t o  t h e  ground s t a t e  
(712-) of 4 1 ~ a  nd t o  t h e  ground s t a t e  (112') and 
f i r s t  exc i t ed  s t a t e  (1/2+) of 3 ~ .  The 4 1 ~ a  d a t a  was 
taken a t  a  146 MeV proton energy and t h e  13c da t a  a t  
159 MeV. A s  can be noted from t h e  f i gu re ,  t h e  4 1 ~ a g . s ,  
asymmetry does n o t  exh ib i t  an asymmetry maximum i n  t he  
forward hemisphere a s  do t h e  o the r  two s t a t e s .  I n  f a c t ,  
of t h e  seven s t a t e s  measured, only t h e  4 1 ~ a g . s .  and 
the  1 1 ~ 4 . 4 6  MeV s t a t e s  d id  not  have maximum negat ive  
asymmetries i n  t h e  forward hemisphere. The f a c t  t h a t  
d i f f e r e n t  asymmetry c h a r a c t e r i s t i c s  have been observed 
f o r  d i f f e r e n t  nuclear  f i n a l  s t a t e s  suggests  t h a t  (p ,IT+) 
asymmetry measurements may play an important r o l e  i n  
d isentangl ing  t h e  pion production process.  
1 )  P.H. P i l e ,  Ph,D. Thesis ,  Indiana Univers i ty ,  1978. 
2) P.H. P i l e ,  R.E. Pollock,  R.D. Bent, R.E. Marrs, 
and M.C. Green, Bul l .  Am. Phys. Soc. 23, 611 (1978). 
3) S .  Dahlgren e t  a l . ,  Nucl. Phys. A211, 243 (1973). 
4) E.  Auld e t  a l , ,  Phys. Rev. L e t t .  41, 462 (1978). 


Measurement of Charged Pion Yields from Nuclei in (p,Pi+) Reactions Very Near Threshold

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Measurement of Charged Pion Yields from Nuclei in (p,Pi+) Reactions Very Near Threshold

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