This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Betker, A.

Cameron, J.

Jacobs, W.

Nann, H.

Peterson, T.

Pitts, W.K.

Shao, J.

Spraker, M.

Szymanski, J.

Vigdor, S.

Warman, K.

English

IUScholarWorks

in a storage ring. Future uses of this facility include a study of pion production as well as 
three-body breakup in the d+p system. 
1. T. Wise, A.D. Roberts, and W. Haeberli, Nucl. Instrum. and Methods A336, 410 
(1993). 
2. W.A. Dezarn, J. Doskow, J.G. Hardie, H.O. Meyer, R.E. Pollock, B. von Przewoski, 
T. Rinckel, F. Sperisen, W. Haeberli, B. Lorentz, F. Rathmann, M.A. Ross, T. Wise, 
P.V. Pancella, contrib. to Eighth Int. Symp. on  Pol. Phen. in Nucl. Phys., p. 62. 
3. M.A. Ross, A.D. Roberts, T. Wise, W. Haeberli, W.A. Dezarn, J. Doskow, H.O. 
Meyer, R.E. Pollock, B. von Przewoski, T. Rinckel, F. Sperisen, and P.V. Pancella, 
Nucl. Instrum. and Methods A344, 307 (1994). 
4. R.E. Pollock, see elsewhere in this report. 
5. B. von Przewoski, H.O. Meyer, P.V. Pancella, S.F. Pate, R.E. Pollock, T. Rinckel, 
F. Sperisen, J. Sowinski, W. Haeberli, W.K. Pitts, and S. Price, Phys. Rev. C44, 44 
(1991). 
6. B. von Przewoski, W.A. Dezarn, J. Doskow, J.G. Hardie, H.O. Meyer, R.E. Pollock, 
T. Rinckel, F. Sperisen, W. Haeberli, B. Lorentz, F. Rathmann, M.A. Ross, T. Wise, 
and P.V. Pancella, Rev. Sci. Instrum. 1, 67 (1996). 
NEAR THRESHOLD PION PRODUCTION VIA 2H(p',?r0)3He 
A. Betker, J. Cameron, W. Jacobs, H. Nann, T. Peterson, 
J. Shao, M. Spraker, J. Szymanski, S. Vigdor, and K. Warman 
Indiana University Cyclotron Facility, Bloomington, Indiana 4 74 08 
W.K. Pitts 
University of Louisville, Louisville, Kentucky 4 0292 
Reactions of the class (N,n) have generated renewed interest because the high mo- 
mentum transfer (necessary to knockout a virtual pion) selects short range aspects of the 
NN interaction. Furthermore, it is expected that close to the pion-production threshold 
these reactions proceed in a non-resonant mode; that is, a real intermediate A(1232) which 
subsequently decays into a nucleon and a pion is not produced. Two previous experiments 
have examined the reaction 2H(p,n0)3He near threshold. One of these was performed at 
IUCF' and the other at S a ~ l a ~ . ~  The results from these experiments show important dis- 
crepancies. The general trend of cross section a versus 7 p,,/m, is linear for the Saclay 
data but has a downward concavity for the IUCF data. Thus, the values of o are not in 
agreement (in general) for a given 7). The largest difference in the value of a is for the 
highest 1) of the IUCF data set, 1) = 0.20: 
IUCF Measurement 2.37 f 0.07 pb, 
Saclay Measurement 3.20 f. 0.04 pb. 
Weak interference between s-wave and p-wave production would produce an upward con- 
cavity for o versus 7.  Thus both experiments imply strong interference between these 
partial waves, but at different strengths. However both data sets are consistent with 
results from pion absorption experiment sa3j4 
To help resolve questions about these discrepancies, experiment CE58 was performed 
to measure the differential cross sections and analyzing powers for the reaction ' H ( f i , ~ ~ ) ~ H e  
at energies near the pion production threshold. The pions were not directly observed; 
instead the recoiling 3He nuclei were detected to identify the reaction. The T-Region 
Magnetic Channel was employed to separate the 3He nuclei cleanly from the background 
of scattered protons and deuterons in two ways. First, the elastically scattered protons 
and deuterons were outside the channel's rigidity acceptance. Second, the 5.7-m flight 
path down the channel allowed velocity selection from time of flight (TOF) information 
as shown in Fig. 1. The channel was instrumented with a thin plastic scintillator (Sl) 
and a drift chamber (DC) at the channel entrance, and a delay-line chamber and thick 
plastic scintillator (S2) at the channel exit. A set of four plastic scintillators and a (one 
dimensional) silicon position-sensitive detector were used to monitor the luminosity by 
observing p-d elastic scattering. The G-Region polarimeter was used to monitor the beam 
polarization at the end of each Cooler cycle via p-12C scattering. 
I I Figure 1. An example of a raw 
TOF spectrum. The trigger re- 
quirement was a coincidence be- - 
tween S1 and S2. The 3He group 
lies between the dashed lines. The 
peaks on each side of the distribu- 
tion correspond to He nuclei going 
forward (left edge) and backward I- 
(right edge) in the center-of-mass 
frame. 
Selection of the 3 ~ e  events was accomplished with a cut on pulse height in S1 as well 
as a cut on the correlation between TOF and pulse height from S2. For one of the runs, 
the data taken in November 1995, another scintillator S3 was placed behind 52. Signals 
from S3 allow a test of the cleanliness of the previously mentioned cuts, because S2 is thick 
enough to range out all of the 3He nuclei. The TOF provides an energy measurement for the 
3He and the DC provides two dimensional position information that allows determination 
of the laboratory-frame scattering angles. The signature of pion production is the proper 
correlation from two body kinematics between the energy and the (laboratory) polar angle 
for the observed 3He, as shown in Fig. 2. 
The cofiguration of the channel's beamlines and magnetic fields creates a geometrically 
limited and non-uniform acceptance. The probability for transmission through the channel 
Figure 2. The correlation between 
the laboratory polar angle and the 
kinetic energy for 'He nuclei. The 
solid curve is determined from two 
body kinematics, known masses, and 
a known beam energy of 200.5 MeV. 
(Lab) Polar Angle (degrees) 
depends on (at least) three variables for each incident particle: the rigidity, and the two 
position coordinates in the front wire chamber. Data for pion production had to be taken 
in several "bites" ; both the momentum setting and the laboratory angle of the channel 
were changed to cover different parts of the phase space for the 'He. Note that Fig. 2 
displays data from a single setting of the channel's angle and momentum. 
In order to normalize the differential cross section properly, the magnetic-channel 
transmission function was measured. These measurements used proton elastic scattering 
- 
from 'H and 12C targets for three beam energies that gave the protons similar rigidity 
to the 'He nuclei from pion production. Furthermore, the channel magnets were set to 
several scalings of the magnetic-tune solution. This gave the transmission as a function of 
relative rigidity that is defined as the ratio of the channel's central momentum setting to 
the beam's momentum. To measure the transmission for a given energy and momentum 
setting, the flux of elastically scattered protons at the channel entrance and the flux at 
the channel exit were both measured. Two plastic scintillators on beam right were used 
to monitor the luminosity and permit normalization between measurements of the flux at 
the entrance and exit. The probability of transmission for a specific momentum setting is 
shown as a function position on the entrance wire chamber in Fig 3. 
Table 1 
'I Run Approximate number of 'He events 
At this time, the CE58 data set is complete and will provide differential cross sections 
and analyzing powers for five different pion momenta near the production threshold (see 
Table 1). Work that remains to be done includes energy-loss calculations to match the 
Transmission Probability 
Figure  3. The probability of 
transmission through the T- 
Region channel as a function 
of position on the entrance 
wire chamber for a specific 
setting of the channel. The 
innermost contour corre- 
sponds to 90% transmission; 
each successive contour cor- 
responds to 80%, 70%, ..., 
10%. The orient ation corre- 
sponds to the wire chamber 
as viewed from the target po- 
sition. 
0 1 2 3 4 5 6 7 8  
X Position (cm) 
proton rigidities from the transmission measurements to the rigidities of the 3He nuclei 
from pion production. After determining the acceptance for 3He nuclei for each channel 
setting (both for varied angle and for varied momentum setting), data from each setting 
need to be normalized and position-matched in order to produce a complete data set for 
each pion momentum. Finally, data from the polarimeter will be analyzed and used to 
normalize rates for each spin state in order to determine analyzing powers. 
1. M. A. Pickar, Ph.D. Thesis, Indiana University, 1982. 
2. A. Boudard e t  al., News from Saturne, 17 (1993). 
3. V. N. Nikulin e t  al., 1996 preprint 
4. M. A. Pickar e t  al., Phys. Rev. C 46, 397 (1992). 


Near Threshold Pion Production via 2-H(p,pi-0)3-He

https://scholarworks.iu.edu/dspace/bitstream/2022/331/1/iucf1995-96_11-14.pdf

Near Threshold Pion Production via 2-H(p,pi-0)3-He

Abstract

Similar works

Full text

Available Versions

IUScholarWorks