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

Bacher, A.D.

Bowyer, S.M.

Bowyer, T.W.

Chang, S.

Franklin, W.

Liu, J.

Sowinski, J.

Stephenson, E.J.

Wells, S.P.

Wissink, S.W.

English

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A CALIBRATION OF THE K600 FPP FROM 120 TO 200 MeV 
S.M. Bowver, A.D. Bacher, T.W. Bowyer, S. Chang, W. Franklin, 
J. Liu, J. Sowinski, E.J. Stephenson, S.P. Wells, and S.W. Wissink 
I n d i a n a  Un ive r s i t y  Cyc lo t ron  Facili ty,  B looming ton ,  I n d i a n a  4 74 08 
Experiment E367 measured D N N /  for p+p elastic scattering at an incident beam en- 
ergy of 200 MeV from 5"-38O.l Over this angular range, the energy of the protons incident 
on the carbon analyzer of the focal plane polarimeter, FPP, ranged from N 200 MeV down 
to 120 MeV. Hence, a calibration of the effective analyzing power of the FPP, AFPP, 
extending down to about 120 MeV was needed. 
The calibration methods employed for the K600 FPP have been described in a previous 
report .2  In brief, by elastically scattering protons from a 0+ target, and then choosing the 
scattering angle of the reaction such that the analyzing power, Ay , is either 0 or close to 
1, the value of the polarization incident on the analyzer is determined. Doing calibration 
measurements at both Ay =O and Ay "1 results in information about possible systematic 
errors. 
The thickness of the carbon analyzer used is a compromise between maximizing the 
efficiency of the reaction and minimizing the total energy lost within the analyzer. Thus, 
the optimal thickness is necessarily energy dependent, and in our calibration, thicknesses 
of 2", l", and 112" were used. 
The calibration data were taken in two running periods, one in February, 1993 and 
the other in August, 1993. During each run, the incident beam energy (Tp) was varied 
and usually several scattering angles ( O l a b ) ,  or equivalently Ay values, were studied. In 
most cases, more than one thickness of carbon analyzer ( tc)  was used. The values of these 
parameters for all of our runs are summarized in Table 1. 
The calibration data were replayed with the intent of minimizing as many systematic 
errors as possible. The angle cuts on the FPP scattering angle are set from 6"-23". The 
6" lower limit is slightly larger than that used in previous calibrations in order to eliminate 
inclusion of the multiple scattering peak at all energies. Gates are consistently placed on 
the FPP AE and E spectra for the calibration by means of an algorithm that is also used 
to make these same cuts on the DNN1 data. A 6-mm thick scintillator, S3, exists just 
upstream of the carbon analyzer block. To avoid including different contributions from S3 
for different analyzer thicknesses, we decided to include all of S3 in our scattering vertex 
cuts. This results in an effective analyzer consisting of S3 plus the carbon block. 
Results for the first part of our calibration are shown in Fig. 1. Energy values are 
assigned to each point as the average of the energy incident on the polarimeter and the 
energy remaining after passing through the carbon analyzer. This allows all points to 
be plotted on the same curve, regardless of the analyzer thicknesses used at the points. 
Hence, for protons of the same energy incident on the carbon analyzer, calibration points 
assigned to significantly different energies resulted by varying the analyzer thickness. The 
curve plotted against the data is a quadratic fit with a XE= 0.68. Analysis of the second 
part of the calibration data is underway. 
Table 1. Summary of FPP calibration running 



A Calibration of the K600 FPP from 120 to 200 MeV

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A Calibration of the K600 FPP from 120 to 200 MeV

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