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

Armstrong, C.

Baghaei, H.

Barkhuff, D.H.

Cameron, J.M.

Chen, J.P.

Dale, D.

Epstein, M.B.

Finn, J.M.

Gilad, S.

Joo, K.

Korsch, W.

Liu, D.J.

Lourie, R.W.

Madey, R.

Markowitz, P.

McIntyre, J.

Milbrath, B.D.

Mitchell, J.H.

Mukhopadhyay, S.

Perdrisat, C.F.

Rinckel, T.

Stephenson, E.J.

Ulmer, P.E.

Van Verst, S.P.

Warren, G.

Weinstein, L.B.

English

IUScholarWorks

DETECTOR DEVELOPMENT AND CALIBRATION 
CALIBRATION OF A PROTON POLARIMETER 
H. Baghaei, D.H. Barkhuff, R.W. Lourie, B.D. Milbrath, and S.P. Van Verst 
University of Virginia, Charlottesville, Virginia 22901 
J.P. Chen, D. Dale, S. Gilad, K. Joo, W. Korsch, and G. Warren 
Massachusetts Inst i tute of Technology, Cambridge, Massachusetts  021 39 
C. Armstrong, J.M. Finn, J .  McIntyre, and C.F. Perdrisat 
College of Wi l l iam and Mary,  Williamsburg, Virginia 291 85 
J.M. Cameron, T. Rinckel, and E.J. Stephenson 
Indiana University Cyclotron Facility, Bloomington, Indiana 47408 
M.B. Epstein, D.J. Liu, and S. Mukhopadhyay 
California S ta te  University, Los Angeles, California 90032 
J.H. Mitchell and P.E. Ulmer 
C E B A F ,  Newport News, Virginia 23606 
R. Madey 
K e n t  S ta te  University, Ken t ,  Ohio 44242 
L.B. Weinstein 
Old Domin ion  University, Norfolk, Virginia 23529 
P. Markowitz 
University of Maryland, College Park,  Maryland 20742 
A prot6n focal plane polarimeter (FPP) has been constructed by a UVa-MIT-William 
& Mary collaboration. This polarimeter, along with the polarized electron beam at MIT- 
Bates, will be used to initiate a program of polarization measurements in coincidence 
electron scattering. The FPP will be installed in the One Hundred Inch Proton Spectrom- 
eter (OHIPS) at MIT-Bates. Beginning this year, we will commence a program of (S,elp') 
measurements on the proton, the deuteron, 4He and complex nuclei. Physics issues to be 
addressed include the quadrupole amplitudes in the N + A transition via the p(e',e1p')7r0 
reaction (the question of "deformation" in the nucleon and A wavefunctions), the elec- 
tromagnetic structure of t he deuteron and helium, and sensitive tests of nucleon-nucleus 
dynamics in the 160(e,e'p') reaction. 
The basic criteria that the device had to meet were 1) complete (0-2~) coverage in 
the azimuthal scattering angle for a position spread corresponding to a 10% momentum 
acceptance and scattering angles in the FPP up to 20°, 2) suitability for use with extended 
targets up to 10 cm in length, 3) resolution in scattering angle of _<lo, and 4) the abil- 
ity to reject events with small (<4") scattering angles in <<I ps. The device is intended 
to operate over the full range of proton energies accessible at Bates: 100-800 MeV. The 
polarimeter consists of two scintillators for polarimeter trigger definition, and four multi- 
wire proportional chambers, two before and two after a graphite scatterer (which can be 
from 0.5 to 30.5 cm thick). The optics of OHIPS, along with the use of extended tar- 
gets, result in a fairly large and diverging beam at the entrance of the polarimeter. These 
characteristics, along with chamber separations large enough to provide adequate angular 
resolution, determined that the first two MWPCs be 70 x 36 cm2 (X by Y) and the last two 
be 140x88 cm2. The wire spacing in the chambers was chosen to be as large as possible 
consistent with the above criteria, resulting in 2-mm spacing in the front two chambers 
while 4-mm spacing was acceptable in the rear two chambers. This results in a total of 
2200 wires (350 in each of the four X chambers, 180 in the first two Y chambers and 220 
in the last two Y chambers). 
I 
The OHIPS FPP was calibrated at IUCF in a direct beam of polarized protons. 
Energies of 120, 150, 180 and 200 MeV were employed. At these energies, the 6-12C 
analyzing power, measured at several laboratories,' is known to k2%. This allowed a 
precise verification of the operation of the OHIPS FPP in a stand-alone mode decoupled 
from the influence of the OHIPS magnetic fields. 
The FPP was installed in the QQSP area. A low-intensity ( 4 0 5 / s )  polarized proton 
beam was obtained starting with the standard cyclotron beam by using a combination of a 
lead degrader, slits and collimators. The polarimeter was mounted on a hydraulic, wheeled 
table that allowed both up-down and left-right motions so that various regions could be 
illuminat ed. 
The calibration run was extremely successful. We acquired all the required data at 
all the energies. Additional studies were made of the graphite thickness dependence of 
the analyzing power and the effect of mixing Freon in the wire chamber gas. The data at 
200 MeV have been completely analyzed; we report those results here. 
We compared the beam polarization as measured by the FPP and by the (previously 
calibrated) IUCF beamline polarimeters. When the beam polarization is reversed, the 
FPP physics asymmetry changes sign, allowing instrument a1 effects to be canceled. The 
magnitude of the beam polarization (at 200 MeV) as measured by the FPP compared 
to the IUCF beam polarimeters is: FPP/IUCF=O.976& 0.006. An even more significant 
result is our determination of the ratio of the spin-up to spin-down polarization. Here, 
an absolute asymmetry must be measured, i.e., instrumental effects do not cancel since 
each spin state is independently analyzed. This same ratio was also measured by a special 
IUCF low-energy polarimeter employing p+a elastic scattering. The ratio of spin-upispin- 
down ratios from the two measurements is: FPP/IUCF=l.O18f 0.011. Thus, the FPP's 
operation is consistent with design goals at the 2% level. Indeed, it is as good as can be 
expected. Figure 1 shows the asymmetry (=beam polarizationx analyzing power) from our 
measurement compared to previous SIN2 and LAMPF~ data. Our data at this energy are 
1 OHlPS FPP: 177 MeV, 5 cm, Off-line results 
0 SRJ: 179 MeV. 7 cm ----- SIN Fit (7 cm) 
0 W F :  171 MeV, 8.4 cm 
Figure 1. Asymmetry vs. scattering angle in the FPP. Solid rectangles: IUCF calibration 
of Bates FPP. Open diamonds: SIN. Open squares: LAMPF. The curves show two fits to 
the SIN data set. 
not only consistent with the previous data but are of significantly greater precision. Data 
from the other energies are still under analysis although "spot checks" indicate that these 
data are comparable in quality to those obtained at 200 MeV. 
Rejection of events with small angle scatterings is necessary in hardware since the 
vast majority of events ( ~ 9 0 % )  undergo only multiple Coulomb scattering in the graphite 
analyzer and, since they have zero analyzing power, are useless. We have constructed a 
hardware trigger system that, when presented with wire number data from the multiwire 
proportional chambers, can test the scattering angle within 180 ns? The total time from the 
receipt of an event to the test result obviously depends on the chamber readout scheme; we 
are employing the PCOS I11 system from LeCroy so that the total decision time is 600 ns. 
This is significantly faster than previous implement at ions such as the 1.2 ps obtained 
using specially designed electronics at CERN5 or the 8-ps test time using time-amplitude 
converters and drift chambers at LAMPF.3 
Our method employs a simple two-level system that utilizes two LeCroy ECLine mod- 
ules: the 2378 Arithmetic Logic Unit (ALU) and the 2372 programmable Memory Lookup 
Unit (MLU). The ALUs are used to generate wire number differences which are then pre- 
sented as addresses to the MLU. The programming of the MLU essentially implements 
a pattern recognition algorithm. The MLU then produces a single output bit that indi- 
cates whether or not the given wire difference pattern corresponds to a scattering angle 
greater than a predetermined minimum. The performance of the system can be seen in 
Fig. 2 which displays the angular distribution observed in the FPP with and without the 
small-angle system activated. One can see the two orders of magnitude enhancement in 
the proportion of large angle events using this system. The angular distribution is also in 
good agreement with previous  measurement^.^ 
Figure 2. Angular distribution observed in the FPP. Solid (dashed) histogram is with 
(without) the small-angle rejection hardware activated. The dots represent the angular 
distribution from Ref. 2. 
1 I  
- 
- 
- 1 - 1  
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- - 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- 
- I 
I 
- 
I 
- 
I-. 
- 
I 
- 
- 
I 
- 
I - - 
- 
- I-I ,--- 1 --I ---,-, -7 - 
- - - 
- 
I - 
I---.---- 
- - 
1-1  I_- I-' 
- 
- 
- - 1-1 I ,-,- ------ - 
1-1 I I I 
- 1 - 8  I-- --I-; - 
L I 
I 1 -  
- 
- 
- 
- 
- 
- 
- 
- 
I 
I - 
I 
1 I I I I I  I  I  I  I I l l 1  I I I I  I  I  I ! l -  
I 
1 1 1 1  I I I  I I  I  I  I  1 1 1 1  I l l 1  
- 
1. M.W. McNaughton, e t  al., Nucl. Inst. Meth. A241, 435 (1985). 
2. E. Aprile-Giboni, e t  al., Nucl. Inst. Meth. 215, 147 (1983). 
3. R.D. Ransome, e t  al., Nucl. Inst. Meth. 201, 309 (1982). 
4. R. W. Lourie, S.P. Van Verst, J.H. Mitchell, D.H. Barkhuff and T.P. Welch, Nucl. Inst. 
Meth. A306, 83 (1991). 
5. D. Aebischer, e t  al., Nucl. Inst. Meth. 99, 405 (1972); 117, 131 (1974). 


Calibration of a Proton Polarimeter

https://scholarworks.iu.edu/dspace/bitstream/2022/569/1/iucf1992-1993_135-139.pdf

Calibration of a Proton Polarimeter

Abstract

Similar works

Full text

Available Versions

IUScholarWorks