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

Berdoz, A.

Dohrmann, F.

Goodwin, J.E.

Meyer, H.O.

Minty, M.G.

Nann, H.

Pancella, P.V.

Pate, S.

Pollock, R.

Rinckel, T.

Ross, A.

Sperisen, F.

von Przewoski, B.

English

IUScholarWorks

PION PRODUCTION 
MEASUREMENT OF THE TOTAL CROSS SECTION 
FOR THE REACTION p+p-+p+p+~O 
A. Berdoz, F. Dohrmann, J.E. Goodwin, H.O. Meyer, M.G. Minty, H. Nann, P.V. 
Pancella, R. Pollock, T. Rinckel, A. Ross, F. Sperisen, B. von Przewoski, and S. Pate 
Indiana University Cyclotron Facility, Bloomington, Indiana 4 74 05 
The IUCF Cooler is the first of many newly constructed ion storage rings to make 
use of electron cooling. The cooling process leads to a decrease in the phase volume of the 
ion beam; this leads to beams with small ernittance and unprecedented energy resolution. 
The first nuclear physics experiment to use electron cooling, CEO1, involves the study of 
the p+p-+p+p+~O reaction near threshold. A thin internal Hz gas jet serves as the target 
and a detector array is used to measure the energy and momentum of the coincident 
protons in the exit channel. The Cooler, together with a thin internal target, is well 
suited for threshold measurements. It provides a well defined interaction energy which 
is crucial since, near threshold, the cross section varies rapidly with energy. The Cooler 
also serves as a synchrotron providing the necessary proton energies from 280 - 320 MeV 
which were previously not available at IUCF. The purity of the internal gas jet (absence 
of taxget windows) greatly reduces the background from N-nucleus pion production which 
has a, rn~ich lower threshold energy. Previous experiments1y2 were limited to T,>320 MeV 
because of this background. 
The operation-of the Cooler is cyclic. First, protons of 45 MeV are ac~umula~ted 
in the ring using stripping injectio11 of 90 MeV Hz+ from the cyclotron. The 45 MeV 
beam is then allowed to cool and injection is repeated. The process of injection followed 
by cooling can be repeated with very little loss of the already cooled beam.3 The beam is 
then ramped to the desired energy where typical beam currents of 10-20 pA were achieved. 
After additional cooling at the final energy, the target was turned on and data acquisition 
started. After most of the bea-m was lost due to beam-target interactions, the taxget and 
data acquisition were turned off, the Cooler was reset and the entire cycle was repeated. 
The timing sequence for a typical CEOl production run is shown in Fig. 1. Duty factors 
of 50-60% were typical during production runs. 
The target used in CEOl is an internal Hz gas jet emerging from a nozzle cooled to 
40°K. The gas inlet line is equipped with fast switching valves which allows the target gas 
to flow only during data acquisition. The jet is mounted in a 1.3 m long, general-purpose 
taxget chamber. There are three locations in the chamber available to the jet, two of 
which (the central and downstream) were used in separate production runs. Three stages 
of differential pumping decouple the jet from the nominal lo-' Torr vacuum of the ring. 
Target thicknesses of several times 1015 atoms/cm2 were achieved. With a cooled nozzle, 
about 70% of the target thickness is contained in the jet while the rest is due to the uniform 
gas density in the central region of the differential pumping system. A thin stainless steel 
Timing Sequence, CEOl run MARP0015 (325 MeV) 
event 6: I 
single prong. I 
NO veto 
100. 
10. 
d ' ' ' ' ' ' ' ' ' ~  
beam current (log) 
I \ 
window at the downstream end of the chamber allows the reaction products to exit. 
Close to threshold, the two protons in the exit channel of p + p + p + p + ~ o  are confined 
in the lab to a narrow cone in the forward direction. A detector array has been designed 
and constructed to detect coincident protons in this cone with good energy and angular 
resolution. The detector consists of three planes of scir~tillators, a front detector (F), a 
stopping detector (E), and a veto detector (V). The planes are segmented in order to obtain 
fast information on the charged-particle multiplicity of an event. The detector array also 
consists of two X-Y wire chambers. One chamber is rotated by 45'; this removes the 
ambiguity associated with multi-prong events. The wire cha.mbers serve to determine the 
direction of the outgoing protons. The cylindrically symmetric detector array covers polar 
angles from 2'-11' with the target in the central position and from 4'-20' with the target 
in the downstream position. 
Once the 4-momenta of the two protons are known, the parameters of the unobserved 
particle can be deduced. Fig. 2 shows the reconstructed missing mass and clearly indicates 
that very little background is present. In order to obtain an absolute cross section for 
p+p-+p+p-+~O, the target thickness and beam current must be known. These quantities 
are difficult to determine individually but their product, the luminosity, can be measured 
using pp elastic scattering for which the cross section is known. Elastically scattered 
protons were detected at the same time and by the same detector as the pion production 
events. In addition, elastic recoil protons were observed by two position-sensitive silicon 
detectors, located in a horizontal plane on either side of the jet. Their position-sensitive 
surface is parallel to the beam and separated from it by 11 cm. The recoil detectors serve 
m -  
Figure 1. Timing sequence for a CEO1 
production run. 
mQ 
a ~ .  
100. 
0 ,  
. . ; 1 I I 
I I I ON WC high voltage I t 
I I RESTORE 
'I I 
I I 
I 
~ c c E ~ R A T l ~ N  1 ON' gas jet, I 
COOLING I data acqisition J and gas jet OFF 
INJECTIOK 
1 I pumping 3 
1 I 
event 5 
2 prongs + veto I 
f- 
Figure 2. Missing mass 
spectrum, P + P + P + P + ( ~ ) ,  100- 
for a bombarding energy of 
282.5 MeV. 
I hlissing Mass ( b l e ~ / c ~ )  %TO 
two purposes: they eliminate contribution from beam energy background protons, and 
because of their position sensitive surface, provide a relative measure of the luminosity 
along the beam. The latter must be known in order to correct for the contribution to pion 
production from the gas outside the acceptance of the silicon detectors. 
With two production runs in the first quarter of 1990, CEOl has concluded taking 
data.. Currently the analysis of the data is in progress. A Monte Carlo simula.tion is used 
to model various aspects of the detector response, such as geometrical losses through the 
central hole of the detector array, loss of events with both tracks in the same E segment, 
effects of an extended target, reaction losses in the scintillators, multiple scattering and 
energy losses, and wire chamber inefficiencies for both pp elastic and pp.lrO reactions. 
An absolute value of the bombarding energy with an error o f f  200 keV is deduced from 
the maximum polar angle of the two protons which is strongly dependent on the incident 
energy. The Monte Carlo code is used to fit the angular distribution of the protons and 
provides an absolute energy calibration. Fig. 3 shows the angular distribution of protons 
and the Monte Carlo fit to the distribution. 
A summary of the production running parameters and statistics is shown in Table I. 
The analysis of CEOl is continuing and data in publishable form are expected by the end 
of the third quarter of 1990. 
1. A.F. Dunaitsev and Yu.D. Prokoshkin, JETP. 36 6 (1179). 
2. T.D.S. Stanislaus, "A Study of  the Reaction jp-+pfpf.lrO From 320 t o  500 MeV", 
Ph.D. Thesis, University of British Columbia, 1987. 
3. R.E. Pollock, IUCF Scientific and Technical Report, ed. E.J. Stephenson, May 1988- 
April 1989, p. 108. 
Figure 3. Polar angu- 
lar distribution for the 
final state protons in 
p+p+p+p+n0. 'I'he 
points are experimen- 
tal da.ta, the histo- 
gram is a result from 
a Monte Carlo simula- 
tion. The bombarding 
energy is adjusted in 
the simulation to give 
the best fit to the data 
(Tp=282.5f 0.2 MeV). 
Table I. 
CEO1 Production Summary 
Machine Performance 
Beam Energies: 
Beam Current: 
Target Thickness (cooled jet): 
Luminosity 
(Acq. Start): 
(Time Avg.): 
Beam Lifetime with Target: 
Run Statistics 
Time: Production: llOh 
Integrated Luminosity (Production): 
Data 
Total # of ppn0 events: 
Statistical Error: 
Systematic Error: 
283-325 MeV (9 values) 
5-25 pA 
2x 1 0 ~ ~ - 5 x 1 0 ' ~  atoms/cm2 
Setup: -2OOh 
16 nb-I 
24000 
1-3% per energy point 
10% (est.) 


Measurement of the Total Cross Section for the Reaction p + p → p + p + pio

https://scholarworks.iu.edu/dspace/bitstream/2022/720/1/iucf1989-1990_52-55.pdf

Measurement of the Total Cross Section for the Reaction p + p → p + p + pio

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