Chamberlain, Owen

Grannis, Paul D

Hansroul, Michel J

Holloway, Leland E

Johnson, Claiborne H

Robrish, Peter R

Steiner, Herbert M

Valentin, Luc

eScholarship - University of California

Lawrence Berkeley National LaboratoryLBL PublicationsTitlePolarization in Pion-Proton Scattering from 670-3750 MeV/cPermalinkhttps://escholarship.org/uc/item/5ct1f3thAuthorsChamberlain, OwenHansroul, Michel JJohnson, Claiborne Het al.Publication Date1966-10-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaUCRL-17186 University of California Ernest , 0. Lawrence Radiation Laboratory POLARIZATION IN PION-PROTON SCATTERING FROM 670-3750 MeV/c TWO-WEEK LOAN COPY This is a LIbrary CirculatIng Copy whIch may be borrowed for two weeks. For a personal retention copy, call Tech. Info. DivIsion, Ext. 5545 Berkeley, California DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. S 	 ¶5 r 5... ..5 .5 Submitted to Physical Review Letters 	UCRL-1fl86 Preprint UNIVERSITY OF CALIFORNIA Lawrence Radiation Laboratory Berkeley, California AEC Contract No. W-7405--eng-48 POLARIZATION IN PION-PROTON SCATTERING FROM 670-3750 MeV/c Owen Chamberlain, Mich.el J. Hansroul, Claiborne H. Johnson, Paul D. Grannis, LelandE. Holloway, Luc Valentin, Peter R. Robrish, and Herbert M. Steiner October 1966 jF -1- 	 UCRL-17186 I POLARIZATION IN PION-PROTON SCATTERING FROM 670-3750 MeV/c * Owen Chamberlain, Michel J. Hansroul, Claiborne H. Johnson, Paul B. Grannis+, ** Leland. E. Holloway , Luc Valentin , Peter R. Robrish, and Herbert M. Steiner Lawrence Radiation Laboratory, University of California, Berkeley, California Using a polarized proton target, we have measured the polarization parameter p(e) in pion-proton scattering for both positive and negative pions. Because there seenis to be a great deal of current interest in the analysis of pion-proton scattering we wish to present these experimental results at this time even though we have not yet completed their analysis. The measurement consisted of scattering pions from polarized target protons and observing the asymmetry in scattered intensity, 1(e) , as the target protons' spin directions were reversed. The intensity for scattering from a target of polarization PT  is I(e)PQl. = I(e)01 (l+P(e)PT) where the parameter p(e) is the same as the recoil proton polarization in scattering pions from unpolarized protons under the assumption that parity is conserved in the process. * • Work done under the auspices of the U.S. Atomic Energy Commission. Present address: State University of New York, Stony Brook, New York. Present Sdd.ress: Institut de Physique Nucleaire, Orsay (S. et o.), France. Present address: Institut d.c Physique Nucleaire, Orsay (S. et 0.), France. .j) -2- The pion beam was momentum analyzed to within ±1% by a counter hodo-scope, and, in the case of 	, separation of protons was achieved by time-of-flight requirements and a gas Cerenkov threshold counter. The beam was focussed on the one-inch-square target and the entrance angles in both planes were measured by counter hodoscopes in the beam. Detec-tion of final-state particles was made with a pair of crossed-counter hodoscopes--one above and one below the emergent beam. Acceptable events were required to show coincidence among elements of the momentum-, beam-, and final-state hodoscopes, as well as with a small counter just below the polarized target crystals. In the case of kinematical ambiguity between t and p in the final state, distinction was made with a liquid Cerenkov counter beneath the lower hodoscope. The polarized target 1 consisted of 1' gm/cm2 of La2Mg3 (NO3 ) 12 .2 11- 1120 in which the protons of the waters of hydration (3% by weight) could be polarized by dynamic nuclear orientation. 2 The average polarization during the experiment was o% and was reversed in sign about once every two hours. Characterization of each accepted event was made by an on-line PDP-5 computer, summaries displayed, and a record written on magnetic tape. In the subsequent analysis, the requirement that the beam and final-state momenta lie in the same plane removed a large fraction of the background from scattering on heavy elements in the target. When attention was restricted to events with a final-state particle hitting a small region of the upper counter array, a plot of numbers of counts versus lower- count er-array position showed a clear peak corresponding (L -3- to elastic scattering from free protons. 	Once the background had been subtracted, the number of counts in the elastic peak could be used to determine the asynmetry in pion-proton scattering. The background under the peak was evaluated by using events which failed the coplanarity requirement. 	For each element of.the upper hodo- scope a conjugate •set of elements in the lower hodoscopes was chosen in a way which was identical to the choice for coplanar elements--except it was displaced perpend.cular to the plane of scattering. 	The set of events selected by these criteria is due to quasi-elastic scattering from bound protons with a transverse component of Fermi momentum and to inelastic scattering. 	It was verified that the distribution of these events with angle is the same as that for coplanar events outside the elastic- scattering peak regions. 	In addition, data were taken at some beam momenta with a dummy targt which contained elements similar to those of the crystalbut no free protons. 	These dummy data gave results which • substantiated those from the non-coplanar events. In order to verify the validity of our method we measured the polarization parameter in p-p scattering at lOO MeV/c using essentially • + the same beam and detection conditions as were. used in the 	ir p 	scatter- ing experiment reported here. 	The results are in good agreement with previous measurements. 3 mhe lower limit in momentum-transfer for which measurements could be made was imposed by the requirement that the recoil proton have a momentum of at least 350 MeV/c, so it could easily escape the target and penetrate the detector array. 	The minimum differential cross section for which polarization measurements were possible was approximately 50 ib/sr (center-of-mass systetu). It was discovered during the run that relatively small amounts of electron contamination in the beam could lead to serious background cau.ed by bremsstrahlurig and subsequent production of electron-positron pairs in the one-third radiation length of the polarized target crystals. The resulting pairs had momenta which closely paralleled the beam momen-tum. The polarized target magnet then separated the e and e and directed one into each of the final-state hodoscopes. These "events" had good coplanarity and tended to obscure the pion-proton elastic peak. The remedr chosen was to insert approximately one radiation length of Pb at the first focusof our doubly focussed beam. The results of this experiment are shown in Figs. 1 and 2. The errors shown are statistical only and do not include a ±10% uncertainty in scale due to inaccurate knowledge of target polarization. At those energies where previous measurements have beenmade, the agreement is good.' 6 ' 	It is seen that the polarization is not small even at the highest energies of this experiment and there is considerable structure in angular dependence. In particular the variation in the polarization with energy near the 1924 MeV I = 3/2 resonance (p ' 1500 MeV/c) , T 	1350 MeV) is very striking. Figure 3 is a plot of the moment um-dependenc e of the coefficients in the Legendre expansion i 0 p = )C.P.(cos e  cm) t -5- fitted to the 7C polarization P presented here and the 3T differen-tial CrO.3 sectIon 10 of Duke et al. 6 	eliminar analysis of these fits indicated that they are consistent with the assignment of JP = 7/2 for the 192  resonance as reorted by Duke et al. 6 on the basis of -P cross section and 7r-P polarization data. More extensive analysis of these data has been initiated; in the loi.yer energy region a phase shift search is in p1-ogress and at higher 'energies attempts are being made to explain the data in terms of inter-ference of Reggé exchange amplitudes with direct channel resonances. We are indebted to Dr. John Rolley for his help in conducting the experiment. We also wish to thank John Arens, Byron Dieterle, Ray Fuzesy, William Gorn, Charles Morehouse; Michael Paciotti, Stephen Rock, and David Weldon for their contributions throughout the course of thiz experiment. Finally, we are grateful to the Bevatron operating crew for their constant support. -6 REFERENCES G. Shapiro, Progr. in Nuci. Techn. and Instrentation, NorthHolland, Janu.ry 1964. C. D. Jeffries, Dynamic Nuclear Orientation, 2, Interscience, New York, (1963). F. Betz, J. Arens, 0. Chamberlain, H. Dost, P. Grannis, M. Hansroul, L.Holloway, C. Schultz, and G. Shapiro, Phys. Rev, 18, 1289 (1966). David Cheng, Lawrence Radiation Laboratoxy, -UCRL-11962 , July 1965 (unpublished). Y. Ducros, A. de Lesquen, J. Movchet, J. C. •Raoul, L. van Rossum, J. Deregel, J. M. Fontaine, A. Boucherie, and J. F. Mougel, Oxford International Conference on Elementary Particles, Sept. 1965 (unpublished). Homer A. Neal, Jr., Technical Report No. 23, University of Michigan, Ann Arbor. . Tabulated values of the results reported may be obtained by writing to the authors. S. Suwa, A. Yokosawa, N. Booth, R. Esterling, and R. Hill, Phys. Rev. Letters 15, 560 (1965). P. J. Duke, D.. - P. Jones, M. A. F. Kemp, P. G. Murphy, J. D. Prentice, J. J. Thresher, H. H. Atkinson, C. R. Cox, and K. S. Heard, Phys. Rev. Letters 15, 468 (1965). RichardD. Eandi, Thomas J. Devlin, Robert W. Kenney, Paul G. McManigal, and Burton J. Moyer, Phys. Rev. 136, B536 and B1187 .(1961). -7.- FIGURE CAPTIONS • 	 Fig. 1. Plots of the polarization parameter P versus cosine of the pion c.m. scattering angle for Tr p scattering. The errors shown are statistical only and do not include a ±io% uncertainty, in scale • 	 due to inaccurate knowledge of target polarization. Pig. 2. Plots of the polarization parameter P versus cosine of thepion • c.m. scattering angle for irp scattering. The errors shown are statistical only and do not include a ±10% uncertaintr in scale due to inaccurate knowledge of target polarization. Fig. . Coefficients in the associated Legendre expansion 1 0 P = 	CP1(cos °cm versus lab mOmentum of the pion for 	scattering. il /4 I 	 I 	 I I 	I 	I I I 	 I 	I 	I g 1+  0.745GeV/c 1.284GeV/c - 	 .869GeV/c 	- III liii III 	II - 	 - II 	Ill - —: 0.895GeV/c 1.352 : 	1.988GeV/c 	: • 	 . GeV/c  iii iii I II'' T1 It • 	 1.024GeV/c 1.441 GeV/c - 	 - 2.535 GeV/c I 	I 	I 	I I I 	I 	I 	I 	 I 	I 	I - I 	I 	I I 	I ~4JI h1: T 	T 1.084GeV/c 1.570 GeV/c I 	I 	I I 	I 	I 	II 3.260GeV/c II 	I I 	I 	I 	I II 	I 	I 	I I 	I 	I • - • I 1.155GeV/c 1.690GeV/c 3.747GeV/c 0 	-II 0 	-II 0 	-I I (3 C 0 (/ cos 9c.m. MUB-12 724 Fig. I a. I - 	0.671GeV/c ir C - 0.745 GeV/c 41 T T A -0.820GeV/c 	f f T I ff I 	I 	I T o 0.895 GeV/c I 111111 I 	I 	I I = 1.155GeV/c 0 -, I 	I fl I 	I 	I 1.352GeV/c 	- tT - - I 	I 	l 1111 - 1.988GeV/c 	- : 2.535GeV/c : 2.912GeV/c : 3.260GeV/c 0 	 -H 	 0 cos 6c.m. MUll- 12725 Fig. 2 -1.0- 0.4 0.2 0.0 -0.2 0€ 0.4 C C o 0.2 U) 0.c -0.2 0.6 0.4 0.2 0.0 -0.2 - 	 CI 6 2 C 3 64 65 	 I 	66 - 	I 	I I 	I + 1.5 	 .5 (GeV/c) MU B 12726 Fig. 3 This report was prepared as an account of Government sponsored work. Neither the United States, nor the Com-mission, nor any person acting on behalf of the Commission: Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa-ratus, method, or process disclosed in this report may not infringe privately owned rights; or Assumes any liabilities with respect to the use of, or for damages resulting from the use of any infor-mation, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Commission" includes any employee or contractor of the Corn-mission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. Ei 1)_ 0 'I 

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Polarization in Pion-Proton Scattering from 670-3750 MeV/c

Polarization in Pion-Proton Scattering from 670-3750 MeV/c

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