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Antiproton-Proton Annihilation Into Four and Five Pions at 2.4 and 2.9 Gev/C Ronald Paul Radlinski Iowa State University

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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1970 Antiproton-proton annihilation into four and five pions at 2.4 and 2.9 GeV/c Ronald Paul Radlinski Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Elementary Particles and Fields and String Theory Commons Recommended Citation Radlinski, Ronald Paul, "Antiproton-proton annihilation into four and five pions at 2.4 and 2.9 GeV/c " (1970). Retrospective Theses and Dissertations. 4191. https://lib.dr.iastate.edu/rtd/4191 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 70-18,900 I I RADLINSKI, Ronald Paul, 194-2^ | ANTIPROTdN-PROTON ANNIHILATION INTO FOUR AND \. FIVE PIONS AT 2.4 AND 2.9 GeV/c. l i lowa State University, Ph.D., 1970 ' Physics, elementary particles | University Microfilms, A )(|ERQ\Company, Ann Arbor, Michigan % THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED ANTIPROTON-PROTON ANNIHILATION INTO FOUR AND FIVE PIONS AT 2.4 AND 2.9 GsV/C by Ronald Paul Radiinski A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requi rements for the Degree of DOCTOR OF PHILOSOPHY Major Subject": High Energy Physics Approved: Signature was redacted for privacy. Signature was redacted for privacy. Heatr ofvMajor Department Signature was redacted for privacy. Iowa State University Of Science and Technology Ames, Iowa 1970 PLEASE NOTE; Not original copy. Several pages have indistinct print. Filmed as received. University Microfilms. 11 TABLE OF CONTENTS Page I. INTRODUCTION 1 II. EXPERIMENTAL PROCEDURE 3 A. Beam Characteristics 3 lo General properties 3 2o Specifics of this experiment 4 Bo Scanning and Measuring 4 Co Identification of Events 5 lo Fitting and biases 5 2o Final state classification 8 Do Data Samples Used for Analysis 11 1. Beam restrictions 11 2. Restrictions on track measurements 12 3o Missing mass squared and chi-squared restrictions 14 4. Final data samples 17 I No CROSS SECTIONS 18 IV. EFFECTIVE MASS DISTRIBUTIONS 23 Ao General Method of Analysis 23 B. Resonance Production in the Four Pion Channel 24 1. General features 24 2o Dipion effective mass distributions 28 3» Three pion effective mass distributions 29 4. Associated production in the four pion channel 34 5. Summary of the production modes in the four pion 37 annihilation channel Co Resonance Production in the Five Pion Channel 39 Mi lo General features 39 2o Dipîon effective mass distributions 45 3o Three pion effective mass distributions 46 4o Four pion effective mass distributions 49 5» Associated production in the five pion channel 56 6o Summary of the production modes in the five pion 57 annihilation channel Do Effective Mass Distributions of the 4itMM Events 57 ANGULAR DISTRIBUTIONS 64 A. Production Angles of Pions 64 Bo Pion Correlation Angles 72 Co Angular Distributions of Resonance Production 82 lo Production angles of resonances 82 2o Decay angular distributions 85 CONCLUSION 89 BIBLIOGRAPHY 91 ACKNOWLEDGMENTS 94 1 I» INTRODUCTION This dissertation is an investigation of the four-prong reactions (1) (2) (3) at incident antiproton momenta of 2.4 and 2»9 GeV/c. The film analyzed in this experiment was exposed in the Brookhaven National Laboratory's 31 inch hydrogen bubble chamber during June, I967. Approximately 60,000 pictures were taken at 2.4 GeV/c and 40,000 pictures at ,2.9 GeV/c. Other experiments involving the above reactions have been reported at momenta of 1.1 to 1.52 GeV/c (0,1.2 GeV/c (2,3), 1.2 to 1.6 GeV/c (4,5), 1.51 to 1.95 GeV/c (6), 1.6 GeV/c (7), 2.5 GeV/c (8,9), 2.7 GeV/c (10), 3.28 GeV/c (11), 3.6 GeV/c (12), 3.66 GeV/c (11), 5.7 GeV/c (13-15), and 6.9 GeV/c (16). \The opportunity to study single and associated resonance production • Is.a prime consideration for analyzing the above final states. The investigation of the energy dependent properties of the resonance particles over a limited momentum range is made possible by performing the experiment at both 2.4 and 2.9 GeV/c. The cross sections for resonance production as well as for the total cross section of the above final states are found, in general to decrease as the incident antiproton momentum is increased from 2.4 GeV/c to 2.9 GeV/c. A high percentage of the pion annihilations is found to proceed through an intermediate three meson state. In the four pion channel, the dominant modes of production at both momenta are through the following three meson reactions — o + • PP -» p ît ît 2 — -O + - pp f jr 3t , .where both the neutral rho meson (p°) and f meson (f°) subsequently decay into a 3t ït pair* Indications of associated production are found in the four pion channel at both momenta. A significant fraction of the five pion events proceed via — o o o PP p P 3C — ± o T pp p p It — o + - pp CU 3t The charged rho (p^) decays into a pair while the omega (iu°) decays via a* ïC jr°. There are also indications of Aj (_> pir), AgC^. p#), and B(-, m%) resonance production in the five pion channel. Evidence for A^ production as well as for a possible f°jt resonance is found in the four pion channel at 2.4 GeV/c. The analysis of the unconstrained pp _• lit nit® (n > 1) events gives evidence only for p° production. Single pion and dipion production angles are investigated in the center of mass system. The tendency of the jt (it ) to be emitted in the direction of the p(p) increases, in general, with energy and decreases with multiplicity. Quantitative measurements of the asymmetry characteristics of angular dis­ tributions are obtained from the forward to backward ratio (F/B), the polar to equatorial ratio (P/E) and the correlation parameter (7). The dependences of the F/B and P/E ratios on pion momentum are investi­ gated for chosen momentum intervals. Production angles and decay angular distributions are given for resonance production in which the signal is strong enough to allow a meaningful background substraction. 3 11. EXPERIMENTAL PROCEDURE Ao Beam Characteristics ]o Genera1 Proper ti es To obtain an antiproton flux of specified properties from the Brook- haven National Laboratory's AGS (Alternating Gradient Synchrotron), hydrogen ions are initially preaccelerated to an energy of 750 keV by a Cockcroft-Walton generator. The ions are further accelerated by a linac (linear accelerator) which increases their energy to 50 MeV. The parti­ cles are then injected into a vacuum tank which is inside the magnets of the synchrotron. The magnetic field then rises in step with the increasing momentum of the protons as they are accelerated by successive traversais of one or more gaps across which R. F. fields are provided. After the protons have reached a desired momentum, a portion of the beam is spilled onto a suitable metallic target. The interaction of the deflected beam and the target results in a flux of secondary particles such as pions, kaons, antiprotons, and muons. This secondary beam of particles passes through a transport system which consists of dipole magnets, quadrupole magnets, and mass slits that focus the beam and select particles of a desired momentum. The next stage, which consists of an electrostatic separator and another mass slit, is tuned to allow only the passage of antiprotons. The beam separator is comprised of crossed electric and mag­ netic fields that pass only particles of a designated velocity. Since all particles have approximately the same momentum at this stage, the process is equivalent to selecting particles of a particular mass. The beam is subsequently refocussed, sent through another momentum selection stage, another mass separator stage, and finally into a beam shaping section that h spreads the beam for a uniform coverage of the bubble chamber in which the reactions are to occur. 2. Specifics of this experiment By placing a scintillation counter behind the second separator during the tuning of the beam, a distinct separation of pions, kaons, and anti- protons was found at each momentum. To insure constant running conditions throughout the experiment a Cerenkov counter was placed behind the second \ mass slit to monitor the pions and muons. Since the beam was estimated to consist of more than 99% antiprotons, no corrections have been made for beam contaminations. A counter at the entrance to the bubble chamber trig­ gered the cameras only when the incident antiproton flux was between six and sixteen particles/pulse. Acceptance of less than six incident particles per picture would decrease the interaction statistics while more than six­ teen incident tracks per picture is too high a density for efficient scanning and measuring of the film. In a later analysis of the beam momenta from events with a unique final state (pp ^ pp It ) (17) the distribution of the beam momentum for the two exposures was determined to be 2375 + 75 MeV/c and 2885 ± 80 MeV/co Although the film was processed with the above values for incident momenta, the two data samples will be referred to in this presentation as having incident antiproton momenta of 2.4 and 2.9 GeV/c. B. Scanning and Measuring From the 100,000 picture exposure, 58,277 pictures at 2.4 GeV/c and 37,189 pictures at 2«9 GeV/c were found suitable for scanning.
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