Subthreshold pion production in the reaction /sup 139/La + /sup 139/La. -->. pi. /sup + -/ + X
We have measured charged pion production in the reaction /sup 139/La + /sup 139/La ..-->.. ..pi../sup + -/ + X at three beam energies (246, 183 and 138 MeVnucleon) below the nucleon-nucleon threshold. Associated multiplicity for charged participants was obtained using a 110-element scintillator multiplicity array. Data were taken over the angular range of 21/degree/ to 67/degree/ in the laboratory (equivalent to 30/degree/ to 90/degree/ in the center of mass). Dependence of the spectra upon pion charge, energy and angle, beam energy, system mass and associated multiplicity was investigated. Based on the isotropic angular distibutions and the associated multiplicities for pion production, it appears that subthreshold pions in the range of our experiment are produced predominantly from a source at rest in the center of mass and involving a large number of nucleons. The general character of the subthreshold pion spectra is comparable to previous results above threshold. However, the scaling of the subthreshold pion yield with system mass deviates from the dependence observed in light systems, to an extent which cannot be explained by a simple nucleon-nucleon model. We also found charge dependent structure in the pion spectra, which we analysed in the framework of both Coulomb distortion and clustering models. We conclude that while we did not find clear evidence of collective effects in subthreshold pion production, it would be very worthwhile to conduct a systematic investigation of pion production for all charge states and over a range of angles, system masses and beam energies, below threshold. 170 refs., 78 figs., 10 tabs.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC03-76SF00098; AS05-76ER04699
- OSTI ID:
- 5051297
- Report Number(s):
- LBL-24275; ON: DE88008228
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
LANTHANUM 139 TARGET
LANTHANUM 139 REACTIONS
PIONS
PARTICLE PRODUCTION
ANGULAR DISTRIBUTION
CALIBRATION
DATA ACQUISITION SYSTEMS
DIFFERENTIAL CROSS SECTIONS
ENERGY DEPENDENCE
ENERGY LOSSES
KINETIC ENERGY
LINEAR MOMENTUM
MATHEMATICAL MODELS
MULTIPLICITY
SPECTROMETERS
TIME-OF-FLIGHT METHOD
TRANSVERSE MOMENTUM
BOSONS
CHARGED-PARTICLE REACTIONS
CROSS SECTIONS
DISTRIBUTION
ELEMENTARY PARTICLES
ENERGY
HADRONS
HEAVY ION REACTIONS
LOSSES
MEASURING INSTRUMENTS
MESONS
NUCLEAR REACTIONS
PSEUDOSCALAR MESONS
TARGETS
651720* - Nuclear Properties & Reactions
A=90-149
Experimental