Use of a large multicell ionization detector - The external particle identifier - In experiments with the BEBC hydrogen bubble chamber

Fast secondary particles from interactions of K+ at 70 GeV/c and K- at 110 GeV/c in the BEBC hydrogen bubble chamber are identified by use of the relativistic rise of ionization in argon. The ionization is measured in a large multicell ionization counter system, the External Particle Identifier (EPI). The operation of this hybrid system, the calibration and the procedures of off-line analysis leading to particle identification are described. For a sample of 9283 secondary particles collected in the K+ p experiment, we present the measurements of ionization, and the determination of acceptance and identification efficiencies. The momentum-dependent populations of pions, kaons and protons have been obtained. Track by track identification procedures yielding samples of pions and kaons with a contamination {less-than or approximate} 12% are discussed. A study of the resolution of the EPI in these experimental conditions shows average values in a range of 7.6% to 11% depending on the number of ionization samples remaining after removal of background. These values extrapolate to a value consistent with the 6.6% fwhm measured over the whole device for single particles during calibration with a 50 GeV/c π- beam. © 1983.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Use of a large multicell ionization detector - The external particle identifier - In experiments with the BEBC hydrogen bubble chamber

Fast secondary particles from interactions of K+ at 70 GeV/c and K- at 110 GeV/c in the BEBC hydrogen bubble chamber are identified by use of the relativistic rise of ionization in argon. The ionization is measured in a large multicell ionization counter system, the External Particle Identifier (EPI). The operation of this hybrid system, the calibration and the procedures of off-line analysis leading to particle identification are described. For a sample of 9283 secondary particles collected in the K+ p experiment, we present the measurements of ionization, and the determination of acceptance and identification efficiencies. The momentum-dependent populations of pions, kaons and protons have been obtained. Track by track identification procedures yielding samples of pions and kaons with a contamination {less-than or approximate} 12% are discussed. A study of the resolution of the EPI in these experimental conditions shows average values in a range of 7.6% to 11% depending on the number of ionization samples remaining after removal of background. These values extrapolate to a value consistent with the 6.6% fwhm measured over the whole device for single particles during calibration with a 50 GeV/c π- beam. © 1983

Measurement of sub threshold resonance contributions to fusion reactions: the case of the 13

The 13C(α, n)16O reaction is the neutron source for the main component of the s-process. It is is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures ≲ 108 K. In this temperature region, corresponding to an energy interval of 140 − 230 keV, the 13C(α, n)16O cross section is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17O. Direct measurements could not establish its contribution owing to the Coulomb barrier between interacting nuclei, strongly reducing the cross section at astrophysical energies. Similarly, indirect measurements and extrapolations yielded inconsistent results, calling for further investigations. The Trojan Horse Method was applied to the 13C(6Li, n16O)d quasi-free reaction to access the low as well as the negative energy region of the 13C(α, n)16O reaction. By using the generalized R-matrix approach, the asymptotic normalization coefficient (C̃17O(1/2+)α13C)2 of the 6.356 MeV level was deduced. For the first time, the Trojan Horse Method and the asymptotic normalization coefficient were used in synergy. Our indirect approach lead to (C̃17O(1/2+)α13C)2 = 7.7−1.5+1.6 fm−1, slightly larger than the values in the literature, determining a 13C(α, n)16O reaction rate slightly larger than the one in the literature at temperatures lower than 108 K, with enhanced accuracy