• T N Rengarajan

Articles written in Proceedings – Section A

• The influence of isobar production on charge ratio and transverse momentum of secondary particles in high energy collisions

An isobar model in which collision between two particles leads to the creation of only two bodies which by subsequent decay give rise to the observed secondaries has been considered. On the basis of such a model, the charge ratios of pions, kaons andΣ-hyperons inp−p andπ−p collisions have been computed and compared with the available experimental data. Some features of transverse momentum of pions and protons in 24 GeV/cp−p collisions have also been studied. The main conclusions can be summarised as follows:

The observed positive excess among pions produced in high energyp−p collisions leading toπ+/π andπ+/π0 ratios of ∼3 and 1·6 respectively for high momentum pions can be explained on the basis of the isobar model. Further, the fast increase of K+/K ratio as the kaon momentum increases, the high ratio (∼4) ofΣ+/Σ in 24 GeV/cp−p collisions and the existence of a strong positive (negative) excess amongΣ-hyperons produced inπ+p(πp) collisions at various primary energies result, in a natural way, from such a model. The agreement results mainly from the restriction of only two bodies in the final states and does not critically depend on the isospins of produced isobars.

The distribution of transverse momentum of pions produced in 24 GeV/cp−p collisions can be represented by the form$$N(p_t )dp_s = \frac{{p_1 }}{{po^2 }}\exp .\left( { - \frac{{p_t }}{{po}}} \right)dp_t$$ withp0=170 MeV/c. The mean value is 340 MeV/c and is independent of multiplicity of collision.

The meanpt of pions is a function of laboratory emission angle. It is low (230 MeV/c) for angles &lt;5°, is more or less a constant (350 MeV/c), between 10° and 30,° and decreases for larger angles.

The mean transverse momentum of protons is around 370 MeV/c. There is a trend for the meanpt to increase with prong number for a certain class of events.

Unlike the meanpt of pions, the meanpt of protons is independent of primary energy (4–24 GeV) both inp−N andπ−N collisions.

The observed features of transverse momentum of pions and protons are consistent with the secondaries being dominantly the decay products of isobars. Further, they indicate a preference for the isobars to decay in cascade rather than through pion resonances.

• γ-rays from discrete radio sources

The fluxes of low energy (∼100 MeV) and high energy (∼5×1012 eV)γ-rays from intense radio sources have been calculated under the hypothesis that radio electrons are continuously produced through nuclear collisions. The effect of expansion of the source which gives rise to a decrease in production rate with time has been taken into account in these calculations. It is found that the fluxes expected from nuclear collision process are generally higher than the fluxes from other processes like bremstrahlung and inverse compton scattering by factors of 10 or more. While the calculated fluxes ofγ-rays of energy &gt;100 MeV are less than the observed upper limits for all the processes, the fluxes calculated for nuclear collision process for E&gt;5×1012 eV, exceed the experimental upper limits for Crab, Cas A and the jet in Virgo A. More sensitive experiments should be able to decide whether the nuclear collision process is ruled out for low energies as well: in this respect Cas A seems to be the most promising source.

• Transient gamma-ray sources

Gamma-ray production by particles escaping from a pulsar into the surrounding nebula is considered. The gamma-ray emission decreases with time and such pulsar-nebula complexes will be observed as transient sources.

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