Production Of Heavy Unstable Particles Research Articles

Chromo-and electrodynamics of heavy unstable particles

Abstract In this lecture I survey some selected physics issues on radiative interference phenomena in the production of heavy unstable particles. A special emphasis is placed on the reactions e+e−→ W+W−→ 4 jets and e+e− → tt → bW+bW−. A transparent recipe is given for quantifying the level of suppression of the interference effects in the inclusive production processes. The influence of the W width on the Coulomb corrections to the threshold W+W− production is briefly addressed.

Final state interaction in the production of heavy unstable particles

We make an attempt to discuss in detail the effects originating from the final state interaction in the processes involving the production of unstable elementary particles and their subsequent decay. Two complementary scenarios are considered: the single-resonance production and the production of two resonances. We argue that part of the corrections due to the final state interaction can be connected with the Coulomb phases of the charged particles involved; the presence of the unstable particle in the problem makes the Coulomb phase “visible”. It is shown how corrections due to the final state interaction disappear when one proceeds to the total cross sections. We derive one-loop non-factorizable radiative corrections to the lowest-order matrix element of both single- and double-resonance production. We discuss how the infrared limit of the theories with unstable particles is modified. In conclusion we briefly discuss our results in the context of the forthcoming experiments on the W + W − and the t t production at LEP2 and NLC.

Interference radiative phenomena in the production of heavy unstable particles.

We discuss the characteristic interference phenomena, including real as well as virtual radiative corrections, to the inclusive cross sections for production of heavy unstable systems such as $t\overline{t}$ or ${W}^{+}{W}^{\ensuremath{-}}$ pairs. We demonstrate explicitly the (fortunate) cancellation between emissions associated with the production of unstable particles and with their decays, and between emissions accompanying the decay stages. As a result the total interference effect is shown to be of $O(\frac{{\ensuremath{\alpha}}_{i}\ensuremath{\Gamma}}{M})$ or better (where ${\ensuremath{\alpha}}_{i}=\ensuremath{\alpha} or {\ensuremath{\alpha}}_{s}$ as appropriate).

Production of heavy unstable particles in extremely energetic nucleon-nucleon collisions

The problem of multiple production of heavy unstable particles is analyzed. Possible reaction schemes are established on the basis of Gell-Mann’s theory. In order to apply the Fermi-Landau thermodynamical model to the production of heavy unstable particles, their interaction with pions is investigated. Some characteristic quantities of the two-proton system are calculated by making use of the aforesaid model. The results seem not to contradict experimental results.

The production of heavy mesons and hyperons by π−-mesons of 4.5 GeV/c

A systematic investigation has been carried out, using nuclear photographic emulsions, into the production of heavy unstable particles by π−-mesons of 4.5 GeV/c. From 2854 stars, 4 hyperons and 4 heavy mesons were found which had velocities of less than 0.7c, and which satisfied certain geometrical selection criteria. One hyperon produces a secondary π-meson which comes to rest in the emulsion stack. The mass of this hyperon, shown to be negatively charged by the nuclear capture of its secondary particle, is (2352±5) mo.

Proton-Proton Interactions at 1.5 Bev

212 interactions of 2.75-Bev protons have been observed in a hydrogen-filled diffusion cloud chamber. The data indicate an elastic cross section of 15 millibarns, with about 9 millibarns cross section for single pion production, 13 millibarns for double, and 4 for triple. There is one example of quadruple pion production. One definite example of the production of heavy unstable particles was observed, and two doubtful cases. The median elastic scattering angle was 19\ifmmode^\circ\else\textdegree\fi{} in the c.m. system. Angle and momentum distributions for inelastic events are consistent with those observed at lower energies.

Proton-Proton Interactions at 2.75 Bev

212 interactions of 2.75-Bev protons have been observed in a hydrogen-filled diffusion cloud chamber. The data indicate an elastic cross section of 15 millibarns, with about 9 millibarns cross section for single pion production, 13 millibarns for double, and 4 for triple. There is one example of quadruple pion production. One definite example of the production of heavy unstable particles was observed, and two doubtful cases. The median elastic scattering angle was 19° in the c.m. system. Angle and momentum distributions for inelastic events are consistent with those observed at lower energies.

Production of aθ0Particle without an Associated Hyperon in aπ−−pCollision

An event is described that is interpreted as evidence for the simultaneous production of a ${\ensuremath{\theta}}^{0}$ and a ${\overline{\ensuremath{\theta}}}^{0}$ according to the scheme of Gell-Mann and Pais. This interpretation assumes the production of a normal ${\ensuremath{\theta}}^{0}$ and a ${K}^{0}$ with no associated hyperon, where the ${\ensuremath{\theta}}^{0}$ is observed and the ${K}^{0}$ is inferred from the rule of associated production of heavy unstable particles. The event was obtained by exposing a high-pressure diffusion cloud chamber to a 4.5-Bev/c ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson beam from the Bevatron. The event is most reasonably interpreted as ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+p+{\ensuremath{\theta}}^{0}+(\mathrm{neutral})$. Energy and momentum conservation are satisfied by an undetected neutral particle having a mass of ${502}_{\ensuremath{-}124}^{+91}$ Mev. This is consistent with the associated production of a ${\ensuremath{\theta}}^{0}$ and a ${\overline{\ensuremath{\theta}}}^{0}$ according to the scheme of Gell-Mann and Pais. Details are given and alternative interpretations are discussed.

Nuclear production of heavy unstable particles

Nuclear production of heavy unstable particles

Production of Heavy Unstable Particles in ap−pCollision

A hydrogen-filled diffusion cloud chamber was exposed to a 2.7-Bev proton beam. In a collection of 202 $p\ensuremath{-}p$ collisions, there was one event interpreted as the associated production of a hyperon and a $K$-meson, via the reaction $p+p\ensuremath{\rightarrow}{\ensuremath{\Lambda}}^{+}+{K}^{+}+n$.

On heavy unstable particles produced in high energy nuclear disintegrations

The results of a systematic investigation into the production of heavy unstable particles in energetic nuclear disintegrations is reported. Mass measurements by the grain density-range method have been made in order to detect K-mesons independently of any secondary effects. Measurements were made on tracks which satisfied certain geometrical criteria and which originated in disintegrations of energy greater than ∼2 GeV. The velocity range studied for K-mesons was from 0.25c to 0.56c. Ten K-mesons and two hyperons were found. The two hyperons and one of the K-mesons decayed in flight. All the particles decayed into single charged secondaries. Both hyperons were emitted from disintegrations which also produced K-mesons. These associated pairs have been reported previously (1). The results are consistent with the view that hyperons and heavy mesons are mainly produced in association, and that, in the energy range considered, K-mesons show a large charge disparity. Two additional hyperons were found one of which appears to be an example of the decay scheme Y± → Λ0 + π± + ∼60 MeV. A value for the lifetime of the hyperons is estimated from six suitable examples found in this laboratory. Mass measurements have been made on the tracks of 17 K-mesons. The mean value obtained is 985 ± 16 me.

Production of Heavy Unstable Particles by 1.37-Bev Pions

Production of Heavy Unstable Particles by 1.37-Bev Pions

XCV. Observations on the associated production of heavy mesons and hyperons

Abstract In a systematic search for K-mesons and hyperons produced in emulsions, two events have been found which appear to be due to the reaction π + N → Y + K, where N represents a bound nucleon. The evidence suggests that such reactions play an important role in the production of heavy unstable particles.

Production of Heavy Unstable Particles by Negative Pions

Production of Heavy Unstable Particles by Negative Pions