Use Of Angular Distributions Research Articles

Probing a dark photon using rare leptonic kaon and pion decays

Rare leptonic kaon and pion decays K+(π+)→μ+νμe+e− can be used to probe a dark photon of mass O(10) MeV, with the background coming from the mediation of a virtual photon. This is most relevant for the 16.7-MeV dark photon proposed to explain a 6.8σ anomaly recently observed in 8Be transitions by the Atomki Collaboration. We evaluate the reach of future experiments for the dark photon with vectorial couplings to the standard model fermions except for the neutrinos, and show that a great portion of the preferred 16.7-MeV dark photon parameter space can be decisively probed. We also show the use of angular distributions to further distinguish the signal from the background.

Probing chromomagnetic and chromoelectric couplings of the top quark using its polarization in pair production at hadron colliders

The Tevatron, where the top quark was discovered, and the currently functional Large Hadron Collider (LHC), with copiously produced top pairs, enable a detailed study of top-quark properties. In particular, they can be used to test the couplings of the top quark to gauge bosons. Several extensions of the standard model (SM) can give rise to anomalous couplings of the top quark to gauge bosons, in particular, the gluons. In this work we examine how top-quark polarization, which is predicted to be negligibly small in the SM, can be used to measure chromomagnetic and chromoelectric couplings of the top quark to gluons. We lay special emphasis on the use of angular distributions and asymmetries of charged leptons arising from top decay as measures of top polarization and hence of these anomalous couplings. Sensitivities that may be reached at the Tevatron and the LHC are obtained.

Reaction dynamics and nuclear structure studies via deep inelastic collisions with heavy-ions: spin and parity assignment in 49Ca

The population and gamma decay of neutron rich nuclei around 48Ca has been measured at Legnaro National Laboratory with the PRISMA-CLARA setup, using deep-inelastic collisions (DIC) on 64Ni, at an energy approximately twice the Coulomb barrier. The reaction properties of the main products are investigated, focusing on total cross sections and angular distributions both integrated in energy and associated to the population of specific excited states. Gamma spectroscopy studies are also performed, giving evidence, for the first time in transfer reactions with heavy ions, of a large spin alignment (~70%), perpendicular to the reaction plane. This makes possible the use of angular distributions and polarization measurements to firmly establish the spin and parity of excited states populated in nucleon transfer channels, as in the case of 49Ca, where candidates for particle-core coupling are investigated. Both reaction and gamma spectroscopy studies demonstrate the relevance of DIC with heavy ions for a detailed investigation of moderately neutron rich systems.

Scattering from long prisms computed using ray tracing combined with diffraction on facets

A new model suitable for rapid computation of scattering on faceted dielectric objects such as ice crystals is presented. It combines ray tracing with diffraction on flat facets. The model allows retaining the ray nature of the internal field by calculating the diffraction component using an approximation for the far field direction of the Poynting vector. While this approach is similar to methods using the uncertainty principle, it does not require the use of angular distributions of diffracted rays, which leads to negligible computational overheads with respect to pure ray tracing. Results showing angle-dependent scattering computed for long hexagonal prisms, including phase functions and degree of linear polarization, are presented and compared with other models and with measurements on hexagonal fibers.

Interpretation of ion-range recoil data obtained from activated-foil measurements of nuclear excitation functions.

Ion-range recoil data were obtained during activated-foil measurements of excitation functions for proton-, deuteron-, and triton-induced reactions on selected targets. These data were analyzed by using the Lindhard, Scharf, and Schiott range-energy theory. An important feature of our analysis was the use of angular distributions from the recent Kalbach systematics based on multistep compound and multistep direct reactions. Furthermore, we used the ({ital p},{ital n}) data to fix the parameters of LSS theory, and then applied the theory to ({ital d},{ital n}), ({ital d},2{ital n}), ({ital t},2{ital n}), ({ital t},{alpha}) and ({ital d},{alpha}) reactions. The adjustments to the LSS-theory parameters were less than 10%. The comparisons of the data with calculations demonstrate several important aspects of the reaction mechanisms, e.g., transition from equilibrium to direct reaction, breakup of the deuteron and triton in the reaction entrance channel, and pickup for triton-induced reactions. Overall, the ion-range measurements give a consistent picture of the reaction mechanisms involved.

The sensitivity of Cerenkov radiation pulses to the longitudinal development of cosmic-ray showers

Monte-Carlo simulation of electron-photon cascades in the atmosphere have been used to calculate fluxes and time distributions of Cerenkov radiation from air showers. Results are presented which allow the longitudinal development of cosmic-ray showers to be mapped from the time structure of Cerenkov pulses (assuming perfect instrumental time resolution) without further recourse to hadron interaction models. Mapping of the development becomes unreliable using pulses observed much within 170-200 m of the axis (depending on zenith angle). The use of angular distributions given in a preceding paper (ibid., vol.8, p.1461, 1982) proved to be a satisfactory substitute for detailed Monte-Carlo cascade simulations for calculating Cerenkov signals. A sharp shoulder is expected to develop in the lateral distribution of the light in small showers; this should be allowed for in analysing observations.

Use of angular distributions of scattered ?-radiation intensity to calculate composite shields

Use of angular distributions of scattered ?-radiation intensity to calculate composite shields

Stripping and pick-up reactions — Experimental

Synopsis Recent advances in the techniques for measuring angular distributions of protons and neutrons from deuteron stripping reactions are described. These involve magnetic analysis in the case of protons and the use of scintillation counters for neutrons. Little work has so far been done on pick-up reactions. The use of angular distributions for the assignment of spins and parities to resultant nuclear states requires a certain amount of care and experience; the nuclear radius is to some extent an adjustable parameter to be used with caution. Relative values of the stripping cross section for different levels of the same nucleus often provide useful hints regarding the structure of the levels. Direct comparison of reduced widths of corresponding states of mirror nuclei have shown fair agreement. A considerable amount of experimental work is being done in an effort to throw some light on the mechanism of the stripping process. Measurements of excitation functions sometimes show resonances which are more prominent at the stripping peak than at large angles, indicating interference between stripping and some other process. Further useful information is being obtained from measurements of ( d , pγ) angular correlations and of the polarisation of the protons.