No Arabic abstract
This paper gives a brief overview of the present and expected future limits on physics beyond the Standard Model (SM) from neutron beta decay, which is described by two parameters only within the SM. Since more than two observables are accessible, the problem is over-determined. Thus, precise measurements of correlations in neutron decay can be used to study the SM as well to search for evidence of possible extensions to it. Of particular interest in this context are the search for right-handed currents or for scalar and tensor interactions. Precision measurements of neutron decay observables address important open questions of particle physics and cosmology, and are generally complementary to direct searches for new physics beyond the SM in high-energy physics. Free neutron decay is therefore a very active field, with a number of new measurements underway worldwide. We present the impact of recent developments.
We investigate several Pb$(n,ngamma$) and Ge$(n,ngamma$) reactions. We measure $gamma$-ray production from Pb$(n,ngamma$) reactions that can be a significant background for double-beta decay experiments which use lead as a massive inner shield. Particularly worrisome for Ge-based double-beta decay experiments are the 2041-keV and 3062-keV $gamma$ rays produced via Pb$(n,ngamma$). The former is very close to the ^{76}Ge double-beta decay endpoint energy and the latter has a double escape peak energy near the endpoint. Excitation $gamma$-ray lines from Ge$(n,ngamma$) reactions are also observed. We consider the contribution of such backgrounds and their impact on the sensitivity of next-generation searches for neutrinoless double-beta decay using enriched germanium detectors.
This White Paper describes recent progress and future opportunities in the area of fundamental symmetries and neutrinos.
Simple dynamics, few available decay channels, and extremely well controlled radiative and loop corrections, make pion and muon decays a sensitive means for testing the underlying symmetries, the universality of weak fermion couplings, as well as for study of pion structure and chiral dynamics. We review the current state of experimental study of the allowed rare decays of charged pions: (a) electronic, $pi^+ to e^+ u_e$, or $pi_{e2}$, (b) radiative, $pi^+ to e^+ u_egamma$, or $pi_{e2gamma}$, and (c) semileptonic, $pi^+to pi^0 e^+ u$, or $pi_{e3}$, as well as muon radiative decay, $mu^+to e^+ u_{text{e}}bar{ u}_{mu}gamma$. Taken together, these data present an internally consistent picture that also agrees well with Standard Model (SM) predictions. However, even following the great strides of the recent decades, experimental accuracy is lagging far behind that of the theoretical description for all above processes. We review the implications of the present state of knowledge and prospects for further improvement in the near term.
We study the sensitivity of future low energy neutrino experiments to extra neutral gauge bosons, leptoquarks and R-parity breaking interactions. We focus on future proposals to measure coherent neutrino-nuclei scattering and neutrino-electron elastic scattering. We introduce a new comparative analysis between these experiments and show that in different types of new physics it is possible to obtain competitive bounds to those of present and future collider experiments. For the cases of leptoquarks and R-parity breaking interactions we found that the expected sensitivity for most of the future low energy experimental setups is better than the current constraints.
Selected topics on precision tests of the Standard Model of the Electroweak and the Strong Interaction at the LEP $e^+e^-$ collider are presented, including an update of the world summary of measurements of $alpha_s$, representing the state of knowledge of summer 1999. This write-up of lecture notes consists of a reproduction of slides, pictures and tables, supplemented by a short descriptive text and a list of relevant references.