Search results for "The Standard Model"
showing 10 items of 466 documents
Meson decay studies from MAMI A2
2019
Decays of the light mesons π0, η, ω, and η’ provide a unique laboratory to test fundamental aspects of hadron physics. Precision studies of such diverse topics as the light quark mass ratio, π−π scattering lengths, and searches for physics beyond the Standard Model are possible. Additionally, Dalitz decays of light mesons provide a way of measuring the electromagnetic meson transition formfactors in the time-like region. The A2 tagged photon facility at the Mainz Microtron provides a high yield of light mesons produced by photo-induced reactions on protons, which makes the experiment ideal for high precision measurements of meson decays. Presented here are the contributions made by the A2 c…
Neutrinoless double β decay with small neutrino masses
2013
Proceedings of the Corfu Summer Institute 2012 "School and Workshops on Elementary Particle Physicsand Gravity", September 8-27, 2012, Corfu (Greece). PoS(Cofu2012)028.
Two-photon exchange correction to2S−2Psplitting in muonicHe3ions
2017
We calculate the two-photon exchange correction to the Lamb shift in muonic $^{3}\mathrm{He}$ ions within the dispersion relations framework. Part of the effort entailed making analytic fits to the electron-$^{3}\mathrm{He}$ quasielastic scattering data set, for purposes of doing the dispersion integrals. Our result is that the energy of the $2S$ state is shifted downwards by two-photon exchange effects by 15.14(49) meV, in good accord with the result obtained from a potential model and effective field theory calculation.
Search for the rare decayB→Kνν¯
2010
We present a search for the rare decays B+→K+νν and B0→K0νν using 459×106 BB pairs collected with the BABAR detector at the SLAC National Accelerator Laboratory. Flavor-changing neutral-current decays such as these are forbidden at tree level but can occur through one-loop diagrams in the standard model (SM), with possible contributions from new physics at the same order. The presence of two neutrinos in the final state makes identification of signal events challenging, so reconstruction in the semileptonic decay channels B→D(*)lν of the B meson recoiling from the signal B is used to suppress backgrounds. We set an upper limit at the 90% confidence level (CL) of 1.3×10-5 on the total branch…
Lepton Flavour Violation in SUSY SO(10)
2008
The study of rare processes, which are suppressed or even forbidden in the Standard Model (SM) of particle physics, has been considered for a long time a powerful tool in order to shed light on new physics, especially for testing low-energy supersymmetry (SUSY). Indeed, taking into account the fact that neutrinos have mass and mix, the Standard Model predicts Lepton Flavour Violating (LFV) processes in the charged sector to occur at a negligible rate [1]. As a consequence, the discovery of such processes would be an unambigous signal of physics beyond the Standard Model. In the present years, we are experiencing a great experimental effort in searching for LFV processes; several experiments…
Solar Neutrino Spectroscopy
2017
More than forty years after the first detection of neutrinos from the Sun, the spectroscopy of solar neutrinos has proven to be an on-going success story. The long-standing puzzle about the observed solar neutrino deficit has been resolved by the discovery of neutrino flavor oscillations. Today's experiments have been able to solidify the standard MSW-LMA oscillation scenario by performing precise measurements over the whole energy range of the solar neutrino spectrum. This article reviews the enabling experimental technologies: On the one hand mutli-kiloton-scale water Cherenkov detectors performing measurements in the high-energy regime of the spectrum, on the other end ultrapure liquid-s…
Sterile neutrinos with secret interactions—lasting friendship with cosmology
2015
Sterile neutrinos with mass ~1 eV and order 10% mixing with active neutrinos have been proposed as a solution to anomalies in neutrino oscillation data, but are tightly constrained by cosmological limits. It was recently shown that these constraints are avoided if sterile neutrinos couple to a new MeV-scale gauge boson A'. However, even this scenario is restricted by structure formation constraints when A'-mediated collisional processes lead to efficient active-to-sterile neutrino conversion after neutrinos have decoupled. In view of this, we reevaluate in this paper the viability of sterile neutrinos with such "secret" interactions. We carefully dissect their evolution in the early Univers…
Impact of New Physics on CP-Asymmetries at Long Baselines
2018
We study the impact of new physics on CP-asymmetries using different oscillation channels at long baseline experiments.
Updated pseudoscalar contributions to the hadronic light-by-light of the muon (g-2)
2016
In this work, we present our recent results on a new and alternative data-driven determination for the hadronic light-by-light pseudoscalar-pole contribution to the muon $(g-2)$. Our approach is based on Canterbury approximants, a rational approach to describe the required transition form factors, which provides a systematic and model-independent framework beyond traditional large-$N_c$ approaches. As a result, we obtain a competitive determination with errors according to future $(g-2)$ experiments including, for the first time, a well-defined systematic uncertainty.
Electroweak penguins in isospin-violating Bs decays
2011
¯Bs ! φ π 0 and ¯ Bs ! φ ρ 0 , which are dominated by EW penguins. Our results extend the analysis in [1] and have recently been published in [2]. Here we give a brief overview of the outcome. We show that in presence of a new EW penguin amplitude the two Bs branching ratios can be enhanced by an order of magnitude without violating any constraints from other hadronic B decays. This makes them very interesting modes for LHCb and Super B factories. We perform both a model-independent analysis and a study within realistic New Physics (NP) models such as a modified- Z 0 -penguin scenario, a model with an additional Z 0 boson and the MSSM, including a fit to B ! πK data and the relevant experim…