Search results for "Standard Model"
showing 10 items of 1206 documents
Measurement of charge asymmetry in hadronic Z decays
1991
A significant charge asymmetry is observed in the hadronic Z decays with the ALEPH detector at LEP. The asymmetry expressed in terms of the difference in momentum weighted charges in the two event hemispheres is measured to be − = −0.0084±0.0015 (stat.) ±0.0004 (exp. sys.). In the framework of the standard model this can be interpreted as a measurement of the effective electroweak mixing angle, sin2Ow (Mz2=0.2300±0.0034 (stat.) ±0.0010 (exp. sys.) ±0.0038 (theor. sys.) or of the ratio of the vector to axual- vector coupling costants of the electron, gvegAe=+0.073±0.024.
Supersymmetric origin of a lowaJ/ψCPasymmetry
2001
We show that general minimal supersymmetric extensions of the standard model (MSSM) allow for a $\mathrm{CP}$ asymmetry in $\stackrel{\ensuremath{\rightarrow}}{B}J/\ensuremath{\psi}{K}_{S}$ well below the SM expectations with dominant supersymmetric contributions to ${\ensuremath{\varepsilon}}_{K}$ and ${\ensuremath{\varepsilon}}^{\ensuremath{'}}/\ensuremath{\varepsilon}.$ Indeed, we provide an explicit example of an MSSM with nonuniversal soft breaking terms fully consistent with the low results of this asymmetry recently announced by BaBar and Belle Collaborations.
New contributions to supersymmetric mechanism of neutrinoless double beta decay
1995
The neutrinoless double beta ($\znbb$) decay is analyzed within the Minimal Supersymmetric Standard Model with explicit R-parity violation (\rp MSSM). We have found new supersymmetric contributions to this process and give the complete set of relevant Feynman diagrams. Operators describing $0^+ \longrightarrow 0^+$ nuclear transitions induced by the supersymmetric interactions of the \rp MSSM are derived. These operators can be used for calculating the $\znbb$ decay rate applying any specific nuclear model wave functions.
Commissioning and performance of the Belle II pixel detector
2021
Belle-II DEPFET and PXD Collaboration: et al.
Isoltrap pins down masses of exotic nuclides
2005
The mass of radionuclides contribute to a variety of fundamental studies including tests of the weak interaction and the Standard Model. The limits of mass measurements of exotic nuclides have been extended considerably by the Penning-trap mass spectrometer ISOLTRAP at the ISOLDE facility at CERN. Recent ISOLTRAP measurements are summarized and current technical improvements are outlined.
Search for heavy neutrinos in K + → μ + ν μ decays
2017
The NA62 experiment recorded a large sample of K+→μ+νμ decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range 2×10−6 to 10−5 have been set on the squared mixing matrix element |Uμ4|2 between muon and heavy neutrino states, for heavy neutrino masses in the range 300–375 MeV/ c2 . The result extends the range of masses for which upper limits have been set on the value of |Uμ4|2 in previous production search experiments.
Tests of the Standard Model with Low-Energy Neutrino Beams
2007
We discuss the possibility of using future high--intensity low--energy neutrino beams for precision tests of the Standard Model. In particular we consider the determination of the electroweak mixing angle from elastic and quasi--elastic neutrino--nucleon scattering at a superbeam or $\beta$--beam.
Search for a neutral Higgs particle in the decay sequence $K^{0}_{L} \to \pi^{0}H^{0}$ and $H^{0} \to e^{+}e^{-}$
1990
Abstract We have searched for the sequence of decays K L 0 → π 0 H 0 and H 0 →e + e − at the CERN Super Proton Synchrotron (SPS), and have allowed for a non-zero H 0 lifetime. Three candidates have been seen, consistent with an expected background of 3.3. Limits on the branching ratio product in the range 10 −8 –10 −7 are presented as a function of the mass and lifetime of the H 0 . These can be used to restrict the neutral Higgs of the minimal standard model.
Sterile neutrino signals from supernovae
2007
We investigate the effects of a mixing of active and sterile neutrinos on the ratios of supernova electron neutrino flux ($F_e$) and antineutrino flux ($F_{\bar e}$) to the total flux of the other neutrino and antineutrino flavours ($F_a$). We assume that the heaviest (in the normal hierarchy) Standard Model neutrino $\nu_3$ mixes with a sterile neutrino resulting in a pair of mass eigenstates with a small mass gap. Using the density matrix formalism we solve numerically the the evolution of neutrino states in the envelope of a supernova and determine the flux ratios $F_e/F_a$ and $F_{\bar{e}}/F_a$ as a function of the active-sterile mixing angle and for the experimentally allowed range of …
Minimal models with light sterile neutrinos
2011
We study the constraints imposed by neutrino oscillation experiments on the minimal extensions of the Standard Model (SM) with $n_R$ gauge singlet fermions ("right-handed neutrinos"), that can account for neutrino masses. We consider the most general coupling to SM fields of the new fields, in particular those that break lepton number and we do not assume any a priori hierarchy in the mass parameters. We proceed to analyze these models starting from the lowest level of complexity, defined by the number of extra fermionic degrees of freedom. The simplest choice that has enough free parameters in principle (i.e. two mass differences and two angles) to explain the confirmed solar and atmospher…