Search results for "Muon"
showing 10 items of 1376 documents
Quantum critical point in the itinerant ferromagnet Ni$_{1-x}$Rh$_x$
2020
We report a chemical substitution-induced ferromagnetic quantum critical point in polycrystalline Ni$_{1-x}$Rh$_x$ alloys. Through magnetization and muon spin relaxation measurements, we show that the ferromagnetic ordering temperature is suppressed continuously to zero at $x_{crit} = 0.375$ while the magnetic volume fraction remains 100% up to $x_{crit}$, pointing to a second order transition. Non-Fermi liquid behavior is observed close to $x_{crit}$, where the electronic specific heat $C_{el}/T$ diverges logarithmically, while immediately above $x_{crit}$ the volume thermal expansion coefficient $\alpha_{V}/T$ and the Gr\"uneisen ratio $\Gamma = \alpha_{V}/C_{el}$ both diverge logarithmic…
Testing WWγ vertex in radiative muon decay
2019
Large numbers of muons will be produced at facilities developed to probe the lepton-flavor-violating process μ→eγ. We show that by constructing a suitable asymmetry, radiative muon decay μ→eγνμν̄e can also be used to test the WWγ vertex at such facilities. The process has two missing neutrinos in the final state, and upon integrating their momenta the partial differential decay rate shows no radiation-amplitude zero. However, we establish that an easily separable part of the normalized differential decay rate that is odd under the exchange of photon and electron energies does have a zero in the case of the standard model (SM). This new type of zero has hitherto not been studied in the liter…
A numerical method to calculate the muon relaxation function in the presence of diffusion
2014
We present an accurate and efficient method to calculate the effect of random fluctuations of the local field at the muon, for instance in the case muon diffusion, within the framework of the strong collision approximation. The method is based on a reformulation of the Markovian process over a discretized time base, leading to a summation equation for the muon polarization function which is solved by discrete Fourier transform. The latter is formally analogous, though not identical, to the integral equation of the original continuous-time model, solved by Laplace transform. With real-case parameter values, the solution of the discrete-time strong collision model is found to approximate the …
A measurement of the tau lifetime
1993
The tau lepton lifetime is measured using four different methods with the DELPHI detector. Three measurements using one prong decays are combined, accounting for correlations, resulting in tau(tau) = 298 +/- 7 (stat.) +/- 4 (syst.) fs while the decay length distribution of three prong decays gives tau(tau) = 298 +/- 13 (stat.) +/- 5 (syst.) fs. The combined result is tau(tau) = 298 +/- 7 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay is found to be 0.985 +/- 0.013, compatible with lepton universality.
Footprints of a left-right symmetric model in a muon collider
2000
Abstract The double charged Higgs bosons, Δ ±± , are one of the benchmarks of left-right symmetric models. We discuss their production and demonstrate that even for small values of the Δ ++ l − l − coupling, they would produce observable signals at muon colliders.
An extension of two-Higgs-doublet model and the excesses of 750 GeV diphoton, muon g-2 and h → μτ
2016
In this paper we simultaneously explain the excesses of the 750 GeV diphoton, muon g-2 and $h\to \mu\tau$ in an extension of the two-Higgs-doublet model (2HDM) with additional vector-like fermions and a CP-odd scalar singlet ($P$) which is identified as the 750 GeV resonance. This 750 GeV resonance has a mixing with the CP-odd scalar ($A$) in 2HDM, which leads to a coupling between $P$ and the SM particles as well as a coupling between $A$ and the vector-like fermions. Such a mixing and couplings are strongly constrained by $\tau\to\mu\gamma$, muon g-2 and the 750 GeV diphoton data. We scan over the parameter space and find that such an extension can simultaneously account for the observed …
The spin-dependent structure function g1(x) of the deuteron from polarized deep-inelastic muon scattering
1997
We present a new measurement of the spin-dependent structure function $g_{1}^{\rm d}$ of the deuteron from deep inelastic scattering of 190 GeV polarized muons on polarized deuterons. The results are combined with our previous measurements of $g_{1}^{\rm d}$. A perturbative QCD evolution in next-to-leading order is used to compute $g_{1}^{\rm d}(x)$ at a constant $Q^{2}$. At $Q^{2} = 10$ GeV$^{2}$, we obtain a first moment $\Gamma_{1}^{\rm d} = \int_{0}^{1} g_{1}^{\rm d}{\rm d}x = 0.041 \pm 0.008$, a flavour-singlet axial charge of the nucleon $a_{0} = 0.30 \pm 0.08$, and an axial charge of the strange quark $a_{s} = -0.09 \pm 0.03$. Using our earlier determination of $\Gamma_{1}^{\rm p}$, …
Restrictions for asymmetry and polarizations of recoil in muon capture
1975
Abstract Using the helicity formalism, we discuss muon capture by targets of spin-zero. Owing to the definite neutrino helicity, three independent observables define a complete experiment. The precise relation between asymmetry α and longitudinal polarization P L of recoil, α = 1 + 2 jP L , comes only from rotational invariance. When time-reversal invariance is inserted, there is an additional restriction between the average polarization P av and the longitudinal polarization P L . On the basis of the experimental result P av = 0.43 ± 0.10 for 12 C, we predict P L = −(0.99 +0.01 −0.04 .
Comparative analysis of muon-capture and 0νββ -decay matrix elements
2020
Average matrix elements of ordinary muon capture (OMC) to the intermediate nuclei of neutrinoless double beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decays of current experimental interest are computed and compared with the corresponding energy and multipole decompositions of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay nuclear matrix elements (NMEs). The present OMC computations are performed using the Morita-Fujii formalism by extending the original formalism beyond the leading order. The $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ NMEs include the appropriate short-range correlations, nuclear form factors, and higher-order nucleonic weak cu…
Search at the Mainz Microtron for light massive gauge bosons relevant for the muon g-2 anomaly.
2014
A massive, but light, Abelian U(1) gauge boson is a well-motivated possible signature of physics beyond the standard model of particle physics. In this Letter, the search for the signal of such a U(1) gauge boson in electron-positron pair production at the spectrometer setup of the A1 Collaboration at the Mainz Microtron is described. Exclusion limits in the mass range of 40 MeV/c^{2} to 300 MeV/c^{2}, with a sensitivity in the squared mixing parameter of as little as ε^{2}=8×10^{-7} are presented. A large fraction of the parameter space has been excluded where the discrepancy of the measured anomalous magnetic moment of the muon with theory might be explained by an additional U(1) gauge …