Local magnetic field at a positive muon in ferromagnetic gadolinium

The local magnetic field at a stopped positive muon has been measured in polycrystalline gadolinium as a function of temperature between 20 K and the Curie point. The measurements show that the muon occupies the octahedral interstitial site and demonstrate the sensitivity of the muon as a probe of the local magnetic structure.     

Muon Knight shift and μ+ site in the monopnictide CeAs

The transverse field μSR-signal from μ⁺ implanted in a CeAs single crystal shows a splitting into two components, displaying a positive and a negative Knight shift, respectively which both scale reasonably well with the magnetic bulk susceptibility above 10 K. The orientation dependence of the frequency shifts, measured at 15 K, is fully accounted for by the demagnetization field, implying an isotropic Knight shift, consistent with the μ⁺ residing at the only interstitial site of high (cubic) symmetry, i.e., at the position (1/4,1/4,1/4). The occurrence of a split signal remains unexplained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Alignment and measurement of the magnetic field for the BESIII muon counter

Based on cosmic ray events without a magnetic field taken with the BESIII detector during the summer shutdown of BEPCII in 2012 and di-muon events from a data sample taken at center-of-mass energy of 3.686 GeV in 2009, we compare the coordinates of hits registered in the BESIII muon counter with the expected interaction point extrapolated from reconstructed tracks from the inner tracking system in the absence of a magnetic field. By minimizing the difference, we align the muon counter with the inner tracking system. Moreover, the strength of the magnetic field in the muon counter is measured for the first time with di-muon events from data taken at a center-of-mass energy of 3.686 GeV. After the alignment and the magnetic field strength measurement, the offsets in the reconstructed hit positions for muon tracks are reduced, which improves the muon identification. The alignment and magnetic field strength measurement have been adopted in the latest version of the BESIII offline software system. This addition to the software reduces the systematic uncertainty for the physics analysis in cases where the muon counter information is used.     

Low temperature thermal—and magnetic properties of CeP and CeAs

CeP and CeAs are characterized by low temperature measurements of the specific heat, the thermal expansion, the electrical resistivity and the magnetization of single crystal specimens. These physical properties are found to be very sensitive to crystal perfection and chemical composition in both the paramagnetic and the magnetically ordered state. In the intrinsically antiferromagnetic CeP, imperfections can give rise to a remanent magnetization belowT _N .     

Off-mass-shell muon anomalous magnetic moment

Interaction of charged leptons with photons is considered for the case when one of the lepton legs is off the mass shell. The effect due to off-mass-shell shift in the anomalous magnetic moment is computed within one-loop approximation. Possible contributions of this effect in the muon g — 2 measurements are discussed.     

The muon magnetic moment and new physics

The impact of the muon magnetic moment measurement on physics beyond the Standard Model is briefly reviewed. Particular emphasis is given on the case of supersymmetry. The sensitivity of g ? 2 to supersymmetry parameters and the potential for model discrimination and parameter measurements is described. The interplay between LHC data on the Higgs boson, limits on new particles, and g ? 2 is discussed.     

Energy losses of a neutron star due to inverse muon decay in the superstrong magnetic field

The emission of a pair of neutrinos by a charged lepton under the influence of a strong magnetic field is examined. The expression found in general form for the probability of the process l l'vV in the strong magnetic field of a neutron star is used to evaluate the contribution of inverse muon decaye vV to the energy losses of the neutron star. The conditions under which this contribution to the energy losses of a neutron star may compete with that due to neutrino pair emission in the processe evV are discussed.Lomonosov State University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 39–44, July, 1995.     

Local hyperfine field vector of positive muon in mono-domain single crystal of antiferromagnetic La2CuO4

By using a monodomain single crystal La₂CuO₄ grown by the travelling solvent floating zone method, the strength and direction of the local hyperfine field vector at positive muon sites were determined. Combining with the ⁺ location determined separately, we found the importance of the local hyperfine field contributions with dipolar symmetry as well as the distant dipolar field from surrounding point dipoles of Cu atomic moments.     

Local magnetic moment and hyperfine field in hydrogenated iron and iron-vanadium alloy

The local magnetic moment and hyperfine fieldB _hf at Fe and V sites in hydrogenated iron and iron-vanadium were calculated using the discrete variational method. The variations in andB _hf with H occupation of the octahedral (O) site were considered. It was found that when H occupies the O site neighbouring an Fe atom, both local moment and hyperfine field at this atom decrease linearly with increasing number of H atoms. The rate of decrease is larger for Fe in iron as compared to iron in vanadium. On the other hand, when H resides at an O site next neighbouring an Fe atom, whether in iron metal or in iron-vanadium, the Fe magnetic moment increases slowly, while the hyperfine field remains almost constant. The V moment in iron, which is negative (–0.83 _B ), becomes less negative (–0.30 _B) as H occupies the neighboring O sites, whereas slight changes occur (–0.88 _B) when H is at the next neighbouring O site. The net effect of H on Fe in iron is to decrease the average magnetic moment at a rate of 1.2 _B per H/Fe for low H content. On the other hand, the average Fe moment in an iron-vanadium alloy increases if H resides at O sites which are immediate neigbours of V and next neighbours of Fe. This may explain the development of a magnetic state on hydrogenation of Fe-V alloys, which is exhibited by the specific heat and susceptibility measurements. The changes in the isomer shift were found to agree with experimental trends.     

Zero field muon spin depolarization revisited

We consider the zero field depolarization of stationary muons at various sites in fcc and bcc crystals. Significant derivations from the classic Kubo-Toyabe treatment are explained as due to violations of some fundamental assumptions underlying this theory.     

Inverse muon decay in a steady external field

A standard Weinberg-Salam model has been used to calculate the cross section of +e »v _e+ in steady crossed fields (EH=E ²–H ²=0). The asymptotic behavior of the cross section has been examined as a function of the kinematic and dynamic (field) invariant parameters.M. V. Lomonosov Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 106–111, December, 1992.     

Effect of zero point motion on the hyperfine field at an interstitial positive muon site in ferromagnetic Ni

Using the inhomogeneous electron charge and spin density distribution around the octahedral site in ferromagnetic nickel from a self-consistent band structure scheme, and the abiabatic approximation, we have calculated the muon hyperfine field as a function of the muon displacement. By folding the electron spin density at the vibrating muon site obtained in a self-consistent Kohn-Sham scheme with the finite width of the muon wave function, we find a striking effect on the average muon hyperfine field. The result agrees better with the experiment than earlier calculations based on the jellium model.     

Hyperfine field of positive muon in ferromagnetic nickel

The electronic structure around a positive muon μ⁺ at an octahedral interstitial site of a ferromagnetic nickel is calculated from first principles. The hyperfine field experienced by μ⁺ at absolute zero is calculated to be ?0.72 kG in satisfactory agreement with the experimental value of ?0.64 kG. The calculation also explains the temperature dependence of the hyperfine field. It is shown that the temperature dependence of the hyperfine field coupling constant A(T) is predominantly determined by single particle excitations.     

Hadronic contributions to the muon magnetic moment

Zeitschrift für Physik A Hadrons and nuclei - Using the recent experimental data on the pion form factor in the time-like region limits are placed on the 2π contribution to the muon...     

Pionic contribution to the muon magnetic moment

A procedure is developed to derive an optimal lower bounds for the pionic contribution to the muon magnetic moment from analyticity of the pion form factor F(t), its normalization F(0)=1 and from experimental information from both the processes e^?p → e^?π⁺n and e⁺e^? → π⁺π^?. It represents essentially the solution of a certain kind of optimization problem in Hilbert space. Numerical results are presented and compared to the recent data for the muon magnetic moment; we find a_μ(π⁺π^?) ? 42 × 10^?9.     

Absence of pressure-induced valence change in CeAs

The pressure-volume relationship for cerium monoarsenide has been determined up to a pressure of 32 GPa using energy dispersive X-ray diffraction. Contrary to expectations based on the behaviour of CeP, cerium arsenide does not show a pressure-induced valence change in this pressure range. Instead we find a structural transition from the NaCl-type to the CsCl-type structure, which exhibits a large hysteresis. Contrary to other results our value of the bulk modulus (B₀ = 69 ± 1 GPa) agrees well with the value expected from an Anderson-Nafe plot for CeAs with the Ce ion in the trivalent state.