Interaction of Muons with H2/H3-Centres in Diamond

We report on transverse field muon spin rotation measurements on a nitrogen-rich type Ia diamond, both before and after the conversion of some of the aggregated nitrogen centres to nitrogen-vacancy complexes known as H2/H3-centres. The prompt fractions f and the spin relaxation rates λ were determined for the diamagnetic (μ_d) and the paramagnetic (Mu_T) states in the temperature range 10–300 K. The production of the nitrogen-vacancy complexes had little effect on the parameters of the Mu_T state for which f and λ remained unchanged at approximately 30% and 4 μs⁻¹, respectively. For the μ_d state, on the other hand, the formation of the H2/H3-centres resulted in an increase of the prompt fraction from 10(2)% to 20(3)%, and (for the first time) the spin relaxation rate showed a non-zero value of 0.020(3) μs⁻¹. These results show evidence of strong μ_d interactions with the nitrogen-vacancy complexes in diamond, and suggest a more complex structure for this state than a bare μ⁺. This revised version was published online in September 2006 with corrections to the Cover Date.     

Influence of ion-molecular reactions on μ-capture in hydrogen and on fusion in 3Hedμ muonic molecule

The de-excitation processes (J=1)→ (J=0) in muonic molecular ions (ppμ)⁺ and (³Hedμ)⁺ are studied. It is shown that the rate of such transitions substantially depends on the chain of ion-molecular reactions initiated by positively charged muonic ions. The probabilities of ortho-para transition in the [(ppμ)⁺H₂] and [(ppμ)⁺e] complexes formed as a result of chemical reactions in the pure hydrogen were estimated. Taking into account the ion-molecular processes in D₂ + He mixtures, the evaluation of the observed rate λ_f of nuclear fusion in the ³Hedμ muonic molecules was performed. The expected yield of fusion reactions per muon at the mixture density φ=0.1 and concentration C _He =0.05 was obtained to be equal to . This revised version was published online in August 2006 with corrections to the Cover Date.     

The theory of neutron scattering from mixed harmonic solids

In the intermediate valent cerium alloys Ce_1–xY_xPd₃, Ce(Pd_1–xRh_x)₃ and Ce(Pd_1–xAg_x)₃ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2KT300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range E _4f (=width of the Ce 4f states). This supposition allows a determination of E _4f from the H(T)-data. For CePd₃:Gd³⁺ we find E _4f=(650±100) K. E _4f increases with Y- and Rh-concentration and decreases with Ag-concentration.     

Charge Carrier Dynamics in Zn-Doped Cuprates

We have measured the static magnetic susceptibility, the resistivity and muon spin relaxation (⁺SR) spectra of Zn and Sr doped La₂CuO₂. Our data show that non-magnetic Zn impurities lead to an increase of the Néel temperature T _N in weakly hole doped compounds. This increase of T _N correlates with an increase of the resistivity. The analysis of our data strongly suggests that the hole mobility is the most important source for the strong suppression of long range antiferromagnetic order in La_2–x Sr _x CuO₄.     

Endomorphisms of the Separated Product of Lattices

To describe the evolution of separated entities remaining separated, we proposeto study endomorphisms (join-preserving maps, sending atoms to atoms) of theseparated product of cao lattices (complete, atomistic orthocomplementedlattices). Morphisms have been used successfully to describe the evolution ofentities, and the separated product is a model for the property lattice of separatedsystems; its set of atoms is the Cartesian product of each atom space. Let L bethe separated product of two cao lattices having the covering property and f anendomorphism of L. We prove that the center F(L) of L is the power set of₁ × ₂ where _i is the atom space ofF(L _i ) (Theorem 1), f preserves irreduciblecomponents (Theorem 2), and if L is irreducible there exist two endomorphismsf ¹ and f ² and a permutation such that the restriction of f to atoms is given byf(p ₁, p ₂) = (f ¹(p ₍₁₎), f ²(p ₍₂₎))(Theorem 3). For generalizations of these resultsto separated products of families of cao lattices, we develop new general argumentsinvolving a topology we define on the set of atoms of a cao lattice.     

Magnetic properties of UN studied by μSR

In the paramagnetic range (T>T _N=53 K) fluctuations of the moments on uranium are too fast to produce a sizeable damping of the SR signal even close toT _N. This rules out the formation of a magnetic precursor state as seen in UAs. In the antiferromagnetic regime all contributions to the field at the muon site cancel due to symmetry. Comparison with analogous data on other uranium mono-pnictides show that the magnitude of the field distribution width in the type I-single k antiferromagnetic state is not an intrinsic property of these materials.Work supported by the German Federal Minister for Research andTechnology (BMFT) under contract number 03-KA2-TUM-4.     

Elementary muon, pion, and kaon particles as resonators for neutrino quanta. Calculations of mass ratios for e, μ, π0, π±, K 0, K ±, and ν e

Masses of a number of elementary particles are calculated on the basis of the model suggested in [1] with the use of one parameter. In this model, an electron is considered as an electric cloud enclosed inside an elastic lepton shell, electron neutrino ν _е is considered as an elastic lepton shell contracted to a minimal size, and muon, pion and kaon are considered as resonators for quanta of virtual neutrinos excited inside the elastic lepton shell. The number and type of these quanta are determined from the decay scheme for μ, π, and K: 2 for the muon (ν _е and ), 3 for the pion (ν _е , ν _μ, and ), and at least 21 for the kaon. The model allows mass ratios approximating the experimental data for these particles to be obtained for the first time, with the ratio of μ and е masses equal to (6πℏс/е ²)^2/3 ≅ 188, the ratio of π ⁰ and μ masses equal to (3/2)^2/3, and the ratio of K ⁰ and π ⁰ equal masses to 7^2/3. The calculated e, μ , π ⁰, and K ⁰ masses are in the 0.547:105.707:134.963:493.87 (MeV) ratios (normalized by the neutral pion mass). This is in good agreement with the available experimental data. The mass ν _е (≅ 0.02 eV) is also estimated in this model, and the variety of K-meson decay schemes is naturally explained as a result of the variety of excited intrinsic neutrino field structures with the same energy. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 23–29, January, 2009.     

μ+SR Study of Ordering Phenomena in the Heavy-Fermion State of Ce3Pd20Ge6

Magnetic and quadrupolar ordering phenomena in a Ce₃Pd₂₀Ge₆ single crystal have been investigated by muon spin rotation/relaxation (μ⁺SR) spectroscopy. We have observed spontaneous precession of muons in zero-field below T _N =0.7 K in the antiferromagnetic state. The precession frequency follows the power law: ν(T)=ν(0)(1−T/T _N ) ⁿ . The exponent n=0.43(2) is close to the mean-field value of 0.5. The muon longitudinal spin relaxation rate 1/T ₁ is found to be nearly independent of temperature in the range of 0.3 to 2 K, i.e., across either T _N or T _Q =1.2 K, the quadrupolar ordering temperature. Two likely mechanisms for the temperature independent behavior of 1/T ₁ are suggested. This revised version was published online in September 2006 with corrections to the Cover Date.     

Observation of quasi-static spin dynamics in the giant anisotropic ferromagnet PrRu2Si2 by μSR spectroscopy

We report zero field and longitudinal fieldSR measurements on single crystals of the ferromagnet PrRu₂Si₂ (T _c15K). BetweenT=T _c and 250K we observe a quasi-static spin dynamics of the Pr³⁺ ion sub-lattice. BelowT _c, depending on the orientation of the initial muon beam polarisation relative to thec axis of the compound, we find either an oscillating signal or an exponential depolarisation function. These latter data allow us to get information related to the muon in PrRu₂Si₂.     

Detailed investigation of the “DIP” structure in the μ+-relaxation rate in Nb

The depolarization rate of positive muons implanted in a number of nominally pure, cylindrical Nb single crystals (maximal 250 ppm Ta, 100 ppm N + O) was investigated at two temperatures, viz. 14.0 and 36.8 K, in a high transverse field of 7.5 kG with the stroboscopicSR technique in order to study the nature of the dip at 22 K. To determine the sites at which the muon is trapped on both sides of this dip, the full angular dependence of the depolarization rate was measured by rotating a large single crystal around its 110 cylinder axis in a transverse magnetic field. The resulting curves for both temperatures are quite different, reflecting clearly the different environment in which the muon is trapped above and below 22 K. The trapping site at 36.8 K was identified to be of tetrahedral symmetry, located near a Ta substitutional impurity and possibly associated with an interstitial impurity. Lattice distortions due to these impurities and radial relaxation around the muon,R/R, were determined. The latter is +6.7(6)% for nearest neighbors and –6(2)% for next nearest neighbors. The 14.0 K angular dependence could not be fitted by considering distorted tetrahedral and octahedral sites and pointlike muons.     

Search for Higgs Boson in UHE Cosmic Rays

Considering the SM Higgs boson mass in the range of (95–235) GeV, we present here a mechanism for indirect searches of this scalar in UHE cosmic rays interactions. The mechanism is the decay of Higgs bosons which are produced through bubble formation due to vacuum excitation in an UHE cosmic rays interactions with air nuclei. We develop a model of hadronic interaction based on algorithms of the GENCL code of the UA5 experiment of CERN and some physics of CORSIKA code (Karlsruhe report), incorporating a fraction of energy transfer to bubble formation through vacuum excitation and subsequent multiparticle production via conversion of Higgs boson to heavy fermion pairs. Such events are expected to have high multiplicity and excess muons. This mechanism has significant effect starting from E _P 10¹⁸eV. It is found that the average muon number decreases gradually upto 175 GeV Higgs boson mass and remain practically constant thereafter for all primary energies (E _P) above 10¹⁸ eV and for all fractions of energy transfer (f _e 0.01–0.5). The fluctuation of muon multiplicity decreases with E _P and increases very slowly with Higgs mass upto 175 GeV, remaining practically invariant thereafter.     

Delayed muon induced fission of209Bi and the role of meson-exchange currents

The probability for delayed muon induced fission of²⁰⁹Bi has been determined from a ( ^–,f ₁ f ₂) measurement. The measured fission probability P _f =(4.2±0.7)×10^–5 is compared with theoretical predictions. The high fission threshold reaction seems well suited for studying the influence of two-body meson-exchange currents in nuclear muon capture.We are indebted to the following institutes or organizations for financial support: Bundesministerium für Forschung und Technologie der Bundesrepublik Deutschland contract number 06 BN 271 (HP, PD, HH, FR, CR), Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization of the Advancement of Pure Research (NWO) (JK, CTAMdL, WL, AT) and the Schweizer Nationalfonds (LS).     

On muon localization in doped aluminium samples

The magnetic field dependence of the transverseSR linewidth has been studied in anAlAg single crystal. The muon site is found to be tetrahedral at 22 K and octahedral at 0.05 K. Both the site change and the magnitudes of the electric field gradients are similar to previous observations onAlMn, although these two impurities create different strain fields in Al.     

Positive muons in [Co(NH3)6]Cl3 and [Co(ND3)6]Cl3

We have carried out SR experiments on [Co(NH₃)₆]Cl₃ and [Co(ND₃)₆]Cl₃. At 293 K, all the muons implanted into the complexes were in the diamagnetic state. The observed Gaussian-type muon spin relaxation function proved that the internal magnetic field was caused by nuclear dipole moments of the atoms in the complexes. In addition, another exponential-type muon spin relaxation function was observed in [Co(ND₃)₆]Cl₃ below 50 K.     

Production rate and decay lifetime measurements ofBs0 mesons at LEP usingDs and? mesons

The study of the properties of inclusive production ofD _s mesons and of events in which a and a muon are present in the same jet provides two independent measurements of the probability,f _s ^w , for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ ⁰ decays. The combined value of these measurements isf _s ^w =0.19±0.06±0.08. From the flight distance distributions ofD _s and of (-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB _s ⁰ meson lifetime. Combining these measurements with a previous result based on the study ofD _s- events, theB _s ⁰ meson lifetime is measured to be: 0.96±0.37 ps.     

The positive muon as a tracer for the study of metal hydrogen systems

We present the first systematic study of dynamic muon H-correlations in a metal hydride (NbH _x ) over a large range of H concentrations. The following observations were made: (i) H loading shifts the motional narrowing range for muons in Nb from 60 K to above 170 K; (ii) in-NbH _x muon () and H correlation times are of the same order but the corresponding activation energies are distinctly different; (iii) the concentration dependence of ^–1 exhibits strong negative deviations from a (1-c) behavior; (iv) the H/D isotope effect in-NbH(D)_0.92 is distinctly non-classical; (v) the ordering of vacancies in the subhydrides suppresses long range muon motion. The experimental features are interpreted in the framework of tracer diffusion theory and bear clear evidence that repulsive muon-H interactions are an important feature of the dynamic muon hydrogen correlations.     

Two successive magnetic transitions in Y2Cu2O5 studied by μSR

Zero field muon spin rotation and magnetic susceptibility experiments on investigation of magnetic properties of cuprateY ₂Cu₂O₅ have been performed in the temperature range 4.2–30 K. Transverse fieldSR-experiments have been also carried out in order to obtain accurate information about transition temperature and to study the influence of the external magnetic field. Our data show that two magnetic phase transitions occur inY ₂Cu₂O₅ with lowering temperature. Upper Neel temperatureT _N=13 K is consistent with previous experimental data. We obtained the temperature dependence of the local magnetic field on the muonB (T) in the antiferromagnetic phase.B (T) reveals a peculiarity (some change of the slope) near the temperatureT _N=7.5 K, which can be interpreted as an additional magnetic phase transition caused by a change in magnetic ordering of the copper subsystem. Applying a small external magnetic field 50 Oe leads to smearing of the peculiarity inB (T) dependence.     

Quantum Hamiltonian for the Rigid Rotator

An excess term exists when using hermitian form of Cartesian momentum p _i (i = 1,2,3) in usual kinetic energy 1/(2) p ² _i for the rigid rotator, and the correct kinetic energy turns to be 1/(2) (1/f _i ) p _i f _i p _i where f _i are dummy factors in classical mechanics and nontrivial in quantum mechanics.     

Investigation of the Parameters of Muon-Catalyzed Fusion in Double D/T Mixture at High Temperature and Density

Experiments on the study of the muon catalyzed fusion (μCF) process in a double D/T mixture of hydrogen isotopes in the temperature range 300–800 K at densities 0.3–0.5 LHD are performed at the JINR phasotron. The values of the effective μCF parameters (cycling rate λ _c , neutron yield Y _n , muon losses w) are obtained. Tentative dtμ-molecule formation rates on D₂ and DT molecules (λ _dtμ−d and λ _dtμ−t ) are obtained for different mixture temperatures and densities. The results obtained show that λ _dtμ−t increases with temperature, but its value is smaller than theoretical predictions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Antiferromagnetic solid oxygen studied by positive muons

We present a zero magnetic field muon spin rotation study of-O₂ (antiferromagnetic phase of solid oxygen) in the temperature range of 10–24 K. Static magnetic order has been observed below the- transition temperatureB =23.8 K. The temperature dependence of the muon precession frequency exhibits behavior characteristic of a two-dimensional Heisenberg spin-1 system with the anisotropy parameter 10^–2 quite similar to that of antiferromagnetic phase of the high-temperature superconductor parent compounds. A unique local field at the muon site has been determined to beB ₀=1.27(5) kG at low temperatures.