Total rates of nuclear capture of negative muons in the isotopes 132Xe and 40Ar

The lifetimes of a negative muon in the isotopes ¹³²Xe and ⁴⁰Ar in the solid phase are measured. The lifetime of μ ⁻ in the 1s state of the isotope ¹³²Xe is τ(¹³²Xe)=101.7±1.7 ns, which corresponds to a total nuclear capture rate Λ_c(¹³²Xe)=9.4±0.2 μs⁻¹. The lifetime of μ ⁻ in the isotope ⁴⁰Ar, viz., τ (⁴⁰Ar)=568±6 ns, corresponding to a capture rate Λ_c(⁴⁰Ar)=1.31±0.01 μs⁻¹, is obtained to several times better accuracy as compared to previously published results. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 181–183 (10 February 1999)     

On the investigation of magnetic critical phenomena in ferromagnets by μSR and PAC

On the basis of current theoretical views on the critical phenomena in isotropic Heisenberg ferromagnets the power temperature behavior Λ=c(τ)λ₀τ^-w has been derived for the muon spin relaxation rate Λ as π-T _c ⁻¹ (T-T _c ) → 0⁺. It is shown that the crossover from an exchange critical regime to a dipolar one is accompanied not only with the change in the critical exponentw in the above law, but also with the reduction of the coefficientc(π). A comparison with the temperature behaviour of the inverse nuclear relaxation timet _R ⁻¹ measured in the PAC experiment is carried out.     

Bound states of the muon-antimuon system: Lifetimes and hyperfine splitting

We examine the properties of an atomic system consisting of a muon and antimuon. Expressions are derived for the probability of decay and the hyperfine splitting of the lower levels with allowance for the leading radiative corrections, which are of relative order α. The results for the lifetimes and the ground-state energy are τ(1³ S ₁)=1.7907(8)×10⁻¹² s, τ(1¹ S ₀)=0.59547(33)×10⁻¹² s, and E _hfs (1s)=4.23284(35)×10⁷ MHz. The relative probabilities for the various decay channels are calculated; in particular, for the 1 ³ S ₁ level it is found that Γ (μμ→eeγ)/Γ(μμ→ee)≈15%. Finally, possible applications are discussed. Zh. éksp. Teor. Fiz. 113, 409–431 (February 1998)     

Production of slow muonic hydrogen isotopes in vacuum

Muonic hydrogen isotopes (μ⁻ p, μ⁻ d, and μ⁻t) are simple quantum mechanical systems ideally suited for studies of numerous fundamental phenomena in electroweak and strong interactions as well as in applied areas such as muon chemistry or muon catalyzed fusion. Emission of muonic hydrogen isotopes into vacuum helps to overcome the limitations which are normally imposed on conventional investigations with gaseous and liquid targets. A proof of principle experiment for this new technique was performed at TRIUMF last year. Negative muons with 30 MeV/c momentum were stopped in a thin film of solid hydrogen and produced very low energy μ⁻d in vacuum. The distribution center of the normal velocity components of emitted μ⁻d atoms was measured to be ∼1 cm/μs. The yield of μ⁻d in vacuum is an increasing function of H₂ film thickness δ up to a value of δ≥1 mm.     

Strange hadron production in Σ-<Emphasis Type="Italic">A</Emphasis> interactions in the SELEX experiment

We report our observations on the resonance signals of masses of 1520, 1670, 1810 (1 820), and 2100 MeV c ⁻², produced inclusively in the reaction Σ⁻ + C(Cu) → p + K⁻ + X, and the signals of masses of 1020 and 1525 MeV c ⁻², produced inclusively in the reaction Σ⁻ + C(Cu) → K⁺ + K⁻ + X, with a 600-GeV c ⁻¹- momentum hyperon beam in the SELEX experiment at the Fermilab. The masses, widths, and branching ratios were measured. The resonance signal of mass of 1520 MeV c ⁻² correspond to the known Λ(1520) hyperon. The signals of masses of 1020 and 1525 MeV c ⁻² in the K⁺K⁻ system correspond to the φ⁰(1020)- and f ₂′(1525) mesons, respectively. The branching ratio of the resonance of mass of 1670 MeV c ⁻² relative to Λ(1520) is (24.92 ± 0.45 ± 0.48)%, while that of the resonance of mass of 1810 (or 1 820) MeV c ⁻² relative to Λ(1520) is (16.13 ± 0.38 ± 0.45)%. The branching ratio of the f ₂′(1525) resonance relative to φ⁰(1020) is (10.75 ± 0.25 ± 0.45)%. Data analysis was performed over 6 × 10⁷ trigger events registered by the SELEX setup on the FNAL Tevatron.     

Determination of very slow μ+ hop rates in Cu by LLF-μSRhop rates in Cu by LLF-μSR

Muon spin relaxation in low (weak) longitudinal magnetic field (LLF-μSR) provides a means of independently determining the static dipolar width Δ characterizing the μ⁺ lattice site and the correlation time τ_c for μ⁺ hopping, in a manner that is nearly model-independent for τ_c and especially accurate in the near-static limit (τ_c>τ_μ). The advantages of this method are illustrated by its application to muon hopping in Cu near the τ_c maximum around 50 K.     

Relaxation and shift of the precession frequency of the spin of a negative muon in n-type silicon

The residual polarization of negative muons in n-type silicon with impurity density (1.6±0.2) · 10¹³ cm⁻³ is investigated as a function of temperature in the range 10–300 K. The measurements are performed in an external magnetic field of 0.08 T oriented transversely to the spin of the muons. Relaxation of the muon spin and a shift of the precession frequency are observed at temperatures below 30 K. The relaxation rate at 30 K equals 0.25±0.08 μs⁻¹. The shift of the precession frequency at 20 K equals 7 · 10⁻³. Both the relaxation rate and the shift of the precession frequency increase as the temperature decreases. At temperatures below 30 K the relaxation rate is described well by the relation Λ=bT ^−q , where q=2.8±0.2. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 7, 539–543 (10 April 1996)     

Λ and K s 0 production in pC collisions at 10 GeV/c

The experimental data from the 2-m propane bubble chamber have been analyzed for pC → Λ(K _s ⁰ )X reactions at 10 GeV/c. The estimation of experimental inclusive cross sections for Λ and K _s ⁰ production in the p ¹²C collision is equal to σ_Λ = (13.3 ± 1.7) mb and σ _{K s} ⁰ = (4.6 ± 0.6) mb, respectively. The measured 〈Λ〉/〈π⁺〉 ratio from pC reaction is equal to (5.3 ± 0.8) × 10⁻², and it is approximately two times larger than the 〈Λ〉/〈π⁺〉 ratio simulated by the FRITIOF model and than that of experimental pp reactions at the same energy. The text was submitted by the authors in English.     

Isotope effect in nuclear capture of negative muons in xenon

The lifetime of negative muons in the ¹²⁹Xe 1_s state was measured. The muon capture rate in ¹²⁹Xe is compared with that in the ^{132, 136}Xe isotopes. The capture rate was found to depend on the mass number of the cited isotopes. The experimental results are compared with the results of calculations by the semiempirical Goulard-Primakoff formula.     

Progress in pion-decay channelling: Refractory bcc metals at high and low temperatures

By means of π⁺/μ⁺ channelling, positive pions (π⁺) implanted intoTa, Mo, andW are investigated up to high temperatures. A striking observation is that the channelling effect disappears in a rather narrow temperature interval centred at 0.26 (Ta) to 0.51 (W) of the melting temperature. From studies of π⁺ trapping by oxygen atoms inTa estimates for the low-temperature π⁺ diffusivity inTa [D _π(23K)=1.4·10^−10±0.3 m²s⁻¹,D _π(47K)=5.7·10^−10±0.3 m²s⁻¹] as well as for the binding enthalpy of π⁺ to 0 atoms (H _B=7·10⁻² eV) have been obtained. The diffusion data are in reasonable agreement with the theory of phonon-assisted tunnelling.     

The search for and study of the strange multibaryon states in systems with Λ-hyperon and Ks0 -meson in pA collision at momentum of 10 GeV/c

Exotic strange multibaryon states have been observed in the effective mass spectra of: Λπ^±, Λπ⁺π⁻, Λp, Λpp, Λπp, ΛΛ and ΛK _s ⁰, K _s ⁰ p, K _s ⁰π^± subsystems. The measured Λ/π⁺ ratio for average multiplicities from the pC reaction is equal to (5.3 ± 0.8) × 10⁻², and it is approximately two times larger than the Λ/π⁺ ratio simulated by the FRITIOF model and than that of experimental pp reactions at the same energy. The observed wellknown resonances Σ*⁺ (1385) and K*^± (892) from PDG are good tests of this method. The mean value of the mass for the Σ*⁻(1385) resonance is shifted to 1370 MeV/c ² and the width is two times larger than the same value from PDG. Such kind of behavior for the width and invariant mass of Σ*⁻ (1385) resonance is interpreted as an extensive contribution from stopped Ξ⁻ → Λπ⁻ and medium effect. There is enhancement of the production contribution for all observed hyperons. A few events were registered by hypothesis of light H ⁰ and heavy H ^{0, +} dihyperons. Dihyperons were observed by weak decay channels: (Σ⁻ p), (Λpπ⁻), (Λpπ⁰), and (K ⁻ pp). The text was submitted by the author in English.     

Measurement of the τ lepton mass at the KEDR detector

A precise τ lepton mass measurement performed at the VEPP-4M collider with the KEDR detector is reported. The mass value is evaluated from the τ⁺τ⁻ cross section behavior around the production threshold. The result based on 6.7 pb⁻¹ of data is m _τ = 1776.81 _−0.23 ^+0.25 ± 0.15 MeV. Using 0.8 pb⁻¹ of data collected at the ψ′ peak, we have also determined that Γ _ee B _ττ(ψ′) = 9.0 ± 2.6 eV. The text was submitted by the authors in English.     

A Measurement of the ψ′ to J/ψ production ratio in 920?GeV proton-nucleus interactions

Ratios of the ψ^′ over the J/ψ production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA storage ring. The ψ^′ and J/ψ states were reconstructed in both the μ⁺μ^- and the e⁺e^- decay modes. The measurements covered the kinematic range -0.35≤x_F≤0.1 with transverse momentum p_T≤4.5 GeV/c. The angular dependence of the ratio has been used to measure the difference of the ψ^′ and J/ψ polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is R_ψ′(μ)/R_ψ′(e)=1.00±0.08±0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B^′(μ)B(e))/(B(μ)B^′(e)), of ψ^′ and J/ψ in the two channels. The ψ^′ to J/ψ production ratio is almost constant in the covered x_F range and shows a slow increase with p_T.     

Properties of synchrotron radiation

Muon capture on hydrogen gives a unique possibility for a measurement of the pseudo-scalar form factor g _p (q _c ² = -0.88 m _μ ² ) of the nucleonic weak current, thus providing a sensitive test of the QCD chiral symmetry perturbation theory which predicts the value of this form factor with a precision of Δg _p /g _p ≃ 2%. For adequate comparison with theory, the muon capture rate Λ_c should be measured with a precision of ΔΛ_c/Λ_c ≤ 1%, that is an order of magnitude better than the precision of the present world data. We report on the project of an experiment designed to provide the required precision. Also, we present the final result of our previous experiment on a high precision measurement of the μ³He capture rate and compare this result with the PCAC prediction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of a New Experimental Method for Studies of Muon Capture in Hydrogen

A new experiment is under preparation with the aim to improve considerably the present knowledge of the rate Λ _s , which should be measured on a level of 1% or better, for the basic electroweak capture reaction of a negative muon on the free proton μp _1s → n + ν_μ. The capture rate will be determined by measuring the lifetime of μ⁻ stopped in ultra pure hydrogen at 10 bar pressure and comparing it with the lifetime of the unbound μ⁺. A new experimental method was developed for this project which should allow measuring the μ⁻ lifetime with at least 10 ppm precision. The basic element of the detector is operating in the hydrogen gas time projection chamber (TPC) surrounded by multi-wire proportional chambers (MWPCs) and scintillator counters. The arrival times and trajectories of the incoming muons and the outgoing decay electrons are measured with this device providing effective suppression of background. Using the TPC as an active target, we can monitor on-line the protium contamination by impurities with a sensitivity better than 10⁻⁸. This can be done by detecting the charged products of the muon capture reaction on these impurities. It was demonstrated that the TPC and MWPCs can operate in pure hydrogen under 10 bar pressure providing gas gain up to 10 000. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phenomenology of the minimal<Emphasis Type="Italic">SO</Emphasis>(10) SUSY model

In this talk I define what I call the minimalSO(10) SUSY model. I then discuss the phenomenological consequences of this theory, vis-a-vis gauge and Yukawa coupling unification, Higgs and super-particle masses, the anomalous magnetic moment of the muon, the decayB _s → μ⁺ itμ⁻ and dark matter. On leave of absence at the Institute for Advanced Study, Princeton, NJ, USA     

1H NMR relaxation investigation of herbicides interacting with photosystem II preparations fromSpinacia oleracea L.

The interaction of three common herbicides, paraquat, acifluorfen and alachlor, with spinach chloroplast photosystem II (PS II) was investigated by measuring¹H nuclear magnetic resonance spin-lattice relaxation rates, transient nuclear Overhauser effect (NOE) and NOE spectroscopy (NOESY) spectra. Binding to PS II was detected by (i) the enhancement of single-selective relaxation rates and (ii) the decrease in the optimal mixing time providing maximal cross-peak intensity in NOESY spectra. Titration of relaxation enhancements was used to calculate the dissociation constants (K _d) from the bound state for paraquat (K _d = 292 ± 71 μM⁻¹) and acifluorfen (K _d = 311 ± 58 μM⁻¹). A similarK _d was apparent for alachlor. Double-selective relaxation rates allowed the isolation of dipolar relaxation terms between selected proton pairs wherefrom dynamic features of the bound state were evaluated. In all cases the motional correlation time of bound herbicide (τ_c = 0.1−0.4 ns at 300 K) was found two orders of magnitude slower than in the free-solution state. In the case of alachlor the E and Z isomers were observed to bind differently to PS II and a change in conformation could be hypothesized.     

Near-threshold photoionization from the excited mp<Superscript>5</Superscript>(m + 1)p J = 0−3 levels of Ar,Kr and Xe (m = 3−5)

Using the configuration interaction Pauli-Fock including core polarization (CIPFCP) approach we have calculated absolute total and partial cross sections for photoionization of excited mp ⁵(m + 1)p J = 0−3 levels in Ar, Kr and Xe (m = 3−5) near threshold. Particular emphasis is paid to the lineshapes of the odd mp _1/2⁵ n(s/d)′ autoionizing resonances and their variation with the character of the intermediate excited J = 0−3 state. For selected intermediate levels of Ar and Kr the computed cross sections are compared with laser spectroscopic measurements; good agreement between the theoretical and experimental lineshapes and branching ratios for different resonances is observed.     

Reciprocity relations for the effective electrical conductivity of randomly inhomogeneous media in the fractal regime

An exact relation for the realization-averaged effective conductivities in the fractal region is found for two-dimensional randomly inhomogeneous media. It has the form {σ _e (τ,L)~× {1/σ _e (−τ,L)~⁻¹=σ _e ² (τ=0, L≫ξ), where ξ is the correlation length (the self-averaging scale), L is the size of the system, τ=(p-p _c )/p _c , and p _c is the percolation threshold. For L≫ ξ, the system is self-averaged, and the relation transforms into the Dykhne reciprocity relation, A. M. Dykhne, Zh. éksp. Teor. Fiz. 59, 110 (1970) [Sov. Phys. JETP 32, 63 (1971)] σ _e (τ)σ _e (−τ])=σ _e ² (τ=0)= σ ₁ σ ₂. A similar relation is obtained for media with an exponentially broad distribution of local conductivities, as well as for individual realizations of some deterministic structures. Zh. éksp. Teor. Fiz. 113, 1484–1490 (April 1998)     

A measurement of the τ lifetime

We have reconstructed 695 three-track τ decay vertices using a high resolution drift chamber close to the interaction point. From the distribution of decay lengths we measure the lifetime to be (3.06 ±0.20±0.14)×10⁻¹³ s. Using this result we find that the ratio of charged weak coupling constant for the τ to that of the μ,G _τ/G _μ=0.967±0.040 consistent with the concept of lepton universality. On leave from Warsaw University, Poland Now at Hasylab, DESY Supported by Bundesministerium für Forschung und Technologie Supported by UK Science and Engineering Research Council Supported by CAICYT Supported by the Minerva Gesellschaft für Forschung GmbH Supported by US Dept. of Energy, contract DE-AC02-76ER000881 and by US Nat. Sci. Foundation Grant no INT-8313994 for travel Partially supported by grant CPBP 01.06