A note on the induced pseudo-scalar coupling constant in μ− + 12C(g.s)→ 12B(1+,g.s+ ν μ

The sum of the induce pseudo-scalar g_P and the second-class induced tensor g_T couplings in muon capture is found to be (g_P + g_T)g_A= (13.3 + 1.8) by comparing with recent data on the recoil polarization of ¹²B(1⁺) in the μ^? + ¹²C→¹²B+ ν_μ process, even aaking into account the corrections due to the gamma decay of the excited states of ¹²B to ¹²B(1⁺;g.s.). With the canonical value for g_P and in the absence of meson exchange effects, our results indicate a large positive value for g_T which is in strong contradiction with the conclusion of the Louvain-Saclay—ETH experiment.     

Muon transverse polarization in K_{l2_\gamma } decay due to the electromagnetic final-state interaction

For the decay process K ⁺ → μ ⁺ νγ, the effect of muon transverse polarization caused by electromagnetic final-state interaction is analyzed. It is shown that, in the one-loop approximation, the muon transverse polarization varies from ?1.3×10^?3 to zero in the region of the Dalitz plot. The mean value of the muon polarization, 〈P _T〉, in the kinematical region E _γ ≥20 MeV is ?5.44×10^?4.     

Average polarization of 12B in 12C(μ, ν)12B(g.s.) reaction: Helicity of the π-decay muon and nature of the weak coupling

The helicity, h^?, of μ^? in π-decay has been determined as positive (h^??+0.90) from the average polarization, P_av≡〈J_B·s_μ〉, of ¹²B produced in the $\text{μ}{}^{\mathrm{?}}\text{+}{}^{12}\text{C}\text{→ν}{}_{\mathrm{\mu }}\text{+}{}^{12}\text{B}$ reaction. We obtain also dynamical information on μ-capture: (i) the weak magnetism form factor, μ=4.5±1.1, and (ii) the sum of the induced pseudoscalar (g_p) and the 2nd class induced tensor (g_T) couplings versus g_A, ($\text{g}{}_{\mathrm{<mtext>P</mtext>}}\text{+g}{}_{\mathrm{<mtext>T</mtext>}}\text{)}\text{g}{}_{\mathrm{<mtext>A</mtext>}}\text{=7.1±2.7}$. The latter result, adopting the “canonical” value of $\text{g}{}_{\mathrm{<mtext>P</mtext>}}\text{g}{}_{\mathrm{<mtext>A</mtext>}}$, leads to $\text{g}{}_{\mathrm{<mtext>T</mtext>}}\text{g}{}_{\mathrm{<mtext>A</mtext>}}\text{=+1±2.7}$ which is compatible with zero and in strong contradiction with the value ?—6 recently advocated by Kubodera, Delorme and Rho.     

NMR studies on polarized12B implanted in highly oriented pyrolytic graphite

NMR measurements on¹²B nuclei implanted in a thin sheet of highly oriented pyrolytic graphite (Grafoil) have been made to study the magnitude of the polarization of¹²B and its electric quadrupole coupling. The magnitude of the residual polarization of¹²B held in carbon material is of crucial importance to the experiment measuring the average polarization of¹²B produced in the muon capture by¹²C. It was found that the polarization of¹²B can be maintained at 101.0±2.2% in Grafoil under a magnetic field of 3 kG. The electric quadrupole coupling was determined to bee ² qQ/h=+1207.3±8.2 kHz. From the magnitude and the sign of the electric field gradienteq, the location of¹²B was found to be a substitutional site in the carbon lattice. The anomalous B-C bond involving thesp ₂ hybrid orbitals with partially filledp _z electrons is also discussed.     

Hadronic contributions to (g−2) of the leptons and to the effective fine structure constant α(M Z 2 )

The new experiment planned at Brookhaven to measure the anomalous magnetic moment of the muona _μ≡(g _μ?2)/2 will improve the present accuracy of 7 ppm by about a factor of 20. This requires a careful reconsideration of the theoretical uncertainties of theg?2 predictions, which are dominated by the error of the contribution from the light quarks to the photon vacuum polarization. This issue is cruicial also for the precise determination of the running fine structure constant at theZ-peak as LEP/SLC experiments continue to increase their precision. In this paper we present an updated analysis of the hadronic vacuum polarization using all presently availablee ⁺e^? data. This seems to be justified because previous work on the subject was based to some extent on preliminary or incomplete experimental data. Contributions from different energy ranges are presented separately forg?2 of the muon and the τ-lepton and for α(M _Z ² ). We obtain the resultsa _μ ^had* =(725±16)×10^?10 anda _τ ^had* =(351±10)×10^?8, where the asterisk indicates the dressed (renormalization group improved) value. For the effective fine structure constant atM _Z=91.1888 GeV we obtainΔα _had ⁽⁵⁾ =0.0280±0.0007 and α(M _Z ² )^?1=128.896±0.090. Further improvement in the accuracy of theoretical predictions which depend on the hadronic vacuum polarization requires more precise measurements ofe ⁺e^? cross-sections at energies below about 12 GeV in future experiments.     

Measurement of the ortho-para transition rate in the pμp molecule and deduction of the pseudoscalar coupling constant gpμ

The ortho-para transition rate in the pμp molecule has been found experimentally to be λ_OP = (4.1 ± 1.4) × 10⁴ s^?1. Our recent result for the muon capture rate in liquid hydrogen can now be interpreted to extract the ortho-molecular capture rate: λ_OM = (531 ± 33) s^?1. A deduction of the pseudoscalar coupling constant g_p^μ is presented: we find g_p^μ = 8.7 ± 1.9.     

Measurement of the average polarization of12B in the polarized-muon capture reaction12C(μ −,v μ)12B (g.s.)

The average polarization P_av of the recoil nucleus¹²B (ground state) produced by the polarized-muon capture reaction¹²C(^–,v )¹²B was measured by a new approach which involved the muon spin resonance, and the adoption of Grafoil as a carbon target where the polarization of¹² B can be preserved completely under 3 kG holding field. Our observed resultP _av=0.473±0.053 yields g_p/g_A=9.6 _–2.7 ^2.4 which seems to be consistent with the canonical PCAC prediction within the error.The authors would like to express their sincere thanks to the members of the Meson Science Laboratory and of the Van de Graaff Accerelator at Osaka University. They also acknowledge helpful discussions and suggestions given by Professors M. Morita, H. Ohtsubo and K. Kubodera. This work is supported by the Grant-in-Aid of the Ministry of Education, Science and Culture.     

New measurement of the beta decay rate of the16N(0−)-16O(0+) transition

The beta decay rate of the¹⁶N(0^?; 120keV) →¹⁶O(0⁺, G.S.) transition has been remeasured. Our result (Λ _β =0.48±0.024 s^?1) is in excellent agreement with a previous measurement but strongly disagrees with another experimental value. The two agreeing results provide an experimental verification of the importance of meson exchange currents in 0⁺-0^? weak transitions. A value ofg _p/g _A～11–12 can be inferred from the correspondingΛ _μ rate.     

Measurements of theg J -factors of12C in the3 P 1 and3 P 2 states

Using the atomic beam magnetic resonance method the Zeeman interactions of¹²C in the³ P ₁ and³ P ₂ states at magnetic fields of about 3.4 kOe have been measured. The measured quantities areg _J (³ P ₁)?g_J(³ P ₂)=15.4(1.0)·10^?6 g _J (³ P ₂)=1.5010616 (50), from which the following value for g_J(³P₁) can be calculated:g _J (³ P ₁)=1.5010770 (50). The experimental results are in moderate agreement with theoretical calculations.     

Magnetic moment and electric quadrupole moment of the anomalous186Ir ground state

The ground state nuclear moments of¹⁸⁶Ir (j ^π=5⁽⁺⁾) have been determined with NMR on oriented¹⁸⁶Ir in Ni as |μ|=3.80 _?0.02 ^+0.12 μ _n andQ=?3.00 (15)b. The quadrupole moment is consistent with an anamolousj ^π K=5⁺0 or 5⁺1 ground state configuration. The explanation of the magnetic moment in terms of pure 5⁺0 or 5⁺1 configurations would require a high collectiveg _R-factor ofg _R≧0.76. On the other hand the magnetic moment can be explained with a “normal”g _R and a mixed ground state configuration.     

The characterisation of three different coal samples by means of various analytical techniques

We report on a new generation of muon lifetime experiments at PSI to measure the nuclear muon capture rate in hydrogen and deuterium with ≤1% accuracy. The goals are to determine in μp capture the induced pseudoscalar coupling g _P predicted in HBchPT, and in μd capture the axial two-body current term L_1A described by modern EFT’s. For the μp experiment a hydrogen TPC was developed as active muon stop detector, surrounded by cylindrical wire chambers and a plastic hodoscope as electron detector. Ultra-high purity of the hydrogen isotope $^1H_1$ at levels below 10^???8 was achieved with a specially developed gas circulation and purification system, and with a novel isotope separation column. About 2 ·10¹⁰ events were collected which are now in final analysis. Data from the first production run result in g _P = 7.3 ± 1.1 in good agreement with theory. The μd experiment is in development. It requires measurements in ultra-pure, cold deuterium gas at ～30K. For this we are constructing a new Cryo-TPC.     

Measurements of the polarization of the 2p and 1s states in muonic atoms and the helicity of the muon in pion decay

We have measured the polarization of the 2p and 1s states in muonic selenium (amorphous and metallic modifications), cadmium, palladium and iodine, in order to study the depolarization of muons in the cascading process and to measure the helicity of the μ^?. In the cases of cadmium, palladium and amorphous selenium good agreement between the measurements and cascade calculations is found. There is an unexpected depolarization of the 2p_{$\text{1}\text{2}$} state in metallic selenium. The helicity of the muon after the pion decay was measured to h_μ^? = + 0.99 ± 0.16.     

Magnetic moments of the 12+ isomeric states in 194, 196, 198Pb

The g-factor of the 12⁺ isomeric state in lead isotopes with A = 194, 196, 198 was measured using the time-differential perturbed angular distribution method (TDPAD). The values obtained are respectively g(194) = ?0.158(6); g(196) = ?0.157(7); g(198) = ?0.144(11). A more precise determination of the 12⁺ level half-life is also made. The g-factprs of these nuclear states, which are described with v(i_{$\text{13}\text{2}$})^?2 as the main configuration, are surprisingly constant over a large mass range (between A = 206 and 194). A core polarization analysis explains this trend: the polarization induced on neutrons in i_{$\text{13}\text{2}$} orbit decreases with the mass number A (blocking effect), but a compensation is provided by the other spin-orbit partners f_{$\text{7}\text{2}$}-f_{$\text{5}\text{2}$} and P_{$\text{3}\text{2}$}-P_{$\text{1}\text{2}$}.     

Transverse muon polarization in the K µ3 0 decay induced by electromagnetic final-state interaction

A calculation of transverse muon polarization in the K _μ3 ⁰ decay due to the electromagnetic interaction in a final state in one-loop approach is presented. Average transverse muon polarization is found to be (2.4±0.1)×10⁻³ in the Dalitz plot region. From Yadernaya Fizika, Vol. 63, No. 2, 2000, pp. 319–323. Original English Text Copyright ? 2000 by Efrosinin, Kudenko. This article was submitted by the authors in English.     

The decay of theT=1 isospin triplet inA=12 systems: II. The induced interactions in the anisotropy of beta-rays

Nuclear Structure: calculation of the asymmetryα _? ofβ rays emitted from polarized¹²B and¹²N nuclei. Comparison with experimental values. Formulae for the asymmetry parametersα _? ofβ rays emitted from polarized nuclei is derived using the formalism developed by Behrens-Bühring. The induced interactions are studied in detail. It is demonstrated that the expressions forα _? are independent of the induced pseudoscalar interaction. It was found that the corrections to the lowest order approximation are small. Experimental data of the Louvain and Osaka laboratories are analyzed. We should point out that the data of the asymmetry of theβ ^? decay of¹²B obtained in these two laboratories are quite different. Although the data reported by the Osaka Group require the existence of the induced pseudotensor (IPT) interaction as it has also been stated by other authors, if we combine data of¹²N from Osaka and of¹²B from Lauvain such experimental results can be understood without including the IPT interaction. Thus, we found some evidence that the IPT interaction could be not necessary to explain the asymmetries in the decay of members of theA=12 system.     

Radio-frequency muon spin resonance studies of endohedral and exohedral muonium adducts of fullerenes

The radio-frequency muon spin resonance technique (RF-μSR) is described, with examples drawn from muon studies of fullerences. Two distinct species can be detected by RF-μSR when solid C₆₀ is irradiated with positive muons. Endohedral muonium (Mu@C₆₀) is characterized by a muon hyperfine constant (A _μ) close to the vacuum value. A remarkable feature of the RF-μSR spectrum is the double quantum transition, which appears when the allowed transitions are saturated. The exohedral muonium adduct (C₆₀Mu) is also detected, and has a much smaller value ofA _μ typical of a carbon-centred organic radical. It has been studied by RF-μSR in dilute solution, which is not possible for transverse field muon spin rotation (TF-μSR). There is a significant difference inA _μ of C₆₀Mu in the solid and in solution, a result of great import to the analysis of avoided-level crossing experiments on¹³C₆₀Mu.     

Elementary-particle treatment of the radiative muon capture in 12C

We consider radiative muon capture to a definite nuclear final state. The example chosen is the ${}^{12}\text{C}\text{(0}{}^{\mathrm{+}}\text{T = 0)(μ}{}^{\mathrm{?}}\text{, γν)}{}^{12}\text{B}\text{(1}{}^{\mathrm{+}}\text{T = 1)}$ transition. The elementary particle treatment adopted in this work discloses several aspects of the reaction mechanism, which remain hidden in the usual impulse approximation calculations. In particular, one sees a considerable enhancement of the capture rate when the q² dependence of the weak form factors F_A(q²) and F_P(q²) is taken into account. The branching ratio of the radiative capture in the region sensitive to the possibly non-zero mass m_νμ of the muon-neutrino is estimated to be ≈1.36 × 10^?10.     

An investigation of theL 2-L 3 Coster-Kronig transition probability for 63≦Z≦96

Nuclear spin polarization in the 4f ¹⁴6s ^{2 1} S ₀ ground state of¹⁷⁵Lu⁺(I=7/2) ions is achieved by optical pumping with the resonance line (¹ S ₀-¹ P ₁,λ=261.5 nm). Nuclear magnetic resonance of the free ions in He buffer gas yields for the magnetic dipole momentμ(¹⁷⁵Lu)=2.2240(11)μ _n (with diamagnetic correction). This value can be used for a more accurate determination of the magnetic dipole moments of other Lu isotopes from knownA factor ratios. A comparison with nuclear induction measurements in solids results in the chemical shiftsδ(LuB₁₂)=?23(5)·10^?4 andδ(LuSb)= ?31(5)·10^?4.     

Measurement of the parameter η&#x0304; in the radiative decay of the muon as a test of the v-a structure of the weak interaction

The parameter η&#x0304; of muon decay has been measured in the radiative decay $\text{μ}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{ν}{}_{\mathrm{<mtext>e</mtext>}}\text{ν}\text{?}{}_{\mathrm{\mu }}\text{γ}$ of unpolarized positive muons. The result $\text{η}\text{?}\text{?0.083}$ (68% confidence) or $\text{η}\text{?}\text{= ?0.03±0.10}$ with ρ fixed at $\text{3}\text{4}$ yields an improvement of the previous value by more than a factor of two. An analysis of all data on muon decay that are presently available slightly improves the constraints on the weak coupling constants to: g_s?0.29g_v, g_p?0.27g_v, g_T?0.23g_v and 0.92g_v?g_A?1.2g_v     

Spin precession of the12C(2 1 + ) state on recoil in polarized iron

A PAC measurement on the 4.43 MeV¹²C(2⁺) state on recoil in magnetized iron has yielded an integral precession angle of ?=+0.85(14) mrad, which exceeds the Lindhard-Winther prediction by about two orders of magnitude. Evidently, large magnetic fields act at nuclei traversing solids at high velocities (v _rec/c = 0.03 in the present case), thereby holding out the prospect ofg-factor measurements for nuclear states in this lifetime range (τ ₂ ⁺ = 6.5 × 10^?14 s).