Radiative muon capture for N = Z nuclei

The commonly used elementary hamiltonian of radiative muon capture has been confirmed, while the alternative Hwang-Primakoff approach is shown not to be gauge invariant.In the inclusive process on N = Z nuclei, the closure approximation is avoided by using a realistic nuclear excitation spectrum.The study is exemplified by a detailed application to ⁴⁰Ca. Predictions are given for the high-energy photon spectrum, circular polarization and asymmetry with respect to the muon polarization for various values of the pseudoscalar coupling constant g_p. A semi-quantitative agreement is found with the data on the spectrum; more precise experiments are necessary to determine g_p.     

Effect of meson exchange corrections on allowed muon capture

Corrections to the impulse approximation calculation of the γ?ν angular correlation coefficient and recoil nuclear polarization in allowed muon capture transitions, arising from meson exchange effects, are studied and the value for the induced pseudoscalar coupling consistent with both observables is found to be (13.3 + 3)_gA, to a large extent free from nuclear wave function uncertainties.     

Muon capture rates on 16O leading to bound states of 16N

The partial muon capture rates on ¹⁶O leading to all four particle-stable states in ¹⁶N have been measured. The results obtained are compared to previous measurements and are also used to extract a value for the induced pseudoscalar coupling constant in muon capture.     

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.     

Effective coupling constant expansion of the muon anomalous magnetic moment

The relationship between the renormalization group and the muon anomalous magnetic moment calculation in QED is reconsidered. A very simple analysis shows that the contribution to the muon anomaly from muon vertex graphs with electron loop insertions in the photon propagators is function of only one dimensionless effective coupling constant $\text{α}{}_{\mathrm{\mu }}\text{?}\text{1}\text{136.0785}$. The perturbative expansion coefficients up to the α³_μ term are given, and comparison is made with the previous calculations.     

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.     

Analysis of the hadronic light-by-light contributions to the muon g − 2

We calculate the hadronic light-by-light contributions to the muon g − 2. We use both 1/N_c and chiral counting to organize the calculation. Then we calculate the leading and next-to-leading order in the 1/N_c expansion low energy contributions using the Extended Nambu-Jona-Lasinio model as hadronic model. We do that to all orders in the external momenta and quark masses expansion. Although the hadronic light-by-light contributions to muon g − 2 are not saturated by these low energy contributions we estimate them conservatively. A detailed analysis of the different hadronic light-by-light contributions to muon g − 2 is done. The dominant contribution is the twice anomalous pseudoscalar exchange diagram. The final result we get is a_μ^{light-by-light} = (−9.2 ± 3.2) × 10⁻¹. This is between two and three times the expected experimental uncertainty at the forthcoming BNL muon g − 2 experiment.     

Particular cases of particle production in inelastic lepton (anti) lepton scattering

As in a previous paper we consider the inclusive reactions e+e→e+e+ anything in the two photon exchange approximation. We present the complete calculation of the differential cross section dσ/dW² for the production of a state of effective mass W and we give the expression for the total cross section. We apply this to the muon pair and the pseudoscalar meson (π⁰, η and η) productions.     

Muon capture on the proton and deuteron

By measuring the lifetime of the negative muon in pure protium (¹H), the MuCap experiment determines the rate of muon capture on the proton, from which the proton’s pseudoscalar coupling g _p may be inferred. A precision of 15% for g _p has been published; this is a step along the way to a goal of 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD’s chiral symmetry. Meanwhile, the MuSun experiment is in its final design stage; it will measure the rate of muon capture on the deuteron using a similar technique. This process can be related through pionless effective field theory and chiral perturbation theory to other two-nucleon reactions of astrophysical interest, including proton-proton fusion and deuteron breakup. for the MuCap [1] and MuSun [2] Collaborations     

A limit on scalar-pseudoscalar weak neutral currents from a new interpretation of atomic electric dipole measurements

We show that the existing measurements of electric dipole moment of heavy atoms exclude a weak electron-nucleon interaction involving the product of a pseudoscalar and a scalar neutral current with a coupling constant larger than 10^?3G_F.     

Vector dominance and radiative meson decays

The vector dominance model is reexamined in a semi-empirical approach. Vector-meson-photon couplings are determined from leptonic decays, and the vector-meson mixing angle and a single vector-vector-pseudoscalar coupling constant for an effective VVP lagrangian, which is constrained by Zweig's rule, is calculated from the V→πλ decay widths. The lagrangian is observed to be the same as that obtained by gauging the U(3)_L × U(3)_R hidden symmetry of the nonlinear pseudoscalar chiral lagrangian. The results are in reasonably good agreement with the data. Discrepancies are isolated and found to be substantially cured by a small symmetry breaking mass factor in the coupling constant.     

Familon → photon transition in a magnetized plasma

The external-magnetic-field-induced interaction of a pseudoscalar particle with a photon is investigated in e^?e⁺ plasma. The familon arising upon the breakdown of a horizontal symmetry between fermion generations is considered for a pseudoscalar particle. The expressions for the plasma and the field contribution to the effective familon-photon coupling are derived in the limit of strongly magnetized plasma and the limit where the plasma being considered occurs in a relatively weak magnetic field.     

The pseudoscalar hadronic channel contribution of the light-by-light process to the muon (<Emphasis Type="Italic">g</Emphasis>−2)<Subscript><Emphasis Type="Italic">μ</Emphasis></Subscript> within the nonlocal chiral quark model

The light-by-light contribution to the anomalous magnetic moment of muon (g−2) _μ from the hadronic exchanges in the neutral pseudoscalar meson channel is calculated in the nonlocal chiral quark model. The full kinematic dependence of the meson two-photon vertices from the virtualities of the mesons and photons is taken into account. It is demonstrated that the effect of the full kinematic dependence in the meson–photon vertices is to reduce the contribution of pseudoscalar exchanges comparing with the most of previous estimates and the result is a_m^PS,LbL=(5.85±0.87)·10^-10a_{\mu}^{\mathrm{PS,LbL}}=(5.85\pm0.87)\cdot10^{-10}. The status of various phenomenological and QCD short-distance constraints is discussed and the comparison with the predictions of other models is performed.     

A microscopic theory of muon capture in nuclei

The muon capture rates are calculated for a series of nuclei, using the Hartree-Fock randomphase approximation, and compared with experiment. The recoil term, the binding energy of the muon and finite size effects are calculated in detail. In a schematic model, the validity of the assumption M²_V = M²_A = M²_P is studied, and found to hold reasonably well even for nuclei as heavy as ²⁰⁸Pb.     

Author index

The photon spectrum of radiative muon capture in the ³He nucleus has been calculated with the help of the Adler and Dothan amplitude, including derivative terms, for both the impulse approximation with a realistic wave function and the elementary particle method. For the latter the sensitivity to the pion-nucleus coupling constant is pointed out.     

Precision measurement of the rate of nuclear muon capture in the muonic hydrogen atom and the determination of the pseudoscalar form factor of the nucleon

The rate Λ _S of nuclear muon capture by a proton from the hyperfine singlet ground state of the µp atom has been measured using a new experimental method based on a time-projection chamber operating in an ultrapure hydrogen gas at a pressure of 10 atm. The capture rate has been determined from the difference between the measured lifetime of the negative muon in hydrogen and the world average lifetime of the positive muon. The analysis of 10% of the collected statistics (2 × 10¹⁰) of µe decays yields the muon capture rate Λ _S = 725.0 ± 17.4 s^?1, from which the pseudoscalar form factor of the nucleon, g _P (q _c ² = ?0.88m _µ ² ) = 7.3 ± 1.1, is determined. The further analysis of the collected experimental data should improve the precision of this measurement by a factor of 3.     

Überprüfung der Form der Myonabsorptionswechselwirkung und des Einflusses der Kernschalenstruktur auf die Myonabsorption mit Hilfe der totalen Absorptionsraten für Cl35 und Cl37

Using the shell model of nuclei the total muon absorption rates in Cl³⁵ and Cl³⁷ have been calculated. This calculation yields the right “isotope effect” in the absorption of muons by chlorine (whereasPrimakoff's theory in which a homogeneous nuclear matter model is assumed predicts an incorrect value). As the energy, being transferred to the absorbing nucleus, does not essentially exceed 10 MeV, only the protons outside the₈O¹⁶-core will contribute to the absorption by Cl³⁷. The calculation was done including and omitting the “weak magnetic interaction” and for positive and negative sign of pseudoscalar coupling. The theoretical prediction\(\frac{{C_P }}{{C_A }} > 0\) was confirmed by comparison of the computed absorption rates in Cl³⁷ with experiment, but the “conserved vector current” hypothesis could not be checked.     

Axial polarizability and weak currents in nuclei

The effect of the isobaric excitations on the weak axial coupling constants in nuclei is studied through P.C.A.C. We first establish the Klein-Gordon equation for the virtual pion field in the nucleus; it takes into account pion rescattering. The influence of isobar excitation is contained in the axial polarizability coefficient which is linked to the p-wave π-N scattering volume. The derivation of this equation stresses its analogies with electromagnetism. We give then a basic relation between the axial current and the pionic field. It incorporates the effects of the isobars in the axial polarizability, which leads naturally to an electromagnetic analog. We show that this relation leads in heavy nuclei to a quenching of the axial coupling constant by the Lorentz-Lorenz factor, which may originate from the short range or the Pauli correlations, depending on the range of the π-N forces. Hence this quenching may have a different origin than the existence of short-range correlations and may arise from a Pauli blocking effect. On the other hand, the pseudoscalar coupling constant is found to be strongly suppressed. In finite nuclei, these basic quenchings can be masked by surface effects, the general features of which are studied with the help of a solvable model. This model is further used to obtain the asymptotic pion field which is linked to the effective pion-nucleus coupling constant and can be determined experimentally through π-nucleus dispersion relations. We find that this quantity is quenched, in agreement with recent experimental data.     

φ production in In–In collisions at 158 A GeV

The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents a high statistics measurement of φ→μ μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of the p _T spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T _eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality. The mass and width are found to be compatible with the PDG values at any centrality and at any p _T : no evidence for in-medium modifications is observed.