Negative muon capture in3He

We compute the partial capture rate of negative muons in³He by following the analysis of Peterson to include the relativistic corrections and the exchange effects, for various values of theg _p /g _A ratio. We also calculate the total capture rate. The ground state of³He is assumed to be spherical. The radial dependence of the ground state wave function is taken to be (a) one parameter Irving function, (b) a modified three-parameter Irving function and (c) a function having ‘soft-core’, whose parameters have been fixed in a variational calculation of the binding energy of the triton using a non-local momentum-dependent potential involvingp ² terms. The calculated values of the capture rates are compared with the experimental data to find a value for theg _p /g _A ratio.     

Neutrino disintegration and muon capture in the deuteron

Neutrino and antineutrino disintegration of the deuteron and muon capture in the deuteron are studied. The final-state interaction between the nucleons is considered. The two-nucleon final state is found for the realistic potentials suggested by Reid and Ulehla et al.     

Kinematical and dynamical considerations of muon capture by deuteron

Proton inducedL X-ray yields from thick targets of In, Sn, Nd, Dy, Pt and Au have been measured in the energy range 1–3 MeV. Cross-sections have been derived from these thick target yields and are compared with the predictions of non relativistic PWBA, BEA and CBEA theories. The ratios σ_Lα/σ_Ll, σ_Lα/σ_Lβ and σ_Lα/σ_Lγ are also presented.     

Precision measurement of nuclear muon capture by3He

In this article we report the results of an experiment performed in 1993 at PSI. The goal was to determine the absolute rate of nuclear muon capture by³He. In the experiment we used a new technique recently developed at Gatchina. As a preliminary result from this experiment we obtained _c=(1496±3(stat)-3(syst)) s^–1.     

Chiral effective field theory and nuclear forces

We review how nuclear forces emerge from low-energy QCD via chiral effective field theory. The presentation is accessible to the non-specialist. At the same time, we also provide considerable detailed information (mostly in appendices) for the benefit of researchers who wish to start working in this field.     

Measurement of the breakup channels in nuclear muon capture by3He and4He

The rates of the breakup reactions _B(³He) and _B(⁴He) in nuclear muon capture by³He and⁴He have been measured. The measurements were performed on the muon beam of PSI with a multi-anode high-pressure ionization chamber filled with isotopically pure³He or⁴He at 120 bar. The chamber was used as a target and detector for both the incoming muons and for the charged reaction products (tritons, deuterons and protons) of the breakup reactions _B(³He) and _B(⁴He). Our statistics, about 5 × 10⁵ of breakup events, provides a possibility to improve the precision of evaluated rates. The preliminary results: _B(³He)=720 ± 70 s^–1, _B(⁴He)=415 ± 40 s^–1 are compared to theoretical predictions and to previous experiments.     

The longitudinal response function of the deuteron in chiral effective field theory

We use chiral effective field theory (χEFT) to make predictions for the longitudinal electromagnetic response function of the deuteron, f _L , which is measured in d(e, e′N) reactions. In this case the impulse approximation gives the full χEFT result up to $\mathcal{O}(P^4 )$ relative to leading order. By varying the cutoff in the χEFT calculation between 0.6 and 1 GeV we conclude that the calculation is accurate to better than 10% for values of q ² within 4 fm^?2 of the quasi-free peak, up to final-state energies E _np = 60 MeV. In these regions χEFT is in reasonable agreement with predictions for f _L obtained using the Bonn potential. We also find good agreement with existing experimental data on f _L , albeit in a more restricted kinematic domain.     

^3 \overrightarrow {He} (γ, π°)^3 \overrightarrow {He} as the nuclear probeas the nuclear probe

The state of polarization of the recoil nucleus inγ+³He→π°+³He as well as the asymmetry in the differential cross-section when the initial³He is polarized are studied together with the differential cross-section taking into consideration theS, S′ andD-state admixtures in the nuclear wavefunctions. In view of the considerable spin dependence in the photoproduction amplitudes these observables are found to be quite sensitive to the small admixtures ofS′ andD-states in the nuclear wave-functions.     

Meson exchange currents for nuclear muon capture by3He leading to the triton final state

We have calculated exchange corrections for nuclear muon capture by³He using the hard-pion model and realistic nuclear wavefunctions. These currents modify the vector and axial part of the weak nuclear current. In their absence the rate is found to be about 12% smaller than experiment. Our aim is to test the hard-pion model by making a realistic estimate of the theoretical uncertainty and comparing the calculated rate with its experimental value. Results for the rate and spin observables will be presented at the symposium. The recent precise measurement of the rate (see the contributions of A.A. Vorobyov and W. Prymas in these proceedings) allows the most stringent test of exchange currents for muon capture to date.Supported by the Sir James Knott Fellowship.Supported by grants nos. 202/94/0370 (GA CR) and 148410 (GA ASC CR).     

Measurement of the heavy neutrino admixture upper limit from muon capture by3He

The triton energy spectrum of the muon capture reaction µ³Het+_µ where µ³He is the ground state of muonic³He, has been measured by means of a high-pressure ionization chamber in order to investigate a possible heavyv admixture into the µ flavor with high sensitivity. The upper limit of the µ-heavy v_i mixing matrix element squared was obtained to be U_µi²10^–3 for heavy neutrino masses in the range of 25 E_0V75 MeV.     

Chiral effective field theory on the light front in the nucleon sector

We propose a new approach to treat the nucleon structure in terms of an effective chiral Lagrangian. The state vector of the nucleon is defined on the light front plane and is decomposed in Fock components. An adequate Fock sector dependent renormalization scheme is applied. We present our first results of the calculation of nucleon properties in a two-body Fock truncation.     

Lattice simulations for light nuclei: Chiral effective field theory at leading order

We discuss lattice simulations of light nuclei at leading order in the chiral effective field theory. Using lattice pion fields and auxiliary fields, we include the physics of instantaneous one-pion exchange and the leading-order S-wave contact interactions. We also consider higher-derivative contact interactions which adjust the S-wave scattering amplitude at higher momenta. By construction our lattice path integral is positive definite in the limit of exact Wigner SU(4) symmetry for any even number of nucleons. This SU(4) positivity and the approximate SU(4) symmetry of the low-energy interactions play an important role in suppressing sign and phase oscillations in Monte Carlo simulations. We assess the computational scaling of the lattice algorithm for light nuclei with up to eight nucleons and analyze in detail calculations of the deuteron, triton, and helium-4.     

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     

Hadronic light-by-light scattering contribution to the muon g - 2: an effective field theory approach

The hadronic light-by-light contribution to a(mu), the anomalous magnetic moment of the muon, is discussed from the point of view of an effective low-energy theory. As an application, the coefficient of the leading logarithm arising from the two-loop graphs involving two anomalous vertices is computed, and found to be positive. This corresponds to a positive sign for the pion-pole contribution to the hadronic light-by-light correction to a(mu), and to a sizable reduction of the discrepancy between the present experimental value of a(mu) and its theoretical counterpart in the standard model.