Muon Capture Rates Research Articles

μCR42β: Muon capture rates for double-beta decay

Gamma-rays following nuclear capture of negative muons in enriched 48Ti, 76Se, 106Cd, as well as natural Se and Cd targets were measured. Time evolution of several gamma-lines allowed to deduce the total μ-capture rates in Ti, Se and Cd isotopes, which are compared to the Primakoff estimate. The data on the partial μ-capture rates will be used for more precise calculation of the 2β-NMEs of 48Ca, 76Se and 106Cd.

Precision Measurement of the Singlet Muon Capture Rate on the Proton at PSI

MuCap, the negative muon capture by a proton, is the first experiment which will unambiguously determine the induced pseudoscalar form factor of the proton, gP. While contradictory experimental results for gP are under discussion, a theoretical calculations on the percent level within the framework of Chiral Perturbation Theory are now challenging the measurements. We will describe our experimental efforts and latest achievements.

Spin-isospin excitations and nuclear muon capture

Muon capture rates in complex nuclei are calculated on basis microscopic models of nuclear structure. The calculation results are consistent with experimental values, unsuppressed spin-isospin transitions, and in contrast to the data obtained from the cross sections for nuclear charge-exchange (p, n) and (n, p) reactions.

Fixing two-nucleon weak-axial couplingL1,Afromμ−dcapture

We calculate the muon capture rate on the deuteron to next-to-next-to-leading order in the pionless effective field theory. The result can be used to constrain the two-nucleon isovector axial coupling ${L}_{1,A}$ to $\ifmmode\pm\else\textpm\fi{}2$ fm${}^{3}$ if the muon capture rate is measured to the 2% level. From this, one can determine the neutrino-deuteron breakup reactions and the pp fusion cross section in the sun to the same level of accuracy.

Erratum: Inclusive quasielastic charged-current neutrino-nucleus reactions [Phys. Rev. C 70, 055503 (2004)

The Quasi-Elastic (QE) contribution of the nuclear inclusive electron scattering model developed in Nucl. Phys. A627 (1997) 543 is extended to the study of electroweak Charged Current (CC) induced nuclear reactions, at intermediate energies of interest for future neutrino oscillation experiments. The model accounts for, among other nuclear effects, long range nuclear (RPA) correlations, Final State Interaction (FSI) and Coulomb corrections. Predictions for the inclusive muon capture in $^{12}$C and the reaction $^{12}$C $(\nu_\mu,\mu^-)X$ near threshold are also given. RPA correlations are shown to play a crucial role and their inclusion leads to one of the best existing simultaneous description of both processes, with accuracies of the order of 10-15% per cent for the muon capture rate and even better for the LSND measurement.

Precision muon lifetime and capture experiments at PSI

The muLan experiment at the Paul Scherrer Institute will measure the lifetime of the positive muon with a precision of 1 ppm, giving a value for the Fermi coupling constant G_F at the level of 0.5 ppm. Meanwhile, by measuring the observed lifetime of the negative muon in pure hydrogen, the muCap experiment will determine the rate of muon capture, giving the proton's pseudoscalar coupling g_p to 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD's chiral symmetry.

Neutrino-nucleus reactions and muon capture inC12

The neutrino-nucleus cross section and the muon-capture rate are discussed within a simple formalism that facilitates nuclear structure calculations. The corresponding formulas depend on only four types of nuclear matrix elements currently used in nuclear \ensuremath{\beta} decay. We have also considered nonlocality effects arising from the velocity-dependent terms in the hadronic current. We show that for both observables in $^{12}\mathrm{C}$ the higher order relativistic corrections are of the order of \ensuremath{\sim}5% only and therefore do not play a significant role. As a nuclear model framework we use the projected quasiparticle random-phase approximation and show that the number projection plays a crucial role in removing the degeneracy between the proton-neutron two-quasiparticle states at the level of the mean field. Comparison is done with both the experimental data and the previous shell model calculations. The possible consequences of the present study on the determination of the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}$ neutrino oscillation probability are briefly addressed.

Inclusive quasielastic charged-current neutrino-nucleus reactions

The quasielastic (QE) contribution of the nuclear inclusive electron scattering model developed by Gil, Nieves, and Oset [Nucl. Phys. A627, 543 (1997); A627, 599 (1997)] is extended to the study of electroweak charged current (CC) induced nuclear reactions, at intermediate energies of interest for future neutrino oscillation experiments. The model accounts for, among other nuclear effects, long range nuclear [random phase approximation (RPA)] correlations, final state interaction (FSI), and Coulomb corrections. Predictions for the inclusive muon capture in $^{12}\mathrm{C}$ and the reaction $^{12}\mathrm{C}$ $({\ensuremath{\nu}}_{\ensuremath{\mu}},{\ensuremath{\mu}}^{\ensuremath{-}})X$ near threshold are also given. RPA correlations are shown to play a crucial role and their inclusion leads to one of the best existing simultaneous description of both processes, with accuracies of the order of 10\char21{}15 % for the muon capture rate and even better for the Liquid Scintillating Neutrino Detector (LSND) measurement.

A formalism for weak interactions in nuclei

The neutrino-nucleus cross-section and the muon capture rate are discussed within a simple formalism which facilitates the nuclear structure calculations. The corresponding formulae only depend on four types of nuclear matrix elements, which are currently used in the nuclear beta decay. We have also considered the non-locality effects arising from the velocity-dependent terms in the hadronic current. We show that for both observables in 12C the higher order relativistic corrections are of the order of ~ 4% only, and therefore do not play a significant role.

Muon capture by3Henuclei followed by proton and deuteron production

The paper describes an experiment aimed at studying muon capture by ${}^{3}\mathrm{He}$ nuclei in pure ${}^{3}\mathrm{He}$ and $\mathrm{D}_2 + {}^{3}\mathrm{He}$ mixtures at various densities. Energy distributions of protons and deuterons produced via $\mu^-+{}^{3}\mathrm{He}\to p+n+n + \nu_{\mu }$ and $\mu^-+{}^{3} \mathrm{He} \to d+n + \nu_{\mu}$ are measured for the energy intervals $10 - 49$ MeV and $13 - 31$ MeV, respectively. Muon capture rates, $\lambda_\mathrm{cap}^p (\Delta E_p)$ and $\lambda_\mathrm{cap}^d (\Delta E_d)$ are obtained using two different analysis methods. The least--squares methods gives $\lambda_\mathrm{cap}^p = (36.7\pm 1.2) {s}^{- 1}$, $\lambda_\mathrm{cap}^d = (21.3 \pm 1.6) {s}^{- 1}$. The Bayes theorem gives $\lambda_\mathrm{cap}^p = (36.8 \pm 0.8) {s}^{- 1}$, $\lambda_\mathrm{cap}^d = (21.9 \pm 0.6) {s}^{- 1}$. The experimental differential capture rates, $d\lambda_\mathrm{cap}^p (E_p) / dE_p $ and $ d\lambda_\mathrm{cap}^d (E_d) / dE_d$, are compared with theoretical calculations performed using the plane--wave impulse approximation (PWIA) with the realistic NN interaction Bonn B potential. Extrapolation to the full energy range yields total proton and deuteron capture rates in good agreement with former results.

Muon capture on nickel and tin isotopes

We calculate total and differential muon capture rates on nickel and tin isotopes ranging from the proton dripline to the neutron dripline. The total rates decrease as the neutron number increases due to the combined effect of gradual blocking of available final-state neutron levels and of decreased phase space. The ordering of single-particle levels determines when blocking becomes important. We show that the total capture rates thereby are sensitive to the evolution of nuclear structure along an isotope chain.

The muon capture rate of 48Ca

The muon nuclear capture rate on 48Ca has been measured to be 1.214(8)×10 6 s −1 at the PSI, Switzerland. An isotopically enriched target was used, and the sensitivity increased further by tagging on known γ-rays observed following the capture. Possible systematic errors in this procedure are discussed. The muon capture rate is compared to theoretical predictions and the isotopic variation of the capture rate is shown to deviate from the Primakoff estimate.

On the nuclear dependence of the μ −→e − conversion branching ratio

The variation of the coherent branching ratio R μe (ratio of the μ −→e − reaction rate divided by the total muon-capture rate) through the periodic table is studied by using exact muon wave functions. It was found that, by using very heavy nuclei (e.g. 197 Au , the SINDRUM II target) as μ −→e − conversion stopping targets, the above ratio is favored by a factor of about four to five than by using light ones (e.g. 48 Ti , chosen as PRIME target).

On the muon–nucleus integrals entering the neutrinoless μ− → e− conversion rates

The muon–nucleus integrals which determine the nuclear-structure dependence of the branching ratio Rμe, i.e. the rate of the flavour-changing muon–electron conversion divided by the total rate of the ordinary muon capture, are extensively studied. Precise muon wavefunctions are employed which are obtained by solving the Schrödinger and Dirac equations. To this aim a method based on modern neural network techniques is developed which gives the radial muon wavefunctions as a linear combination of sigmoid functions.

Microscopic study of muon-capture transitions in nuclei involved in double-beta-decay processes

Total and partial ordinary muon-capture (OMC) rates to 1 + and 2 − states are calculated in the framework of the proton–neutron quasiparticle random-phase approximation (pnQRPA) for several nuclei involved in double-beta-decay processes. The aim is to obtain information on intermediate states involved in double-beta-decay transitions having these nuclei as either daughter or parent nuclei. It is found that the OMC observables, just like the 2 νββ-decay amplitudes, strongly depend on the particle–particle part of the proton–neutron interaction. First experiments measuring the partial OMC rates for nuclei involved in double beta decays have recently been performed.

RPA puzzle in 12C weak decay processes

We explain the origin of the difficulties that appear in a straightforward application of the QRPA in 12C, and we demonstrate that it is imperative to use the projected QRPA (PQRPA). Satisfactory results, not only for the weak processes among the ground states of the triad { 12 B, 12 C, 12 N} , but also for the inclusive ones are obtained. We sketch as well a new formalism for the neutrino–nucleus interaction that furnishes very simple final formulae for the muon capture rate and neutrino induced cross sections.

Radiative muon capture by3He

The rate of the nuclear reaction $^3He+\mu^- \to ^3H+\gamma+\nu_{\mu}$ has been calculated using both the elementary particle model (EPM) approach and the impulse approximation (IA) approach. Using the EPM approach, the exclusive statistical radiative muon capture (RMC) rate for photon energy greater than 57 MeV is found to be $0.245 s^{-1}$ and the ordinary muon capture (OMC) rate to be $1503 s^{-1}$. The IA calculation exhibits a slight dependence on the type of trinucleon wave functions used. The difference between the IA and EPM calculation is larger for RMC than for OMC. To resolve the difference between the two approaches a more detailed investigation including meson exchange corrections will be required.

Ordinary and radiative muon capture in liquid hydrogen reexamined

A simultaneous analysis is made of the measured rates of ordinary muon capture (OMC) and radiative muon capture (RMC) in liquid hydrogen, using theoretical estimates for the relevant atomic capture rates that have been obtained in chiral perturbation theory with the use of the most recent values of the coupling constants. We reexamine the basic formulas for relating the atomic OMC and RMC rates to the liquid-hydrogen OMC and RMC rates, respectively. Although the analysis is significantly influenced by ambiguity in the molecular state population, we can demonstrate that, while the OMC data can be reproduced, the RMC data can be explained only with unrealistic values of the coupling constants; the degree of difficulty becomes even more severe when we try to explain the OMC and RMC data simultaneously.

Microscopic calculation of total ordinary muon capture rates for medium-weight and heavy nuclei

Total ordinary muon capture (OMC) rates are calculated on the basis of the quasiparticle random phase approximation for several spherical nuclei from 90Zr to 208Pb. It is shown that total OMC rates calculated with the free value of the axial-vector coupling constant gA agree well with the experimental data for medium-size nuclei and considerably exceed the experimental rates for heavy nuclei. The sensitivity of theoretical OMC rates to the nuclear residual interactions is discussed.

Inclusive neutrino and antineutrino reactions in 56Fe

We obtain cross sections for the inclusive neutrino and antineutrino reactions in 56Fe for the processes νe + 56Fe ⟶ e− + X, ν̄e + 56Fe ⟶ e+ + X, νμ + 56Fe ⟶ μ− + X and ν̄μ + 56Fe ⟶ μ+ + X. For the former two reactions we do this for incident neutrino energies from threshold to 240 MeV and for the latter two reactions from threshold to 300 MeV. We make use of a tensor model, which depends upon data obtained from the total muon capture rate in 56Fe, to calculate our results. We also obtain the electron neutrino cross section averaged over the Michel spectrum and the muon neutrino cross section averaged over the LAMPF muon neutrino spectrum. We find that these cross sections are substantial as would be expected from the neutron content of the 56Fe nucleus and might therefore be a serious background for nuclear neutrino experiments with substantial iron or steel shielding. We compare our calculation with the experimental results of the KARMEN Collaboration and discuss our results in light of planned experiments in iron.