T. P. Gorringe

Radiative Muon Capture on Hydrogen and the Induced Pseudoscalar Coupling

Next to the hydrogen atom, the µ − p system is the most fundamental lepton-hadron system; therefore it can be used to test and extend our basic knowledge of the weak semi-leptonic interaction between leptons and quarks. Radiative muon capture (RMC) is much more sensitive than ordinary muon capture (OMC) to the induced pseudoscalar coupling constant of the weak semi-leptonic current because of the much larger range of momentum transfers which can occur in RMC. A status report on TRIUMF E452, Radiative Muon Capture on Hydrogen, which is anticipating a 10% measurement of this coupling constant, is presented.

Measurement of hyperfine transition rates in muonic 19F, 23Na, 31P, and natCl

Abstract From the time dependence of the ( μ − , nν ) reaction we have determined the hyperfine transition rates for the muonic atoms of 19 F, 23 Na, and nat Cl, obtaining Λ h =4.9±1.2 μ s −1 , 8.4±1.9 μ s −1 , and 6.5±0.9 μ s −1 , respectively. Further, from the branching ratios of the ( μ −1 , ν ) reaction on muonic 31 P we have inferred a hyperfine transition rate that is much faster than the muon disappearance rate, Λ h ⪢ Λ D . These results are in reasonable agreement with the rates calculated for Auger emission, and qualitatively confirm the correction to the muonic atoms hyperfine splitting due to the distribution of magnetism in the nucleus. The 31 P result, however, disagrees with an earlier suggestion of the inhibition of Auger emission.

Test of isospin symmetry via low-energy 1H(pi{-},pi{0})n charge exchange.

We report measurements of the pi;{-}p-->pi;{0}n differential cross sections at six momenta (104-143 MeV/c) and four angles (0 degrees -40 degrees ) by detection of gamma-ray pairs from pi;{0}-->gammagamma decays using a photon-pair spectrometer at TRIUMF. This kinematic region exhibits a vanishing zero-degree cross section from destructive interference between s and p waves, thus yielding special sensitivity to pion-nucleon dynamics. Our data and previous data do not agree, with important implications for earlier claims of large isospin-violating effects.

Observation of double radiative capture on pionic hydrogen

We report the first observation of double radiative capture on pionic hydrogen. The experiment was conducted at the TRIUMF cyclotron using the RMC spectrometer and detected gamma-ray coincidences following pi(-) stops in liquid hydrogen. We found the branching ratio for double radiative capture to be [3.05+/-0.27(stat)+/-0.31(syst)]x10(-5). The measured branching ratio and angle-energy distributions support the theoretical prediction of a dominant contribution from the pipi-->gammagamma annihilation mechanism.

Search for d∗ dibaryon by double-radiative capture on pionic deuterium

Abstract We report a search for d ∗ dibaryon production by double-radiative capture on pionic deuterium. The experiment was conducted at the TRIUMF cyclotron using the RMC cylindrical pair spectrometer, and detected γ-ray coincidences following pion stops in liquid deuterium. We found no evidence for narrow dibaryons, and obtained a branching ratio upper limit, BR d ∗ production in the mass range from 1920 to 1980xa0MeV.

Gamma rays from muon capture in 14N

Abstract Many new γ -rays have been observed, following muon capture on 14 N. One had been reported before, and the low yield is confirmed, indicating that the nuclear structure of 14 N is still not understood. Gamma rays from 13 C resulting from the reaction 14 N( μ − , ν n) 13 C compare favourably with states observed in the reaction 14 N( γ ,xa0p) 13 C. More precise energies are also given for the 7017 and 6730 keV γ -rays in 14 C.

A cylindrical drift chamber for radiative muon capture experiments at TRIUMF

Radiative muon capture (RMC), mu Z to nu (Z-1) gamma , is a process which is particularly sensitive to the induced pseudoscalar coupling constant, g/sub p/, which is still very poorly determined experimentally. Due to the extremely small branching ratio ( approximately 6*10/sup -8/), the elementary reaction mu p to nu n gamma has never been measured. To date, efforts have been concentrated on nuclear RMC where the branching ratio is much larger, but the interpretation of these results is hindered by nuclear structure uncertainties. A measurement is being carried out at TRIUMF to determine the rate of RMC on hydrogen to a precision of 8%, leading to a determination of g/sub p/ with an error of 10%. The detection system is based on a large-volume cylindrical drift chamber, in an axial magnetic field, acting as an e/sup +/e/sup -/ pair spectrometer with a solid angle of approximately=2 pi . At a magnetic field of 2.7 kG, the acceptance of 70-MeV photons is about 0.8% for a 1.0-mm-thick Pb photon converter. Monte Carlo calculations indicate a photon energy resolution of >

Double radiative pion capture on hydrogen and deuterium and the nucleon's pion cloud

We report measurements of double radiative capture in pionic hydrogen and pionic deuterium. The measurements were performed with the RMC spectrometer at the TRIUMF cyclotron by recording photon pairs from pion stops in liquid hydrogen and deuterium targets. We obtained absolute branching ratios of [3.02{+-}0.27(stat.){+-}0.31(syst.)]x10{sup -5} for hydrogen and [1.42{+-}{sub 0.12}{sup 0.09}(stat.){+-}0.11(syst.)]x10{sup -5} for deuterium and relative branching ratios of double radiative capture to single radiative capture of [7.68{+-}0.69(stat.){+-}0.79(syst.)]x10{sup -5} for hydrogen and [5.44{+-}{sub 0.46}{sup 0.34}(stat.){+-}0.42(syst.)]x10{sup -5} for deuterium. For hydrogen, the measured branching ratio and photon energy-angle distributions are in fair agreement with a reaction mechanism involving the annihilation of the incident {pi}{sup -} on the {pi}{sup +} cloud of the target proton. For deuterium, the measured branching ratio and energy-angle distributions are qualitatively consistent with simple arguments for the expected role of the spectator neutron. A comparison between our hydrogen and deuterium data and earlier beryllium and carbon data reveals substantial changes in the relative branching ratios and the energy-angle distributions and is in agreement with the expected evolution of the reaction dynamics from an annihilation process in S-state capture to a bremsstrahlung process in P-state capture. Lastly, we comment on the relevance of the double radiative processmorexa0» to the investigation of the charged pion polarizability and the in-medium pion field.«xa0less

Search for exotic baryons in double radiative capture on pionic hydrogen

We report a search for low-lying exotic baryons via double radiative capture on pionic hydrogen. The data were collected at the TRIUMF cyclotron using the RMC spectrometer by detecting gamma-ray pairs from pion stops in liquid hydrogen. No evidence was found to support an earlier claim for exotic baryons of masses 1004 and 1044 MeV/

Radiative Muon Capture on 3He

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