C. Petitjean

A precision measurement of nuclear muon capture on 3He

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 obtainedλc=(1496±3(stat)-3(syst)) s−1.

Measurement of the Rate of Muon Capture in Hydrogen Gas and Determination of the Proton's Pseudoscalar Coupling g P

The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation. The capture rate from the hyperfine singlet ground state of the microp atom was obtained from the difference between the micro(-) disappearance rate in hydrogen and the world average for the micro(+) decay rate, yielding Lambda(S)=725.0+/-17.4 s(-1), from which the induced pseudoscalar coupling of the nucleon, g(P)(q(2)=-0.88m(2)(micro))=7.3+/-1.1, is extracted.

Progress in muon catalyzed fusion

Abstract The state of the art and the recent progress made in μCF is reviewed. Resonant dμd formation is now quantitatively understood, but the dμt kinetics is more complicated and full interpretation still difficult. Experiments demonstrated 100 to 150 dt fusions per muon. The most reliable value for dt sticking is ∼ 0.6%. New theoretical results extending over the full energy range, describe now most kinetic processes with high precision and yield ultra large rates for dμt formation at collision energies ϵ ≈ 0.1 − 2 eV. For future exploration the use of H/D/T triple mixtures is discussed. In energy applications, the concept of Yu. Petrovs μCF Hybrid Reactor is sketched, in the context of combining it for uranium breeding with the electronuclear channel. There are prospects for using μCF for intense neutron sources.

Observation of Long-Lived Muonic Hydrogen in the 2S State

The kinetic energy distribution of ground state muonic hydrogen atoms mup(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keV component is discovered and attributed to radiationless deexcitation of long-lived mu p(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1%, and a pressure-dependent lifetime (e.g., 30.4 +21.4/-9.7 ns at 64 hPa) of the long-lived mu p(2S) population, equivalent to a 2S quench rate in mu p(2S)+H2 collisions of 4.4 +2.1/-1.8 x 10(11) s(-1) at liquid-hydrogen density.

First observation of hyperfine transitions in muonic deuterium atoms via resonant dμd formation at 34 K

Abstract We discovered a resonant formation process of the dμd-mesomolecule from the upper F = 3 2 hyperfine state of the μd-atom, while detecting neutrons from muon catalyzed fusion in deuterium gas at 34 K. This new effect enabled us to directly observe transitions between hyperfine states of the μd-atom for the first time and to determine an accurate experimental value for this transition rate.

Measurement of muon capture on the proton to 1% precision and determination of the pseudoscalar coupling gP

The MuCap experiment at the Paul Scherrer Institute has measured the rate Λ(S) of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. Λ(S) is determined from the difference between the μ(-) disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 × 10(10) μ(-) decays, from which we extract the capture rate Λ(S) = (714.9 ± 5.4(stat) ± 5.1(syst)) s(-1) and derive the protons pseudoscalar coupling g(P)(q(0)(2) = -0.88 m(μ)(2)) = 8.06 ± 0.55.

Experimental investigation of muon-induced fusion in liquid deuterium

Abstract The aim of this work was the accurate determination of the absolute values of the formation rates of muonic molecules from both hyperfine states of the muonic atoms in liquid deuterium (23.8 K) by measuring the absolute yield and time distribution of 2.45 MeV neutrons from dd fusion. The resulting dμd formation rates are λ 1 2 = [5.00 ± 0.34 (stat.) ± 0.22 (syst.)] × 10 4 s −1 and λ 1 2 = [3.25 ± 0.23 (stat.) ± 0.23 (syst.)]× 10 6 s −1 , respectively. In addition, the hyperfine transition rate between the upper and the lower hyperfine state was determined to be λhf = [3.05 ± 0.04(stat.) ± 0.06(syst.)]×107s−1. All results are normalized to the density of liquid hydrogen.

Measurement of the Fermi constant by FAST

An initial measurement of the lifetime of the positive muon to a precision of 16 parts per million (ppm) has been performed with the FAST1 detector at the Paul Scherrer Institute. The result is τμ=2.197083(32)(15)μs, where the first error is statistical and the second is systematic. The muon lifetime determines the Fermi constant, GF=1.166352(9)×10−5GeV−2 (8 ppm).

High precision study of muon catalyzed fusion in D2 and HD gas

Muon catalyzed dd fusion in D2 and HD gases in the temperature range from 28 to 350 K was investigated in a series of experiments based on a time-projection ionization chamber operating with pure hydrogen. All main observables in this reaction chain were measured with high absolute precision including the resonant and non-resonant ddμ formation rates, the rate for hyperfine transitions in dμ atoms, the branching ratio of the two charge symmetric fusion channels 3He + n and t + p and the muon sticking probability. The report presents the final analysis of the data together with a comprehensive comparison with calculations based on recent μCF theories. The energy of the loosely bound ddμ state with quantum numbers J = 1, ν = 1, which is central to the mechanism of resonant molecule formation, is extracted with precision ɛ11(fit) = −1.9651(7) eV. in impressive agreement with the latest theoretical results ɛ11(theory) = −1.9646 eV.

Laser spectroscopy of the Lamb shift in muonic hydrogen

The muonic hydrogen atom in the 2s state provides the possibility of achieving high precision laser spectroscopy experiments from which a high precision value of the proton radius can be deduced. This will ultimately allow an increased precision in the test of QED in bound systems. Important progress has been made in recent years in the ability to stop muons in a low pressure gas target and in the understanding of the 2s-metastability in muonic hydrogen. As a consequence the 2s–2p laser spectroscopy experiment is now feasible and we present here the basic experimental concept considered by our collaboration.