Muon absolute lifetime evaluation for neutrino nuclear response using ruthenium oxide thin films target

Abstract

Muon absolute lifetime is a measured lifetime of the trapped muons particle in a target nucleus by the ordinary muon capture (OMC) process. OMC is the probe for neutrino and astro-antineutrino nuclear response (NNR) that is relevant to double beta decay (DBD). The total OMC rates with relative capture strength can be used to determine the muon matrix element. The OMC rates for several DBD candidates reported in the theoretical and experimental studies show the quenching effect in the experimental OMC rate values which lead to high discrepancies in the DBD nuclear matrix element (NME). Ruthenium (Ru) is one of the DBD nucleus that is important for neutrino studies in nuclear and astroparticle physics using muon capture reactions. The present experimental work is the first measurement on Ru for NNR study by OMC experiment. Muon irradiation will transform the ?? ?? nucleus to ?? ?? nucleus via the exchange of weak bosons. A new synthesis method of Ru thin film target is developed in the present study to fulfil the muon irradiation criteria. A ruthenium oxide (RuO2) thin film target is carefully synthesised using normal evaporation method. Poly (vinyl alcohol) (PVA) and RuO2 powder are mixed with H2O separately to form two solutions. The thin film is analysed using several instruments to investigate the target’s characteristics. Field emission scanning electron microscope with energy dispersive X-ray (FESEM-EDX) is used to determine the thickness, uniformity, morphology and elemental identification of the thin film. Inductively coupled plasma-triple quadrupole mass spectrometer (ICPMS) and inductively coupled plasma-optical emission spectrometer (ICPOES) are essential for analyses as they can confirm the concentration of natural contamination (40K, 238U, 232Th) in the thin film. X-ray diffraction (XRD), Raman, and Fourier transform infrared with attenuated total reflection (FTIR-ATR) are used for extended analyses to confirm the hydration phenomena observed in FESEM-EDX. The target was irradiated using negative muons at MuSIC facility at Osaka University, Japan. The muon to electron decay and radioisotope (RI) gamma-rays are processed and recorded by scintillation detectors and high purity germanium (HPGe) detectors. The new synthesis method is suitable for multiple productions of thin film targets. The final thickness for the OMC experiment can be controlled as obtained from some hydration evidence of RuO2 thin film. The muon absolute lifetime of Ru obtained in this experiment is 132.7 ns, equivalent to 7.54 × 106 s -1 total muon capture rate. Present observations confirm slight quenching to the effective axial coupling constant (geff) parameter at about 33% error. The experimental OMC rates of Ru can deduce the absolute neutrino and antineutrino nuclear responses for DBD and neutrino properties of astrophysics origin.