Precision measurement of proton recoil spectrum and proton asymmetry in neutron decay using the spectrometer aSPECT (ILL contribution)

• Antragsteller: Professor Dr. Oliver Zimmer
• Fachliche Zuordnung: Kern- und Elementarteilchenphysik, Quantenmechanik, Relativitätstheorie, Felder
• Förderung: Förderung von 2013 bis 2019
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 237545110

We propose to perform accurate measurements of two neutron decay observables using the spectrometer aSPECT at the cold neutron beam facility PF1b at the ILL in Grenoble. The antineutrino-electron angular correlation coefficient “a” shall be measured via the proton recoil spectrum with an accuracy of 0.3%, and the asymmetry “C” of proton emission with respect to the neutron spin direction with accuracy 0.1%. Within the standard model of particle physics, they are both functions of the ratio of the weak axial-vector and vector coupling constants λ = gA/gV. This value is an important input to calculate many semi-leptonic weak cross sections such as those relevant for big-bang nucleosynthesis, stellar fusion and detection of neutrinos. It also enters the determination of the largest element of the CKM matrix which parameterizes mixing within the weak charged current interactions of quarks. On the other hand, both coefficients have different sensitivity to physics beyond the standard model as, e.g., scalar or tensor interactions. Our experiments will provide valuable input to global analyses of weak interaction parameters for applications and for tests of physics beyond the standard model. The spectrometer aSPECT has been developed and commissioned in collaboration of Universities from Mainz and Munich with the ILL. During the last funding period aSPECT has been equipped with a large surface silicon drift detector offering an excellent separation of the signal from noise for protons accelerated to only a few keV. The understanding of the spectrometer and its performance were significantly improved, so that aSPECT is now ready for exploitation. The proposed experiments will not only improve the knowledge of the physics observables by more than an order of magnitude but also deliver important experience for the operation of the instrument PERC under construction at the FRM II, and the design of its secondary spectrometers.

• DFG-Verfahren: Schwerpunktprogramme
• Teilprojekt zu: SPP 1491: Precision experiments in particle- and astrophysics with cold and ultracold neutrons
• Internationaler Bezug: Frankreich
• Beteiligte Person: Dr. Torsten Soldner