Messung des gebundenen Betazerfalls freier Neutronen

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The project aims at the detection of a new decay branch of the neutron, namely the two-body decay n→H+ve expected to make up about 4(10-6 of the standard decay. This decay has the potential to offer a new access to the measurement of the coupling scheme of weak interaction and constitutes a direct measurement of the ve in beta decays. The Lorentz structure of weak interaction can be tested by measuring the population of the different hyperfine states of the emerging hydrogen which also serves as a mirror for the measurement of the helicity of the emitted ve Following the ideas outlined in reference 9 we want to spectroscopically analyse hydrogen atoms emerging with a kinetic energy of about 326 eV from the reactor core of a neutron source (FRMII in Munich) and subsequently detect them as such. Detection of neutral hydrogen atoms emerging in a random (untriggerable) way from neutron decays within a beam tube tangential to the core are identified by their being in the 2s quantum state (population of those is about 10% of all hydrogen atoms from this decay branch) from which they are either quenched emitting characteristic Lyman-α photons or resonance ionized by laser techniques. The discrimination against background hydrogen (thermal and continuous spectrum) is done by means of magnetic spectrometer acting on the ionized hydrogen atoms selecting the mono-energetic ones.The project is split into two parts, the first one being the first detection of this decay channel with subsequent proof of principle of such a spectroscopic measurement, the second part will address the precision measurement of the hyperfine states of the emerging 2s hydrogen atoms. Only the first part is subject of this application. For the second part the laser system will be developed by Th. Udem from the Max-Planck Institute for Quantum Optics (MPQ) in Munich. Here we use existing lasers (argon-ion laser and titanium-safire laser) and development work will focus on resonators and the complete set-up.Stage one of this experiment will be conducted at the beam tube SR6 at the FRMII (or alter-natively at ILL in Grenoble). Hydrogen atoms will pass an axial (w.r.t. to the direction of flight) electric field about 10 m downstream of the core and the H(2s) states are detected. In a first experiment they are quenched with the emitted light being detected by a photo sensor. The branching ratio as compared to the standard decay will be determined. For a second ex-periment hydrogen atoms will pass a spin filter in which all unwanted HFS-states of H(2s) are quenched to H(1s) and the resulting hydrogen ‘beam’ is momentum analyzed with a selectiv-ity for detection of the surviving H(2s) states of about 10:1.The final experiment (2nd stage) will foresee Doppler corrected resonant ionization of the surviving H(2s) state, which has been selected according to its HFS state in a spin filter. Protons are subsequently detected and identified. The final accuracy will depend much on the efficiencies obtained and on backgrounds not known today. Under ideal conditions Hve can be determined to a precision of 10-3 within one month of measuring time. The physics measurements for this stage will only take place after 2013.