Precision measurement of the angular correlation coefficient a in neutron beta-decay

点击翻译按钮获取中文摘要

In this proposal we ask for an expiry-financing of the aSPECT experiment. aSPECT has been funded in recent years via the DFG priority programme 1491 which expires end of 2016. In that period we were capable to perform a successful production run with the aSPECT spectrometer at ILL, Grenoble. We measured the electronantineutrino electron angular correlation coefficient a in ß decay of the free neutron via the recoil spectrum of the decay protons. A preliminary analysis of the data results in a relative uncertainty of ~ 0.7%. The total error bar is essentially determined by systematic errors which we want to investigate at the final analysis stage of our project in more detail. For that particle tracking simulations will be used for the recoil protons in the E und B field configurations of the aspect spectrometer. The final result will be published in peer reviewed journals. The present PDG value on a is known to 4%, relative. With our final result we will improve the accuracy on a significantly. Within the standard model of particle physics, a can be expressed as a function of lambda, the ratio of the weak axialvector and vector coupling constants. 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, a is sensitive 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.