Tübingen 2003 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 2: Kernphysik/Spektroskopie I
HK 2.6: Vortrag
Montag, 17. März 2003, 17:30–17:45, A
Precision Measurement of the neutrino electron angular correlation coefficient in the decay of the free neutron with the proton retardation spectrometer aSPECT — •Stefan Baeßler1, Ferenc Glück1, Werner Heil1, Yuri Sobolev1, Simone Bago2, Joachim Hartmann2, Igor Konorov2, Gerd Petzoldt2, Oliver Zimmer2, Jim Byrne3, and Maurits van der Grinten3 — 1Institut für Physik, Universität Mainz — 2Physik Department E18, TU München — 3University of Sussex, Falmer, Brighton, UK
In this talk the retardation spectrometer aSPECT should be presented. With aSPECT we measure the proton recoil spectrum in the decay of free neutrons. Such a measurent enables us to determine the neutrino electron correlation coefficient a. We hope we can reach a precision which is more than an order of magnitude better than that of older experiments.
For the most precise test of the unitarity of the Cabbibo-Kobayashi-Maskawa matrix it is crucial to know its upper left element Vud. It can be determined from a measurement of a in combination with a measurement of the neutron lifetime. With present neutron decay data the unitarity test fails by about 3σ. aSPECT should clarify the situation.
The working principle is as follows: Protons emitted in neutron decay taking place in a well-defined decay volume are guided by a magnetic field to a proton detector. Only protons with high enough kinetic energy can pass a region with a variable electrostatic barrier potential which is between decay volume and proton detector. Since the proton spectrum is sensitive to the value of a, we can deduce a from the ratio of the event rates of higher energy protons to total decay events.