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HK: Physik der Hadronen und Kerne
HK 21: Instrumentation und Anwendungen
HK 21.4: Talk
Monday, March 7, 2005, 15:00–15:15, TU MA042
A superconducting magnetic UCN trap for the precise measurement of the neutron lifetime — •Rüdiger Picker, Igor Altarev, Johannes Bröcker, Andreas Frei, Erwin Gutsmiedl, F. Joachim Hartmann, Axel R. Müller, Stephan Paul, Gerd Petzoldt, Daniele Tortorella, and Oliver Zimmer — Physik-Department E18, Technische Universität München
The lifetime τn of the neutron has important implications
on our picture of the weak interaction and on cosmology. The
latest experimental result for τn is smaller by
7.2 s (≈ 6 σ) than the value recommended by
the Particle Data Group (PDG), τn = (885.7 ± 0.8) s.
The new measurement was performed by storing ultra-cold neutrons
(UCN) in material bottles, similar to the most precise earlier
experiments. Losses during the UCN collisions with the bottle
walls prevent the systematic errors to be
decreased to values well below 0.5 s.
Magnetic storage is a good alternative.
In our planned experimental set-up UCN shall be stored in
a large (≈ 800 dm3) volume between two nested cylinders:
superconducting coils at walls and bottom of the cylinder
produce a magnetic multipole field that reaches about 2 Tesla
at 1 cm distance from the magnets. Gravitation serves as the upper
cover of the trap. We intend to determine τn not only
from the number of surviving neutrons but also, more important,
by real-time detection of the decay protons.
Using the new UCN source of FRM-II at Garching,
we envisage to trap up to 108 neutrons
per cycle. We thus expect to reach an accuracy for τn of
≈ 10−4.
Supported by Maier-Leibnitz-Laboratorium and BMBF.