Folie 1

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• Experiments on the Beta Decay of the Free
  Neutron
• Subproject leader K.
  Schreckenbach, L. Beck
• Topics
• I. Lifetime of the free neutron
• Pichlmaier, V. Varlomov, P. Geltenbort, K.
  Schreckenbach
• II. Angular correlations of the decay products
• coefficient A angular correlation of the betas
  relative to the neutron spin direction
• coefficient D Test of the time reversal
  invariance
• L. Beck, T. Soldner, Ch. Plonka, K.
  Schreckenbach, P. Liaud, R. Kossakowski,
  A. Bussiere

SFB 375, 9.10.2006
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• Experimental Methods
• Storage of ultracold neutrons (UCN)
• Track detectors for the betas (TPC, MWPC)
• Physics output
• Coupling constants of the weak interaction
• Reaction cross sections vep -gt ne
  pp -gt dvee
• primordial pe- lt-gt
  nve
• 
  ne lt-gt pve
• Test of the standard model
• unitarity of CKM, ...
• Test of the time reversal invariance

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• W beta emission probability relative to the
  spin of the neutron
• angle of beta emission
• from coefficient A the value of is computed
  
• From the values of gV und gA are
  determined
• From the coefficient D the relative phase
  between the
• coupling constants is determined

Vud-gtVus
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tn measurement by UCN population in a fomblin oil
coated storage of variable size
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NIM A440(2000)517
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Problems Very long measuring times due to low
UCN density Vacuum was not very good Losses in
the storage walls were compensated by
extrapolation to indefinitely large volume. This
correction includes also gravity corrections and
thus needs some knowledge of the loss mechanism
(new evaluation in progress).
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4He CO2 filled TPC with internal decay of
through going slow neutron bursts.
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Events in the time window capture
cross section at 3He density
result Nucl.Phys. A503(1989)473
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PL B349(1995)427 Nucl.Phys. A612(1997)53
Status 1997
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PDG 2006
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Serebrov et al, PL B605(2005)72
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Stand 2006
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• Conclusion
• In 1997 the neutron data were consistent and in
  agreement with the predictions of the standard
  model
• Today, 2006, in particular the experimental data
  on the neutron lifetime are no longer consistent
  (ca. 5 s deviation!). The unitarity of the CKM is
  only fulfilled for a selection of experimental
  data.