Nab Experiment Electronneutrino correlation, a, in neutron beta decay

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Nab ExperimentElectron-neutrino correlation, a,
in neutron beta decay
David Bowman - ORNL For the Nab Collaboration Pre
Town Meeting Pasadena, December 7-8, 2006
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Physics Motivation

• Neutron lifetime determines GV23 GA2
• a determines GA/Gv
• Together, ?n and a determine Vud and test CKM
  unitarity
• a is measured with an uncertainty of 5, 1
  proposed at NIST
• SNS measurement will reduce uncertainty to 0.1
• b probes S and T weak currents

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How to reconstruct ?e? withoutobserving the
neutrino
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Proton time of flight spectrometer
Electron tof is 20 ns. Proton tof is 1-10 ?s.
Measure tof difference.
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Field expansion longitudinalizes proton momentum.
tof L Mp/ Pp.
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Monte-Carlo calculation of ?a
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Conclusions

• Nab measures a in neutron beta decay with 0.1
  uncertainty, few 106 sec runs
• New proton TOF method using field-expansion
  magnetic spectrometer
• FNPB PAC recommended common magnet design study
  for Nab, abBA, and PANDA
• National beta-decay spectrometer facility for a
  series of precision experiments
• Design study is underway