UCN beta decay Dan Melconian University of Washington

Neutron beta decay n p e W (SM)

Experiments in beta decay show: and to 1% and

Angular correlations The canonical expression (JTW 1957): with and in the SM,

But there’s also … Not as famous, but is a P- and T-odd observable

Present values PDG 06: To be competitive: Measure all of these parameters to 0.1% Sensitive to new physics (leptoquarks, SUSY, RHC, extra Higgs, …) Search for non V-A interactions (S,T currents, RH currents); CVC and V ud

Neutrons, Vud and current discrepancies

Limits on RH currents

Beta asymmetry parameter UCNA – LANL UCNA – LANL PERKEO – ILL PERKEO – ILL abBA – SNS abBA – SNS - PNPI - PNPI (cold) if you can measure A, you’re pretty much ready to measure B

UCNA at Los Alamos Goal: measure beta asymmetry to 0.2% using UCNs (easy to transport and polarize) started ~ 1998 started ~ 1998 hoping for 2% measurement this year hoping for 2% measurement this year production run in 2008? production run in 2008?

And here’s reality …

UCNA decay region and 1 st UCN beta spectrum

Beta-neutrino correlation acorn - NIST acorn - NIST aSPECT - Munich aSPECT - Munich Nab/abBA - SNS Nab/abBA - SNS Also: F. Wietfeldt

D-coefficient emiT emiT P. Mumm

PSI R-correlation measurement

Recent neutron lifetimes PDG doesn’t know what to do with Serebrov result … In-beam In-beam bottle bottle meas exp meas exp decay decay UCN are (relatively) easy to trap!

E.g.: UCN Gravitrap also: Ioffe trap (NIST); magnetic trap in 4He (NCState);

And yet others … J. Nico (TRIUMF?)

My (personal!) thoughts … All these experiments are tough All these experiments are tough All these experiments have lifetimes on the scale of decades All these experiments have lifetimes on the scale of decades Any new experiment needs to happen quickly and should have a new angle Any new experiment needs to happen quickly and should have a new angle A 2x10 4 UCN/cm 3 source would be worth it! A 2x10 4 UCN/cm 3 source would be worth it! TRIUMF is more attractive than LANL TRIUMF is more attractive than LANL After this round of experiments, what’s next for fundamental neutron physics …?? After this round of experiments, what’s next for fundamental neutron physics …??