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UCN beta decayUCN beta decay
Dan MelconianDan Melconian
University ofUniversity of WashingtonWashington
Neutron beta decayNeutron beta decay
53 '
2iienp
F CCOOxdG
H
n
p
e
W
TAVPSi ,,,,(SM)
Experiments in beta decay Experiments in beta decay show:show:
VV CC ' AA CC '
1.0'
, V
S
V
S
C
C
C
C
and to 1%
2.0'
, A
T
A
T
C
C
C
C
002.0'
V
SS
C
CC 01.0'
A
TT
C
CC
and
and
Angular correlationsAngular correlations
The canonical expression (JTW 1957):The canonical expression (JTW 1957):
2
2
2
2
31
)Re(20
31
1
Aba
VA gg /with and in the SM,
22
2
31
)Im(2
31
)Re(2
DB
But there’s also …But there’s also …
Not as famous, but is a Not as famous, but is a P- and T-odd observableP- and T-odd observable
22
***
3
''2Im
AV
SSATTAV
CC
CCCCCCCR
Present valuesPresent values
sec8.07.8853
1
0029.02695.1
024.0026.0
0006.0
004.0981.0
0013.01173.0
004.0103.0
22
AV gg
R
D
B
A
a
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 Vud
Neutrons, Vud and current Neutrons, Vud and current discrepanciesdiscrepancies
Limits on RH currentsLimits on RH currents
Beta asymmetry parameterBeta asymmetry parameter UCNA – LANLUCNA – LANL PERKEO – ILLPERKEO – ILL abBA – SNSabBA – SNS - PNPI- PNPI
(cold)
if you can measure A, if you can measure A, you’re pretty much you’re pretty much ready to measure Bready to measure B
UCNA at Los AlamosUCNA at Los AlamosGoal: measure beta asymmetry to 0.2% using UCNs (easy to transport and polarize)
started ~ started ~ 19981998
hoping for hoping for 2% 2% measuremenmeasurement this yeart this year
production production run in 2008?run in 2008?
And here’s reality …And here’s reality …
UCNA decay region and UCNA decay region and 11stst UCN beta spectrum UCN beta spectrum
Beta-neutrino correlationBeta-neutrino correlation acorn - NISTacorn - NIST
aSPECT - MunichaSPECT - Munich Nab/abBA - SNSNab/abBA - SNS
Also:
F. WietfeldtF. Wietfeldt
D-coefficientD-coefficient emiTemiT
P. MummP. Mumm
P. MummP. Mumm
PSI R-correlation PSI R-correlation measurementmeasurement
Recent neutron lifetimesRecent neutron lifetimes
PDG doesn’t know what to PDG doesn’t know what to do with Serebrov result …do with Serebrov result …
• In-beamIn-beam• bottlebottle• meas meas expexp decaydecayUCN are UCN are
(relatively)(relatively)easy to trap!easy to trap!
E.g.: UCN GravitrapE.g.: UCN Gravitrap
also: Ioffe trap (NIST); magnetic trap in also: Ioffe trap (NIST); magnetic trap in 4He (NCState); 4He (NCState);
And yet others …And yet others …
J. NicoJ. Nico
(TRIUMF?)(TRIUMF?)
My My (personal!)(personal!) thoughts … thoughts … All these experiments are All these experiments are toughtough All these experiments have lifetimes All these experiments have lifetimes
on the scale of decadeson the scale of decades Any new experiment needs to happen Any new experiment needs to happen
quicklyquickly and should have a and should have a new anglenew angle
A 2x10A 2x1044 UCN/cm UCN/cm33 source source would would be worth it!be worth it! TRIUMF is more attractive than LANLTRIUMF is more attractive than LANL After this round of experiments, what’s next After this round of experiments, what’s next
for fundamental neutron physics …??for fundamental neutron physics …??