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 …??