ARIS 2014

2 June 2014

To first order, β decay ft values can be expressed as:phase space (Q-value)
half-life, branching ratio

Kft = 2g |Mfi|2constantsmatrix element

Weak coupling strength

For the special case of 0+ 0+ (pure Fermi) β decays between isobaric
analogue states (superallowed) the matrix element is that of an isospin
ladder operator:|Mfi|2 = (T – TZ)(T + TZ + 1) = 2(for T = 1)

Strategy: Measure superallowed ft-values, deduce GV and VudVector couplingconstant

GV2 =K
2ft|Vud| = GV / GF

Fermi coupling
constant

To first order, β decay ft values can be expressed as:
constants
K
phase space (Q-value)ft = 22
Superallowed Fermi β Emitters
beenmatrix
usedelement
to:g |Mfi|have
half-life, branching ratio• Confirm the CVC
hypothesis
to better than 2 parts in 104
Weakcoupling strength

For the special case of 0+ 0+ (pure Fermi) β decays between isobaric• Provide the most precise experimental measure for V
analogue states (superallowed) the matrix element is that of an ud
isospinladder operator:• Test extensions of the Standard Model|Mfi|2 = (T – TZ)(T + TZ + 1) = 2(for T = 1)

Strategy: Measure superallowed ft-values, deduce GV and Vud
Vector coupling
constant

GV2 =K
2ft|Vud| = GV / GF

Fermi coupling
constant

ft ≈K= constant (CVC)
22 Gv
2%

J.C. Hardy and I.S. Towner, Phys. Rev. C 79, 055502 (2009)

K
2V = constant
2GV(1 + ΔR)“Corrected”
ft valueCalculated corrections (~1%)
Experiment
CVC Hypothesis(nucleus dependent)◦ Half-life◦ Q-value
Inner radiative correction (~2.4%)◦ Branching Ratio(nucleus independent)

DR = nucleus independent inner radiative correction: 2.361(38)%dR = nucleus dependent radiative correction to order Z2a3: ~1.4%- depends on electron’s energy and Z of nucleus

dNS = nuclear structure dependent radiative correction: -0.3% to 0.03%
dC = nucleus dependent isospin-symmetry-breaking (ISB) correction: 0.2% to 1.5%
- strong nuclear structure dependence (radial overlap)
Note: This is one of several approaches for making the necessary theoretical corrections. Although others exist, the procedure ofTowner & Hardy are highlighted here.

FtWS = 3072.38(75)χ2/ν = 0.32

P. Finlay, et al., Phys. Rev. Lett. 106, 032501 (2011)
R. Dunlop, et al., Phys. Rev. C 88, 045501 (2013)

1.00

0.90
0.80
0.70
0.60
0.50

0.97425(22)

0.40
0.30
0.20

0.22564(53)

0.10
0.00

Vud

0.00393(35)Vus

J.C. Hardy and I.S. Towner, Phys. Rev. C 79, 055502 (2009)
R.J. Dowdall et al., Phys. Rev. D 88, 074504 (2013)
Particle Data Group J. Beringer et al., Phys Rev D 86, 010001 (2012)

VubVudVus

Vub…

0.90

0.92

0.94

0.96

0.98

|Vud|2 + |Vus|2 + |Vub|2 = 1.00009(43)Vud(24)Vus

1.00

To first order, β decay ft values can be expressed as:
constants
K
phase space (Q-value)ft = 2
2
Superallowed Fermi β Emitters
beenmatrix
usedelement
to:g |Mfi|have
half-life, branching ratio• Confirm the CVC
hypothesis
to better than 2 parts in 104
Weakcoupling strength

For the special case of 0+ 0+ (pure Fermi) β decays between isobaric• Provide the most precise experimental measure for V
analogue states (superallowed) the matrix element is that of an udisospin
ladder operator:• Test extensions of the Standard Model|Mfi|2 = (T – TZ)(T + TZ + 1) = 2(for T = 1)

Strategy: Measure superallowed ft-values, deduce GV and Vud
Vector coupling
constant

GV2 =K
2ft|Vud| = GV / GF

Fermi coupling
constant

Testing Extensions of the SM
Set sensitive limits on the existence of scalar currents in nuclear β decay Ft values for 10C, 14O, and 18Ne are the most important Complementary to measurements of β-ν angular correlation
coefficients “a”
 Resolving trivial sources of systematic uncertainty in superallowed
data are essential

CS/CV ± 0.2%

28 cm

4π continuous-flow gas-proportionalcounter and tape transport system Uses methane (CH4) gas
 100% efficient β counter Very low background rates
 Insensitive to γ-rays8π γ-Ray Spectrometer

Spherical array of 20 BGO Compton suppressed HPGe detectors
 ~1% photopeak efficiency
 Works with an array of ancillary detectorsZero Degree Scintillator (ZDS)

A fast plastic scintillator used for β counting
 Covers ~20% of the solid angle
 Impose fixed non-extendible dead-times
Simultaneous independent direct βand γ-ray counting experiments
using the 8π spectrometer and the
Zero-Degree Scintillator.
γ Counting:-Decay Selective-Slow & Inefficientβ Counting:-Fast & Efficient-Not Decay
Selective

Previous measurements
reveal a systematic
discrepancy between
detection method

1.6σ discrepancy → Ft value couldchange by up to 0.5σ12C-14O: TBeam

26Alm: T
26Na: T

1/2 = 70.620 s

1/2 = 6.3465 s

1/2 = 1.072 s

βγ

Status of 14O Half-Life
Performing simultaneous
β and γ half-life
measurements for 14O will
help address the current
systematic discrepancy.
 A follow-up experiment isscheduled for July to push
below 0.03% precision.
 Precision ft
determination of lightsuperallowed Fermi βemitters will help push thelimits of scalar currents inthe Weak interaction.
A.T. Laffoley et al., Phys. Rev. C 88, 015501 (2013)

18Ne Decay Scheme0+T = 1 18Ne
T½ = 1.6654(11) s β+
Q = 4443.6 keV

1+ 1701 0.19%
β+0- 1081 0.0002%

0+ 1042 7.70%

T=1β+
T=018FT½ = 109.73(2) min
Q = 1655.5 keV

1+ 092.11%

β+T=118O
stable0+Half-life precision improvedby a factor of 3, to 0.025%!

PreliminaryE. F. Zganjar
G. C. Ball
P. C. Bender
T. Bruhn
A. B. Garnsworthy
G. Hackman
S. Ketelhut
K. G. Leach
B. Mills
M. Moukaddam
M. M. Rajabali
E. Tardiff
C. Unsworth
H. Bouzomita
G. F. Grinyer
J. C. Thomas

B. Blank
J. Giovinazzo

J. R. Leslie

C. Andreoiu
D. S. Cross
P. Voss
R. A. E. Austin