testing the standard model in beta-decay · 2018. 12. 10. · 6he decay...
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Testing the Standard
Model in beta-decay:status and prospects
PSI 2016October 20th, 2016
Nathal Severijns
KU Leuven University, Belgium
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Outline
- Exotic weak currents
scalar / tensor contributions
- correlation / beta asymmetry measurements
- Nuclear / neutron beta decay versus LHC
- Weak magnetism
- Beta spectrum shape measurements
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1. Exotic weak currents (scalar, tensor)
e
e
p qa
E E
=
1
e
e
mb
E
aa
2with 1 ( )Z
2A
2'T
2T
2V
2's
2S
|C|
|C| |C| 1
3
1
|C|
|C| |C| 1
GT
F
a
a
A
'TT
V
'SS
C
C C e
C
C C e
Rb
Rb
GT
F
Fierz term
a) - correlation
exp.
!!! for pure transitions weak interaction results are
independent of nuclear matrix elements !!!
(assuming maximal P-violation and T-invariance for V and A interactions)
recoil corr. (induced form factors) 10-3 ; radiative corrections 10-4
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Limits on scalar currents
32Ar: Adelberger et al., PRL 83 (1999) 1299
B. R. Holstein, J. Phys. G 41 (2014) 114001
'
1
(1 )Fb
with
'' e S SF
e V
m C Cb
E C
(Fierz term)
Hardy & Towner , Phys. Rev. C 91 (2015) 025501
38mK: Gorelov, Behr et al., PRL 94 (2005) 142501
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- TRINAT (MOT): 38mK repeat (prep.)
- LPCTrap @ GANIL (Paul): 19Ne, 35Ar (analysis)
- Jerusalem (MOT): 19Ne (prep.)
- TamuTrap, Texas A&M (Penning): 32Ar, … (T = 2, βp) (prep.)
- WISARD @ ISOLDE (foil): 32Ar, … (T = 2, βp) (prep.)
0 2 4 6 8 10 120
1000
2000
3000
<1 % 35
Cl5+
1.7 (0.2) % 35
Cl4+
5.7 (0.2) % 35
Cl3+
17.3 (0.4) % 35
Cl2+
Counts
/ tim
e b
in
Time of flight (s)
74.6 (1.0) % 35
Cl+
35Cl charge state distrib.
from the decay of 35Ar
(LPCTrap - GANIL)
a/a ~ 0.3%(analysis in progress)
ongoing experiments in search for scalar weak currents:
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Tensor currents - -- correlation with Paul-trapped 8Li Ions
aβν = −0.3342 (26)stat (29)sys
M.G. Sternberg, G.Savard et al., PRL 115 (2015) 182501
Tensor currents - LPCTrap @ GANIL - 6He
-particle breakup of 8Be*Axial
Tensor
2006 (6He): aβν = −0.3335(73)stat(75)syst X. Fléchard et al. J. Phys. G 38 (2011) 055101
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Tensor currents - 6He EIB Trap (Weizmann Inst., Univ. Jerusalem, … )(M. Hass, G. Ron et al.)
Tensor currents - 6He MOT Trap setup @ Univ. Washington, Seattle
A. Knecht et al., NIM A 660 (2011) 43, Phys .Rev. C 86 (2012) 035506 & arXiv:1208.6433v2 [nucl-ex]
0.1 % measurement - 2015
P. Mueller, A. Garcia, et al.
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b) -asymmetry parameter in nuclear beta decay
pol
unpol
N(θ) vW(θ) = = 1 + A P Q cosθ
N(θ) c
Geant4
Analysis:
SM
SM
exp exp
Geant
Geant
v A P Q cosθ
W(θ) 1 c A = =
v W(θ) 1 A A P Q cosθ
c
(P from independent meast.)
''
' with
1
e T TGT
GT e A
m C CAA b
b E C
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Geant4
F. Wauters et al.,
Phys. Rev. C 82 (2010) 055502
Nucl. Instr. Meth. A 604 (2009) 563
3He - 4He dilution refrigerator set-up
magnet
3He-4He
system
region
analysed
3He - 4He dilution refrigerator set-up
60Co, B = 13 T
(KU Leuven, NICOLE-ISOLDE,
NPI Rez-Prague, Uni Bonn)
experiment
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F. Wauters et al., Phys.
Rev. C 80 (2009) 062501(R)
Aexp (60Co) = - 1.014 (12)stat (16)syst
Aexp (114In) = - 0.990 (10)stat (10)syst
Aexp (67Cu) = 0.587(8)stat (12)syst
F. Wauters et al., Phys. Rev. C 80 (2009) 062501(R)
F. Wauters et al., Phys. Rev. C 82 (2010) 055502
G. Soti et al., Phys. Rev. C 90 (2014) 035502
β asymmetry – Leuven / ISOLDE / Prague 3/3
60CoCu , Bext = 13 T
114InFe , Bhf = 27 T
67CuFe , Bhf = 21 T
IS431-experiment
I
60CoCu
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Limits on tensor currents
A(60Co)
A(67Cu)
a(6He)
--(8Li)
a(6He)C. Johnston et al.,
PR 132 (1963) 1149
--(8Li)M.G. Sternberg, G.Savard et al.,
PRL 115 (2015) 182501
A(60Co)F. Wauters, N.S. et al.,
PR C 82 (2010) 055502
A(67Cu)G. Soti, N.S. et al.,
PR C 90 (2014) 035502
Also: Poster F. Lenaers – 35Ar
PhD Behling 2015 – 37K
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O. Naviliat-Cuncic and M. Gonzalez-Alonso
Annalen der Physik 525 (2013) 600.
V. Cirigliano, et al.,
J. High. Energ. Phys. 1302 (2013) 046
90% CL90% CL
nuclear and neutron decay, pion decay limits on scalar/tensor couplings
obtained by CMS collaboration in
pp e + MET + X channel
S. Chatrchyan et al. (CMS Collab.)
J. High. Energ. Phys. 08 (2012) 023
2. Measurements in nuclear/neutron decay in the LHC era
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weak magnetism bWM
3. Good knowledge of induced / recoil terms required
neutron / nuclear beta decay:
quark involved in β decay is not free
but bound in a nucleon
extra terms induced by strong interaction
affects values for correlation coefficients at level of per mil to 1%
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GT decays of isospin triplet states
from -valueA GTc g M ft
weak magnetism term bWM (CVC) (N.S. et al., in prep.)
T = 1/2 J J mirror transitions
0
( )
( ) 1
M D
WM F
Jb A M
J
F.P. Calaprice and B.R. Holstein, NP A 273 (1976) 301
N. Severijns, I.S. Towner et al., PR C 78 (2008) 055501 from -valueA GTc g M t
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weak magnetism term bWM - experimental data
1
4
3
= 0.8(4)% MeV
n
dN b
dE M Ac
AN. Severijns, I.S. Towner, et al., to be published
12
10
8
6
4
2
0
-2
mirror transitions: - updated Ft-values (A < 75; rel. prec. < 0.2% for A < 41)
- extracted weak magnetism form factor
bWM/Ac
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weak magnetism term bWM - experimental data
N. Severijns, I.S. Towner, et al., to be published
1
4
3
= 0.8(4)% MeV
n
dN b
dE M Ac
A
mirror transitions
j = l - 1/2
WM p nb
j = l + 1/2
12
10
8
6
4
2
0
-2
bWM/Ac
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weak magnetism bWM - mirror transitions
N.S., I.S.Towner et al., to be published
------------------------------------------------
mirror (A = 3-45) 0.97(11)
triplet (A = 6-30) 1.01(15)WM VM L
A A GT
b gg M
Ac g g M
B. R. Holstein, RMP 46 (1974) 789
F.P. Calaprice et al., PR C 15 (1977) 2178
avg = 0.96(8)
avg = 1.01(25)
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MSU-NSCL
also of interest to Reactor Neutrino Anomaly
Mueller et al.,
Phys. Rev. C 83
(2011) 054615
Too crude approximation for bWM in fission fragment beta decays
may be (in part) responsible (see also A.C. Hayes et al., PRL 112 (2014) 202501)
Poster by L. Hayen
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bWM/Ac
AA
A
|c|
j = l - 1/2
j = l + 1/2
1
Effect on spectral shape:
1 +
4
3
Shift of by 0.5% MeV
shift in -rate of -1%
WM
n
E
dN b
dE M Ac
dN
dE
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New vistas and prospects in the LHC era
- new generation of (trap-based) correlation experiments
towards 0.1% precision level
- precise -spectrum shape measurements:
bFierz : scalar / tensor weak currents
bWM : weak magnetism (Standard Model term)
- induced by strong interaction because decaying quark is
not free but bound in a nucleon;
- is to be known better when reaching sub-percent precisions
Note the different energy dependence of both effects !!
'1 ( , ) 1 k F Fierz WMd G F Z E b k E b
E
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e+
e
nucleus
Analytical description + code,
accurate to few 10-4 level
L. Hayen, N. Severijns et al., in prep.
4. spectrum shape measurements
Poster by L. Hayen
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miniBETA spectrometer (Leuven / Krakow)
multi-wire drift chamber
scintillator (later DSSDD)
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double-Si spectrometer (Leuven / LANL, A. Young)
two 2 mm segmented Si detectors in B- field, replacing UCNA MWPCs
- data in May 2016
- analysis ongoing
Talk of J. Wexler
2 mm Si45Ca
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[Run182-segs:0,1-Ew:500-2500]
6He decay
[Run145-segs:0,1,2-Tw:550-850]
Pile-up
fraction
<1.8x10-3
Electron kinetic energy (chan)
• Long term goal: Measure the Fierz interference term
(b) in 6He decay to search for weak tensor currents.
• Current goal: measure the weak magnetism (WM)
form factor in 6He decay for a tests of the strong form of
CVC. The WM is the largest "hadronic SM background"
in a measurement of b.
Effect of weak magnetism(Monte-Carlo simulation)
2×107 events• Principle: use a fragmented separated beam to eliminate distortions in beta spectrum due to back-scattering, out-scattering or dead-layers.
6He
46 MeV/A
Experiment at NSCL range of
particles
radioactive 6He source
single detector
Beta energy spectrum shape in 6He decay - NSCL/MSU
Collected statistics
enables extracting
the WM form factor
at ~5% relative error
(O. Naviliat-Cuncic et al.)
2%Poster of Xuejing Huyan
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microcalorimeter measurements (CEA-Saclay)
X. Mougeot et al., PR A 86 (2012) 042506 and PR A 90 (2014) 012501
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1. - correlation and asymmetry measurements + Ft-values
improved limits on scalar and tensor type weak currents;
2. searches for new physics (bosons) at low energies are competitive
with direct searches at LHC for 10-3 precisions of b and beyond
many experiments ongoing or in preparation / planned
3. at sub-0.5% level of precision have to include effects induced by strong interaction
largest is weak magnetism
best observable: beta-spectrum shape
scalar / tensor currents & weak magnetism
Conclusions and Outlook
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e+
e
nucleus
distribution in
- electron and neutrino directions and in
- electron energy
from polarized nuclei :
Fermi
function
phase space
Fierz
interference term
( b 0 in
standard model )
-
correlation
-asymmetry
e
e
p qa
E E
2
= with = (1- Z
1
e
e
mb
X
E
X
J.D. Jackson, S.B. Treiman, H.W. Wyld, Nucl. Phys. 4 (1957) 206
R-correlation
0d nuclear
matrix elements
J
p
e
e
pJA
J E
20 ( , ) ( ) x
x 1 .. .
e e e e e e
e
e
e
e e
e
p q pJa A
d F Z E p E E E dE d d
EE
m
E J Eb
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the Standard Model and beyond:
* CA = -1.27 ( gA/gV = -1.2699(7) from n-decay )
* CV’ = CV & CA
’ = CA (maximal P-violation)
* CS = CS’ = CT = CT
’ = CP = CP’ 0 (only V- and A-currents)
experimental upper limits: at few % level
(neutron and nuclear -decay)
N.S., O. Naviliat-Cuncic and M. Beck, Rev. Mod. Phys. 78 (2006) 991,
J. Nico, J. Phys. G 39 (2009) 104001,
D. Dubbers and M.G. Schmidt, Rev. Mod. Phys. 83 (2011) 1111,
V. Cirigliano et al., Prog. Part. Nucl. Phys. 71 (2013) 93,
F. Wauters et al., Phys. Rev. C 89 (2014) 025501,
B.R. Holstein, J. Phys. G 41 (2014) 114001.
* no time reversal violation(except for the CP-violation described by the phase in the CKM matrix)
( ' ) ( ' )/ and / T A S VC C C C
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T. Bhattacharya et al., Phys. Rev. D 85 (2012) 054512
V. Cirigliano, et al., J. High. Energ. Phys. 1302 (2013) 046
O. Naviliat-Cuncic and M. Gonzalez-Alonso, Annalen der Physik 525 (2013) 600.
V. Cirigliano, et al., Progr. Part. Nucl. Phys. 71 (2013) 93
Precision measts in nuclear/neutron decay in the LHC era
if particles that mediate new interactions are above threshold for LHC
Effective Field Theory allowing
direct comparison of low-energy and collider constraints
low-scale O(1 GeV) effective Lagrangian for semi-leptonic transitions
(contributions from W-exchange diagrams and four-fermion operators)
link betw. EFT couplings i and Lee-Yang nucleon-level effect. couplings Ci:
(0) with ( ), 4 ( ), ...
2
Fi ud i S S S S T T T T
GC V C C g C g
(0)2 2 1/2
3
, / with = (2 2 ) 170 GeV
if 5 TeV 10
i i BSM F
BSM i
G
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Vud quark mixing matrix element & CKM unitarity
Hardy & Towner , Phys. Rev. C 91 (2015) 025501
= 3072.27(72) s
from
experiment
nucleus dependent
corrections nucleus independent
|Vus| = 0.2253(8) (PDG14)
|Vud| = 0.97417(21)
Hardy & Towner, PR C 91 (2015) 025501
2 2 2 0.99978(55)ud us ubV V V
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prospects - 1
1. pure Fermi transitions: - new data to improve Ft values
- testing isospin corrections C
- nucleus-independent radiative correction R
3. T = 1/2 mirror transitions:
A GT
V F
C M
C M 2 0 0
2 21 2 =
(1 )
A
V
mirror
V
F ud R
f
f
KFt Ft
G V
O. Naviliat-Cuncic & N.S., PRL 102 (2009) 142302
N.S. , I.S. Towner et al.,
Phys. Rev. C 78 (2008) 055501|Vud| = 0.9719(17)
2. neutron decay: - lifetime (tSPECT, … )
- beta-asymmetry parameter A (PERKEO, UCNA)
- -correlation a (aSPECT, Nab, AbBa, aCORN, … )
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e+
e
nucleus
6. spectrum shape measurements
- phase space factor x constants
- F(Z,p): Fermi function
- L0 & C: finite size of nucleus
- Rn : finite mass of nucleus
- RC: radiative corrections
- S(E): spectrum shape factor
141 0.8 % MeV
3
WMe
n
bdNE
dE M Ac
( for a pure GT transition and neglecting terms 1/M2 and me2/E )
' '' ( , ) 1 Fierz
F WM
bd G F Z E k b E k
E