1. Tests of symmetries with nuclei (in nuclear b decay)
Oscar Naviliat-Cuncic
LPC-Caen, (ENSI–CNRS/IN2P3) and
Université de Caen Basse-Normandie
Caen, France

2. Goal and Outline 1. General context
Review achievements of precision measurements in nuclear beta decay aiming to test fundamental symmetries.
Present (selected) ongoing projects.
(Biased choice)
1. General context
2. Tests of Maximal parity violation
3. Tests of Time Reversal Invariance
4. Searches for other exotic interactions
5. Summary
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

3. Context and motivations
evidence for “new physics” is expected to manifest itself either at the high energy frontier (direct production of new particles) or at the high precision frontier (search for tiny effects).
effects have to be looked for everywhere where improvements in experimental sensitivities are possible (atoms, nuclei, particles) (unless strong theoretical counter arguments)
consider here experiments in nuclear beta decay (including neutron)
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

4. Beta decay correlations
What we imagine to occur
(at the quark-lepton level)
1. Integrate over all vectors:
decay rates or lifetimes
2. Integrate/average over all spin vectors: angular correlation
3. Integrate some spins and momenta:
pseudo-scalar correlations
What we have access to
(experimentalist toolbox) e pe Pp Jn p
4. Integrate (less) spins and momenta: triple correlations
a, A, G, D, R contain the dynamics and probe the symmetries
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

5. P 1. Parity violation P is assumed to be maximally violated in the SM
Searching for deviations probe new physics (like RHC)
Look at pseudo-scalar quantities P
space inversion
r → -r
axial vector J → J (invariant)
polar vector p → -p (changes sign)
Terms in the decay rate distribution that change sign under parity
( J · p ) "decay asymmetry"
( s · p ) "longitudinal polarization"
…Enhanced sensitivity if one combines both of them
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

6. Polarization-Asymmetry correlation
“Beta particles from polarized nuclei should be polarized”
H.A. Tolhoek and S.R. DeGroot Physica 17 (1951) 1
Absolute b longitudinal polarization from polarized nuclei
(within V-A)
A asymmetry parameter
J degree of nuclear polarization
q angle between J and pe
Perform relative measurement at different emission angles J
beta polarimeter b
nuclear spin q
…and look for deviations from SM
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

7. Measurement in 12N decay b+ Decay (R-1)x104 Lab. 107In 740±410 LLN '93
Stack Target
reaction chamber
10 cm
TDC start
stop
spectrometer
polarimeter b+ B
MgO powder
(LLN, ETH-Zurich, Wisconsin, Leuven)
production:
polarization analysis: time resolved spectroscopy of hf Ps decay
[E. Thomas et al., NP 694 (2001) 559]
Results
Decay
(R-1)x104
Lab.
107In
740±410
LLN '93
12N
6±34
PSI '01
Can be considered as the most precise tests of maximal parity violation in nuclear beta decay (in terms of constraints on RHC)
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

8. (Slow) progress on constraints: global fits
Maximal parity violation implies C’V = CV
Boothroyd, Markey, Vogel, 1984
PRC 29 (1984) 603
Severijns, Beck, Naviliat-Cuncic, 2006
RMP 78 (2006) 991
= 96 data values
96-(61+13)+34 = 56 data values
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

9. Neutrino asymmetry: K MOT at TRIUMF
D.Melconian, J.Behr & Co
Top view
Side view J pv
Not competitive yet with present constraints.
Setup has been upgraded: new beta detectors, larger chamber,…
New data expected soon.
Pioneering work on 38mK atom trapping
Measured the bn angular correlation in 38mK
Extended setup to polarize 37K
Detect recoiling ions in coïncidence
Bn = (24)
[D.Melconian et al., PLB 649 (2007) 370]
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

10. 2. Time reversal invariance
T violation = CP violation
In processes involving the lightest quarks, the CKM CP violating effect is strongly suppressed (out of experimental reach)
Large window for new physics (provided FSI effects are accounted for) T
Time reversal
t → -t
axial vector J → -J (changes sign)
polar vector p → -p (changes sign)
P-even, T-odd correlation:
P-odd, T-odd correlation:
(mixed)
(GT and mixed)
Do not probe the same physics
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

11. R in a mixed transition : neutron at PSI
(Cracow, PSI, Caen, Leuven, Katowice) lead by Prof. K.Bodek & Co
Maximum sensitivity for mutually perpendicular vectors
Polarized cold neutrons
Transverse polarization analysis by Mott scattering on Pb-foil
MWPC
scintillator
Pb-foil
50 cm
Tracking of electrons in low-mass, low-Z MWPC
Identification of Mott events by vertex
Frequent neutron spin flipping and foil IN/OUT
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

12. R in a mixed transition : neutron at PSI
Analysis in terms of geometric form factors averaged over the setup geometry
Vertex identification
Example of data sample
Pb-foil
Rexp = 0.008(16) Nexp = 0.056(12)
RSM = (2) NSM = 0.068(1)
[A. Kozela at al., PRL 102 (2009) ]
Already obsolete (additionally analyzed data will improve precision by a factor 2)
Determines also the N coefficient (electron polarization along neutron spin) to check polarimetry
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

13. R in a GT : 8Li at TRIUMF
(Rikkyo, KEK, TRIUMF), J.Murata & Co.
Goal: improve by a factor 20 the best measurement so far in a GT transition [R. Huber et al., PRL 90 (2003) ] (reach the FSI level).
8Li source ~107 pps – 80% 30keV
Implanted in annealed Pt at room temp.; B=500G
Apparatus installed at TRIMF
Test beam run planned in Nov.2010
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

14. 3. Exotic couplings bn angular correlation within the SM beyond the SM
(even under P and T transformations)
within the SM
x : Fermi fraction; r : GT/F mixing ratio
beyond the SM
a contains quadratic S and T contributions
…detect the recoiling ion to deduce neutrino momentum
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

15. a in GT : 6He Paul trap @ GANIL
“ideal” 3D Paul trap
First transparent prototype
Fully transparent trap (rings)
URF
ring
hat
RFQ cooler
buncher
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

16. LPCTrap results
GOAL: Measure the bn angular correlation in 6He decay with (Da/a)stat < 0.5%
First data taking run in [X. Fléchard et al., PRL101 (2008) ]
All position sensitive detectors; complete kinematics
neutrino
mass
TOF
(2008): collected 4×106 (for stat) and 2×106 (for sys studies) events.
Statistical precision reached; data analysis under way.
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

17. a in Fermi : WITCH Penning trap @ ISOLDE
(K.U.Leuven, Uni. Munster, ISOLDE, GSI, NPI Rez-Prague) N.Severijns et al.
Goal: measure bn correlation in 35Ar with (a/a)stat  0.5 %
Detect recoiling ions in singles
Select ion energies sequentially: retardation potential
First recoil ion spectrum
Retardation potential (V)
124Sn recoils
[V.Yu. Kozlov et al., NIM B 266 (2008) 4515]
Too low 35Ar production/transport so far
System being upgraded
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

18. Summary
Precision measurements in nuclear beta decay have made significant progress over the past decade. (progress is slow)
Dozens of new projects using radioactive nuclei, cold neutron beams and UCNs are under way (patience needed)
New results are expected soon, in particular from experiments with atom and ion traps.
Thanks to: K.Bodek, D.Melconian, J.Murata, N.Severijns, for inputs
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

19. Constraints on Scalar couplings
[J.C. Hardy and I.S. Towner, PRC 79 (2009) ]
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

20. Constraints on Tensor couplings
A in 114In
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic

21. Constraints on sums of exotic couplings
MESON 2010, Cracow, June 10-16, O. Naviliat-Cuncic