Transcript Neutron Lifetime - Jagiellonian University

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
Goal and Outline
• 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, 2010
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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, 2010
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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)
4. Integrate (less) spins and momenta:
triple correlations
Jn
Pp
e
p
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pe
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a, A, G, D, R contain the dynamics
and probe the symmetries
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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
space
inversion
P
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"
(·p)
"longitudinal polarization"
…Enhanced sensitivity if one combines both of them
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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
q
b
nuclear spin
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…and look for deviations
from SM
beta polarimeter
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Measurement in 12N decay
reaction chamber
spectrometer
polarimeter
B
b+
Stack
Target
(LLN, ETH-Zurich, Wisconsin, Leuven)
Injector1@PSI
 12 
• production: 12C( p
, n) N
MgO powder
• polarization analysis: time resolved
spectroscopy of hf Ps decay
stop
10 cm
TDC start
[E. Thomas et al., NP 694 (2001) 559]
Results
Decay
(R-1)x104
Lab.
107In
740±410
LLN '93
12N
6±34
PSI '01
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Can be considered as the most precise tests
of maximal parity violation in nuclear beta
decay (in terms of constraints on RHC)
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(Slow) progress on constraints: global fits
Maximal parity violation implies C’V = CV
Boothroyd, Markey, Vogel, 1984
Severijns, Beck, Naviliat-Cuncic, 2006
PRC 29 (1984) 603
RMP 78 (2006) 991
96-(61+13)+34 = 56 data values
69-1+28 = 96 data values
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Neutrino asymmetry: K MOT at TRIUMF
D.Melconian, J.Behr & Co
Top view
Side view
•
•
•
•
38mK
Pioneering work on
atom trapping
Measured the b angular correlation in 38mK
Extended setup to polarize 37K
Detect recoiling ions in coïncidence
B = -0.755(24)
J
pv
• Not competitive yet with present
constraints.
• Setup has been upgraded: new
beta detectors, larger chamber,…
• New data expected soon.
[D.Melconian et al., PLB 649 (2007) 370]
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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)
(mixed)
P-even, T-odd correlation:
P-odd, T-odd correlation:
(GT and mixed)
Do not probe the same physics
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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 (SINQ@PSI)
• Transverse polarization analysis by Mott
scattering on Pb-foil
z
scintillator
Pb-foil
y
MWPC
x
50 cm
Pb-foil
scintillator
• Tracking of electrons in low-mass, low-Z MWPC
• Identification of Mott events by vertex
• Frequent neutron spin flipping and foil IN/OUT
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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)
RSM = 0.0006(2)
Nexp = 0.056(12)
NSM = 0.068(1)
[A. Kozela at al., PRL 102 (2009) 172301]
• Determines also the N coefficient (electron
polarization along neutron spin) to check
polarimetry
MESON 2010, Cracow, June 10-16, 2010
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• Already obsolete (additionally analyzed
data will improve precision by a factor 2)
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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) 202301] (reach the FSI level).
• 8Li source ~107 pps – 80% pol. @ 30keV
• Implanted in annealed Pt at room temp.; B=500G
• Apparatus installed at TRIMF
• Test beam run planned in Nov.2010
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3. Exotic couplings
• b angular correlation
(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
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a in GT : 6He Paul trap @ GANIL
“ideal” 3D Paul trap
First transparent prototype
Fully transparent trap (rings)
URF
hat
ring
LPCTrap@GANIL
RFQ cooler
buncher
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LPCTrap results
• GOAL: Measure the b angular correlation in 6He decay with (Da/a)stat < 0.5%
• First data taking run in 2006
[X. Fléchard et al., PRL101 (2008) 212504]
All position sensitive detectors; complete kinematics
TOF
neutrino
mass
• (2008): collected 4×106 (for stat) and 2×106 (for sys studies) events.
• Statistical precision reached; data analysis under way.
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a in Fermi : WITCH Penning trap @ ISOLDE
(K.U.Leuven, Uni. Munster, ISOLDE, GSI, NPI Rez-Prague) N.Severijns et al.
Goal: measure b correlation in 35Ar with (Da/a)stat  0.5 %
• Detect recoiling ions in singles
• Select ion energies sequentially: retardation potential
First recoil ion spectrum
124Sn
[V.Yu. Kozlov et al., NIM B 266 (2008) 4515]
recoils
Retardation potential (V)
• Too low 35Ar production/transport so far
• System being upgraded
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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
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Constraints on Scalar couplings
[J.C. Hardy and I.S. Towner, PRC 79 (2009) 055502]
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Constraints on Tensor couplings
A in 114In
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Constraints on sums of exotic couplings
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