EURONS 2007 1
The LPCTrap experiment
Measurement of the ββββ-νννν angular correlation parameterin 6He ββββ-decay
Alain MERYLPC Caen
EURONS meeting
April 11-15, 2007, Saariselkä, Finland
Outline:
-Motivations
- Experimental Set-up
- Preliminary results (2006)
- Improvements
- Conclusion & outlook
Standard Model:Weak Interaction = Vector and Axial currents (V-A theory)
No Tensor or Scalar currents
Weak interaction and ββββ decay
Decay rate distribution for allowed β transitions: (Jackson 1957)
a : β-ν angular correlation parameter
eν .
−e +He
6++
Li6
θ
ν
ν
ννν θ ee
e
e
e
e
eeeeee ddEEE
ppa
E
mbENEZFCddEEN Ω
++=ΩΩ cos
.1)(),(),( 0
eeLiHe ν++→−6
3
6
2
(depends on the coupling constants of weak interaction)
- Pure Gamow-Teller transition (∆J = +1)
- Half life T1/2 = 0.806 s
-Tβmax=3.5 MeV
-TRmax=1.4 keV
- Production @ SPIRAL: ~ 108 pps
Most precise measurement : Johnson et al. 1963
0030.03308.0 ±−=GTa
For pure Gamow-Teller transitions :
3
1a GT −=SM predicted value :
ββββ-νννν correlation parameter
2'2
2'2
2'2
2'2
3
1
TTAA
TTAA
GT
CCCC
CCCCa
+++
−−+−=
(from 6He β-decay)
Measurement in coincidence of the electron and the recoiling ion
3 observables : - β energy- ion Time Of Flight- β-ion angle
LPCTrap experiment
� Control of systematic effects
LPCTrap experiment
Cinematic of the decay in this ‘back-to-back’ configuration:
Ion TOF (ns)
ββ ββen
erg
y(k
eV
)
( a=-1/3 )
ν
ν
ννν θ ee
e
e
e
e
eeeeee ddEEE
ppa
E
mbENEZFCddEEN Ω
++=ΩΩ cos
.1)(),(),( 0
LPCTrap experiment
___ Axial ( a = -1/3 )
___ Tensor ( a = +1/3 )
Ion TOF (ns)
Nb of evts for 0.5 % precision : ~ 106 evts
���� a value extracted from comparison with Monte-Carlo simulations
Cinematic of the decay in this ‘back-to-back’ configuration:
LIRAT
LIRAT
RFQ
Trap
Production target ECR source
Primary beam : 13C at 75 MeV/ATarget: 12C
SPIRAL and the LIRAT beam line
Source offline
RFQCB
LIRAT
Paul trap +Detection setupRIB
6He+
E~10 keV
ProductionSeparationTransport
Beam preparationCooling & Bunching (H2)
FWHM(TOF) ≈ 500 nsUp to a few 106 ions per bunches
Trapping &
β decay measurement
LPCTrap setup
RFQ Cooler Buncher Paul trap
LPCTrap setup
1 cm
- 6 rings- opened geometry- potential well ~ 10 Volts
The transparent Paul trap (Delahaye 2002)
Injection : 20 %Capacity : > 105 ionsLife time : > 1 second
(6Li+ ions,VRF = 120 Vpp, fRF = 1.15 MHz)
1 cm
The transparent Paul trap (Delahaye 2002)
Ion cloud:size : ~1mmtemperature : ~ 0.1 eV
(from simulation)
� Evolution of the decay source with RF voltage
Ion bunchesfrom RFQ
ββββ telescopeEnergy + Position
Paul trap
Recoil ion detectorTOF + Position
Detection Setup
DSSSD +Plastic scintillator
MCP +Delay lines
Ion beam from LIRAT: . E = 10 keV
. ~ 1.5 108 6He+/s (~20 pA)
. from 100 pA to 100 nA 12C2+ ions
No significant effect of 12C2+ beam contamination on RFQ transmission
slit FH13D (mm)
Inte
nsit
y(p
ps)
6He experiment (July 2006) : Preliminary results
Coincidence rate: ~ 0.5 per second
105 coincidence events
� statistical error < 2 %
� study of systematic effects
Transmissions : RFQ = 3 %transfert = 2 %trapping = 9 %
~ 700 trapped ions(extraction rate: 1OO ms)
6He experiment (July 2006) : Preliminary results
Signal/Background ratio ≈ 10
‘background’ = accidental coincidencescoincidence events from gaz or implanted ions
6He experiment (July 2006) : Preliminary results
Cinematic of the decay : Reconstruction of the neutrino mass
- Global shape of the Mν � identification of other decay sources
- Width = resolution of the detection set-up
Te , TOF, θθθθ ���� Mνννν
- a = -1/3 - realistic ion cloud
space phase- detectors resolution- no RF voltage- no β scattering
Simulation parameters:
6He experiment (July 2006) : Preliminary results
Cinematic of the decay : Reconstruction of the neutrino mass
- Global shape of the Mν � identification of other decay sources
- Width = resolution of the detection set-up
accidental coincidences+…
Te , TOF, θθθθ ���� Mνννν
6He experiment (July 2006) : Preliminary results
Cinematic of the decay : Reconstruction of the neutrino mass
���� Selection of events coming from the trap
Ion TOF (ns)
ββ ββen
ergy
(keV
)
6He experiment (July 2006) : Preliminary results
Cinematic of the decay : Reconstruction of the neutrino mass
���� Selection of events coming from the trap
Signal/Background ratio ≈ 100
2/1 cMeVM
Cinematic of the decay : Reconstruction of the neutrino mass
���� Selection of events coming from the trap 1
� a value extracted from adjustement with TOF spectrum
Experimental data:
- Substraction of accidental events
- Signal in DSSSD
- a = -1/3 - realistic ion cloud space phase- detectors resolution- no RF voltage- no β scattering
Simulation parameters:
6He experiment (July 2006) : Preliminary results
6He experiment (July 2006) : Preliminary results
Need for a complete simulation of the experiment: in progress…
6He experiment (July 2006) : Preliminary results
Experimental data:
4 different RF phases
… Have to be taken into account in the simulation
~ 20 ns
6He experiment (July 2006) : Preliminary results
► Tests with 6Li+ ions: (off-line source – E= 10 keV)
- more than 105 trapped 6Li+ ions (incoming intensity: 85 pA)
- global efficiency ~ 0.2 % (extraction rate = 100 ms)
� factor of 40 better than in 6He experiment
� 4. 106 coincidence events ???
Improvements: overall efficiency
► New PM for β detection � - factor of 2 on energy resolution
- linear response
Improvements: detection set-up
► Control of the position of MCP (and β detector) relative to the trap
�Shift – distorsion of the TOF spectrum
1 mm ↔↔↔↔ 5 ns for Tion =1.4 keV
► Control of the position of MCP (and β detector) relative to the trap
� Asymetry of events distribution
Improvements: detection set-up
LPCTrap facility :
- Efficient Cooling and Bunching of light ions (buffer gas : H2)
- Coupling to the transparent Paul trap� precision measurement in β decay
6He experiment July 2006
105 coincidence events
� first estimation of a with 2% statistical errorand investigation of systematic effects
data analysis & simulation in progress
Next 6He beam time: scheduled for 2007-2008
Conclusion
e- shake-off measurement
eeLiHe ν++→−+ ?6
3
6
2
For 6He atoms: P(1+) ≈ 90% (Carlson et al., 1963)
For 6He+ ions: no measured value for P(2+) & P(3+)
� Influence of RF field on the recoil ion trajectory
Measurement by TOF between β and accelerated recoil ion
β detector
ion detector
MCP10 kV
LPC: Gilles BanDominique DurandFlorian DuvalXavier FléchardMustafa HerbaneMarc LabalmeEtienne LiénardFrançois MaugerAlain MéryOscar Naviliat-CuncicDaniel Rodriguez+technical staff
…
GANIL: Bertrand JacquotJean-Charles Thomas
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