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