The b -delayed deuteron-decay of 6 He J. Ponsaers, R. Raabe, F. Aksouh, D. Smirnov, I. Mukha, A. Sanchez, M. Huyse, P. Van Duppen, C. Angulo, O. Ivanov, J.C. Thomas 1.Introduction 2.Experiment 3.Analysis 4.Conclusion

Discovered in 1985: high interaction cross section.[1] Extended matter distribution. 6 He is a Borromean system of a + n + n 6 He E r Usual probability density of a neutron E r Probability density of a halo neutron 6 He = 2n-halo-nucleus [1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)

II I Discovered in 1985: high interaction cross section.[1] Extended matter distribution. 6 He is a Borromean system of a + n + n 6 He E r Usual probability density of a neutron E r Probability density of a halo neutron 6 He = 2n-halo-nucleus [1] : Tanihata I. et al. ; Phys. Rev. Letters (1985)

II I Discovered in 1985: high interaction cross section.[1] Extended matter distribution. 6 He is a Borromean system of a + n + n 6 He E r Usual probability density of a neutron E r Probability density of a halo neutron 6 He = 2n-halo-nucleus [1] : Tanihata I. et al. ; Phys. Rev. Letters (1985) We want to measure: Branching ratio of the decay channel II: very small (~10 -6 )  very difficult Energy spectrum of the decay particles E a +d

Information provided by the deuteron-branch of 6 He 1. High branching ratio  dineutron correlation

Information provided by the deuteron-branch of 6 He 1. High branching ratio  dineutron correlation 2. Low branching ratio  cigar correlation

Information provided by the deuteron-branch of 6 He [1] K. Riisager et al., Phys. Lett. B 235(1990)30 [2] M. J. G. Borge et al., Nucl. Phys. A 560(1993)664 [3] D. Anthony et al. Phys., Rev. C 65(2002) [ 4] P. Descouvement and C. Leclercq- Willain, J. Phys. G 18(1992)L99 [5] M. V. Zhukov et al., Phys. Rev. C 47(1993)2937 [6] A. Csoto and D. Baye, Phys. Rev. C 49(1994)818 [6] suggests that we need a detailed description of the wave functions to explain the decay. 1. High branching ratio  dineutron correlation 2. Low branching ratio  cigar correlation

The method Problems in previous experiments: High threshold energies for deuterons Large uncertainties (difficult to normalize)

The method Problems in previous experiments: High threshold energies for deuterons Large uncertainties (difficult to normalize) New method: 6 He implantation in DSSSD (Double Sided Silicon Strip Detector)  This can count implantations AND a + d decays

The method DSSSD divided into 48 strips x 48 strips = 2304 pixels Small pixel size (300mm) Get the energy drop of b -particles below the spectrum of the br.ratio No problem for a + d detection Problems in previous experiments: High threshold energies for deuterons Large uncertainties (difficult to normalize) New method: 6 He implantation in DSSSD (Double Sided Silicon Strip Detector)  This can count implantations AND a + d decays

The experiment Beam on (1s): implantation and detection of 6 He nuclei  number of implantations counted  absolute normalization for br.rat. very accurate Beam off (2s): detection of decay of 6 He nuclei caught inside the detector 6 He nuclei at 8 MeV periodically implanted into DSSSD detector. Experiment: performed at CRC, Louvain-la-Neuve, Belgium

Analysis 1. b -peak 2. 6 He implants 3. partial E-collection Beam on + off E (keV) 2 1 (Number of events)/(10keV) 3

Beam off E (keV) (Number of events)/(10keV) 1 Analysis 1 Time spectrum exp. fit 1: T 1/2 = 806.0ms 1. b -peak 2. 6 He implants 3. partial E-collection 4. a + d events Beam on + off E (keV) 2 1 (Number of events)/(10keV) 3 4

Beam off E (keV) (Number of events)/(10keV) 1 Analysis 1 Time spectrum exp. fit 1: T 1/2 = 806.0ms 1. b -peak 2. 6 He implants 3. partial E-collection 4. a + d events Beam on + off E (keV) 2 1 (Number of events)/(10keV) 3 4 Suspicious: background much higher than expected!

Beam off E (keV) (Number of events)/(10keV) 1 Analysis Beam off E (keV) Time spectrum exp. fit 1: T 1/2 = 806.0ms 2: T 1/2 = 1102ms 1. b -peak 2. 6 He implants 3. partial E-collection 4. a + d events Beam on + off E (keV) 2 1 (Number of events)/(10keV) Suspicious: background much higher than expected! 3 4

Beam off E (keV) (Number of events)/(10keV) 1 Beam off E (keV) Time spectrum exp. fit 1: T 1/2 = 806.0ms 2: T 1/2 = 1102ms 1. b -peak 2. 6 He implants 3. partial E-collection 4. a + d events Beam on + off E (keV) 2 1 (Number of events)/(10keV) Suspicious: background much higher than expected! 2.New fit: 162 ± 69 background events425 a + d events 3 4 Analysis

Total branching ratio: W = (2.03 ± 0.35) x Corresponds with the value from microscopic description Large uncertainty from background events. No reliable energy spectrum of a + d because we don’t know the energy spectrum of the background. Conclusion and outlook New measurement on 6 He in Louvain-la-Neuve Same experiment on 11 Li at TRIUMF