1. Neutron-Neutron Correlations in the Dissociation of Halo Systems: 6He
Group "Exotiques" LPC-Caen
Collaboration LPC-CHARISSA-DEMON

2. Neutron-Neutron Correlations in the Dissociation of Halo Systems: 6He
Motivation + History
Principles of neutron-neutron interferometry
6He breakup
Limitations – coherence, theory…
Conclusions & Perspectives

3. Two-Neutron Halo Systems 
“Borromean”

4. n-n interaction in field of core binds the system ...
Two-Neutron Halo Systems 
n-n interaction in field of core binds the system ...

5. Halo neutron correlations … ?
Two-Neutron Halo Systems 
rnn
Halo neutron correlations … ?

6. Halo n-n Spatial Configuration
6He
“cigar”
“dineutron”
RNBT Collaboration – 3-body Faddeev

7. 3-body Model Calculations * : 6He = a + n +n
ground state wavefunction
“cigar”
“dineutron”
r1 = r2 =
rc-nn = 3.6 fm ; rnn = 4.6 fm
* Hagino, Sagawa, Phys Rev C72 (2005)

8. A History of Probes … dissociation: pcore v’s pn [Hansen]
dissociation: pnn [Ieki et al.]
very high EB dissociation: s-2n v’s s-1n [Bertsch et al.]
see also JA Tostevin (today)
2n transfer [Oganessian et al.]
see also T Roger, N Keeley (yesterday)
radiative capture [Sauvan et al.]
dissociation: E1 strength + Rrms [Hagino, Sagawa]
Rrms charge [Mueller et al.] ……

9. “That was the beginning, and the idea seemed so obvious to me and so elegant that I fell deeply in love with it. And, like falling in love with a woman, it is only possible if you do not know much about her, so you cannot see her faults. The faults will become apparent later, but after the love is strong enough to hold you to her."
Richard Feynman
Nobel Lecture (1965)

10. Correlation Function - Cnn
Intensity Interferometry - HBT Effect* : Source Size
Correlation Function - Cnn
FM Marqués et al., PLB (2000)
Cnn dominated by n-n FSI * incoherent emission

11. Cnn(r,t) : r0 = 3 fm ; t = 0, 100, 300*, 1000 fm/c
* 5Hegs G ~ 0.7 MeV
Group Exotiques - G. Normand et al.

12. 3-Body Breakup: “Complete Kinematics”
vn1
vn2 v0
vcore
Target
pn-n = pn1 - pn2 Erel = m(vcore- vnn)2/2

13. Intensity Interferometry - HBT Effect
U. of Sydney Stellar Interferometer, Narrabri, NSW
“Hanbury-Brown’s Steamroller“ D Kleppner, Physics Today, August 2008

14. Setup: Kinematically “Complete” Measurement
DEMON
90 modules (NE213)
 ToF & position
en ~ 10% enn ~ 1%
FM Marqués et al., NIMA450 (2000)
+ Cross-talk Rejection !!

15. n-n Separation : EMD + Cnn + Gaussian Source*
* R Lednicky, VL Lyuboshits, Yad. Fiz. (1982)
Event mixing – residual correlations
FM Marqués et al., PLB (2000)

16. * * * rnn  average of n-n configurations of 6He breakup states
30 MeV/u : Cnn + Gaussian Source * *
* rnn  average of n-n configurations of 6He breakup states
Group Exotiques - G. Normand et al.

17. C/Pb(6He,a+n+n)X @ 30 MeV/nucleon2+ 2+
(1-, … )
Group Exotiques - G. Normand et al.

18. C/Pb(6He,a+n+n)X @ 30 MeV/nucleon2+ 2+
Ed(6He) after subtraction of uncorrelated distribution
Groupe Exotiques - G. Normand et al.

19. Three-body continuum spatial correlations in 6He *
* B Danilin et al., PRC69 (2004)

20. Effects of a coherent n-n source *
* Yamashita et al., PRC72 (2005), NUPA735 (2004) [ Data: FMM et al. PLB (2000) ]

21. Conclusions & Perspectives
Neutron-neutron correlations …
breakup + “interferometry˝ (Cnn) as a possible tool to explore halo n-n correlations in unbound Ex/continuum
Improvements …
First step : account for coherence in emission
Ideally : realistic structure + reaction + FSI to generate pnn, Cnn, pcore, ds/dE, …

22. Pb(11Li,9Li+n+n)X @ 28 MeV/nucleon
3-body model wave function + EMD + FSI (c-n et nn)
H Esbensen et al., PRC48 (1993)

24. C/Pb(6He,a+n+n)X @ 30 MeV/nucleon
Group Exotiques - G. Normand et al.

25. C/Pb(6He,a+n+n)X @ 240 MeV/nucleon
GSI/LAND – T. Aumann et al.