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TRANSCRIPT
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V. Lapoux et N. Alamanos
We have reanalyzed the date of direct reactions induced by the
radioactive 6,8He nuclei. The idea was to study their consistency and
use these data as a bench mark to test the validity of the different
structure theories.
V. Lapoux and N. Alamanos from a review paper to be published
The context :
Scattering of 6,8He nuclei on proton targets
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V. Lapoux et N. Alamanos 2
Nuclear Physics of exotic nuclei is a 30 years old field. In the beginning of the 1990
nuclear physics was crossing a very difficult period. Since ten years, GANIL was
delivering, beams with the aim to study central collisions ….. The board of directors
was questioning the future of the discipline.
With the advent of the physics of exotic nuclei we have hired a new generation of
experimentalists and theoreticians and this was beneficial not only for the physics at
the drip lines but for the ensemble of the field.
With new tools the theoreticians and reshaping the old nuclear physics landscape.
Physics of exotic nuclei
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V. Lapoux et N. Alamanos 3
Weakly‐bound Borromean structures of the exotic 6,8He nuclei
through direct reactions on proton
o Introduction about exotic nuclei physics
o An experimental setup
o Weakly‐bound Borromean structures of :
The exotic 6,8He nuclei (structure, excited states, radii, transition densities,…)
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V. Lapoux et N. Alamanos 4
Ground state
Mass, deformation, superfluidity, size…
Spectroscopy
Reaction processes
Fusion, transfer, knock‐out…
Limits of existence
Drip lines, mass, clusters, halos… excitation modes
Radioactive decays
(2), , (2)p, fission…
Quickly varying properties
Magic numbers, half‐lives…
An extra‐ordinary diverse nuclear phenomenology /1
L. P. Canto
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V. Lapoux et N. Alamanos 5
How many nuclides may exist? 6000? More? Heaviest element? Enhanced stability near Z = 120? Are magic numbers the same for increasing |N‐Z|? Location of the neutron drip line beyond Z = 8? What about replacing nucleons with hyperons?and all questions deriving from the above + many others
An extra‐ordinary diverse nuclear phenomenology /2
From the experimental perspective
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V. Lapoux et N. Alamanos 6
How many nuclides may exist? 6000? More? Heaviest element? Enhanced stability near Z = 120? Are magic numbers the same for increasing |N‐Z|? Location of the neutron drip line beyond Z = 8? What about replacing nucleons with hyperons?and all questions deriving from the above + many others
An extra‐ordinary diverse nuclear phenomenology /2
New theoretical approaches: As an exemple the 3N forces derived from EFT have been
implemented within ab‐initio shell model calculations, coupled‐cluster theory, calculations with extended valence space
3N forces today is considered as a key to explain the evolution of shell structure of magic numbers.
What about reaction calculations ?
From the experimental perspective
A renewal of the theory
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V. Lapoux et N. Alamanos 7
K. Hebeler, J. D. Holt, J. Menendez, A. Schwenk, Ann. Rev. Nucl. Part. Sci., in press (2015).
State‐of‐the‐art ab‐initio calculations
2NC 2N+3N
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V. Lapoux et N. Alamanos 8
K. Hebeler, J. D. Holt, J. Menendez, A. Schwenk, Ann. Rev. Nucl. Part. Sci., in press (2015).
State‐of‐the‐art ab‐initio calculations
Towards ab‐initio methods
for open‐shell nuclei
Extending existing methods Gorkov‐SCGF[V. Somà, T. Duguet, C. Barbieri, PRC 84, 064317 (2011)]
MR‐IMSRG[H. Hergert et al., PRL 110, 242501 (2013)]
Bogoliubov‐CC[A. Signoracci, T. Duguet, G. Hagen, G. R. Jansen, arXiv:1412.2696]
Bogoliubov TDDM[M. Tohyama, P. Schuck, arXiv:1411.5730 ]
2NC 2N+3N
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V. Lapoux et N. Alamanos
• Recent theoretical developments have shown that neutron‐rich nuclei become
increasingly sensitive to three‐nucleon forces, which are at the forefront of
theoretical developments based on effective field theories of quantum
chromodynamics.
This includes the formation of shell structure, the spectroscopy of exotic nuclei, and
the location of the neutron dripline.
• Three‐nucleon forces provide an exciting link between theoretical, experimental
and observational nuclear physics frontiers.
• We are missing “strong” developments in reaction theories
State‐of‐the‐art ab‐initio calculations
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V. Lapoux et N. Alamanos 10
Weakly‐bound Borromean structures of the exotic 6,8He nuclei
through direct reactions on proton
o Introduction about exotic nuclei physics
o An experimental setup (see also talk by R. Lichenthäler)
o Weakly‐bound Borromean structures of :
The exotic 6,8He nuclei (structure, excited states, radii, transition densities,…)
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V. Lapoux et N. Alamanos
11
Structure and spectroscopy of 6,8He isotopes via direct reactions
8He(p,d)Extreme cases of the nuclear binding and isospin N/Z =2 , 3.
rms radii very similar – role of pairing correlations.
Interplay between correlations, cluster and shell effects.
Resonant and scattering states close to the ground state –continuum effects.
Stringent testes of our reaction and structure theory.
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V. Lapoux et N. Alamanos
Experimental set‐up at GANIL for the direct reactions
12
6He
t
40 cm
8He2+
CATS
CH2target
X, Y, TSPIRAL 8He2+ beam15.4 A.MeV~2 104 part/s
E525S - GANIL
wall of 4 MUST2 + 5th detector at ~40 cm
Plastics at 0°
Si 300µm 128(X,Y); 4cm CsI
10cm
∆E,E X, Y, Tof
beam spoton target
FWHM ΔXc ~ 4 mm ΔYc ~ 5 mm; Δ ~0.5°
MUST2: E. Pollacco et al., EPJA 25, s01, 287 (2005).
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V. Lapoux et N. Alamanos 13
Kinematical reconstruction, Ex spectra of (6He) from 8He(p,t)6He*
The black, red and blueLines correspond to (p,p), (p,d) and (p,t)
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V. Lapoux et N. Alamanos
Kinematical reconstruction, Ex spectra of (6He) from 8He(p,t)6He*
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Beam tracking CATSimpact on target; θinc
MUST2X,Y, E,TOF
identificationEtot, θ
8He + p → 6He + t
8He + p → 6He* + t→ 4He +n+n + t
8He + p → 7He + d
8He + p→ 6He+ n + d→ 4He +3n+ d
Spectra Ex +d/d
Missing mass method Signature of reaction Coincidence (ejectile, proton)Eexc (6He) from (p, E) of proton
8He + p → 6He + t
8He + p → 6He* + t
8He + p → 7He + d
8He + p → 8He + p
Resolution : 0.6 mmEfficiency : 94 %
Precision on the 6He gs position:5‐10 keVEnergy resolution: 720 keVwith a 50µm (4.48mg/cm2) CH2 target
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V. Lapoux et N. Alamanos 15
Weakly‐bound Borromean structures of the exotic 6,8He nuclei
through direct reactions on proton
o Introduction about exotic nuclei physics
o An experimental setup
o Weakly‐bound Borromean structures of :
The exotic 6,8He nuclei (structure, excited states, radii, transition densities,…)
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V. Lapoux et N. Alamanos
Spectroscopy of 6He
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V. Lapoux et N. Alamanos
6He excitation energy spectrum (with background subtraction)
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E525S dataPLB 718, 441 (2012).
from 8He(p,t) 6He
Distribution of resonances modeled by Breit‐Wigner Functions;
Two new states: 2+ and L=1
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V. Lapoux et N. Alamanos
6He excitation energy spectrum (with background subtraction)
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E525S dataPLB 718, 441 (2012).
from 8He(p,t) 6He
Distribution of resonances modeled by Breit‐Wigner Functions;
Two new states: 2+ and L=1
More in the years to come in Sao‐Paulo
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V. Lapoux et N. Alamanos 19
[16] J. Jȁnecke et al., PRC 54, 1070 (1996).[17] S. Nakayama et al., PRL 85, 262 (2000).[19] T. Nakamura et al., PLB 493, 209 (2000); EPJA13, 33 (2002).
CSM Volya, Zelevinsky, PRL94, 052501 (‘05).
GSMbHagen, Hjorth‐Jensen,Vaagen, PRC71, 044314 (‘05).
FewBDanilin et al.PRC 55, 577 (‘97).
QMCPieper et al.PRC 70,054325 (‘04)
NCSMNo Core Shell ModelNavratil, Barrettet al.
Fig ‐ E525S resultsPLB 718, 441 (2012).N.B. AME2003 Sn =1.86 MeV 2015: AME2012 1.71 MeV
COSM T. Myo et al, PRC 76 (‘07); PRC 80 (09).
Spectroscopy of 6He
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V. Lapoux et N. Alamanos 20
Comparisons of the data sets for SPIRAL 8He+p
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V. Lapoux et N. Alamanos
Comparisons of the data sets for SPIRAL 8He+p
21
SPIRAL data obtained with MUST2, at the same energy
E405S (MUST) 8He (p,p’)@ 15.6 A.MeVElastic PLB 619, 82 (2005)+ transfer 8He(p,d) , PRC 73, 044301(’07)8He(p,t) 6He (gs) and (p,t) 6He(2+) PLB 646, 222 (‘07)
E525S (MUST2) for 6He resonances8He @ 15.4 A.MeV8He(p,p) , 8He(p,d) ,8He(p,t) 6He(gs) and (p,t) 6He(2+) PLB 718, 441 (2012)
E525S
E405S
8He(p,d)
8He(p,p)
Large (p,d), (p,t) cross sections compared to 8He+p entrance channel one‐step DWBA not valid
GENERAL framework : Coupled Reactions Channel analysis
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V. Lapoux et N. Alamanos
[1] 8He(p,d)7He C2S = 4.4 ± 1.3 [CCBAanalysis]CRC (p,p) (p,d) C2S = 3.3 ± 1.3 PLB 619, 82 (’05)
Configuration mixing : (p3/2)4 and (p3/2)2 (p1/2)2
Structure of 8He extracted from direct reactions on proton
CRC analysis: N. Keeley (SPhN, Warsaw)
CRC calc
8He(p,t)6He(0+)
8He(p,t)6He2+
8He(p,d)
8He(p,t)6He(0+)
8He(p,t)6He (2+)
Data: A. A.Korsheninnikov et al, PRL 90, 082501 (‘03)
RIKEN 61.3 A.MeV
CRC calc
p n1s1/21p3/21p1/2
p n1s1/21p3/21p1/2
Data: SPIRAL‐MUST [1] PRC73, 044301(’07)[2] PLB 646, 222(‘07) CRC analysis
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V. Lapoux et N. Alamanos
[1] 8He(p,d)7He C2S = 4.4 ± 1.3 [CCBAanalysis]CRC (p,p) (p,d) C2S = 3.3 ± 1.3 PLB 619, 82 (’05)
Configuration mixing : (p3/2)4 and (p3/2)2 (p1/2)2
Structure of 8He extracted from direct reactions on proton
CRC analysis: N. Keeley (SPhN, Warsaw)
CRC calc
8He(p,t)6He(0+)
8He(p,t)6He2+
8He(p,d)
8He(p,t)6He(0+)
8He(p,t)6He (2+)
Data: A. A.Korsheninnikov et al, PRL 90, 082501 (‘03)
RIKEN 61.3 A.MeV
CRC calc
p n1s1/21p3/21p1/2
p n1s1/21p3/21p1/2
Data: SPIRAL‐MUST [1] PRC73, 044301(’07)[2] PLB 646, 222(‘07) CRC analysis
But we cannot exclude
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V. Lapoux et N. Alamanos
Structure of 8He extracted from direct reactions on proton
Our analysis shows that the 8He(p,t) reaction is a rather more sensitive probe of
the 8He ground state (then the (p,d)).
While the (1p3/2)4 is probably the more dominant component of the 8He
ground state, there is a significant probability of finding the valance neutrons in
other configuration's such as (1p3/2)2(1p1/2)2.
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V. Lapoux et N. Alamanos
Structure of 8He extracted from direct reactions on proton
Consistent with the results from
quasi‐elastic scattering of 8He
LV Chulkov et al, NPA759, 43(’05)
And theoretical calculations: Hagino, Takahashi, Sagawa PRC 77, 054317
Neutron configurations % 8He (gs.) : (1p3/2)4 : 34.9 % ; [(1p3/2)2(p1/2)2] : 23.7 %
p n1s1/21p3/21p1/2
p n1s1/21p3/21p1/2
Our analysis shows that the 8He(p,t) reaction is a rather more sensitive probe of
the 8He ground state (then the (p,d)).
While the (1p3/2)4 is probably the more dominant component of the 8He
ground state, there is a significant probability of finding the valance neutrons in
other configuration's such as (1p3/2)2(1p1/2)2.
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V. Lapoux et N. Alamanos
Spectroscopy of 8He
26
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V. Lapoux et N. Alamanos 27
On the Spectroscopy of 6He and 8He
The resonances predicted by various ab‐initio theories like QMC or
NCSM overestimate the 6,8He results.
Coupling of bound and scattering states is missing in most of these
theories. This may explain some of the observed discrepancies.
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V. Lapoux et N. Alamanos 28
Weakly‐bound Borromean structures of the exotic 6,8He nuclei
through direct reactions on proton
o Introduction about exotic nuclei physics
o An experimental setup
o Weakly‐bound Borromean structures of :
The exotic 6,8He nuclei (structure, excited states, radii, transition densities,…)
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V. Lapoux et N. Alamanos
Experiment versus theories for proton and matter Rms radii
Values obtained in the present analysis using the proton radii available in the literature
rp from laser spectroscopy rm from elastic scattering
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V. Lapoux et N. Alamanos
Experiment versus theories for proton and matter Rms radii
30
AMD‐m56 K. En’yo PRC 76 (‘07)FMD T. Neff, H. Feldmeier, NPA 738, 357 (2004)HF+corr H.Sagawa et al PLB 286 (1992)COSM T. Myo et al, PRC 76 (‘07); PRC 80 (09) GSM11 G. Papadimitriou PRC 84 (‘11)
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V. Lapoux et N. Alamanos
Experiment versus theories for proton and matter Rms radii
31
AMD‐m56 K. En’yo PRC 76 (‘07)FMD T. Neff, H. Feldmeier, NPA 738, 357 (2004)HF+corr H.Sagawa et al PLB 286 (1992)COSM T. Myo et al, PRC 76 (‘07); PRC 80 (09) GSM11 G. Papadimitriou PRC 84 (‘11)
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V. Lapoux et N. Alamanos 32
Experiment versus theories for proton and matter Rms radii
The matter and neutron radii are underestimated by most of the models.
The matter and neutron radii consistent with most of the presented models.
However inconsistent with HFB calculations : Rrms = 3.23 fm
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V. Lapoux et N. Alamanos 33
Experiment versus theories for proton and matter Rms radii
The configuration's such as (1s1/2)2(1p3/2)2 may increase the value of the radius (VL private communication – Discussion between H.S and V.L. ‐ H. Sagawa plans to control the calculations ).
Rrms = 3.23 fmInstead ofRrms = 2.50 fm
Strong di‐neutronCorrelations in 8He and 18C
PRC77, 054317
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V. Lapoux et N. Alamanos 34
Weakly‐bound Borromean structures of the exotic 6,8He nuclei
through direct reactions on proton
o Introduction about exotic nuclei physics
o An experimental setup
o Weakly‐bound Borromean structures of :
The exotic 6,7,8He nuclei (structure, excited states, radii, transition densities,…)
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V. Lapoux et N. Alamanos 35
Experiment versus theories for transition densities
A curiosity
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V. Lapoux et N. Alamanos 36
Experiment versus theories for transition densities
The transition matrix elements can defined as the radial moments of the density transitions
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V. Lapoux et N. Alamanos 37
Experiment versus theories for transition densities
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V. Lapoux et N. Alamanos 38
Experiment versus theories for transition densities
Since the NN effective interaction is dominated by the isoscalar channel 3S1 the proton scattering mainly probes the
neutron density (and the Mn value).
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V. Lapoux et N. Alamanos 39
Experiment versus theories for transition densities
The contribution of p and n to the excitation of the nucleus is given by:
Since the NN effective interaction is dominated by the isoscalar channel 3S1 the proton scattering mainly probes the
neutron density (and the Mn value).
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V. Lapoux et N. Alamanos 40
Experiment versus theories for transition densities
Illustration of the weak sensitivity of the (p,p’) to proton transition densities
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V. Lapoux et N. Alamanos 41
Experiment versus theories for transition densities
The arrows indicate the extremes of the losange
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V. Lapoux et N. Alamanos 42
Conclusions
I have presented few aspects concerning the structure of 6,8He.
Some of the open questions may be elucidated in the Sao‐Paulo facility
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V. Lapoux et N. Alamanos 43
Conclusions
I have presented few aspects concerning the structure of 6,8He.
Some of the open questions may be elucidated in the Sao‐Paulo facility
“Science is facts; just as houses are made of stones, so is science made of facts; but a pile of stones is not a house and a collection
of facts is not necessarily science”. Henri Poincaré
Our goal is not to collect data but to reach a better understanding and modelling of exotic nuclei…..
However …………
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V. Lapoux et N. Alamanos 44
Nuclear Physics of exotic nuclei is a 30 years old field. In the beginning of the 1990
nuclear physics was crossing a very difficult period. Since ten years, GANIL was
delivering, beams with the aim to study central collisions ….. The board of directors
was questioning the future of the discipline.
With the advent of the physics of exotic nuclei we have hired a new generation of
experimentalists and theoreticians and this was beneficial not only for the physics at
the drip lines but for the ensemble of the field.
With new tools the theoreticians and reshaping the old nuclear physics landscape.
Physics of exotic nuclei
What about the future ???