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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

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


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,…)


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


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


From the experimental perspective


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


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


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


K. Hebeler, J. D. Holt, J. Menendez, A. Schwenk, Ann. Rev. Nucl. Part. Sci., in press (2015).


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


• 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






o An experimental setup (see also talk by R. Lichenthäler)




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.


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).


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)


Kinematical reconstruction, Ex spectra of (6He) from 8He(p,t)6He*

14

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


Spectroscopy of 6He


6He excitation energy spectrum (with background subtraction)

17

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


6He excitation energy spectrum (with background subtraction)

18

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


[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


Comparisons of the data sets for SPIRAL 8He+p


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


[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


[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


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



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.



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.


Spectroscopy of 8He

26


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.


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



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)



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)



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



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







The exotic 6,7,8He nuclei (structure, excited states, radii, transition densities,…)


Experiment versus theories for transition densities

A curiosity



The transition matrix elements can defined as the radial moments of the density transitions



Since the NN effective interaction is dominated by the isoscalar channel 3S1 the proton scattering mainly probes the

neutron density (and the Mn value).



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).



Illustration of the weak sensitivity of the (p,p’) to proton transition densities



The arrows indicate the extremes of the losange


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


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 …………


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 ???

use these data as a bench mark to test the validity of the ... › media › pdf ›...

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