Search for Fingerprints of Tetrahedral Symmetry in 156 Gd QuangTuyen Doan Nuclear Matter Group, IPNLyon TetraNuc collaboration Zakopane, Poland, September 1-7, 2008
Outline
Physics motivations The experiment Some preliminary results Conclusions and perspectives
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Nucleon Levels in Function of Tetrahedral Deformation
Observe gaps at Z=64 and N=90 (Levels for neutrons are very similar that the levels for protons.)
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Nucleon Levels in Function of Tetrahedral Deformation
Gap
Gap
Observe gaps at Z=64 and N=90 (Levels for neutrons are very similar that the levels for protons.)
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156
Physics motivations 156
Gd nucleus
Gd: a good theoretical candidate to look for Tetrahedral symmetry
Predicted magic numbers(?) N: 40, 56, 70, 90, 112, 136 Z: 40, 56, 64, 70, 90
⇒ 156 64 Gd92
Signature Pure symmetry: E2 transitions forbidden because Q2 = 0 (?)
J.Dudek et al., Phys. Rev. Lett. 88, 252502 (2002)
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Current
156
Gd level scheme (from ENSDF)
g.s. band
K π = 1− Octupole vibrational
K π = 1− Octupole vibrational
band (odd-spin members)
band (even-spin members)
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Current
156
Gd level scheme (from ENSDF)
g.s. band
K π = 1− Octupole vibrational
K π = 1− Octupole vibrational
band (odd-spin members)
band (even-spin members)
?
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Physics motivations 156
156
Gd nucleus
Gd: a good experimental candidate to look for Tetrahedral symmetry
Previous studies J. Konijn: The B(E2)/B(E1) ratios are about a factor 50 lower for the odd-spin states than those for the even-spin states M. Sugawara: existence of a minimum for the branching ratios
⇒ low statistics, only γ − γ coincidences
Transition
B(E2)/B(E1)(106 fm2 ) J. Konijn(??)
17− 15− 13− 11− 10− 8− 6−
exp with α
M. Sugawara(?) exp with 13 C
··· ··· ··· 8 240 700 350
16 (±3) 6 (±2) 7 (±2) 15 (±7) ··· ··· ···
(?) M. Sugawara et al., NPA 686 (2001) 29-40 (??) J. Konijn et al., NPA 352 (1981) 191-220
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Physics motivations 156
156
Gd nucleus
Gd: a good experimental candidate to look for Tetrahedral symmetry
Previous studies J. Konijn: The B(E2)/B(E1) ratios are about a factor 50 lower for the odd-spin states than those for the even-spin states M. Sugawara: existence of a minimum for the branching ratios
⇒ low statistics, only γ − γ coincidences
Transition
B(E2)/B(E1)(106 fm2 ) J. Konijn(??)
17− 15− 13− 11− 10− 8− 6−
exp with α
M. Sugawara(?) exp with 13 C
··· ··· ··· 8 240 700 350
16 (±3) 6 (±2) 7 (±2) 15 (±7) ··· ··· ···
Experimental problem: a lot of multiplets in coincidence and in parallel Difficulties or even impossibilities to extract accurate branching ratios (?) M. Sugawara et al., NPA 686 (2001) 29-40 (??) J. Konijn et al., NPA 352 (1981) 191-220
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The experiment Experiment with the JUROGAM detector at Jyv¨askyl¨a (september 2007) Reaction: α (27.5MeV) + 144 Sm → 156 Gd + 2n (92 %) → 155 Gd + 3n (7.7 %) Excitation function to determine the bombarding energy (pilot experiment at Orsay) Minimization of other channels Optimization of the population at low and medium spin
For the current results 268 106 real γγγ events used (analysed on a Cube)
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Results
Spectra gated by 199 keV and all (E1) transitions
Illustration of the very low intensity of the (E2) transitions at low spin in the band candidate to carry Tetrahedral symmetry: odd spin negative band o.n.p band g.s. band
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Results
Spectra gated by 199 keV and all (E1) transitions
Illustration of the very low intensity of the (E2) transitions at low spin in the band candidate to carry Tetrahedral symmetry: odd spin negative band o.n.p band g.s. band
(AND) Q.T. Doan et al.,
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Results
Spectra gated by 199 keV and all (E1) transitions
Illustration of the very low intensity of the (E2) transitions at low spin in the band candidate to carry Tetrahedral symmetry: odd spin negative band o.n.p band g.s. band
(AND) Q.T. Doan et al.,
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Results
Spectra gated by 199 keV and all (E1) transitions
Illustration of the very low intensity of the (E2) transitions at low spin in the band candidate to carry Tetrahedral symmetry: odd spin negative band o.n.p band
contamination?
g.s. band
(AND) Q.T. Doan et al.,
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Results
Spectra gated by 199 keV and all (E1) transitions
Illustration of the more intense E2 transitions for the even-spin negative parity band e.n.p band g.s. band
(AND) Q.T. Doan et al.,
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Results
Spectra gated by 199 keV and all (E1) transitions
Illustration of the more intense E2 transitions for the even-spin negative parity band e.n.p band g.s. band
(AND) Q.T. Doan et al.,
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Results
Spectra gated by 199 keV and all (E1) transitions
Comparison of intra-band E2 transitions Odd spin negative band
Even spin negative band
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Results
Spectra gated by 199 keV and all (E1) transitions
Comparison of intra-band E2 transitions Odd spin negative band
Even spin negative band
⇒ The E2 transitions disappear as the spin decrease for the odd-spin band Q.T. Doan et al.,
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Results
Spectrum gated by 380 keV and 400 - 402 keV
The 402 keV transition (E2) in the odd-negative band is much weaker than the 400 keV in the even-negative band o.n.p band
e.n.p band
g.s.p band
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Results
Spectrum gated by 380 keV and 400 - 402 keV
The 402 keV transition (E2) in the odd-negative band is much weaker than the 400 keV in the even-negative band o.n.p band
e.n.p band
g.s.p band
(AND)
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Results
Spectrum gated by 380 keV and 400 - 402 keV
The 402 keV transition (E2) in the odd-negative band is much weaker than the 400 keV in the even-negative band o.n.p band
e.n.p band
g.s.p band
(AND)
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Results
Spectrum gated by 380 keV and 400 - 402 keV
The 402 keV transition (E2) in the odd-negative band is much weaker than the 400 keV in the even-negative band o.n.p band
e.n.p band
g.s.p band
(AND)
Q.T. Doan et al.,
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Results
Spectrum gated by 380 keV and 400 - 402 keV
The 402 keV transition (E2) in the odd-negative band is much weaker than the 400 keV in the even-negative band o.n.p band
e.n.p band
g.s.p band
No 521 keV !
(AND)
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Results
Spectrum gated by 380 keV and 400 - 402 keV
The 402 keV transition (E2) in the odd-negative band is much weaker than the 400 keV in the even-negative band o.n.p band
e.n.p band
g.s.p band
No 521 keV !
(AND) ⇒ Flux going through intra-band E2 is very different beetwen the two bands Q.T. Doan et al.,
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Preliminary
156
Gd level scheme from our experiment
g.s. band
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Preliminary
156
Gd level scheme from our experiment o.n.p band
g.s. band
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Preliminary
156
Gd level scheme from our experiment o.n.p band
e.n.p band
g.s. band
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Preliminary
156
Gd level scheme from our experiment o.n.p band
e.n.p band
g.s. band
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Branching ratios o.n.p band
Transition 17− 15− 13− 11− 9− 7− 5− 12− 10− 8− 6− 4−
e.n.p band
B(E2)/B(E1)(106 fm2 ) (our preliminary results)
(previous results)
··· 4.5 (±1.0) 5.5 (±0.6) ≺9 (-2.0) ≺ 26 (-5.0) ≺ 92 (-11.0) ··· ··· 640 (±100) 330 (±10) 210 (±15) ···
16 (±3) 6 (±2) 7 (±2) 15 (±7)
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Branching ratios o.n.p band
Transition 17− 15− 13− 11− 9− 7− 5− 12− 10− 8− 6− 4−
e.n.p band
B(E2)/B(E1)(106 fm2 ) (our preliminary results)
(previous results)
··· 4.5 (±1.0) 5.5 (±0.6) ≺9 (-2.0) ≺ 26 (-5.0) ≺ 92 (-11.0) ··· ··· 640 (±100) 330 (±10) 210 (±15) ···
16 (±3) 6 (±2) 7 (±2) 15 (±7)
240 700 350
⇒ The B(E2)/B(E1) ratios are about a factor 100 lower for the odd-spin NPB than those for the even-spin NPB
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Conclusions and perspectives E2 are not seen at the level of 10−4 (checked in triples) at the bottom of the negative parity band odd-spin partner Very different behaviors of B(E2)/B(E1) beetwen the two known partners reported as vibrational octupole bands
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Conclusions and perspectives E2 are not seen at the level of 10−4 (checked in triples) at the bottom of the negative parity band odd-spin partner Very different behaviors of B(E2)/B(E1) beetwen the two known partners reported as vibrational octupole bands
⇒ Tetrahedral symmetry: a natural explanation
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Conclusions and perspectives E2 are not seen at the level of 10−4 (checked in triples) at the bottom of the negative parity band odd-spin partner Very different behaviors of B(E2)/B(E1) beetwen the two known partners reported as vibrational octupole bands
⇒ Tetrahedral symmetry: a natural explanation
Work in progress: To find more inter-band transitions and perform angular distribution More bands without established E2 at the lowest spins to be explored existing candidates with both parities already reported in the literature
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Conclusions and perspectives Next step: Coulex experiment at Legnaro (end 2008) with GASP
Future: Better measurement of branching ratios: neutron rich (exotic) beam to populate 156 Gd at higher spin (e.g.: 20 0 on 138 Ba with SPIRAL II at GANIL)
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TetraNuc collaboration D. Curien, J. Dudek, J. Piot, G. Duchˆene, B. Gall, H. Molique, M. Richet, P. Medina - IPHC, Strasbourg, France N. Redon, Ch. Schmitt, O. St´ezowski, Q.T. Doan - IPN Lyon, France P. Jones, R. Julin, P. Peura, S. Ketelhut, M. Nyman, U. Jakobsson Departement of Physics, University of Jyv¨ askyl¨ a, Finland
A. Maj, K. Zuber, K. Mazurek, P. Bednarczyk - The H. Niewodnicza ski Institute of Nuclear Physics PAN, Krak´ ow, Poland N. Schunck - Oak Ridge National Laboratory, Oak Ridge, TN-37831, USA J. Dobaczewski - Institute of Theoretical Physics, Warsaw University, Warsaw, Poland A. Astier, I. Deloncle - CSNSM Orsay, France D. Verney - IPN Orsay, France G. de Angelis - INFN, Laboratori Nazionali di Legnaro, I-35020 Legnaro, Italy
J. Gerl - GSI Darmstadt, 64291 Darmstadt, Germany . . . + Many others from the TetraNuc collaboration !
Thank you ! Q.T. Doan et al.,
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