The γ decay of the elusive narrow, near-threshold proton resonance in $^{11}$B was investigated at Laboratori Nazionali di Legnaro (INFN) in a particle-γ coincidence experiment, using the $^{6}$Li($^{6}$Li,pγ) fusion-evaporation reaction and the GALILEO-GALTRACE setup. No clear signature was found for a possible E1 decay to the 1/2<math><msubsup><mrow></mrow><mrow><mn>1</mn></mrow><mrow><mo>−</mo></mrow></msubsup></math>, first-excited state of $^{11}$B, predicted by the Shell Model Embedded in the Continuum (SMEC) with a branching of <math><msubsup><mrow><mn>0.98</mn></mrow><mrow><mo>−</mo><mn>69</mn></mrow><mrow><mo>+</mo><mn>167</mn></mrow></msubsup><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math> with respect to the dominant particle-decaying modes. The statistical analysis of the γ-ray spectrum provided an average upper limit of <math><mn>2.37</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math> for this γ-ray branching, with a global significance of 5σ. On the other hand, by imposing a global confidence level of 3σ, a significant excess of counts was observed for E<math><mmultiscripts><mrow><mo>=</mo></mrow><mprescripts></mprescripts><mrow><mi>γ</mi></mrow><none></none></mmultiscripts><mn>9300</mn><mo>(</mo><mn>20</mn><mo>)</mo></math> keV, corresponding to a resonance energy of 11429(20) keV (namely 200(20) keV above the proton separation energy of $^{11}$B) and a γ-ray branching of <math><mn>1.12</mn><mo>(</mo><mn>35</mn><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math>. This result is compatible with the SMEC calculations, potentially supporting the existence of a near-threshold proton resonance in $^{11}$B.

Italy

S. Bottoni

G. Corbari

S. Leoni

Poland

B. Fornal

A. Goasduff

S. Capra

D. Mengoni

E. Albanese

S. Ziliani

G. Benzoni

Spain

A.M. Sánchez-Benítez

A. Bracco

D. Brugnara

F. Camera

M. Ciemała

N. Cieplicka-Oryńczak

F.C.L. Crespi

J.A. Dueñas

A. Gadea

F. Galtarossa

E. Gamba

A. Gottardo

A. Gozzelino

J. Ha

Ł.W. Iskra

T. Marchi

R. Menegazzo

B. Million

D.R. Napoli

G. Pasqualato

J. Pellumaj

R.M. Pérez-Vidal

S. Pigliapoco

M. Polettini

C. Porzio

F. Recchia

K. Rezynkina

J.J. Valiente-Dóbon

O. Wieland

I. Zanon

G. Zhang

Search for the Decay of the Narrow Near-threshold Proton Resonance in B

This letter reports on the first observation of an octupole band in the neutron-deficient <math><mo>(</mo><mi>N</mi><mo>=</mo><mi>Z</mi><mo>+</mo><mn>2</mn><mo>)</mo></math> nucleus $^{110}$Xe. The $^{110}$Xe nuclei were produced via the $^{54}$Fe($^{58}$Ni,2n) fusion-evaporation reaction. The emitted γ rays were detected using the jurogam 3 γ-ray spectrometer, while the fusion-evaporation residues were separated with the MARA separator at the Accelerator Laboratory of the University of Jyväskylä, Finland. The experimental observation of the low-lying 3$^{−}$ and 5$^{−}$ states and inter-band E1 transitions between the ground-state band and the octupole band proves the importance of octupole correlations in this region. These new experimental data combined with theoretical calculations using the symmetry-conserving configuration-mixing method, based on a Gogny energy density functional, have been interpreted as an evidence of enhanced octupole correlations in neutron-deficient xenon isotopes.

Finland

A. Illana

D. Stramaccioni

J.J. Valiente-Dobón

T.R. Rodriguez

L.M. Robledo

A. Poves

K. Auranen

O. Beliuskina

C. Delafosse

T. Eronen

Z. Ge

S. Geldhof

W. Gins

T. Grahn

P.T. Greenlees

H. Joukainen

R. Julin

H. Jutila

A. Kankainen

M. Leino

J. Louko

M. Luoma

D. Nesterenko

J. Ojala

J. Pakarinen

P. Rahkila

P. Ruotsalainen

M. Sandzelius

J. Sarén

J. Uusitalo

G.L. Zimba

Octupole correlations in the N = Z + 2 = 56 Xe nucleus

The lifetimes of the low-lying excited states <math><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></math> and <math><msup><mrow><mn>4</mn></mrow><mrow><mo>+</mo></mrow></msup></math> have been directly measured in the neutron-deficient $^{106,108}$Sn isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted γ rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>0</mn></mrow><mrow><mi>g</mi><mo>.</mo><mi>s</mi><mo>.</mo></mrow><mrow><mo>+</mo></mrow></msubsup><mo>)</mo></math> values and it describes well the experimental pattern for $^{104−114}$Sn; the <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>)</mo></math> values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in $^{108}$Sn.

France

M. Siciliano

F. Nowacki

A.P. Zuker

D. Bazzacco

A. Lopez-Martens

E. Clément

Germany

T. Braunroth

M. Doncel

Türkiye

S. Ertürk

G. de France

C. Fransen

G. Georgiev

A. Goldkuhle

Sweden

U. Jakobsson

G. Jaworski

P.R. John

Hungary

I. Kuti

A. Lemasson

C. Michelagnoli

Croatia

T. Mijatović

C. Müller-Gatermann

J. Nyberg

M. Palacz

B. Sayği

D. Sohler

S. Szilner

D. Testov

M. Zielińska

CERN

D. Barrientos

B. Birkenbach

United Kingdom

H.C. Boston

A.J. Boston

B. Cederwall

J. Collado

D.M. Cullen

P. Désesquelles

C. Domingo-Pardo

J. Dudouet

J. Eberth

F.J. Egea-Canet

V. González

L.J. Harkness-Brennan

H. Hess

D.S. Judson

A. Jungclaus

W. Korten

M. Labiche

A. Lefevre

H. Li

A. Maj

A. Pullia

P. Reiter

M.D. Salsac

E. Sanchis

O. Stezowski

Ch. Theisen

Pairing-quadrupole interplay in the neutron-deficient tin nuclei: First lifetime measurements of low-lying states in Sn