Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 53

Evolution of collectivity and mirror symmetry along N = Z
K. Wimmer,∗1,∗2 T. Hüyük,∗1 F. Browne,∗3 P. Doornenbal,∗3 T. Koiwai,∗2,∗3 H. Sakurai,∗2,∗3 T. Arici,∗4
M. Bentley,∗5 M. L. Cortés,∗6 N. Imai,∗7 A. Jungclaus,∗1 N. Kitamura,∗7 S. Lenzi,∗8,∗6 B. Longfellow,∗9R. Lozeva,∗10 B. Mauss,∗3 D. Napoli,∗6 M. Niikura,∗2 X. Pereira-Lopez,∗5 F. Recchia,∗8,∗6 P. Ruotsalainen,∗11R. Taniuchi,∗2,∗3 S. Uthayakumaar,∗5 V. Vaquero,∗1 R. Wadsworth,∗5 and R. Yajzey∗5,∗12BigRIPS PID

Unlike any other physical system the nucleus represents a unique dual quantum many-body system. Itsconstituents, the protons and neutrons, are assumed
to be identical, except for their electric charge. They
can be seen as two representations of the nucleon, withisospin components tz = ±1/2 for neutrons and protons, respectively. Under the assumption of charge independence of the strong interaction, hence invarianceunder rotation in the isospin space, the properties ofmirror nuclei should be identical.
Mirror symmetry is typically studied through energy
diﬀerences between excited states of mirror nuclei or+
isospin triplets. Measurements of B(E2; 0+gs → 21 )values for T = 1 isospin triplets allow to extract information on the proton and neutron matrix elements andto test isospin symmetry.1) The proton and neutron
multipole matrix elements can be written in isospin
representation

32

30

103

61

Ga
62

Zn

28

102

63

Z

Cu
64

Ni

26

1024

222

2.02

2.04

2.06

2.08

2.1
A/Q

2.12

2.14

2.16

2.182.2ZDS PID
341033230
2810226(1)Z

1Mn/p = (M0 (Tz ) ± M1 (Tz ))224
22

where M0 (Tz ) is the isoscalar and M1 (Tz ) the isovector multipole matrix element. Assuming isospin conservation the proton matrix elements of isobars area linear function of Tz only, i.e. M0 (Tz ) = M0 and
M1 (Tz ) = M1 · Tz , with constant M0/1 for all Tz . The
linearity provides a direct test of the isospin purity ofthe states. So far this has been tested for light nuclei, mostly in the sd shell, the heaviest case where+the B(E2; 0+gs → 21 ) values of all three members aremeasured is the A = 46 system.2)
In order to test this relation in heavier nuclei we havestudied the Coulomb excitation of A = 62 nuclei. All
three nuclei were studied under identical experimental conditions to reduce the statistical and theoreticaluncertainties. The 62 Zn, 62 Ga, and 62 Ge beams were
produced by the fragmentation of a 345 AMeV primary78
Kr beam provided by the SRC. Unique particle identiﬁcation in BigRIPS and the ZeroDegree Spectrome-20

1018
16
2

2.02

2.04

2.06

2.08

2.1

2.12

2.14

2.16

2.18

2.2

A/Q

Fig. 1. Particle identification plots for the 62 Zn beam impinging on the Be target.

ter was achieved by means of ∆E-Bρ-TOF measurements. Secondary Be and Au targets were used to+determine the B(E2; 0+gs → 21 ) values. The particle
62
identiﬁcation plots for the Zn beam impinging on theBe target is shown in Fig. 1.
The beams impinged on secondary targets located atthe F8 focus. γ rays from excited states were detectedin the DALI2+ array. Suﬃcient statistics for all threemembers of the A = 62 multiplet were collected todetermine the linearity of the proton multipole matrix
elements with a precision of about 5%. Additionally
new states were observed in nuclei beyond the N = Zline. The results will shed new light on the evolutionof collectivity along the N = Z line and provide one of
the most stringent tests of isospin symmetry.

∗1IEM-CSIC
Department of Physics, The University of Tokyo∗3 RIKEN Nishina Center∗4 GSI Helmholtzzentrum für Schwerionenforschung∗5 Department of Physics, University of York
∗6 INFN-Laboratori Nazionali di Legnaro∗7 Center for Nuclear Study, The University of Tokyo∗8 Department of Physics, University of Padova∗9 NSCL, Michigan State University∗10 CSNSM, Université Paris-Sud∗11 Department of Physics, University of Jyväskylä∗12 Physics Department, Jazan University∗2References

1) A. M. Bernstein, V. R. Brown, V. A. Madsen, Phys.
Rev. Lett. 42, 425 (1979).
2) A. Boso et al., Phys. Lett. B 797, 134835 (2019).

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