Physics Letters B 741 (2015) 128–133
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Separation of the 1
+
/1
−
parity doublet in
20
Ne
J. Beller
a
, C. Stumpf
a
, M. Scheck
a,b,c
, N. Pietralla
a,∗
, D. Deleanu
e
, D.M. Filipescu
e
,
T. Glodariu
e
, W. Haxton
f
, A. Idini
a
, J.H. Kelley
h
, E. Kwan
d,1
, G. Martinez-Pinedo
a,g
,
R. Raut
d,2
, C. Romig
a
, R. Roth
a
, G. Rusev
d,3
, D. Savran
i,j
, A.P. Tonchev
d,4
, W. Tornow
d
,
J. Wagner
a
, H.R. Weller
d
, N.-V. Zamfir
e
, M. Zweidinger
a
a
Institut für Kernphysik, TU Darmstadt, D-64289 Darmstadt, Germany
b
School of Engineering, University of the West of Scotland, Paisley PA1 2BE, UK
c
SUPA, Scottish Universities Physics Alliance, Glasgow G12 8QQ, UK
d
Triangle Universities Nuclear Laboratory, Duke University, Durham, NC, USA
e
Horia Hulubei National Institute of Physics and Nuclear Engineering, ELI-NP, Bucharest-Magurele, Romania
f
University of California, Berkeley, CA, USA
g
GSI Helmholtzzentrum für Schwerionenforschung, D-64291 Darmstadt, Germany
h
Triangle Universities Nuclear Laboratory, North Carolina State University, Raleigh, NC, USA
i
ExtreMe Matter Institue EMMI and Research Division, GSI Helmholtzzentrum für Schwerionenforschung, D-64291 Darmstadt, Germany
j
Frankfurt Institute for Advanced Studies FIAS, D-60438 Frankfurt am Main, Germany
a r t i c l e i n f o a b s t r a c t
Article history:
Received
30 July 2014
Received
in revised form 5 December 2014
Accepted
6 December 2014
Available
online 11 December 2014
Editor:
D.F. Geesaman
Keywords:
Parity
doublet
Parity
violation
The ( J , T ) = (1, 1) parity doublet in
20
Ne at 11.26 MeV is a good candidate to study parity violation
in nuclei. However, its energy splitting is known with insufficient accuracy for quantitative estimates
of parity violating effects. To improve on this unsatisfactory situation, nuclear resonance fluorescence
experiments using linearly and circularly polarized γ -ray beams were used to determine the energy
difference of the parity doublet E = E(1
−
) − E(1
+
) =−3.2(±0.7)
stat
(
+0.6
−1.2
)
sys
keV and the ratio of
their integrated cross sections I
(+)
s,0
/I
(−)
s,0
= 29(±3)
stat
(
+14
−7
)
sys
. Shell-model calculations predict a parity-
violating
matrix element having a value in the range 0.46–0.83 eV for the parity doublet. The small
energy difference of the parity doublet makes
20
Ne an excellent candidate to study parity violation in
nuclear excitations.
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP
3
.
1. Introduction
Since 1956, when Lee and Yang postulated a mirror-symmetry
violation in β-decay [1] and 1957 when Wu experimentally ver-
ified
the symmetry-violating effect [2], parity non-conservation is
well established. These results are of paramount importance to our
notion and understanding of fundamental symmetries in nature.
While the strong force conserves parity, the effective nuclear force
violates parity due to contributions of the weak interaction to the
*
Corresponding author.
E-mail
address: beller@ikp.tu-darmstadt.de (J. Beller).
1
Present address: National Superconducting Cyclotron Laboratory, Michigan State
University, East Lansing, MI 48824, USA.
2
Present address: UGC-DAE Consortium for Scientific Research, Kolkata Centre,
Kolkata, India.
3
Present address: Los Alamos National Laboratory, Los Alamos, NM, USA.
4
Present address: Lawrence Livermore National Laboratory, Livermore, CA, USA.
effective nucleon–nucleon interaction. Hence, various theoretical
and experimental approaches have been employed to investigate
parity violation in nuclei (Reviews in [3,4]). At the current stage,
the weak meson–nucleon coupling constants deduced from vari-
ous
experiments are not consistent [5]. Further investigations of
parity violation in nuclei are desirable.
In
particular, studies of parity doublets J
±
are well suited to
the observation of parity violation in nuclei. Depending on the de-
tails
of the nuclear wave functions, the weak interaction matrix
element between states of opposite parity is typically calculated to
be on the order of 1 eV [3,5]. Due to the parity-violating character
of the weak interaction, the physical |φ
±
J
doublet states contain
an admixture of the opposite parity, e.g.,
φ
−
J
=
α
J
−
+ β
J
+
,
(1)
with α
2
+ β
2
= 1. Here, | J
±
denote the doublet eigenstates with
good parity obtained from the parity-conserving part of the Hamil-
tonian.
Within first-order perturbation theory, the contribution of
http://dx.doi.org/10.1016/j.physletb.2014.12.018
0370-2693/
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by
SCOAP
3
.