Test of IMME in fp shell via direct
mass
measurements of T_{Z }= −3/2nuclides, Y. H.
Zhang, Institute of Modern
Physics, Chinese Academy
of Sciences, Lanzhou, China − The isobaric multiplet mass
equation (IMME)
is the most basic prediction to follow from the concept of isospin
in nuclear
physics, and the test of IMME is clearly of fundamental importance
for which
precise binding energies of at least four T_{Z}³3/2 members are needed. In a recently commisioned
cooler storage ring
CSRe in Lanzhou, atomic masses of eight T_{Z }= −3/2isotopes ^{41}Ti, ^{43}V,
^{45}Cr,
^{47}Mn, ^{49}Fe, ^{51}Co, ^{53}Ni,
and ^{55}Cu
have been measured using the isochronous mass spectroscopy,
providing mass data
for testing the validity of IMME in the fp shell. In this talk,
experimental
details and data analysis method are described and atomic masses
of the
above-mentioned T_{Z }= −3/2 isotopes are reported. We have fitted the mass
data of four isobars
of A = 41, 45, 49, and 53, respectively, using a cubic expression
by inclusion
of a d×T_{Z}^{3} term. The d
coefficients are consistent with zero within error bars for
the A= 41, 45,
and 49 isobars. However
the d coefficient for
the A=53 isobar is
more than 3σ deviated from zero, giving a signature of breakdown
of the
isobaric multiplet mass equation at A=53, T=3/2. This result calls for more
precise
determinations (in the order of keV) of ground-state mass of ^{53}Ni
and
excitation energy of the isobaric analog state in ^{53}Co.