Isobar collisions which were thought with a same background and different
magnetic fields provide an opportunity to verify the chiral magnetic effect
(CME) in relativistic heavy-ion collisions. However, the first result from the
RHIC-STAR isobar experiment did not observed the CME signal, but discovered
that the backgrounds are different between
4496​Ru+4496​Ru and
4096​Zr+4096​Zr collisions. We test eighteen
cases of Woods-Saxon parameter settings resulted from different nuclear
deformation or nuclear structure effects using a mutiphase transport model. We
find out that seven cases can reasonably reproduce three reference ratios
measured by the STAR experiment. With considering both the halo-type neutron
skin structure and CME-like charge separation, we demonstrate that it is
difficult for the CME observables (Δδ, Δδ ratio,
Δγ and Δγ/v2​ ratio) to distinguish the presence or
absence of the CME, if the CME strength is weak in isobar collisions. It is
because the final state interactions significantly weaken the initial CME
signal, resulting in non-linear sensitivities of the CME observables to the CME
strength. Therefore, more sensitive observables are required to search for the
possible small CME signal in isobar collisions.Comment: 10 pages, 6 figure