Fusion Suppression in Super Heavy Element ^{263}Bh Formation via ^{54}Cr+^{209}Bi.

The precise quantification of fusion suppression in heavy-projectile induced reactions is obscured by dominant noncompound processes, limited data, and uncertain models. Mass-total kinetic energy (MTKE) distributions for the reaction ^{54}Cr+^{209}Bi were measured at three beam energies, E_{beam}=261, 271, and 278 MeV. The fission fragments were detected using the newly developed TOSCA spectrometer setup. This Letter reveals, for the first time, two asymmetric mass modes at ∼80  u (complementary ∼183  u), and ∼105 u (complementary ∼158  u), likely associated with the spherical N=50 shell and the deformed Z≈42/N≈94 shells, respectively. At the lowest energy, the symmetric mode exhibits a narrow, super-short-like width and high correlated TKE caused likely by Z=50, N=82 shells. The fusion probability (P_{CN}) from multi-Gaussian fits to gated mass (and TKE) distributions using a refined tail-subtraction approach to remove the quasifission background remains robust despite model dependence. P_{CN} peaks near the barrier and decreases on either side, with a slower decrease at the above-barrier energy, differing from the sub-barrier fusion enhancement reported in [Phys. Rev. Lett. 122, 232503 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.232503] and indicating an open question for further study.