  Transverse emission of preequilibrium nucleons, light clusters (complex
particles) and charged pions from the isotopic $^{112,124}$Sn+$^{112,124}$Sn
reactions at a beam energy of 400\emph{A} MeV, to extract the high-density
behavior of nuclear symmetry energy, are investigated within an isospin and
momentum dependent transport model. Specifically, the double ratios of
neutron/proton, triton/helium-3 and $\pi^{-}/\pi^{+}$ in the squeeze-out domain
are analyzed systematically, which have the advantage of reducing the influence
of the Coulomb force and less systematic errors. It is found that the
transverse momentum distribution of isospin ratios strongly depend on the
stiffness of nuclear symmetry energy, which would be a nice observable to
extract the high-density symmetry energy. The collision centrality and the mass
splitting of neutron and proton in nuclear medium play a significant role on
the distribution structure of the ratios, but does not change the influence of
symmetry energy on the spectrum.

Nuclear Theory