  We study s-wave Cooper pairing in heavy-fermion systems. We analyze the
periodic Anderson model by means of the variational cluster approach (VCA)
focusing on the interorbital Cooper pairing between a conduction electron ($c$
electron) and an $f$ electron, called the "$c$-$f$ pairing." It is shown that
the s-wave superconductivity appears coexisting with long-range
antiferromagnetic order when electrons or holes are doped into the system at
half filling. The antiferromagnetic order vanishes when the doping
concentration exceeds a certain critical value, leading to a pure s-wave
superconducting state. Moreover, the comparative study with different reference
systems used in the VCA shows that the interorbital $c$-$f$ pairing is
essential for the appearance of the s-wave superconductivity.
