ComplexConjugate[expr] complex conjugates expr. It operates on fermion lines, i.e., products of Spinor[..] .DiracMatrix[..] . Spinor[..], and changes all occuring LorentzIndex[mu] into LorentzIndex[ComplexIndex[mu]]. For taking the spin sum (i.e. constructing the traces) use FermionSpinSum. WARNING: In expr should be NO explicit I's in denominators!
See also: ComplexIndex, FermionSpinSum, LorentzIndex.
Notice that SpinorUBar and SpinorU are only input functions. Internally they are converted to Spinor objects.
The FeynCalc Book | CommutatorExplicit | ComplexIndex |