No, a selectron is not a fundamental particle found in atoms. Selectrons are hypothetical superpartner particles of electrons predicted by supersymmetry, a proposed extension of the Standard Model of particle physics.

In supersymmetry, every known particle has a superpartner with similar properties but different spin. Selectrons would be the superpartners of electrons and would have the same electric charge as electrons but would differ in mass and spin.

Supersymmetry has not been experimentally confirmed, and the existence of selectrons and other superpartner particles remains purely theoretical. If supersymmetry is correct, selectrons could be produced in high-energy particle collisions and studied at particle accelerators like the Large Hadron Collider (LHC) at CERN. However, no evidence of selectrons or other superpartner particles has been found in LHC data so far.