Finite groups with a unique real $2$-block

Abstract

Let $p$ be a prime, and let $B$ be a $p$-block of a finite group $G$. A $p$-block $B$ is called \emph{real} if the set of irreducible ordinary characters contained in $B$ is invariant under complex conjugation. Motivated by Harris' classification of the finite groups with a unique $p$-block for an arbitrary prime $p$, and by McHugh and Schaeffer Fry's classification of the finite quasi-simple groups with a unique real $2$-block, we classify, in this paper, all finite groups admitting exactly one real $2$-block.