Blocks with central hyperfocal subgroups

Let p be a prime, G a finite group, b a p-block of G with maximal Brauer pair (P,eP), l(b) the number of irreducible Brauer characters in the block b, and D the hyperfocal subgroup of b with respect to (P,eP). Set R=CP(NG(P,eP)p '). In this paper, we show that if D is central in P, then l(b)=l(eR) where (R,eR)<=(P,eP). Consequently, we show that if b is a 2-block and D is central in P, then l(b)=l((eP)NG(P)).