Wonderful developments, a correct ray from the mutrack to the respective dom given a chrenkov angle can be calculated

		TVector3 ip = p.start_point->Vect();
		TVector3 ep = p.end_point->Vect();

		TVector3 emi = doms[i]->getEmisionPoint(&p);

		// rejc_lines->AddLine(sp.X(), sp.Y(), sp.Z(), sp.X() +
min_cone_vec.X(), sp.Y() + min_cone_vec.Y(), sp.Z() + min_cone_vec.Z());
		TVector3 cdir = ((*doms[i]->position - ip) - emi).Unit() ;
		printf("Angle wrt mudir: %f, h %f\n", (cdir.Angle((ep  -
ip).Unit())-0.73)*deg, hitval);

        cdir.SetMag(40);
		rejc_lines->AddLine(ip.X()+emi.X(), ip.Y()+emi.Y(),ip.Z()+ emi.Z(),
ip.X()+emi.X() + cdir.X(), ip.Y()+emi.Y() + cdir.Y(), ip.Z()+emi.Z() +
cdir.Z());