How to put a dot in Tikz Feynman vertices

I wrote this code

    begin{tikzpicture}
    begin{feynman}
        vertex (a1) {(overline b)};
        vertex[right=1.5cm of a1] (a2);
        vertex[right=1.5cm of a2] (a3);
        vertex[right=2cm of a1] (aa);
        vertex[right=2cm of aa] (a4) {(overline{s})};
        
        vertex[below=1cm of a1] (b1) {(s)};
        vertex[right=2cm of b1] (b2);
        vertex[right=2cm of b2] (b3) {(s)};
        
        vertex[above=1cm of a4] (d1) {(c)};
        vertex[above=1cm of d1] (d2) {(overline{c})};
        
        vertex (c1) at ($(a2)+(0.75,0.75)$);
        vertex (c2) at ($(d1)+(-1.25,0.5)$);
        
        vertex (e1) at ($(a2)+(-0.4, 0.4)$) {(V^{*}_{qb} )};
        vertex (e2) at ($(a3)+(0.4, 0.4)$) {(V^{vphantom{0}}_{qs} )};

        diagram* {
        (a2) -- [fermion, very thick] (a1),
        (a4) -- [fermion, very thick] (a3),
        (b1) -- [fermion, very thick] (b3),
        (a2) -- [boson, bend right, very thick, edge label'=(W^+)](a3),
        (a3) -- [fermion, very thick,  out=90, in=0] (c1) -- [fermion, very thick,  out=-180, in=90, edge label=({t,c,u})] (a2),
        (c1) -- [gluon, very thick] (c2),
        (c2) -- [fermion, very thick] (d1),
        (d2) -- [fermion, very thick] (c2),
        };
        
        draw [decorate, decoration={brace, amplitude=5pt}, thick] (b1.south west) -- (a1.north west) node [pos=0.5, left] {(B^0_shspace{0.75ex})};
        draw [decorate, decoration={brace, amplitude=5pt}, thick] (a4.north east) -- (b3.south east) node [pos=0.5, right] {(hspace{0.75ex}phi(1020))};
        draw [decorate, decoration={brace, amplitude=5pt}, thick] (d2.north east) -- (d1.south east) node [pos=0.5, right] {(hspace{0.75ex}J/psi)};

    end{feynman}
    end{tikzpicture}

to produce the following diagram:

Can someone help me?

Thanks.

So far so good. Now I’d like to add a dot on some of the vertices (a2 and a3). I have read the package documentation (https://arxiv.org/pdf/1601.05437.pdf), but I was not able to use the "dot" command (page 15, section 3.2.3).