I am looking for some books where I can find the determination of the space $M_2(\Gamma _0 (11))$. I know that there is no oldforms in this space. Thus I am interested a way of finding the (I know ther is only one) newforms in $M_2(\Gamma _0 (11))$.
I also know that it might be connected with the study of Hecke operators which I only know that the Hecke operators $T_n$ commute and are codiagonalizables.
Is there a good reference for my question available ? Because I can't find one.
Thank you for helping me,