Turning up and down strong magnetic fields in relativistic nuclear collisions

I show that the average transverse momentum, $⟨p_t⟩$, of the hadrons emitted in relativistic nuclear collisions can be used as a ``knob’’ to control the strength of the magnetic field induced by the spectator and the participant protons over the overlap region. I thus argue that any observable sensitive to this magnetic field is nontrivially correlated with $\langle p_t \rangle$ at a given collision centrality.