Modification of Z0 leptonic invariant mass in ultrarelativistic heavy ion collisions as a measure of the electromagnetic field

An extraordinary strong magnetic field, eB0≈1018 Gauss, is expected to be generated in non-central ultrarelativistic heavy ion collisions and it envisaged induce several effects on hot QCD matter including the possibility of local parity charge conjugation symmetry violations. A direct signature such e.m. fields a first quantitative measurement its strength lifetime are still missing. We point out that both mean value leptonic invariant mass Z0 boson, reconstructed by decaying lepton pairs, relative width modified relativistic due presence initial fields. propose as novel probe By. Both shifts could up about few hundred MeV found depend integral By over time duration quadratically (approximate). Hence provides clear electromagnetic fields, which can tested experimentally.