Modification of $Z^0$ leptonic invariant mass in ultrarelativistic heavy ion collisions as a measure of the electromagnetic field

TL;DR

This paper proposes using modifications in the leptonic invariant mass of Z^0 bosons produced in ultrarelativistic heavy ion collisions as a new method to measure the strength and duration of the strong electromagnetic fields generated during these collisions.

Contribution

It introduces a novel experimental approach to quantify electromagnetic fields in heavy ion collisions by analyzing shifts in Z^0 leptonic invariant mass distributions.

Findings

Leptonic invariant mass shifts up to a few hundred MeV due to electromagnetic fields.

The mass shift depends quadratically on the integral of the magnetic field over time.

Proposes experimental measurement of Z^0 decay products as a probe of electromagnetic field strength.

Abstract

An extraordinary strong magnetic field, $eB_0 \approx 10^{18}$ Gauss, is expected to be generated in non-central ultrarelativistic heavy ion collisions and it is envisaged to induce several effects on hot QCD matter including the possibility of local parity and local parity and charge conjugation symmetry violations. A direct signature of such e.m. fields and a first quantitative measurement of its strength and lifetime are still missing. We point out that both the mean value of leptonic invariant mass of $Z^0$ boson, reconstructed by its decaying lepton pairs, and the relative width are modified in relativistic heavy ion collisions due to the presence of strong initial e.m. fields. We propose a measurement of the leptonic invariant mass of $Z^0$ as a novel probe of the strength of the $B_y$. Both shifts could be up to about few hundred MeV and are found to depend on the integral of $B_y$ over the time duration quadratically (approximate). Hence it provides a novel and clear probe of electromagnetic fields, which can be tested experimentally.