Asymmetric muon-antimuon emission from $Z^0$ decays: a clear magnetometer in relativistic heavy-ion collisions

TL;DR

The paper proposes using asymmetric muon-antimuon emission from Z^0 decays as a clear indicator of strong magnetic fields in early-stage relativistic heavy-ion collisions, revealing anisotropic emission patterns and spectral features.

Contribution

It introduces a novel method to detect strong magnetic fields in heavy-ion collisions via Z^0 decay dimuon pairs, highlighting their anisotropic emission and spectral characteristics.

Findings

Dimuon pairs are mainly emitted out of plane, indicated by negative v_2.

The antimuon transverse momentum peaks higher than the muon peak.

The Z^0 spectral function remains largely undistorted.

Abstract

We show that a very clear signal of the presence of a strong magnetic field during the early stage of a high-energy heavy-ion collision is provided by the decay of the $Z^0$ into dimuon pairs. We find that the process is highly anisotropic, producing pairs mainly out of plane, as signaled by a negative value of $v_2$, and leads to an antimuon transverse momentum distribution which peaks at a higher value of the transverse momentum compared to the peak of the muon transverse momentum distribution. We also show that the process does not produce a significant distortion of the $Z^0$ spectral function. The signal can be identified by comparing the dimuon-invariant mass and the individual muon and antimuon spectra produced in semicentral heavy-ion collisions with the corresponding scaled spectra produced in p+p collisions at the $Z^0$ peak.