Probing hidden sectors with a muon beam: Total and differential cross sections for vector boson production in muon bremsstrahlung

Vector bosons, such as dark photon A' or Z', can couple to muons and be produced in the bremsstrahlung reaction mu(-) + N -> mu(-) + N + A'(Z'). Their possible subsequent invisible decay can be detected in fixed target experiments through missing energy/momentum signature. In such experiments, not only is the energy transfer to A'(Z') important but also the recoil muon angle psi mu 0. In this paper, we derive the total and the double differential cross sections involved in this process using the phase space Weizsacker-Williams and improved Weizsacker-Williams approximations, as well as using exact-tree-level calculations. As an example, we compare the derived cross sections and resulting signal yields in the NA64 mu experiment that uses a 160 GeV muon beam at the CERN Super Proton Synchrotron accelerator. We also discuss its impact on the NA64 mu expected sensitivity to explore the (g - 2)(mu) anomaly favored region with a Z' boson considering 10(12) muons accumulated on target.

Automated summary

This study focuses on the coupling of vector bosons with muons and their potential production and detection methods in fixed target experiments, aiming to explore the favored region of the (g - 2)(mu) anomaly.