Prompt acceleration of a μ ⁺ beam in a toroidal wakefield driven by a shaped steep-rising-front Laguerre–Gaussian laser pulse

Abstract

The recent experimental data of anomalous magnetic moments strongly indicates the existence of new physics beyond the standard model. An energetic µ + beam is a potential option to the µ + rare decay, µSR(the spin rotation, resonance and relaxation) technology, future muon colliders and neutrino factories. It is proposed a prompt µ + acceleration in a nonlinear donut wakefield driven by a shaped steep-rising-front Laguerre-Gaussian (LG) laser pulse. An analytical model is given and shows that a µ + beam can be focused by the electron cylinder at the center line of the donut bubble and accelerated by the front part of the longitudinal wakefield. A shaped LG laser with a shorter rise time can push plasma electrons to generate a higher-density electron sheath at the front of the bubble, which can enlarge the acceleration field. The acceleration field driven by the steep-rising-front shaped LG laser pulse is about four times higher than that driven by a normal LG laser pulse. Our simulation results show that a 300MeV µ + bunch can be accelerated to 2GeV and its transverse size is focused from initial w0 = 5µm to w = 1µm in the donut bubble driven by the steep-rising-front shaped LG laser pulse with the normal intensity a = 22.