A simulation study of impact of muon beam performance in [formula omitted]SR data analysis

Abstract

The Experimental Muon Source (EMuS) is under design to serve as a multidisciplinary research platform including muon spin rotation/relaxation/resonance (μSR) applications at China Spallation Neutron Source (CSNS). The muon beam at EMuS will operate in a pulsed mode. The influences of the beam performance on μSR data analysis have been quantitatively estimated using Monte Carlo simulations. The measurable range of depolarization rate is inversely proportional to the pulse width with a factor of ∼0.75 for the single-bunch mode or ∼0.6 for the double-bunch mode using the direct fit. This range can be extended by ∼4–8 times in variation with the total positron counts if the fitting function is convoluted with the beam time structure. Due to the superposition of the second muon bunch, the measurable range reduces ∼20% (∼30%) using the direct fit (convoluted fit). There is a crossover for the depolarization rate at 4/Δt (time interval between two muon bunches), with the double-bunch mode being clearly better for slow relaxation and the single-bunch mode better for fast relaxation measurements. The effective asymmetry for muon spin rotation measurements presents a damped oscillation trend for the double-bunch mode. Consequently, the continuous measurable range is divided into several discrete subregions correlated with the time interval Δt.