Development of Spin Flip Analysis for the J-PARC Muon g − 2/EDM Experiment

Abstract

The value of the muon anomalous magnetic moment (g − 2) exhibits a discrepancy of 3-4 σ between the standard model (SM) calculation and the experiment at the BNL. This may indicate physics beyond the SM. The J-PARC muon g−2/EDM experiment is a new approach for measuring the muon g−2 and electric dipole moment (EDM) with a reaccelerated thermal muon beam . This unique muon beam eliminates the systematic uncertainties related to the beam in the previous experiment at BNL. In contrast, new systematic uncertainties related to the detection efficiency are of concern. "Spin flip analysis" is effective in evaluating this effect. We can use this analysis method with a spin-flipped dataset. Our experiment uses a low-momentum muon beam, whose spin can be easily flipped. Data generated by a simplified Monte Carlo simulation with a time-dependent detection efficiency model motivated by the event pileup are analyzed with conventional and spin flip analyses for comparison. In conclusion, the spin flip analysis method is useful in studying the bias due to time-dependent inefficiency and then use more data for the g − 2 analysis. We developed a Wien-filter as a spin rotator for the reaccelerated thermal muon beam . The growth of the transverse emittance during spin rotation should not be substantial enough to satisfy the experimental requirements. The main cause of the emittance growth is the difference between the magnetic and electric forces along the beam path. Detailed designs of the magnetic yoke and electrodes are necessary. After a full model design, the emittance growth is evaluated as being +64% in the horizontal plane (x-x') and +56% in the vertical plane (y-y'). This is mainly caused by the additional electric fields. A detailed design will be conducted so that the additional electric fields can be minimized.