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Status of the Muon g-2/EDM Experiment at J-PARC

Graziano Venanzoni

TL;DR

The paper presents the J-PARC E34 experiment as a novel, cross-checking approach to measuring the muon g-2 and EDM using ultra-cold muons stored in a compact MRI-type magnet. The method avoids electric-field focusing by employing spiral injection and magnetic confinement, enabling precise extraction of the spin-precession frequency and the EDM signal from decay positrons in a high-resolution tracker. Current projections target a statistical precision for the muon g-2 value of about 450 ppb, with systematic uncertainties below 70 ppb, and an EDM sensitivity of 1.5e-21 e cm (stat) and 0.36e-21 e cm (syst). To push beyond these goals, three upgrades are under study: optical repolarization to boost polarization, higher momentum up to 600 MeV/c with a high-gradient linac, and a storage-field increase toward 6 T, each with distinct technical challenges. Overall, the J-PARC program offers a crucial independent benchmark for the storage-ring measurements and contributes to resolving tensions in the Standard Model prediction for the muon sector.

Abstract

The Muon g-2/EDM Experiment at J-PARC will employ a novel way to measure the muon magnetic anomaly, a_mu = (g-2)_mu/2, by using a low-emittance beam of positive muons stored in a compact muon storage magnet. The experimental method includes new technologies such as a three-dimensional spiral injection, an MRI-type storage magnet with superb field uniformity, and a positron tracking detector. The expected systematic uncertainty will be at the same level as that of the Fermilab Muon g-2 experiment, providing an important cross-check of the "storage-ring method" employed at BNL and Fermilab. I will present the current status of the experiment, ongoing tests and design optimizations, and the plans for improvements of the experimental precision.

Status of the Muon g-2/EDM Experiment at J-PARC

TL;DR

The paper presents the J-PARC E34 experiment as a novel, cross-checking approach to measuring the muon g-2 and EDM using ultra-cold muons stored in a compact MRI-type magnet. The method avoids electric-field focusing by employing spiral injection and magnetic confinement, enabling precise extraction of the spin-precession frequency and the EDM signal from decay positrons in a high-resolution tracker. Current projections target a statistical precision for the muon g-2 value of about 450 ppb, with systematic uncertainties below 70 ppb, and an EDM sensitivity of 1.5e-21 e cm (stat) and 0.36e-21 e cm (syst). To push beyond these goals, three upgrades are under study: optical repolarization to boost polarization, higher momentum up to 600 MeV/c with a high-gradient linac, and a storage-field increase toward 6 T, each with distinct technical challenges. Overall, the J-PARC program offers a crucial independent benchmark for the storage-ring measurements and contributes to resolving tensions in the Standard Model prediction for the muon sector.

Abstract

The Muon g-2/EDM Experiment at J-PARC will employ a novel way to measure the muon magnetic anomaly, a_mu = (g-2)_mu/2, by using a low-emittance beam of positive muons stored in a compact muon storage magnet. The experimental method includes new technologies such as a three-dimensional spiral injection, an MRI-type storage magnet with superb field uniformity, and a positron tracking detector. The expected systematic uncertainty will be at the same level as that of the Fermilab Muon g-2 experiment, providing an important cross-check of the "storage-ring method" employed at BNL and Fermilab. I will present the current status of the experiment, ongoing tests and design optimizations, and the plans for improvements of the experimental precision.
Paper Structure (4 sections, 2 equations, 2 figures, 1 table)

This paper contains 4 sections, 2 equations, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experimental Approach
  3. Comparison of $g\!-\!2$ Experiments
  4. Higher sensitivity studies for the J-PARC Muon $g\!-\!2$/EDM Experiment

Figures (2)

  • Figure 1: Left: Schematic view of the accelerator complex for the muon $g-2$/EDM experiment at J-PARC (courtesy of T. Mibe). Right: Overview of the muon storage magnet (from Abe:2019thb).
  • Figure 2: Statistical uncertainty $\delta\omega_a/\omega_a$ vs. muon momentum for J-PARC E34, shown for beam polarizations of 50% (blue) and 70% (red). Dashed lines indicate a muon momentum of 300 MeV/c (current proposal) and a possible upgrade at 600 MeV/c.