Status of the DeeMe Experiment, an Experimental Search for $\mu$-$e$ Conversion at J-PARC MLF

Abstract

The DeeMe experiment is planned to search for muon-to-electron conversion at J-PARC MLF. Our goal is to measure the process with a single event sensitivity of 1 × 10 −13 or 2 × 10 −14 for a graphite or silicon carbide target. That is one or two orders of magnitude better than the current upper limits, 7 × 10 −13 for a gold target by the SINDRUM-II experiment at PSI and 4.6 × 10 −12 for a titanium target by the experiment at TRIUMF. We are in the middle of preparation for the experiment. The construction of the secondary beamline, H Line, is now in progress. Four tracking detectors have been manufactured in 2017, and the optimization study of the filling gas is ongoing to improve the performance. After getting the better hit efficiency, we measured the momentum spectrum of electrons produced through muon-decay-in-orbit from a carbon target at J-PARC MLF D2 Area in March, 2019. In this paper, the preparation status of the DeeMe experiment will be presented.

Isotope dependence of muon decay in orbit

“…Ultimately, the quantity of interest for µ − → e − conversion experiments is not the binding energy E b but the related endpoint energy E end , given by Eq. (5). Since E b is itself only a small correction to the leading-order estimate E end ∼ m µ , small uncertainties in E b are even less relevant in E end .…”

“…Ref. [21] also provided an expansion of the DIO spectrum near the endpoint of the form dΓ/dE e Γ 0 B(E e − E end ) 5 , where Γ 0 = G 2 F m 5 µ /(192π 3 ) is the leading-order free-muon decay rate and B is a coefficient of mass dimension −6 that depends on several overlap integrals over products of wavefunctions.…”

“…Particularly clean processes are the decays µ → eγ and µ → 3e as well as the coherent µ − → e − conversion in the field of a nucleus, µ − +(A, Z) → e − +(A, Z), the latter being especially sensitive to effective LFV operators involving quarks [2,3]. An immense jump in sensitivity to µ − → e − conversion in nuclei is expected in the near future with experiments such as DeeMe [4,5], COMET [6,7], and Mu2e [8,9]. Since the µ − → e − conversion rate depends on the target nucleus (notably its charge Z), it is possible to differentiate between different LFV effective operators using complementary target nuclei in the event of a positive signal observation [3,[10][11][12][13][14].…”

Online DAQ and slow control interface for the Mu2e experiment

“…The current world's best limit < 7 × 10 −13 (on gold) is from the SINDRUM II experiment at Paul Scherrer Institut [2]. In addition to Mu2e, the COMET experiment in preparation at J-PARC has an expected SES of 3×10 −15 for Phase-I and O (10 −17 ) for Phase-II (on aluminum) [3], while the DeeMe experiment, also in preparation at J-PARC, has an expected SES of 10 −14 (on carbon) [4].…”

Slow control and data acquisition systems in the Mu2e experiment

“…The current world's best limit 𝑅 𝜇𝑒 < 7 × 10 −13 (on gold) is from the SINDRUM II experiment at Paul Scherrer Institut [2]. In addition to Mu2e, the COMET experiment in preparation at J-PARC has an expected SES of 3×10 −15 for Phase-I and O (10 −17 ) for Phase-II (on aluminum) [3], while the DeeMe experiment, also in preparation at J-PARC, has an expected SES of 10 −14 (on carbon) [4]. The Mu2e apparatus includes three superconducting solenoids: The Production Solenoid, the Transport Solenoid and the Detector Solenoid [5].…”