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Spin-dependent μ → e conversion

Cirigliano, Vincenzo·Davidson, Sacha·Kuno, Yoshitaka
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Abstract

The experimental sensitivity to μ→e conversion on nuclei is expected to improve by four orders of magnitude in coming years. Here, we consider the impact of μ→e flavour-changing tensor and axial-vector four-fermion operators which couple to the spin of nucleons. Such operators, which have not previously been considered, contribute to μ→e conversion in three ways: in nuclei with spin they mediate a spin-dependent transition; in all nuclei they contribute to the coherent (A 2 -enhanced) spin-independent conversion via finite recoil effects and via loop mixing with dipole, scalar, and vector operators. Furthermore, we estimate the spin-dependent rate in Aluminium (the target of the upcoming COMET and Mu2e experiments), show that the loop effects give the greatest sensitivity to tensor and axial-vector operators involving first-generation quarks, and discuss the complementarity of the spin-dependent and independent contributions to μ→e conversion.

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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSAtomic and Nuclear Physics

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Cirigliano, Vincenzo, Davidson, Sacha, Kuno, Yoshitaka. 2017-05-22. Spin-dependent μ → e conversion. https://doi.org/10.1016/j.physletb.2017.05.053

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