Statistical sensitivity estimates for oscillating electric dipole moment measurements in storage rings
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Regular Article - Experimental Physics
Statistical sensitivity estimates for oscillating electric dipole moment measurements in storage rings J. Pretz1,2,3,a , S. P. Chang4,5 , V. Hejny1, S. Karanth6 , S. Park4 , Y. Semertzidis4,5 , E. Stephenson7 , H. Ströher1,8 1
Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich, Germany III. Physikalisches Institut B, RWTH Aachen University, 52056 Aachen, Germany 3 JARA-FAME, Forschungszentrum Jülich, RWTH Aachen University, Aachen, Germany 4 Center for Axion and Precision Physics Research, IBS, Daejeon 34051, Republic of Korea 5 Department of Physics, KAIST, Daejeon 34141, Republic of Korea 6 Marian Smoluchowski Institute of Physics, Jagiellionian Univsersity, Cracow, Poland 7 Indiana Univ., Bloomington, IN 47408, USA 8 JARA–FAME (Forces and Matter Experiments), Forschungszentrum Jülich, RWTH Aachen University, Aachen, Germany
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Received: 4 December 2019 / Accepted: 19 January 2020 © The Author(s) 2020
Abstract In this paper analytical expressions are derived to describe the spin motion of a particle in magnetic and electric fields in the presence of an axion field causing an oscillating electric dipole moment (EDM). These equations are used to estimate statistical sensitivities for axion searches at storage rings. The estimates obtained from the analytic expressions are compared to numerical estimates from simulations in Chang et al. (Phys Rev D 99(8):083002, 2019). A good agreement is found.
1 Introduction and motivation Axions and axion like particles (ALPs) are candidates for dark matter. There is thus a huge experimental effort for the search of these kind of particles. For a detailed review, we refer the reader to references [2,3]. Axions and ALPs can interact with ordinary matter in various ways. Reference [4] identifies three terms: a Fμν F˜μν , f0
a G μν G˜ μν , fa
∂μ a Ψ¯ f γ μ γ5 Ψ fa
(1)
describing the coupling to photons, gluons and to the spin of fermions, respectively. The vast majority of experiments makes use of the first term [e.g. Cavity experiments (ADMX), helioscopes (CAST), light-through-wall experiments (ALPS)]. In addition, astrophysical observations also provide sensitive limits to the axion-photon coupling. In general, it is rather difficult for these experiments to reach masses below 10−6 eV, one reason being that the axion wave length a e-mail:
becomes too large. Furthermore, these experiments are measuring rates proportional to at least a small amplitude squared. For the second (and third) term in the list (1) this is different. It turns out that the second term has the same structure as the QCD-θ term which is also responsible for an electric dipole moment (EDM) of nucleons. The axion field gives rise to an effective time-dependent θ -term and oscillates at a frequency proportional to the mass of the axion m a . This gives rise to an oscillating EDM. New opportunities to search for axions/ALPs with much higher sensitivity arise, because the signal is proportional to an amplitude A and not to its square. To date, NMR based m
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