Speaker
Description
The study of permanent and oscillating Electric Dipole Moments (EDMs) of
fundamental particles for charged hadronic systems such as proton and deuteron (possibly also 3 He) can help to find answers to two of the most important current scientific questions in particle physics and cosmology: (i) What happened to antimatter after the Big Bang? and (ii) What is dark matter?
The current Standard Model of Cosmology (SMC) is not able to explain the
observed asymmetry between matter and antimatter in our universe. Obviously, physics beyond the SMC is needed, which can be explored either by using highest energies (e.g., at LHC) or by striving for highest precision and sensitivity (e.g., in the search for electric dipole moments). Permanent electric dipole moments (EDMs) and oscillating EDMs (oEDMs) caused by axions or axion-like particles (ALPs) violate both time reversal ($T$) and parity invariance ($P$) and are also $CP$-violating via the $CPT$ theorem. The discovery of EDMs or ALPs far above the immeasurably small SMC background would thus be strong evidence for physics beyond the SMC.
While many EDM searches focus on neutral systems (neutrons, atoms, and
molecules), storage rings offer the possibility to measure EDMs/ALPs of charged particles by observing their influence on the spin motion in the ring [1]. Direct searches for proton and deuteron EDMs hold the potential to achieve sensitivities of the order of $10^{-29}$ e cm. In this talk, the JEDI experiments for the first direct measurement of deuteron EDMs and the first search for axion-like particles in a storage ring will be presented and recent results will be discussed.
The next inevitable step on the way to a precision EDM facility is the construction of a prototype storage ring (PSR), comprising both an all-electric version and a hybrid ring in which the electric fields are supplemented by magnetic fields. The technical design of the PSR is the main goal (beam energy of about 30 − 40 MeV, circumference of about 100 m), and once available, it should demonstrate all remaining ambiguities and technologies and enable the first direct proton EDM measurement with sensitivity comparable to that of the neutron. Upon successful completion, the subsequent precision EDM facility (energy 230 MeV, circumference about 500 m) may eventually be able to improve the current static EDM limit of the neutron by up to three orders of magnitude and open the possibility for a unique discovery.
[1] F. Abusaif et al. Storage ring to search for electric dipole moments of charged particles: Feasibility study. CERN Yellow Reports: Monographs, 2021-003. CERN, Geneva, Jan 2021. URL https://cds.cern.ch/record/2654645.
