Joint Seminar in Nuclear Physics

01 February 2021, 14:00 
Joint Seminar in Nuclear Physics





14:00 - 15:00 - "Exciting Exotic Atoms", Ben Ohayon, ETH Zürich


Recent and ongoing developments of low energy beamlines, as well as the refinement of production and measurement techniques, are heralding a new era of precision measurements with exotic atoms, which are made by exchanging at list one constituent of an atom with an exotic particle.  This year the CERN antiproton decelerator upgrade, ELENA (Extra Low Energy Antiproton ring), will enter into operation , making available record luminosity of low-energy antiprotons, while the PSI LEM (Low Energy Muon) beamline is consistently providing an intense, slow, positive muon beam. These particle beams, paired with novel neutralization schemes, are ideal for creating slow neutral exotic atoms, such as antihydrogen and muonium, which are targets for precision spectroscopy.

In this talk I will present the ongoing efforts to measure the 1S-2S interval in muonium with a precision of 2 ppt [1], and the Lamb Shift (2S-2P) in muonium and antihydrogen with a precision of 100 kHz (100 ppm) [2,3]. These goals comprise a 2-3 orders of magnitudes improvement upon the state-of-the-art. Such improvements provide unique opportunities to shed light on the Baryon Asymmetry Problem, ND search for  Lorentz and CPTviolation , dark-sector particles, new muonic forces and hidden dimensions. Such a measurement will also determine the charge radius of the antiproton, comprising the first size determination of antimatter [3].

[1] P. Crivelli, Hyperfine Interactions, 239(1), (2018)

[2] G. Janka, Ben Ohayon,  et. al. EPJC 80, 804 (2020)

[3] P. Crivelli, D. Cooke, and M. W. Heiss PRD 94 (2016)


15:00 - 16:00 - break


16:00 - 17:00 - "Status and prospects of the NEXT experiment", Lior Arazi, Ben-Gurion University


The search for neutrinoless double beta decay is the most promising approach to determine whether the neutrino is its own antiparticle. If detected, it will be a first demonstration of lepton number violation, with far-reaching implications in particle physics and cosmology. Because of the extremely long half-lives of the decay (>1026 years), a successful detection requires outstanding background suppression capability. The NEXT experiment searches for neutrinoless double beta decay in xenon 136, using an electroluminescent high-pressure gaseous xenon time projection chamber (TPC). While other experiments in the field rely predominantly on a high energy resolution for discriminating between candidate signal and background events, NEXT has in addition a unique capability to reconstruct the full topology of events in 3D and thus provide an extra handle for signal-background discrimination. In this talk we will present a new image restoration method recently developed at Ben-Gurion University, which allows for unprecedented accuracy in track reconstruction, resulting in a 5 fold improvement in background suppression. We will demonstrate the use of this method on real data from the experiment, showing – for the first time – sharp images of two-neutrino double beta decay tracks. In addition, we will present ongoing R&D towards the capability to identify in situ the appearance of a single barium-136 atom in running TPC. If successful, this approach will enable an essentially background-free search for neutrinoless double beta decay on the tonne-scale, with half-life sensitivities far above 1027 years.



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