Phase Locking the Spin Precession in a Storage Ring

Axion dark matter: How to see it?

The axion is a highly motivated elementary particle that could address two fundamental questions in physics-the strong charge-parity (CP) problem and the dark matter mystery. Experimental searches for this hypothetical particle started reaching theoretically interesting sensitivity levels, particularly in the micro-electron volt (gigahertz) region. They rely on microwave resonators in strong magnetic fields with signals read out by quantum noise limited amplifiers. Concurrently, there have been intensive experimental efforts to widen the search range by devising various techniques and to enhance sensitivities by implementing advanced technologies. These orthogonal approaches will enable us to explore most of the parameter space for axions and axion-like particles within the next decades, with the 1- to 25-gigahertz frequency range to be conquered well within the first decade. We review the experimental aspects of axion physics and discuss the past, present, and future of the direct search programs.

Noninvasive 3D Field Mapping of Complex Static Electric Fields

Many upcoming experiments in antimatter research require low-energy antiproton beams. With a kinetic energy in the order of 100 keV, the standard magnetic components to control and focus the beams become less effective. Therefore, electrostatic components are being developed and installed in transfer lines and storage rings. However, there is no equipment available to precisely map and check the electric field generated by these elements. Instead, one has to trust in simulations and, therefore, depend on tight fabrication tolerances. Here we present, for the first time, a noninvasive way to experimentally probe the electrostatic field in a 3D volume with a microsensor. Using the example of an electrostatic quadrupole focusing component, we find excellent agreement between a simulated and real field. Furthermore, it is shown that the spatial resolution of the probe is limited by the electric field curvature which is almost zero for the quadrupole. With a sensor resolution of 61  V/m/sqrt[Hz], the field deviation due to a noncompliance with the tolerances can be resolved. We anticipate that this compact and practical field strength probe will be relevant also for other scientific and technological disciplines such as atmospheric electricity or safeguarding near power infrastructure.

Measurement of the Spin Tune Using the Coherent Spin Motion of Polarized Protons in a Storage Ring

This Letter reports the first spin tune measurement at high energies (24 and 255 GeV) with a driven coherent spin motion. To maintain polarization in a polarized proton collider, it is important to know the spin tune of the polarized proton beam, which is defined as the number of full spin precessions per revolution. A nine-magnet spin flipper has demonstrated high spin-flip efficiency in the presence of two Siberian snakes [H. Huang et al., Phys. Rev. Lett. 120, 264804 (2018).10.1103/PhysRevLett.120.264804]. The spin flipper drives a spin resonance with a given frequency (or tune) and strength. When the drive tune is close to the spin tune, the proton spin direction is not vertical anymore, but precesses around the vertical direction. By measuring the precession frequency of the horizontal component, the spin tune can be precisely measured. A driven coherent spin motion and fast turn-by-turn polarization measurement are keys to the measurement. The vertical spin direction is restored after turning the spin flipper off and the polarization value is not affected by the measurement. The fact that this manipulation preserves the polarization makes it possible to measure the spin tune during the operation of a high energy accelerator.

EDM Experiments at Storage Rings

According to our present understanding, the early Universe contained the same amount of matter and anti-matter and, if the Universe had behaved symmetrically as it developed, every particle would have been annihilated by one of its antiparticles. One of the great mysteries in the natural sciences is therefore, why matter dominates over antimatter in the visible Universe. The breaking of the combined chargeconjugation and parity symmetries (CP-violation, CPV) in the Standard Model of particle physics (SM) is insufficient to explain this and further sources of CPV must be sought. These could manifest themselves in electric dipole moments (EDMs) of elementary particles, which occur when the centroids of positive and negative charges are mutually and permanently displaced. An EDM observation would also be an indication for physics beyond the SM. No EDM has been observed so far; after its discovery, investigations on different systems will be required to pin down CPV sources. In this respect the idea to search for EDMs of charged hadrons (i.p. proton and deuteron) in a new class of precision storage rings has recently been put forward. In addition, such searches bear the potential to reach sensitivities of 10-29 e·cm. The EDM measurement principle, the time development of the polarization vector subject to a perpendicular electric field, is simple, but the smallness of the effect makes this an enormously challenging project. A stepwise approach, from R&D for key-technologies towards the holy grail of a double-beam precision storage ring with counter-rotating beams, is needed. The ongoing research of the JEDI Collaboration at the cooler synchrotron COSY of Forschungszentrum Jülich (Germany) provides invaluable information: recent experimental milestones are presented and discussed.