BASE is a multinational collaboration at the Antiproton Decelerator (AD) of CERN which aims at precise comparisons of the fundamental properties of antiprotons and protons. Such comparisons provide stringent tests of charge-parity-time reversal invariance which is the most fundamental symmetry in the Standard Model of particle physics. The BASE collaboration observed the first spin flips with a single trapped proton, measured the magnetic moment of the proton with a fractional precision at the ppm level, observed first single proton spin filps, and performed the first direct high-precision measurement of the magnetic moment of a single trapped proton. Our value has a precision of 3.3 ppb, outperforms previous Penning trap experiments by a factor of 760. In addition BASE performed the most precise test of CPT invariance with baryons, by comparing the antiproton-to-proton charge-to-mass ratio with a fractional precision of 69 parts in a trillion. Very recently BASE measured the magnetic moment of the antiproton with a fractional precision of 0.8 parts in a million and observed first single spin transitions with a single trapped antiproton.

First Observation of Single Antiproton Spin Transitions

Today we have published a paper in Phys. Lett. B, in which we report on the detection of individual spin quantum transitions of a single trapped antiproton in a Penning trap. The spin state determination is based on the unambiguous detection of axial frequency shifts which are induced by the spin transition in presence of a magnetic bottle. We have achieved a detection fidelity of 92.6 % and demonstrated spin state initialization with 99.9% fideltiy.

First circulating beam in ELENA

The construction of ELENA, the Extra Low Energy Antiproton Ring, which is dedicated to slow-down the 5.3 MeV AD antiprotons to keV energies has been finished and is entering the commissioning phase. In a recent AD users meeting the ELENA team around project coordinator Christian Carli has reported on first circulating beam, CONGRATULATIONS! For more information read the CERN courier article.

New Article on Single Particle Detection Systems Published.

Our article "Highly sensitive superconducting circuits at ∼700 kHz with tunable quality factors for image-current detection of single trapped antiprotons" has been published in Review of Scientific Instruments. There we describe highly sensitive image-current detection systems based on superconducting toroidal coils and ultra-low noise amplifiers for non-destructive measurements of the axial frequencies (550–800 kHz) of single antiprotons stored in the BASE multi-Penning-trap system.

BASE Celebrates First Antiproton Birthday

A crucuial device in the BASE multi-Penning trap system is a reservoir trap for antiprotons. This trap is loaded with a cloud of antiprotons provided by CERN's antiproton decelerator and methods were developed to extract single particles from this reservoir and to supply them to our high precision measurement traps. This allows BASE to continuously perform experiments with antiprotons, independent from accelerator maintenance and shutdown cycles.


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