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 are interesting because any measured asymmetry would hint at physics beyond the Standard Model. The experiment consists of measuring the cyclotron and Larmor frequencies of single trapped (anti)protons, and optionally negatively charged hydrogen ions. By measuring the ratio of these two frequencies the magnetic moment of the (anti)proton is obtained in units of the nuclear magneton. 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 demonstrated the double Penning trap technique for the first time. Recently we 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, and improves the currently acceped CODATA literature value by a factor of 2.5. By applying this technique to the antiproton magnetic moment a 1000-fold improvement in precision is possible, which will provide one of the most sensitive tests of CPT invariance. 

In addition we 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. We aim at improving this measurement by another factor of 10. 

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.

Research Prizes for BASE Members

BASE members Takashi Higuchi and Andreas Mooser received research prizes for their work in BASE.

Takashi Higuchi was awarded a poster prize at the LEAP2016 conference in Kanazawa, Japan, which was sponsored by Nature Physics.

For his PhD thesis, in which he performed the first direct high-precision measurement of the magnetic moment of a single trapped proton, Andreas Mooser received the PhD thesis-prize of GSI Darmstadt and the prize of the friends of the University of Mainz. Andreas' work contains the most precise measurement of the proton magnetic moment, the work was carried-out at the BASE-Mainz experiment.


Comparison of the Antiproton to Proton Charge to Mass Ratio

In a paper published today in Nature we report the high-precision comparison of the antiproton-to-proton charge to mass ratio. In our measurements we compared the cyclotron frequencies of antiprotons to that of negatively charged hydrogen ions, which are used as a proxy for the proton. We achieved a fractional precision of 69 parts in a trillion, which corresponds in our magnetic field of 1.95 Tesla to an absolute energy resolution of 2mHz. Our result is consistent with CPT invariance.

IUPAP Prize 2014

BASE member Stefan Ulmer has been selected to receive the IUPAP Young Scientist Prize 2014 in Fundamental Metrology. With this prize the International Union of Pure and Applied Physics (IUPAP) honors his work on proton and antiproton magnetic moment measurements.


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