BASE (CERN)

BASE (CERN). The Baryon Antibaryon Symmetry Experiment (BASE) is a fundamental physics experiment located at the CERN laboratory. It utilizes ultra-sensitive Penning trap techniques to perform high-precision comparisons of the fundamental properties of protons and antiprotons. The primary goal is to test the fundamental symmetries of the Standard Model, particularly CPT symmetry, by searching for any differences between matter and antimatter.

Overview

BASE is part of the rich experimental program at the Antiproton Decelerator facility, which provides the world's lowest-energy antiprotons for experiments. The collaboration focuses on precision metrology of single trapped particles, building upon techniques pioneered by the TRAP and ATRAP experiments. Its research directly addresses one of the great open questions in modern physics: the observed asymmetry between matter and antimatter in the universe. By comparing the charge-to-mass ratio and the magnetic moment of protons and antiprotons with unprecedented precision, BASE conducts stringent tests of CPT invariance.

Experimental Setup

The core apparatus consists of a sophisticated, multi-stage Penning trap system housed in a cryogenic environment at superfluid helium temperatures. This setup includes a precision trap for high-accuracy frequency measurements and an analysis trap for determining the quantum state of a single particle via the continuous Stern–Gerlach effect. Antiprotons are delivered from the Antiproton Decelerator and carefully injected into the trap stack. The entire experiment is shielded by a superconducting magnet providing a highly stable and homogeneous magnetic field, which is crucial for the precision measurements. Advanced cryogenics and ultra-high vacuum systems ensure a stable and isolated environment for the long-term storage of antimatter.

Scientific Goals and Results

The central scientific objective is to test CPT symmetry by comparing the proton and antiproton magnetic moments and charge-to-mass ratios. A violation of CPT symmetry would have profound implications for the Standard Model and theories of quantum gravity. BASE has set the world's most precise limit on the charge-to-mass ratio equality, finding agreement at the level of 16 parts per trillion. Furthermore, the collaboration achieved the first direct high-precision measurement of the antiproton magnetic moment, finding it to be equal to that of the proton within experimental uncertainty. These results provide strong confirmation of CPT invariance and constrain potential new physics models.

Technical Specifications

The experiment operates at a temperature of approximately 4.2 kelvin using a superfluid helium bath cryostat. The central superconducting magnet produces a field of 1.9 tesla with exceptional temporal stability. The multi-trap system includes a precision trap with an orthogonalized design to minimize systematic errors and an analysis trap equipped with a magnetic bottle for spin-state analysis. Single particles can be stored for over a year, enabling extremely long measurement times. Detection systems rely on non-destructive image current detection techniques, where the particle's axial motion is coupled to a high-quality LC circuit and read out with ultra-low-noise amplifiers.

Collaboration and Timeline

The BASE collaboration is an international team of scientists from institutions including CERN, the Max Planck Institute for Nuclear Physics, Johannes Gutenberg University Mainz, the University of Tokyo, and the RIKEN research institute. The experiment was approved in 2013 and began taking data with antiprotons shortly thereafter. Major milestones include the first precision comparison of charge-to-mass ratios in 2015, the groundbreaking measurement of the antiproton magnetic moment in 2017, and subsequent measurements pushing the precision even further. The collaboration continues its research with upgrades and new measurement cycles at the Antiproton Decelerator, and is involved in developing the BASE experiment for the future Extra Low ENergy Antiproton (ELENA) ring at CERN.

Category:Experiments at CERN Category:Antimatter experiments Category:Particle physics experiments