Following the Big Bang over 13 billion years ago, the universe was filled with high-energy radiation that produced pairs of matter and antimatter particles, such as protons and antiprotons. When these pairs collide, they annihilate each other, reverting to pure energy. This process should result in equal amounts of matter and antimatter, implying a matterless universe. However, the existence of material objects indicates an imbalance - a small but critical asymmetry not accounted for by the standard model of particle physics.
The BASE collaboration ("Baryon Antibaryon Symmetry Experiment") includes universities from Dusseldorf, Hanover, Heidelberg, Mainz, and Tokyo, the Swiss Federal Institute of Technology in Zurich, CERN in Geneva, GSI Helmholtz Centre in Darmstadt, the Max Planck Institute for Nuclear Physics in Heidelberg, the National Metrology Institute of Germany (PTB) in Braunschweig, and RIKEN in Wako, Japan.
Professor Stefan Ulmer, spokesperson of BASE, said, "The central question we are seeking to answer is: Do matter particles and their corresponding antimatter particles weigh exactly the same and do they have exactly the same magnetic moments, or are there minuscule differences?" Ulmer is a professor at the Institute for Experimental Physics at HHU and conducts research at CERN and RIKEN.
The physicists aim to achieve extremely high-resolution measurements of proton spin-flip - quantum transitions of the proton spin - in individual, ultra-cold, low-energy antiprotons. "From the measured transition frequencies, we can, among other things, determine the magnetic moment of the antiprotons - their minute internal bar magnets," Ulmer explained. "The aim is to see with an unprecedented level of accuracy whether these bar magnets in protons and antiprotons have the same strength."
Preparing antiprotons for such precise measurements is a complex task. The BASE collaboration has now made a significant leap forward in this area.
Dr. Barbara Maria Latacz from CERN, the lead author of the study published in Physical Review Letters, explained, "We need antiprotons with a maximum temperature of 200 mK, extremely cold particles. Previously, cooling antiprotons to this temperature took 15 hours. Our new method shortens this to eight minutes."
The new technique involves combining two Penning traps into a "Maxwell's daemon cooling double trap." This device selects only the coldest antiprotons for subsequent spin-flip measurements, discarding warmer particles, thus eliminating the need for additional cooling time.
This reduced cooling time allows for the necessary measurement statistics to be achieved much faster, significantly reducing measurement uncertainties. Latacz noted, "We need at least 1,000 individual measurement cycles. With our new trap, we need about one month for this - compared to almost ten years with the old technique."
Ulmer added, "With the BASE trap, we have measured that the magnetic moments of protons and antiprotons differ by a maximum of one billionth (10^-9). We have improved the error rate of spin identification by more than a factor of 1,000. In our next measurement campaign, we hope to improve magnetic moment accuracy to 10^-10."
Looking ahead, Ulmer stated, "We aim to build a mobile particle trap to transport antiprotons generated at CERN in Geneva to a new laboratory at HHU. This setup could improve measurement accuracy by at least a factor of 10."
Background: Traps for Fundamental Particles
Traps store individual electrically charged fundamental particles, their antiparticles, or atomic nuclei using magnetic and electric fields. Storage periods can exceed ten years, allowing targeted particle measurements.
Two basic types of traps exist: Paul traps, using alternating electric fields, were developed by Wolfgang Paul in the 1950s. Penning traps, using a homogeneous magnetic field and an electrostatic quadrupole field, were developed by Hans G. Dehmelt. Both physicists received the Nobel Prize in 1989 for their contributions.
Research Report:Orders of Magnitude Improved Cyclotron-Mode Cooling for Non-Destructive Spin Quantum Transition Spectroscopy with Single Trapped Antiprotons
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