Double-penning trap for the storage of one individual proton and the detection of spin quantum-jumps. |
Researchers
at Johannes Gutenberg Univ. Mainz (JGU) and the Helmholtz
Institute Mainz (HIM), together with their colleagues from the Max
Planck Institute for Nuclear Physics in Heidelberg and the GSI Helmholtz
Center for Heavy Ion Research in Darmstadt, have observed spin
quantum-jumps with a single trapped proton for the first time.
The
result is a pioneering step forward in the endeavor to directly measure
the magnetic properties of the proton with high precision. The
measuring principle is based on the observation of a single proton
stored in an electromagnetic particle trap. As it would also be possible
to observe an anti-proton using the same method, the prospect that an
explanation for the matter-antimatter imbalance in the universe could be
found has become a reality. It is essential to be able to analyze
antimatter in detail if we are to understand why matter and antimatter
did not completely cancel each other out after the Big Bang—in other
words, if we are to comprehend how the universe actually came into
existence.
The
proton has an intrinsic angular momentum or spin, just like other
particles. It is like a tiny bar magnet; in this analogy, a spin quantum
jump would correspond to a (switch) flip of the magnetic poles.
However, detecting the proton spin is a major challenge. While the
magnetic moments of the electron and its anti-particle, the positron,
were already being measured and compared in the 1980s, this has yet to
be achieved in the case of the proton.
“We
have long been aware of the magnetic moment of the proton, but it has
thus far not been observed directly for a single proton but only in the
case of particle ensembles,” explains Stefan Ulmer, a member of the work
group headed by Professor Dr. Jochen Walz at the Institute of Physics
at the new Helmholtz Institute Mainz.
The
real problem is that the magnetic moment of the proton is 660 times
smaller than that of the electron, which means that it is considerably
harder to detect. It has taken the collaborative research team five
years to prepare an experiment that would be precise enough to pass the
crucial test.
“At
last we have successfully demonstrated the detection of the spin
direction of a single trapped proton,” says an exultant Ulmer, a
stipendiary of the International Max Planck Research School for Quantum
Dynamics in Heidelberg.
This
opens the way for direct high-precision measurements of the magnetic
moments of both the proton and the anti-proton. The latter is likely to
be undertaken at CERN, the European laboratory for particle physics in
Geneva, or at FLAIR/GSI in Darmstadt. The magnetic moment of the
anti-proton is currently only known to three decimal places. The method
used at the laboratories in Mainz aims at a millionfold improvement of
the measuring accuracy and should represent a new highly sensitive test
of the matter-antimatter symmetry. This first observation of the spin
quantum jumps of a single proton is a crucial milestone in the pursuit
of this aim.
Proton-spin quantum-jump resonance curve. |
Matter-antimatter
symmetry is one of the pillars of the Standard Model of elementary
particle physics. According to this model, particles and anti-particles
should behave identically once inversions of charge, parity, and time—referred to as CPT transformation—are applied simultaneously.
High-precision comparisons of the fundamental properties of particles
and anti-particles make it possible to accurately determine whether this
symmetrical behavior actually occurs, and may provide the basis for
theories that extend beyond the Standard Model. Assuming that a
difference between the magnetic moments of protons and anti-protons
could be detected, this would open up a window on this “new physics”.
The
results obtained by the Mainz cooperative research team were published
online in Physical Review Letters.
The
research work carried out by the team of Professor Dr Jochen Walz on
anti-hydrogen and the magnetic moment of protons forms part of the
“Precision Physics, Fundamental Interactions and Structure of Matter”
(PRISMA) Cluster of Excellence, which is currently applying for future
sponsorship under the German Federal Excellence Initiative.
