The ALICE (A Large Ion Collider Experiment) experiment at the CERN LHC has demonstrated symmetry between light atomic nuclei protons and anti-protons to a higher level than previously by a factor of about 100 times and this takes place just 50 years since the discovery of the anti-proton.
Symmetry in physics is a basic concept in modern physics which depends on “mirror” images being equivalent – see the explanation below.
Determining the exact energy-mass of particles and their anti-particles is critical to determining whether The Standard Model and in particular the symmetry aspect of TSM is accurate.
Using the power of the LHC scientists have measured the ratio of electrical charge and mass to a new higher precision at both high and low levels.
Reporting in the Journal Nature Physics dated August 17th (pre-publication) (http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3432.html) this is the first real update in these numbers in 40 and 50 years and come from a device not even designed to make this measurement.
“The ALICE collaboration has measured the difference between mass-to-charge ratios for deuterons (a proton, or hydrogen nucleus, with an additional neutron) and antideuterons, as well as for helium-3 nuclei (two protons plus a neutron) and antihelium-3 nuclei. Measurements at CERN, most recently by the BASE experiment, have already compared the same properties of protons and antiprotons to high precision. The study by ALICE takes this research further as it probes the possibility of subtle differences between the way that protons and neutrons bind together in nuclei compared with how their antiparticle counterparts form antinuclei.”
“The measurements by ALICE and by BASE have taken place at the highest and lowest energies available at CERN, at the LHC and the Antiproton Decelerator, respectively,” said CERN Director-General Rolf Heuer. “This is a perfect illustration of the diversity in the laboratory’s research programme.”
The particle in question is a deuteron. That is better known as hydrogen when there is also an electron but technically a deuteron is a proton and neutron pair. The measurement wasn’t done directly which can only be done to certain precision but instead it compared the deuteron with its anti-deuteron pair which means the difference rather than the absolute values is measured and this can be done to a much higher precision.
Measurements of the mass and velocity of charged particles is relatively easy because they can be curved in a magnetic field. The time-of-flight detector in ALICE is basically looking at the curve of the particle track and can be done to a resolution of 80 picoseconds. A picosecond is one millionth of one millionth of a second.
The Standard model of particle physics has three related natural near-symmetries, every particle has an antiparticle (charge symmetry), time symmetry, and parity – mirror).
This is a rather abstract concept but since every part of a scientific theory must be correct or the entire theory is wrong, measurements made of particles and their anti-particle pairs must show identical if mirror image properties or the entire Standard Model must be reevaluated.
