Stringent Tests of CPT Invariance

What is CPT Invariance?

C = charge conjugation (changing a particle into its antiparticle)
P = party transformation (r → -r)
T = time reversal transformation (motion reversal)

CPT is the application of all of these symmetry operations.

CPT Theorem

The CPT theorem, one of the most basic assertions of physics, arises from the success of quantum field theories. Quantum field theories seem to provide a very successful description of all interactions except for gravitational interactions. Where a quantum field theory is a correct description, along with the usual assumptions such as invariance under Lorentz transformations, the necessary result is that the reality that is described is invariant under a CPT transformation. This is called the CPT theorem. However, since gravity has not yet been successfully described by a quantum field theory, it is possible that the CPT is not universal. The only way to tell is to look.

CPT invariance implies that particles and antiparticles have the same:

• mass
• charge-to-mass (except opposite sign)
• magnetic moment (except opposite sign)
• mean life
• atomic structure

Testing to see whether particles and antiparticles have properties related in this way is thus a test of CPT invariance.

A simple explanation of CPT invariance is in a popular account of our low energy antiproton methods and Q/M measurements.

The Most Stringent Tests of CPT Invariance with Mesons, Leptons and Baryons

Important to check CPT invariance in at least one meson, lepton and baryon system

What We Have Done

• We have made the most stringent baryon CPT test (comparison of Q/M for antiproton and proton).

What We Aspire to Do

• We are currently trying to dramatically improve the best lepton CPT test (by making a much more precise comparison of the positron and electron magnetic moments).
• We hope to make a baryon CPT test (comparing the antiproton and proton magnetic moments) that has an precision improved by a factor of a million or more.
• We (and others) aspire to compare antihydrogen and hydrogen to make even more precise lepton and baryon CPT tests.