R. S. Conti

Search for C-violating, P-conserving interactions and observation of 23S1 to 21P1 transitions in positronium

Possible C-forbidden transitions between 23S1 and 21P1 states of positronium are investigated. Limits are placed on the CP-violating state-mixing matrix element:|〈21P1|HHCP| 23P1〉| < 65MHz. Zeeman induced transitions yield the first observation of 21P1 states and measurement of the 23S1 to 21P1 transition frequency, v0=11181 ± 13 MHz, verifying QED calculations.

Experimental Tests of QED in Positronium: Recent Advances

The current experimental situation regarding tests of fundamental physics using positronium is reviewed. Five measurements are discussed and compared with theoretical predictions: the singlet and triplet annihilation decay rates, the ground state and the n = 2 energy intervals, and the Doppler-free two-photon excitation of the 1S to 2S transition. Previous results, recent progress (where appropriate), and the outlook for future improvements in these measurements are discussed.

A viable superluminal hypothesis: Tachyon emission from orthopositronium

Tachyons are hypothetical particles that travel faster than the vacuum speed of light. Previous experiments have searched for, but have not found evidence of tachyons. Long-standing, anomalous measurements of the orthopositronium (o-Ps) decay rate are interpreted as evidence for two tachyons being occasionally emitted when o-Ps decays. Restricting the coupling of tachyon pairs to a single photon (no tachyon coupling to matter) yields a new theory where tachyons are only observed in o-Ps decay and not in the previous tachyon experiments. Combining the single photon coupling theory with all previous experiments predicts that these tachyons must deposit energy while traversing scintillator detectors. A new tachyon search experiment will use this energy loss prediction to attempt to find tachyons passing through the apparatus or set limits disproving the original o-Ps to tachyon hypothesis. Viewing an intense o-Ps source, a time-of-flight spectrometer uses the superluminal property of tachyons for identificat...

Positronium Decay Rates

In this paper we briefly review all positronium (Ps) decay rate measurements (including those of the excited states and the Ps negative ion) that have been completed to date. The results are compared with theoretical values. The Ps system represents the most rigorous confrontation with theoretical decay rate calculations for any QED system.

Precision Measurement of the Triplet Positronium Decay Rate in Gases

In a recent publication1, we presented a new 200 ppm measurement of the vacuum decay rate,λT of orthopositronium (o-Ps) formed in a gas. Our result, λT = 7.0516 ± 0.0013 µs−1, represents a factor of four improvement over previous measurements. Our result is in substantial agreement with experimental results, the most recent of which are2–5: 7.056 ± 0.007 µs−1, 7.045 ± 0.006 µs−1, 7.051 ± 0.005 µs−1, and 7.050 ± 0.013 µs−1. These values are 1–2.5 standard deviations above the present theoretical value6,7 and our new measurement exceeds theory by 10 experimental standard deviations.

Magnetic Moments of Electrons and Positrons

In this report we describe a number of new features in our precision experiments currently in progress to measure the anomalous magnetic moments of the electron and positron, and we will point out the impact these improvements will have in testing several fundamental theories in physics. In the electron experiment, reduction in both statistical and systematic errors will result in a comparison with QED predictions at the level of the eighth-order term in the expansion of the anomaly in powers of α. In addition, by varying the energy of the electrons we can test special relativity to an accuracy of 2×10-11. The positron experiment will test CPT by comparing the electron and positron magnetic moments.