New precision measurement of hyperfine splitting of positronium

Abstract

The ground state hyperfine splitting of positronium ∆ HFS is sensitive to high order corrections of quantum electrodynamics (QED) in bound state. The theoretical prediction and the averaged experimental value for ∆ HFS has a discrepancy of 15 ppm, which is equivalent to 3.9 standard deviations (s.d.). A new precision measurement which reduces the systematic uncertainty from the positronium thermalization effect was performed, in which the non-thermalization effect was measured to be as large as 10 ± 2 ppm in a timing window we used. When this effect is taken into account, our new result becomes ∆ HFS = 203.394 2 ± 0.001 6(stat., 8.0 ppm) ± 0.001 3(sys., 6.4 ppm) GHz, which favors the QED prediction within 1.2 s.d. and disfavors the previous experimental average by 2.6 s.d. (A. Ishida) 1 Ps thermalization is a process that Ps loses its kinetic energy from initial energy E 0 to room temperature.

Formation of positron-atom bound states in collisions between Rydberg Ps and neutral atoms

“…This would be achieved by observing the charge-transfer reaction (2), with the incident Ps in a Rydberg state. We have provided theoretical estimates for the cross section of this reaction.…”

“…(A.10), this latter result is valid for any Ps momentum K. Instead of having a plateau, the ionization cross section will then decrease with the Ps energy, following the decrease of the positron and electron cross sections σ ± . For Cu, supposing the incident Ps has an energy of 0.05 eV, for n = 15 the ionization cross section is estimated to be about 25πa 2 0 , while the charge-transfer cross section is approximately 125πa 2 0 , i.e., much greater. Depending on the Ps energy and the value of n, this may or may not be the case, but we have shown that there should be a 'window' of Ps energies and values of n where charge transfer is the dominant process.…”

“…Being antimatter particles, positrons (e + ) are of fundamental importance for tests of QED and the Standard Model [1][2][3], and in astrophysics [4]. They also find numerous applications in condensed matter physics, surface science, atomic physics, and medicine (see, e.g., Refs.…”

“…It would also be interesting to apply this method to molecules for which the binding energies are known from the resonant annihilation studies [15,[19][20][21][22]. Unlike positron-molecule annihilation which probes resonant, quasibound states, the molecular analog of reaction (2) should lead to population of the true positron-molecule bound states. Molecules also allow one to explore reaction (2) for systems with very small binding energies, e.g., C 2 H 6 or CH 3 F. Their positron affinities are expected to be ∼1 meV [53,54] but have not be measured directly because such shifts of the annihilation resonances are much smaller than the energy resolution of the positron beam.…”

Testing Quantum Electrodynamics with Positronium State

“…Recently a new result with reduced systematic uncertainty from the positronium thermalization effect has been reported [5] ∆ν exp = 203.394 2(16) stat. (13) syst.…”