Physics at CERN’s Antiproton Decelerator

Abstract

The Antiproton Decelerator (AD) facility of CERN began operation in 1999 to serve experiments for studies of CP T invariance by precision laser and microwave spectroscopy of antihydrogen (H) and antiprotonic helium (pHe + ) atoms. The first 12 years of AD operation saw cold H synthesized by overlapping clouds of positrons (e + ) and antiprotons (p) confined in magnetic Penning traps. Cold H was also produced in collisions between Rydberg positronium (P s) atoms and p. Ground-state H was later trapped for up to ∼ 1000 s in a magnetic bottle trap, and microwave transitions excited between its hyperfine levels. In the pHe + atom, deep ultraviolet transitions were measured to a fractional precision of (2.3-5) × 10 −9 by sub-Doppler two-photon laser spectroscopy. From this the antiproton-to-electron mass ratio was determined as M p /m e =1836.1526736(23), which agrees with the p value known to a similar precision. Microwave spectroscopy of pHe + yielded a measurement of the p magnetic moment with a precision of 0.3%. More recently, the magnetic moment of a single p confined in a Penning trap was measured with a higher precision, as µ p = −2.792845(12)µ nucl in nuclear magnetons. Other results reviewed here include the first measurements of the energy loss (−dE/dx) of 1-100 keV p traversing conductor and insulator targets; the cross sections of low-energy (< 10 keV) p ionizing atomic and molecular gas targets; and the cross sections of 5-MeV p annihilating on various target foils via nuclear collisions. The biological effectiveness of p beams destroying cancer cells was measured as a possible method for radiological therapy. New experiments under preparation attempt to measure the gravitational acceleration of H or synthesize H + . Several other future experiments will also be briefly described.

Antiproton-nucleus annihilation cross section at low energy

“…The measurement has been performed at AD [25][26][27][28][29] which is presently the only existing source of slow antiprotons. Theps delivered by AD have a momentum p = 100 MeV/c (corresponding to an energy of 5.3 MeV) with a spread of ∆p/p = 0.01% and an emittance of (2-3)π mm mrad.…”

Antiproton–to–electron mass ratio determined by two-photon laser spectroscopy of antiprotonic helium atoms

“…The experiments were carried out at the Antiproton Decelerator (AD) facility of CERN as part of its atomic physics [15] program. The AD provided 200-ns-long pulsed beams, which contained ∼ 10 7 antiprotons of kinetic energy 5.3 MeV.…”

Nuclear effects in protonium formation low-energy three-body reaction: p̄ + (pμ)1s→ (p̄p)α+μ−: Strong p̄–p interaction in p̄ + (pμ)1s

“…Obtaining and storing of low-energy antiprotons (p) is of significant scientific and practical interest and importance in current research in atomic and nuclear physics [1][2][3][4]. For example, with the use of slowp's it would be possible to make low temperature ground state antihydrogen atomsH 1s -a bound state ofp and e + , i.e.…”