Physics at CERN's Antiproton Decelerator

Abstract

The Antiproton Decelerator of CERN began operation in 1999 to serve experiments for studies of CPT invariance by precision laser and microwave spectroscopy of antihydrogen ($\bar{\mathrm{H}}$) and antiprotonic helium ($\bar{p}{\mathrm{He}}^{+}$). The first 12 years of operation saw cold $\bar{\mathrm{H}}$ synthesized by overlapping clouds of positrons ($e^{+}$) and antiprotons ($\bar{p}$) confined in magnetic Penning traps. Cold $\bar{\mathrm{H}}$ was also produced in collisions between Rydberg positronium atoms and $\bar{p}$. Ground-state $\bar{\mathrm{H}}$ was later trapped for up to $\sim 1000$ s in a magnetic bottle trap, and microwave transitions excited between its hyperfine levels. In the $\bar{p}{\mathrm{He}}^{+}$ atom, UV transitions were measured to a precision of (2.3-5) $\times$ $10^{-9}$ by sub-Doppler two-photon laser spectroscopy. From this the antiproton-to-electron mass ratio was determined as $M_{\bar{p}}/m_e=$1836.1526736(23), which agrees with the p value. Microwave spectroscopy of $\bar{p}{\mathrm{He}}^{+}$ yielded a measurement of the $\bar{p}$ magnetic moment with a precision of 0.3%. More recently the magnetic moment of a single $\bar{p}$ confined in a Penning trap was measured with a higher precision, as ${\mu }_{\bar{p}}=-2.792845(12)$${\mu }_{\mathrm{nucl}}$ in nuclear magnetons. Other measurements include the energy loss of 1-100 keV $\bar{p}$ traversing conductor and insulator targets; the cross sections of <10 keV $\bar{p}$ ionizing gas targets; and the cross sections of 5-MeV $\bar{p}$ annihilating on target foils via nuclear collisions. The biological effectiveness of $\bar{p}$ beams destroying cancer cells was measured as a possible method for radiological therapy. New experiments under preparation attempt to measure the gravitational acceleration of $\bar{\mathrm{H}}$ or synthesize $\obar{\rm H}^+$.

To be published in Progress in Particle and Nuclear Physics

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Cited by in corpus (12)

• In-beam measurement of the hydrogen hyperfine splitting - towards antihydrogen spectroscopy
• Production of multistrange hadrons, light nuclei and hypertriton in central Au+Au collisions at $\sqrt{s_{NN}}=$ 11.5 and 200 GeV
• Hyperfine spectroscopy of hydrogen and antihydrogen in ASACUSA
• Radiation from matter-antimatter annihilation in the quark nugget model of dark matter
• Analysis of the timing of freely falling antihydrogen
• The leading term of the He$-\bar{p}\mbox{He}^+$ long-range interaction
• Lead fluoride Cherenkov detector read out by avalanche photodiodes for measuring the intensities of pulsed antiproton beams
• Limitations for field-enhanced atom interferometry
• BASE-STEP: A transportable antiproton reservoir for fundamental interaction studies
• Quantum interference measurement of the free fall of anti-hydrogen
• Design and Performance of a Novel Low Energy Multi-Species Beamline for the ALPHA Antihydrogen Experiment
• Improving the statistical analysis of anti-hydrogen free fall by using near edge events