Observation of the 1S–2S transition in trapped antihydrogen

Abstract

The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S-2S transition by Hänsch 1 to a precision of a few parts in 10 15 . Recent technological advances have allowed us to focus on antihydrogen-the antimatter equivalent of hydrogen 2-4 . The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today's Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S-2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 × 10 −10 .

Observation of the hyperfine spectrum of antihydrogen

“…et al, submitted) bode well for the feasibility of observing this transition in trapped antihydrogen. The absolute energy scales for the positron and antiproton spin-flip transitions in ALPHA-2 are respectively five and eight orders of magnitude smaller than that of the laser transition that was recently observed 15 . In addition to probing different interactions in the anti hydrogen Hamiltonian, these energy scales offer very high sensitivity to potential new physics 23 .…”

“…The goal of such studies is to search for any differences that might exist between this archetypal pair of atoms, and thereby to test the fundamental principles on which quantum field theory is constructed. Magnetic trapping of antihydrogen atoms 13,14 provides a means of studying them by combining electromagnetic interaction with detection techniques that are unique to antimatter 12,15 . Here we report the results of a microwave spectroscopy experiment in which we probe the response of antihydrogen over a controlled range of frequencies.…”

Sympathetic cooling of protons and antiprotons with a common endcap Penning trap

“…As the fundamental symmetry of the Standard Model, any measured CPT-violation will provide a clear indication of new physics. Current experimental limits constrain CPT violating effects to a fractional precision of 0.5 × 10 −12 for leptons (1, 2), 1.3 × 10 −18 for mesons (3) and 2.0 × 10 −10 for hydrogen and antihydrogen (4,5). Our experiments target comparisons of the fundamental properties of protons (p) and antiprotons (p), chiefly by measuring charge-to-mass ratios (q/m) p,p and magnetic moments μ p,p in Penning traps.…”

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.…”