Antihydrogen accumulation for fundamental symmetry tests

Abstract

Antihydrogen, a positron bound to an antiproton, is the simplest anti-atom. Its structure and properties are expected to mirror those of the hydrogen atom. Prospects for precision comparisons of the two, as tests of fundamental symmetries, are driving a vibrant programme of research. In this regard, a limiting factor in most experiments is the availability of large numbers of cold ground state antihydrogen atoms. Here, we describe how an improved synthesis process results in a maximum rate of 10.5 ± 0.6 atoms trapped and detected per cycle, corresponding to more than an order of magnitude improvement over previous work. Additionally, we demonstrate how detailed control of electron, positron and antiproton plasmas enables repeated formation and trapping of antihydrogen atoms, with the simultaneous retention of atoms produced in previous cycles. We report a record of 54 detected annihilation events from a single release of the trapped anti-atoms accumulated from five consecutive cycles.

Ion generation and loading of a Penning trap using pulsed laser ablation

“…Presently, there is considerable interest in the antihydrogen trapping community to use beryllium ions to sympathetically cool positrons for antihydrogen production [18][19][20][21]. The antihydrogen trapping experiments take place in a Penning trap under extreme high vacuum (P<10 −12 mbar) and cryogenic temperatures (T<100 K).…”

On the formation of trappable antihydrogen

“…Finally, we make a comparison of our results with experimentally observed trapping fractions. In a recent publication by ALPHA [18],H formation at T=18 K and n e =6.5×10 13 m −3 (at the beginning of the mixing with antiprotons) resulted in,  f 0.4 H and f trap ;10 −4 . For similar conditions our results give  f 0.5 H and f trap ;10 −3 , and further multiplication of f trap by 0.13 (to account for the trap depth of 2 K in the simulations, compared to 0.5 K in the experiment) reduces this number to 1.3×10 −4 .…”

“…Techniques such as evaporative [14] and adiabatic [15] cooling have been developed, whilst compression techniques (see, e.g., [16,17]) have allowed the density and radial extent of the clouds to be carefully manipulated. Whilst this has led to marked improvements inH trapping efficiencies (here, defined as the number ofH trapped per injectedp), from about 5×10 −6 in the earliest work [10] to over 10 −4 in a recent study [18], it is clear that many measurements will benefit markedly from increases in the yield of trappedH.…”

Formation of antihydrogen beams from positron–antiproton interactions

“…These, and other, advances were made possible by the confinement of H in magnetic minimum traps [4][5][6]. Recently, these techniques have been improved at CERN's antiproton decelerator (AD) [7] such that about 10-20 H s can be trapped per antiproton (p) bunch, and through the accumulation of H s from successive bunches [8] several hundred H s can be held simultaneously [2].…”