Monte-Carlo based performance assessment of ASACUSA's antihydrogen detector

An antihydrogen detector consisting of a thin BGO disk and a surrounding plastic scintillator hodoscope has been developed. We have characterized the two-dimensional positions sensitivity of the thin BGO disk and energy deposition into the BGO was calibrated using cosmic rays by comparing experimental data with Monte-Carlo simulations. The particle tracks were defined by connecting BGO hit positions and hits on the surrounding hodoscope scintillator bars. The event rate was investigated as a function of the angles between the tracks and the energy deposition in the BGO for simulated antiproton events, and for measured and simulated cosmic ray events. Identification of the antihydrogen Monte Carlo events was performed using the energy deposited in the BGO and the particle tracks. The cosmic ray background was limited to 12 mHz with a detection efficiency of 81 %. The signal-to-noise ratio was improved from 0.22 s^{-1/2} obtained with the detector in 2012 to 0.26 s^{-1/2} in this work

Minimizing plasma temperature for antimatter mixing experiments

The ASACUSA collaboration produces a beam of antihydrogen atoms by mixing pure positron and antiproton plasmas in a strong magnetic field with a double cusp geometry. The positrons cool via cyclotron radiation inside the cryogenic trap. Low positron temperature is essential for increasing the fraction of antihydrogen atoms which reach the ground state prior to exiting the trap. Many experimental groups observe that such plasmas reach equilibrium at a temperature well above the temperature of the surrounding electrodes. This problem is typically attributed to electronic noise and plasma expansion, which heat the plasma. The present work reports anomalous heating far beyond what can be attributed to those two sources. The heating seems to be a result of the axially open trap geometry, which couples the plasma to the external (300 K) environment via microwave radiation

SDR, EVC, and SDREVC: Limitations and Extensions

Methods for reducing the radius, temperature, and space charge of nonneutral plasma are usually reported for conditions which approximate an ideal Penning Malmberg trap. Here we show that (1) similar methods are still effective under surprisingly adverse circumstances: we perform SDR and SDREVC in a strong magnetic mirror field using only 3 out of 4 rotating wall petals. In addition, we demonstrate (2) an alternative to SDREVC, using e-kick instead of EVC and (3) an upper limit for how much plasma can be cooled to T < 20 K using EVC. This limit depends on the space charge, not on the number of particles or the plasma density.Comment: Version 2: a small discrepancy between the N values for Table 1 and Fig. 3 led to an investigation of the charge counting diagnostic. There is a small energy dependence which only became apparent following improvements to pre-SDREVC. The pulsed dump was modified to reduce this dependence. The data for Table 1 and Fig. 3 was taken again with the improved method

Upgrade of the positron system of the ASACUSA-Cusp experiment

The ASACUSA-Cusp collaboration has recently upgraded the positron system to improve the production of antihydrogen. Previously, the experiment suffered from contamination of the vacuum in the antihydrogen production trap due to the transfer of positrons from the high pressure region of a buffer gas trap. This contamination reduced the lifetime of antiprotons. By adding a new positron accumulator and therefore decreasing the number of transfer cycles, the contamination of the vacuum has been reduced. Further to this, a new rare gas moderator and buffer gas trap, previously used at the Aarhus University, were installed. Measurements from Aarhus suggested that the number of positrons could be increased by a factor of four in comparison to the old system used at CERN. This would mean a reduction of the time needed for accumulating a sufficient number of positrons (of the order of a few million) for an antihydrogen production cycle. Initial tests have shown that the new system yields a comparable number of positrons to the old system.Comment: 10 pages, 5 figures, under consideration for the Special Collection "Non-Neutral Plasmas: Achievements and Perspectives" in JP

Slow positron production and storage for the ASACUSA-Cusp experiment

The ASACUSA Cusp experiment requires the production of dense positron plasmas with a high repetition rate to produce a beam of antihydrogen. In this work, details of the positron production apparatus used for the first observation of the antihydrogen beam, and subsequent measurements are described in detail. This apparatus replaced the previous compact trap design resulting in an improvement in positron accumulation by a factor of ($52\pm3)$Comment: 9 pages, 7 figure

Hyperfine spectroscopy of hydrogen and antihydrogen in ASACUSA

The ASACUSA collaboration at the Antiproton Decelerator of CERN aims at a precise measurement of the antihydrogen ground-state hyperfine structure as a test of the fundamental CPT symmetry. A beam of antihydrogen atoms is formed in a CUSP trap, undergoes Rabi-type spectroscopy and is detected downstream in a dedicated antihydrogen detector. In parallel measurements using a polarized hydrogen beam are being performed to commission the spectroscopy apparatus and to perform measurements of parameters of the Standard Model Extension (SME). The current status of antihydrogen spectroscopy is reviewed and progress of ASACUSA is presented.Comment: Proceedings of the 7th International Syposium on Symmetries in Subatomic Physics SSP2018, Aachen (Germany), 10 - 15 Jun 2018. Corrected error in Fig. 1, updated caption, add titles to reference

Transition energy measurements in hydrogenlike and heliumlike ions strongly supporting bound-state QED calculations

For the hydrogenlike Ar17+ ion, the 1s Lamb shift was absolutely determined with a 1.4% accuracy based on Lyman-α wavelength measurements that have negligible uncertainties from nuclear size effects. The result agrees with state-of-the-art quantum electrodynamics (QED) calculations, and demonstrates the suitability of Lyman-α transitions in highly charged ions as x-ray energy standards, accurate at the five parts-per-million level. For the heliumlike Ar16+ ion the transition energy for the 1s2p1P1→1s21S0 line was also absolutely determined on an even higher level of accuracy. Additionally, we present relative measurements of transitions in S15+,S14+, and Fe24+ ions. The data for the heliumlike S14+,Ar16+, and Fe24+ ions stringently confirm advanced bound-state QED predictions including screened QED terms that had recently been contested