Characterization Of Neutral Trapped Antihydrogen In The Alpha Experiment

In 2010 the ALPHA collaboration succeeded in trapping antihydrogen atoms for the first time.[i] Stored antihydrogen promises to be a unique tool for making high precision measurements of the structure of this first anti-atom. Achieving this milestone presented several substantial experimental challenges and this talk will describe how they were overcome. The unique design features of the ALPHA apparatus will be explained.[ii] These allow a high intensity positron source and an antiproton imaging detector similar to the one used in the ATHENA[iii] experiment to be combined with an innovative magnet design of the anti-atom trap. This seeks to minimise the perturbations to trapped charged particles which may cause particle loss and heating[iv]. The diagnostic techniques used to measure the diameter, number, density, and temperatures of both plasmas will be presented as will the methods developed to actively compress and cool of both plasma species to sizes and temperatures [v], [vi], [vii] where trapping attempts with a reasonable chance of success can be tried. The results of the successful trapping experiments will be outlined as well as some subsequent experiments to improve the trapping rate and storage time. [i] 'Trapped antihydrogen' G.B. Andresen et al., Nature 468, 673 (2010) [ii]'A Magnetic Trap for Antihydrogen Confinement' W. Bertsche et al., Nucl. Instr. Meth. Phys. Res. A566, 746 (2006) [iii] Production and detection of cold antihydrogen atoms M. Amoretti et al., Nature 419, 456 (2002). [iv]' Antihydrogen formation dynamics in a multipolar neutral anti-atom trap' G.B. Andresen et al., Phys. Lett. B 685, 141 (2010) [v]' Evaporative Cooling of Antiprotons to Cryogenic Temperatures', G.B. Andresen et al. Phys. Rev. Lett 105, 013003 (2010) [vi]'Compression of Antiproton Clouds for Antihydrogen Trapping' G.B. Andresen et al. Phys. Rev. Lett 100, 203401 (2008) [vii] 'Autoresonant Excitation of Antiproton Plasmas' G.B. Andresen et al., Phys. Rev. Lett. 106, 025002 (2011) Organizer: Ferdinand Hahn PH/DT Detector Seminar webpage.

The recent demonstration of trapping of antihydrogen atoms by the ALPHA collaboration at CERN opened great possibilities to study antimatter and perform precision measurements on it. In this work, a retrospective analysis of the 2010 and 2011 experimental runs in ALPHA, together with comprehensive studies of the apparatus and detailed simulations of the manipulations of anti-atoms, are performed and used to measure the electric charge of antihydrogen. This result is an example of a precision measurement on antimatter that may ultimately lead to keys for solving some of the most important problems in physics today, such as the asymmetry between matter and antimatter, by comparison to measurements carried out on normal matter atoms. A procedure similar to the one presented may lead to increased precision with a larger data sample, perhaps using the new ALPHA2 apparatus. Nevertheless, a method using stochastic heating is proposed that could increase the precision of the measurement by many orders of magnitude. The technique offers many other advantages that make it very attractive for future experimental implementations.

In 2010, the ALPHA collaboration achieved a first for mankind: the stable, long-term storage of atomic antimatter, a project carried out a the Antiproton Decelerator facility at CERN. A crucial element of this observation was a dedicated silicon vertexing detector used to identify and analyze antihydrogen annihilations. This thesis reports the methods used to reconstruct the annihilation location. Specifically, the methods used to identify and extrapolate charged particle tracks and estimate the originating annihilation location are outlined. Finally, the experimental results demonstrating the first-ever magnetic confinement of antihydrogen atoms are presented. These results rely heavily on the silicon detector, and as such, the role of the annihilation vertex reconstruction is emphasized.

The advent of high-precision antihydrogen spectroscopy has opened up the possibility of direct tests with unprecedented accuracy of some of the most fundamental principles of physics, notably Lorentz and CPT symmetry and the Einstein equivalence principle. This book reviews these principles, emphasising their interconnections in quantum field theory and general relativity and the special role of antimatter, and explores how they may be tested in current and forthcoming experiments on antihydrogen. Original research results relevant to the experimental programme of the ALPHA collaboration at CERN are presented, together with the implications for antihydrogen of proposed theories featuring novel `fifth-force' interactions.

This dissertation focuses on three ideas useful to the nonneutral plasma experiment at UC Berkeley and the ALPHA experiment at CERN. While these may seem like disparate ideas, in all cases, a careful mathematical treatment of the problems yield useful insights. First, we present improvements to the analysis for diagnostics of temperature and den- sity of plasmas in Penning-Malmberg trap experiments. Our new methods are faster and more accurate than previously used methods of analysis. This allows us to conduct these diagnostics in real-time without any input from a human. We then theoretically consider the problem of enhanced cooling of an electron plasma from a coupling of the plasma to cavity modes. We make more rigorous the previous analysis that was done on the topic, and then extend these results to a longitudinally dynamic plasma. We compare our theoretical results with experimental observations from the Berkeley plasma trap and with simulations and find good agreement. Finally, we consider analyses of ALPHA data to measure antihydrogen properties. We place a statistically rigorous bound on the antihydrogen charge from ALPHA data. This improves the previous bound on antihydrogen charge by a factor of 20, and assuming super- position, improves the bound on the positron charge anomaly by a factor of 25. Finally, we consider analyses for a future measurement of the gravitational mass of antihydrogen. We find that with reasonable constraints, a measurement of the gravitational mass of antihydro- gen with a precision of 1% should be feasible.

In 2010, the ALPHA collaboration achieved a first for mankind: the stable, long-term storage of atomic antimatter, a project carried out a the Antiproton Decelerator facility at CERN. A crucial element of this observation was a dedicated silicon vertexing detector used to identify and analyze antihydrogen annihilations. This thesis reports the methods used to reconstruct the annihilation location. Specifically, the methods used to identify and extrapolate charged particle tracks and estimate the originating annihilation location are outlined. Finally, the experimental results demonstrating the first-ever magnetic confinement of antihydrogen atoms are presented. These results rely heavily on the silicon detector, and as such, the role of the annihilation vertex reconstruction is emphasized.

With the exception of positron emission tomography (PET), the field of low energy positron science produces relatively few academic articles each year compared to more accessible fields. Though much has been achieved since the publication of two related volumes earlier in this series: Positron Solid State Physics (1981) and Positron Spectroscopy of Solids (1993), only the first steps have been made towards 'physics with many positrons': physical situations where the interactions of positrons with positrons can be observed. This 2009 "Enrico Fermi School" aims to stimulate the field o.

This volume provides detailed insight into the field of precision spectroscopy and fundamental physics with particles confined in traps. It comprises experiments with electrons and positrons, protons and antiprotons, antimatter and highly charged ions together with corresponding theoretical background. Such investigations represent stringent tests of quantum electrodynamics and the Standard model, antiparticle and antimatter research, test of fundamental symmetries, constants and their possible variations with time and space. They are key to various aspects within metrology such as mass measurements and time standards, as well as promising to further developments in quantum information processing. The reader obtains a valuable source of information suited for beginners and experts with an interest in fundamental studies using particle traps.

This conference brought together about 150 physicists and covered the entire field of research with antiprotons, from atomic physics at low energies to hadronic reactions at high energies. The conference demonstrated that this field is evolving, with new physics being studied at existing and planned facilities.