Theses

Theses

One of the greatest problems facing modern physics is the apparent asymmetry between matter and antimatter. While the standard model of particle physics predicts that equal amounts of matter and antimatter were produced following the Big Bang, astronomical observations have revealed that our universe contains little or no primordial antimatter. Precision measurements of cold, trapped antiparticles can be used to probe fundamental symmetries, and may shed light on why antimatter is so scarce in our universe. The ALPHA experiment at the CERN Antiproton Decelerator studies magnetically trapped antihydrogen atoms, produced by slowly merging cold plasmas of positrons (e +) and antiprotons (¯p). The precision spectroscopy of antihydrogen has already provided unique, high-resolution tests of CPT invariance and theories of new physics beyond the standard model. During 2018, the ALPHA experiment was expanded with the addition of ALPHA-g, a vertical atom trap that is intended to make the first direct measurements of antimatter gravitation. [...]

Mark A. Johnson

A new technique for rapidly generating a sequence of target plasmas in a Penning-Malmberg trap is presented and applied in the first demonstration of cavity-resonant cooling in a plasma. This "reservoir'' technique further enables the in situ magnetic field to be measured to high precision by microwave ECR spectroscopy. A precision antihydrogen gravity experiment being constructed at CERN will rely on this method, as there is no other method with comparable absolute, spatial, and temporal resolution which can be implemented in the Penning-Malmberg trap. These cavity and microwave measurements require accessing new regimes with the plasma parallel energy analyzer, to which end the sensitivity of the latter technique has been increased twenty-fold.

Eric Hunter

The ALPHA (Antihydrogen Laser Physics Apparatus) collaboration creates and performs precise measurements on antihydrogen to test Charge-Parity-Time (CPT) symmetry. Prior to creating antihydrogen we must prepare the antiproton and positron plasmas to have optimal and repeatable parameters. This thesis presents the development of a new method to simultaneously control the number of particles and plasma density of lepton plasmas, developments that increased our antihydrogen trapping rate, precision physics measurements performed on antihydrogen, and other plasma studies still under development. The method to stabilize the number of particles was based on a zero-temperature plasma model, which states that the plasma's on-axis self potential and density uniquely define a plasma. [...]

Celeste Carruth

Our current understanding of physics suggests that matter and antimatter should be created and destroyed in equal amounts, but this seems inconsistent with the observation that our universe consists almost entirely of matter. Comparisons between matter and antimatter could reveal new physics which explains why the universe has formed with this apparent imbalance. The 1S-2S transition of hydrogen has been measured with incredible precision, and a similarly precise measurement of the 1S-2S transition of antihydrogen would constitute one of the best comparisons between matter and antimatter.

Steven Armstrong Jones

One of the best ways to study antimatter is to investigate antihydrogen, the bound state of an antiproton and a positron. Antihydrogen atoms do not exist naturally and must be synthesized in the lab by merging carefully-prepared plasmas of positrons and antiprotons. If the atoms are created in a magnetic trap like the one used by the ALPHA experiment at CERN, then a fraction of the coldest atoms remain trapped, while the rest escape and annihilate on the trap walls. The trapped atoms may then be probed using microwaves or lasers to make high-precision comparisons with hydrogen.
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Muhammed Sameed

Antihydrogen is the simplest pure antimatter atomic system, and it allows for direct tests of CPT symmetry as well as the weak equivalence principle. Furthermore, the study of antihydrogen may provide clues to the matter- antimatter asymmetry observed in the universe - one of the major unanswered questions in modern physics. Since 2010, it has been possible to perform such tests on magnetically trapped antihydrogen, and this work reports on several recent studies.

Chris Ørum Rasmussen

Antihydrogen is the simplest neutral antimatter atom. Precision comparisons between hydrogen and antihydrogen would provide stringent tests of CPT (charge conjugation/parity transformation/time reversal) invariance and the weak equivalence principle. In the last few years, the ALPHA collaboration has produced, and trapped antihydrogen [1, 2]. Most recently, this collaboration has probed antihydrogen’s internal structure by inducing hyperfine transitions in ground state atoms [3]. In this thesis, many details of the cold antihydrogen formation, trapping and measurements of antihydrogen performed in the ALPHA apparatus are presented, with a focus on antiproton cloud compression. Such compression is an important tool for the formation and trapping of cold antihydrogen, since it allows control of the radial size and density of the antiproton cloud. Compression of non-neutral plasmas can be achieved using a rotating time-varying azimuthal electric field, which has been called rotating wall technique.
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Andrea Gutierrez

The asymmetry between matter and antimatter in the universe and the incompatibility between the Standard Model and general relativity are some of the greatest unsolved questions in physics. The answer to both may possibly lie with the physics beyond the Standard Model, and comparing the properties of hydrogen and antihydrogen atoms provides one of the possible ways to exploring it. In 2010, the ALPHA collaboration demonstrated the first trapping of antihydrogen atoms, in an apparatus made of a Penning–Malmberg trap superimposed on a magnetic minimum trap. Its ultimate goal is to precisely measure the spectrum, gravitational mass and charge neutrality of the anti-atoms, and compare them with the hydrogen atom. These comparisons provide novel, direct and model–independent tests of the Standard Model and the weak equivalence principle. Before they can be achieved, however, the trapping rate of antihydrogen atoms needs to be improved. [...]

Chukman So

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. [...]

Marcelo Baquero-Ruiz

We have every reason to believe that equal amounts of matter and antimatter were produced in the early universe. Moreover, theory predicts that the laws of physics make no distinction between the two. In this light, the fact that the observable universe is overwhelmingly dominated by matter is inexplicable. ALPHA is an international project located at CERN involving approximately 40 physicists from 15 different institutions in 7 countries. The primary goal of the collaboration is to study the antihydrogen atom at the highest level of precision possible, and thereby enable comparisons between hydrogen and antihydrogen. Through these comparisons it hopes to improve our understanding of the distinction between matter and antimatter, and perhaps shed some light on the puzzle of why we live in a matter dominated universe. The hyperfine energy intervals of ground-state hydrogen and antihydrogen represent an opportunity for a precision comparison. A discrepancy between the energy levels of these two atomic systems would indicate a major revolution in physics, and in our understanding of the universe. [...]

Mohammad Dehghani Ashkezari

Antihydrogen, the bound state of a positron and an antiproton, is the simplest pure anti-atomic system and an excellent candidate to test the symmetry between matter and antimatter. This thesis focuses on the magnetic confinement of antihydrogen and the first ever resonant interaction with trapped antihydrogen, as performed by the ALPHA collaboration. The ALPHA apparatus and the techniques that have been developed to form, trap, probe, and detect antihydrogen atoms will be described in detail. The first successful demonstration of trapped antihydrogen will then be described. In the initial demonstrations, 38 trapped antihydrogen atoms were detected after being confined for at least 172 ms. Since then, over 400 antihydrogen atoms have been trapped and confinement times of 1000 s (over 15 minutes) have been demonstrated. Spectroscopy of these trapped antihydrogen atoms is the next major step forward. As an initial proof-of-principle demonstration, ALPHA induced and observed resonant positron spin flip (PSR) transitions between the ground states of antihydrogen. [...]

Timothy Peter Friesen

The ALPHA experiment is an international effort to produce, trap, and perform precision spectroscopic measurements on antihydrogen (the bound state of a positron and an antiproton). Based at the Antiproton Decelerator (AD) facility at CERN, the ALPHA experiment has recently magnetically confined antihydrogen atoms for the first time. A crucial element in the observation of trapped antihydrogen is ALPHA’s silicon vertexing detector. This detector contains sixty silicon modules arranged in three concentric layers, and is able to determine the three-dimensional location of the annihilation of an antihydrogen atom by reconstructing the trajectories of the produced annihilation products. [...]

Richard A. Hydomako

One proposed technique for trapping anti-atoms is to superimpose a Ioffe-Pritchard style magnetic-minimum neutral trap on a standard Penning trap used to trap the charged atomic constituents. Adding a magnetic multipole field in this way removes the azimuthal symmetry of the ideal Penning trap and introduces a new avenue for radial diffusion. Enhanced diffusion will lead to increased Joule heating of a non-neutral plasma, potentially adversely affecting the formation rate of anti-atoms and increasing the required trap depth. We present a model of this effect, along with an approach to minimizing it, with comparison to measurements from an intended anti-atom trap.

Steven Francis Chapman

Antihydrogen, the simplest pure-antimatter atomic system, holds the promise of direct tests of matter-antimatter equivalence and CPT invariance, two of the outstanding unanswered questions in modern physics. Antihydrogen is now routinely produced in charged-particle traps through the combination of plasmas of antiprotons and positrons, but the atoms escape and are destroyed in a minuscule fraction of a second. The focus of this work is the production of a sample of cold antihydrogen atoms in a magnetic atom trap. This poses an extreme challenge, because the state-of-the-art atom traps are only approximately 0.5 K deep for ground-state antihydrogen atoms, much shallower than the energies of particles stored in the plasmas. [...]

Eoin Butler

Evaporative cooling has proven to be an invaluable technique in atomic physics, allowing for the study of effects such as Bose-Einstein condensation. One main topic of this thesis is the first application of evaporative cooling to cold non-neutral plasmas stored in an ion trap. We (the ALPHA collaboration) have achieved cooling of a cloud of antiprotons to a temperature as low as 9 K, two orders of magnitude lowerthan ever directly measured previously. The measurements are well-described by appropriate rate equations for the temperature and number of particles. The technique has direct application to the ongoing attempts to produce trapped samples of antihydrogen. In these experiments the maximum trap depths are ex tremely shallow (~0.6 K for ground state atoms), and careful control of the trapped antiprotons and positrons used to form the (anti)atoms is essential to succes. Since 2006 powerful tools to diagnose and manipulate the antiproton and positron plasmas in the ALPHA apparatus have been developed and used in attempts to trap antihydrogen. [...]

Gorm Bruun Andresen

This thesis details the development and commissioning of the ALPHA antihydrogen trapping apparatus. It discusses the history of antimatter physics that led to and enabled the design of the apparatus. It discusses the importance of antihydrogen trapping in testing one of the basic assumptions of the Standard Model of particle physics (that of CPT invariance). It goes on to discuss the design and construction of the apparatus. Finally, it presents results that demonstrate antihydrogen formation in the new magnetic field configurations that together constitute a magnetic minimum trap for neutral antihydrogen. This is an important preliminary result for any antihydrogen trapping apparatus, and confirms that the ALPHA apparatus does present a potential route towards laser spectroscopy of antihydrogen.

Matthew Jenkins

This thesis describes several models of antihydrogen formation as well as the commissioning of the ALPHA antihydrogen during the 2006 Antiproton Decelerator (AD) physics run. Three models are given to describe the short-time production of antihydrogen, including the Simple Temperature Dependant Model, Inverse Velocity Model, and Scaled Inverse Velocity Model. All three models are compared to results from the ATHENA experiment. After an introduction to the ALPHA apparatus and some of the techniques used to produce antihydrogen the commissioning process is described, focusing on the optimization of the antiproton capture, cooling, and manipulation. Also included is an appendix describing in detail the ALPHA data acquisition system as of the end of the 2006 physics run

Richard A. Hydomako