The recent demonstration of trapped atomic antihydrogen for 15 to 1000 seconds is a milestone towards precise spectroscopy for tests of CPT invariance. The confinement of a total of 105±21 atoms in a quadrupole magnetic trap was made possible by several improved methods. Improved accumulation techniques give us the largest numbers of constituent particles yet: up to 10 million antiprotons and several billion positrons. A novel cooling protocol leads to 3.5 K antiprotons, the coldest ever observed. Characterizing and controlling the geometry and density of these confined antimatter plasmas allow for consistency in antihydrogen production. Continued use of these methods along with the larger trap depth of a unique second-generation magnet are expected to yield greater numbers of trapped antihydrogen. The new magnet generates both quadrupole and octupole trap geometries, which should make it possible to reduce charged particle loss and will prove useful for laser cooling and spectroscopy. The ultra-low inductances of the magnet have been shown to vastly reduce turn-off times, which will optimize single-atom detection. Finally, improved detector characterization already makes us sensitive to smaller numbers of trapped antihydrogen atoms than before.
The recent demonstration of trapped atomic antihydrogen for 15 to 1000 seconds is a milestone towards precise spectroscopy for tests of CPT invariance. The confinement of a total of 105±21 atoms in a quadrupole magnetic trap was made possible by several improved methods. Improved accumulation techniques give us the largest numbers of constituent particles yet: up to 10 million antiprotons and several billion positrons. A novel cooling protocol leads to 3.5 K antiprotons, the coldest ever observed. Characterizing and controlling the geometry and density of these confined antimatter plasmas allow for consistency in antihydrogen production. Continued use of these methods along with the larger trap depth of a unique second-generation magnet are expected to yield greater numbers of trapped antihydrogen. The new magnet generates both quadrupole and octupole trap geometries, which should make it possible to reduce charged particle loss and will prove useful for laser cooling and spectroscopy. The ultra-low inductances of the magnet have been shown to vastly reduce turn-off times, which will optimize single-atom detection. Finally, improved detector characterization already makes us sensitive to smaller numbers of trapped antihydrogen atoms than before.
<!--HTML-->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 production and study of cold antihydrogen will require the manipulation of dense and cold, single component plasmas of antiprotons and positrons. The undertaking will build upon the experience of the nonneutral plasma physics community. Annihilations of the antimatter particles in the plasmas can be imaged, offering unique diagnostic opportunities not available to this community when electrons and protons are used. The techniques developed by our TRAP collaboration to capture and cool antiprotons will certainly be used by our expanded ATRAP collaboration, and by the competing ATHENA Collaboration, both working at the nearly completed AD facility of CERN. We recently demonstrated a new techniques for accumulating cold positrons directly into a cryogenic vacuum system. The closest we have come to low energy antihydrogen so far is to confine cold positrons and cold antiprotons within the same trap structure and vacuum container. Finally, we mention that stored electrons have been cooled to 70 mK, the first time that elementary particles have been cooled below 4 K. In such an apparatus it should be possible to study highly magnetized plasmas of electrons or positrons at this new low temperature.
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. This thesis will outline the main parts of the ALPHA experiment, with an overview of the important physical processes at work. Antihydrogen production techniques will be described, and an analysis of the spatial annihilation distribution to give indications of the temperature and binding energy distribution of the atoms will be presented. Finally, we describe the techniques needed to demonstrate confinement of antihydrogen atoms, apply them to a data taking run and present the results, making a definitive identification of trapped antihydrogen atoms.
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. This thesis will outline the main parts of the ALPHA experiment, with an overview of the important physical processes at work. Antihydrogen production techniques will be described, and an analysis of the spatial annihilation distribution to give indications of the temperature and binding energy distribution of the atoms will be presented. Finally, we describe the techniques needed to demonstrate confinement of antihydrogen atoms, apply them to a data taking run and present the results, making a definitive identification of trapped antihydrogen atoms.
ATRAP has made many important improvements since CERN's Antiproton Decelerator (AD) was restarted in 2006. These include substantial increases in the number of positrons (e+) and antiprotons (Pbars) used to make antihydrogen (Hbar) atoms, a new technique for loading electrons (e−) that are used to cool Pbars and e+, implementation of a completely new, larger and more robust apparatus in our second experimental zone and the inclusion of a quadrupole Ioffe trap intended to trap the coldest Hbar atoms produced. Using this new apparatus we have produced large numbers of Hbar atoms within a Penning trap that is located within this quadrupole Ioffe trap using a new technique which shows promise for producing even colder atoms. These observed Hbar atoms resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap.
Antihydrogen, the opposite number of hydrogen, is the simplest antimatter, and stable in vacuum, which guarantees a long observation time for high precision spectroscopy. This review discusses a short history of antimatter followed by the motivation of the cold antihydrogen research, and then a couple of latest results, which open a new era of antihydrogen research enabling high precision spectroscopy for the first time. A comparison of the spectroscopic properties of antihydrogen with those of hydrogen constitutes a stringent test of the CPT symmetry, the most fundamental law of physics. One of the important achievements of cold antihydrogen study in the last couple of years is the trapping of antihydrogen atoms in an octupole magnetic bottle. Considering the bottle depth, the trapped antihydrogen atoms were really cold, less than 0.5K in their temperature. High precision laser spectroscopy of 1S-2S transition is foreseen once antihydrogen atoms can be laser-cooled. The other milestone development was a successful synthesis of antihydrogen atoms in a so-called cusp trap, where an anti-Helmholtz coil configuration is adopted. The cusp trap enables extraction of antihydrogen atoms in a field-free region as an intensified spin-polarized beam,which realizes high resolution microwave spectroscopy of ground state hyperfine transitions.