Eoin Butler

Publications (42) View all

• Article: Antihydrogen formation by autoresonant excitation of antiproton plasmas

  William Alan Bertsche, G. B. Andresen, M. D. Ashkezari, M. Baquero-Ruiz, P. D. Bowe, P. T. Carpenter, E. Butler, C. L. Cesar, S. F. Chapman, M. Charlton, [......], F. Robicheaux, E. Sarid, D. M. Silveira, C. So, J. W. Storey, R. I. Thompson, D. P. van der Werf, J. S. Wurtele, Y. Yamazaki, ALPHA Collaboration
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  ABSTRACT: In efforts to trap antihydrogen, a key problem is the vast disparity between the neutral trap energy scale ( ~ 50\upmueV\sim\!50\,\upmu\mathrm{eV}), and the energy scales associated with plasma confinement and space charge (~1 eV). In order to merge charged particle species for direct recombination, the larger energy scale must be overcome in a manner that minimizes the initial antihydrogen kinetic energy. This issue motivated the development of a novel injection technique utilizing the inherent nonlinear nature of particle oscillations in our traps. We demonstrated controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm or tenuous plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination. The nature of this injection overcomes some of the difficulties associated with matching the energies of the charged species used to produce antihydrogen. KeywordsAntihydrogen–Plasma–Nonlinear–Dynamics
  Hyperfine Interactions 05/2012; · 0.21 Impact Factor
• Article: Trapped antihydrogen

  E. Butler, G. B. Andresen, M. D. Ashkezari, M. Baquero-Ruiz, W. Bertsche, P. D. Bowe, C. L. Cesar, S. Chapman, M. Charlton, A. Deller, [......], E. Sarid, S. Seif el Nasr, D. M. Silveira, C. So, J. W. Storey, R. I. Thompson, D. P. van der Werf, J. S. Wurtele, Y. Yamazaki, ALPHA Collaboration
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  ABSTRACT: Precision spectroscopic comparison of hydrogen and antihydrogen holds the promise of a sensitive test of the Charge-Parity-Time theorem and matter-antimatter equivalence. The clearest path towards realising this goal is to hold a sample of antihydrogen in an atomic trap for interrogation by electromagnetic radiation. Achieving this poses a huge experimental challenge, as state-of-the-art magnetic-minimum atom traps have well depths of only ∼1T (∼0.5K for ground state antihydrogen atoms). The atoms annihilate on contact with matter and must be ‘born’ inside the magnetic trap with low kinetic energies. At the ALPHA experiment, antihydrogen atoms are produced from antiprotons and positrons stored in the form of non-neutral plasmas, where the typical electrostatic potential energy per particle is on the order of electronvolts, more than 104 times the maximum trappable kinetic energy. In November 2010, ALPHA published the observation of 38 antiproton annihilations due to antihydrogen atoms that had been trapped for at least 172ms and then released—the first instance of a purely antimatter atomic system confined for any length of time (Andresen etal., Nature 468:673, 2010). We present a description of the main components of the ALPHA traps and detectors that were key to realising this result. We discuss how the antihydrogen atoms were identified and how they were discriminated from the background processes. Since the results published in Andresen etal. (Nature 468:673, 2010), refinements in the antihydrogen production technique have allowed many more antihydrogen atoms to be trapped, and held for much longer times. We have identified antihydrogen atoms that have been trapped for at least 1,000s in the apparatus (Andresen etal., Nature Physics 7:558, 2011). This is more than sufficient time to interrogate the atoms spectroscopically, as well as to ensure that they have relaxed to their ground state. KeywordsAntihydrogen–Antimatter–CPT–Atom trapping
  Hyperfine Interactions 04/2012; · 0.21 Impact Factor
• Source

  Available from: Alex Povilus

  Article: Towards antihydrogen trapping and spectroscopy at ALPHA

  E. Butler, G. B. Andresen, M. D. Ashkezari, M. Baquero-Ruiz, W. Bertsche, P. D. Bowe, C. C. Bray, C. L. Cesar, S. Chapman, M. Charlton, [......], E. Sarid, D. M. Silveira, C. So, J. W. Storey, R. I. Thompson, D. P. van der Werf, D. Wilding, J. S. Wurtele, Y. Yamazaki, ALPHA Collaboration
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  ABSTRACT: Spectroscopy of antihydrogen has the potential to yield high-precision tests of the CPT theorem and shed light on the matter-antimatter imbalance in the Universe. The ALPHA antihydrogen trap at CERN’s Antiproton Decelerator aims to prepare a sample of antihydrogen atoms confined in an octupole-based Ioffe trap and to measure the frequency of several atomic transitions. We describe our techniques to directly measure the antiproton temperature and a new technique to cool them to below 10K. We also show how our unique position-sensitive annihilation detector provides us with a highly sensitive method of identifying antiproton annihilations and effectively rejecting the cosmic-ray background. KeywordsAntihydrogen–Antimatter–CPT–Penning trap–Atom trap
  Hyperfine Interactions 04/2012; 199(1):39-48. · 0.21 Impact Factor
• Source

  Available from: Niels Madsen

  Article: Resonant quantum transitions in trapped antihydrogen atoms.

  C Amole, M D Ashkezari, M Baquero-Ruiz, W Bertsche, P D Bowe, E Butler, A Capra, C L Cesar, M Charlton, A Deller, [......], C Ø Rasmussen, F Robicheaux, E Sarid, C R Shields, D M Silveira, S Stracka, C So, R I Thompson, D P van der Werf, J S Wurtele
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  ABSTRACT: The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.
  Nature 03/2012; 483(7390):439-43. · 36.28 Impact Factor
• Source

  Available from: Eoin Butler

  Article: Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap

  C Amole, G B Andresen, M D Ashkezari, M Baquero-Ruiz, W Bertsche, E Butler, C L Cesar, S Chapman, M Charlton, A Deller, [......], A Povilus, P Pusa, F Robicheaux, E Sarid, D M Silveira, C So, J W Storey, R I Thompson, D P van der Werf, J S Wurtele
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  ABSTRACT: Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the magnetic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilate. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antiproton and antihydrogen trajectories in this magnetic geometry, and reconstruct the antihydrogen energy distribution from the measured annihilation time history.
  New Journal of Physics 01/2012; 14(1):015010. · 4.18 Impact Factor