A. Soter

The University of Tokyo, Tokyo, Tokyo-to, Japan

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Publications (18)60.65 Total impact

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    ABSTRACT: The Atomic Spectroscopy and Collisions Using Slow Antiprotons experiment at the Antiproton Decelerator (AD) facility of CERN constructed segmented scintillators to detect and track the charged pions which emerge from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. A system of 541 cast and extruded scintillator bars were arranged in 11 detector modules which provided a spatial resolution of 17 mm. Green wavelength-shifting fibers were embedded in the scintillators, and read out by silicon photomultipliers which had a sensitive area of 1 × 1 mm(2). The photoelectron yields of various scintillator configurations were measured using a negative pion beam of momentum p ≈ 1 GeV/c. Various fibers and silicon photomultipliers, fiber end terminations, and couplings between the fibers and scintillators were compared. The detectors were also tested using the antiproton beam of the AD. Nonlinear effects due to the saturation of the silicon photomultiplier were seen at high annihilation rates of the antiprotons.
    The Review of scientific instruments 02/2014; 85(2):023302. · 1.52 Impact Factor
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    ABSTRACT: The resonance transition (n, l) = (40, 36) → (41, 35) of the antiprotonic helium (\overline{{p}}^{4}He+) isotope at a wavelength of 1154.9 nm was detected by laser spectroscopy. The population of \overline{{p}}^{4}He+ occupying the resonance parent state (40, 36) was found to decay at a rate of 0.45 ± 0.04 μs-1, which agreed with the theoretical radiative rate of this state. This implied that very few long-lived \overline{{p}}^{4}He+ are formed in the higher-lying states with principal quantum number n ⩾ 41, in agreement with the results of previous experiments.
    Journal of Physics B Atomic Molecular and Optical Physics 12/2013; 46(24):5004-. · 2.03 Impact Factor
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    ABSTRACT: Physical laws are believed to be invariant under the combined transformations of charge, parity and time reversal (CPT symmetry). This implies that an antimatter particle has exactly the same mass and absolute value of charge as its particle counterpart. Metastable antiprotonic helium (pHe(+)) is a three-body atom consisting of a normal helium nucleus, an electron in its ground state and an antiproton (p) occupying a Rydberg state with high principal and angular momentum quantum numbers, respectively n and l, such that n ≈ l + 1 ≈ 38. These atoms are amenable to precision laser spectroscopy, the results of which can in principle be used to determine the antiproton-to-electron mass ratio and to constrain the equality between the antiproton and proton charges and masses. Here we report two-photon spectroscopy of antiprotonic helium, in which p(3)He(+) and p(4)He(+) isotopes are irradiated by two counter-propagating laser beams. This excites nonlinear, two-photon transitions of the antiproton of the type (n, l) → (n - 2, l - 2) at deep-ultraviolet wavelengths (λ = 139.8, 193.0 and 197.0 nm), which partly cancel the Doppler broadening of the laser resonance caused by the thermal motion of the atoms. The resulting narrow spectral lines allowed us to measure three transition frequencies with fractional precisions of 2.3-5 parts in 10(9). By comparing the results with three-body quantum electrodynamics calculations, we derived an antiproton-to-electron mass ratio of 1,836.1526736(23), where the parenthetical error represents one standard deviation. This agrees with the proton-to-electron value known to a similar precision.
    Nature 07/2011; 475(7357):484-8. · 38.60 Impact Factor
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    ABSTRACT: We report on the first experimental results for microwave spectroscopy of the hyperfine structure of p¯3He+. Due to the helium nuclear spin, p¯3He+ has a more complex hyperfine structure than p¯4He+, which has already been studied before. Thus a comparison between theoretical calculations and the experimental results will provide a more stringent test of the three-body quantum electrodynamics (QED) theory. Two out of four super-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were observed. The measured frequencies of the individual transitions are 11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current theoretical values, but still within their estimated errors. Although the experimental uncertainty for the difference of these frequencies is still very large as compared to that of theory, its measured value agrees with theoretical calculations. This difference is crucial to be determined because it is proportional to the magnetic moment of the antiproton.
    Physics Letters B 05/2011; 700(1):1-6. · 4.57 Impact Factor
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    ABSTRACT: In this work we describe the latest results for the measurements of the hyperfine structure of antiprotonic helium-3. Two out of four measurable super-super-hyperfine SSHF transition lines of the (n,L)=(36,34) state of antiprotonic helium-3 were observed. The measured frequencies of the individual transitions are 11.12548(08) GHz and 11.15793(13) GHz, with an increased precision of about 43% and 25% respectively compared to our first measurements with antiprotonic helium-3 [S. Friedreich et al., Phys. Lett. B 700 (2011) 1--6]. They are less than 0.5 MHz higher with respect to the most recent theoretical values, still within their estimated errors. Although the experimental uncertainty for the difference of 0.03245(15) GHz between these frequencies is large as compared to that of theory, its measured value also agrees with theoretical calculations. The rates for collisions between antiprotonic helium and helium atoms have been assessed through comparison with simulations, resulting in an elastic collision rate of gamma_e = 3.41 +- 0.62 MHz and an inelastic collision rate of gamma_i = 0.51 +- 0.07 MHz.
    Journal of Physics B Atomic Molecular and Optical Physics 03/2011; · 2.03 Impact Factor
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    ABSTRACT: The spin magnetic moment $\mu^{\overline{p}}_{s}$ of the antiproton can be determined by comparing the measured transition frequencies in $\overline{p}^4$ He + with three-body QED calculations. A comparison between the proton and antiproton can then be used as a test of CPT invariance. The highest measurement precision of the difference between the proton and the antiproton spin magnetic moments to date is 0.3%. A new experimental value of the spin magnetic moment of the antiproton was obtained as $\mu^{\overline{p}}_{s} = -2.7862(83)\mu_{N}$ , slightly better than the previously best measurement. This agrees with $\mu^{p}_{s}$ within 0.24%. In 2009, a new measurement with antiprotonic 3He has been started. A comparison between the theoretical calculations and experimental results would lead to a stronger test of the theory and address systematic errors therein. A measurement of this state will be the first HF measurement on $\overline{p}^3$ He + . We report here on the new experimental setup and the first tests.
    Hyperfine Interactions 01/2011; 199(1-3). · 0.21 Impact Factor
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    ABSTRACT: We report the first measurements of the inelastic spin exchange collision rate between the Hyperfine (HF) levels of antiprotonic helium. We measure the time dependent evolution of the (37, 35) substates to obtain an inelastic collision rate which qualitatively agrees with recent theoretical calculations. We evaluate these results by using the obtained rate as a parameter in a rigorous simulation which we then compare to to previously measured data. We find that our measurement slightly underestimates the collision rate and therefore conclude that the actual value most probably falls within the upper, rather than lower, limit of the error. Comment: 15 pages, 10 figures
    07/2009;
  • Anna Soter, Masaki Hori
    Hyperfine Interactions 05/2009; · 0.21 Impact Factor
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    ABSTRACT: We report a determination of the antiproton magnetic moment, measured in a three-body system, independent of previous experiments. We present results from a systematic study of the hyperfine (HF) structure of antiprotonic helium where we have achieved a precision more than a factor of 10 better than our first measurement. A comparison between the experimental results and three-body quantum electrodynamic (QED) calculations leads to a new value for the antiproton magnetic moment is -2.7862 (83) nuclear magnetons, which agrees with the magnetic moment of the proton within 2.9 x 10e-3.
    Physics Letters B 05/2009; 678:55-59. · 4.57 Impact Factor
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    A. Soter, M. Hori
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    ABSTRACT: Two detectors which will be used to commission a superconducting radiofrequency Paul trap for antiprotons, now being constructed at CERN and MPQ, are described. One is a microwire secondary electron emission monitor which will nondestructively measure the spatial profile of a low energy (E= 10−100keV) antiproton beam. The other is a system of electromagnetic shower counters which will detect the secondary particles emerging from the antiproton annihilations occurring in the trap.
    Hyperfine Interactions 04/2009; 194(1):201-205. · 0.21 Impact Factor
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    ABSTRACT: We report a determination of the antiproton magnetic moment, measured in a three-body system, independent of previous experiments. We present results from a systematic study of the hyperfine (HF) structure of antiprotonic helium where we have achieved a precision more than a factor of 10 better than our first measurement. A comparison between the experimental results and three-body quantum electrodynamic (QED) calculations leads to a new value for the antiproton magnetic moment μsp¯=−2.7862(83)μN, which agrees with the magnetic moment of the proton within 2.9×10−3.
    Physics Letters B 01/2009; 678(1):55-59. · 4.57 Impact Factor
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    ABSTRACT: The longitudinal and transverse beam coupling impedance of the first final TOTEM Roman Pot unit has been measured in the laboratory with the wire method. For the evaluation of transverse impedance the wire position has been kept constant, and the insertions of the RP were moved asymmetrically. With the original configuration of the RP, resonances with fairly high Q values were observed. In order to mitigate this problem, RF-absorbing ferrite plates were mounted in appropriate locations. As a result, all resonances were sufficiently damped to meet the stringent LHC beam coupling impedance requirements.
    07/2008;
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    ABSTRACT: TOTEM is an LHC experiment around the same interaction point as CMS. It contains cathode strip chambers (CSC) and gas electron multiplier detectors (GEM) in the CMS cavern and 24 Roman Pots with silicon strip detectors in the LHC tunnel. TOTEM should run both standalone and together with CMS, and should be fully compatible with CMS. All three sub-detectors provide level one trigger building signals and use the same chips: VFAT2 providing both tracking data and fast trigger generation signals, the programmable Coincidence Chip, and the LVDS repeater chip. The same counting room hardware receives and handles both trigger building and tracking data.
    Topical Workshop on Electronics for Particle Physics. 01/2007;
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    ABSTRACT: The existing data of antinucleon-nucleon and antinucleon-nuclei annihilation cross-sections are confined to energies above about 1MeV. Experimental limitations have prevented till now the lower energies data to be achieved in spite of the interest they represent for theoretical models. One of the unresolved question concerns the antiproton annihilation cross-section measured at LEAR on light nuclei in the MeV region, which show a saturation with the mass number of the target nucleus against any naive expectation. With regard to fundamental cosmology, the knowledge of the annihilation cross-sections at energies below 1MeV can contribute to understand the matter-antimatter asymmetry in the Universe. We present here the experimental demonstration of the feasibility of the measurement of antiproton-nuclei annihilation cross-sections in the 100 keV region.
    European Physical Journal Plus 127(10). · 1.30 Impact Factor
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    ABSTRACT: The results of the annihilation cross sections measurement of 5.3 MeV antiprotons on nickel, tin, platinum and Mylar targets performed by the ASACUSA Collaboration at CERN are presented and compared with the existing data and models. From the experimental point of view the presented data are the first measurement of antinucleon annihilation cross sections at low energies obtained with a pulsed beam. This results open the road for the next measurements at the very low energies of the order of 100 keV that are in progress by the ASACUSA Collaboration. The experimental method foreseen for the 100 keV measurement is illustrated.
    Hyperfine Interactions 213(1-3). · 0.21 Impact Factor
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    ABSTRACT: We shall present here the first experimental results for microwave spectroscopy of the hyperfine structure of antiprotonic He-3 and a comparison to numerical simulations of the measurement. Due to the helium nuclear spin, antiprotonic He-3 has a more complex hyperfine structure than antiprotonic He-4 which has already been studied before. Thus a comparison between theoretical calculations and the experimental results will provide a more stringent test of the three-body quantum electrodynamics (QED) theory. The comparison of measured data to simulations allows to investigate the collisional processes between the helium atoms of the target medium and the antiprotonic helium atomcules. The collision rates can not be calculated exactly, but estimated by comparison of numeric simulations with the experimental results. Two out of four super-super-hyperfine (SSHF) transition lines of the (n, L) = (36, 34) state were observed. The measured frequencies of the individual transitions are 11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current theoretical values, but still within their estimated errors. The frequency difference between the two lines also agrees with theoretical calculations.
    Hyperfine Interactions 212(1-3). · 0.21 Impact Factor
  • M. Hori, A. Dax, A. Soter
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    ABSTRACT: The ASACUSA collaboration has developed injection-seeded Ti:sapphire lasers of linewidth Γpl ∼ 6 MHz, pulse energy 50–100 mJ, and output wavelength λ = 726–941 nm. They are being used in two-photon spectroscopy experiments of antiprotonic helium atoms at the Antiproton Decelerator (AD) of CERN. Ti:sapphire lasers of larger linewidth Γpl ∼ 100 MHz but more robust design will also be used in collinear resonance ionization spectroscopy (CRIS) experiments of neutron-deficient francium ions at the ISOLDE facility.
    Hyperfine Interactions 212(1-3). · 0.21 Impact Factor
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    ABSTRACT: The ASACUSA (the Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration is planning to measure the cross sections of antiproton annihilations at kinetic energy 100 keV on targets of various mass numbers (C, Ni, Sn, and Pt) using the Antiproton Decelerator (AD) of CERN. No previous measurement exists in this region where the A-dependence of the cross section is expected to deviate from the A $^{\frac{2}{3}}$ (Batty et al, Nucl Phys A 689:721, 2001) as reported by the Obelix collaboration. A beam profile monitor based on secondary electron emission with a grid of electrode pads fabricated on an FR4-type glass-epoxy circuit board was developed for this measurement. The advantage of this kind of detector is that it is simple, lightweight, and low cost. It was used to measure the spatial profile of 100-ns-long beam pulses containing > 6 × 104 antiprotons with an active area of 40 mm × 40 mm and a spatial resolution of 4 mm.
    Hyperfine Interactions 213(1-3). · 0.21 Impact Factor