Koichi Todoroki

Buffer-gas cooling of antiprotonic helium to 1.5 to 1.7 K, and antiproton-to–electron mass ratio

Exotic molecule tests fundamental symmetry Spectroscopy of exotic molecules can offer insight into fundamental physics. Hori et al. studied the transition frequencies of an unusual helium atom in which one of the two electrons was substituted by an antiproton, the negatively charged antiparticle partner of the proton (see the Perspective by Ubachs). The antiprotonic helium was cooled down to low temperatures to allow the frequencies to be measured with high precision. The extracted mass of the antiproton (relative to the electron mass) was in good agreement with previous measurements of the proton mass. This finding is in keeping with the implications of the combined charge, parity, and time-reversal symmetry of physical laws. Science, this issue p. 610; see also p. 546 Spectroscopy of a cold exotic molecule yields a precise value of the antiproton mass relative to the mass of the electron. Charge, parity, and time reversal (CPT) symmetry implies that a particle and its antiparticle have the same mass. The antiproton-to-electron mass ratio Mp¯/me can be precisely determined from the single-photon transition frequencies of antiprotonic helium. We measured 13 such frequencies with laser spectroscopy to a fractional precision of 2.5 × 10−9 to 16 × 10−9. About 2 × 109 antiprotonic helium atoms were cooled to temperatures between 1.5 and 1.7 kelvin by using buffer-gas cooling in cryogenic low-pressure helium gas; the narrow thermal distribution led to the observation of sharp spectral lines of small thermal Doppler width. The deviation between the experimental frequencies and the results of three-body quantum electrodynamics calculations was reduced by a factor of 1.4 to 10 compared with previous single-photon experiments. From this, Mp¯/me was determined as 1836.1526734(15), which agrees with a recent proton-to-electron experimental value within 8 × 10−10.

Segmented scintillation detectors with silicon photomultiplier readout for measuring antiproton annihilations

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.

Observation of the 1154.9 nm transition of antiprotonic helium

The resonance transition (n, l) = (40, 36) ? (41, 35) of the antiprotonic helium (He+) isotope at a wavelength of 1154.9?nm was detected by laser spectroscopy. The population of He+ occupying the resonance parent state (40, 36) was found to decay at a rate of 0.45 ? 0.04 ?s?1, which agreed with the theoretical radiative rate of this state. This implied that very few long-lived He+ are formed in the higher-lying states with principal quantum number n ? 41, in agreement with the results of previous experiments.

Beam profile monitor for antiproton-nucleus annihilation cross section measurements

The ASACUSA (the Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration is planning to measure the antiproton-nucleus annihilation cross sections at kinetic energy 120 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 this cross section is expected to deviate from the A(2/3) as reported by the Obelix collaboration. For this measurement, 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. The advantage of this 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.

First observation of two hyperfine transitions in antiprotonic 3He

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.

Microwave spectroscopic study of the hyperfine structure of antiprotonic 3He

In this work, we describe the latest results for the measurements of the hyperfine structure of antiprotonic 3 He. Two out of four measurable super–super-hyperfine (SSHF) transition lines of the (n,L) = (36, 34) state of antiprotonic 3 He were observed. The measured frequencies of the individual transitions are 11.125 48(08) GHz and 11.157 93(13) GHz, with the increased precisions of about 43% and 25%, respectively, compared to our first measurements with antiprotonic 3 He (Friedreich et al 2011 Phys. Lett. B 700 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 0.032 45(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 γe = 3.41 ± 0.62 MHz and an inelastic collision rate of γi = 0.51 ± 0.07 MHz. (Some figures may appear in colour only in the online journal)

Beam diagnostics for measurements of in-flight annihilation cross sections of antiprotons at 130 keV

Hossein Aghai-Khozani1,2, Daniel Barna3,4, Maurizio Corradini5,6, Ryugo Hayano4, Masaki Hori1,4, Takumi Kobayashi4, Marco Leali5,6, Evandro Lodi-Rizzini5,6, Valerio Mascagna5,6, Michela Prest7,8, Anna Soter1, Koichi Todoroki4, Erik Vallazza9, Luca Venturelli5,6, and Nicola Zurlo5,6 1Max-Planck-Institut fur Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany 2Physics Department, CERN, 1211 Geneva 23, Switzerland 3Wigner Institute for Particle and Nuclear Physics, H-1525 Budapest, Hungary 4Department of Physics, University of Tokyo, Hongo7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan 5Dipartimento di Collegato di Brescia, 25133 Brescia, Italy 6INFN, Gruppo Collegato di Brescia, 25133 Brescia, Italy 7Dipartimento di Scienze Fisiche e Matematiche, Universita di Como, I-22100 Como, Italy 8INFN, Sezione di Milano Bicocca, I-20126 Milano, Italy 9INFN, Sezione di Trieste, I-34127 Trieste, Italy

Segmented scintillators with SiPM readout for measuring antiproton annihilations

The Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA) experiment at CERN constructed some segmented scintillation counters to measure and track the charged pions emerging from antiproton annihilations in a future superconducting radiofrequency Paul trap for antiprotons. The photoelectron yields of various scintillator configurations were measured using a p beam of momentum p 1 GeV/c at the T9 beamline of the CERN Proton Synchrotron (PS). 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 Antiproton Decelerator (AD). At high antiproton rates a saturation was observed in the scintillator signal. We review the detector construction and measurement results.

The Deeply Bound Pionic States in 121Sn Produced by (d,3He) Reaction

T. Nishi , G.P.A. Berg, M. Dozono, H. Fujioka, N. Fukuda, T. Furuno, H. Geissel, R.S. Hayano, N. Inabe, K. Itahashi, S. Itoh, D. Kameda, T. Kubo, H. Matsubara, S. Michimasa , K. Miki, H. Miya , Y. Murakami, M. Nakamura, N. Nakatsuka, S. Noji, K. Okochi, S. Ota , H. Suzuki, K. Suzuki, M. Takaki , H. Takeda, Y.K. Tanaka, K. Todoroki, K. Tsukada, T. Uesaka, Y.N. Watanabe, H. Weick, H. Yamada, and K. Yoshida

Status and future plan of the spectroscopy of pionic atoms

The spectroscopy of deeply bound pionic atoms provides a way to understand the restoration of chiral symmetry breaking at finite density. We have been performing a series of experiments of missing-mass spectroscopy of the (d,3He) reaction at RIBF to investigate pionic atoms of several Sn isotopes. As a first step, we conducted a pilot experiment to measure deeply bound pionic states of 121Sn and successfully observed the deeply bound pionic states. In addition to the experiment at RIBF, we are planning the spectroscopy of deeply bound pionic atoms in inverse kinematics and conducted a feasible study by simulations. We showed that by using a deuterium gaseous active target TPC and silicon detectors, the Q-value resolution is about 500 keV (FWHM) and the yield of the pionic 1s state is 20 counts/day, indicating the experiment is feasible.