Tetsuya Yoshida

Prepared for 28th International Cosmic Ray Conferences (ICRC 2003), Tsukuba, Japan, 31 Jul - 7 Aug 2003. <br /> Published in *Tsukuba 2003, Cosmic Ray* 1163-1166<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt;&lt;a href=&quot;http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/291.pdf

Prepared for 28th International Cosmic Ray Conferences (ICRC 2003), Tsukuba, Japan, 31 Jul - 7 Aug 2003. <br /> Published in *Tsukuba 2003, Cosmic Ray* 1797-1800<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt; &lt;a href=&quot;http://www-rccn.icrr.u-tokyo.ac.jp/icrc2003/PROCEEDINGS/PDF/445.pdf

Prepared for 8th Accelerator and Particle Physics Institute (APPI 2003), Appi, Iwate, Japan, 25-28 Feb 2003. <br /> Published in *Appi 2003, Accelerator and particle physics* 284-293

The vertical absolute fluxes of atmospheric muons and muon charge ratio have been measured precisely at different geomagnetic locations by using the BESS spectrometer. The observations had been performed at sea level (30 m above sea level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada. The vertical cutoff rigidities in Tsukuba (36.2degreesN, 140.1degreesE) and in Lynn Lake (56.5degreesN, 101.0degreesW) are 11.4 and 0.4 GV, respectively. We have obtained vertical fluxes of positive and negative muons in a momentum range from 0.6 to 20 GeV/c with systematic errors &lt;3% in both measurements. By comparing the data collected at two different geomagnetic latitudes, we have seen an effect of cutoff rigidity. The dependence on the atmospheric pressure and temperature, and the solar modulation effect have been also clearly observed. We also clearly observed the decrease of charge ratio of muons at low momentum side with at higher cutoff rigidity region. (C) 2002 Elsevier Science B.V. All rights reserved.

BESS

J-GLOBAL ID 200902109906977366 <br /> 整理番号 02A0351952 <br /> JST資料番号 G0925B <br />

An extremely thin superconducting solenoid magnet is being developed to investigate cosmic-ray antiparticle in the Universe. The uniform solenoidal field is provided in a particle detector system to analyze the particle momentum. The solenoid coil is wound with advanced aluminum stabilized superconductor recently developed by using micro-alloying with Ni, followed by cold-work mechanical hardening. It is designed with a central magnetic field of 1.2 T in a volume of 0.9 m in diameter and 1.4 m in length, the radiation thickness of the coil is to be 0.056 X-o with a physical coil thickness of 3.4 mm. This paper describes the conceptual design and progress of the basic development work.

Prepared for 7th Accelerator and Particle Physics Institute (APPI 2002), Appi, Iwate Ken, Japan, 13-16 Feb 2002. <br /> Published in *Appi 2002, Accelerator and particle physics* 117-138 <br />

The energy spectra of cosmic-ray low-energy antiprotons ((p) over bar 's) and protons (p's) have been measured by BESS in 1999 and 2000, during a period covering reversal at the solar magnetic field. Based an these measurements, a sudden increase of the (p) over bar /p flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.

We have searched for antihelium nuclei in cosmic rays using the data obtained from balloon flights of the BESS magnetic spectrometer. The search was mainly based on track-quality selection, followed by rigidity analysis, and on the time-of-flight and dE/dx measurements by the scintillation counter hodoscope. We analysed all the data collected during 1993-2000 with a common analysis procedure. No antihelium nuclei events were found in the energy range from 1 to 14 GV. In order to determine a new upper limit, we have simulated the loss in the air and in the instrument of He (He) using the GEANT/GHEISHA code. Combined with the data collected in 1993 through 2000, a new 95 % confidence upper limit for the ratio of He/He at the top of the atmosphere of 6.8 × 10-7 has been obtained to be after correcting for the interactions in the air and in the instruments.

The BESS-Polar experiment with long-duration balloon flights at Antarctica aims at extremely sensitive measurement of low energy antiprotons to search for novel primary origins in the early Universe, and to study cosmic-ray propagation and solar modulation. The search for cosmic antimatter is a fundamental objective to study baryon asymmetry in the Universe. The BESS experiment with high rigidity resolution and large geometrical acceptance will maximize advantages of long duration flights at Antarctica where the rigidity cut-off is lowest. A very compact and thin superconducting magnet spectrometer is being developed to maximize the detector performance in low energies. The BESS-Polar project and progress of the development are described.

An accelerator experiment was performed using a low-energy antiproton beam to measure antiproton detection efficiency of BESS, a balloon-borne spectrometer with a superconducting solenoid. Measured efficiencies showed good agreement with calculated ones derived from the BESS Monte Carlo simulation based on GEANT/GHEISHA. With detailed verification of the BESS simulation, the relative systematic error of detection efficiency derived from the BESS simulation has been determined to be +/-5%, compared with the previous estimation of +/- 15% which was the dominant uncertainty for measurements of cosmic-ray antiproton flux. (C) 2002 Elsevier Science B.V. All rights reserved.

The Balloon-borne Experiment with a Superconducting Spectrometer, BESS, aims to study elementary particle/antiparticle phenomena in the early history of the Universe. The instrument has a unique feature of a thin superconducting solenoid magnet enabling a large geometrical acceptance with a horizontally cylindrical configuration. Seven balloon flights have been successfully carried out since 1993. More than 10(3) comic-ray antiproton have been unambiguously detected, and the energy spectrum has been measured with the characteristic peak at 2 GeV. The search for cosmic-ray antihelium brought the upper-limit of the antiheliuni/helium ratio down to &lt; 10(-6). To extend the highly sensitive measurements, we are planning polar long duration flights in Antarctica focusing on the very low energy antiproton spectrum towards the solar-minimum in the next decade. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

Prepared for 5th RESCEU International Symposium on New Trends in Theoretical and Observations Cosmology, Tokyo, Japan, 13-16 Nov 2001. <br /> Published in *Tokyo 2001, New trends in theoretical and observational cosmology* 111-118

27th International Cosmic Ray Conference (ICRC 2001), Hamburg, Germany, 7-15 Aug 2001.<br /> Published in *Hamburg 2001, Cosmic ray* 1699-1700<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt; &lt;a href=&quot;http://www.copernicus.org/icrc/papers/ici6875_p.pdf

Contributed to 27th International Cosmic Ray Conference (ICRC 2001), Hamburg, Germany, 7-15 Aug 2001, Hamburg, Germany. <br /> Published in *27th International Cosmic Ray Conference (ICRC 2001), Hamburg, Germany, 7-15 Aug 2001, Vol.3* 950-953<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt; &lt;a href=&quot;http://www.copernicus.org/icrc/papers/ici7271_p.pdf

BESS<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt; &lt;a href=&quot;http://www.copernicus.org/icrc/papers/ici7127_p.pdf

BESS<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt; &lt;a href=&quot;http://www.copernicus.org/icrc/papers/ici7339_p.pdf

BESS<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;&lt;/a&gt; &lt;a href=&quot;http://www.copernicus.org/icrc/papers/ici6699_p.pdf

Contributed to 27th International Cosmic Ray Conference (ICRC 2001), Hamburg, Germany, 7-15 Aug 2001. <br /> Published in *27th International Cosmic Ray Conference (ICRC 2001), Hamburg, Germany, 7-15 Aug 2001, Vol.3* pp. 927-930 Also in *Hamburg 2001, Cosmic ray*<br /> <br /> 0&quot; target=&quot;_blank&quot;&gt;0&lt;/a&gt; &lt;a href=&quot;http://www.copernicus.org/icrc/papers/ici6926_p.pdf

A series of Balloon-borne Experiments with a Superconducting Spectrometer, BESS, has been made since 1993. We report here the absolute cosmic-ray proton and helium spectra in energy ranges of 1 to 120 GeV and I to 54 GeV/nucleon, respectively, as measured by the 1998 balloon flight of the BESS spectrometer. Those spectra were determined within overall uncertainties of +/-5 % for protons and +/- 10 % for helium nuclei including statistical and systematic errors. The covered energy range is relevant to the atmospheric neutrinos observed as "fully contained events" in Super-Kamiokande. In order to extend the energy range up to around I TeV, we have started to design and develop new tracking detectors. Those energy spectra in a higher energy region will help to estimate the interstellar spectra of primary cosmic rays and the absolute fluxes of "up-going muons." (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

The BESS spectrometer has measured the energy spectrum of cosmic-ray antiprotons successively in 1993, 1995, 1997 and 1998. In total, 848 antiprotons were clearly identified in energy range 0.18 to 4.20 GeV based on magnetic-rigidity, time-of-flight, energy loss, and Cherenkov radiation measurements. The measured antiproton spectra and antiproton/proton ratios were nearly identical at the upper end of the instrumental energy range, which is consistent with theoretical calculations. In the low energy region. our data show variations that are somewhat larger than expected. This might be due to statistical fluctuation, or might suggest a contribution of primary antiprotons from novel sources. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

The energy spectrum of cosmic-ray antiprotons (p's) has been measured by BESS successively in 1993, 1995, 1997 and 1998. In total, 848 (p) over bar 's were clearly identified in energy range 0.18-4.20 GeV. From these successive measurements of the (p) over bar spectrum at various solar activity, we discuss about the effect of the solar modulation and the origin of cosmic-ray (p) over bar 's. The (p) over bar /p ratios showed no distinctive year-to-year variation during the positive Sun's polarity phase. (C) 2001 Elsevier Science B.V. All rights reserved.

BESS

BESS

The energy spectrum of cosmic-ray antiprotons ((p) over bar's) has been measured in the range 0.18-3.56 GeV, based on 458 (p) over bar's collected by BESS in a recent solar-minimum period. We have detected for the first time a characteristic peak at 2 GeV of (p) over bar's originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS data with still higher statistics will allow us to study the solar modulation and the propagation in detail and to search for primary (p) over bar components.

We have obtained the absolute spectra of H and He by analyzing data collected by a series of annual flights of the Balloon borne Experiment with a Superconducting solenoid Spectrometer payload. This instrument is configured with a cylindrical magnet, a Time-of-Flight system, a set of cylindrical multiwire drift chambers inside and outside the magnet, and a central tracking device Jet chamber. The analysis involves Monte Carlo simulations of the effective geometry factor, studies of various efficiencies, and corrections for the ionization energy loss, attenuation and atmospheric secondaries. Variations of the H and He fluxes at different levels of solar modulation are presented. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

The absolute fluxes of the cosmic-ray antiproton are measured at solar minimum in the energy range 0.2 to 3.2 GeV, based on 460 antiprotons unambiguously detected by BESS spectrometer during its '95 and '97 balloon flights from Lynn Lake, Canada. In the resultant antiproton spectrum we have detected a clear peak around 2 GeV and measured its flux to 10% accuracy. The position and the absolute flux of the peak agree with the prediction of the Standard Leaky Box model for the "secondary" antiprotons. At low energies below I GeV, we observe an excess antiproton flux over the simple Standard Leaky Box prediction. This might indicate that the propagation mechanism needs to be modified, or might suggest a contribution of low-energy antiproton component from novel sources such as evaporating primordial black holes or the annihilating neutralino dark matter. Data from '98 and future Rights are expected to help us to clarify the situation. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

We describe the design and performance of a large-area scintillator hodoscope onboard the BESS rigidity spectrometer an instrument with an acceptance of 0.3 m2 sr. The hodoscope is configured such that 10 and 12 counters are, respectively, situated in upper and lower layers. Each counter is viewed from its ends by 2.5 in. fine-mesh photomultiplier tubes placed in a stray magnetic field of 0.2 T. Various beam-test data are presented. Use of cosmic-ray muons at ground-level confirmed 50 ps timing resolution for each layer, giving an overall time-of-flight resolution of 70 ps rms using a pure Gaussian-resolution function. Comparison with previous measurements on a similar scintillator hodoscope indicates good agreement with the scaling law that timing resolution is proportional to 1/√Npc, where Npc is the effective number of photoelectrons.

We report cosmic-ray proton and helium spectra in energy ranges of 1-120 GeV nucleon(-1) and 1-54 GeV nucleon(-1), respectively, measured by a flight of the Balloon-borne Experiment with Superconducting Spectrometer (BESS) in 1998. The magnetic rigidity of the cosmic ray was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 T. Those spectra were determined within overall uncertainties of +/-5% for protons and +/- 10% for helium nuclei including statistical and systematic errors.

The BESS detector is a new type of balloon-borne spectrometer which utilizes various technologies recently developed for collider experiments. The principal scientific objectives include a measurement of cosmic-ray antiproton spectrum, search for anti-nuclei in cosmic radiation, and precise meaurements of cosmic-ray primaries. A thin superconducting solenoidal coil produces a uniform magnetic field of 1 T. Cylindrical drift chambers are located inside and outside the coil and perform continuous tracking. The momentum resolution is 0.5% at 1 GeV/c. i.e., the maximum detectable rigidity is 200 GV. Scintillation counter hodoscopes, placed above and below the solenoid, provide timing and dE/dx measurements and trigger generation. The timing resolution is 80 ps/counter. This cylindrical configuration achieves a large geometrical acceptance of 0.35 m(2) sr which is essential to detect rare cosmic-ray particles. In order to cope with high trigger rate and large data size, intelligent trigger circuits and a fast and parallel data acquision system are also developed. In 1993, the first scientific flight of the BESS apparatus was carried out and the first mass-measured antiprotons were detected at energies below 500 MeV (C) 2000 Elsevier Science B.V. All rights reserved.

Prepared for 26th International Cosmic Ray Conference (ICRC 99), Salt Lake City, Utah, 17-25 Aug 1999. <br /> In *Salt Lake City 1999, Cosmic ray, vol. 3* 93-96.<br /> http://adsabs.harvard.edu/abs/1999ICRC....3...93T

Prepared for 26th International Cosmic Ray Conference (ICRC 99), Salt Lake City, Utah, 17-25 Aug 1999. <br /> In *Salt Lake City 1999, Cosmic ray, vol. 3* 85-88.

Prepared for 26th International Cosmic Ray Conference (ICRC 99), Salt Lake City, Utah, 17-25 Aug 1999. <br /> In *Salt Lake City 1999, Cosmic ray, vol. 3* 37-40. <br />

The absolute fluxes of the cosmic-ray antiprotons at solar minimum are measured in the energy range 0.18 to 1.4 GeV, based on 43 events unambiguously detected in BESS 1995 data. The resultant energy spectrum appears to be flat below 1 GeV, compatible with a possible admixture of primary antiproton component with a soft energy spectrum, while the possibility of secondary antiprotons alone explaining the data cannot be excluded with the present accuracy. Further improvement of statistical accuracy and extension of the energy range are planned in future BESS flights. [S0031-9007(98)07573-5].

BESS<br /> KEK-PREPRINT-98-119<br /> May 27, 1998 (ISTS-98)<br /> <br /> Author list (Full version)<br /> A. Yamamoto <br /> KEK, Tsukuba <br /> S. Orito <br /> Tokyo U. <br /> <br /> J. Ormes <br /> NASA, Goddard <br /> <br /> T. Yoshida <br /> KEK, Tsukuba <br /> <br /> K. Yoshimura, K. Abe, K. Anraku, Y. Asaoka, M. Fujikawa, M. Imori, T. Maeno <br /> Tokyo U. <br /> <br /> Y. Makida <br /> KEK, Tsukuba <br /> <br /> H. Matsumoto <br /> Kobe U. <br /> <br /> N. Matsui, H. Matsunaga <br /> Tokyo U. <br /> <br /> J. Mitchell <br /> NASA, Goddard <br /> <br /> T. Mitsui <br /> Kobe U. <br /> <br /> A. Moiseev <br /> NASA, Goddard <br /> <br /> M. Motoki <br /> Tokyo U. <br /> <br /> J. Nishimura <br /> Sagamihara, Inst. Space Astron. Sci. <br /> <br /> M. Nozaki <br /> Kobe U. <br /> <br /> T. Saeki, T. Sanuki <br /> Tokyo U. <br /> <br /> M. Sasaki <br /> Kobe U. <br /> <br /> E. Seo <br /> Maryland U. <br /> <br /> Y. Shikaze, T. Sonoda <br /> Tokyo U. <br /> <br /> R. Streitmatter <br /> NASA, Goddard <br /> <br /> J. Suzuki, K. Tanaka <br /> KEK, Tsukuba <br /> <br /> I. Ueda <br /> Tokyo U. <br /> <br /> N. Yajima, T. Yamagami <br /> Sagamihara, Inst. Space Astron. Sci.

A very sensitive search for cosmic-ray antihelium was performed using data obtained from three scientific flights of the BESS magnetic rigidity spectrometer. We have not observed any antihelium; this places a model-independent upper limit (95% C.L.) on the antihelium flux of 6 x 10(-4) m(-2)sr(-1)s(-1) at the top of the atmosphere in the rigidity region 1 to 16 GV, after correcting for the estimated interaction loss of antihelium in the air and in the instrument. The corresponding upper limit on the &lt;(He)over bar&gt;/He flux ratio is 3.1 x 10(-6), 30 times more stringent than the limits obtained in similar rigidity regions with magnetic spectrometers previous to BESS. (C) 1998 Published by Elsevier Science B.V.

http://adsabs.harvard.edu/abs/1997ICRC....3..373S

We have searched for antihelium in the galactic cosmic rays using data obtained on the flight of the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) launched from Lynn Lake, Manitoba, in northern Canada on 1995 July 25. The balloon reached an altitude of 36.5 km with a residual overburden of 5 g cm(-2). The total observation time was 12.2 kr with a live-time fraction of 0.61. No antihelium was observed after selections based on dE/dx and event quality cuts at rigidities between 1.6 and 16 GV/c; we infer that 536,420 helium nuclei survived the same cuts. This result leads to an upper limit to the &lt;(He)over bar&gt;/He abundance ratio of 8.1 x 10(-6) (95% confidence level), a factor of 2.7 over the lowest previous limit. Because this limit is for the first time at the level where predicted limits become astrophysically interesting (Ahlen et al.), we have reexamined the transport of cosmic rays in intergalactic space. We show that little can be learned about distant (&gt; 10 Mpc) domains of antimatter from a null result.

Balloon-borne experiment using a superconducting spectrometer were carried out successfully in northern Canada, in summer 1993 to 1995. In `93 flight, seven antiprotons were detected in the kinetic range between cen 200 and 600 MeV. The corresponding cosmic ray antiproton flux at the top of the atmosphere is fond to be 6.4(-3.5)(+5.5) x 10(-3)(m(2) sr s GeV)(-1). In '95 flight. improvement on the TOF resolution resulted to the observation of the forty antiprotons in the kinetic energy region 175 MeV to 1.3 GeV. The analysis on '95 flight is under way. (C) 1997 COSPAR.

We have studied the low-energy antiprotons in the cosmic rays by utilizing data obtained by the Balloon-borne Experiment with a Superconducting magnetic rigidity Spectrometer (BESS) flown in 1993 July from Lynn Lake, Manitoba, Canada. A detailed description of the event selection criteria and back-ground corrections is given. Seven antiprotons are found that give an antiproton flux of 6.4(-3.5)(+5.5) x 10(-3)(m(2) sr s GeV)(-1) and an antiproton/proton ratio of 5.2(-2.8)(+4.4) x 10(-6) in the 200-600 MeV energy range. These results are consistent with a secondary origin of low-energy cosmic-ray antiprotons within our uncertainties, but they still require the precise measurement of the spectrum shape below 500 MeV to clarify exactly the model of particle propagation and possible contributions from exotic sources.

BESS

Spectrometer and Balloon Borne Experiment<br /> http://www.isas.ac.jp/publications/hokokuSP/index1996.html

http://www.isas.ac.jp/publications/hokokuSP/index1996.html

A balloon-borne experiment using a superconducting solenoidal magnet spectrometer is being carried out with aims at making a precise measurement of low energy antiproton flux in cosmic rays and a highly sensitive search for primordial antimatter in the Universe. The spectrometer has a unique cylindrical configuration associated with a thin superconducting solenoidal magnet and is realizing a geometrical acceptance of 0.5 m(2)sr. The first scientific ballooning flight was successfully carried out in northern Canada, in summer, 1993, and the second flight is being prepared to he carried out in summer, 1994. Performance of the spectrometer in the first night and progress of the experiment are described.