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John W. Mitchell NASA GSFC Akira Yamamoto KEK

Antimatter and Dark Matter from Space: BESS-Polar Results. John W. Mitchell NASA GSFC Akira Yamamoto KEK. Balloon-borne Experiment with a Superconducting Spectrometer. BESS-Polar Collaboration. NASA/Goddard Space Flight Center T.Hams, J.W.Mitchell , M.Sasaki, R.E. Streitmatter

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John W. Mitchell NASA GSFC Akira Yamamoto KEK

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  1. Antimatter and Dark Matter from Space: BESS-Polar Results • John W. Mitchell NASA GSFC • Akira Yamamoto KEK Balloon-borne Experiment with a Superconducting Spectrometer

  2. BESS-Polar Collaboration • NASA/Goddard Space Flight Center T.Hams, J.W.Mitchell, M.Sasaki, R.E. Streitmatter • KEKS. Haino, M. Hasegawa, A. Horikoshi, Y.Makida, S. Matsuda, M. Nozaki, J.Suzuki, K.Tanaka, A. Yamamoto, K.Yoshimura • The University of Tokyo J.Nishimura, K. Sakai, R. Shinoda • Kobe University • K. Abe, A. Kusumoto, Y. Matsukawa, R. Orito • University of Maryland K.C. Kim, M.H. Lee, S.E. Lee, E.S. Seo • ISAS/JAXA H. Fuke, T. Yoshida • University of Denver • J. Ormes, N. Thakur

  3. BESS-Polar Science BESS antiproton measurements from 1995-1997 Solar minimum suggest possible excess at low energy. • Cosmic-ray particles and antiparticles probe the early Universe • Antinucleitest symmetry of matter and antimatter • Antiprotons: • Mainly secondary origin - cosmic ray interactions • Possible small primary component; • Evaporation of primordial black holes (PBH) initially near ~5x1014g? • Decay of super-symmetric particles? • Cosmic ray spectra and composition • p, He, Li, Be isotopic and elemental spectra • B, C, N, O elemental spectra • Atmospheric muons • Heliospheric influence on Galactic cosmic rays • Charge-sign dependent Solar modulation • Short-term transients and diurnal variation • Future program • High-energy positrons • Radioactive 10Be to high velocity (time dilation)

  4. Magnetic Spectrometers - Post-ASTROMAG Antimatter LEAP PBAR MASS IMAX BESS CAPRICE HEAT BESS-Polar PAMELA AMS Isotopes SMILI MASS IMAX BESS CAPRICE ISOMAX BESS-Polar PAMELA AMS

  5. Cosmic-Ray Antiproton Chronology 1979: First Antiproton Report (Golden et al.) 1979: Russian PM (Bogomolov et al.) 1981: Low-energy excess (Buffington et al.) 1985: ASTROMAG Study Started 1986: HEAO Antinucleus upper limits 1987:LEAP, PBAR (upper limits) 1991: MASS 1992:IMAX (16 mass-resolved antiprotons) 1993:BESS (6 mass-resolved antiprotons) 1994:CAPRICE94 1998: CAPRICE98, AMS-01 2000: HEAT-pbar 2004: BESS-Polar I 2006:PAMELA 2007: Solar minimum 2007: BESS-Polar II 2010:AMS-02

  6. BESS Instrumentation • Measures charge, charge-sign, mass, and energy • Superconducting magnetic spectrometer: momentum • Fully active “JET” drift chamber with 52 points on trace,  ~100 m • MDR 200 - 1400 TV • Time-of-flight system (TOF): velocity and charge • Silica-aerogel Cherenkov detector (ACC, n=1.02/1.03): background rejection

  7. Evolution of BESS • Nine northern latitude BESS flights (1+ days) 1993-2002 and Two multi-day (8.5 & 24.5 days) Antarctic flights in 2004, 2007 • Through BESS-Polar I 3757 antiprotons recorded between 0.2 and 4.2 GeV 2001-2002 2004, 2007 6,2 43 415, 398 668, 558 147 1,512, ~10,000

  8. BESS Program Summary • BESS Exposure • Total: 254 m2 sr hr • Solar minimum: 187 m2 sr hr • >100 GeV: 3.4 m2 sr hr • BESS-Polar: Polar I 36 m2 sr hr, Polar II 176 m2 sr hr

  9. BESS-Polar I BESS-Polar I particle ID x 5 10-3 Z=1 • Minimum material in path of particle (4.5 g/cm2) • Middle TOF (MTOF): low energy TOF/trigger • No pressure vessel • Outer detectors (TOF, ACC) in ambient near-vacuum • No in-flight data selection - all data recorded on 3.6 TB hard disk array • High speed data acquisition - 2.5 kHz trigger rate • Cryogen lifetime ~11.5 days

  10. BESS-Polar I Flight • Duration: 8 days, 17 hours (December 13-22 2004) • Altitude: 120 - 129 kft (37 - 39 km) • Trajectory: circumpolar 77.9° - 86° S • Events recorded: > 9 x 108 • Data volume: ~ 2 terabytes

  11. Protons • Proton spectra measured to ~500 GeV • Proton spectra to 100 GeV measured for full solar cycle • Upper solid line shows local interstellar (LIS) proton spectrum from best fit to BESS data • Lower curves show the variation with time (Solar modulation) of the measured proton spectra extrapolated to the top of the atmosphere

  12. Antiprotons • BESS (95+97) Solar min data show a possible flattening of the antiproton spectrum at lower energies compared to secondary production. (Upper dash curve leaky box with spherically symmetric modulation @ 550 MV.) • BESS-Polar I data taken at higher solar activity (851 MV - lower dashed curve) are consistent with secondary production, as expected. • Primary source suppressed at higher modulation levels. • Solid curve diffusive reacceleration with break at 30° Solar tilt angle

  13. Antihelium • No antihelium candidate has been found by any investigation • BESS-TeV 1 - 500 GV, 7 x 104 He events • BESS-Polar I 0.6 - 20 GV, 106 He events • BESS combined upper limit for the Antihelium to Helium flux ratio2.7 x 10-7 • 24.5-day flight of BESS-Polar II will give sensitivity <3 x 10-8. • Science News article May 12, 2007

  14. Antideuteron • Secondary D probability is negligible at low energiesdue to kinematics • Any observed D almost certainly has a primary origin ! • D upper limit (first reported), 1.92 x 10-4 (m2 s sr GeV/n)-1

  15. BESS-Polar I: Space Environment

  16. Lasco Images of Coronal Ejections • Dec 15, 2004: a small high speed stream was ejected on the west limb of the sun arriving at Earth on the 17th. • Dec 13 and 14th also show some similar activity

  17. BESS-Polar I Proton Spectrum - Solar Effects • General trend of BESS-Polar I proton flux tracks the neutron monitor • BESS-Polar I sees diurnal variation in the proton flux (work in progress) • First direct measurement of this effect (requires large collecting area)

  18. Antiproton/Proton Ratio - Solar Modulation • Antiprotons and protons differ only in charge-sign • Simultaneous measurements of proton and antiproton spectra provide a powerful test of models of charge-dependent Solar modulation of cosmic-rays (protons are most sensitive)

  19. BESS-Polar II p d t p • Longer Observing Time • Increased magnet cryogen life: >25 days • Enlarged data storage volume :16 TB • Improved Reliability • Pressurized enclosure for the TOF PMT • Improved electronics efficiency • Improved Performance • ACC rejection power • Middle TOF resolution/position determination • Outer TOF resolution

  20. BESS-Polar II - 2007

  21. BESS-Polar II Launch - December 22, 2007

  22. BESS-Polar II Flight Positive Events • Launch 12/22/07 17:30 UTC • Science Termination 1/16/08 2:00 UTC • Observation time at float - 24 days 10 hours • Average altitude ~36 km (118,000 ft) • Latitude 77.9° - 83° South Negative Events

  23. End of BESS-Polar II Flight • Flight termination January 20, 2008 ~30 days • Location 83 ° 51.23’ S, 73° 5.47’ W • On West Antarctic ice sheet - 225 nm from Patriot Hills Camp, 185 nm from AGO-2, 357 nm from South Pole • Data successfully recovered February 3!

  24. BESS-Polar II Recovery Plan • Planned for Winter 2008-2009 • Staging from South Pole baselined • Camp on site ~1-2 weeks for disassembly • Bassler (mod DC-3 turboprop) planned due to range and instrument size

  25. BESS-Polar II Performance p d t p BESS-Polar II Preliminary BESS Polar-I 2004BESS Polar-II 2007 • Spectrometer - ~130 m, MDR ~240 GV • Outer TOF - 120 ps • Middle TOF - 260-360 ps • Aerogel Cherenkov - 15 pe, 3360 rejection factor • Data Acquisition - 2.5 kHz event rate, 82% live

  26. BESS Polar II Observations/Expectations • Event rate ~2.5 kHz; Total events ~4.7 x 109 • Total data volume 13.5 TB (3.07 kB/event) • Expected antiprotons ~10,000 10-20 times previous Solar minimum dataset Antiproton Antideuteron Antihelium (Search for PBH) (Search for PBH) (Search for Antimatter)

  27. BPII Solar Conditions • Flight at true Solar minimum • Sunspot resulted in high-speed stream in solar wind • Variation in rate clearly correlates with solar wind and neutron monitor • Daily variation of proton spectrum and antiproton/proton ratio important for further study

  28. Summary • BESS-Polar I - 8.5 day flight before Solar minimum • 9 108 events • Antiproton and proton spectra and increased antihelium sensitivity • Transient effects and diurnal variation • BESS-Polar II - 24.5 day flight at Solar minimum • 4.7 109events • BESS-Polar II data increase the statistics on low-energy antiprotons at Solar minimum ~10 (95+97) - 20 (97) fold - Definitive for PBH search using antiprotons • BESS-Polar II performed well and analysis is underway

  29. BESS Instrument Comparison

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