Searching for Cosmological Antimatter Bob Streitmatter For the BESS Collaboration (KEK / NASA-GSFC / Tokyo / Kobe / Maryland / ISAS) Outline • Briefly: (TEE), Theory Explained by Experimentalist • Review History of Experimental Search for CAM • Instruments, Techniques and measurements • BESS Program • Current Status of Data •The Future In the Beginning … •Dirac, in 1928, was the first to realize that the physics of relativity and quantum mechanics taken together required the existence of matter whose additive quantum numbers (e.g. charge, baryon number, lepton number, spin) were the negative of “normal” matter. (Proc. R. Soc. London, A, 117, (1928), 610) •Positron discovered, August 2, 1932. Positron produced by cosmic radiation seen in a cloud chamber. (Anderson, Phys. Rev. (1933) 491) Baryon Symmetric Universe “We must regard it rather as an accident that the Earth and presumably the whole Solar System contains a preponderance of negative electrons and positive protons. It is quite possible that for some of the stars it is the other way about” -- Dirac, 1933 Noble acceptance speech Antimatter Miscellanea • 1955: Antiprotons are “manufactured” at Bevatron - Chamberlain et al. Phys. Rev. 100 (1955) 947 • Experimental evidence that antimatter is normal in the gravitational sense - High and Holzschieter Phy. Rev. Lett. 66 (1991) 854 • Contrary to popular myth among Trekkies, the 1908 Tunguska meteor was not antimatter - Cowan, Atluri and Libby, Nature, May 29, 1965 But: Simple Big Bang BSU Fatal Problems •The “Annihilation Catastrophe” - not enough baryons •SBB predicts baryon/photon ratio ≈ 10-18 at freezeout •Observed baryon/photon raio ≈ 10-9 •How did the matter and antimatter get separated? •Fluctuations won’t do it •e.g. Kolb and Turner, Ann. Rev. Nucl. Part. Sci. 33 (1983) 645 •No viable “mechanism” for separation ever suggested Sakharov’s Solution to the BSU Problem The Universe doesn’t have to be baryon symmetric IF: 1) Direct violation of baryon number conservation “X” particle decay breaks baryon symmetry 2) CP symmetry is violated If CP not violated, “mirror” antiparticle decays will compensate and maintain overall net baryon number 3) Universe must have a period out of thermal equilibrium Otherwise inverse processes will compensate and maintain overall net baryon number - Sakharov, JETP Lett. 5 (1967) 24 Maybe It’s Symmetric After All •The Sakharov conditions offer a way to explain the apparent baryon asymmetry of the Universe •BUT, they also offer the possibility for the separation of matter and antimatter. •Is the sign of CP violation universal, built into the rules? Or is the sign of CP violation local, spontaneous, with domain of matter and antimatter existing? -Brown and Stecker, Phys. Rev. Lett. 43 (1979) 315 - Sato, Phys. Lett. B, 99 (1981) 66 Status of the Sakharov Conditions 1) NO baryon-number-violating decay has been seen 2) CP violation is seen Kaons - Christianson et al., Phys. Rev. Lett., 13 (1964) 138 ==> B NEW BABAR RESULT <== 3) Thermal nonequilibrium OK Chronology 1928 Dirac theory 1932 Positron discovered 1955 Antiprotons “manufactured” 1930s-1960s: BSU cosmologies in fashion - Alfven, Reviews of Modern Physics 37 (1965) 652 1965 Microwave Background, Big Bang dominant 1967 Sakharov conditions 1960s Begin antimatter searches in cosmic radiation 4” x 6” Emulsion Stack, Balloon-borne “Finally, we would like to point out the following conclusion. Namely, there has been no single case of antiparticles among the observed stopping particles of about 500 alpha particles, 300 (C, N, O), and heavier elements, and more than 1000 singly charged particles. Even with a somewhat larger interaction cross section of antiparticles, this will set an upper limit for the amount of antimatter the the primary radiation at about 0.1%.” Aizu et al., Phys. Rev. ≈ 500 MeV/n 121 (1961) 1206 Count δ-rays, measure residual range Emulsion Stack with SC Magnet •1 foot diameter superconducting magnet •Emulsion ≈ 4” x 6” x 10” •Z > 3 Nuclei •Rigidity (P/Z): •4 - 125 GV •8 hours at 120,000 ft. -3 •FAN < 5 x 10 Golden et al., ApJ 192 (1974) 747 Permanent Magnet with Spark Chambers •Rigidity (P/Z) + dE/dX •80 cm detector array, with TOF •Z = 2 •0.2 - 4.3 GeV/n -3 •Upper limit FAHe = 1.4 x 10 Evenson, ApJ 176 (1972) 797 Permanent Magnet + Spark Chambers -5 FAN < 8 x 10 , rigidity 4 -33 GV/c Smoot, Buffington and Orth, Phys. Rev. Lett. 35 (258)1975 Instruments of Some Complexity Smith et al., Rev. Sci. Instru. 43 (1972) 1 Antiprotons Reported, 1979 • P-bar/P ratio • 5 x 10-4 • Rigidity interval 5.6 -12 GV/c • “ratio consistent with secondary production” (in the ISM) - - a little high Golden et al., Phys. Rev. Lett. 43 (1979) 1196 Antiprotons by Deduction • “Negative” deflection • It’s not an electron or muon (no-Cherenkov) • Must be an antiproton Golden et al., Phys. Rev. Lett. 43 (1979) 1196 Antiprotons Reported, 1979 • P-bar/P ratio • 6 x 10-4 •2-5 GeV Bogomolov et al., Proc. 16th ICRC, Kyoto 1 (1979) 330 Antiprotons Reported, 1981 • P-bar/P ratio • 2.2 x 10-4 • 130 - 330 MeV • NOT consistent with secondary production Buffington, Schindler and Pennypacker, ApJ 248 (1981) 1179 Antiproton by Annihilation Signature Buffington, Schindler and Pennypacker, ApJ 248 (1981) 1179 Antiprotons in CR, 1980s Uncertainty Streitmatter et al., Adv. Space Res. 9 (1989) (12)69 But Anti-galaxies Are Not the Only (possible) Source Now that there are antiproton measurements (ca. 1980) what do they mean? •And there is a background of antiprotons produced in the atmosphere ! Go to Space: No Atmosphere, Long Duration HEAO: used geomagnetic cutoff -4 FAN Z > 9, 1.5 10 , ≈ 2 - 11 GeV/n Lund and Rothenberg Astron. Astrophys. 164 (1986) 231 Astromag Influence on Spectrometers Isotopes Antimatter SMILI LEAP MASS PBAR IMAX MASS BESS IMAX CAPRICE BESS ISOMAX TS93 PAMELA CAPRICE HEAT PAMELA Chronology 1979: First observation (Golden et al) 2004: BESS-Polar 1979: Russian PM (Bogomolov et al) 2005: PAMELA 1981: Low-energy excess (Buffington et al) 2006: BESS-Polar 1985: ASTROMAG Study Started 2007: Solar minimum 1986: HEAO Antinucleus upper limits 2008: AMS-02 1987: LEAP, PBAR (upper limits) 1991: MASS 1992: IMAX (16 mass-resolved antiprotons) 1993: BESS (6 mass-resolved antiprotons) 1994: CAPRICE94 1996: Solar minimum 1998: CAPRICE98, AMS-01 2000: HEAT-pbar WiZard Balloon Program: CAPRICE94/98 Cosmic AntiParticle Ring Imaging Cherenkov Experiment U. Bari, Tata Institute of Fundamental Research, U. Firenze, Laboratori Nazionali INFN di Frascati, NASA/Goddard Space Flight Center, New Mexico State U., U. Tor Vergata (Rome), U. Siegen, Royal Institute of Technology, Centre des Recherches Nucleaires, U. Trieste TOF: flight direction, β, charge Spectrometer: charge sign, momentum Si Imaging Calorimeter: electron/hadron separation CAPRICE94: NaF proximity focused RICH 0.6-3.2 GeV p CAPRICE98: Mirror focused gas RICH 3-49 GeV p p events 20-50 GV HEAT (High Energy Antimatter Telescope) U of Chicago, Eastern New Mexico U., Indiana U., UC Irvine, U. of Michigan, Washington U. St. Louis U of Chicago, Northern Kentucky U., Indiana U., U. of Michigan, Penn State U., U. Minnesota TOF: flight direction, β, charge Spectrometer: charge sign, momentum HEAT-pbar: multiple dE/dx: p / π-µ / e separation 4-50 GeV p HEAT-e±: PID by TRD and Electromagnetic Calorimeter Negative rigidity Positive rigidity BESS Collaboration (from 1992 to present) (Balloon Experiment with a Superconducting Spectrometer) • High Energy Accelerator Research Organization (KEK) A. Yamamoto, H. Fuke, T. Kumazawa, K. Matsumoto, Y. Makida, H. Omiya, J. Suzuki, K. Tanaka, T. Yoshida, K. Yoshimura • NASA Goddard Space Flight Center J.W. Mitchell, T. Hams, A. Moiseev, J.F. Ormes, M. Sasaki, A. Stephens, R. Streitmatter • The University of Tokyo Y. Asaoka, K. Anraku, M. Fujikawa, S. Haino, M. Imori, K. Izumi, S. Matsuda, N. Matsui, H. Matsumoto, H. Matsunaga, M. Motoki, J. Nishimura, S. Orito*, T. Saeki, T. Sanuki, T. Sonoda, I. Ueda, Y. Yamamoto • Kobe University K. Abe, N. Ikeda, A. Itazaki, T. Maeno, T. Matsukawa, T. Mitsui, M. Nozaki, A. Ogata, M. Oikawa, Y. Shikaze, Y. Takasugi, K. Takeuchi, K. Tanizaki, K. Yamato • Institute of Space and Astronautical Science Y. Yajima, T. Yamagami • The University of Maryland M.H. Lee, K.C. Kim, Z.D. Myers, E.S. Seo, J.Z. Wang * Deceased BESS Measurement Technique Particle identification by mass and charge β-1 Charge-sign from deflection direction - + - + Rigidity •Superconducting magnetic spectrometer: measures momentum (R = P/Ze) •Precision time-of-flight system: measures velocity and charge RZe •Silica-aerogel Cherenkov detector: background rejection m = γβc BESS Antiproton Measurements 1993 - 2002 Antiproton-Events-by-2000-t •BESS has carried out nine 2500 each year successful flights since 1993 integrated 2000 •Since 1997, 400-600 antiprotons Aerogel Cherenkov Counter 1997-2002 recorded in each 1-day flight 1500 n=1.03 1.02 •BESS has recorded more than 1000 2400 antiprotons through 2002 Antiproton Events First Flight 500 1993 0 1993 1994 1995 1996 1997 1998 1999 2000 2001 Year Evolution of the BESS Instrument BESS Particle Identification Evolution • PID (charge and mass) by dE/dx together with βTOF vs. Magnetic Rigidity • 1993/1994 σTOF 280 ps • 1995 σTOF 110 ps • 1997 σTOF 75 ps BESS ‘97 BESS ‘97 TOF and TOF,dE/dx • 1997 Aerogel Cherenkov dE/dx and Ck Counter added to suppress background from light particles Data Accumulation With Successive Flights 1993 1994 1995 1997 1998 1999 2000 DAQ (hrs) 14.0 15.0 17.5 18.3 20.0 31.3 32.5 Rec’d Event 4.0 4.2 4.5 16.2 19.0 16.8 15 (M Events) # of 6 2 43 415 384 668 558 Antiprotons Antiproton 0.18~0.5 0.18~1 0.18~3. 0.18~4.2 PID (GeV) .5 6 He/He 2.2×10-5 4.3×10-6 2.4×10-6 1.4×10-6 8.8×10-7 6.7×10-7 BESS An Instrument of Some Complexity Understanding Solar Modulation with BESS Field Reversal Negative Positive Negative Positive Polarity Polarity Polarity Polarity • Solar magnetic field 22 year cycle • Sunspot Number 11 year cycle • Neutron Monitor 11year cycle • BESS data already 2000 covers 9 years Modulation of P-bar and P Flux Measured With BESS The drift model explains the ratio, but still needs to be fine-tuned.