The BESS Program

Akira Yamamoto (KEK) for the BESS collaboration

SpacePart-06, Beijing, April 20, 2006

1 Outline

z BESS Experiment and Spectrometer z Recent and New Results

z BESS TeV : Precise measurement of cosmic-rays

z BESS-Polar I : Search for of primary origin z Plan for future z Summary

2 BESS Collaboration As of April, 2006

High Energy Accelerator National Aeronautical and Research Organization(KEK) Space Administration Goddard Space Flight Center BESS The University University of Maryland of Tokyo Collaboration

Kobe University University of Denver (Since June 2005)

Institute of Space and Astronautical Science/JAXA

3 BESS Balloon-borne Experiment with a Superconducting Spectrometer

Search for Primordial Antiparticle : Novel primary origins (PBH,DM) antihelium: Asymmetry of / Precise Measurement of Cosmic-ray flux:

highly precise measurement at < 1 TeV 4 BESS Detector Rigidity measurement JET/IDC SC Solenoid (L=1m, B=1T) Rigidity Min. material (4.7g/cm2) Uniform field TOF Large acceptance β, dE/dx Central tracker (Drift chamber δ ~200μm Z, m measurement R,β --> m = ZeR√ 1/β2-1 dE/dx --> Z 5 BESS-TeV Deflection Resolution MDR 1.4 TV BESS-98 MDR 200 GV

6 BESS-TeV Spectrometer

TOF

ODC

MAGNET

JET/IDC

7 Progress of BESS Experiment

1993~ 2000, BESS, North Canada 2002, BESS-TeV

1999, 2001, BESS-Ground, Japan

2001, BESS-TeV, Fort Sumner

2004, BESS-Polar I, Antarctica

10 scientific balloon flights during1993-2004 8 Primary Cosmic-ray Spectra (1998: Bess-98, AMS-I, Caprice)

Error: < +/-5 % @ 100 GeV

Sanuki et al. ApJ. 545 (2000) 1135 9 Primary Cosmic-ray Spectra (BESS-TeV)

Error: < +/-15 % @ 500 GeV

Haino et al. PLB 594 (2004) 35 10 BESS-TeV Result Anchor the P and He Spectra in Low Energy (< TeV)

φ -γ F = Ek

Proton (Ek> 30 GeV) φ = (1.37 ± 0.12)x104 γ = 2.732 ± 0.022

Helium (Ek> 20 GeV) φ = (7.06 ± 1.15)x102 γ = 2.699 ± 0.059

Fitting based on the BESS-TeV results only

11 Low Energy Cosmic-ray Spectra Precisely Measured by BESS 104 BESS Rigidity Measurement -1

Precise spectra sr s GeV)

proton (0.2~500 GeV) 2 helium (0.2~250 GeV/n) antiproton (0.2~ 4 GeV) Flux (m

Anchor the spectrum in the lowest energy region.

10-28 12 0.1 Energy (GeV) 1012 Search for of Cosmic Origins

-1 10

Primary Detectable ) -1 GeV -1

sec -2 -1 10 sr -2 flux (m – p

SecondarySecondary 10(+) PBH R=0.5 x 10 -2 pc -3 yr -1 SUSY 2 Neutralino m χ = 53.6GeV/c PBH

-3 10 -1 10 1 10 Kinetic Energy (GeV)

• Most antiprotons are secondary products from nuclear interactions of primary cosmic rays with the ISM. • “Exotic” sources may relatively enhance antiproton flux at energies well below or above secondary peak. 13 Observation of Cosmic-rayAntiprotons in p-bar/p Ratio

1979: First observation (Golden et al) -3 10 Solar minimum in + phase 1979: Russian PM (Bogomolov et al) Solar maximum in + phase 1981: Excess reported (Buffington et al) Solar maximum in - phase 1985: ASTROMAG Study Started 1987: LEAP, PBAR (upper limits) -4 1991: MASS 10 1992: IMAX (16 antiprotons) /p ratio – 1993: BESS (6 antiprotons), TS93 p 1994: CAPRICE94, HEAT-e± -5 1996: Solar minimum 10 Golden et al. Bogomolov et al. 1998: CAPRICE98, AMS-01 Buffington et al. 2000: HEAT-pbar 2004: BESS-Polar -6 10 -1 2006: PAMELA 10 1 10 2007: Solar minimum, BESS-Polar Kinetic Energy (GeV) 2008: AMS-02 Before the BESS Experiment 14 Observation of Cosmic-rayAntiprotons in p-bar/p Ratio 10 1979: First observation (Golden et al) Y. Asaoka et al., Phys. Rev. Lett., in press. BESS(97) 1979: Russian PM (Bogomolov et al) BESS(99) 1981: Excess reported (Buffington et al) /P ratio BESS(00) ñ P 1985: ASTROMAG Study Started p/p Ratio -4 1987: LEAP, PBAR (upper limits) 10 1991: MASS 1992: IMAX (16 antiprotons) 1993: BESS (6 antiprotons), TS93 1994: CAPRICE94, HEAT-e± -5 1996: Solar minimum 10 Bieber et al, 1999 BESS 10, ( +) ~ 1997 1998: CAPRICE98, AMS-01 solar min. at positive phase 70, ( +) ~ 1999 2000: HEAT-pbar solar max. at positive phase 2004: BESS-Polar 70, ( −) ~ 2000 solar max. at negative phase -6 2006: PAMELA 10 -1 10 1 10 2007: Solar minimum, BESS-Polar Kinetic Energy (GeV) 2008: AMS-02 By the BESS Experiment 15 Low Energy Cosmic-ray Antiprotons in last solar minimum (1995~97)

10-1

Mostly secondary particles BESS(95+97) BESS(93) with specific peak at 2 GeV IMAX CAPRICE ] Study: -1 GeV -1 sec

Propagation model -1 sr Solar modulation 10-2 -2 Search for: Novel Primary Origin? Pbar flux [m (PBH, DM)

10-3 Flatter spectrum in low energy 10-1 110 Kinetic Energy (GeV)

More Statistics necessary ->> Long-duration Flight16 BESS-Polar Experiment

Very precise measurement Low energy Antiprotons Around south-pole, Antarctica Long duration flight High latitude Solar minimum With a new spectrometer Ultimately small material Ultra-thin superconducting solenoid

17 Feature of BESS-Polar Spectrometer

BESS-2000 BESS-Polar TOF Upper

Coil JET/IDC

MTOF 5g/cm2 ACC 18g/cm2 TOF Lower 10g/cm2

Minimize material in spectrometer Energy range extended New detector (Middle TOF) down to 0.1 GeV

Low power electronics Long duration flight Solar Power System, Longer life of cryogen, LHe 18 BESS-Polar 2004 8.5 day flight successful 35-37 km in altitude 900 million events recorded - Acceptance limited to ~ 0.2 m2.sr

Altitude～38000m Residual air～4g/cm2

Floating 19 Low Energy Antiproton Observed in BESS Polar I (in 2004)

Preliminary

～2000 Antiproton Candidates

• ~ 2000 antiproton (total) candidate observed • ~ 400 antiprotons below 1 GeV 20 Lowest Energy Events Observed

Antiproton RGT -0.4GV event 1/β 2.47 Limit by MTOF Trigger

Limit by ★Kinetic Energy ～0.11GeV (@ TOA) BTOF Trigger ★Multi-track events to be further studied

21 Antiprotons Observed (Preliminary)

KineticEnergy(@TOA) BESS-97 Polar 4~5 times statistics (than that of 1997), 0.1- 0.18 (GeV) - In Analysis With ~0.2 m2sr (2/3),

0.18-0.28 4 25 8 days flight 0.28-0.40 9 39

0.40-0.56 16 63 18/44 TOF-PMT turned-off

0.56-0.78 31 123

0.78-0.92 19 90 ＰＭＴ－ＨＶ 0.92-1.08 16 92 Both-end Single-end Dead Total (below 1.08 GeV) 95 432

22 Pbar/P Ratio Observation Extended

• The measurement consistent

with the prediction, Bieber et al. 23 Progress in Antihelium Search

• Preliminary Results

– The upper limit of antihelium/helium ratio pushed down • ~5 x 10E-7 @ BESS-Polar I – Generally, two order of magnitude lowered by BESS in last ten years.

24 Further Plan for BESS-Polar II

z Solar minimum in 2006~07 z Realize further long duration flight of 20 days with two circle around the pole, 4~5 x BESS-Polar I statistics

Record at Tiger flight 25 Improvement toward BESS-Polar II

Subject (BESS-Polar I) (BESS-Polar II) Magnet Cryogen Life ~ 11 days > 25 days Track detector (JET) gas ~ 10 days > 20 days quality TOF-PMT housing Resin potting Pressurized housing ACC Particle ID Rejection ~ 630 >> 1000 Solar-power gen. 4 stage 900 W 3 stage 675 W Effective Acceptance 0.2 m2sr 0.3 m2sr Observation time 8.5 days > 20 days Statistics 4 x BESS97 20 x BESS97 Data storage 2 of 3.6 TB (recorded) 12 ~ 16 TB 26 BESS Polar II Observation (Expected)

-1 10 )

-1 Simulation for secondary only (20 days) Simulation for secondary +PBH (20 days)

GeV BESS95+97 real data -1 sec -1 sr -2

-2 10 Secondary

PBH

BESS Antiproton Flux (m BESS Polar

-3 10 -1 10 1 10 Kinetic Energy (GeV)

Antiproton Spectrum Search for Antideuteron and AntiHelium (Search for PBH) 27 BESS-Polar Feature

(3 years)

(10+20 days) AMS02 PAMELA

BESS-Polar realize (3 years) the best sensitivity in lowest energy

Acceptance Flight Time Latitude Altitude Launch (m2sr) (km) AMS 0.5 3 years < 51.7 280~500 2008 PAMELA 0.0021 3 years <70.4 350-600 2006 BESS-Polar2 0.3 20 days > 75 36 2007

28 Summary

■ BESS measured:

z Precise Cosmic-ray Proton (Helium) spectrum with errors within

z 5 % @ 100 GeV, and 15 % @ 500 GeV

z with anchoring the spectrum at the lowest energy z Low energy Antiproton spectra at 0.1 - 4 GeV to

z Mostly secondaries,

z Useful information on cosmic-ray propagation and solar modulation

z Search for novel primary origin suchs as PBH, z Antidueteron search with the first upper limit reported, z Antihelium search reaching down to the upper limit ~3 x 10-7 z BESS-Polar II planned, and important for

z Ultimately sensitive search for primordial antiparticle with the long duration flight in solar minimum in 2007, and

z Further precise measurement of cosmic rays, in a complimentary29 approach to PAMELA and AMS. 30 BESS Deflection Resolution 1993~1998 L B ±δ BESS: dRR-1 Rd/ Max. Det. Rigidity: 200 GV (BL2)

Sharp peak of resolution

Strong and uniform field

31 BESS-TeV Upgrade 2001~2002 Central Tracker (JET/IDC) improvement BESS-98 BESS-TeV δ = 200 -->150 μm ODC N = 28 --> 52

New detector (ODC) installed L = 0.8 --> 1.6 m JET/IDC ODC MDR: 200 GV --> 1400 GV

32 Charge-Sign-Dependent Solar Modulation p/p Ratio Spanning a Solar Magnetic Field Reversal

10 Y. Asaoka et al., Phys. Rev. Lett., in press. BESS(97) BESS(99) /P ratio BESS(00) ñ P p/p Ratio -4 10

-5 10 Bieber et al, 1999 10, ( +) ~ 1997 solar min. at positive phase 70, ( +) ~ 1999 solar max. at positive phase 70, ( −) ~ 2000 solar max. at negative phase -6 10 -1 10 1 10 Charge dependence consistent with Kinetic Energy (GeV) 33 e+/(e+ + e-) reported by J. Clem et al. Cosmic-ray Antiprotons Observed by BESS

5000 10-1 each year BESS(95+97) integrated BESS(93)

] IMAX 4000 -1 CAPRICE GeV -1

sec 3000 -1 sr -2 10-2 Solar Minimum 2000 P-bar Events Pbar flux [m 1000

0

10-3

10-1 1 10 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Kinetic Energy (GeV) Year • More than 4000 antiprotons (candidates) observed 34 BESS-Polar ●Trigger Configuration

★UL Trigger ★UM Trigger

35 BESS-Polar II Cross Section

TOF Counters

Solenoid

JET chamber LHe Reservior Inner DC LHe Extension Middle TOF

Silica Aerogel Cherenkov 00.5 1m TOF Counters

36 TOF PMT Problem and Improvement of Housing 18/44 PMTs turned off due to low pressure discharge and excessive current Geometrical Acceptance limited to 67 %

PMT housing to be improved by using pressure vessel as on BESS-Polar I ACC, instead of Resin Potting

ＰＭＴ－ＨＶ Both-end Single-end Dead

37 TOF PMT Problem and Improvement of Housing 18/44 PMTs turned off due to low pressure discharge and excessive current Geometrical Acceptance limited to 67 %

PMT housing to be improved by using pressure vessel as on BESS-Polar I ACC, instead of Resin Potting

ＰＭＴ－ＨＶ Both-end Single-end Dead

38 Primary Cosmic-ray Spectra (~1990)

39 Correlation of cosmic-ray flux with solar modulation

40