1

The BESS Program

Akira Yamamoto (KEK) for the

BESS collaboration

SpacePart-06, Beijing, April 20, 2006

2

Outline

BESS Experiment and Spectrometer

Recent and New Results

BESS TeV : Precise measurement of cosmic-rays

BESS-Polar I : Search for antiparticle of primary origin

Plan for future

Summary

3

BESSCollaboration

The Universityof Tokyo

High Energy AcceleratorResearch Organization(KEK)

University of Maryland

Kobe University

Institute of Space andAstronautical Science/JAXA

National Aeronautical andSpace AdministrationGoddard Space Flight Center

University of Denver(Since June 2005)

BESS CollaborationAs of April, 2006

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BESSBalloon-borne Experiment with a Superconducting Spectrometer

Search for Primordial Antiparticle

antiproton: Novel primary origins (PBH,DM)antihelium: Asymmetry of matter/antimatter

Precise Measurement of Cosmic-ray flux: highly precise measurement at < 1 TeV

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BESS DetectorRigidity measurement

SC Solenoid (L=1m, B=1T)

Min. material (4.7g/cm2)

Uniform field Large acceptance

Central tracker (Drift chamber~200m

Z, m measurementR, --> m = ZeR 1/2-1dE/dx --> Z

JET/IDCRigidity

TOF, dE/dx

√

6

BESS-TeV Deflection ResolutionMDR 1.4 TV

BESS-98MDR 200 GV

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BESS-TeV Spectrometer

JET/IDC

MAGNET

TOF

ODC

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Progress of BESS Experiment

1993~ 2000, BESS, North Canada2002, BESS-TeV

2001, BESS-TeV, Fort Sumner

2004, BESS-Polar I, Antarctica

1999, 2001, BESS-Ground, Japan

10 scientific balloon flights during1993-2004

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Primary Cosmic-ray Spectra (1998: Bess-98, AMS-I, Caprice)

Sanuki et al. ApJ. 545 (2000) 1135

Error: < +/-5 % @ 100 GeV

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Primary Cosmic-ray Spectra (BESS-TeV)

Haino et al. PLB 594 (2004) 35

Error: < +/-15 %@ 500 GeV

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BESS-TeV Result Anchor the P and He Spectra in Low Energy (< TeV)

F = Ek-

Proton (Ek> 30 GeV) = (1.37 ± 0.12)x104

= 2.732 ± 0.022

Helium (Ek> 20 GeV)

= (7.06 ±

1.15)x102

= 2.699 ± 0.059

Fitting based on the BESS-TeV results only

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Low Energy Cosmic-ray SpectraPrecisely Measured by BESS

Rigidity Measurement

Precise spectra proton (0.2~500 GeV) helium (0.2~250 GeV/n) antiproton (0.2~ 4 GeV)

Anchor the spectrum in the lowest energy region.

10120.1

104

10-28

Flu

x (m

2 sr

s G

eV)-1

Energy (GeV)

BESS

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Search for Antiprotons of Cosmic Origins

• 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.

Primary Detectable

Secondary SUSYPBH

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Observation of Cosmic-rayAntiprotonsin p-bar/p Ratio

1979: First observation (Golden et al)

1979: Russian PM (Bogomolov et al)1981: Excess reported (Buffington et al)

1985: ASTROMAG Study Started1987: LEAP, PBAR (upper limits)1991: MASS1992: IMAX (16 antiprotons)1993: BESS (6 antiprotons), TS931994: CAPRICE94, HEAT-e

1996: Solar minimum1998: CAPRICE98, AMS-012000: HEAT-pbar2004: BESS-Polar2006: PAMELA 2007: Solar minimum, BESS-Polar2008: AMS-02 Before the BESS Experiment

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1979: First observation (Golden et al)

1979: Russian PM (Bogomolov et al)1981: Excess reported (Buffington et al)

1985: ASTROMAG Study Started1987: LEAP, PBAR (upper limits)1991: MASS1992: IMAX (16 antiprotons)1993: BESS (6 antiprotons), TS931994: CAPRICE94, HEAT-e

1996: Solar minimum1998: CAPRICE98, AMS-012000: HEAT-pbar2004: BESS-Polar2006: PAMELA 2007: Solar minimum, BESS-Polar2008: AMS-02 By the BESS Experiment

Annual Variation of P /P Ratio

10-6

10-5

10-4

10-3

10-1

1 10

(GeV)

Pñ/P ratio

Kinetic Energy

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

. ., . . ., .Y Asaoka et al Phys Rev Lett in press

(97)BESS(99)BESS(00)BESS

p/p Ratio

BESS

Observation of Cosmic-rayAntiprotonsin p-bar/p Ratio

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BESS(95+97)BESS(93)IMAXCAPRICE

Kinetic Energy (GeV)10-1 1 10

Pb

ar

flu

x [

m-2sr-

1sec

-1G

eV

-1]

10-3

10-2

10-1

Low Energy Cosmic-ray Antiprotonsin last solar minimum (1995~97)

Mostly secondary particleswith specific peak at 2 GeV

Study:

Propagation model Solar modulation

Search for:

Novel Primary Origin?

(PBH, DM)

Flatter spectrum in low energy

More Statistics necessary ->> Long-duration Flight

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BESS-Polar Experiment

Very precise measurement Low energy Antiprotons

Around south-pole, Antarctica Long duration flight High latitude Solar minimumWith a new spectrometer Ultimately small material Ultra-thin superconducting solenoid

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Feature of BESS-Polar Spectrometer

Minimize material in spectrometerNew detector (Middle TOF)

Energy range extended down to 0.1 GeV

Low power electronicsSolar Power System, Longer life of cryogen, LHe Long duration flight

BESS-2000 BESS-PolarTOF Upper

Coil

JET/IDC

ACC

MTOF

TOF Lower18g/cm2

5g/cm2

10g/cm2

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BESS-Polar 20048.5 day flight successful35-37 km in altitude900 million events recorded - Acceptance limited to ~ 0.2 m2.sr

Altitude ～ 38000mResidual air ～ 4g/cm2

Floating

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Low Energy Antiproton Observed

in BESS Polar I (in 2004)

• ~ 2000 antiproton (total) candidate observed• ~ 400 antiprotons below 1 GeV

～ 2000AntiprotonCandidates

Preliminary

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Lowest Energy Events Observed

Limit by BTOF Trigger

★Kinetic Energy ～ 0.11GeV (@ TOA)

Antiproton event

★Multi-track events to be further studied

RGT -0.4GV1/β 2.47

Limit by MTOF Trigger

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Antiprotons Observed (Preliminary)

KineticEnergy(@TOA) BESS-97 Polar

0.1- 0.18 (GeV) - In Analysis

0.18-0.28 4 25

0.28-0.40 9 39

0.40-0.56 16 63

0.56-0.78 31 123

0.78-0.92 19 90

0.92-1.08 16 92

Total (below 1.08 GeV) 95 432

4~5 times statistics

(than that of 1997),

With ~0.2 m2sr (2/3),

8 days flight

Both-endSingle-endDead

ＰＭＴ－ＨＶ

18/44 TOF-PMT turned-off

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Pbar/P Ratio Observation Extended

• The measurement consistent with the prediction, Bieber et al.

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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.

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Further Plan for BESS-Polar II

Solar minimum in 2006~07 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

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Improvement toward BESS-Polar II

Subject (BESS-Polar I) (BESS-Polar II)

Magnet Cryogen Life ~ 11 days > 25 days

Track detector (JET) gas quality

~ 10 days > 20 days

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

StatisticsData storage

4 x BESS972 of 3.6 TB (recorded)

20 x BESS97 12 ~ 16 TB

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BESS Polar II Observation

(Expected)

Antiproton Spectrum Search for Antideuteron and AntiHelium(Search for PBH)

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BESS-Polar Feature

AMS02 PAMELA(10+20 days)

(3 years)

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

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350-600

280~500

Altitude

(km)

2007> 7520 days0.3BESS-Polar2

2006<70.43 years0.0021PAMELA

2008< 51.73 years0.5AMS

LaunchLatitude

Flight Time

Acceptance

(m2sr)

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Summary ■ BESS measured:

Precise Cosmic-ray Proton (Helium) spectrum with errors within 5 % @ 100 GeV, and 15 % @ 500 GeV with anchoring the spectrum at the lowest energy

Low energy Antiproton spectra at 0.1 - 4 GeV to Mostly secondaries, Useful information on cosmic-ray propagation and solar modulation Search for novel primary origin suchs as PBH,

Antidueteron search with the first upper limit reported, Antihelium search reaching down to the upper limit ~3 x 10-7

BESS-Polar II planned, and important for Ultimately sensitive search for primordial antiparticle with the long

duration flight in solar minimum in 2007, and Further precise measurement of cosmic rays, in a complimentary

approach to PAMELA and AMS.

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Cosmic-ray Antiprotons Observed by BESS

• More than 4000 antiprotons (candidates) observed

0

1000

2000

3000

4000

5000

each yearintegrated

Year

Solar Minimum

BESS(95+97)BESS(93)IMAXCAPRICE

Kinetic Energy (GeV)10-1 1 10

Pb

ar

flu

x [

m-2sr-

1sec

-1G

eV

-1]

10-3

10-2

10-1

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BESS-Polar

●Trigger Configuration

★UL Trigger ★UM Trigger

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BESS-Polar II Cross Section

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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 %

Both-end

Single-end

Dead

ＰＭＴ－ＨＶ

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

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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 %

Both-end

Single-end

Dead

ＰＭＴ－ＨＶ

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