Search for Antihelium progressed with BESS

1
Search for Antihelium Progress with BESS
2006 July 22 36th COSPAR Scientific
Assembly Sasaki, M. Haino, S. BESS Collaboration
2
Introduction

• Science Objective
• Baryon symmetric universe or Baryon asymmetric
  universe?
• Search for Antihelium using the BESS spectrometer
• We had first scientific flight in 1993.
• Using the seven successive flights (1993, 1994,
  1995, 1997, 1998, 1999 and 2000) data, we
  reported the most stringent upper limit (6.8 x
  10-7, 1GV lt R lt 14GV) in 2002 (SpacePart)
• No antihelium events were found, yet.
• Two New Flights
• Extend the energy range (BESS-TeV)
• More sensitive search (BESS-Polar I)

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BESS-TeV Flight

• Extended energy range
• Upgraded Central Tracker (JET/IDC)
• s 200 ? 150µm
• N 28 ? 52
• New detector (ODC) installed
• L 0.8 ? 1.6m
• MDR 200GV

?Lynn Lake
BESS 2000
BESS-TeV
1400GV
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BESS-Polar I Flight

• More sensitive search
• Reduced the material
• Ultra-thin transparent Solenoid
• Middle TOF
• Placed the Aerogel Cherenkov Counter at bottom
• No pressure vessel
• Long duration flight
• Total 8.5 days flights, collected 900 millions
  events.

Mcmurdo stationUSA/NSF/NASA
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Data Analysis

• Event selection
• Choose good single track
• 1 or 2 hodoscopes have hits in both the Upper and
  Lower TOF
• Only 1 track in the Drift Chambers
• Require track quality
• Particle Identification
• TOF-ß selection
• Z 2 (dE/dx) selection

m ZeR 1/ß2 -1
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Track quality selections

• Require the good track path
• Nshould gt 32
• PathLength gt 640 mm
• Abs(Zpos) lt 450mm
• Require the TOF Track matching
• XTOF XTrack lt 75 mm
• ZTOF ZTrack lt 100 mm
• Require the good track fittng
• Nrfit gt 26
• ChisqX lt 5
• ChisqZ lt 5
• Require the wire hits along the track
• Ndrop lt 10

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Data Analysis

• Event selection
• Choose good single track
• 1 or 2 hodoscopes have hits in both the Upper and
  Lower TOF
• Only 1 track in the Drift Chambers
• Require track quality
• Particle Identification
• TOF-ß selection
• Z 2 (dE/dx) selection

m ZeR 1/ß2 -1
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TOF beta, Z 2 selections
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Search Results
1/RGT Plot for BESS-Polar I 8.4 x 106 Helium
Events between 1 to 20 GV
1/RGT Plot for BESS-TeV 2.8 x 104 Helium Events
between 5 to 500 GV
BESS-Polar I Z 2
BESS-TeV Z 2
No He Events
No He Events
500GV
20GV
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Set upper limit
?
__
___ __ __ __ __ __
Nobs,He / ( SWhe snglebe dE/dxe TQ ) dE

_______________________________________
?
Nobs,He / ( SWhe snglebe dE/dxe TQ ) dE
__

• Nobs,He lt 3.1 (95 C.L.)

__
If we have assumed that the spectrum of He has
a same of He
__
__
__
eb eb , e dE/dx e dE/dx and
e TQ e TQ
3.1
?
__ __
Nobs,Hehe sngl / (he sngl) dE
SW, h and e sngl were determined using the
Monte Carlo simulation
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Results

• Using only the BESS-TeV data, we can set an
  upper limit of 1.4 x 10-4 ( 5 500 GV)
• Using only the BESS-Polar I flight data, we can
  set an upper limit of 4.4 x 10-7 ( 1 20 GV)
• Combining all BESS flight data, we can set an
  upper limit of 2.7 x 10-7 ( 1 14 GV)

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Results

• Using the BESS-TeV data, we could set the upper
  limit of 1.4 x 10-4 ( 5 500 GV)
• Using the BESS-Polar I flight data, we could set
  the upper limit of 4.4 x 10-7 ( 1 20 GV)
• combined all BESS flight data, we could set the
  upper limit of 2.7 x 10-7 ( 1 14 GV)

We plan the BESS-Polar II flight in 2007 with an
anticipated sensitivity 3 x 10-8
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Summary

• We have extended the search for antihelium with
  two flights of BESS-TeV in 2002 and BESS-Polar I
  in 2004
• No antihelium events were found in the 2002 or
  2004 data.
• We have set upper limits He/He 1.4 x 10-4 for
  BESS-TeV up to 500 GV, 4.4 x 10-7 for BESS-Polar
  I, 2.7 x 10-7 for ALL BESS Flights combined
• We will search for antihelium in the BESS-Polar
  II flight with anticipated sensitivity 3 x 10-8.