Electron identification and shower analysis in ECC

1
Electron identificationand shower analysis in ECC
8.Mar.2002 EW2002_at_Nagoya

• T.Toshito (Nagoya Univ.)

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Test experiment at CERN PS in May 1999
2GeV/c
Scanned at Nagoya
8GeV/c
To achieve low background emulsion plates are
used as doublet.
2GeV/c 2events 8GeV/c 4events
More statistics are required!
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Test experiment at CERN PS in May 2001
P 2 and 4GeV/c e enriched p- beam
Interesting energy region for OPERA

• electron identification
• Analysis of cascade shower

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To achieve low background
1 tracks/mm2

• Fuji-emulsions stored for about 2 month are
  refreshed at Nagoya
• Packed in transportation from Nagoya to CERN
• Developed soon after the beam exposure

Real erasing
In-flight
Virtual erasing
Emulsion plates are used as singlet.
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Beam exposure (May 17th 2000)
27layer 5X0

• Low density ( a few 102/cm2) run
• to study cascade shower
• in low background condition
• r(e)10(2GeV/c),2(4GeV/c)
• 10electron

• High density (103/cm2) run
• to study e/p identification
• with high statistics
• r(e)60(2GeV/c),30(4GeV/c)
• 100300electron

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Net Scan by UTS at Nagoya

• High density Oct. 2000 (one week)
• (1cm1cm)1 beam spot27 plates
• Low density Dec. 2000 (one month)
• (1cm1cm)7 beam spots27 plates

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Tracking in ECC by two kind of configuration
Only Em
Cosmic-ray In-flight
300tracks/cm2
Isotropic
Beam at CERN
300tracks/cm2
Parallel
EmPb
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e/p identification (High density)
electron
stopped with shower
Shower detection
stopped without shower
X05.6mm in lead
p
punch through
?int170mm in lead
stopped without shower
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?2 analysis to measure energy variation
separator
1mm
2.3mrad
In practical experiments incident momentum are
unknown,
so E0 is treated as a free parameter to minimize
chi-square.
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Track following of low momentum trackand
detection of shower track
tolerance
Angle lt 75mrad
Position lt 45µm
Pmin100MeV/c
Shower tracks are searched in these tolerances.
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Results of track following
electron-like
?2analysis
?2analysis
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?2 for punch through
No interacting p
Data and pure pMC agree very well
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Momentum measurement by multiple coulomb
scattering for punch through tracks
26 error
29 error
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?2 for stopped tracks
Mixture of electron interacted p
Data and MC agree very well
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e-like shower negative chi-square
278 events 2GeV/c
126 events 4GeV/c
According to MC
Efficiency 88 mis-id Prob. 6
_at_2GeV/c Efficiency 91 mis-id Prob. 4 _at_4GeV/c
Comparison with cherenkov counter
Installed in the upstream of ECC to monitor e/p
ratio.
e/p ratio
Consistent
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Data and MC agree very well in ??2.e/p ratio
measured by ECC and cherenkov counteragree very
much.
Performance of electron identification in ECC
is well understood based on high statistics
experimental data.
next
Low density run to study cascade shower
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Analysis of cascade shower (Low density)
14 electron events _at_2GeV/c 14 electron events
_at_4GeV/c detected in low density sample
Detection efficiency is estimated as 95.
Contamination of p is estimated as 2 events at
most.

• Energy reconstruction
• by counting track segments

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Counting track segments in horn
??beamlt250mrad
Determined as containing 68 _at_ 4GeV
2GeV/c
x
4GeV/c
y
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Estimation of background
At random volume
Track segments from another electron
and interaction are seen.
Random background 1track/mm2
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Results
DATA(B.G.)
average 51
DATA(shower)
Number of events
r.m.s. 14
MC(shower)DATA(B.G.)
Number of segments
average 94
Number of events
r.m.s. 18
Number of segments
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Summary

• electron identification
• 278 e-like events _at_ 2GeV
• 126 e-like events _at_ 4GeV
• Efficiency 90 mis-id Prob. 5
• Analysis of cascade shower
• 14 electrons _at_ 2GeV
• 14 electrons _at_ 4GeV
• E?(number of segments)

?E
0.4

E(GeV)
E
_at_ a few GeV
These performances can be improved in lower
background condition.
Refresh in the underground
Lower track density