Hermeticity, boost factor and other issues

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Hermeticity, boost factor and other issues

• Koji Hara (Nagoya University)

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Introduction

• Studies based on the physics cases are needed to
  validate and optimize the design of the detector
  performance and the accelerator.
• Boost factor and Hermeticity
• How the boost factor affect measurements using Dt
  and full reconstruction method.
• KL detection efficiency
• How important for the mode with missing energy.
• Test cases
• B?J/yK0, fK0 tCPV measurement
• B?tn Br measurement
• Based on our results from Belle data.

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Principle of tCPV measurement
CP-side
m
J/y
m-
?(4S) resonance
B1
electron (8GeV)
KS/L
B0
positron (3.5GeV)
nm
B2
p-
bg 0.425 (Belle)
K
p-
Flavor tag and vertex reconstruction
Dz 200mm (Belle)
m

1. Fully reconstruct one B-meson which decays to CP
   eigenstate
2. Tag-side determines its flavor
3. Proper time (Dt) is measured from decay-vertex
   difference (Dz)

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B?tn Analysis Concepts_at_Belle

• B decays with missing neutrinos lack the
  kinematic constraints which are used to separate
  signal events from backgrounds (Mbc and DE)
• Reconstruct the decay of the non-signal B
  (tagging), then look for the signal decay in
  whatever is left over

More than 2 neutrinos appear in B ?tn decay
Tagging side Fully reconstruct hadronic modes
Signal side Reconstruct particles from t decay
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B?tn Signal Selection

• Extra neutral energy in calorimeter EECL
• - Most powerful variable for separating signal
  and background
• -Total calorimeter(ECL) energy from the neutral
  clusters which are not associated with the tag B

Background
B?tn Signal
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Hermeticity and boost factor

• Large boost factor
• ? better Dt resolution
• less acceptance in forward region
• Small boost factor
• ? worse Dt resolution
• more acceptance in forward region
• Baseline detector design
• study of adding super forward detector
• ? K.-F. Chens talk

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Boost factor Dependence

• Toy MC results considering Dt resolution and
  geometrical acceptance.
• Geometrical acceptance is assumed to be same as
  the current Belle detector.

• - J/yK0 tCPV
• - fK0 tCPV
• - B?tn BR

KEKB can operate
worse
better
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KL Veto Efficiency for B?tn

• Main background in B?tn are B decays with KL .
• How KL detection efficiency affect the precision
  of Br(B?tn)?
• ? requirement for super KLM

e
B
ne
D0
KL
KL
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KL Veto Efficiency Dependence

• Toy MC results for several KL veto efficiencies.
• Current is set to 35
• guess by geant simulation J/yKL data
• Q How can we improve KL detection efficiency of
  super KLM?

worse
better
KL veto efficiency
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Summary

• Boost factor and Hermeticity
• Considering both tCPV and B?tn measurements,
  current KEKB energy (8x3.5) seems the preferable
  point within the region KEKB can operate.
• KL veto efficiency for B?tn
• Higher KL veto efficiency is effective for B?tn
  measurement
• How can we improve KL detection efficiency of
  super KLM?
• Dependence of other detector performances (PID,
  trackingvertexing) must be checked and
  optimized.
• Studies based on the fast simulator are being
  done.