KEK-PS E391a Run3???????KL?p0???????

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KEK-PS E391a Run3???????KL?p0???????

• JPS 2008 Autumn Meeting
• Hideki MORII (Kyoto Univ.)
• ? E391a Collaboration

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Contents
Overview

• Introduction
• Physics of KL ? p0nn
• E391a Experiment
• Strategy for Run3 analysis
• Status of Run3 analysis
• calibration stability
• KL flux estimation
• To get further from Run2
• Run2 opened box analysis
• better halo neutron MC
• Summary

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Introduction
Introduction

1. Physics Motivation
2. E391a Experiment

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Physics Motivation for Kpi0nunu
Introduction

• KL?p0nn
• direct CP violation
• gold-plated mode
• small theoretical uncertainty
• measures eta of CKM matrix
• small BR 2.5x10-11
• Sensitive to
• precise check of standard model
• sensitive to new physics

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E391a Experiment
Introduction

• E391a
• KL?p0?? measurement _at_ KEK 12GeV PS
• pilot experiment for J-PARC E14
• Three data taking
• Run1 Feb 2004 Jul 2004
• Run2 Feb 2005 Apr 2005
• Run3 Nov 2005 Dec 2005
• Run2 Result
• Blind analysis
• No events found in the signal box
• Upper limit 6.7x10-8 (90 C.L.)
• (Phys.Rev.Lett. 100 201802, 2008. )

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Principle of E391a Experiment
Introduction

• E391a principle
• require (p0?)2g nothing else
• CsI calorimeter (2g detection)
• hermetic veto system
• reconstruct decay vertex
• assuming p0 mass
• Mgg Mp0
• 3. requre missming pT vertex
• inside the fiducial region

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E391a Detector
Introduction
Back Anti
Upgraded
Aerogel Photon Counter (APC)
Added
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Strategy for E391a Run3 Analysis
Strategy for Run3 Analysis

• Strategy for Run3 Analysis

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Strategy for Run3 Analysis
Strategy for Run3 Analysis
Step0 Preparation
Calibration
MC Develop Run3 MC
Step1 Confirmation
Run3 Data Data quality check
MC MC mass production
kdecay, halo-n, eta
Step2 Optimization
Run2 Data / MC Cut optimization
Step3 Physics Output
Results
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Current Status of Run3 Analysis
Current Status of Run3 Analysis

• Calibration Run Stability
• KL flux estimation with 3 decay modes

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Calibration Run Stability Check
Current Status of Run3 Analysis
6g invariant mass

• Calibration run stability
• completed / confirmed

peak 497.6 MeV RMS1
M6g (GeV/c2)
? quite stable !
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Reconstructed Mass Distribution
Current Status of Run3 Analysis

• Reconstructed mass for 6g(KL?3p0), 4g (KL?2p0)
• KL mass spectrum matches well to MC

Rec. mass of 6g sample
Rec. mass of 4g sample
dots Run3 data blue K?3p0MC red K?2p0MC
of events
of events
reconstructed mass (GeV)
reconstructed mass (GeV)
ratio (data/MC)
ratio (data/MC)
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KL Flux Estimation
Current Status of Run3 Analysis

• Flux estimation is done by K?3p0, K?2p0, K?gg

mode of events in data of events in MC(addbg) acceptance flux
3p0 56350 3464 (stat. 2.0e9) 8.09 x 10-5 3.56 x 109 (-2.7)
2p0 1254 12646 (stat. 1.5e9) 3.94 x 10-4 3.66 x 109 (---)
gg 11111 21896 (stat. 2.0e8) 5.12 x 10-3 3.96 x 109 (8.2)
Run3 Statistics 71 of Run2
cf. Run2 3p0 5.02 x 109 (-2.1)
2p0 5.13 x 109 (---) gg 5.45 x
109 (6.2)
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Optimization
Optimization

• Run2 Opened Box Analysis
• Improved halo-neutron MC

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Acceptance Study with Run2 Data
Optimization Get Further from Run2 Analysis

• To get more acceptance
• try to see Run2 data with opened box
• Acceptance list (veto)
• single hit CsI 64.4
• MainBarrel 79.0
• ChargedVeto 82.9
• Acceptance list (kinematic cuts)
• g-RMS 57.9
• p0 kinematics 77.7

g-RMS cut has the largest acceptance loss ?
try to loosen this cut and see other cuts
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Functionality of g-RMS cut
Optimization Get Further from Run2 Analysis
fusion like
normal

• g-RMS cut
• cut for g cluster shape on CsI
• to reject fusion cluster
• Fusion cluster
• gamma gamma KL? 2p0 BG
• which effectively results in photon inefficiency
• gamma neutron CV halo neutron BG
• which results in p0 misreconstruction
• ? see next page

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Mechanism of CV Background
Optimization Get Further from Run2 Analysis

• Mechanism of CV-bg
• halo neutron hits on CV
• create p0 something
• misreconstruct 2g to signal box
• due to extra activity

extra particle
beam line
reconstructed vertex
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Alternative to RMS cut Fusion-NN Cut
Optimization Get Further from Run2 Analysis
pT vs z plot w/ and w/o g-RMS cut

• g-RMS cut
• requires cluster RMS smaller than 4cm
• Fusion Neural Network cut
• study with K?3p0 MC
• 0 fusion like, 1 normal
• requires gt0.7 for NN val.

black w/ g-RMS cut red w/o g-RMS cut
pT (GeV/c)
i run over all crystals di distance from g
center
z (cm)
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Alternative to RMS cut Fusion-NN Cut
Optimization Get Further from Run2 Analysis

• replacing g-RMS cut by fusion-NN cut
• no events in signal box
• acceptance 58 ? 77 (33 recovery)

pt vs z plot w/ w/o g-RMS cut
pt vs z plot w/ w/o fusion NN cut
pT (GeV/c)
pT (GeV/c)
z (cm)
z (cm)
black w/ g-RMS cut red w/o g-RMS cut
black w/ fusionNN cut red w/o fusionNN cut
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Improved Neutron MC
Optimization Other Analysis Effort in Run3

• For getting better understanding to neutron BG
• trying FLUKA model for halo-n MC
• better estimation for hadronic interaction
• Recycling Method
• recycle MC seed for dangerous events
• speeding up MC (need 2weeks for Run3 data
  equivalent)

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Summary
Summary

• E391a experiment
• KL ? p0nn measurement _at_ KEK 12GeV PS
• Now, Run3 analysis is ongoing
• Status of Run3 analysis
• calibration stability
• KL flux estimation
• To get further from Run2
• Run2 opened box analysis
• better halo neutron MC

? Seems good quality
? To get more acceptance
? To understand more about neutron BG
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backup
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Mechanism of CV Background
odd
evenextra

fusion
1g from p0 extra
and 2g extra
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Mechanism of CV background

• removing Veto odd p01gextra
• removing g-selection evenextra
• with bifurcation for each mechanism, evenextra
  is dominant

setup box g selection veto
veto - g selection all cuts
all 3277 44 6 0 (.081)
evenextra 306 4 2 0 (.026)
odd 210 26 0 0 (0.0?)
fusion 226 3 1 0 (.013)
p0 1g extra 2525 11 3 0 (.013)
extra 2clustr 10 0 0 0 (0.0?)
tighten
loosen
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Features of E391a apparatus
CsI calorimeter
Front Barrel (FB)

• Decay region
• High vacuum 10-5 Pa
• to suppress the backgroundfrom interactions w/
  residual gas
• Detector components
• Set in the vacuum 0.1 Pa
• separating the decay regionfrom the detector
  regionwith membrane 0.2mmt film

Charged Veto (CV)
Main Barrel (MB)
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Back Anti Upgrade
Step0 Preparation
Run2 BA

• Upgrade Back Anti
• lead plate plastic scinti. quartz
• -gt PWO crystal quartz
• segmentation
• longitudinal
• -gt transverse
• Benefits
• better n/g separation
• (shower shape analysis)
• lower rate
• (typ. 1/2 _at_ center crystal)

beam
Run3 BA
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Aerogel Photon Counter
Step0 Preparation

• Aerogel Photon Counter (APC)
• Aerogel Cherenkov counter only sensitive to
  fast particle
• insensitive to neutrons / sensitive to g shower
• Can be used as photon tag counter (for BA study)
• prototype of E14 BA

Pb convertor 2mm thick (0.3 X0) Aerogel
30cm(x) x 30cm(y) x 5cm(z)