KEK-PS E391a Run3 データを用いた K L →π 0 νν 解析の現状
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Transcript of KEK-PS E391a Run3 データを用いた K L →π 0 νν 解析の現状
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KEK-PS E391a Run3データを用いたKL→π0νν解析の現状
JPS 2008 Autumn Meeting Hideki MORII (Kyoto Univ.) 他 E391a Collaboration
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Contents
• Introduction – Physics of KL 0
– 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
Overview
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Introduction
Introduction
1. Physics Motivation2. E391a Experiment
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Physics Motivation for Kpi0nunu
• KL0– “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
Introduction
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E391a Experiment
• E391a– KL→π0νν measurement @ 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. )
Introduction
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Principle of E391a Experiment
• E391a principle
1. require (0)2 + nothing else CsI calorimeter (2 detection) hermetic veto system
2. reconstruct decay vertex
assuming 0 mass M = M0
3. requre missming pT & vertex
inside the fiducial region
Introduction
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E391a DetectorIntroduction
Aerogel Photon Counter(APC)
Upgraded
Added
Back Anti
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Strategy for E391a Run3 Analysis
Strategy for Run3 Analysis
1. Strategy for Run3 Analysis
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Strategy for Run3 AnalysisCalibration
kdecay,halo-n, eta
Strategy for Run3 Analysis
Results
Step1Confirmation
Step2 Optimization
Step0Preparation
Step3Physics Output
[MC] Develop Run3 MC
[Run3 Data] Data quality check
[Run2 Data / MC] Cut optimization
[MC] MC mass production
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Current Status of Run3 Analysis
Current Status of Run3 Analysis
1. Calibration & Run Stability2. KL flux estimation with 3 decay modes
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Calibration & Run Stability Check
• Calibration & run stability– completed / confirmed
Current Status of Run3 Analysis
M6(GeV/c2)
Run Stability of CsI gain value Run Stability of reconstructed KL mass
(6 sample : KL30)±1% ±1%
(typical crystal)
peak497.6 MeVRMS~1%
quite stable !
6 invariant mass
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Reconstructed Mass Distribution
• Reconstructed mass for 6(KL30), 4 (KL20)– KL mass spectrum matches well to MC
Current Status of Run3 Analysis
reconstructed mass (GeV) reconstructed mass (GeV)
Rec. mass of 6 sample Rec. mass of 4 sample
dots : Run3 datablue :K30MCred : K20MC
# of
eve
nts
# of
eve
nts
ratio
(da
ta/M
C)
ratio
(da
ta/M
C)
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KL Flux Estimation
• Flux estimation is done by K30, K20, K
mode # of events
in data
# of events
in MC(addbg)
acceptance flux
30 56350 3464
(stat. 2.0e9)
8.09 x 10-5 3.56 x 109
(-2.7%)
20 1254 12646
(stat. 1.5e9)
3.94 x 10-4 3.66 x 109
(---)
11111 21896
(stat. 2.0e8)
5.12 x 10-3 3.96 x 109
(+8.2%)
cf. Run2 30 : 5.02 x 109 (-2.1%) 20 : 5.13 x 109 (---)
: 5.45 x 109 (+6.2%)
Run3 Statistics : ~71% of Run2
Current Status of Run3 Analysis
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Optimization
Optimization
1. Run2 Opened Box Analysis2. Improved halo-neutron MC
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Acceptance Study with Run2 Data
• 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)– -RMS : 57.9%– 0 kinematics : 77.7%
-RMS cut has the largest acceptance loss try to loosen this cut and see other cuts
Optimization : Get Further from Run2 Analysis
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• -RMS cut– cut for cluster shape on CsI– to reject fusion cluster
• Fusion cluster– gamma + gamma : KL 20 BG
• which effectively results in photon inefficiency– gamma + neutron : “CV halo neutron BG”
• which results in 0 misreconstruction
see next page
Functionality of -RMS cutOptimization : Get Further from Run2 Analysis
normalfusion like
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• Mechanism of CV-bg1. halo neutron hits on CV
2. create 0 + something
3. misreconstruct 2 to signal box
due to extra activity
Mechanism of CV BackgroundOptimization : Get Further from Run2 Analysis
reconstructed vertex
beam line
extra particle
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veto
Alternative to RMS cut : Fusion-NN Cut
• -RMS cut
– requires cluster RMS smaller than 4cm
• Fusion Neural Network cut– study with K30 MC– 0 : fusion like, 1 : normal– requires >0.7 for NN val.
Optimization : Get Further from Run2 Analysis
i i
ii
E
dERMS
2
i : run over all crystalsdi : distance from center
pT vs z plot w/ and w/o -RMS cutblack : w/ -RMS cutred : w/o -RMS cut
z (cm)
p T (
Ge
V/c
)
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Alternative to RMS cut : Fusion-NN Cut
• replacing -RMS cut by fusion-NN cut– no events in signal box– acceptance : 58% 77% (33% recovery)
Optimization : Get Further from Run2 Analysis
pt vs z plot w/ & w/o -RMS cut pt vs z plot w/ & w/ofusion NN cut
black : w/ -RMS cutred : w/o -RMS cut
black : w/ fusionNN cutred : w/o fusionNN cut
z (cm)z (cm)
p T (
Ge
V/c
)
p T (
Ge
V/c
)
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Improved Neutron MC
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)
Optimization : Other Analysis Effort in Run3
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Summary
• E391a experiment – KL 0 measurement @ 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
Summary
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
even+extra odd
and 2 extra
fusion 1 from 0 + extra
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Mechanism of CV background• removing Veto : odd & 01+extra• removing g-selection : even+extra• with bifurcation for each mechanism, even+extra is dominant
setup + box + selection + veto
-veto - selection all cuts
all 3277 44 6 0 (.081)
even+extra 306 4 2 0 (.026)
odd 210 26 0 0 (0.0?)
fusion 226 3 1 0 (.013)
1+ extra
2525 11 3 0 (.013)
extra 2clustr 10 0 0 0 (0.0?)
tighten
loosen
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Features of E391a apparatus
• 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
CsI calorimeterCsI calorimeter
Charged Veto (CV)Charged Veto (CV)Main Barrel (MB)Main Barrel (MB)
Front Barrel (FB)Front Barrel (FB)
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Back Anti Upgrade• Upgrade Back Anti
– lead plate + plastic scinti. + quartz
PWO crystal + quartz– segmentation :
longitudinal
transverse
• Benefits– better n/ separation
(shower shape analysis)– lower rate
(typ. 1/2 @ center crystal)
Run2 BA
beam
Run3 BA
Step0 : Preparation
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Aerogel Photon Counter• Aerogel Photon Counter (APC)
– Aerogel Cherenkov counter : only sensitive to fast particle• insensitive to neutrons / sensitive to 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)
γ
e+
e-
Cerenkov light
Step0 : Preparation