1 K L →π 0 νν 探索実験 KEK-PS E391a における Run3 データ解析の現状 JPS 2008 Spring Meeting Hideki MORII (Kyoto Univ.)

2 Contents Introduction – E391a Run3 – Detector Upgrades in Run3 BA (calibraion plot) APC (calibration / g-tagging) Current Status & Strategy for Run3 analysis – calibration – MC development – Run3 data quality check – Optimize cuts Plan Summray Overview

3 E391a Run3 E391a – K L →π 0 νν 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 Run3 –Detector Upgrade new Back Anti (in-beam  veto) Aerogel Photon Counter (  -tagger) –Data Taking (almost) stable DAQ condition Introduction

4 Detector Upgrade in Run3 aaa Introduction Aerogel Photon Counter (APC) Upgraded Added Back Anti

5 Back Anti Upgrade Introduction PWO crystal construction In-beam  veto counter Back Anti Upgraded

6 Aerogel Photon Counter Introduction Prototype of E14 BA Aerogel Photon Counter (APC) Added γ e+e+ e-e- Cerenkov light

7 Run3 Data Full Intensity Run (C only mode) – with Be aborber – ~ spills – ~70% of Run2 data Half Intensity Run (A&C mode) – w/o Be absorber – ~98000 spills – ~10% of Run2 data c.f. ) Run2 – with Be absorber – ~ spills Introduction KEK 12GeV PS East Counter Hall E391a C-line A-line Be absorber to reduce neutron (betteer n/K ratio) # of K L ~60% / # of n ~ 40% ※ ※ ※

8 Strategy for Run3 Analysis Calibration kdecay, halo-n, eta Strategy for Run3 Analysis Results Step1 Confirmation Step2 Optimization Step0 Preparation Step3 Physics Output [MC] Develop Run3 MC [Data] Data quality check [Data] Cut optimization [MC] MC mass production

9 Step0 : Preparation Calibration kdecay, halo-n, eta Step0 : Preparation Results Step1 Confirmation Step2 Optimization Step0 Preparation Step3 Physics Output [MC] Develop Run3 MC [Data] Data quality check [Data] Cut optimization [MC] MC mass production

10 Step0 : Preparation Calibration – completed (including upgraded / new detectors) MC development – detector upgrades are implemented – now under middle-size production : confirming results – preparing for mass-production Step0 : Preparation

11 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. center crystal) Run2 BA beam Run3 BA Step0 : Preparation

12 Calibration of Back Anti Calibration – Calibration has been done with Muon Run ADC count MIP peak with Muon Run Muon Run : use  from upstream (with beam shutter closed) MIP peak Step0 : Preparation

13 Step1 : Confirmation Calibration kdecay, halo-n, eta Step1 : Confirmation Results Step1 Confirmation Step2 Optimization Step0 Preparation Step3 Physics Output [MC] Develop Run3 MC [Data] Data quality check [Data] Cut optimization [MC] MC mass production

14 Step1 : Confirmation Confirm Run3 data quality – compare with Run3 MC : MC middle size production – compare with Run2 data K L  3  0  6  sample, 4  (K L  2  0  4 , 2  Step1 : Confirmation Run2Run3 Mass (GeV/c 2 ) Invariant Mass of 6  sample Matchs well  CsI calibration is good in Run3

15 Step2 : Optimization Calibration kdecay, halo-n, eta Step2 : Optimization Results Step1 Confirmation Step2 Optimization Step0 Preparation Step3 Physics Output [MC] Develop Run3 MC [Data] Data quality check [Data] Cut optimization [MC] MC mass production

16 Step2 : Optimization Develop complete BA veto (algorithm, threshold, etc…) Study with Run2 opened box – to get more acceptance – optimize veto & event selections Step2 : Optimization Veto kinematic cut Acceptance Loss / Rejection Power in Run2

17 Plan Calibration kdecay, halo-n, eta Plan Results Step1 Confirmation Step2 Optimization Step0 Preparation Step3 Physics Output [MC] Develop Run3 MC [Data] Data quality check [Data] Cut optimization [MC] MC mass production Completed Almost done Ongoing (~1-2 month) OK ~4-5 month In parallel with MC mass prod.

18 Summary E391a Run3 –Data : ~70% of Run2 (~80% with A&C mode) –Detector Upgrade Upgraded Back Anti (BA) : in-beam  -veto New Aerogel Photon Counter : prototype of E14 BA both worked well Current Status – calibration is completed – finalizing MC development – Now checking data quality Future Plan – Develop BA veto – Precise study with Run2 opened box for more acceptance Summary

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20 The E391a experiment K L production with KEK 12GeV PS – Slow extraction – K0 beamline in the East Counter Hall Intensity – 2 x protons on target (POT) per 2sec spill, 4sec cycle production angle: 4°, K L peak momentum 2GeV/c, n/K L ratio: ~40 Physics runs – Run I: February to July of 2004 “Express” analysis with 10% data published in PRD (2006) – Run II: February to April of 2005 The main topic of this seminar Full data analysis – Integrated protons: 1.4x10 18 POT » ~ 32 days without break – Run III: October - December of 2005 Calibration ready, MC development in progress

21 Principle of the experiment 1. require 2 photons – Hermetic veto system 2. measure the photon energies and positions 3. reconstruct the decay vertex on the beamline assuming M 2γ = M π0 halo/core ~ cm 4. require missing P T and the vertex in the fiducial region “Pencil” beam line to improve P T resolution  8cm 16m from the target

22 Features of E391a apparatus Decay region – High vacuum: Pa to suppress the background from interactions w/ residual gas Detector components – Set in the vacuum: 0.1 Pa separating the decay region from the detector region with “membrane”: 0.2mmt film CsI calorimeter Charged Veto (CV) Main Barrel (MB) Front Barrel (FB)

23 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 X 0 ) Aerogel : 30cm(x) x 30cm(y) x 5cm(z) γ e+e+ e-e- Cerenkov light Step0 : Preparation

24 Calibration of Aerogel Photon Counter Light yield – calibrated with Muon Run – MIP peak appears clearly Photon Tagging – checked with KL decay – 2 MIPs (= e + e - ) peak seen Muon Run Physics Run (K L decay sample) ADC count MIP peak ~300count 2 MIPs peak ~ 600 count Step0 : Preparation

25 Response to photons (3) N-cluster trigger Accidental trigger (TMON) (Black) – (Red) 15 p.e. Clear peak around 15 p.e. is observed. Response to photon is well reproduced by MC. Tagging quality is 94 % (#p.e. > 10).  will be improved by using (for example) 5  sample.

26 Mechanism of CV Background even+extra odd and 2  extra fusion 1  from  0 + extra

27 Mechanism of CV background removing Veto : odd &  0 1  +extra removing g-selection : even+extra with bifurcation for each mechanism, even+extra is dominant setup + box +  selection + veto -veto -  selection all cuts all (.081) even+extra (.026) odd (0.0?) fusion (.013)   1  + extra (.013) extra 2clustr10000 (0.0?) tighten loosen

28 Electronics and DAQ Number of channels – CsI calorimeter: ~600ch – Veto counters: ~400ch “AmpDiscri” Module – Discrimination for TDC – Set near the detector low noise – min. threshold: ~0.5 mV (ex. ~0.7MeV for CsI) – 8ch sum for the trigger Trigger – Logic CsI hardware clustering (thres. 80MeV) + Veto (20-100MeV) – ~300 events / 2 sec spill = 150Hz DAQ live time – ~90% PMT 8ch Analog each out Analog sum out Digital out for timing Trigger logic CsI FASTBUS-VME FASTBUS ADC Veto FASTBUS ADC AmpDiscri FASTBUS-VME TKO TDC TKO-VME GbE Event Builder Storage

29 Problems in Run-I core neutron background – hitting on the membrane sagging into the beam-line

30 Result from Run-I 1week Using 10% of Run-I data set new limit – Br < 2.1x10 -7 (PRD 74:051105, 2006)

31 Can we speed up MC mass production? Halo-n needs large amount of MC – needed 3 months in Run2 halo-n MC – in Run2 analysis, we used bifurcation method for CV bg Recycling Method – collect only BG-like events with strong online-veto (discard “safe” events in production stage) – then, full simulation for “dangerous” events Strategy for Run3 Analysis