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KEK-PS E391a Run3 データを用いた K L →π 0 νν 解析の現状

KEK-PS E391a Run3 データを用いた K L →π 0 νν 解析の現状. JPS 2008 Autumn Meeting Hideki MORII (Kyoto Univ.) 　　他 E391a Collaboration. Overview. Contents. Introduction Physics of K L  p 0 nn E391a Experiment Strategy for Run3 analysis Status of Run3 analysis calibration & stability

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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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  1. 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

  2. Overview Contents • 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

  3. Introduction Introduction • Physics Motivation • E391a Experiment

  4. Introduction Physics Motivation for Kpi0nunu • 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

  5. Introduction 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. )

  6. Introduction Principle of E391a Experiment • 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

  7. Introduction E391a Detector Back Anti Upgraded Aerogel Photon Counter (APC) Added

  8. Strategy for Run3 Analysis Strategy for E391a Run3 Analysis • Strategy for Run3 Analysis

  9. 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

  10. Current Status of Run3 Analysis Current Status of Run3 Analysis • Calibration & Run Stability • KL flux estimation with 3 decay modes

  11. Current Status of Run3 Analysis Run Stability of CsI gain value Run Stability of reconstructed KL mass (6g sample : KL3p0) ±1% ±1% (typical crystal) Calibration & Run Stability Check 6g invariant mass • Calibration & run stability • completed / confirmed peak 497.6 MeV RMS~1% M6g(GeV/c2)  quite stable !

  12. Current Status of Run3 Analysis Reconstructed Mass Distribution • 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)

  13. Current Status of Run3 Analysis KL Flux Estimation • Flux estimation is done by K3p0, K2p0, Kgg 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%)

  14. Optimization Optimization • Run2 Opened Box Analysis • Improved halo-neutron MC

  15. Optimization : Get Further from Run2 Analysis 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) • 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

  16. Optimization : Get Further from Run2 Analysis Functionality of g-RMS cut 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

  17. Optimization : Get Further from Run2 Analysis Mechanism of CV Background • 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

  18. Optimization : Get Further from Run2 Analysis veto Alternative to RMS cut : Fusion-NN Cut 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 >0.7 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)

  19. Optimization : Get Further from Run2 Analysis Alternative to RMS cut : Fusion-NN Cut • 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/ofusion 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

  20. Optimization : Other Analysis Effort in Run3 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)

  21. Summary Summary • E391a experiment • KL p0nn 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  Seems good quality  To get more acceptance  To understand more about neutron BG

  22. backup

  23. Mechanism of CV Background odd even+extra fusion 1g from p0 + extra and 2g extra

  24. Mechanism of CV background • removing Veto : odd & p01g+extra • removing g-selection : even+extra • with bifurcation for each mechanism, even+extra is dominant tighten loosen

  25. 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)

  26. Step0 : Preparation Back Anti Upgrade Run2 BA • Upgrade Back Anti • lead plate + plastic scinti. + quartz ->PWO crystal + quartz • segmentation : longitudinal -> transverse • Benefits • better n/g separation (shower shape analysis) • lower rate (typ. 1/2 @ center crystal) beam Run3 BA

  27. Step0 : Preparation e+ γ e- Cerenkov light Aerogel Photon Counter • 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)

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