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Status of the KEK E391a Experiment

Status of the KEK E391a Experiment. G. Y. Lim IPNS, KEK. 質量起源と超対称性物理の研究 2005 年 3 月 7 日. E391a searching for K L  p o nn decay Very clean FCNC process Golden mode for a test of the SM and search for a new physics The first dedicated experiment to the K L  p o nn decay.

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Status of the KEK E391a Experiment

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  1. Status of the KEK E391a Experiment G. Y. Lim IPNS, KEK 質量起源と超対称性物理の研究 2005年3月7日

  2. E391a searching for KL ponn decay Very clean FCNC process Golden mode for a test of the SM and search for a new physics The first dedicated experiment to the KL ponn decay Contents Detection principle Data taking The 1st version of analysis (M. Doroshenko – Ph.D. theses) Run-II Summary JPARC,KOPIO Introduction A dream of theorist and a nightmare of experimentalist

  3. Detection Principle Clear single p 0 with high PT • KLpo n n • ggNothing • pure CsI calorimeter4pveto system

  4. High g-detection efficiency • Expected main background is KL popo • 4p veto system without any dead space • Low energy threshold for g-detection • Noise reduction • Accidental hits • Making a correct inefficiency table for g-detection

  5. Pencil beam and vacuum system

  6. E391a detector setup KL beam

  7. E391a detector setup

  8. Data Taking • Data taking during 18, Feb ~ 1, July 2004 • Detector/ DAQ tuning (44 shifts ) - with low intensity (30 shifts) • Beam break due to water leakage of beam line magnets (21 shifts) • Additional fine tuning of DAQ, beam line (8 shifts) • Start stable data taking from 15th, March • ~ 28, April (116 shifts) • 19th, May ~ 21th June (71 shifts) • Calibration Run • Data with air / po production (24 shifts) • 6 TB of data • Tape library on KEK computer center • Data analysis • 1 Day  1 Week (1/10 of the full data) • We are trying to understand characteristics of the backgrounds correctly estimate the ponn sensitivity

  9. 6-g event sample 4-g event sample 2-g event sample M.C. reproduce data reasonably KL popo KL gg KL popopo Pure data sample for Photo Veto counters Invariant Mass of 6g (GeV/c2) Invariant Mass of 4g (GeV/c2) Reconstructed decay vertex of KL (cm) Fine monitoring channels Normalization for the number of KL Pure signal and background sample for veto counter study

  10. Study of photon veto counters (example)

  11. KL  p0p0p0 KL  p0p0 KL  gg KL  p+p-p0 KL Decay KL  p-e+n KL  p-m+n Two gamma events M.C. for KL decays ( Without Normalization) Data without tight veto PT(GeV/c) CsI Surface Reconstructed vertex (cm) Hard to explain using KL decay only

  12. Unexpected po production by Neutrons

  13. Core n Counts Halo n Kgg Kp2 Halo neutron generate 2-g in the CsI calorimeter (M.C.) Reconstructed vertex (cm) Various contributions to the 2-gamma sample Neutron related events are dominant n/g separation

  14. Shower shape at the calorimeter Distance between gammas Example of n/g separation There are varieties in real application in detail. Current acceptance reduce to 0.14~0.5 due to these additional cuts.

  15. After finishing Photon Veto / Kinematical cuts B.G. events can be controlled Acceptance loss - Shower leakage - Neutron related events po production at the detector To study fiducial region events More statistics (in progress) Clearer beam condition(Run-II) BR(Kp0nn) < @ 1-day statistics

  16. Run-II Semi-online plots for 2-cluster events Improve sensitivity • Increasing statistics • by removing the membrane • by installation of CC00 Understand B.G. • Characterize neutron B.G. by comparing Run-I and Run-II • Clearer condition to understand backgrounds related to the KL decays Data taking for 100 shifts from 2nd, Feb. 2005 Run-III in this autumn RUN-I RUN-II RUN-II RUN-I PT (GeV/c) Decay Vertex (cm)

  17. BR(Kp0nn) < Summary • The data taking has taken successfully • 300 shifts in Run-I (187 shifts for physics data) • The first version of analysis (1-day) • Good indication for data quality • Identify the nature of background • Make a direction for further study (expecting improvements) • Run-II • After fixing a hardware trouble • Clearer condition to study about the background • Diligent progress in step-by-step to the JPARC • New physics search across the Grossman-Nir limit

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