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Status of E391a

Status of E391a. G.Y.Lim IPNS, KEK. K L  p o nn decay. Experimental difficulties Tiny branching fraction Great number of K L decays Weak Kinematical constaints Background suppression From K L decays K L  p o p o Other modes ? Beam related events p o production Accidentals

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Status of E391a

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  1. Status of E391a G.Y.Lim IPNS, KEK

  2. KL ponn decay • Experimental difficulties • Tiny branching fraction • Great number of KL decays • Weak Kinematical constaints • Background suppression • From KL decays • KL popo • Other modes ? • Beam related events • po production • Accidentals • What would be a main obstacle ? • How to estimate backgroud level? KTeV, Phys. Lett. B447(1999) Hyperon decays – lower momentum ? Multi-po events – tighter vetoing ? Neutron events – removing sources ?

  3. KEK-PS E391a • The first dedicate experiment • To confirm the methodology • Large acceptance • Single po (po gg) detection • Background rejection • Tight vetoing • High PT selection • E391a concepts • Pencil beam • Hermetic veto system • Double decay chamber • Highly evacuated decay region • Step-by-step approach J-PARC

  4. E391a collaboration Joint Institute for Nuclear Research (Dubna), Russia High Energy Accelerator Research Organization, KEK, Japan Department of Physics, Kyoto University, Japan National Defense Academy of Japan, Japan Department of Physics, National Taiwan University, Taiwan Department of Physics, Osaka University, Japan Department of Physics, Pusan National University, Korea Research Center for Nuclear Physics, Osaka University, Japan Faculty of Science and Engineering, Saga University, Japan Department of Physics, University of Chicago, USA Department of Physics, Yamagata University, Japan More than 50 collaborators from 11 institutes from 5 countries

  5. Milestones of the E391a • Dec.1996: conditionally approved • Mar.1999: constructed the beam line • July 2001: approved • Oct. 2002: engineering run • Jan. 2004: finish detector assembling • Feb. –June 2004: Data taking • Feb. –Mar. 2005 : Run-II • Fall 2005 : Run-III (conditionally approved)

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

  7. KL popo Main possible background source Br(KLp0nn)/Br(KLp0p0)~10-8 High detection efficiency Hermetic veto system Double decay chamber Low detection threshold High PT selection with pencil beam Reject dominant multi-g events High energy g-missing Rejection of odd pairing Related to the KL decays Making a correct inefficiency table for g-detection

  8. Hyperondecays L  npo Short lifetime/low momentum Length of beam line po production n + A  po + n + A With detector components Clean beam With Residual gas Evacuated decay region 0.1 S.M. event @ 10-5 pa Related to the Beam

  9. Pencil Beam 5 stages of collimators made of heavy metal (tungsten) 2 stages of sweeping magnets Thermal neutron absorber Lead/Be plug for controls gamma/neutron flux Fine alignment using telescope GEANT M.C. agree well to the measurements

  10. Covered by plastic scintillators (Charged Veto (CV)) Recycled 576 Un-doped CsI (70X70X300 mm3 (from E162) 50X50X500 mm3 (from KTeV)) CC03 (Tungsten + Scin.) E391a detector setup KL beam

  11. Assembled three parts Detector Integration was finished on Jan 22, 2004

  12. 80 μm LDPE 15 μm EVAL (aluminized) 15 μm nylon 80 μm LDPE Detector inside vacuum To reject po production by neutron interaction with residual gas Differential pumping technique

  13. Data taking • Run time (physics run) • Run-I : Feb. 16th – Jul. 1st 2004: (~60days) • KEK 12 GeV PS : Incident protons • 2.2 X 1012/spill at target • 2-sec spill length & 4-sec repetition • KL flux in front of detector • 5x105 /spill • Peak momentum : ~2 GeV/c • Trigger : No. of cluster >=2 • Energy threshold for a cluster : 60 MeV. • DAQ live-time ratio : 75 % • Vacuum : ~10-5 Pa Online event display

  14. p0 production at target Calibration • Energy & timing • Cosmic-ray muon.  CsI, barrels • Punch-through muon. Collar counters • p0 production at Al target.  Precise calibration of CsI Muon Data (KEK-preprint-2004-85, accepted for publication in NIM.)

  15. Normalization channels (without tight vetoing) 4g events 2g events 6g events PT+decay-position cut Vertex-finding cut Vertex-finding cut + fusion-cut KL popo KL gg KLp0popo Invariant Mass of 4g (GeV/c2) Invariant Mass of 6g (GeV/c2) Reconstructed vertex of KL (cm) Monte-Carlo simulation well reproduces data. Pure kaon sample.  Veto counter study

  16. po produced at CC02 po produced at CV (?) KL popopo KL p+p-po KL  popo KL gg 2g analysis Data without tight veto M.C. for KL decays ( Without Normalization) PT(GeV/c) Reconstructed vertex (cm)

  17. CH2, ~1g/cm3 • 10 g/cm3 & 2 mm-thick PT(GeV/c) Reconstructed vertex (cm)  Well reproduces data distributions. MC ~material in front of CV?~

  18. Remove neutron events Kinematical constraints for two gammas 1) Distance between two gammas 2) Energy balance of two gammas Unexpected acceptance loss

  19. Veto Optimization ~Main-barrel timing (low E sample)~ KLgg pure sample gg B.G.sample upstream ② ① early late downstream Backsplash should NOT veto! • Real photon hit  should veto. • Backsplash  should NOT veto.

  20. Results of 1-Day analysis • Intensive study using part of data • obtained during 1-day (2 %) • B.G. events can be controlled • Acceptance loss • - Neutron related events • - Tight photon vetoing • More statistics – 1 week analysis • - po production at the detector • - To study fiducial region event • Clearer beam condition(Run-II) S.E.S ~ @ 1-day statistics

  21. 1-Week Analysis Energy distribution of veto counters • Lager size of data sample • Factor of 5 • Deeper understanding about the background events • Another sources ? • Access to the KL decays • Detailed M.C. study for veto counters • Pure M.C. + accidental overlay • Reproduce the low energy distribution • Finer veto counter tuning Preliminary results will be reported at the KAON 2005

  22. Beam-line endpoint Detector upstream section CC00 30cm-long x 40φ (20mm-W / 5mm-Scinti.) Run-II • To fix the dropped membrane • Install additional collimator in front of detector • Minor up-dates of detector systems • Apply the Be absorber (better KL/n ratio) • Finer tuned DAQ / beam condition • Data taking during 40 days from Feb. 2005

  23. Membrane Correction

  24. Better quality of data (online plots) Run-I Run-II PT(GeV/c) Reconstructed vertex (cm) Run-II analysis Run-III on this fall ( Conditionally approved )

  25. Better quality of data Vertex PT Run-II Run-I (GeV/c) (cm) Eg Eg (GeV) (GeV)

  26. Summary • KEK-PS E391a – The first dedicated experiment • To get a guideline for the precise measurement • Lots of list to study (hoping to various suggestions) • Successful data taking • To realize a trial of one method • We are on right track • Too early to declare • To find problem  To fix it • 1-day analysis • Close to the KTeV limit • Feed-back to the Run-II • 1-Week analysis • Preliminary results at the KAON2005 • Better data quality at Run-II • Run-III in coming fall

  27. Acceptance for KLp0nn • Acceptance loss due to kinematical  M.C. • Acceptance loss due to veto  Pure Kaon samples • Decay probability is included

  28. Prospect ~Run-II~ Membrane at Endcap • Membrane was fixed. • Additional collar counter was installed.  to reduce halo-neutron effects. • Be absorber was installed in the beam line.  better n/K ratio, less halo-neutron. CC00 W/Scintillator Sandwich(2.5lI) in front of detector. We are working hard on (and enjoying) this challenging experiment.

  29. Kaon Reconstruction (KL3p0 ,2p0 ,gg) • No. of reconstructed g-cluster : equal to 2,4,6 (E >= 50MeV) • No other cluster ( E < 20 MeV) in CsI • p0 reconstruction (assuming p0-mass  vertex Z) • Best chi2 • Kinematical cuts - Chi2 < 2 - 2nd Chi2 >20 - Pt < 10(MeV/c) - Beam size< 4cm g1 Example : KL2p0 g2 z1 g3 z2 g4 Pt beam direction

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