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K L  p 0 nn experiment at J-PARC

K L  p 0 nn experiment at J-PARC. Mitsuhiro YAMAGA Osaka Univ. Oct. 7, 2004 Workshop on Physics at an Upgraded Fermilab Proton Driver. Contents: Introduction J-PARC K L → p 0 nn experiment KEK PS-E391a At Proton Driver.

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K L  p 0 nn experiment at J-PARC

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  1. KL  p0nn experiment at J-PARC Mitsuhiro YAMAGA Osaka Univ. Oct. 7, 2004 Workshop on Physics at an Upgraded Fermilab Proton Driver • Contents: • Introduction • J-PARC KL → p0nn experiment • KEK PS-E391a • At Proton Driver

  2. Br(KL →p0nn)=6k1(Im(VtdV*ts))2X2(xt) ~ 1.94x10-10h2A4X2 ~ 3x10-11 Theoretical uncertainty is small (~1%). Golden Channel in K Decays _ KL→ p0nn : • CP violation in FCNC process. • Clean measurement of Im(Vtd) ~ h. • Test of the Standard Model • Clue for new physics in comparison with B physics.

  3. Ligeti Still Room for Future Progress

  4. Remains as a Frontier Rare decay (Br～10-11) and no definite kinematical constraint. KL→ p0 nn → 2 g + nothing ⇒Very difficult experiment BG : KL→2p0 , 2g-missing (Br ~ 10-3) 10-3 ⇒ 10-11 obtained by (10-4)2 The main concern is how we can lower the veto threshold. _

  5. Two Concepts Two methods have been proposed: • KOPIO : Kinematical constraint as much as possible to reduce background. • TOF by pulsed beam, angular measurement of g, … • Acceptance is not so high. • Low momentum KL → g inefficiency • E391a, J-PARC : Simply observe 2g (high PT ) + nothing. • High Acceptance • High momentum KL → Better g inefficiency

  6. Strategy • Pencil beam • Narrow beam for PT resolution • Detector system in vacuum • Suppress interactions with materials • High acceptance • Hermetic detector system • Higher energy • Better g-inefficiency • Constraints if possible. • Angular measurement of g.

  7. Goal • Present experimental limit : • Br ~ 5.9 x 10-7 (KTeV) Goal : • < 10-13 of the sensitivity • >100 SM events • Dh/h < 5% ⇒ High-intensity machine is necessary.

  8. J-PARC :Accelerator Complex 3x1014 ppp • Neutron • Muon

  9. Hadron Hall Layout Plan ← Phase 1 plan KL Phase 2 plan →

  10. Now Construction Schedule

  11. LOI • LOI was submitted for the J-PARC Kaon experiment: • L-05 : Measurement of the KL→p0nn Branching Ratio. [T.Inagaki(KEK)] Regarded as one of the highlight of experiment of the J-PARC Phase-1 by the facility committee. • Full proposal will be prepared within 2005.

  12. Sensitivity Estimation by MC • KL production target : • 50 GeV protons on 1 lI length of target. • 5° extraction to minimize n/KL ratio. • <pKL> ~ 6 GeV/c. • Neutral beamline : • 1.2 mstr of solid angle. n/KL ratio 50GeV protons 1 lIlength target 0 5 10 15 20 25 30 35 40 ext.angle(deg)

  13. Detector • 15m-long, 2m-f cylinder. • Located at z=50m to avoid BG from L→np0 decays. • Both of side- and endcap- calorimeters are the active g detectors. • Beam-anti completely dead due to high rate (~GHz).

  14. Event Selection Reconstruct p0 from two g’s by assuming p0-mass. • Signal : KL→p0nn • Background : KL→2p0, 2g-missing. Selection Criteria : • Eg> 100 MeV • 135 < pT < 240 MeV/c • Z-vertex: SS : 210 < z < 795 cm SE : 210 < z < 975 cm EE : 210 < z < 1050 cm (Determined to give best Dh/h) SS: Side-Side SE: Side-Endcap EE: Endcap-Endcap _ e = 1 for Eg<2 MeV

  15. Event Selection (cont’d) KL→p0nn KL→2p0 Zvtx Zvtx pT pT

  16. Sensitivity • At 2x1014 ppp intensity, • 1.8x1021 protons / 3 years(=3x107 sec) • 1.5x1015 KL / 3 years@ z=50m • 10 MHz of KL decay rate @ fiducial (52~60m) ⇒ Signal yield ~900 events/3years (3x10-14 of s.e.s). S/N ~ 3. → Dh/h ~ 4% (Optimization still underway)

  17. First run: Feb.18 – June 30, 2004 KEK PS-E391a : A pilot experiment

  18. E391a apparatus K0 beam line • Pencil beam • 2mrad of beam aperture =12mstr of solid angle. • Detector system in vacuum • Differential pumping • Whole detector system: low vacuum < 0.1Pa • Decay region: high vacuum ~ 10-5 Pa • Hermetic veto system • Double decay chamber • Reject KLdecay in front of fiducial region E391a detector n g g KL n

  19. Detector Integration Jan 22, 2004

  20. X-Y coe mass COE-X COE-Y Vertex Momentum Data taking Online monitoring using KL 3p0 decay 12 GeV incident protons 2.2 X 1012/spill at target 2s spill length 4s repetition KL Yield in front of detector 5x105 /spill peak momentum : 2 GeV/c DAQ live-time ratio : 75 % Vacuum pressure : 1X10-5 Pa

  21. Performance KL→3p0 Clean neutral beam s ~ 6 MeV/c2 KL→2p0

  22. E391a status & prospects • First physics run Feb-June this year • 2.21012 POT, 50% duty factor • 5 105 KL/pulse • Detector worked well • Analysis underway • Nominal s.e.s. ~ 410-10 • First sight of the enemy • Halo neutrons, self-vetoing, etc. • Second run proposed for next year. Good start for p0nn experiment.

  23. At Proton Driver What can we do after J-PARC experiment ? • 120 GeV, 2 MW beam at Proton Driver : • Intensity ~ 1.5x1014 ppp : Half of the J-PARC • Statistic enhancement might not be big. • Higher energy : • Better n/KL ratio, g-inefficiency → better S/N, Dh/h. • Optimum detector design might be different from J-PARC due to the decay kinematics of higher-energy KL : KAMI–type ? • ~1000 Event at 120GeV in 3 years (KAMI). • Huge (~100m of calorimeter cylinder). • …

  24. Summary • KL →p0nn decay is pure and clean mode to measure a basic parameter of the SM and to look for new physics. • At J-PARC 50 GeV PS, we will achieve the goal of <10-13 sensitivity (~900 SM events with S/N~3). • KEK PS-E391a, a pilot experiment, is the first dedicated experiment for this decay. Run-1 was successfully carried out from Feb. to June 2004. We are asking to double the statistics by Run-2 in 2005. • At Proton Driver, better S/N and Dh/h might be expected.

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