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THE CERN Experiment P326 for Rare Kaon Decays

THE CERN Experiment P326 for Rare Kaon Decays. Massimo Lenti INFN Sezione di Firenze. Outline of the presentation. Physics motivations for K + → p + nn The beam The main background channels The apparatus The signal acceptance and S/B Time schedule and Conclusions.

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THE CERN Experiment P326 for Rare Kaon Decays

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  1. THE CERN Experiment P326for Rare Kaon Decays Massimo Lenti INFN Sezione di Firenze

  2. Outline of the presentation • Physics motivations for K+→p+nn • The beam • The main background channels • The apparatus • The signal acceptance and S/B • Time schedule and Conclusions M. Lenti

  3. Physics motivations for K+→p+nn CP • Standard Model predictions • BR(K+p+nn)  (1.6×10-5)|Vcb|4[sh2+(rc-r)2]  (8.0 ± 1.1)×10-11 • BR(KLp0nn)  (7.6×10-5)|Vcb|4h2  (3.0 ± 0.6)×10-11 M. Lenti

  4. Physics motivations, II • Theoretically very clean • Sensitive to Vtd • Very sensitive to New Physics • Present (E787/949):BR(K+p+nn) = 1.47 ×10-10 with 3 events +1.30 -0.89 Need a 10% measurement (100 events): P326 M. Lenti

  5. How many K+ decays? ] ~1013 K+ decays • BR(K+→p+nn) ~ 8×10-11 • Look for ~100 signal events • Signal acceptance ~ 10% NA48/P326 Use the existing CERN accelerators Use the existing NA48 experimental hall M. Lenti

  6. The Beam • Primary Beam: • 400 GeV/c protons • 3×1012 protons/pulse (3×NA48/2) • 4.8/16.8 s duty cycle • Secondary Beam: • 75 GeV/c momentum (Dp/p~1%) • Beam acc.: 15 mstr(30×NA48/2) • Total rate: 800 MHz • K+ ~ 6% • 4.8×1012 K+decays/y M. Lenti

  7. The Beam purity • Only 6% K+ but: • protons and electrons don’t decay... • pions and muons decays cannot mimic K+ decays • but beam-gas interactions !! Keep vacuum at 10-6 mbar: use existing NA48 decay tank (already directly measured) Tag the K+ in the beam: use a CEDAR M. Lenti

  8. The CEDAR The CEDAR is a Cherenkov counter Used at CERN since long time Vary gas pressure and diaphragm aperture to select K+ November 2006: test beam with a CEDAR 100 GeV/c beam Filled with Nitrogen Adapt to P326 needs: Fill with Hydrogen Change Phototubes and electronics Pions Protons Kaons M. Lenti

  9. p Kinematics qKp K+ n n m2miss=(PK-Pp)2 92% K+ decays 8% K+ decays PK : beam spectrometer Pp: straw chambers spectrometer M. Lenti

  10. Beam Spectrometer (I) Achromat CEDAR Achromat p Gigatracker • 3 Silicon Pixels stations across the 2nd Achromat: • 36(X) × 48(Y) mm per station • Beam rate: 800 MHz (“Gigatracker”), 50 MHz/cm2 M. Lenti

  11. Beam Spectrometer (II) s(PK)/PK ~ 0.4% s(qK) ~ 16 mrad • 300×300 mm pixels • 200 mm Si sensor + 100 mm chip • 0.13 mm CMOS technology Low X/X0 s(t) ~ 200 ps/station Important for beam pile-up Strong R&D ongoning... M. Lenti

  12. 3 coordinates 4 coordinates 2 coordinates 1 coordinate 5.4 m 5.4 m 10 cm 186.3 m from T0 8.8 m 7.2 m 7.2 m Straw Chambers Spectrometer Gas CF4-CO2-isoC4H10 • 6 chambers with 4 double layers • Ø 9.6 mm straw tubes in vacuum • 0.1% X0 per view • 130 mm hit resolution per view • 2 magnets (270 and 360 MeV/c pt kick) • holes follow beam path M. Lenti

  13. Kinematics Reco. qpK qp PK qK Pp Missing mass measurement: dominated by angle between Kaon and pion Double spectrometer: almost independent momentum measurement M. Lenti

  14. Background 1: K+→m+n (Km2) • Largest BR: 63.4% • Need ~10-12 rejection factor • Kinematics: 10-5 • Muon Veto: 10-5 • Particle ID: 5×10-3 MAMUD RICH M. Lenti

  15. Muon Veto: MAMUD MAgnetized MUon Detector Sampling calorimeter + Magnet for beam deflection Em/hadronic clusters separation Sensitivity to MIP 10-5m detection inefficiency M. Lenti

  16. RICH • p-m 3s separation up to 35 GeV/c • 18 m long • Neon at 1 atm (p thr.: 12 GeV/c) • 2000 PMT • 18 mm granularity • 100 ps resolution (to disentangle • pileup in the Gigatracker) • PMTs tested in 2006 CEDAR test • Prototype test beam in 2007 M. Lenti

  17. Background 2: K+→p+p0 (Kp2) 2nd Largest BR:20.9% • Need ~10-12rejection factor • Kinematics: 5×10-3 • Photon Veto: 10-5per photon • Large angle:13ANTIs (10 < acceptance < 50 mrad) • Medium angle:NA48 LKr (1 < acceptance < 10 mrad) • Small angle: IRC1,2 SAC (acceptance < 1 mrad) M. Lenti

  18. Large Angle Veto • 13 ring em calorimeters in vacuum • 10-4ineff. 0.05<Eg<1 GeV • 10-5 ineff. Eg>1 GeV • Two options under test: • lead-scint. tiles read by WLS fibers • lead+scint.fibers (KLOE like) Prototypes under constructions Tests at Frascati tagged photon beam M. Lenti

  19. Small Angle Veto • shaslyk calorimeter on the beam axis • 10-5ineff. High energy g Tested in October 2006 In the NA48 tagged photon beam (see later) M. Lenti

  20. Liquid Kripton Calorimeter • Use the existing NA48 LKr calorimeter • 10-5 ineff. Eg>5 GeV • 10-4 ineff. 1<Eg<5 GeV Ineff. for Eg>10 GeV tested on data collected by NA48/2 (K+→p+p0) p g g M. Lenti

  21. Liquid Kripton Calorimeter (II) Kevlar window Magnet Calorimeter October 2006 test: Tagged photon beam Using the existing NA48 setup vacuum e- g Electron beam (25 GeV/c) Bremsstrahlung Drift chambers Energy deposition in LKr electron • 2×108 electrons collected • 10-5 ineff.sensitivity below 10 GeV g Energy GeV M. Lenti X LKr cm

  22. The P326 Layout 11 MHz 800 MHz 50 MHz M. Lenti

  23. Signal Acceptance Region I: 0<mmiss2<0.01 GeV2/c4 Region II: 0.026<mmiss2<0.068 GeV2/c4 Remind: Km2mmiss2 < 0 Kp2mmiss2 = 0.0182 GeV2/c4 Momentum range: 15 <pp< 35 GeV/c Fiducial decay region: 60 m Acceptance: 4% (Region I), 13% (Region II): 17% (I+II) 10% goal feasible (after analysis cuts, etc.) M. Lenti

  24. Signal/Background • S/B ~ 8 (Region I ~5, Region II ~9) M. Lenti

  25. Trigger Levels • 11 MHzL0 trigger input • 1track × m! × g! → 1 MHzL1 trigger input → PC farm • Software trigger reduction ~ 40 M. Lenti

  26. Conclusions • 2006-2007: R&D, test beam • 2008-2010: Construction • 2011: start data-taking • Full approval and funding expected end of 2007 • Still need to strengthen the collaboration • Clear Physics case • many other physics channels M. Lenti

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