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Proposal to Measure the Rare Decay K +  p + n n at the CERN SPS

CERN-SPSC-2005-013 SPSC-P-326. Proposal to Measure the Rare Decay K +  p + n n at the CERN SPS. CERN, Dubna, Ferrara, Florence, Frascati, Mainz, Merced, Moscow, Naples, Perugia, Protvino, Pisa, Rome, Saclay, San Luis Potos i , Sofia, Turin.

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Proposal to Measure the Rare Decay K +  p + n n at the CERN SPS

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  1. CERN-SPSC-2005-013 SPSC-P-326 Proposal to Measure the Rare Decay K+p+ n n at the CERN SPS CERN, Dubna, Ferrara, Florence, Frascati, Mainz, Merced, Moscow, Naples, Perugia, Protvino, Pisa, Rome, Saclay, San Luis Potosi, Sofia, Turin P-326@SPSC73

  2. Physics Introduction:CKM matrix and CP-Violation Quark mixing is described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix KM mechanism: Ng=2 Nphase=0  No CP-Violation Ng=3 Nphase=1  CP-Violation Possible e.g., Im lt= Im Vts*Vtd ≠ 0  CP l=Vus Im lt = A2l5h Re lt = A2l5r The unitarity of the CKM matrix can be expressed by triangles in a complex plane. K+→p+nnis sensitive to |Vtd| P-326@SPSC73

  3. Physics Motivation • The Kobayashi-Maskawa mechanism appears to be the main (only?) source of CP-violation • Now look for inconsistencies in SM using independent observables affected by small theoretical uncertainties and different sensitivity to new physics • The rare process K+ p+nn belongs to the theoretically cleanest decays in the field of K- and B-mesons • It allows one to determine |Vtd|independently from B0-B0 mixing, thus providing a decisive test of the Standard Model P-326@SPSC73

  4. K→pnn : Theory in Standard Model charm contribution top contributions The Hadronic Matrix Element is measured and isospin rotated (~10% correction) P-326@SPSC73

  5. Predictions in SM This used to be the largest theoretical error (+/- 0.037). It was reduced by a NNLO calculation (Buras et al. hep-ph/0508165) The errors are due to the uncertainty of the CKM parameters and not to the hadronic uncertainties P-326@SPSC73

  6. Setting the bar for the next generation of K+→p+nn experiments E787/E949: BR(K+→ p+ nn ) = 1.47+1.30-0.89 × 10-10 Current constraint on r,hplane ? 100 events Mean=SM 100 events Mean=E787/949 P-326@SPSC73

  7. Some BSM Predictions P-326@SPSC73

  8. Other Physics Opportunities • The situation is similar to NA48, which was designed to measure “only” e’/e but produced many more measurements • Accumulating ~100 times the flux of NA48/2 will allow us to address, for instance: • Cusp like effects (p-p scattering) • K+ p0 p0 e+n • Lepton Flavour Violation K+ p+ m+ e- , K+p- m+ e+, (Ke2/Km2) • Search for new low mass particles • K+ p+ X • K+p+ p0 P (pseudoscalar sGoldstino) • Study rare p+ & p0 decays • Improve greatly on rare radiative kaon decays • Compare K+ and K- (alternating beam polarity) • K+/- p+/-p0g(CPV interference) • T-odd Correlations in Kl4 • And possibly, given the quality of the detector, topics in hadron spectroscopy P-326@SPSC73

  9. Principle of the measurement • Collect ~ 5 1012 Kaon decays/year from a secondary SPS hadron beam (K12) • high energy kaons: • high acceptance • good resolution • good photon detection efficiency • redundancy • pions and protons cannot be separated: • large rate in the beam tracker P-326@SPSC73

  10. P-326 Detector Layout p+ K+ ~11 MHz n 800 MHz beam p/K/p n P-326@SPSC73

  11. Background rejection • Guidance: S/B = 10~10-12 rejection • Kinematical rejection based on the missing mass: 2)Veto and Particle ID • g, m, charged particles • m – p - e separation P-326@SPSC73

  12. Backgrounds kinematically constrained Allows us to define the signal region 92% of K+ decays K+p+p0forces us to split it into two parts • Region I: 0 < m2miss < 0.01 GeV2/c4 • Region II: 0.026 < m2miss < 0.068 GeV2/c4 P-326@SPSC73

  13. Backgrounds not kinematically constrained They span accross the signal regions Must rely on Particle ID and veto 8% of K+ decays P-326@SPSC73

  14. Signal Acceptance • Acceptance (5 m < Zvertex < 65 m) • REGION I: 4% • REGION II: 13% • Total: 17% For safety, a 10% acceptance is quoted in the proposal P-326@SPSC73

  15. Signal & backgrounds from K decays / year P-326@SPSC73

  16. Summary • Signal events expected per year@BR=8 10-11 • 65 (16 Region I, 49 Region II) • Background events • ~9 (3 Region I, ~6 Region II) • Signal/Background ~ 8 • S/B (Region I) ~5 • S/B (Region II) ~ 9 For Comparison:In the written proposal we quoted 40 events/year@BR=10-10to account for some reconstruction and deadtime losses Backgrounds from beam scattering and interactions not included P-326@SPSC73

  17. Choice of positive beam • At 75 GeV/c from 400 GeV/c protons • K+/K- per proton ~ 2.1 • (K+/p+)/(K-/p-) ~ 1.2 • (K+/Total +ve)/(K-/Total –ve) ~ 1.0 4 3 2 Choice of K+ momentum: 7 = 5 x 6 5 (for 400 GeV/c proton momentum) 1 6 (reg. 1, no pp cut) P-326@SPSC73

  18. New high-intensity K+ beam for P-326 Already Available P-326@SPSC73

  19. Required vacuum in the decay tank • A FLUKA simulation led us to conclude that the vacuum should be better than 6 10-8 mbar to keep the background to less than one event per year • This figure can be relaxed by an order of magnitude by positively tagging the kaons • The best vacuum achieved in the current tank is about 10-5 mbar, compatible with the outgassing of painted steel • To reach the specified vacuum either a stainless steel tank or a new pumping system is required P-326@SPSC73

  20. CEDAR • Positive identification of Kaons is important to avoid mistaking a beam pion interaction in the residual gas as signal • Upgraded version of an existing West type CEDAR • Use H2 (3 bars) to reduce multiple scattering • Excellent time resolution (< 100 ps) is required • Use, for example, 8 Hamamatsu Linear Array H7260 (32 pixel/unit) as photon detectors to stand the high rate (50 MHz) 6 m P-326@SPSC73

  21. P-326@SPSC73

  22. qp PK Pp qK Gigatracker Provide precise measurements on all beam tracks (out of which only ~6% are K+) Provide very good time resolution Do not spoil beam and downstream measurements Sustain high, non-uniform rate ( 800 MHz total) • Instrument the 2nd beam achromat for redundant • momentum and angular measurement: • Two Silicon micro-pixel detectors (SPIBES) • Timing • Pattern Recognition • One FTPC (Improved KABES) • To minimise scattering in the last station SPIBES: X/X0 << 1% Pixel size ~ 300 x 300 mm s(p)/p ~ 0.4% s(t)GT ~100ps on the track:time coincidence to select the right kaon track P-326@SPSC73 22

  23. Required Gigatracker time resolution P(>1hit in Dt) =1-exp(-Dt*rate) Dt ( ±2s) @0.8GHZ @1GHZ 400 27% 33% 500 33% 39% 600 38% 45% K+p+p0 Dependence of the signal to background (from K+p+p0) as a function of the gigatracker time resolution P-326@SPSC73

  24. ➊ p+ p+ ➊ ➋ h e- n-sub n+ n+ n+ ➋ e- p-sub h p+ Gigatracker: SPIBES Front-End Simulation of signal collection: Alice pixel size (425 * 50 mm) Signal simulation: G4 v6.2 75 GeV/c K Si sensor 200 mm thick (e.g. ALICE SPD) at least 11000 e-/holes MeV Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/ED Groups with the ALICE SPD P-326@SPSC73

  25. SPIBES Read out Chip • To achieve the time resolution a very complex read-out chip bump-bonded on the sensor is needed (technology choice required: 0.25 vs. 0.13 mm CMOS) • Photolithographic process max 20-21mm wide chip • Beam spot adjusted to fit maximum chip size • GT area per pixel station: 36mm(X) x 48mm(Y) - 2 half detectors to cover the area w/o overalp • beam rate: high and not uniform 20-21 mm N chips 2-3mm I/O y Maximum rate in the hottest regions: (Normalized to total rate of 1GHz) ~1.5MHz/mm2 in station1, ~1.6MHz/mm2 in station2, ~1.9MHz/mm2 in station3 2mm/bin x 2mm/bin Station 1(pixels) 2(pixels) 3(FTPC) P-326@SPSC73 25

  26. KABES principle: TPC + micromegas Tdrift2 Micromegas Gap 25 μm Micromegas Gap 25 μm Tdrift1 FTPC (KABES) Pioneered in NA48/2 Tested in 2004 at high intensity (see Villars) Latest Developments: Signal occupancy with Gas Compass 50µm strip + V1 = 30 ns 50µm strip + FAMMAS = 22 ns 25µm strip + V1 = 22 ns 25µm strip + FAMMAS = 10 ns New electronic + 25µm mesh strip signal occupancy divided by 3 P-326@SPSC73

  27. Straw Tracker Advantages: • can (in principle) operate in vacuum decay volume • can be designed without internal frames and flanges • can work in high rate of hits • good space resolution (~130 m/hit for 9.6 straw) • small amount of material (~0.1% X0 per view) but no previous straw system has been operated in high vacuum P-326@SPSC73

  28. 12.5 m 0.2 m Al Glue – 5m 9.6 mm 25 m Gold plated Tungsten wire 30 m 2300 mm 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 Elements and Design 12 ns rise time 100 ns total width Polycarbonate spacer, 25 mg Two double layers form a view Gas mixture: 20%Ar+80%CO2 To fit easily into decay volume an octagonal shape is proposed k12hika+ (Niels)  About 2000 * 6 -> 12000 straws in total P-326@SPSC73

  29. Layout of the Straw Tracker • Holes in Straw-Chambers 5 cm radius • Chambers 3, 4, 5 and 6 are off-axis • Magnets: pt kick 270 and 360 MeV/c P(p-) = 60 GeV/c P(K+) = 75 GeV/c The off-axis layout in the bending plane is essential to reject K+ p+ p-e+ n decays in which the e+ is lost and the p- carries most of the kaon momentum P-326@SPSC73

  30. RICH Layout P-326@SPSC73

  31. RICH as velocity spectrometer…. Resolution of a 17m P-326 RICH (CKMGEANT) P-326@SPSC73

  32. …and RICH for p-m separation P-326@SPSC73

  33. MAMUD • To provide pion/muon separation and beam sweeping. • Iron is subdivided in 150 2 cm thick plates (260  260 cm2 ) • Two coils magnetise the iron plates to provide a 5 Tm field integral in the beam region • Active detector: • Strips of extruded polystyrene scintillator (as in Opera) • Light is collected by WLS fibres with 1.2 mm diameter Pole gap is 2 x 11 cm V x 30 cm H Coils cross section 10 cm x 20cm P-326@SPSC73

  34. Photon Vetoes P-326@SPSC73

  35. P-326@SPSC73

  36. Photon Vetoes P-326 Simulation: Allowed inefficiency/photon From: Ajimura et al., NIMA, in press P-326@SPSC73

  37. Energy of photons from K+ p+p0 hitting LKr: > 1 GeV GeV NA48 LKr as Photon Veto Urgent consolidation of the safety/control system is needed P-326@SPSC73

  38. Large Angle Vetoes (ANTI) • Two designs under test: • spaghetti (KLOE) • lead/scintillator sandwich (CKM) • Extensive simulation under way • A tagged photon beam is available in Frascati to test existing prototypes P-326@SPSC73

  39. Fast Hodoscope (MGG-RPCs) • To make tight time coincidence with gigatracker • Propose to use the Multi-gap Glass RPC (ALICE-TOF technology) • High rate tests are mandatory to validate performance up to 5 kHz/cm2 • A prototype PCB suitable for P-326 application is under fabrication ALICE-TOF ALICE-TOF P-326@SPSC73

  40. Trigger & DAQ • Total input to L0: 11 MHz • L0 (example): • > 1 hit hodoscope  73% • muon veto  24% • Photon Veto  18% • <2 EM quadrants & E<50 GeV  3% • L0 output: • 3% x 11 MHz = 330 KHz Keep: L0 + Control + Calibration + Spin-offs < 1 MHz • L1 in PC farm (à la LHCb) to keep as much flexibility as possible • Software trigger reduction ~40 P-326@SPSC73

  41. Cost Estimation (Materials) P-326@SPSC73

  42. Strengthening P-326 • The demise of the US kaon programme has triggered negotiations with members of KOPIO/CKM to join P-326 • The following groups have signed up since the proposal submission: • San Luis Potosi (Mexico, J. Engelfried) • Moscow, INR • Interest to join has been expressed by the following groups: • Fermilab (P. Cooper) • BNL (L. Littenberg, S. Kettell) • British Columbia (D. Bryman) • George Mason (P. Rubin) • It is our understanding that a possible participation of US groups is subject to: • DOE support towards a strong contribution to the construction of the detector (notably the RICH counter) • The involvement of US University in addition to National Labs P-326@SPSC73

  43. Status of R&D • A talk in itself, but in a nutshell: • Gigatracker (CERN/INFN TO/FE) • Study of sensors for fast signal collection • Study of chip architecture • Straw Tracker (Mainz/Dubna) • Study of prototype in vacuum • Photon vetoes (INFN, CERN, Protvino, Sofia) • Tests of existing prototypes with photon sources (Frascati) • Construction of prototypes for IRC/SAC • Use of LKr as photon detector (more data needed in 2006) • Fast Hodoscope (INFN FI/PG) • Investigation of MGG-RPC operated at high rate (≤5 KHz/cm2) • CEDAR (CERN) • Fast photon detectors P-326@SPSC73

  44. SPS Availability • There are two approved competitors for beam: LHC and CNGS • P-326 requires ~5 105 SPS pulses/year with 4.8 s flat top • For comparison, the Fixed Target request quoted in the Villars Report (SPSC-M-730) is 7.2 105 pulses/year • P-326 is completely compatible with the simultaneous running of COMPASS in the M2 beam line and with experiments and tests in the H2, H4, H6 and H8 beams P-326@SPSC73

  45. Beam Request 2006 • We request 30 days of K12 beam in 2006 to operate the NA48/2 hardware as P-326 test facility in order to: • Measure beam induced backgrounds • Measure LKr inefficiency collecting K+p+p0 • Test prototype elements of the new detectors • In addition we request that a standard (nitrogen gas-filled) CEDAR-W counter is made available in a beam to test the device with new, high rate, photon detectors P-326@SPSC73

  46. Timeline • 2006 • Tests in the present K12 beam • 2007-2008 • Construction, installation and tests of the new beam (2007) and new detectors (2007-2008) • 2009-2010 • Data Taking P-326@SPSC73

  47. Spares P-326@SPSC73

  48. Possibly the Cleanest SM test • In The phase b derives from Z0 diagrams (DS=1) whereas in A(J/y KS) originates in the box diagram (DB=2) • Any non-minimal contribution to Z0 diagrams would be signalled by a violation of the relation: • A deviation from the predicted rates of SM would be a clear indication of new physics • Complementary programme to the high energy frontier: • When new physics will appear at the LHC, the rare decays may help to understand the nature of it P-326@SPSC73

  49. Kaon Rare Decays and the SM |Vtd| Kaons provide quantitative tests of SM independent from B mesons… …and a large window of opportunity exists! Im lt = A2l5h Re lt = A2l5r G. Isidori P-326@SPSC73

  50. K+→p+nn : State of the art hep-ex/0403036 PRL93 (2004) AGS Stopped K ~0.1 % acceptance • BR(K+→ p+ nn ) = 1.47+1.30-0.89 × 10-10 • Compatible with SM within errors P-326@SPSC73

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