1. April 25, 2006Munich MPI1 Physics Introduction –Rare Kaon Decays in the SM…. –…and Beyond Flavour as a probe of New Physics complementary to the high energy frontier Experimental state-of-the-art –Recent results and world-wide perspectives Description of the CERN proposal P-326 –Technique –Status A Proposal to Study Rare Kaon Decays at the CERN SPS Augusto Ceccucci/CERN

2. April 25, 2006Munich MPI2 Quark Mixing and CP-Violation N g =2 N phase =0  No CP-Violation N g =3 N phase =1  CP-Violation Possible Cabibbo-Kobayashi-Maskawa (CKM) matrix: Non-diagonal (e.g. V us ≠0)  Flavour Violation 3 or more quark generations  CP-Violation in SM (KM) e.g., Im t = Im V ts *V td ≠ 0  CPV

3. April 25, 2006Munich MPI3 CKM Unitarity and Rare Kaon Decays The unitarity of the CKM matrix can be expressed by triangles in a complex plane. There are six triangles but one is more “triangular”: V ud V ub *+V cd V cb *+V td V tb *=0 It is customary to employ the Wolfenstein parameterization: V us ~ V cb ~   V ub ~   i  V td ~   i  Sensitive to |V td | Im t =  2 5  Re t =  2 5  CP

4. April 25, 2006Munich MPI4 Status of Unitarity Triangle Rare kaon decays are loop-dominated. They are a unique probe of the s  d transitions and provide independent CKM tests Sides+angles Sides vs. CPV

5. April 25, 2006Munich MPI5 The four golden modes of Kaon Physics Short-distance contrib (  sd /  ) Irreducible theory err. on amplitude Total SM BR K  L    >99%1% 3  10 -11 K     88%3% 8  10 -11 KLeeKLee 38%15% 3.5  10 -11 K  L       28%30% 1.5  10 -11 Adapted from G. Isidori @ Flavour in the LHC era, 5-7 Nov 05, CERN Short distance dynamics: – W-top quark loops constitute the dominant contribution: The EW short-distance amplitude is common in the SM… …but potentially different beyond SM Important to address all these decays

6. April 25, 2006Munich MPI6 K→  : Theory in Standard Model charm contribution top contributions The Hadronic Matrix Element is measured and isospin rotated NLO Calculation: Buchalla & Buras, 1993

7. April 25, 2006Munich MPI7 Predictions in SM This used to be the largest theoretical error (+/- 0.037). It was reduced by a NNLO calculation A. Buras, M. Gorbahn, U. Haisch, U. Nierste hep-ph/0508165) The errors are mostly due to the uncertainty of the CKM parameters and not to the hadronic uncertainties Standard Model predictions BR(K +  + )  (1.6×10 -5 )|V cb | 4 [  2 +(  c -  ) 2 ]  (8.0 ± 1.1)×10 -11 BR(K L  0 )  (7.6×10 -5 )|V cb | 4  2  ± 0.6  ×10 -11

8. April 25, 2006Munich MPI8 Theory vs. Experiment SM ObservableTheoretical errorExperimental error B(K  L    ~3%?? B(K     ~6%~75% A FB (B  X s l  l  ) ~8%?? B(B  X s  ) ~10%~9% B(B  X s l  l  ) ~13%~20% A FB (B  K ( * ) l  l  ) ~15%~30% B(B  (K ( * )  )  ) ~25%~40% B(B s      ) ~30%?? B(B  K*l  l  ) ~35%~13% Adapted from U. Haisch @ Flavour in the LHC era, 6-8 Feb 06, CERN

9. April 25, 2006Munich MPI9 Intrinsic theory error Combining information from BR(K  →   ) and BR(K  →   ) one obtains: (Buras et al. hep-ph/0508165) So for a 10% uncertainty on P c, one can extract, in priciple, a 3.4%  exp. determination of sin2  from kaon decays. It is currently 4.6% from B decays

10. April 25, 2006Munich MPI10 Beyond Standard Model Compare two scenarios: –Minimal Flavour Violation All mixing governed by universal CKM matrix –No Extra Complex Phases Same operators as in SM Different coefficients Stringent correlation with B rare decays –New sources of Flavour Symmetry Breaking ~ TeV scale Extra phases can lead to large deviations from SM predictions, especially for the CP-Violating modes

11. April 25, 2006Munich MPI11 MFV: Sensitivity to Z 0 Penguin from Bobeth et a. (2005)

12. April 25, 2006Munich MPI12 New Sources of Flavour Symmetry Breaking Generic MSSM Enhanced EW Penguins

13. April 25, 2006Munich MPI13 Experimental State-of-the-art

14. April 25, 2006Munich MPI14 K + →  + BR(K + →  + ) = 1.47 +1.30 -0.89 × 10 -10 Compatible with SM within errors hep-ex/0403036 PRL93 (2004) Stopped K + ~0.1 % acceptance AGS

15. April 25, 2006Munich MPI15 Setting the bar for the next generation of K + →  + experiments 100 events Mean=SM 100 events Mean=E787/949 Current constraint on  plane ? E787/E949: BR(K + →  + ) = 1.47 +1.30 -0.89 × 10 -10

16. April 25, 2006Munich MPI16 K 0 L     E391a Upper Limit BR(K 0 L    )<2.86  10 -7 90%CL Preliminary (Ken Sakashita@KAON2005)  6 improvement over KTeV one day special run  2 improvement over published limit (KTeV Dalitz technique) For the future: JPARC LOI-05 Recently, J-PARC made a call for proposals 10% of RUN I Pencil beam Expected background from K 0 L decays: 0.02 Acceptance: 0.73%

17. April 25, 2006Munich MPI17 K 0 S,L →  0 e  e  and K 0 S,L →  0     K S →  0  BR(K S →  0 ee)  10 -9 = 5.8 +2.8 -2.3 (stat) ± 0.8(syst) PLB 576 (2003) 7 events, expected back. 0.15 BR(K S →  0  )  10 -9 = 2.9 +1.4 -1.2 (stat) ± 0.2(syst) PLB 599 (2004) 6 events, expected back. 0.22 NA48/1 BR(K L →  0 ee ) < 2.8 × 10 -10 @90%CL KTeV PRL93, 021805 (2004) BR(K L →  0  ) < 3.8 × 10 -10 @90%CL KTeV PRL86, 5425 (2001)

18. April 25, 2006Munich MPI18 Constructive now favored by two independent analyses* (Isidori, Unterdorfer, Smith, EPJC36 (2004)) Destructive *G. Buchalla, G. D’Ambrosio, G. Isidori, Nucl.Phys.B672,387 (2003) *S. Friot, D. Greynat, E. de Rafael, hep-ph/0404136, PL B 595 * K 0 L →  0 ee (  ) in SM With the K S measurements, the K L BR can be predicted * Interference between short- and long-distance physics*

19. April 25, 2006Munich MPI19 Summary K +    –Already 3 clean events are published (E787/E949) –Experiment in agreement with SM within large errors –Next round of exp. need to collect O(100) events to be useful –Move from stopped to in flight technique (FNAL Proposal turned down by P5) –Proposal for in-flight decays: CERN P-326 –Letter of Intent at J-PARC to continue the study with decays at rest K 0 L    –Large window of opportunity exists. –Upper limit is 4 order of magnitude from the SM prediction –First results E391a (proposed SES~3 10 -10 ) –Proposal being prepared to continue at J-PARC –KOPIO TERMINATED K 0 L    ee(  ) –Long distance contributions under good control –Measurement of K S modes has allowed SM prediction –K S rates to be better measured –Background limited (study time dep. Interference?) –100-fold increase in kaon flux to be envisaged

20. April 25, 2006Munich MPI20 Proposal to Measure the Rare Decay K     at the CERN SPS CERN, Dubna, Ferrara, Florence, Frascati, Mainz, Merced, Moscow, Naples, Perugia, Protvino, Pisa, Rome, Saclay, San Luis Potosi, Sofia, Turin CERN-SPSC-2005-013 SPSC-P-326

21. April 25, 2006 Munich MPI 21 Background rejection Guidance: S/B = 10 ~10 -12 rejection 1) Kinematical Rejection 2) Photon vetoes and PID (  ) Basic idea to reject K +  +  0 P(K  ) = 75 GeV/c Require P(   ) < 35 GeV/c P(   ) > 40  GeV/c It cannot be missed in the calorimeter/photon veto

22. April 25, 2006 Munich MPI 22 Backgrounds kinematically constrained DecayBR K +    K  2 )0.634 K +  +  0 0.211 K +  +  +  - K +    0  0 0.070 92% of K + decays Allows us to define the signal region K   +  0 forces us to split it into two parts Region I: 0 < m 2 miss < 0.01 GeV 2 /c 4 Region II: 0.026 < m 2 miss < 0.068 GeV 2 /c 4

23. April 25, 2006 Munich MPI 23 Backgrounds not kinematically constrained Decay BR K +  0 e + (K e3 ) 0.049 K3K3K3K3 0.033 K2K2K2K2 5.5×10 -3 +0K++0+0K++0 1.5×10 -3 K e4 4×10 -5 K4K4K4K4 1×10 -5 8% of K + decays They span accross the signal regions Must rely on Particle ID and veto

24. April 25, 2006Munich MPI24 P-326 Detector Layout 75 GeV/c 800 MHz beam  /K/p K+K+ ++ ~11 MHz Gigatracker (KABES) K    

25. April 25, 2006Munich MPI25 P-326 Detector Layout 75 GeV/c 800 MHz beam  /K/p K+K+ ++   ~11 MHz Gigatracker (KABES) KK

26. April 25, 2006 Munich MPI 26 Signal & backgrounds from K decays / year TotalRegion IRegion II Signal651649 K++0K++0 2.7±0.21.7±0.21.0±0.1 K2K2 1.2±0.31.1±0.3<0.1 K e4 2±2negligible2±2 K   +  +   and other 3-tracks bckg. 1±1negligible1±1 22 1.3±0.4negligible1.3±0.4 K2K2 0.4±0.10.2±0.1 K e3, K  3,others negligible  Total bkg9±33.0±0.26±3

27. April 25, 2006 Munich MPI 27 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 -10 to account for some reconstruction and deadtime losses

28. April 25, 2006Munich MPI28 Beam: Present K12 (NA48/2) New HI K + > 2006 Factor wrt 2004 SPS protons per pulse on T101 x 10 12 3 x 10 12 3.0 Duty cycle (s./s.)4.8 / 16.8 1.0 Solid angle (  sterad)  0.40  16 40 Av. K + momentum (GeV/c)6075 K + ~ 1.5 Mom. band RMS: (  p/p in %)  4  1 ~0.25 Area at Gigatracker (cm 2 )  7.0  14  2.0 Total beam per pulse (x 10 7 ) per Effective spill length MHz MHz/cm 2 (gigatracker) 5.5 18 2.5 250 800 60 ~45 (~27) ~24(~15) Eff. running time / yr (pulses)3 x 10 5 1.0 K + decays per year1.0x10 11 4.8x10 12  48 New high-intensity K + beam for P-326 Already Available

29. April 25, 2006Munich MPI29 Decay Tank Specification: 10 -6 mbar –Study performed with Monte Carlo using Fluka and Gheisha to simulate the hadronic interactions with the residual gas. Measurements: –Vacuum test performed on the existing tube of NA48. –A 10 -5 mbar level reached with only 1 pump. –With a few 50000 l/s diffusion or cryogenics pumps the requested vacuum level can be achieved Conclusions: –The existing decay tank can be used

30. April 25, 2006Munich MPI30 Gigatracker 30 X/X 0 << 1% Pixel size ~ 300 x 300  m  (p)/p ~ 0.4% excellent time resolution to select the right kaon track Provide precise measurements on all beam tracks (out of which only ~6% are K + ) Provide very good time resolution Minimise mass (multiple scattering and beam interactions) Sustain high, non-uniform rate ( 800 MHz total) PP PKPK   Two Silicon micro-pixel detectors (SPIBES) Timing Pattern Recognition Improved KABES (micromegas TPC) To minimise scattering in the last station SPIBES: Dependence of the signal to background (from K +      ) ratio as a function of the gigatracker time resolution

31. April 25, 2006Munich MPI31 SPIBES (Hybrid Pixel) 200  m Silicon sensor (>11 000 e/h mip) –Following Alice SPD –Bump-bonding Read-out chip –Pixel 300  m x 300  m –Thinned down to ~100  m (Alice SPD 150  m) Beam surface ~ 14 cm 2 –Adapted to the size of the SPIBES r-o chips ~125  m Cfibre for cooling & support y x 2mm/bin Station 1(pixels) 2(pixels) 3(FTPC) G. Anelli, M. Scarpa, S. Tiuraniemi Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/ED Groups with the ALICE SPD MeV

32. April 25, 2006Munich MPI32 FTPC (KABES) T drif t1 T drift2 Micromegas Gap 25 μm Micromegas Gap 25 μm KABES principle: TPC + micromegas Pioneered in NA48/2 Tested in 2004 at high intensity with 1 GHz FADC In NA48/2 KABES has achieved: Position resolution ~ 70 micron Time resolution ~ 0.6 ns Rate per micro-strip ~ 2 MHz New electronic + 25µm mesh strip signal occupancy divided by 3

33. April 25, 2006Munich MPI33 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% X 0 per view) but no previous large straw system has been operated in high vacuum Straw Tracker

34. April 25, 2006 Munich MPI 34 Downstream straw tracker 6 chambers with 4 double layers of straw tubes each (  9.6 mm) Rate: ~45 KHz per tube (max 0.5 MHz) (  +  ) Low X/X 0 Operate in high vacuum X/X 0 ~ 0.1% per view Good space resolution 130  m / hit  (P)/P = 0.23%  0.005%P  (  ) ~ 50  20  rad Redundant momentum measurement 2 magnets: 270 and 360 MeV P t kick 8.8 m 7.2 m 5.4 m Veto for charged negative particles up to 60 GeV/c 5 cm radius beam holes displaced in the bending plane according to the 75 GeV/c beam path z x y 2.3 m

35. April 25, 2006Munich MPI35 RICH Layout

36. April 25, 2006Munich MPI36 RICH as velocity spectrometer…. Resolution of a 17m P-326 RICH (CKMGEANT)

37. April 25, 2006Munich MPI37 …and RICH for  -  separation

38. April 25, 2006Munich MPI38 NA48 LKr as Photon Veto Energy of photons from K       hitting LKr: > 1 GeV GeV Consolidation of the safety/control system and read-out under way

39. April 25, 2006Munich MPI39 LKr efficiency measured with data Cluster not reconstructed E  = 22 GeV Pion P=42 GeV/c Photon E=11 GeV Expected position K +      collected by NA48 in 2004 Events are kinematically selected.   track and lower energy  are use to predict the position of the other  +00+00

40. April 25, 2006Munich MPI40 Example: “hadronic” cluster of a photon Expected  position Maximum energy ~300 MeV Expected energy: ~29 GeV Deposited energy: ~9 GeV Measured LKr inefficiency per photon (E g > 10 GeV):  = (2.8 ± 1.1 stat ± 2.3 syst ) × 10 -5 (preliminary)

41. April 25, 2006Munich MPI41 Beam test 2006 Idea for measuring inefficiency in the range 2 GeV < E  < 10 GeV –Use of the NA48 set-up. –Photons produced by bremsstrahlung. –SPS can provide a suitable electron beam. vacuum Electron beam (25 GeV/c) Bremsstrahlung Kevlar window Drift chambers Magnet Calorimeter  e- Calorimeter inefficiency below E  < 5 GeV is not critical Beam test foreseen during the 2006 SPS run

42. April 25, 2006Munich MPI42 ANTI-Photon Rings From: Ajimura et al., NIMA 552 (2005) 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

43. April 25, 2006Munich MPI43 Other Physics Opportunities The situation is similar to NA48, which was designed to measure “only”  ’/  but produced many more measurements Accumulating ~100 times the flux of NA48/2 will allow us to address, for instance: 1.Cusp like effects (  scattering) –K       e  2.Lepton Flavour Violation K        e , K       e +, (K e2 /K  2 ) 3.Search for new low mass particles –K      X –K       P (pseudoscalar sGoldstino) 4.Study rare     decays 5.Improve greatly on rare radiative kaon decays 6.Compare K + and K - (alternating beam polarity) –K        (CPV interference) –T-odd Correlations in K l4 7.And possibly, given the quality of the detector, topics in hadron spectroscopy

44. April 25, 2006Munich MPI44 Status of P-326 (a.k.a. NA48/3) Presented at the CERN SPSC in September 2005 –Strong endorsement of the Physics Case –Review of the proposed technique 2006 R&D plan endorsed by CERN RB on December 05 –Resources being appropriated Beam Test foreseen in Sept-Oct 2006 –Measure LKr efficiency for 1-10 GeV photons –Equip a CEDAR counter with fast read-out Collaboration still open to new groups –RICH responsibility Seeking full approval by end of 2006…. –Enter CERN Medium Term Plan …to be able to start data taking some time in 2009-2010

45. April 25, 2006Munich MPI45 Summary Clear physics case –The discovery of New Physics will dramatically increase the motivation for searches of new flavour phenomena Healthy competition worldwide: – J-PARC   SPS Exploit synergies and existing infrastructures NA48  ’ /   NA48/1 K S rare decays  NA48/2  g/g in K  3   P-326      SPS –SPS used as LHC injector (so it will run in the future) –No flagrant time overlap with CNGS –P-326 fully compatible with the rest of CERN fixed target because P-326 needs only ~1/20 of the SPS protons Join us!

46. April 25, 2006Munich MPI46 Spare Slides

47. April 25, 2006Munich MPI47 Direct CP-violation in K        K        |M(u,v)| 2 ~ 1 + gu + hu 2 + kv 2 Centre of mass frame u = 2m K ∙(m K /3-E odd )/m  2 ; v = 2m K ∙(E 1 -E 2 )/m  2. Measured quantity sensitive to direct CP violation: Slope asymmetry: A g = (g + -g - )/(g + +g - )≠0 Lorentz-invariants u = (s 3 -s 0 )/m  2 ; v = (s 2 -s 1 )/m  2 ; s i = (P K -P  i ) 2, i=1,2,3 (3=odd  ); s 0 = (s 1 +s 2 +s 3 )/3. SM estimates vary within an order of magnitude few 10 -6 …8x10 -5 (few 10 -6 …8x10 -5 ). Models beyond SM predict substantial enhancement

48. April 25, 2006Munich MPI48 Selected Statistics 2003 U |V| even pion in beam pipe Data-taking 2003: 1.61x10 9 1.61x10 9 events selected K + : 1.03x10 9 events K  : 0.58x10 9 events  odd pion in beam pipe  M =1.7 MeV/c 2 Events

49. April 25, 2006Munich MPI49 Stability and Systematics Systematic uncertainties Effect on Δx10 4 Acceptance and beam geometry 0.3 Spectrometer alignment0.1 Analyzing magnet field0.1 π ±  decay 0.4 U calculation and fitting0.2 Pile-up0.2 Total systematics0.6 Trigger efficiency: L20.5 Trigger efficiency: L10.4 Control of Detector asymmetry Control of Beamline asymmetry Jura Jura(Left) A+ A- Salève(Right) Z XY Achromats: K + Up Achromats: K + Down B+ B-B-B-B-

50. April 25, 2006Munich MPI50 NA48/2 (2003 data) K        Slope difference: Δg = (-0.7±0.9 stat. ±0.6 stat.(trig.) ±0.6 syst. )x10 -4 = (-0.7±1.0)x10 -4 Charge asymmetry: A g = (1.7±2.1 stat. ±1.4 stat.(trig.) ±1.4 syst. )x10 -4 = (1.7±2.9)x10 -4 K        Slope difference: Δg = (2.3 ± 2.8 stat. ± 1.3 trig.(stat.) ± 1.0 syst. ± 0.3 ext. )x10 -4 = (2.2 ± 3.1)x10 -4 Charge asymmetry: Charge asymmetry: [using g 0 =0.638 ] A 0 g = (1.8 ± 2.2 stat. ± 1.0 trig.(stat.) ± 0.8 syst. ± 0.2 ext. )x10 -4 = (1.8 ± 2.6)x10 -4 hep-ex/0602014; PLB 634 (2006) Order of magnitude improvement

51. April 25, 2006Munich MPI51 Observation of  scattering effect in K→3  decays 1 bin = 0.00015 GeV 2 K ±  ±  0  0 4m π + 2 30M events 4m π + 2 NA48/2 has made the first observation the of the charge exchange process  +    0  0 in the K   0  0   decay. M 2 (  0  0 ) (GeV/c 2 ) 2 NA48/2 PLB 633 (2006) hep-ex/0511056 N. Cabibbo, hep-ph/0405001 PRL 93121801 (2004) N. Cabibbo and G. Isidori, hep-ph/0502130 JHEP 503 (2005)  ~|M 0 +M 1 | 2

52. April 25, 2006Munich MPI52 Difference between  scattering length in I=0 and I=2 states (a 0 – a 2 )m + = 0.268 ± 0.010(stat) ± 0.004(syst) ± 0.013(theor) In agreement with theory (a 0 – a 2 )m + = 0.265 ± 0.004 (Colangelo 2001) NA48/2 PLB 633 (2006) hep-ex/0511056

53. April 25, 2006Munich MPI53 hep-ph/0511289 NA48/2 EPS05 R K =  (K   e  ) /  (K    

54. April 25, 2006Munich MPI54 MAMUD Pole gap is 2 x 11 cm V x 30 cm H Coils cross section 10 cm x 20cm To provide pion/muon separation and beam sweeping. –Iron is subdivided in 150 2 cm thick plates (260  260 cm 2 ) 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

55. April 25, 2006Munich MPI55 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 Important synergies with LHC to be exploited: for instance, the LHCb TELL1 board

56. April 25, 2006Munich MPI56 NA48@CERN 1997 1998 1999 2000 2001 2002 2003 NA48:  ’/   ’/   ’/  lower inst. intensity NA48/1 K S NA48/1: K S KLKL no spectrometer NA48/2: K  1996 2004 NA48/2: K  Re  ’/  = 14.7 ± 2.2  10 -4 First observation of K 0 S →  0 e  e  and K 0 S →  0     Ave: Re  ’/  = 16.7 ± 2.3  10 -4 + K L Rare Decays Search for Direct CP-Violation in charged kaon decays  scattering: PLB 633 (2006) (a 0 -a 2 )m + = 0.268 +/- 0.017 Direct CP-Violation established

57. April 25, 2006Munich MPI57 Glue – 5  m 12.5  m 0.2  m Al 9.6 mm25  m Gold plated Tungsten wire 30  m Straw Elements and Design 8.8 m186.3 m from T0 5.4 m 7.2 m k12hika+ (Niels)  About 2000 * 6 -> 12000 straws in total 3 coordinates 4 coordinates 2 coordinates 1 coordinate 10 cm 2300 mm To fit easily into decay volume an octagonal shape is proposed Two double layers form a viewGas mixture: 20%Ar+80%CO 2 12 ns rise time 100 ns total width Polycarbonate spacer, 25 mg

58. April 25, 2006Munich MPI58 hep-ph/0511289

59. April 25, 2006Munich MPI59 [1] Helicity suppressed decay : Physics Motivation : left-handed (in SM): spin 0 (A) Neutrino mass : implies. [3] Cosmological Interests Neutron star cooling model through pion pole mechanism : (B) Neutrino type : Majorana neutrino  x2 larger branching ratio. [2] Decay Form of (B) Decay into different neutrino flavors : (A) Sensitive to any hypothetical weakly-interacting neutrals.  0 copiously collected from K +     

60. April 25, 2006Munich MPI60 New upper limit (E949) : A factor of 3 improvement from the previous best result. Branching Ratio # signal < 113 (90%CL) subtracting the non-K  2 bkgnds; Conservative upper limit 2/3 sample Saturation at 3.5x10 6 1/3 sample