A proposal to Study Rare Kaon Decays at

A proposal to Study Rare Kaon Decays at the CERN SPS Augusto Ceccucci/CERN • 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 March 27, 2006 Saclay - Orsay 1

Quark Mixing and CP-Violation Cabibbo-Kobayashi-Maskawa (CKM) matrix: • Non-diagonal (e. g. Vus ≠ 0) Flavour Violation • 3 or more quark generations CP-Violation in SM (KM) Ng=2 Nphase=0 No CP-Violation Ng=3 Nphase=1 CP-Violation Possible e. g. , Im lt= Im Vts*Vtd ≠ 0 CPV March 27, 2006 Saclay - Orsay 2

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”: Vud. Vub*+Vcd. Vcb*+Vtd. Vtb*=0 It is customary to employ the Wolfenstein parameterization: Vus ~ l Vcb ~ l 2 A Vub ~ l 3 A(r ih) Vtd ~ l 3 A(1 r ih) CP Sensitive to |Vtd| Im lt = A 2 l 5 h Re lt = A 2 l 5 r March 27, 2006 Saclay - Orsay 3

Status of Unitarity Triangle Sides vs. CPV Sides+angles Rare kaon decays are loop-dominated. They are a unique probe of the s d transitions and provide independent CKM tests March 27, 2006 Saclay - Orsay 4

The four golden modes of Kaon Physics Short-distance contrib (Gsd /G) Irreducible Total SM BR theory err. on amplitude K 0 L p 0 n n >99% 1% 3 10 -11 K+ p+ n n 88% 3% 8 10 -11 K 0 L p 0 e+e- 38% 15% 3. 5 10 -11 K 0 L p 0 m+m- 28% 30% 1. 5 10 -11 • 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 Adapted from G. Isidori @ Flavour in the LHC era, 5 -7 Nov 05, CERN March 27, 2006 Saclay - Orsay 5

K→p nn : Theory in Standard Model charm contribution top contributions The Hadronic Matrix Element is measured and isospin rotated March 27, 2006 Saclay - Orsay 6

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) Standard Model predictions BR(K+ +nn) (1. 6× 10 -5)|Vcb|4[sh 2+(rc-r)2] (8. 0 ± 1. 1)× 10 -11 BR(KL 0 nn) (7. 6× 10 -5)|Vcb|4 h 2 (3. 0 ± 0. 6)× 10 -11 The errors are mostly due to the uncertainty of the CKM parameters and not to the hadronic uncertainties March 27, 2006 Saclay - Orsay 7

Theory vs. Experiment SM Observable Theoretical error Experimental error B(K 0 L p 0 n n) ~3% ? ? B(K+ p+ n n) ~6% ~75% AFB(B Xsl+l-) ~8% ? ? B(B Xsg) ~10% ~9% B(B Xsl+l-) ~13% ~20% AFB(B K(*)l+l-) ~15% ~30% B(B (K(*), r, w)g) ~25% ~40% B(Bs m+m-) ~30% ? ? B(B K*l+l-) ~35% ~13% Adapted from U. Haisch @ Flavour in the LHC era, 6 -8 Feb 06, CERN March 27, 2006 Saclay - Orsay 8

Intrinsic theory error Combining information from BR(K+→p+ nn ) and BR(K 0→p 0 nn ) one obtains: (Buras et al. hep-ph/0508165) So for a 10% uncertainty on Pc, one can extract, in priciple, a 3. 4% exp. determination of sin 2 b from kaon decays. It is currently 4. 6% from B decays March 27, 2006 Saclay - Orsay 9

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 ~ Te. V scale • Extra phases can lead to large deviations from SM predictions, especially for the CP-Violating modes March 27, 2006 Saclay - Orsay 10

MFV: Sensitivity to Z 0 Penguin from Bobeth et a. (2005) March 27, 2006 Saclay - Orsay 11

New Sources of Flavour Symmetry Breaking Generic MSSM March 27, 2006 Enhanced EW Penguins Saclay - Orsay 12

Experimental State-of-the-art March 27, 2006 Saclay - Orsay 13

K+→p+ nn hep-ex/0403036 PRL 93 (2004) AGS Stopped K+ ~0. 1 % acceptance BR(K+ → p+ nn ) = 1. 47+1. 30 -0. 89 × 10 -10 • Compatible with SM within errors March 27, 2006 Saclay - Orsay 14

Setting the bar for the next generation of K+→p+nn experiments E 787/E 949: BR(K+ → p+ nn ) = 1. 47+1. 30 -0. 89 × 10 -10 Current constraint on r, h plane ? 100 events Mean=SM 100 events Mean=E 787/949 March 27, 2006 Saclay - Orsay 15

K 0 L p 0 nn : E 391 a Upper Limit 10% of RUN I • Pencil beam • Expected background from K 0 L decays: 0. 02 • Acceptance: 0. 73% BR(K 0 L p 0 nn )<2. 86 10 -7 90%CL Preliminary (Ken Sakashita@KAON 2005) 6 improvement over KTe. V one day special run 2 improvement over published limit (KTe. V Dalitz technique) • For the future: JPARC LOI-05 • Recently, J-PARC made a call for proposals March 27, 2006 Saclay - Orsay 16

K 0 S, L →p 0 e+e- and K 0 S, L →p 0 m+m. BR(KS→p 0 ee) 10 -9 = 5. 8 +2. 8 -2. 3(stat) ± 0. 8(syst) BR(KS→p 0 mm) 10 -9 = 2. 9 +1. 4 -1. 2(stat) ± 0. 2(syst) PLB 576 (2003) PLB 599 (2004) KS →p 0 mm NA 48/1 6 events, expected back. 0. 22 7 events, expected back. 0. 15 BR(KL → p 0 ee ) < 2. 8 × 10 -10 @90%CL BR(KL → p 0 mm ) < 3. 8 × 10 -10 @90%CL March 27, 2006 NA 48/1 Saclay - Orsay KTe. V PRL 93, 021805 (2004) KTe. V PRL 86, 5425 (2001) 17

K 0 L→p 0 ee (mm) in SM With the KS measurements, the KL BR can be predicted * Interference between short- and long-distance physics* (Isidori, Unterdorfer, Smith, EPJC 36 (2004)) Constructive now favored by two independent analyses* Destructive *G. Buchalla, G. D’Ambrosio, G. Isidori, Nucl. Phys. B 672, 387 (2003) *S. Friot, D. Greynat, E. de Rafael, hep-ph/0404136, PL B 595 * March 27, 2006 Saclay - Orsay 18

Summary • • • K+ p+nn – – – Already 3 clean events are published (E 787/E 949) Experiment in agreement with SM within 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 P 5) Proposal for in-flight decays: CERN P-326 Letter of Intent at J-PARC to continue the study with decays at rest – – – Large window of opportunity exists. Upper limit is 4 order of magnitude from the SM prediction First results E 391 a (proposed SES~3 10 -10) LOI to continue at J-PARC KOPIO TERMINATED – – – Long distance contributions under good control Measurement of KS modes has allowed SM prediction KS rates to be better measured Background limited (study time dep. Interference? ) 100 -fold increase in kaon flux to be envisaged K 0 L p 0 nn K 0 L p 0 ee(mm) March 27, 2006 Saclay - Orsay 19

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 March 27, 2006 Saclay - Orsay 20

Background rejection • Guidance: S/B = 10 1) Kinematical Rejection ~10 -12 rejection 2) Photon vetoes and PID ( ) Basic idea to reject K+ p+p 0 P(K+) = 75 Ge. V/c Require P( +) < 35 Ge. V/c P( 0) > 40 Ge. V/c It cannot be missed in the calorimeter/photon veto March 27, 2006 Saclay - Orsay 21

Backgrounds kinematically constrained Decay BR K+ + (K 2) 0. 634 K+ + 0 0. 211 K+ + + K+ + 0 0 0. 070 Allows us to define the signal region 92% of K+ decays K+ p+p 0 forces us to split it into two parts Region I: 0 < m 2 miss < 0. 01 Ge. V 2/c 4 Region II: 0. 026 < m 2 miss < 0. 068 Ge. V 2/c 4 March 27, 2006 Saclay - Orsay 22

Backgrounds not kinematically constrained Decay K+ 0 e+ (Ke 3) K 3 BR 0. 049 0. 033 K 2 g 5. 5× 10 -3 K+ + 0 g 1. 5× 10 -3 Ke 4 K 4 4× 10 -5 1× 10 -5 8% of K+ decays March 27, 2006 They span accross the signal regions Must rely on Particle ID and veto Saclay - Orsay 23

P-326 Detector Layout K+ p+ n n Gigatracker + K+ ~11 MHz 75 Ge. V/c 800 MHz beam /K/p March 27, 2006 n n (KABES) Saclay - Orsay 24

P-326 Detector Layout K+ p+p 0 Gigatracker K+ g ~11 MHz 75 Ge. V/c 800 MHz beam /K/p March 27, 2006 + g (KABES) Saclay - Orsay 25

Signal & backgrounds from K decays / year Total Region II Signal 65 16 49 K+ + 0 2. 7± 0. 2 1. 0± 0. 1 K 2 1. 2± 0. 3 1. 1± 0. 3 <0. 1 Ke 4 2± 2 negligible 2± 2 K+ + + - and other 3 -tracks bckg. 1± 1 negligible 1± 1 K 2 g 1. 3± 0. 4 negligible 1. 3± 0. 4 K 2 g 0. 4± 0. 1 0. 2± 0. 1 Ke 3, K 3 , others negligible - - Total bkg 9± 3 3. 0± 0. 2 6± 3 March 27, 2006 Saclay - Orsay 26

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 March 27, 2006 Saclay - Orsay 27

New high-intensity K+ beam for P-326 Beam: SPS protons per pulse on T 10 Duty cycle (s. /s. ) Already Available Present K 12 (NA 48/2) New HI K+ > 2006 Factor wrt 2004 1 x 1012 3. 0 1. 0 4. 8 / 16. 8 0. 40 16 40 Av. K+momentum <p. K> (Ge. V/c) 60 75 K+ ~ 1. 5 Mom. band RMS: (Dp/p in %) 4 1 ~0. 25 7. 0 14 2. 0 Total beam per pulse (x 107) per Effective spill length MHz/cm 2 (gigatracker) 5. 5 18 2. 5 250 800 60 ~45 (~27) ~24(~15) Eff. running time / yr (pulses) 3 x 105 1. 0 x 1011 4. 8 x 1012 48 Solid angle ( sterad) Area at Gigatracker (cm 2) K+ decays per year March 27, 2006 Saclay - Orsay 28

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 NA 48. – 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 March 27, 2006 Saclay - Orsay 29

Gigatracker 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) • Two Silicon micro-pixel detectors (SPIBES) • Timing • Pattern Recognition • Improved KABES (micromegas TPC) • To minimise scattering in the last station SPIBES: q PK q K P X/X 0 << 1% Pixel size ~ 300 x 300 m s(p)/p ~ 0. 4% excellent time resolution to select the right kaon track Dependence of the signal to background (from K+ p+p 0 ) ratio as a function of the gigatracker time resolution March 27, 2006 Saclay - Orsay 30 30

SPIBES (Hybrid Pixel) G. Anelli, M. Scarpa, S. Tiuraniemi • • • y Front End and R/O considerations based on the experience of the CERN-PH/MIC and PH/ED Groups with the ALICE SPD 2 mm/bin • 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 2 mm/bin x Station 1(pixels) March 27, 2006 2(pixels) 3(FTPC) Saclay - Orsay Me. V 31

FTPC (KABES) KABES principle: TPC + micromegas Tdrift 2 Pioneered in NA 48/2 Tested in 2004 at high intensity with 1 GHz FADC Micromegas Gap 25 μm Tdrif In NA 48/2 KABES has achieved: • Position resolution ~ 70 micron • Time resolution ~ 0. 6 ns • Rate per micro-strip ~ 2 MHz t 1 New electronic + 25µm mesh strip signal occupancy divided by 3 March 27, 2006 Saclay - Orsay 32

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% X 0 per view) but no previous large straw system has been operated in high vacuum March 27, 2006 Saclay - Orsay 33

6 chambers with 4 double layers of straw tubes each ( 9. 6 mm) Rate: ~45 KHz per tube (max 0. 5 MHz) ( + ) X/X 0 ~ 0. 1% per view x m 130 m / hit 5 cm radius beam holes displaced in the bending plane according to the 75 Ge. V/c beam path m Veto for charged negative particles up to 60 Ge. V/c 5. 4 2 magnets: 270 and 360 Me. V Ptkick 8. 8 Redundant momentum measurement 7. 2 s(P)/P = 0. 23% 0. 005%P s(q) ~ 50 20 rad m Good space resolution z m y 7. 2 Low X/X 0 Operate in high vacuum 2. 3 m Downstream straw tracker March 27, 2006 Saclay - Orsay 34

RICH Layout March 27, 2006 Saclay - Orsay 35

RICH as velocity spectrometer…. Resolution of a 17 m P-326 RICH (CKMGEANT) March 27, 2006 Saclay - Orsay 36

…and RICH for - separation March 27, 2006 Saclay - Orsay 37

NA 48 LKr as Photon Veto Energy of photons from K+ p+p 0 hitting LKr: > 1 Ge. V Consolidation of the safety/control system and read-out under way March 27, 2006 Ge. V Saclay - Orsay 38

LKr efficiency measured with data K+ + 0 collected by NA 48 in 2004 Events are kinematically selected. + track and lower energy g are use to predict the position of the other g Photon E=11 Ge. V Pion P=42 Ge. V/c K+ + 0 0 Cluster not reconstructed Eg = 22 Ge. V Expected position March 27, 2006 Saclay - Orsay 39

Example: “hadronic” cluster of a photon Expected energy: ~29 Ge. V Deposited energy: ~9 Ge. V Maximum energy ~300 Me. V Expected g position Measured LKr inefficiency per photon (Eg > 10 Ge. V): h = (2. 8 ± 1. 1 stat ± 2. 3 syst) × 10 -5 March 27, 2006 (preliminary) Saclay - Orsay 40

Beam test 2006 • Idea for measuring inefficiency in the range 2 Ge. V < Eg< 10 Ge. V – Use of the NA 48 set-up. Beam test foreseen during – Photons produced by bremsstrahlung. the 2006 SPS run – SPS can provide a suitable electron beam. Kevlar window Magnet vacuum eg Electron beam (25 Ge. V/c) Bremsstrahlung Calorimeter Drift chambers Calorimeter inefficiency below Eg < 5 Ge. V is not critical March 27, 2006 Saclay - Orsay 41

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 March 27, 2006 Saclay - Orsay 42

Other Physics Opportunities • • The situation is similar to NA 48, which was designed to measure “only” ’/ but produced many more measurements Accumulating ~100 times the flux of NA 48/2 will allow us to address, for instance: 1. Cusp like effects ( scattering) K+ 0 0 e + n – 2. Lepton Flavour Violation 3. Search for new low mass particles 4. 5. 6. 7. K+ + + e , K+ + e+, (Ke 2/K 2) – – K+ + X K+ + 0 P (pseudoscalar s. Goldstino) – – K+/ +/ 0 g (CPV interference) T-odd Correlations in Kl 4 Study rare + & 0 decays Improve greatly on rare radiative kaon decays Compare K+ and K- (alternating beam polarity) And possibly, given the quality of the detector, topics in hadron spectroscopy March 27, 2006 Saclay - Orsay 43

Status of P-326 (a. k. a. NA 48/3) • Presented at the CERN SPSC in September 2005 – – • 2006 R&D plan endorsed by CERN RB on December 05 – • RICH responsibility Seeking full approval by end of 2006…. – • Measure LKr efficiency for 1 -10 Ge. V photons Equip a CEDAR counter with fast read-out Collaboration still open to new groups – • Resources being appropriated Beam Test foreseen in Sept-Oct 2006 – – • Strong endorsement of the Physics Case Review of the proposed technique Enter CERN Medium Term Plan …to be able to start data taking some time in 2009 -2010 March 27, 2006 Saclay - Orsay 44

Summary • Clear physics case – • The discovery of New Physics will dramatically increase the motivation for searches of new flavour phenomena Healthy competition worldwide: – • Exploit synergies and existing infrastructures • NA 48/1 NA 48/2 P-326 ’/ KS rare decays Dg/g in K 3 K+ p+nn SPS – – – • J-PARC 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! March 27, 2006 Saclay - Orsay 45

Spare Slides March 27, 2006 Saclay - Orsay 46

Stability and Systematics Systematic uncertainties Control of Detector asymmetry March 27, 2006 Control of Beamline asymmetry Effect on Δx 104 Acceptance and beam geometry 0. 3 Spectrometer alignment 0. 1 Analyzing magnet field 0. 1 π± decay 0. 4 U calculation and fitting 0. 2 Pile-up 0. 2 Total systematics 0. 6 Trigger efficiency: L 2 0. 5 Trigger efficiency: L 1 0. 4 Saclay - Orsay 47

NA 48/2 (2003 data) K+/ + Slope difference: Δg = (-0. 7± 0. 9 stat. ± 0. 6 stat. (trig. )± 0. 6 syst. )x 10 -4 = (-0. 7± 1. 0)x 10 -4 hep-ex/0602014 Charge asymmetry: Ag = (1. 7± 2. 1 stat. ± 1. 4 stat. (trig. )± 1. 4 syst. )x 10 -4 = (1. 7± 2. 9)x 10 -4 K+/ 0 0 Slope difference: Δg = (2. 3 ± 2. 8 stat. ± 1. 3 trig. (stat. ) ± 1. 0 syst. ± 0. 3 ext. )x 10 -4 = (2. 2 ± 3. 1)x 10 -4 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. )x 10 -4 = (1. 8 ± 2. 6)x 10 -4 Order of magnitude improvement March 27, 2006 Saclay - Orsay 48

Observation of scattering effect in K→ 3 decays NA 48/2 has made the first observation the of the charge exchange process + 0 0 in the K 0 0 decay. 1 bin = 0. 00015 Ge. V 2 30 M events NA 48/2 PLB 633 (2006) hep-ex/0511056 4 mπ+2 K± ± 0 0 4 mπ+2 G~|M 0+M 1|2 N. Cabibbo, hep-ph/0405001 PRL 93121801 (2004) N. Cabibbo and G. Isidori, hep-ph/0502130 JHEP 503 (2005) March 27, 2006 Saclay - Orsay M 2( 0 0) (Ge. V/c 2)2 49

Difference between scattering length in I=0 and I=2 states • the pionium contribution has been fixed to the prediction: Z. K. Silagadze, hep-ph/9411382 (a 0 – a 2)m+ to pionium has low sensitivity (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) March 27, 2006 Saclay - Orsay 50

MAMUD • To provide pion/muon separation and beam sweeping. –Iron is subdivided in 150 2 cm thick plates (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) Pole gap is 2 x 11 cm V x 30 cm H –Light is collected by WLS fibres with 1. 2 mm diameter Coils cross section 10 cm x 20 cm March 27, 2006 Saclay - Orsay 51

Trigger & DAQ • Total input to L 0: 11 MHz • L 0 (example): – – • > 1 hit hodoscope 73% muon veto 24% Photon Veto 18% <2 EM quadrants & E<50 Ge. V 3% L 0 output: – 3% x 11 MHz = 330 KHz Keep: L 0 + Control + Calibration + Spin-offs < 1 MHz • L 1 in PC farm (à la LHCb) to keep as much flexibility as possible • Software trigger reduction ~40 March 27, 2006 Important synergies with LHC to be exploited: for instance, the LHCb TELL 1 board Saclay - Orsay 52

NA 48@CERN Direct CP-Violation established 1996 NA 48: ’/ 1997 ’/ 1998 ’/ 1999 no spectrometer KL ’/ NA 48/1 KS lower inst. intensity NA 48/1: KS 2000 Ave: Re ’/ = 16. 7 ± 2. 3 10 -4 2001 + KL Rare Decays First observation of K 0 S →p 0 e+e- and K 0 S →p 0 m+m 2002 NA 48/2: K 2003 NA 48/2: K 2004 March 27, 2006 Re ’/ = 14. 7 ± 2. 2 10 -4 - • Search for Direct CP-Violation in charged kaon decays • scattering: PLB 633 (2006) (a 0 -a 2)m+= 0. 268 +/- 0. 017 Saclay - Orsay 53

Straw Elements and Design 12 ns rise time 100 ns total width 12. 5 m 0. 2 m Al Glue – 5 m Polycarbonate spacer, 25 mg 9. 6 mm 25 m Gold plated Tungsten wire 30 m Two double layers form a view Gas mixture: 20%Ar+80%CO 2 2300 mm To fit easily into decay volume an octagonal shape is proposed 3 coordinates 4 coordinates 2 coordinates 1 coordinate 5. 4 m 10 cm 186. 3 m k 12 hika+ (Niels) from T 0 March 27, 2006 8. 8 m 5. 4 m 7. 2 m About 2000 * 6 -> 12000 straws in total Saclay - Orsay 54

hep-ph/0511289 March 27, 2006 Saclay - Orsay 55

: Physics Motivation 0 copiously collected from K+ + 0 : spin 0 : left-handed (in SM) [1] Helicity suppressed decay (A) Neutrino mass : implies . (B) Neutrino type : Majorana neutrino x 2 larger branching ratio. [2] Decay Form of (A) Sensitive to any hypothetical weakly-interacting neutrals. (B) Decay into different neutrino flavors : [3] Cosmological Interests Neutron star cooling model through pion pole mechanism : March 27, 2006 Saclay - Orsay 56

Branching Ratio Conservative upper limit # signal < 113 (90%CL) subtracting the non-K 2 bkgnds; 1/3 sample 2/3 sample Saturation at 3. 5 x 106 New upper limit (E 949) : A factor of 3 improvement from the previous March best 27, 2006 result. Saclay - Orsay 57