1. Дмитрий ВавиловИФВЭ 2005, 19 Декабря1 New results on rare kaon and pion decays from BNL E949 Dmitry Vavilov E949 is an high rate K + decay at rest experiment with the primary goal of measuring |Vtd| via a measurement of the branching ratio of the ultra-rare charged kaon decay K + K + K +  + . The report mostly concerns related limits from the decays K +   + , K +   +  and  0  .

2. Дмитрий ВавиловИФВЭ 2005, 19 Декабря2 E949 Collaboration US BNL, FNAL, New Mexico Canada Triumf, UBC, Alberta Japan Fukui, KEK, Kyoto, Osaka Russia IHEP, INR

3. Дмитрий ВавиловИФВЭ 2005, 19 Декабря3 E949 Detector in LESB II at BNL IHEP contributions: MC calculation for micro-Collar, Downsteam PV, RS Monitoring system, Slow Control, Data Analysis

4. Дмитрий ВавиловИФВЭ 2005, 19 Декабря4 E787 / E949 Data Taking Summary

5. Дмитрий ВавиловИФВЭ 2005, 19 Декабря5 K +  +  n 3d candidate event “E949A” found Updated branching Br(K +  + ) = (1.5 +1.3 -0.9 ) x 10 -10 SM predicted branching Br(K +  + ) = (0.78±0.12 ) x 10 -10 n PNN2 analysis is in progress Goal is to reach S/N1 at comparable to PNN1 sensitivity 2x Acc and 5x Rej improvements needed E787AE787CE949A 0.0060.020.07

6. Дмитрий ВавиловИФВЭ 2005, 19 Декабря6 K + K +   +  Introduction

7. Дмитрий ВавиловИФВЭ 2005, 19 Декабря7 K + Offline Analysis K +   +  Offline Analysis Backgrounds: K +   +  0 (K  2)  + kinematics measured Photon energies/angles mis-measured Or photon overlaps charged track K  2 with K  Decay In Flight (DIF)  + Kinematics measured Fakes K decay at rest K +   + ,  0  +  or K  2 with  DIF  + kinematics measured   e decay sequence fooled Two beam particles Suppressed with good segmentation and timing in the K tracking system

8. Дмитрий ВавиловИФВЭ 2005, 19 Декабря8 Backgrounds, Acceptance, Sensitivity BackgroundsNumber of Events K  2 0.017 ± 0.006 Overlapping Photon 0.065 ± 0.065 Muon 0.090 ± 0.020 K decay in flight 0.025 ± 0.014 Two Beam<0.006 (90%CL) Total 0.197 ± 0.070

9. Дмитрий ВавиловИФВЭ 2005, 19 Декабря9 K + K + K +   +  K +   +  results Blind analyses No events seen in signal boxes Br(K +   +  ) < 8.3 x 10 -9 (90%CL) p(  ) > 213 MeV/c Assuming spectrum from ChPT with unitarity corrections (c = 1.8) Factor of 8 sensitivity improvement over E787; but, cannot confirm or rule of unitarity corrections. Same data set is used to search for K +   +  which violates angular momentum conservation and gauge invariance Br(K +   +  ) < 2.3 x 10 -9 (90%CL) Factor of 160 improvement over E787

10. Дмитрий ВавиловИФВЭ 2005, 19 Декабря10  0   Forbidden by angular momentum conservation if W’s and neutrinos are purely left handed. Can proceed if neutrinos have mass. Br(  0   ) < 1.1 x 10 -9 for m(  )<18.2 MeV/c 2 Best previous limit comes from E787 Br(  0   ) < 8.3 x 10 -7 (90%CL) Method: Copious supply of clean  0 from K +   +  0 tagged by monochromatic  +. Look for K  2 events with no activity other than K + and  +. Trigger sample is same as K +   + . Select K  2 events; apply tightest photon veto. Tune photon veto on 1/3 of data, use other 2/3 for search.

11. Дмитрий ВавиловИФВЭ 2005, 19 Декабря11  0    0 Rejection Maxed out at ~4x10 6 99 events survive all cuts

12. Дмитрий ВавиловИФВЭ 2005, 19 Декабря12  0   Results n 99 events remain after all photon veto cuts We presume these to be  0   with undetected photons –The e949 photon veto inefficiency in not known and probably not knowable at this level. –A background subtraction is not a reasonable option. n The corresponding branching ratio upper limit is: Br(  0   ) < 2.7 x 10 -7 (90%CL) Factor of 3 improvement beyond E787

13. Дмитрий ВавиловИФВЭ 2005, 19 Декабря13 Conclusions  Present E949 results Br(K +  +  ) = (1.5 +1.3 -0.9 ) x 10 -10 [3 events, E787(2) + E949(1)] Br(K +   +  ) 213 MeV/c Br(K +   +  ) < 2.3 x 10 -9 (90%CL) Br(  0   ) < 2.7 x 10 -7 (90%CL)  Expected new E949 Results Br(K +  +  ) from region below Kp2 peak  Further Progress in ultra-rare Kaon decays P326(Cern), Jparc(Japan) References K +   +  Phys.Rev.Lett. 93 (2004) 031801, hep-ex/0403036 K +   +  K +   +  T. Yoshioka, Univ. of Tokyo thesis, KEK K-decay Report 2005-2, Hep-ex/0505069, Phys.Lett.B 623 (2005) 192-199  0   K.Mizouchi, Kyoto Uinv. Thesis (in preparation), hep-ex/0506028, submitted to Phys.Rev.D. Rapid Communications

14. Дмитрий ВавиловИФВЭ 2005, 19 Декабря14 K + K +   +  in Chiral Perturbation Theory