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New results on rare kaon and pion decays from BNL E949

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

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New results on rare kaon and pion decays from BNL E949

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  1. 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++ n`. The report mostly concerns related limits from the decays K+ +gg , K+ +g and 0  n`. ИФВЭ 2005, 19 Декабря

  2. E949 Collaboration • USBNL, FNAL, New Mexico • CanadaTriumf, UBC, Alberta • JapanFukui, KEK, Kyoto, Osaka • RussiaIHEP, INR ИФВЭ 2005, 19 Декабря

  3. E949 Detector in LESB II at BNL IHEP contributions: MC calculation for micro-Collar, Downsteam PV, RS Monitoringsystem, Slow Control, Data Analysis ИФВЭ 2005, 19 Декабря

  4. E787 / E949 Data Taking Summary ИФВЭ 2005, 19 Декабря

  5. K++ n` • 3d candidate event “E949A” found • Updated branchingBr(K++n`) = (1.5 +1.3-0.9 ) x 10-10 • SM predicted branchingBr(K++n`) = (0.78±0.12 ) x 10-10 • PNN2 analysis is in progressGoal is to reach S/N1 at comparable to PNN1 sensitivity2x Acc and 5x Rej improvements needed ИФВЭ 2005, 19 Декабря

  6. K+ +gg Introduction ИФВЭ 2005, 19 Декабря

  7. K+ +gg Offline Analysis Backgrounds: K+ +0 (Kp2) • + kinematics measured • Photon energies/angles mis-measured • Or photon overlaps charged track Kp2 with KDecay In Flight (DIF) • + Kinematics measured • Fakes K decay at rest K+ m+ng , 0m+ng or Kp2 with p DIF • m+ kinematics measured •   m edecay sequence fooled Two beam particles • Suppressed with good segmentation and timing in the K tracking system ИФВЭ 2005, 19 Декабря

  8. Backgrounds, Acceptance, Sensitivity • Backgrounds Number of Events • Kp20.017 ± 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 ИФВЭ 2005, 19 Декабря

  9. K+ +gg, K+ +g results Blind analyses No events seen in signal boxes Br(K+ +gg ) < 8.3 x 10-9 (90%CL) p(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+ +gwhich violates angular momentum conservation and gauge invariance Br(K+ +g ) < 2.3 x 10-9 (90%CL) Factor of 160 improvement over E787 ИФВЭ 2005, 19 Декабря

  10. 0n` • Forbidden by angular momentum conservation if W’s and neutrinos are purely left handed. Can proceed if neutrinos have mass. Br(0 n`) < 1.1 x 10-9 for m(nt)<18.2 MeV/c2 • Best previous limit comes from E787 Br(0 n`) < 8.3 x 10-7 (90%CL) • Method: Copious supply of clean 0fromK+ +0tagged by monochromatic +. Look for Kp2 events with no activity other than K+ and +. Trigger sample is same as K+ + n`. Select Kp2 events; apply tightest photon veto. Tune photon veto on 1/3 of data, use other 2/3 for search. ИФВЭ 2005, 19 Декабря

  11. 0n` 0Rejection Maxed out at ~4x106 99 events survive all cuts ИФВЭ 2005, 19 Декабря

  12. 0n` Results • 99 events remain after all photon veto cuts • We presume these to be 0ggwith 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. • The corresponding branching ratio upper limit is: Br(0 n`) < 2.7 x 10-7 (90%CL) Factor of 3 improvement beyond E787 ИФВЭ 2005, 19 Декабря

  13. Conclusions • Present E949 results Br(K++n`) = (1.5 +1.3-0.9 ) x 10-10 [3 events, E787(2) + E949(1)] Br(K+ +gg ) < 8.3 x 10-9 (90%CL) p(p) > 213 MeV/c Br(K+ +g ) < 2.3 x 10-9 (90%CL) Br(0 n`) < 2.7 x 10-7 (90%CL) • Expected new E949 Results Br(K++n`) from region below Kp2 peak • Further Progress in ultra-rare Kaon decays P326(Cern), Jparc(Japan) References K+ + n` Phys.Rev.Lett. 93 (2004) 031801, hep-ex/0403036 K+ +gg, K+ +g T. Yoshioka, Univ. of Tokyo thesis, KEK K-decay Report 2005-2, Hep-ex/0505069, Phys.Lett.B 623 (2005) 192-199 0 n` K.Mizouchi, Kyoto Uinv. Thesis (in preparation), hep-ex/0506028, submitted to Phys.Rev.D. Rapid Communications ИФВЭ 2005, 19 Декабря

  14. K+ +gg in Chiral Perturbation Theory ИФВЭ 2005, 19 Декабря

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