New results on rare kaon and pion decays
- Slides: 14
New results on rare kaon and pion decays from BNL E 949 Dmitry Vavilov E 949 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+ + `. The report mostly concerns related limits from the decays K+ +gg , K+ +g and 0 `. Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 1
E 949 Collaboration US BNL, FNAL, New Mexico n Canada Triumf, UBC, Alberta n Japan Fukui, KEK, Kyoto, Osaka n Russia IHEP, INR Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 2
E 949 Detector in LESB II at BNL IHEP contributions: MC calculation for micro-Collar, Downsteam PV, RS Monitoring system, Slow Control, Data Analysis Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 3
E 787 / E 949 Data Taking Summary Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 4
K+ + ` n 3 d candidate event “E 949 A” found E 787 A E 787 C E 949 A 0. 006 n 0. 02 0. 07 Updated branching Br(K+ + ` ) = (1. 5 +1. 3 -0. 9 ) x 10 -10 n SM predicted branching Br(K+ + ` ) = (0. 78± 0. 12 ) x 10 -10 n PNN 2 analysis is in progress Goal is to reach S/N 1 at comparable to PNN 1 sensitivity 2 x Acc and 5 x Rej improvements needed Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 5
K+ +gg 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+ m+ g , 0 m+ g or K 2 with DIF • m+ kinematics measured • m e decay sequence fooled Two beam particles • Дмитрий Вавилов Suppressed with good segmentation and timing in the K tracking system ИФВЭ 2005, 19 Декабря 7
Backgrounds, Acceptance, Sensitivity Backgrounds Number of Events K 2 Overlapping Photon Muon K decay in flight Two Beam Total 0. 017 ± 0. 006 0. 065 ± 0. 065 0. 090 ± 0. 020 0. 025 ± 0. 014 <0. 006 (90%CL) 0. 197 ± 0. 070 Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 8
K+ +gg, K+ +g results Blind analyses No events seen in signal boxes Br(K+ +gg ) < 8. 3 x 10 -9 (90%CL) p( ) > 213 Me. V/c Assuming spectrum from Ch. PT with unitarity corrections (c = 1. 8) Factor of 8 sensitivity improvement over E 787; but, cannot confirm or rule of unitarity corrections. Same data set is used to search for K+ +g which violates angular momentum conservation and gauge invariance Br(K+ +g ) < 2. 3 x 10 -9 (90%CL) Factor of 160 improvement over E 787 Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 9
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( t)<18. 2 Me. V/c 2 • Best previous limit comes from E 787 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. Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 10
0 ` 0 Rejection Maxed out at ~4 x 106 99 events survive all cuts Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 11
0 ` Results n 99 events remain after all photon veto cuts n We presume these to be 0 gg with undetected photons – The e 949 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 E 787 Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 12
Conclusions § Present E 949 results Br(K+ + ` ) = (1. 5 +1. 3 -0. 9 ) x 10 -10 [3 events, E 787(2) + E 949(1)] Br(K+ +gg ) < 8. 3 x 10 -9 (90%CL) p( ) > 213 Me. V/c Br(K+ +g ) < 2. 3 x 10 -9 (90%CL) Br( 0 ` ) < 2. 7 x 10 -7 (90%CL) § Expected new E 949 Results Br(K+ + ` ) from region below Kp 2 peak § Further Progress in ultra-rare Kaon decays P 326(Cern), Jparc(Japan) References K+ + ` 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 ` K. Mizouchi, Kyoto Uinv. Thesis (in preparation), hep-ex/0506028, submitted to Phys. Rev. D. Rapid Communications Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 13
K+ +gg in Chiral Perturbation Theory Дмитрий Вавилов ИФВЭ 2005, 19 Декабря 14
