1. WIN09 September 18, 20091 Measurement of K    Final Results from E949 Steve Kettell, BNL September 18 th, 2009 22 nd International Workshop on Weak Interactions and Neutrinos

2. WIN09 September 18, 2009Steve Kettell, BNL2 K    Motivation One of the Golden Modes for study of the CKM matrix and CP violation. The rate can be calculated precisely from fundamental parameters and any deviation in the measured rate will be a clear signal for new physics. 1.FCNC, hard GIM suppression 2.No long distance contribution 3.Hadronic Matrix element from Ke3 & isospin 4.NNLO QCD calculation of c-quark contribution SM = 8x10-11

3. WIN09 September 18, 2009Steve Kettell, BNL3 K    Motivation

4. WIN09 September 18, 2009Steve Kettell, BNL4 K    Motivation

5. WIN09 September 18, 2009Steve Kettell, BNL5 “PNN1” “PNN2” Outline of K    Experimental Method  Problem: 3-body decay (2 missing ’s); BR<10 -10  Event signature = single K + in, single  + out  Basic concepts Precise and redundant measurement of kinematics e.g. Energy (E) / Momentum (P) / Range (R) or Velocity (V) / Momentum (P) / Range (R) PID:  -  -e decay chain and/or P/R, P/V, dE/dx… Hermetic veto detectors (  )  Major backgrounds K +   + (Br=63%) Kinematics (monochromatic) PID:  + /  + K +   +  0 (Br=21%) Kinematics (monochromatic) Photon veto Scattered beam particles Timing PID: K + /  + Primary signal region Exploit with E949 upgrades

6. WIN09 September 18, 2009Steve Kettell, BNL6 Outline of K    Experimental Method  Measure background from data A priori identification of background sources. Suppress each background with at least two independent cuts. Measure background with data, if possible, by inverting cuts and measuring rejection taking any correlation into account. Automatically accounts for electronics glitches and variations in veto performance  Blind Analysis Don’t examine signal region until all backgrounds verified. To avoid bias, set cuts using 1/3 of data, then measure backgrounds with remaining 2/3 sample. Verify background estimates by loosening cuts and comparing observed and predicted rates.

7. WIN09 September 18, 2009Steve Kettell, BNL7 Measurement of backgrounds with data Tag with  Tag kinematics outside  box – in K  peak kinematics Photon veto

8. WIN09 September 18, 2009Steve Kettell, BNL8 E787 E787 was initiated by Ted Kycia and Stew Smith and was led by Laurie Littenberg, Stew Smith and Doug Bryman: Engineering run in 1988 Data runs in 1989–1991 Upgrade 1991–1994 Data runs in 1994–1999 Discovery of K   

9. WIN09 September 18, 2009Steve Kettell, BNL9 E787 1998 Event PRL 88, 041803 (2002) Below K  2 (pnn2) limit: 1996: PL B537, 211 (2002) 1997: PR D70, 037102 (2004) 140<p  <195 MeV/c 1 candidate event with an expected background of 1.22 +/- 0.24 events. Background limited, with S/N<0.2 Set an upper limit of B(K +  + ) < 22 x 10 -10 Two events above the K  2 (pnn1) B(K +  + ) = 1.57 +1.75 -0.82  10 -10

10. WIN09 September 18, 2009Steve Kettell, BNL10 E949 Experiment V.V. Anisimovsky 1,A.V. Artamonov 2, B. Bassalleck 3, B. Bhuyan 4, E.W. Blackmore 5, D.A. Bryman 6, S. Chen 5, I-H. Chiang 4, I.-A. Christidi 7, P.S. Cooper 8, M.V. Diwan 4, J.S. Frank 4, T. Fujiwara 9, J. Hu 5, A.P. Ivashkin 1, D.E. Jaffe 4, S. Kabe 10, S.H. Kettell 4, M.M. Khabibullin 1, A.N. Khotjantsev 1, P. Kitching 11, M. Kobayashi 10, T.K. Komatsubara 10, A. Konaka 5, A.P. Kozhevnikov 2, Yu.G. Kudenko 1, A. Kushnirenko 8, L.G. Landsberg 2, B. Lewis 3, K.K. Li 4, L.S. Littenberg 4, J.A. Macdonald 5, J. Mildenberger 5, O.V. Mineev 1, M. Miyajima 12, K. Mizouchi 9, V.A. Mukhin 2, N. Muramatsu 13, T. Nakano 13, M. Nomachi 14, T. Nomura 9, T. Numao 5, V.F. Obraztsov 2, K. Omata 10, D.I. Patalakha 2, S.V. Petrenko 2, R. Poutissou 5, E.J. Ramberg 8, G. Redlinger 4, T. Sato 10, T. Sekiguchi 10, T. Shinkawa 15, R.C. Strand 4, S. Sugimoto 10, Y. Tamagawa 12, R. Tschirhart 8, T. Tsunemi 10, D.V. Vavilov 2, B. Viren 4, N.V. Yershov 1, Y. Yoshimura 10 and T. Yoshioka 10 1. Institute for Nuclear Research (INR), 2. Institute for High Energy Physics (IHEP), 3. University of New Mexico (UNM), 4. Brookhaven National Laboratory (BNL), 5. TRIUMF, 6. University of British Columbia, 7. Stony Brook University, 8. Fermi National Accelerator Laboratory (FNAL), 9. Kyoto University, 10. High Energy Accelerator Research Organization (KEK), 11. Centre for Subatomic Research, University of Alberta, 12. Fukui University, 13. Research Center for Nuclear Physics (RCNP), Osaka University, 14. Osaka University, 15. National Defense Academy. BNL/FNAL/SBU/UNM, U.S.A IHEP/INR, Russia Fukui/KEK/Kyoto/NDA/Osaka, Japan TRIUMF/UA/UBC, Canada E949 was proposed in 1998 and approved in 1999 (D. Bryman, S, Kettell, S. Sugimoto): Use entire AGS flux (65 Tp) high duty factor low K momentum various detector improvements Photon Veto (esp. for pnn2) Ran for 12 weeks in 2002

11. WIN09 September 18, 2009Steve Kettell, BNL11 Side view (cutaway)End view (top half) E949 Overview (1) ~700 MeV/c K + beam (75%) Active target (scintillation fibers) to stop K + Wait at least 2ns for K + decay (delayed coincidence) Drift chamber to measure  + momentum 19 layers of scintillator, Range Stack (RS) to measure E and R Stop  + in RS, waveform digitizer to record  + -  + -e + decay chain Veto photons, charged tracks over 4  (BV/BVL/Endcap/…)

12. WIN09 September 18, 2009Steve Kettell, BNL12 E949 Overview (2): Data Taking Conditions E787 collected N K =5.9  10 12 in 81 weeks over 5 years. E949 proposed N K =18  10 12 in 60 weeks over 3 years. E949 collected N K =1.7  10 12 in 12 weeks in 2002. Beam conditions were less than optimal: broken separator: more  + less K + spare M.G.: lower p + mom., poor duty factor Detector worked very well Smooth data taking E787E949 Prop. E949 AGS mom. GeV/c25.5 21.9 Beam intensity Tp15-3565 Duty factor %41-556341 K + /p + 3.7-4.24.03.0 N K 10 12 5.9181.8

13. WIN09 September 18, 2009Steve Kettell, BNL13 E949 Overview (3): Performance Goal: double sensitivity while increasing s/b = 1 2  acceptance and 5  rejection Improved PV: new detectors at small angles Improved algorithms to identify π + scatters in target Improved PV key to pnn2 exploitation P ER  =2.3MeV/c  =3.0MeV  =0.9cm Photon Veto Kinematics K  2 momentum, energy and range E949 (yellow histogram) vs. E787 (circle) Same or even better resolution in 2 x higher rate environment

14. WIN09 September 18, 2009Steve Kettell, BNL14 E949 pnn1 analysis PRL 93, 031801 (2004) E949 observed one new event in the primary pnn1 region

15. WIN09 September 18, 2009Steve Kettell, BNL15 After the trigger P vs. R of  + pnn2 pnn1  More phase space than pnn1  Fewer  + N interactions  Probe K    spectrum E949 pnn2 analysis  Need photon detection near beam  Must identify  + target scattering kink in the pattern of target fibers   + track that does not point back to the K + decay point energy deposits inconsistent with an outgoing  + unexpected energy deposit in the fibers traversed by the K + Advantages Disadvantages

16. WIN09 September 18, 2009Steve Kettell, BNL16 K       target scattering background Target kink: transverse scatter Typical target pattern:

17. WIN09 September 18, 2009Steve Kettell, BNL17 Longitudinal scattering CCD pulse cut

18. WIN09 September 18, 2009Steve Kettell, BNL18 K +  +  0 background Photon tagged CCD pulse Target cut B  scat tagged C+D Photon cut C

19. WIN09 September 18, 2009Steve Kettell, BNL19 Beam background Single beam: particle ID, timing Single beam: particle ID, timing Double beam: Double beam: redundant particle ID along beam line redundant particle ID along beam line Cerenkov Cerenkov Wire chamber Wire chamber Target Target B4 B4 AD

20. WIN09 September 18, 2009Steve Kettell, BNL20 Muon background Range momentum Range momentum dE/dx range stack dE/dx range stack chain  →  → e chain K++K++K++K++K++K++K++K++

21. WIN09 September 18, 2009Steve Kettell, BNL21 Ke4 (K +  +  - e + ) background Ke4 MC event K+K+K+K+ ++++ ---- e+e+e+e+ A Ke4 candidate from data - e + energy can be very low  - e + energy can be very low signal region K +  +  − e + can be a background if the  − and e + have very little kinetic energy and evade detection.

22. WIN09 September 18, 2009Steve Kettell, BNL22 Ke4 (K +  +  - e + ) background A Ke4-rich sample is tagged in data by selecting events with extra target energy. A Ke4-rich sample is tagged in data by selecting events with extra target energy. Use MC to evaluate the rejection of cuts Use MC to evaluate the rejection of cuts The  - annihilation The  - annihilation energy spectrum is from our experimentalmeasurement

23. WIN09 September 18, 2009Steve Kettell, BNL23 Charge exchange ( K  n  K 0 p ) background A CEX rich data sample is tagged by a gap between K + and  + A CEX rich data sample is tagged by a gap between K + and  + Model K L momentum from K S monitors Model K L momentum from K S monitors Use MC to evaluate the rejection Use MC to evaluate the rejection Characteristics: a gap between K + and  + a gap between K + and  + z info of  + is not consistent with K + track z info of  + is not consistent with K + track

24. WIN09 September 18, 2009Steve Kettell, BNL24 Total background and sensitivity SES is the branching ratio for a single event observed w/o background For E787+E949 pnn1 SES=0.63×10 -10

25. WIN09 September 18, 2009Steve Kettell, BNL25 Outside box study (verify bkg. est.) Keep signal region hidden Keep signal region hidden Relax photon veto or CCD pulse cut Relax photon veto or CCD pulse cut Check the predicted events and observed events in the extended region A’ Check the predicted events and observed events in the extended region A’

26. WIN09 September 18, 2009Steve Kettell, BNL26 Inside-the-box study The background is not uniformly distributed in the signal region. Use the remaining rejection power of the photon veto, delayed coincidence,  µ  e and kinematic cuts to divide the signal region into 9 cells with differing levels of signal acceptance (S i ) and background (B i ). Calculate B(K +  + ) using S i /B i of any cells containing events using the likelihood ratio method. Momentum (MeV/c) of: Signal K +  +  - e + K +  +  - e + p box: p>140 Tight p box: p>165

27. WIN09 September 18, 2009Steve Kettell, BNL27 Measured  + →  + BR of this analysis _ BR= (7.89± )×10 -10 BR= (7.89± )×10 -10 The probability of all 3 events to be due to background alone is 0.037 The probability of all 3 events to be due to background alone is 0.037 …due SM signal + background is 0.056 …due SM signal + background is 0.056 SM prediction: SM prediction: BR=(0.85±0.07)×10 -10 9.26 5.10

28. WIN09 September 18, 2009Steve Kettell, BNL28 Combined with all E787/E949 result BR= (1.73± )×10 -10 BR= (1.73± )×10 -10 The probability of all 7 events to be due to background alone is 0.001 The probability of all 7 events to be due to background alone is 0.001 …due to SM signal + background is 0.06 …due to SM signal + background is 0.06 SM prediction: SM prediction: BR=(0.85±0.07)×10 -10 1.15 1.05

29. WIN09 September 18, 2009Steve Kettell, BNL29 Implications for K L  0 Implications for K L  0

30. WIN09 September 18, 2009Steve Kettell, BNL30 BR of Scalar and Tensor form factors Trigger simulation BR (×10 -10 ):

31. WIN09 September 18, 2009Steve Kettell, BNL31 Limit on the BR of  + →  + X The mass of X is unknown. X might have limited lifetime We assume the detection efficiency of decay products of X is 100% if the decay occurs within the detector

32. WIN09 September 18, 2009Steve Kettell, BNL32 Summary & Outlook  Based on seven E787/E949 K    events the BR is consistent with the SM, but remains higher than expected…more data is needed!  E949 is finished, but NA62 at CERN is moving forward and experiments at J-PARC and FNAL are under consideration  Plans are underway to move the E949 detector to Japan  K  remains an incisive test of the flavor structure of our physical world, whether described by the SM or new physics and some combination of experiments should go forward!  Together K +  + and K L  0 provide a unique opportunity for discovery of new physics. E949 92 78