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Measurement of K+-->π+νν: Final Results from E949 - Steve Kettell

This presentation discusses the motivation and experimental method for the measurement of the rare K+-->π+νν decay mode, which can provide valuable insights into the CKM matrix and CP violation. The presentation also highlights the measurement of background sources and the E787 and E949 experiments.

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Measurement of K+-->π+νν: Final Results from E949 - Steve Kettell

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

  2. 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. • FCNC, hard GIM suppression • No long distance contribution • Hadronic Matrix element from Ke3 & isospin • NNLO QCD calculation of c-quark contribution SM = 8x10-11 Steve Kettell, BNL

  3. K Motivation Steve Kettell, BNL

  4. K Motivation Steve Kettell, BNL

  5. Outline of K Experimental Method “PNN1” “PNN2” • Problem: 3-body decay (2 missing ’s); BR<10-10 • Event signature = single K+ in, single p+ 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: p-m-e decay chain and/or P/R, P/V, dE/dx… • Hermetic veto detectors (g) • Major backgrounds • K+m+n (Br=63%) • Kinematics (monochromatic) • PID: p+/m+ • K+p+p0 (Br=21%) • Kinematics (monochromatic) • Photon veto • Scattered beam particles • Timing • PID: K+/p+ Primary signal region Exploit with E949 upgrades Steve Kettell, BNL

  6. 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. Steve Kettell, BNL

  7. Measurement of backgrounds with data Tag with  kinematics Photon veto Tag kinematics outside pnn box – in Kp2 peak Steve Kettell, BNL

  8. 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 Steve Kettell, BNL

  9. E787 PRL 88, 041803 (2002) Two events above the Kp2 (pnn1) B(K++  ) = 1.57+1.75-0.8210-10 1998 Event Below Kp2 (pnn2) limit: 1996: PL B537, 211 (2002) 1997: PR D70, 037102 (2004) 140<pp<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 Steve Kettell, BNL

  10. E949 Experiment 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 V.V. Anisimovsky1,A.V. Artamonov2, B. Bassalleck3, B. Bhuyan4, E.W. Blackmore5, D.A. Bryman6, S. Chen5, I-H. Chiang4, I.-A. Christidi7, P.S. Cooper8, M.V. Diwan4, J.S. Frank4, T. Fujiwara9, J. Hu5, A.P. Ivashkin1, D.E. Jaffe4, S. Kabe10, S.H. Kettell4, M.M. Khabibullin1, A.N. Khotjantsev1, P. Kitching11, M. Kobayashi10, T.K. Komatsubara10, A. Konaka5, A.P. Kozhevnikov2, Yu.G. Kudenko1, A. Kushnirenko8, L.G. Landsberg2, B. Lewis3, K.K. Li4, L.S. Littenberg4, J.A. Macdonald5, J. Mildenberger5, O.V. Mineev1, M. Miyajima12, K. Mizouchi9, V.A. Mukhin2, N. Muramatsu13, T. Nakano13, M. Nomachi14, T. Nomura9, T. Numao5, V.F. Obraztsov2, K. Omata10, D.I. Patalakha2, S.V. Petrenko2, R. Poutissou5, E.J. Ramberg8, G. Redlinger4, T. Sato10, T. Sekiguchi10, T. Shinkawa15, R.C. Strand4, S. Sugimoto10, Y. Tamagawa12, R. Tschirhart8, T. Tsunemi10, D.V. Vavilov2, B. Viren4, N.V. Yershov1, Y. Yoshimura10 and T. Yoshioka10 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. Steve Kettell, BNL

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

  12. E949 Overview (2): Data Taking Conditions • E787 collected NK=5.91012 in 81 weeks over 5 years. • E949 proposed NK=181012 in 60 weeks over 3 years. • E949 collected NK=1.71012 in 12 weeks in 2002. • Beam conditions were less than optimal: • broken separator: more p+ less K+ • spare M.G.: lower p+ mom., poor duty factor • Detector worked very well • Smooth data taking Steve Kettell, BNL

  13. E949 Overview (3): Performance E R P s=0.9cm s=2.3MeV/c s=3.0MeV Photon Veto Kinematics Kp2 momentum, energy and range E949 (yellow histogram) vs. E787 (circle) Improved PV key to pnn2 exploitation • 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 Same or even better resolutionin 2 x higher rate environment Steve Kettell, BNL

  14. E949 pnn1 analysis E949 observed one new event in the primary pnn1 region PRL 93, 031801 (2004) Steve Kettell, BNL

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

  16. K+p+p0target scattering background Typical target pattern: Target kink: transverse scatter Steve Kettell, BNL

  17. Longitudinal scattering CCD pulse cut Steve Kettell, BNL

  18. K+p+p0background Photon tagged pscat tagged C+D Target cut CCD pulse Photon cut B C Steve Kettell, BNL

  19. Beam background Single beam: particle ID, timing Double beam: redundant particle ID along beam line Cerenkov Wire chamber Target B4 AD Steve Kettell, BNL

  20. Muon background K+m+ng K+m+np0 • Range momentum • dE/dx range stack • p→m→echain Steve Kettell, BNL

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

  22. Ke4 (K+p+p-e+n) background • A Ke4-rich sample is tagged in data by selecting events with extra target energy. • Use MC to evaluate the rejection of cuts • The p- annihilation • energy spectrum • is from our • experimental • measurement Steve Kettell, BNL

  23. Charge exchange (K+n K0p) background • Characteristics: • a gap between K+ andp+ • z info of p+ is not consistent with K+ track • A CEX rich data sample is tagged by a gap between K+ and p+ • Model KL momentum from KS monitors • Use MC to evaluate the rejection Steve Kettell, BNL

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

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

  26. 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, pµ e and kinematic cuts to divide the signal region into 9 cells with differing levels of signal acceptance (Si ) and background (Bi ). • Calculate B(K++) using Si/Bi of any cells containing events using the likelihood ratio method. Momentum (MeV/c) of: K+p+p-e+n Signal p box: p>140 Tight p box: p>165 Steve Kettell, BNL

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

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

  29. Implications for KLp0nn Steve Kettell, BNL

  30. BR of Scalar and Tensor form factors Trigger simulation BR (×10-10): Steve Kettell, BNL

  31. 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 Steve Kettell, BNL

  32. 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 KL0 provide a unique opportunity for discovery of new physics. E949 92 78 Steve Kettell, BNL

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