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First results from BNL E949 on the rare decay K +  p + nn

First results from BNL E949 on the rare decay K +  p + nn. Tadashi Nomura (Kyoto Univ.) for BNL E949 collaboration BNL/FNAL/New Mexico/Stony Brook (USA) Alberta/British Columbia/TRIUMF (Canada) IHEP/INR (Russia) Fukui/KEK/Kyoto/NDA/Osaka/RCNP (Japan). Introduction. Experiment. Analysis.

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First results from BNL E949 on the rare decay K +  p + nn

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  1. First results from BNL E949 on the rare decay K+p+nn Tadashi Nomura (Kyoto Univ.) for BNL E949 collaboration BNL/FNAL/New Mexico/Stony Brook (USA) Alberta/British Columbia/TRIUMF (Canada) IHEP/INR (Russia) Fukui/KEK/Kyoto/NDA/Osaka/RCNP (Japan) 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  2. Introduction Experiment Analysis Results Conclusions Outline • Introduction • The E949 experiment • Analysis • Results • Conclusions 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. 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  3. Introduction Experiment Analysis Results Conclusions Introduction • K+p+nn in the Standard Model • Z penguin and Box diagram • Top in the loop, Sensitive to |Vtd| • Charm contrib. well calculated • Small theoretical uncertainty ~7% • One of golden modes to explore CKM matrix • Br (SM) ≈ 0.8 x 10-10 • Experimental status • 2 events observed by BNL E787 (1995-98) • BR=1.57(+1.75/-0.82) x 10-10 • Now, E949, as the successor of E787, aimed at 5-10 SM events 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  4. Introduction Experiment Analysis Results Conclusions E949 Experiment • Event signature = K+ comes in, only p+ comes out • Basic concepts (common to E787) • Stopped K+ experiment • Measure full kinematics of decay particle (p+) Energy (E) / Momentum (P) / Range (R) • PID by recording p-m-e decay chain • Hermetic veto detectors (g) • Reduce two major backgrounds • K+m+n (Br=63%) • Kinematics (monochromatic) • PID (p/m separation) • K+p+p0 (Br=21%) • Kinematics (monochromatic) • Photon veto Signal regionin this analysis 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  5. Introduction Experiment Analysis Side view (cutaway) End view (top half) Results Conclusions E949 Detector • Active target (scintillation fibers) to stop K+ • Drift chamber and the magnetic field to measure p+ momentum • 19 layers of scintillators (“Range Stack”) to measure E and R • Waveform digitizer to record p-m-e decay chainin the p+ stopping RS counter • Photon vetoes surrounding 4p solid angle (BV / BVL / Endcap /…) Renew inner 5 layers! Equip gain monitor! New! 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  6. Introduction Experiment Analysis E R P Results Conclusions s=0.9cm s=2.3MeV/c s=3.0MeV Highlight of Upgrade - from E787 to E949 - • To having higher sensitivity… • 2 times higher beam intensity • Better photon vetoes • Better kinematics measurement Kp2 Rejection E949 (red) vs. E787 (blue) Kp2 momentum, energy and range E949 (yellow histogram) vs. E787 (circle) 2 times better rejectionat 80% acceptance Same or even better resolutionin 2 x higher rate environment 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  7. Introduction Experiment Analysis Results Conclusions Physics Run in 2002 • 12 weeks in 2002 (1/5 of approved 60 weeks) • Detector worked well • Data taken smoothly • Accumulated K+=1.8x1012 AGS power supply failure (energy, duty factor) Conditions not optimized due to … DC separator trouble (K/p ratio) 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  8. Introduction Experiment Analysis Results Conclusions Analysis Overview How do signal/backgrounds look like in the R-P plane? • Signal • P > P(Kp2) region (“PNN1”) • Background sources • K+p+p0 • K+m+n, m+ng • Beam backgrounds • Strategy • Blind analysis • Evaluate background levelwith real data • characterized by functions • Likelihood ratio technique 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  9. Introduction Experiment Analysis P for p and m crm=(Rmeas–Rexpect)/sR Results Conclusions Neural net function for p and m Evaluation of Backgrounds • Invert one of the cuts and then measure BG rejection K+m+n, but short range P and NN function K+m+ng, … crmand NN function K+p+p0 P(E,R) and Photon veto BG level evaluated as functions of cut positions p-m-e decay chain in the p stopping RS 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  10. Introduction Experiment Analysis Results Conclusions Sensitivity and Background • Sensitivity • Background • 10% larger acceptance,by enlarging the signalbox to lower edge ofE/P/R space,resulting in largerKp2 backgrounds • All the cuts fixed and BG level estimated. Now, how to calculate the branching ratio? 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  11. Introduction Experiment Analysis Results Conclusions Likelihood method • The signal region is divided into cells by binning parameter space (E,P,R,NN func, photon veto…) • Once cuts are fixed, calculate BG level in each cell bi • Expected signal Si from BR and calculated acceptance AiSi = BR(as a free parameter) x NK x Ai • Likelihood technique in small Si, bi(T.Junk, NIM A434, 435 (99)) • Ratio of two Poisson probabilities (S+B or B only) • Estimator defined as (di = # of observed candidate in the cell) • When maximum X(BR), the central value of the BR 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  12. Introduction Experiment Analysis Results Conclusions Open the Box • Range vs Energyafter all the cuts • Single candidatein the box !! E949 E787 Simulation solid : E949 box dashed : E787 box 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  13. pm decay in the stopping RS (identified as 2 pulses) Introduction Experiment Analysis Results Conclusions Target fibers around K+ stopping Event Display 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  14. Introduction Experiment Analysis Results Conclusions Branching Ratio • E949 alone • Combine E949 & E787 • errors for 68% C.L. E949(02) = combined E787&E949 E949 projection with 60 weeks run (assuming current BR value) 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  15. Introduction Experiment Analysis Results Conclusions Impact on Unitary Triangle • Contour in r-h plane by the courtesy of G. Ishidori Green arcs indicate this K+p+nn result (including theoretical uncertainties) Central value off the “SM” Need more data!! Central value 68% interval 90% interval 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

  16. Introduction Experiment Analysis Results Conclusions Conclusions • E949 successfully ran as a first step • Upgrade to E787 successfully • 12 weeks, NK=1.8x1012 • Likelihood applied to evaluate branching ratio • E949 (02) has observed an additional candidate • Combining the E787 and E949 results, • Prospects • E949 PNN2 analysis (Pp+ < 195 MeV/c region) in progress • Further E949 run? • We are ready to complete the experiment and waiting for funding !! 5th Recontres du Vietnam - Particle physics and astrophysics - Hanoi, Vietnam

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