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Baryonic B decays

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  1. Baryonic B decays Outline: • Introduction • B+ K+ • Threshold enhancement • Pentaquark search • B+ p   • Charmed baryonic modes • Two body decays • Conclusion J. Schümann National Taiwan University (Belle Collaboration) Moriond QCD '05 jan@hep1.phys.ntu.edu.tw Moriond QCD ‘05

  2. Electron 8 GeV Positron3.5 GeV The KEKB-factory Interaction Point Tsukuba 3Km Υ(4S) (10.58GeV/c2)  = 0.425 Moriond QCD '05

  3. Accumulated Data Lpeak = 15.16 nb-1s-1 Lday  1 fb-1 Ltot = 377 fb-1 Moriond QCD '05

  4. Aerogel Cherenkov Cnt. n=1.015~1.030 SC solenoid 1.5T 3.5 GeV e+ ECL CsI(Tl) TOF counter Extreme Forward Calorimeter 8 GeV e- Central Drift Chamber small cell +He/C2H6 Silicon VertexDetector KLM  / KL detection 14/15 lyr. RPC+Fe Belle Detector Moriond QCD '05

  5. Introduction • Baryonic decays: a unique and well-established feature of B meson decay (but not charm decay) • B(2 body) < B(3 body) < B(4 body) • Threshold enhancement in the invariant mass of the baryon-antibaryon system for 3-body BKBB decays • Angular distributions discriminate between decay mechanisms, e.g. two-body decays and fragmentation • Can search for exotic states in 3-body and 4-body decays Moriond QCD '05


  6. 140fb-1 b s g s s B+ΛΛK+ threshold peaking • First Charmless B decay with two Λ! • Threshold enhancement. • Complements BφK(*)(bsss penguin) First observation of bs s s decay Signal Yield in 2D fit: 19.9 Efficiency: 4.0%-6.9% Statistical Significance: 7.4σ B : (2.91  0.38) x 10-6 +6.5- 5.1 +0.90- 0.70 PRL 93, 211801 Moriond QCD '05

  7. 140fb-1 • Compare with Bppπ • buud transition with ss popping Search for B+ΛΛπ+ b u • Result • Number of Background: 37.5±1.0 • Number of Observed events:41 • Number of Signal UL: < 21.7 No significant signal found 90% confidence-level upper-limit: B (B+ΛΛπ+)<2.8x10-6 PRL 93, 211801 Moriond QCD '05

  8. 140fb-1 Improved B+ppK+measurement b s threshold peaking Signal Yield in 2D fit: 216.5 Efficiency: 28.3%-35.2% with Mpp<2.85 GeV/c2 B(Belle): (4.59  0.50) x 10-6 (4.89 x 10-6 PRL92, 131801, 2004) B(Belle): (5.30  0.58) x 10-6 , full range (charm veto for Mpp) B(BABAR): (6.7  0.9  0.6) x 10-6(81 fb-1, hep-ex/0408037) +17.3- 16.6 +0.38- 0.34 +0.45- 0.39 Moriond QCD '05

  9. p Өp X K+ p at pp rest frame p Angular distribution: ppK+& glueball search ppK signal Angular- Asymmetry: bs dominant process Fragmentation picture N+-N- A = N++N- +0.08 - 0.07 s u = 0.59 s u u u d u u d K+ p Proton against K- (p against K+) : flavor dependence! Possible Hints and Search for Glueball Production in Charmless Rare B Decays Chun-Khiang Chua, Wei-Shu Hou and Shang-Yuu Tsai(PLB544,2002) No significant signal: B(B+ glueball K+) x B( glueball  pp) < 4.1x10-7 Moriond QCD '05

  10. 140fb-1 Improved B0ppKs measurement b s threshold peaking Signal Yield in 2D fit: 28.6 Efficiency: 15.4%-21.0% with Mpp<2.85 GeV/c2 B: (1.04  0.12) x 10-6( 0.78 x 10-6 PRL92, 131801, 2004) B: (1.20 0.14) x 10-6 (full range, charm veto) +6.5- 5.8 +0.26- 0.19 +0.32- 0.22 Moriond QCD '05

  11. n K+ Θ+ p K0 Θ+ d d u u d u d u u d d u s s d u u d s s Pentaquark search in BppKs, ppK+ • Θ+(1540) : uudds (Belle) • Θ+ K+n Θ+  K0 p • B0  Θ+ pB0 ppK0, B ppKsSearch for B signal with a 20 MeV pKs mass window cut at 1540MeV, the nominal mass of the pentaquark • Θ++(1540) : uuuds (Belle,BABAR) • B0  Θ++ p • Θ++  K+ p Moriond QCD '05

  12. Pentaquark search in ppKs/K+ ++: BABAR : 81 fb-1 +: Belle : 140 fb-1 Fixed background shape from sideband data Count the events in signal region and compare with background estimation Upper limit B(B0+p)x B(+pK0s)< 2.3x10-7at90% C.L. ++: Belle: B < 9.1 x 10-8 Moriond QCD '05

  13. 140fb-1 Improved B0pΛπ- measurement b s threshold peaking Signal Yield in 2D fit: 48.8 Efficiency: 10.4%-12.6% B: (2.62  0.31) x 10-6 (Mpp < 2.85 GeV/c2) B: (3. 27  0.39) x 10-6 (full range) (3.97 x 10-6 PRL90, 201802, 2003) +8.2- 7.5 +0.44- 0.40 +0.62- 0.51 Moriond QCD '05

  14. p p π- Өp Өp X X Λ at pπ- rest frame π- Λ Angular distribution: pΛπ- at pΛ rest frame Fragmentation picture Moriond QCD '05

  15. 140fb-1 B+pΛγ b s bsγMC pΛγSignal First observation! • Simultaneous fit on BpΛγ & BpΣ0γSignal Yield for BpΛγ with MpΛ<2.4GeV/c2: 34.1 • Statistical Significance: 8.6σ • B(BpΛγ ): (2.16  0.20) x10-6B(BpΣ0γ):<3.3 x 10-6 threshold peaking Theoretical prediction: *Pole Model: Phys.Lett. B533 (2002) B(B pΛγ ) ~ 1.2x10-6 B(B pΣ0γ) ~ 2.9x10-9 *QCD counting rules: (hep-ph/0405283) B(B pΛγ ) ~ (1.2-2.4)x10-7 B(B pΣ0γ) ~ (2.8-6.5)x10-7 +7.1- 6.6 +0.58- 0.53 Moriond QCD '05

  16. 140fb-1 b c u d B- LC+ p p - 264±20 signals B x 10-5 +0.74 - 0.66 +0.56 - 0.49 + 6.6 - 5.9 SC(2455)0 32.6 + 5.7 - 5.0 SC(2520)0 12.8 Observation of a new 2-body decay sideband ~ 25% of the total Bcp- BF Moriond QCD '05

  17. B- LC+ p p- - M(Lc+p) structure (Lc+p) mass (LC+p) Low mass structure B signals by DE fit for each mass bin M(Lc+p -)>2.6 & M(pp-) >1.6GeV/c2 to remove Sc(2455/2520) & D(1232) 6.2 s significance +0.01 -0.02 +0.04 -0.03 M = 3.35 0.02 GBW = 0.07 ±0.04 +0.77 - 0.72 SC0(LC+p-) B = ( 3.870.431.01 ) x 10 - 5 Moriond QCD '05

  18. M(Lc+p) <3.6GeV/c2 p B- LC+ p p - Helicity distribution Helicity angle Lc+ MC J c2 /nd Solid line : 0 0.97 Dashed line : 1 1.58 Q in B - at rest (Lc+p) direc. data: dots MC : histograms Angular-Asymmetry: |N+-N-| = 0.32  0.14 A = N++N- ( by DE fit for each mass bin ) Moriond QCD '05

  19. 140fb-1 B0 LL, Lp, pp and other 90% confidence level UL: B0 pp: 4.1 x 10-7 B0 Lp: 4.9 x 10-7 B0 LL: 6.9 x 10-7 Belle:B+ J/pL: 4.1 x 10-5 BABAR:B+ J/pL: 2.6 x 10-5 B+ J/pp: 1.9 x 10-5 BABAR, 81fb-1 Belle, 78fb-1 Moriond QCD '05

  20. Conclusion • First b → sss hyperonic decay found • First b → s γ baryonic decay found • The threshold enhancement in the baryon-antibaryon pair for 3-body Bbaryon decayse supports the fragmentation picture • Intriguing structure found in the cp mass for Bcp- decays • No hints for pentaquarks and glueballs yet • Keep searching for all kinds of baryonic decay channels, possible pentaquarks, glueballs and especially direct CP violation with increasing statistics Moriond QCD '05

  21. γ θx p Λ Photon energy and Angular distribution Fit results in bins of cosθX with Mp<4.0GeV/c2 (Assuming XpΛ, calculated in X rest frame.) qq background bsγMC Signal Yield Signal Yield Lab frame Moriond QCD '05

  22. M(Lc+p) structure in 3, 4 body decays B-  (Lc+p) p- Preliminary MC phase space, consistent with 4-body fine structures ? B0  (Lc+p) p+ p- B Signals by DE fit MC 4-body phase space SC++/0 (2455/2520) excluded Moriond QCD '05

  23. 140fb-1 B0 LC+ p p - p - Intermediate 3-body decays Sc0(2455) Sc++(2455) 41.0±8.0 35.2±7.8 M(Lc+p +)+c.c. Sc++(2520) Sc0(2520) M(Lc+p -)+c.c. 58±14 19±11 (*1) total BF M(Lc+p ) Moriond QCD '05

  24. Glueball Search Possible Hints and Search for Glueball Production in Charmless Rare B Decays Chun-Khiang Chua, Wei-Shu Hou and Shang-Yuu Tsai(PLB544,2002) Scanning through the mass region from 2.2 to 2.4 GeV region No significant signal 90% confidence-level upper limit:BF(B+ glueball K+) x BF( glueball  pp) < 4.1x10-7 Moriond QCD '05

  25. Particle Selection • We use the PID (ACC+CDC+TOF) system to identify the charged particles. • Proton: • Kaon: • Pion: • Λ: reconstructed from Λpπ- TO From Fake rate Moriond QCD '05

  26. e- e- e+ e+ Υ(4S) B B B Signal Reconstruction ∆E In Υ(4S) rest frame: Mbc 2D scatter plot 1D projection plot Moriond QCD '05

  27. Υ(4S) B decay continuum events Background suppression • The main background for B0pΛπ- and B+ΛΛπ+is continuum qq events. (q=u,d,s,c). • The Topology of continuum events and B decays are different. We choose |cosθThrust| S⊥ R2so R4so R2oo R3oo R4ooas the fisher input and combine it with cosθBto calculate the likelihood ratio. • We define the Super-fox wolfram moment (F) like:We use Fisher’s discriminant to optimize the coefficients. Moriond QCD '05

  28. uds charm off Data sideband uds charm off Data sideband Background Suppression SFW Moment (F) Likelihood Ratio (LR) Signal MC uds charm cosθB distribution Data sideband off Optimized by study Moriond QCD '05

  29. Signal Extraction ∆E Mbc • PDFs: • Background modeling: a line (curve) to represent the ∆E and the following parametrization first suggested by ARGUS group to represent the Mbc. • Signal modeling: a double Gaussian for ∆E and a Gaussian for Mbc. • 1D-binned fit: maximum Likelihood fit • Branching fraction are calculated by ∆E fit • Mbc fit for cross-check. • 2D-unbinned fit (∆E-Mbc): Extended maximum likelihood fit. ∆E Mbc Moriond QCD '05

  30. Angular distribution: ppK+ Background yield of ppK+ J/ψK+ (J/ψpp) Consistent with qq background process No fragmentation signature in J/ψK+ Moriond QCD '05