Rare B  baryon decays Jana Thayer University of Rochester CLEO Collaboration EPS 2003 July 19, 2003 Motivation Baryon production in B decays Semileptonic B decays to ep final states B  pe  e X (Abstract: 141) Baryon-containing radiative penguin decays: B  X s (baryons)  (Abstract: 121) B   p  B    p  Conclusions

Baryon production in B decay If mechanism is External W Emission then b  s  and b  cl final states MAY contain baryons. If mechanism is Internal W Emission then b  s  and b  cl final states will NOT contain baryons. Internal W Emission baryon anti- baryon c External W Emission c baryon anti-baryon Mechanism for baryon production in B decay not completely understood:

Why B  pe  e X ? [1] = PDG 2000 [2] = CLEO II, limit using full reconstruction on  c  pK    [3] = ARGUS BUT, kinematic argument against baryon production in b  cl Semileptonic B decays distinguish between internal and external W emission There is no positive evidence for baryons in semileptonic B decays: –B    c e   anything   [1] –B   c + pe  e    –B   pe  e X   

Search for exclusive modes: B    p  with some sensitivity to B –       p  –Clean; easiest of baryon modes to reconstruct –Largest fraction above threshold Why B  X s (baryon)  ? Relevance for b  s  –Previous b  s  measurement less sensitive to B  baryon  –Could shift  E   down by as much as 56 MeV (1.7  ) NOTE: Only interested in photons with E  > 2.0 GeV  2.05 < M sq < 2.6 GeV

Technique: Study angular distribution between electrons and antiprotons to search for semileptonic baryon decays from B mesons. Experimental technique: B   pe  e X Partially reconstruct the decay B  pe  e X: –Identify hadronic events with an e  (0.6 GeV < p e < 1.5 GeV) and p (0.2 GeV < p p < 1.5 GeV) emerging promptly from the B –Examine angular distributions between e  and p  the angle between the electron and the antiproton  Use the difference between the signal and background shapes in cos  to fit for the amount of signal

B   c + pe  e signal Uncorrelated background Correlated background Continuum background (data) e  /p angular distributions Signal events: cos  Sources of background: Uncorrelated background e/p combinations where e and p are from opposite B’s Flat distribution Correlated background Non-prompt e/p combinations from the same B but not from signal, i.e. B +   c  X,  c    e  X,   pX Peaked near cos , but less sharply than signal. Continuum background Background due to non-BB sources, (e  e   qq, where q = u, d, s, c) Fake e/p background Misidentified e  or p

Yield: B   pe  e X Partially reconstruct the decay B  pe  X b  c signal 9.1 fb -1 On-  (4s) 4.6 fb -1 Off-  (4s) Continuum and fakes have been subtracted from data –Obtain cos  distribution for sample –Subtract fake e  and p backgrounds using data distributions –Subtract continuum background using Off-  (4s) data –Using MC generated shapes for uncorrelated and correlated backgrounds, fit to a sum of these components to get signal yield N signal =  834  634 (stat.)  380 (syst.)   Upper limit:  BF(B   pe  e X) < 5.9  10 -4

Implications for B  Xe BF(B  baryon e  < 1% of BF(B  Xe ) Want limit on B  baryon e  factor of 2 for neutrons:  Upper limit on BF(B  baryon e ): (2  (5.9  )) ~ CLEO B  Xe measurement: BF(B  Xe ) = (10.49 ± 0.17± 0.43)  Limit on B  pe  e X: BF(B   pe  e X) < 5.9  BF(B  baryon): BF(B  p/p anything  = (8.0 ± 0.4)% [2] [1] CLEO (1996) [2] PDG 2000 Limit on B  pe  e X is a limit on ep final states ONLY.  (B  baryon) external W < 1% of B  X  External W emission * does not contribute significantly to baryonic decays of B mesons * Baryon production at lower vertex via external W emission

Experimental technique: B    p  Fully reconstruct events: B    p    p  Background sources: –BB - negligible ( smaller than continuum by a factor of 60!) –Continuum (e + e   qq, qq = uu, dd, ss, cc) For remaining events, feed shape variables into neural net, cut on net output Obtain signal and background yields in  E, M B signal box |  E|  GeV ≤ M B ≤ GeV/c % Real  80.5%Real p 95.5% Real  After shape variable cuts are applied to remove continuum: 19.6%  8.8%Other 32.2% 00 34.2%ISR * * ISR = Initial State Radiation

 E and M B (beam-constrained mass)  (4s) ~ 20 MeV above BB threshold.  Energy of each candidate B (E cand ) is same as beam energy (E beam ) Reconstruct B meson candidate, impose the constraint E cand = E beam to form the following standard reconstruction variables: Energy Difference,  E Resolution:  E ~ MeV Beam-constrained mass, M B Resolution:  M ~ 2-4 MeV ~ 10  better than the resolution obtained without the constraint To find BB events, look at M B distributions for events with  E ~ 0

Experimental technique: B     p  B pB p  E   E (GeV) MBMB  E =  114 MeV  (B    0 p  ) max = 0.42   (B    p  ) max B pB p  E  MeV Instead, preserve all features of B    p  analysis and slide the  E  M B signal box to  E –The soft  is not included in  p , so  E will be shifted by the energy of the  for  0 p  Reconstructing B        p  not feasible because of low efficiency and high fake rate

Yield: B    p  and B     p  CLEO II + II.V: (9.7  10 6 BB events) On  (4s): 9.1 fb -1 Off  (4s): 4.4 fb -1 On  (4s): 0 events Off  (4s): 1 event (Expect 0.6 events)    p  On  (4s): 1 events Off  (4s): 0 event (Expect 0.2 events)     p   E vs. M B signal box: < M B < GeV |  E| < GeV  E shifted by -114 MeV for   p 

Upper Limit: B      p   1.5 GeV = 10.5%  2.0 GeV = 12.4% Systematic errors: Combined systematic error on the efficiency:  = 8.4% Increase upper limit on BF by 1.28  Efficiency: Use efficiencies calculated from a signal sample of unpolarized  ’s and using a P 3 /M phase space factor (p-wave system) for the  p (   p) mass distribution: Conservative 90% CL upper limits (including syst. error): [Br(B –   p  Br(B –   0 p  ] 1.5 GeV < 3.9 x [Br(B –   p  Br(B –   0 p  ] 2.0 GeV < 3.3 x [Br(B –   0 p  Br(B –   p  ] 1.5 GeV < 7.9 x [Br(B –   0 p  Br(B –   p  ] 2.0 GeV < 6.4 x 10 -6

Upper Limit on B  X s (baryon)  What we HAVE is a limit on BF(B     p  + B    p  ) What we WANT is limit on BF(B  X s , X s containing baryons) –Extrapolate from our measured exclusive baryon modes –We can use either B    p  or B     p  to get this limit, but using B     p  relies on fewer theoretical assumptions. To obtain upper limit on B  X s (baryon) , need to know Limits on b  s  decays to baryons: BF(B  X s  X s containing baryons) 1.5 GeV ≤ 9.5 x BF(B  X s  X s containing baryons) 2.0 GeV ≤ 3.8 x For E  > 1.5 GeV: R  p  = 12; For E  > 2.0 GeV: R  p  = 6

Implications for b  s  Recent CLEO b  s  measurements: BF(b  s  ) 2.0 GeV = (2.94 ± 0.41± 0.26) x  E   2.0 GeV = ± 0.032± GeV  E      E   GeV = ± ± GeV 2 43% 47% 36% Efficiency for b  s  decays to baryons ≈ 1/2 that for b  s  to mesons only Branching Fraction  Upper limit on correction to BF(b  s  ): (1/2  13%) = 6.5% Mean Photon Energy  E   baryons ≈ 2.10 GeV (250 MeV lower than our published number)  Upper limit on correction to  E   : (1/2  13%  250 MeV) = 16 MeV Variance in Photon Energy Estimate the effect of photons missed due to baryons by placing them at 2.1 GeV  Upper limit on correction to  E      E   GeV : GeV 2 Limit on b  s  from baryons (obtained from the   p  search): BF(B  X s , X s containing baryons) ≤ 3.8  (13%)

 External W emission is NOT the dominant mechanism for baryon production in B decays. Conclusions  Corrections to (b  s  ) BF,  E   2.0 GeV, and  E      E   GeV are less than half the combined stat.  syst. errors quoted. Upper limits at 90% C.L. using 9.7  10 6 BB’s: BF(B  pe  e X) < 5.9  B  pe  e X All upper limits at 90% C.L. using 9.7  10 6 BB’s: [BF(B    p  ) BF(B     p  )] E  >2.0 < 3.3  [BF(B     p  ) BF(B    p  )] E  >2.0 < 6.4  BF(B  X s , X s containing baryons) E  >2.0 < 3.8  B  X s  (X s containing baryons) To be published in PRD