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New Results on Heavy Flavor Baryons Charm 2006

New Results on Heavy Flavor Baryons Charm 2006. Outline Qqq Masses and Lifetimes – theoretical issues and new results L c mass shift L b lifetime Charm baryon lifetime systematics –new data Qqq Decay and Excitation Properties L b Branching Ratios More New L c states

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New Results on Heavy Flavor Baryons Charm 2006

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  1. New Results on Heavy Flavor BaryonsCharm 2006 • Outline • Qqq Masses and Lifetimes – theoretical issues and new results Lc mass shift Lb lifetime Charm baryon lifetime systematics –new data • Qqq Decay and Excitation Properties • Lb Branching Ratios More New Lc states • Lc Branching Ratio Measurements • QQq States – an update • Conclusions Jim Russ - Carnegie Mellon

  2. A Weighty Matter - What is the Lc Mass? PDG value static for a decade, dominated by CLEO and NA32 results New results from BaBar and Selex with much smaller errors pull mass 1.5 MeV/c2 higher Important information for any future studies of LcLc resonant production at e+e- machines. Jim Russ - Carnegie Mellon

  3. Qqq Baryon Lifetime Issues • HQET [ (1/mQ)2 suppression of non-spectator effects]  all B-hadron lifetimes should be very similar. t(Lb0 )/t(Bd0 ) is well below prediction in LEP, CDF Run I data. • Charm baryon lifetime hierarchy predicted from quark models already in 1984-86. HQET agrees. • Data match HQET except for Xc+.The ratio t(Xc+ )/ t(Lc0 ) is off by the same factor as the lifetime. Problem for HQET: lifetime ratios vary as (1/mQ)3 while the lifetime itself varies like (1/mQ)2 . Jim Russ - Carnegie Mellon

  4. Selected Lifetime Ratios PDG 2005 lifetimes • Theory Data(PDG05) • B+/ B0 1.061.086  0.017 • b0/ B0 0.9-1.0 0.797  0.052 Xc+/ Lc+ 1.5 2.2  0.1 Lc+/ Wc0 2.72.9 0.5 Model calculations describe lifetime systematics well, with two conspicuous problems. Jim Russ - Carnegie Mellon

  5. New Lb0 Results from CDF CDF and D0 measure lifetime using Lb0 J/ L. First results using fully-reconstructed decays. New CDF measurement (1 fb-1): t = 1.59  0.08 (stat)  0.03 (syst) ps Ratio to B0 J/ Ks minimizes systematics: tLb / tBo = 1.037  0.058 B0 lifetime agrees well with PDG: 1.524  0.030  0.016 ps Jim Russ - Carnegie Mellon

  6. Restoration of Order in HQET? Bigi and Uraltsev: ‘natural’ range of tLb / tBo is 0.94  0.05 - competing effects from positive and negative interference. Models enhanced sub-leading terms in 1/mb matrix element expansion  faster decay rate. Predictions for tLb / tBo range from 0.86 to 0.90 in these models. With this new result, are we back to the basic model for b decays? Jim Russ - Carnegie Mellon

  7. One Disagreement gone – what about Xc+? t(Xc+)/ t(Lc+) ~ 1.5 in models  t(Xc+) ~ 300 fs SELEX Preliminary t(Xc+) 301 evts CLEO: t(Xc+) = 503  47  18 fs (250 evts) FOCUS: t(Xc+) = 439  22  9 fs (532 evts) New SELEX Result SELEX: t(Xc+) = 419  24  9 fs (301 evts) Excellent agreement with FOCUS Problem with t(Xc+) is not experiment ! Jim Russ - Carnegie Mellon

  8. WcoLifetime Recent Results from FOCUS, SELEX SELEX(600 GeV S- beam): 76  10 evts in 2 modes t = 74  14(stat)  11 (syst) fs FOCUS (180 GeV g beam): 59  12 evts in 2 modes t = 72  11(stat)  11 (syst) fs signal backgnds for 2 modes Using PDG Lc+ lifetime, the lifetime ratio becomes t(Lc+)/ t(Wc0)= 2.81  0.37 compared with the model prediction of 2.7 Jim Russ - Carnegie Mellon

  9. Branching Ratio Measurements Lifetimes are inclusive calculations. What about BRs, where W-scattering and Pauli Interference terms are important, as in the Xc0system studied in great detail recently by BaBar and Belle Xc0:WS + Pauli Xc0:Spectator + Pauli Tevatron, e+ e- B-factories producing new b- and c-baryon branching ratio measurements. Theoretical predictions for some baryon modes now available from Soft Collinear Effective Theories (SCET). Jim Russ - Carnegie Mellon

  10. New Lb Branching Ratio Measurements CDF: BR for single-pion emission in Bo and Lb decays – test of SCET. Note complex background for Lb. Limiting error comes from the BR for Lc pK- p+ , not statistics! G(LbLc+p-)/G(BoD+ p-)= 3.3  0.3(stat)  0.4(sys)  1.1(frag+BR) while SCET (Leibovich, Ligeti, Stewart and Wise) predicted 1.7 We wish we knew the Lc pK-p+ BR better. Jim Russ - Carnegie Mellon

  11. More SCET Tests SCET + HQET + 1/Nc predicts Lb semileptonic decays dominated by Lc+ ground state (6%) + p-wave excitations (2-3% for each state) and predicts that Sc modes are suppressed. Predict G(LbLc+m-n)/ G(LbLc+p-) ~ 15 New CDF measurements of these quantities. Good news for theory: CDF measurement G(LbLc+m-n)/ G(LbLc+p-) = 20.0  3.0(stat) 1.2(sys)  1.2(BR) And not so good news – CDF has first measurements of semileptonic decays to excited charm baryon states. Four different channels measured : G(LbLc+(2593)m-n)/ G(LbLc+m-n) ~ .048  .016 … not ½ . G(LbSc++ p- m- n)/G(LbLc+m-n) ~ .042  .016 - same order. Jim Russ - Carnegie Mellon

  12. BELLE and BABAR Xc0 Studies For charm SCET arguments break down. Excellent new data on branching ratios is compared to venerable quark models. BABAR BELLE G(Xc0L KS)/ G(Xc0X- p+) 0.21  0.02 (stat)  0.02 (syst) [1st] G(Xc0W- K+)/ G(Xc0X- p+) 0.296  0.018 (stat)  0.030 (syst) CLEO(92) 0.50  0.21 (stat)  0.05 (syst) Zenczykowski (94) quark model + CA 0.28 (WS + Internal W)/Spectator Körner and Kramer (92) quark model 0.32 (WS / Spectator) Quark Models do pretty well. How can we move beyond them? Jim Russ - Carnegie Mellon

  13. BaBar Wc0 Studies BaBar reports a lovely Wc primarily in the two-body Wp decay channel. They report G(Wppp)/ G(Wp) < 0.30 at 90% C.L. This is a surprising result. For the spin-1/2 charm baryons Lc+and Xc+the 3p/1p relative branching ratios are of order 3.3! CLEO and E687(photoproduction) had also reported only an upper limit for G(Wppp)/ G(Wp) . Is there something unusual about the spin-3/2 decay mechanism? Jim Russ - Carnegie Mellon

  14. Charm Baryon Spectroscopy – from harmonic oscillator to the lattice • State of the art in spectroscopy still based on Copley, Isgur and Karl from 1979 – valence quarks in harmonic oscillator potential. Model has huge number of states, but only a few are seen. • New lattice calculation program underway (LHPC, Colin Morningstar) – aims to compute excitation spectra for normal and charmed baryons with dynamic pions as light as 300 MeV. – expect first results in 2007. • Meanwhile, Belle and Babar report new Sc and Lc states. Jim Russ - Carnegie Mellon

  15. Belle Data Show New Sc State Quark model candidate state: Sc2 D-wave excitation  Lc+ p- Quark model calculations predict width ~ 15 MeV/c2 Experimental width ~ 70 MeV/c2 Mixing with other states? nearby Sc1 ? Reflection from Lc+(2880) Lc+ p+ Sc+ Sc++ Sc0 Jim Russ - Carnegie Mellon

  16. New Lc+ from BaBar No trace of either state in CDF data with comparable mass resolution. BaBar data show known narrow Lc(2880) and new Lc (2940) state, both in pDo (new decay mode for Lc(2880) ). New state 6 MeV below pD*o threshold, one pion mass above Belle Sc(2800) state. Jim Russ - Carnegie Mellon

  17. Spectroscopy Conclusions BaBar CLEO BELLE • Quark model spectroscopy accomodates the observed Lc+ , Scstates with reasonable accuracy. Width predictions generally not good. Fixing quantum numbers is hard. without a model as a guide. • The 2880 decays both to pDo and Lcpp. 2940 goes only to pDo . • Lattice gauge calculations are starting to treat low-lying states with almost-physical pions. Data have fascinating regularities as a challenge for theory. Jim Russ - Carnegie Mellon

  18. Now QQq Baryons • First QQq candidate comes from baryon beam expt: • (ccd)+Lc+ K- p+ Cabibbo-favored spectator mode • state seen from S-, p but not p- • not seen in FOCUS photoproduction expt • lifetime is very short – disagrees with extrapolation from single charm Production cross section is a sizeable fraction of Lc+ production – consistent with intrinsic charm model. Phys Rev Lett 89 (2002)112001 Jim Russ - Carnegie Mellon

  19. A Different Xcc+ Decay Mode Xcc+ pD+K-is another ccd all-charged decay mode. • Have automatic background check with pD-K+ • Event-mixed background (grn) gives absolutely-normalized description of bkg . • Wrong-sign pD-K+ are featureless at same level as combinatoric. Jim Russ - Carnegie Mellon

  20. Combine Xcc+ Mass Distributions Phys. Lett. B628,18 (2005) Gaussian with width fixed from MC fitted to pD+K-data to fix mass: 3518  3 MeV/c2 . Combine with 3519  2 MeV/c2 from other mode: m(Xcc+) = 3518.7  1.8 MeV/c2 . G(pD+K-)/G(Lc+K-p+) = 0.20  0.12 Jim Russ - Carnegie Mellon

  21. Also a Xcc++ Excited State Candidate Look at Q=2 candidates in Lc+ K- p+p+ final state from S- beam. No new cuts. • See broad structure at 3780 MeV/ c2 – wider than resolution – either has natural width or two states • Combinatoric background from event mixing describes high-mass side of plot • fitted background under peak compares well with event-mixed level. • Have one (or maybe HQET pair of) ccu excited state(s). Jim Russ - Carnegie Mellon

  22. BaBar and Belle Null Searches for Xcc+,++ BaBar sample: 600,000 Lc+ pK-p+with PID (DIRC) BaBar finds no hint of a signal in any double-charm state from continuum annihilation at 10.58 GeV/c and sets a 95% C.L upper limit corresponding to 7% of the production of singly-charmed Xc0 X-p+ Xcx(3077)+ Belle (Preliminary!) also finds no Xcc+but they report two new Xc+states at 2980 and 3077 MeV/c2 from the search. higher mass state is narrow. Lattice, where are you? Xcx(2980)+ Jim Russ - Carnegie Mellon

  23. Conclusions • Belle and Babar continue CLEO tradition of charmed baryon spectroscopy. New Lc+states not seen in hadron experiments,e.g., CDF. • CDF has new Lb0 measurements in fully-reconstructed modes. CDF lifetime result removes conflict with HQET/1/mQ expansion. Await Xb0,- , Wb- measurements for further tests of lifetimes and SL decay widths . • Charm baryon lifetimes agree well with model calculations except for the Xc+ . Experiments agree well. Theory??? • New Lc+ , Sc0,+,++ , Xc+states from BaBar and Belle challenge lattice spectroscopy to predict sparse charm baryon mass population. • SELEX double charm baryons are statistically significant, limited signal populations. Production definitely baryon-baryon – not seen in photoproduction. Intrinsic charm? Jim Russ - Carnegie Mellon

  24. And Wishes • Many Qqq baryon studies hinge on knowing the BR for Lc pK- p+. I wish for e+e- running at 2mLc to nail the BRs. • Experiment continues to add new Qqq states. I wish for high statistics samples of B decays to c-baryons for JP analysis. Belle has made a start. • Collider experiments are starting precision tests of SCET and factorization for baryons as well as mesons. I wish for continued developments in theory and data. I hope for the b-c baryon soon to be seen at the Tevatron. • Double charm studies are still active and point to purely hadron-hadron production. I wish there were future hadron experiments to pursue such issues in flavor physics. (maybe LHCb) Jim Russ - Carnegie Mellon

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