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Charmed Baryon spectroscopy at Belle

Charmed Baryon spectroscopy at Belle. Y. Kato Nagoya University. Mainly based on the paper recently accepted by PRD (  arXiv:1312.1026 ). Physics of heavy baryons. Mass of the charm quark is ~ 1.5 GeV . This is much heavier than…. 1. Momentum of quarks inside the baryon

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Charmed Baryon spectroscopy at Belle

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  1. Charmed Baryon spectroscopy at Belle Y. Kato Nagoya University Mainly based on the paper recently accepted by PRD ( arXiv:1312.1026)

  2. Physics of heavy baryons Mass of the charm quark is ~1.5 GeV. This is much heavier than…. 1. Momentum of quarks inside the baryon radius~1fm → 200MeV/c. →Non-relativistic quark model is a good approximation. Study of QQ potentialfrom doubly charmed baryon. (Similar to QQbar potential by charmonium spectroscopy) 2. Mass of the u,d,s quarks (300-500 MeV) spin-spin interaction∝1/m1m2 Di-quark correlation in light quarks. Study of qq interaction from single charmed baryon. c d u

  3. Observed charmed baryons Ξc1/2+ Ξ’c1/2+ Ξc(2645) 3/2+ Ξc(2790) 1/2- Ξc(2815) 3/2- [Ξc(2930) ??] Ξc(2980) ?? [Ξc(3055) ??] Ξc(3080) ?? [Ξc(3123) ??] Σc(2455) 1/2+ Σc(2520) 3/2+ Σc(2800) ?? Λc+ 1/2+ Λc(2595)+ 1/2- Λc(2625)+ 3/2- [Λc(2765)+ ?? ] Λc(2880)+ 5/2+ Λc(2940)+ ?? Ωc 1/2+ Ωc(2770) 3/2+ c c s s d u c d u c CLEO 8(7) (1995～2001) BELLE 3 (2006～) BABAR 5(2) (2007～) s u ・16/21 (12/17) charmed baryons are observed ine+e- collider experiment. ・All the ground state of single charmed baryons are discovered. ・Except for Λc(2595)+, Λc(2880)+, Σc(2455), spin/parity are not measured.

  4. Charm production in e+e- collider e+e-→ ccbar e- c √s=10.58 GeV γ* e+ c ・Cross section for e+e-→qqbar does not depend on the flavor of quarks. Depends only on the charge2. →σ(e+e-→ccbar)=σ(e+e-→uubar)=4σ(e+e-→ssbar)=4σ(e+e-→ddbar) ・Belle has highest statistics in the world =1000fb-1 (×~75 of CLEO, ×2 of BaBar) ・Detect decay particles only (inclusive reaction)⇔J-PARC.

  5. Still many things to do.......... ・Many missing resonances yet.. --Only one excited Σc, no excited Ωc.. ・Almost no spin-parity measurement. ・There are several 1 star, 2 star states. -Λc(2765)+, Ξc(2930), Ξc(3055), Ξc(3123) ・Only upper limit is given for the width. - Λc(2625), Σc(2455), Ξc(2645), Ξc(2790), Ξc(2815) ・No established doubly charmed baryon (Ξcc). Answer part of these thing today!

  6. Outline of today’s talk ・Doubly charmed baryon(Ξcc) search ・Excited charm-strange baryons (Ξc*) ・Study on going:Λc/Σc(2765)

  7. Past experimental search for Ξcc Evidence from SELEX in 2003 Mass:~3.52 GeV/c2 B-factories BaBar@232fb-1 Belle@461.5fb-1 M(Λc+K-π+) hep-ex/0606051 M(Λc+K-π+) hep-ex/0605075 hep-ex/0208014 ・Evidence by SELEX was not supported by FOCUS, B-factories. ・No established state even for ground state. ・Prediction of the mass: ~3.5-3.75 GeV by quark model, 3.6 GeV by LQCD

  8. Λc+ yield ~8×105 ⇔ ~3×106for Belle

  9. Ξcc decay modes ・Ground state baryon decays via weak interaction. ・Ξcc+ is expected to decay into ΛcK-π+and Ξc0π+ π+ π+ u u d W+ d W+ Ξcc+ c Ξcc+ s K- c s c u c c d u Ξc0 c d d Λc+ d ・Belle searched Ξcc with Λc+K-π+ mode only. ・Background: inclusive Λc+ or Ξc0 production. ・σ(e+e-→Λc+X)×Br(Λc+→pKpi)/σ(e+e-→Ξc0X)×Br(Ξc0→Ξ-π+) ~10.

  10. Since previous studies... ・Use full statistics of Belle data (~1000 fb-1). (2×previous Belle, 4×previous BaBar). ・Decay modes including Ξc0 is also studied . ・Use several sub decays of Λc+ and Ξc0.

  11. Reconstruction of Λc+ M(pK-π+) M(pKs) ・Previous studies used pK-π+ only. ・Inclusion of pKS mode increases statistics by ~20 %. ・S/N ratio is comparable.→Combine two decay modes. ・Total Λc+ yield is around 3×106⇔ ~1600 Λc+ by SELEX. ・Apply mass constraint on Λc+→Mass resolution for Ξcc is 2.5-3.5 MeV/c2 ・Xp>0.5 is required (Xp = pcm/pmax pmax = sqrt(Ecm2-MΞcc2) ).

  12. Result for Λc+K-π+ decay mode M(Λc+K-π+) Data MC expectation for signal σ=500 fb, Br(Ξcc→Λc+K-π+) = 5% Theoretical prediction: 70, 230 fb ・Significance from -2ln(L/L(0)) ・Significance is less than 3σ in all mass region... 95% C.L Upper limit of σ(e+e-→ΞccX)×Br(Ξcc→ΛcK-π+)

  13. Reconstruction of Ξc0 M(Ξ-π+) M(ΛK-π+) M(pK-K-π+) ・Total yield of the Ξc0 is 1.6×105 ・Previous study by BaBar use Ξ-π+ only. ・S/N largely depends on the decay mode. →Simultaneous fitting with fixing relative signal yield gives better sensitivity.

  14. Study of the Ξc+(2645) Ξc0π+ is a strong decay mode of Ξc+(2645) (JP=3/2+) as well as weak decay of Ξcc. →Use yield of Ξc+(2645) to determine signal ratio. M(Ξc0π+) in low mass region Ξ-π+ ΛK-π+ Ξc+(2645) feed down of Ξc(2790)+ ・Signal PDF: Gaussian convoluted B.W. (σ of Gaussian = 1.05 MeV from MC) ・Shape of feed down of Ξc(2790)+ is made from MC. ・Ξ-π+ :pK-K-π+:ΛK-π+: =1298±51:974±47:1444±58 ・Inclusion of pK-K-π+ and ΛK-π+ modes effectively increase statistics 1.8 times for Ξcc+. pK-K-π+

  15. Result of Ξcc+ search:Ξc0π+ Ξ-π+ ΛK-π+ Data Signal MC (assuming 500 fb-1 and 5% for branching farctions.) ・Simultaneous fitting with fixing signal yield ratio. ・3.2σ for 3.553 GeV/c2 but probability to observe a peak with significance>3.2 in this the mass range of 3.2-4.0 GeV is 26%. pK-K-π+ 95% UL of σ(e+e-→ΞccX)×Br(Ξcc+→Ξc0π+)×Br(Ξc+→Ξ-π+)

  16. Study of double charm production in progress ・Production mechanism of double charm production is poorly known. →predicted cross section is not reliable. ・e+e-→ J/ψ+ccbar by Belle No measurement on the double charm production without J/ψ so far. ・O. Seon in Nagoya University is studying the elementary DD production using Belle data.

  17. By-product of the Ξcc search. Ground hadrons decays via the weak interaction. This is also a strong decay of hadrons in light quark configuration. ex. pπ is a weak decay mode of Λand strong decay mode of Δ Kπ is a weak decay mode of D and strong decay mode of K* Ξcc+ Ξc*+ weak (c→s) Λc+ c strong c c s K- u u π+ Let’s study Ξc*

  18. Charmed strange baryons (Ξc) 3.2 Ξc Ξc(3123)? C 3.1 Ξc(3080) Ξc(3055)? 3.0 Ξc(2980) λ mode 2.9 S u (3/2-) Ξc(2815) ρ mode 2.8 Ξc(2790) (1/2-) u/d-s diquark system! 2.7 Ξc(2645) (3/2+) Identification of ρ mode excitation is essential for di-quark spectroscopy. (only λ mode excitation is observed) 2.6 Ξc’(1/2+) 2.5 Ξc(1/2+)

  19. Excited Ξc+ in Λc+K-π+ by Belle and BaBar Babar@384fb-1 hep-ex :0710.5763 hep-ex/0606051 Belle@461.5fb-1 Ξc(3080) M(Λcπ+) Σc(2520) Ξc(2980) Σc(2455) Ξc(2980) Ξc(3080) Ξc(3055)? M(ΛcK-π+) select Σc(2455) Ξc(3123)? select Σc(2520) M(ΛcK+π-) ・Belle: First evidence of Ξc(3080), Ξc(2980) ・BaBar: Confirmed them and reported another two states. Ξc(3055)→2star, Ξc(3123)→1star. M(ΛcK-π+)

  20. M(Σc(2455)++K-) by Belle χ2/ndf = 54.8/51 ・Structure near 3055 MeV/c2 is seen. ・Significance from -2log(Lmax/L(0). ・Signal pdf is Gaussian convoluted Breit-Wigner (σ from signal MC). ・ BG shape ・Significance of 6.6 σ. Mass/width of Ξc+(3055) Result of the Babar is confirmed with 6.8 σ.

  21. M(Σc*(2520)++K-) by Belle Ξc(3080)+ χ2/ndf = 28.6/42 ・Structure near 3123 MeV/c2 is not seen ・Signal PDF:Gaussian convoluted Breit Wigner. Mean, width was fixed from measurement by BABAR. ・Yield = 8.2±22.0 → Measurement of upper limit σ×Br(Λc+→pK-π+) of Ξc+(3123) < 0.34 fb @95%C.L ⇔ 1.6±0.6±0.2 fbby BaBar Result of the Babar was not reproduced...

  22. Comparison of Λc+ andΞc orΣc andΞc’ spin0 di-quark spin1 di-quark ・The mass difference of Λc and Ξc is ~200 MeV/c2,Σc and Ξc’ is ~120 MeV Λc+ with 3055-200 = 2855? Σc with 3055-120 = 2935?

  23. Further study for Ξc* ・We confirmed Ξc(3055)+ but its isospin partner Ξc(3055)0 is not found. ・Spin-parity and excitation mode is not known for excited states. ・Relative branching fraction is sensitive to the excitation mode. ・More excited states? c arxiv:0710.5763 M(Λc+KS0π-) by BaBar Ξc(3080)0 λ mode Ξc(2980)0 s u ρ mode 2.95 3.0 3.05 3.10 3.15 ・All the Ξc* are observed in (heavy baryon) + (light meson) final states. π, K Λc+, Σc, Ξc, Ξc’.. study ΛD! ・How about the (light baryon) + (heavy meson) ? →

  24. Analysis of ΛD+ M(K-π+π+) M(pπ-) D+ selection D+ sideband Λ selected region ・D+ from K-π+π+, Λ from pπ-. Vertex information on Λ. ・xp>0.7 is applied to reduce combinatorial background.

  25. M(ΛD+) distribution ・Peaks corresponds to Ξc(3055)+, Ξc(3080)+. ・No peak structure in D+ sideband region and wrong-sign ΛD-combination. ・Third order Chebychev for background. ・Significance of the peaks are: 11.7σfor Ξc(3055)+ and 4.7σ for Ξc(3080)+. ・Further confirmation for Ξc(3055)+ ・Most precise mass/width for Ξc(3055)+ and consistent with previous measurements. M(ΛD+) D+ sideband M(ΛD-) Ξc(3055)+ Ξc(3080)+

  26. Analysis of ΛD0 D0→K-π+π+π- D0→K-π+ D0 selection D0 sideband ・D0 from K-π+, K-π+π+π-, K-π+π0 ・Relative yields are comparable. D0→K-π+π0

  27. M(ΛD0) distribution M(ΛD0) D0 sideband M(ΛD0bar) ・Sum of three D0 decay modes. ・Peaks corresponds to Ξc(3055)0, Ξc(3080)0. ・No peak structure in D0 sideband region and wrong-sign D0barΛcombination. ・Third order Chebychev for background. ・Significance of the peaks are: 7.6σfor Ξc(3055)0 and 2.6σ for Ξc(3080)0. ・First observation of Ξc(3055)0! Ξc(3055)0 Ξc(3080)0

  28. Discussion ・The Ξc* with mass around 3.0 GeV/c2 is likely to be in N=2 shell. Prediction by chiral quark model for Ξc(3055) is inconsistent with this observation. arXiv:1205.2943 Lei-Hua Liu et al ・Ξc(3055)/(3080) can decay into both of (heavy baryon) + (light meson) and (light baryon) + (heavy meson) K- Λ D Σc c Naively thinking, λ mode → (light baryon) + (heavy meson) ρ mode →(heavy baryon) + (light meson) λ mode Both ρ and λmode excitation?? s u Help of the theorist is necessary! ρ mode

  29. Width of the Ξc+(2645) Only upper limit is given in PDG ・Gaussian convoluted Breit-Wigner (σ=1.05 MeV) ・Each modes gives consistent values. →Simultaneous fitting. ・Systematic error comes from.. --BG shape, fitting region (0.3 MeV). --Result of Ensemble study (0.15 MeV) --7% difference of resolution of Ξc0 for data and MC (0.1 MeV) First significant measurement of the width of Ξc+(2645)

  30. Another interest: Λc/Σc(2765)+ Most poorly known Λc/Σc state hep-ex/0010080 hep-ex/0608043 ・First evidence by CLEO ・By Belle p+D0 2803MeV/c2 Λc(2765) Λc(2880)+ Λc(2880) 38MeV/c2 Λc(2765)+ 2765 MeV/c2 Λc+(2765) Λc(2940) M(Σcπ) M(Λc+π+π-)

  31. Prediction from coupled channel approach hep-ph:1205.2275 Coupled channel calculation in I=0 channel. Λc(2595)+ is clearly seen. Calculate amplitude in I=1 channel Λc(2595)+ If the scenario is correct, it must be... ・Isospin = 1 (Σc state) ・Jp= 1/2- (S-wave DN scattering )

  32. Spin-parity measurement of Λc(2880)+ ・Spin/parity measurement by Belle@553fb-1 (hep-ex/0608043) Σcπ decay angular distribution About 5σ exclusion for spin 1/2, 3/2 M(Λc+π±) for Λc(2880)+ events Σc(2455) Prediction by Heavy Quark Spin Symmetry R=0.23 for 5/2+ R=1.45 for 5/2- Σc(2520)

  33. Summary ・Ξcc is not discovered with full data of Belle. U.L is comparable with some of the predictions. Further study of double charm production is on going. ・Ξc(3055) is confirmed but not for Ξc(3123). ・First observation of Ξc(3055) in ΛD final state. Need help of theorist for more detail of Ξc(3055). ・First significant measurement of Ξc(2645)+ width. ・Quantum number measurement of Λc/Σc(2765) is on going. ・Many other things to do!

  34. Backup

  35. Fragmentation property of Ξc(3055) M(ΛD+) for each xp M(ΛD0) for each xp 0.7<xp<0.8 0.8<xp<0.9 0.7-0.8 0.8-0.85 0.9-0.95 0.85-0.9 0.9<xp<0.95 0.95<xp<1.0 0.95-1.0 ・Fix the mean and width from global fit. (Systematic error on it is taken into account) ・S/N ratio improved as xp becomes larger.

  36. dσ/dxp Ξc(3055)+ Ξc(3055)0 xp xp ・Error bars are quadratic sum of stat and syst. ・In other charmed baryons, dσ/dxp show peaks in 0.7-0.8.

  37. Integrated luminosity of B-factories CLEO:13.7fb-1

  38. Belle detector SC solenoid 1.5T Aerogel Cherenkov cnt. n=1.015~1.030 3.5 GeVe+ CsI(Tl) 16X0 TOF conter m / KL detection 14/15 lyr. RPC+Fe 8 GeVe- ・General purpose detector ・Momentum measurement by SVD, CDC ・p/K/π ID by CDC (dE/dx), TOF, ACC → cover p<~3.5 GeV/c Central Drift Chamber Si vtx. det. 3/4 lyr. DSSD

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