charm baryon spectroscopy and decays at Belle Recent studies of charm baryon spectroscopy and decays at Belle Y. Kato (KMI, Nagoya) 2018/3/6 Moriond QCD

Physics of charmed baryons (1) ・Charm quark is heavier than u,d,s quarks ・spin-spin interaction∝1/m1m2 ・Di-quark structure in light quarks - Di-quark as new degree of freedom. - Easier to understand baryons. Nucleon Charmed baryon Every pair can not be distinguished. Light di-quark and charm quark. 2018/3/20 Moriond QCD

Physics of charmed baryons (2) q c s c s W- q q q W W c s q q q q q q q q q q q q q q Spectator Internal W W-exchange ・ The weak decay of charmed baryon is not understood well. - Three diagrams contribute in the tree level, strength of each is not known. ・ Ground state charm baryon is a good laboratory to study strange baryons as decay proceed via c->s transition. ・ Belle has collected ~1 ab-1 e+e- data samples (mainly at Υ(4S)). - 109 e+e-→ cc samples - 7.7× 108 BB samples ・ Huge data sample enable to study various charmed baryons. 2018/3/20 Moriond QCD

Contents (4) Confirmation of excited Ωc (3) Observation of Ξc(2930) (2) Ωc decay (5) Production rates of various baryons (1) Search for strange pentaquark via Λc+→π0pφ decay 2018/3/6 Moriond QCD

(1) Search for pentaquark via Λc+→π0φp ・ LHCb observed hidden charm pentaquark state in the Λb0 → K- Pc+ → K- (J/ψ p). ・ Analogue search for hidden-strange pentaquark by switching b->c (Λb0 →Λc+), c->s (J/ψ -> φ) :Λc+→ π0 Ps+ → π0 (φ p) ・ Λc+→π0φp decay itself is not observed so far. 2018/3/6 Moriond QCD

Search for pentaquark via Λc+→π0φp (result) M(K+K-pπ0) Phys. Rev. D 96, 051102(R) M(K+K-) M(φp) ・ Perform 2D fit on M(K+K-pπ0) and M(K+K-) plane. No significant Λc+ signals is observed. New upper limits: - Br (Λc+→φ p π0) < 15.3x10-5 - Br (Λc+→K+K-pπ0 )NR < 6.3x10-5 ・ Also perform 2D fit in each M(φp) bin. No significant Ps+ signal observed. - Br(Λc+→π0Ps+)xBr(Ps+→φp) < 8.3×10-5 2018/3/6 Moriond QCD

(2) Hadronic decays of Ωc ・ Among 4 ground state charmed baryons (Λc, Ξc0 Ξc+, Ωc), information of Ωc (css) is not studied well as cross section is small. ・Only Ωc has the same flavor light quarks (ss). Constructive interference is thought to be the origin of its short life time. ・ Precise measurements will shed light on the dynamics of baryon weak decays. ・ Belle performed measurements of 8 decay modes relative to the bench mark mode: Ω-π+ Life time (ps) Phys. Rev. D 97, 032001 Λc+ Ξc0 Ξc+ Ωc 200±6 112+13-10 442±26 69±12 M(Ωπ+) どの崩壊をstudyしたか良く分からない。 2018/3/20 Moriond QCD

Mass distributions for eight decay modes Ω-π+π-π+ Ω-π+π0 Ξ-K-π+π+　 Ξ0K-π+ Ξ-KSπ+ (New!)　 Ξ0KS (New!) ΛKSKS (new!) Σ+K-K-π+ Phys. Rev. D 97, 032001 2018/3/20 Moriond QCD

Intermediate states K*0 K*0 Ξ(1530) ρ- M(Ξ-π+) in Ξ-K-π+π+ M(π+π0) in Ω-π+π0 Ξ(1530) ρ- M(K-π+) in Ξ-K-π+π+ M(K-π+) in Ξ0K-π+ K*0 K*0 Phys. Rev. D 97, 032001 ・ Intermediate resonances are studied for the first time in 3 decays. 2018/3/20 Moriond QCD

Results of the branching fraction Phys. Rev. D 97, 032001 New! ・Precision improved by ~factor 2 for already measured modes. ・First measurements of intermediate resonances. - Dominant contributions. ・Three first observations. 2018/3/20 Moriond QCD

(3) Observation of Ξc(2930) ・ A weak evidence of Ξc(2930) was reported by BaBar in B-→Ξc(2930)Λc ,Ξc(2930)→Λc+K- ・ Assigned as one star in PDG (need confirmation) . ・ Belle performed the study with ~3 times statistics. Previous study by BaBar New study by Belle arXiv:1712.03612 (Appear in EPJC) Phys. Rev. D 77, 031101(R) Mass (MeV/c2) Width (MeV) BaBar 2931±3±5 36±7±11 Belle 2928.9±3.0+0.8-12.0 19.5±8.4+5.4-7.9 ・ The statistical significance of the peak at Belle is 5.1σ. ・ Mass and width are consistent each other 2018/3/20 Moriond QCD

Some comments on Ξc(2930) ・ Ξc(2930)0 is the first charmed charmed baryon established in the B-decay. ・Candidates of corresponding Λc, Σc states? ・As it is two-body B-decay, spin can be determined un-ambiguously from helicity constraint if we have enough statistics. Phys. Rev. D 77, 012002 M(Λc+K-) in e+e-→cc by BaBar. No signal. B→(Λc+π) p by BaBar Mass = (2846±8±10) MeV/c2, Width = 86+33-22 MeV Possibly Σc(2800), may be a different state. The Ξc’ -Σc mass difference is ~120 MeV. Good candidate as partner of Ξc(2930). Need confirmation by Belle. 10.1103/PhysRevD.78.112003 2018/3/6 Moriond QCD

(4) Excited Ωc states Phys. Rev. Lett. 118, 182001 Ωc(3050) Ωc(3066) Ωc(3000) Ωc(3090) Ωc(3119) Ωc(3188)? ・ LHCb reported 5 (+1) excited Ωc states in the Ξc+K- final states. ・ Belle studied the same final state to confirm existence. ・ Though statistical sensitivity of Belle is much lower than LHCb, study with different production may shed light on the nature of these states. 2018/3/20 Moriond QCD

Confirmation by Belle ・ The Ξc+ is reconstructed in 7 decay modes: (Ξ-π+π+, ΛK-π+π+, Ξ0π+, Ξ0π+π-π+, Σ+K-π+, ΛKSπ+, ad Σ0Ksπ+) ・ Widths are fixed to the value obtained by LHCb in the fit. ・ 4 of 5 states are confirmed (>3σ) Only Ξc(3119) was not confirmed. ・ The mass is consistent with LHCb. Ξc+K+ (wrong sign) Ξc+ sideband arXiv:1711.07927 (appear in PRD) LHCb Belle Ωc(3000) 3000.4±0.2±0.4+0.3-0.5 3000.7±1.0±0.2 (3.9σ) Ωc(3050) 3050.2±0.1±0.1＋0.3-0.5 3050.2±0.4±0.2 (4.6σ) Ωc(3066) 3065.6±0.1±0.3+0.3-0.5 3064.9±0.6±0.2 (7.2σ) Ωc(3090) 3090.2±0.3±0.5+0.3-0.5 3089.3±1.2±0.2 (5.7σ) Ωc(3119) 3119.1±0.3±0.9+0.3-0.5 3119.0±0.3±0.9 (0.4σ) 2018/3/20 Moriond QCD

(5) Production rate of various baryons arXiv:1706.06791 (Appear in PRD) Charmed baryons Hyperons ・ Production ratio = σ/(2J+1) for various baryons in e+e- collision. - Lie on exp(-αm). Explained by string fragment model. - First measurement for charmed baryons. - Feed down from higher resonance subtracted. ・ A factor three suppression of Σc is observed (not for hyperons). - If charmed baryon production proceeds via diquark-anti-diquark pair production, the mass difference of spin-0 di-quark (Λc) and spin-1 di-quark (Σc) can explain this. Suggesting a di-quark structure in the charmed baryon. 2018/3/20 Moriond QCD

Conclusion ・ Belle is still actively working on the charmed baryons. - Hidden-strange pentaquark in Λc+ -> pφπ0 - Branching fractions of hadronic decay of Ωc - Observation of Ξc(2930) - Confirmation of excited Ωc - Production rate of various baryons ・ Belle II will enable us to discover more states, determination of quantum numbers! 2018/3/6 Moriond QCD