1 Hadron spectroscopy results from Belle Y Kato

1 Hadron spectroscopy results from Belle Y. Kato (KMI, Nagoya University) 2019/2/14 KEK-FF 2019 1

2 Introduction Success of constituent quark model Mesons Int. J. Mod. Phys. A, 21, 5583 (2006) Phys. Rev. D 18 (1978) 4187 Baryons ”Constituent quark” must be a good approximation… but not the end. ・Why does it work so well? Exotic hadrons ・Where is the adaptive limit? Heavy hadrons ・Any other degrees of freedom? e+e- collider (especially B-factory) is a powerful probe! 2019/2/14 KEK-FF 2019 2

“New hadrons” from B-factories Charmonium B-decay Reaction 1: Br(B+→K+Xcc) ηc(2 S) ψ2(3823) X(3872) X(3915) Zc(4050) Zc(4250) Zc(4430) Zc(4200) Initial State Radiation Y(4260) Z(3900) Y(4008) Y(4360) Y(4660) Double charmonium X(3860) ≒ χc 0(2 P) X(3940) X(4160) Two-photon χc 2(2 P) Bottomonium Charm baryon decay 2019/2/14 Charmed baryon D*0(2400) D 1(2430) Ξc(2930) Hyperon Belle Ba. Bar 3: Observation of Ξc(2930) 4: Absolute branching fraction of Ξc e+e-→ccbar Y(n. S) decay D, D(s) 2: X(3872/3915)→π0χc 1 3 Hadron Type D*s 0 (2317) D 0(2550) DJ*(2600) DJ(2740) D 3*(2750) D*s 1(2700) D*s 1(2860) Ds. J(3040) Σc(2800) Λc(2940) Ξc(2980) Ξc(3080) Ωc(2770) Ξc(3055) Zb(10610) Zb(10650) ηb(1 S) ηb(2 S) hb(1 P) hb(2 P) 5: Observation of Ξc→Ξ(1620) π ~ 40 new hadrons! (Some states may be missed) KEK-FF 2019 Ω(2012) Ξ(1620) 3

4 X(3872) ・ The poster boy of XYZ exotics, firstly observed by Belle. - JPC = 1++ - Decay into both of J/ψρ (I=1) and J/ψω (I=0): isospin breaking - Mass consistent with DD* with O(0. 1) Me. V presicion. - Differential cross section at LHC consistent with χc 1(2 P) DD* molecule? cc? χc 1(2 P) Decays and production are essential to identify the nature ・Currently, only the product of two branching fractions are measured. - (B → K+ X) and (X(3872) → f) ・Former is production, and latter is the decay. ・Belle performed measurement of Br(B+→K+X(3872)) - This also leads to the Br(X(3872)→f). 2019/2/14 JHEP 01(2017)117 B+ K+ X Br(B+→K+X(3872)) × Br(X(3872)→f) KEK-FF 2019 4

5 Principle of the measurement ・Extract Br (B+→Xcc K+) → Do not look for Xcc decays - Fully reconstruct B meson decaying hadronically. - Reconstruct K+ mesons from the signal B meson. - Reconstruct Xcc from Missing mass: Mx 2 = (Pbeam-PBTag-PK+)2 ・ Belle performed the analysis with full data sets and measured 9 X ηc, J/ψ, χc 0, χc 1, ηc(2 S), ψ(3770), X(3872), and X(3915) Detect Reconstruct Hadronic decay B 2019/2/14 cc states: + B KEK-FF 2019 K+ X 5

K+ Missing Mass distributions 6 Phys. Rev. D 97, 012005 Low mass High mass 2019/2/14 KEK-FF 2019 6

7 Results Xcc σ Br (B+→Xcc. K+) (10 -4) Ba. Bar PDG (10 -4) ηc 14. 2 12. 0± 0. 8± 0. 7 8. 4± 1. 3± 0. 8 9. 6± 1. 1 ηc(2 S) 4. 1 4. 8± 1. 1± 0. 3 3. 4± 1. 8 X(3872) 1. 1 1. 2± 1. 1 (<2. 6) <3. 2 (<3. 2) X(3915) 0. 3 0. 4± 1. 6± 0. 0 (<2. 8) - - ・The best precision for ηc. ・First significant measurement of ηc(2 S). : Br(ηc(2 S)→KKπ) = (1. 3± 0. 4)× 10 -2 (my personal calculation) ・The most stringent upper limit for X(3872). : (Br(X 3872)→J/ψπ+π-) > 3. 2% @PDG ・The first limit for X(3915) : Br(X(3915)→J/ψω) > ~10%. Γ(J/ψω) > O( 1 Me. V). Very large as OZI suppressed mode 2019/2/14 KEK-FF 2019 7

8 Search for X(3872/3915)→χc 1π0 in B decays ・ BES III observed X(3872) → χc 1π0 in e+e- → γX(3872) (ar. Xiv: 1901. 03992) Br(π0χc 1)/Br(J/ψπ+π-) = 0. 88+0. 33 -0. 27± 0. 10 ・ π0χc 1 is isospin 1, which is suppressed in pure cc state. - Another evidence for non-cc. ・ Belle previously measured B+→χc 1π0 K+ using full statistics and found no structure in M(χc 1π0 ) (Phys. Rev. D 93, 052016). However, no upper limit is put. ・ Belle re-analyzed the same data and set upper limit for Br(X(3872/3915)→π0χc 1). 2019/2/14 KEK-FF 2019 8

9 Upper limit on X(3872/3915)→χc 1π0 in B decays 0) Zoomed M(χ π P c 1 ・ No X(3872/3915) signals. rel ・ c 1 (0. 88+0. 33 -0. 27± 0. 10 @ BES III) Br(π0χ )/Br(J/ψπ+π-) < 0. 97 at 90% C. L. im ina r y ・ Belle neither confirms nor rejects BES III result. ・ First limit on the X(3915)→π0χc 1 Yields X(3872) 2. 7± 5. 5 X(3915) 42± 14 2019/2/14 Significance Br(B+X)×Br(X→π0χc 1) Pre 0. 3 <8. 1× 10 -6 lim ina -5 ry 2. 3 <3. 8× 10 KEK-FF 2019 9

10 Physics of charmed baryons (1) Di-quark structure in the baryon ・Spin-spin interaction∝ 1/m 1 m 2 ・Di-quark + charm quark - Di-quark as new degree of freedom. - Easier to understand baryons. Nucleon Charmed baryon Pairs can not be distinguished. Light di-quark and charm quark. (2) Charm baryon as a hyperon laboratory ・ Ground-state dominantly decay via c→s. ・ Variety of hyperons are produced. 2019/2/14 KEK-FF 2019 10

11 Currently observed charmed baryons LHCb Belle Ba. Bar CLEO - State with [] observed in single exp. - JP with () is QM prediction 2019/2/19 2019/2/14 (udc) KMI 2019 KEK-FF 2019 (udc, uuc, ddc) (usc, dsc) (ssc) 11 ar. Xiv: 1810. 03748

12 Observation of Ξc(2930)0 ・ Weak evidence of Ξc(2930) was reported by Ba. Bar in B-→Ξc(2930)Λc , Ξc(2930)→Λc+K・ Assigned as one star in PDG (need confirmation). ・ Belle performed the same study with ~3 times statistics. Previous study by Ba. Bar (2008) New study by Belle (2018) Eur. Phys. J. C (2018) 78: 252. Phys. Rev. D 77, 031101(R) 2019/2/14 Mass (Me. V/c 2) Width (Me. V) Ba. Bar 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. KEK-FF 2019 ・ Mass and width are consistent each other 12

13 Evidence for charged partner Ξc(2930)+ Belle also found 4. 1σ evidence for charged partner Ξc(2930)+ in B 0→ Ξc(2930)+ Λc-, Ξc(2930)+→ Λc+KS 0 Ξc(2930)+ Mass (Me. V/c 2) 2928. 9± 3. 0+0. 8 -12. 0 2942. 3± 4. 4± 1. 5 Width (Me. V) 19. 5± 8. 4+5. 4 -7. 9 14. 8± 8. 8± 2. 5 Eur. Phys. J. C (2018) 78: 928 2019/2/14 KEK-FF 2019 13

14 Some comments on Ξc(2930) ・ Ξc(2930)0 is the first charmed baryon established in the B-decay. Phys. Rev. D 77, 012002 M(Λc+K-) in e+e-→cc by Ba. Bar. ・As it is two-body B-decay, spin can be determined un-ambiguously from helicity constraint if we have enough statistics. 2019/2/14 Λc B Ξc* J=1/2 J=0 J=? Jz = 1/2 KEK-FF 2019 14

15 Absolute branching fractions of Ξc 0 ・Absolute branching fractions for ground state charmed baryons are not determined except for Λ c+ - For Ξc 0, all the branching fractions are measured relative to Ξc 0→Ξ-π+ ・Belle determined Ξc 0→ Ξ-π+, ΛK-π+, p. K-K-π+ in following steps: 1): Measure Br(B-→Λc-Ξc 0) using missing mass technique. 2): Measure Br(B-→Λc-Ξc 0) × Br(Ξc 0→f) by exclusively reconstructing Ξc 0 (f = Ξ-π+, ΛK-π+, p. K-K-π+). 3): Divide 2) by 1). 1) Reconstruct Hadronic decay + B B Missing mass 2019/2/14 2) Λ c- Ξc 0 KEK-FF 2019 B Λ c. Reconstruct Ξc 0 Ξ -π + ΛK-π+ p. K-K-π+ 15

16 Results on branching ratios 1) Missing mass against Btag Λc- ar. Xiv: 1811. 09738 ・Ξc 0 signal is observed by missing mass for the first time with 5. 5σ (40. 9± 9. 0 counts) ・Br(B-→Λc-Ξc 0) = (9. 51± 2. 10± 0. 88)× 10 -4 2) M(Ξc)-M(Λc) Mbc ΔE ・ Signal yields are obtained by 2 D fit on Mbc-ΔE after selecting signal region in M(Ξc)-M(Λc) plane. Ξc 0→Ξ-π+ Ξc 0→ΛK-π+ Ξc 2019/2/14 0→p. K-K-π+ KEK-FF 2019 3) Decay Br(B→ΞcΛc)x. Br(Ξc→f) (10 -5) Br(Ξc 0→f) (%) Significance Ξ-π+ 1. 71± 0. 28± 0. 15 1. 8± 0. 5± 0. 14 9. 5σ ΛK-π+ 1. 11± 0. 26± 0. 10 1. 17± 0. 37± 0. 09 6. 8σ p. K-K-π+ 0. 547± 0. 178± 0. 057 0. 58± 0. 23± 0. 05 4. 6σ 16

17 Ξc+→Ξ(1620/1690)π+, Ξ(1620/1690)→Ξ-π+ ・Not much is known about the S=-2 baryon family(Ξ). - Even first orbital excitation with JP=1/2 - is not identified. - In the S=-1, JP=1/2 - = Λ(1405) is a candidate of meson-baryon molecule state. - Ξ(1620/1690) are candidates of Ξ analogue of Λ(1405). Evidence for Ξ(1620) is poor (1 star state) in PDG. ・ Belle studied Ξ* in Ξc+→(Ξ-π+)π+ decay chain. Ξc+ from Ξ-π+π+ decay Belle has ~50000 Ξc+ on ~11500 BG. Ξ(1620) Phys. Lett. 38 B (1972) 177 -180 2019/2/14 KEK-FF 2019 17

18 M(Ξ-π+) distribution ・Peaks correspond to Ξ(1530), Ξ(1620), and Ξ(1690) can be seen. - Ξ(1620) and Ξ(1690) are not visible in the Ξc sideband. ・Fit are performed with floating Ξ(1530) and Ξ(1620) masses/widths. Ξ(1690) mass and width are fixed with PDG values. ar. Xiv: 1810. 06181 (Accepted by PRL) Ξ(1530) Ξ(1620) Ξ(1690) ・Interference with non-resonant background is included. Mass (Me. V/c 2) Width (Me. V) Significance Ξ(1620) 1610. 4± 6. 0+6. 1 -4. 2 59. 9± 4. 8+2. 8 -7. 1 25σ Ξ(1690) fixed 4σ ・Ξ(1620) is the first hyperon established by charm baryon decay! 2019/2/14 KEK-FF 2019 18

19 Summary ・After ~10 years from the end of data taking, Belle is actively working on the hadron spectroscopy. ・Decay properties of X(3872), X(3915) are investigated. ・A Charmed baryon Ξc(2930) is observed, and branching fractions of Ξc 0 are determined for the first time. ・Ξ(1620)0 observed from Ξc+ decay. ・Still many analyses ongoing, and some of them will be taken over at Belle II. 2019/2/14 KEK-FF 2019 19