Charmed baryon decays at Belle Yuji Kato (KMI, Nagoya University)

Transcription

1 1 Charmed baryon deays at Belle Yuji Kato (KMI, Nagoya University) Ξ * ΛD Doubly Cabibbo Suppressed deay Λ pk π - Hidden Strange pentaquark via Λ π 0 φ p deay 2017/11/8 1

2 Charmed baryon prodution at Belle 2 e - e γ* Charmed baryons are produed mainly via e e - γ* Total integrated luminosity ~=1.0 ab -1. ~ e e -. Many harmed baryons are disovered by Belle and BaBar so far. ( Λ (2940), Σ (2800), Ξ (2980), Ξ (3055), Ξ (3080), Ω (2770) ) 2017/11/8 2

3 Charmed strange baryons (Ξ ) 3 u C Ξ S u/d-s diquark system! u-s di-quark, whih an not be ahieved in the Λ state. The states below Ξ (2815) are well desrived by the quark model. Higher exited states ontains rih dynamial information! Ξ (3123)? Ξ (3080) Ξ (3055) Ξ (2980) Ξ (2815)(3/2 - ) Ξ (2790)(1/2 - ) Ξ (2645) (3/2 ) Ξ (1/2 ) Ξ (1/2 )

4 Higher exited Ξ states in K - (past studies) 4 Phys. Rev. D 77, M( K - ) Phys. Rev. D 89, M( * K - ) Ξ (2980) Ξ (3055) Ξ (3080) M( K - ) Ξ (3080) Ξ (3123) M( * K - ) Both Belle and BaBar observed Ξ (2980), Ξ (3055), and Ξ (3080) in K - final state. Ξ (3080) in * K - final state (only BaBar observed Ξ (3123) ) Deays where harm quark in ontained in meson will give more insight Λ D! 2017/11/8 4

5 M(ΛD) 5 Phys. Rev. D 94, M(ΛD ) Ξ (3055) Ξ (3080) M(ΛD 0 ) D 0 K - π D 0 K - π π π - D 0 K - π π 0 Ξ (3055) 0 Ξ (3080) 0 First observation of the deay of Ξ (3055/3080) into ΛD. N(Ξ (3055) ) > N(Ξ (3080) ): Opposite to Σ K -. First observation of Ξ (3055) 0 (8.6σ)

6 Relative branhing frations Ξ (3055) Prefer ΛD Br(ΛD )/Br(Σ K - ) = 5.09±1.01± Phys. Rev. D 94, Ξ (3080) Similar in 3 deays Br(ΛD )/Br(Σ K - ) = 1.29±0.30±0.15 Br(Σ * K - )/Br(Σ K - ) = 1.07±0.27±0.01 First ever measurement of relative branhing fration of (heavy-baryon light-meson) and (light-baryon heavy-meson). Partial width of Ξ (3055) by hiral quark model (MeV) Inonsistent with our measurement! 2017/11/8 Phys. Rev. D 86,

7 Doubly Cabibbo Suppressed deay: Λ pk π - 7 In the baryon setor, Doubly Cabbibo Suppressed (DCS) deay had never been observed. Λ pk π - is expeted to be sensitive. Naively, ratio to CF deay, pk - π is expeted to be B( B( pk pk ) 4 ) tan W-exhange diagram an ontribute only in CF deay. DCS deays CF deays 2017/11/8 7

8 Results CF mode: pk - π DCS mode: pk π - 8 (1.452±0.015) 10 6 events 3587±380 events Signifiane: 9σ Branhing fration ratio = ( 2.35±0.27(Stat)±0.21(Sys) ) 10-3 = (0.82±0.12) tan 4 Θ After subtrating ontribution of Λ(1520) or Δ intermediate, whih ontribute only on the CF deay, the ratio is (1.10±0.17) tan 4 Θ Phys. Rev. Lett. 117, Contribution from W exhange diagram is not large. 8

9 Searh for pentaquark via Λ π 0 φp 9 LHCb observed hidden harm pentaquark state in the Λ b 0 K - P K - (J/ψ p) Natural extension is analogue searh for hidden-strange pentaquark by swithing b-> (Λ b 0 Λ ), ->s (J/ψ -> φ) :Λ π 0 P s π 0 (φ p) Λ π 0 φp deay itself is not observed so far. 2017/11/8 9

10 Results Phys. Rev. D 96, (R) M(K K - pπ 0 ) M(K K - ) 10 M(φp) Perform 2D fit on M(K K - pπ 0 ) and M(K K - ) plane. No signifiant Λ signals is observed. New upper limits: - Br (Λ φ p π 0 ) < 15.3x Br (Λ K K - pπ 0 ) NR < 6.3x10-5 Also perform 2D fit in eah M(φp) bin. No signifiant P s signal observed. - Br(Λ P s π 0 )xbr(p s φp) < /11/8 10

11 Summary 11 First observation of the deay Ξ (3055) and Ξ (3080) Λ D - Br(ΛD)/Br(Σ K - ) are different for two states. - First observation of Ξ (3055) 0 First observation of Doubly Cabibbo Suppressed deay: Λ pk π - - The ratio to CF deay an be explained by CKM suppression. Contribution from W-exhange diagram is small. Searh for hidden strange pentaquark P s in Λ π 0 (φ p) - No signal for P s as well as the deay Λ π 0 (φ p) Stay tune for more results on harmed baryon from Belle! 2017/11/8 11

12 Bakup /11/8 12

13 Physis of single harmed baryons 13 Charm quark is heavy: (1500 MeV/ 2 ) > u,d,s quarks ( MeV/ 2 ) spin-spin interation 1/m 1 m 2 Di-quark orrelation in light quarks (more simple!). Nuleon Charmed baryon Every pair an not be distinguished. Light di-quark and harm quark. 2017/11/8 13

14 Observed harmed baryons 14 Λ (1/2 ) Λ (2595) 1/2 - Λ (2625) (3/2 - ) [Λ (2765)?? ] Λ (2880) 5/2 Λ (2940)?? d u 2017/11/8 Σ (2455) (1/2 ) Σ (2520) (3/2 ) Σ (2800)?? d u CLEO 8(7) (1995~2001) BELLE 3 (2006~) BABAR 5(2) (2007~) Ξ (1/2 ) Ξ (1/2 ) Ξ (2645) (3/2 ) Ξ (2790) (1/2 - ) Ξ (2815) (3/2 - ) [Ξ (2930)?? ] Ξ (2980)?? Ξ (3055)?? Ξ (3080)?? [Ξ (3123)?? ] s u 16/21 (12/17) harmed baryons are observed in e e - ollider experiment. All the ground states predited by quark model are disovered. Still many things to do! Spin-parity almost from quark model predition (). Some states has only poor evidene (states in []). Many states are observed in only 1 deay mode. Today s topi Auray of mass/width is not good enough. No λ and ρ mode exitation states identified. Ω (1/2 ) Ω (2770)(3/2 ) s s 14

15 Belle experiment 15 B e - Υ(4S) bb e 8 GeV 3.5 GeV B Asymmetri energy e e - ollider. s=10.58 GeV = Υ(4S) mass (and other energies) Peak luminosity = m -2 s -1 = World highest luminosity! General purpose feature of the Belle detetor make it possible to study hadron spetrosopy. Mt. Tsukuba 3.5 GeV e 8 GeV e - ~1 km Lina 2017/11/8 15

16 Comparison with quark model predition 16 In the quark model, they should be N=2 shell and these states are identified as: Ξ (3055) = 2 D λλ (3/2 ) or 2 D ρρ (3/2 ). (Phys. Rev. D 86, ) Partial width (MeV) They predited - ΛD deay is suppressed for both Ξ (3055) Inonsistent with this measurement. Challenge for theorists! 2017/11/8 16

17 Comparison of Λ and Ξ or Σ and Ξ J p Λ Ξ ΔM(Mev/ 2 ) Note 1/2 Λ (2286) Ξ (2470) 181 ground state 1/2 - Λ (2595) Ξ (2790) 194 Λ(1405) like 3/2 - Λ (2625) Ξ (2815) 188 Λ(1520) like?? Λ (2765)? Ξ (2980)? 205 Isospin not determined 5/2 Λ (2880) Ξ (3080)? 200 J p Σ Ξ ΔM(Mev/ 2 ) Note 1/2 Σ (2455) Ξ (2575) 120 ground state 3/2 Σ (2520) Ξ (2645) 125 Σ(1385) like?? Σ (2800)?? 17 spin0 di-quark spin1 di-quark The mass differene of Λ and Ξ is ~200 MeV/ 2, Σ and Ξ is ~120 MeV 2017/11/8 Ξ (3055) has no orresponding state in Λ /Σ 17

18 DCS deay of the Λ 18 In the baryon setor, Doubly Cabbibo Suppressed (DCS) deay has NEVER been observed. Λ pk π - is expeted to be sensitive. Naively, ratio to CF deay, pk - π is expeted to be B( B( In the CF deay, the W exhange diagram may ontribute. DCS deay pk pk ) 4 ) tan CF deay with W exhange u d u d W W 2017/11/8 18

19 Dalitz plot for Λ pk - π Phys. Rev. Lett. 117, ?? K* 19?? Λ(1520) Weak deay of harmed baryon is unique light baryon laboratory 2017/11/8 19