What is the charmed analog of  (1405)? Kiyoshi Tanida (Seoul National University) Aug. 23, 2011 APFB2011, Seoul

Λ （ 1405 ）

How is it in charmed sector? Large mass difference of πΣ and DN → mixing should be small Both of Σπ resonance and ND bound state can be seen as separate peaks? strangecharm MΛMΛ MΣMΣ MK（MD）MK（MD） Σπ NK （ ND ） MΛ*MΛ* 1405 ？

Σ c π resonance? Just on Σ c π threshold Still, the main decay mode is Σ c π

Is there DN bound state? J P are unknown, but they may be the bound state. Binding energies: 45MeV & 10MeV, respectively In the strangeness sector, attraction for I=0 channel is stronger than I=1.

Λ c （ 2765 ） PRL86 （ 2001 ） 4479 data from CLEO B decay →Λ c * →Λ c ππ （ Σ c π 、 Σ c *π included ） Width ～ 50 MeV Λ c （ 2765 ） Λ c （ 2880 ）

CLEO data Λ c （ 2880 ）  Σ c π BR=31±7% Rough estimation in similar way: Λ c （ 2765 ）  Σ c π ～ 26% Λ c （ 2765 ）  Σ c *π ～ 33% via Σ c π via Σ c *π Λ c （ 2880 ） Λ c （ 2765 ）

BELLE data PRL98 (2007) This paper’s main subject is Λ c (2880), but Λ(2765) was clearly seen, too. Black: via Σ c π Red ： sideband background （ scaled ） Width ： 73±5 MeV (Not used in PDG)

Σ c π partial decay rate? Λ c (2595): – Full width= MeV – BR(Σ c π) > 70%. Partial width ~ 2.5 MeV Λ c (2765): – Rough estimation: Γ(Σ c π) ～ 30MeV Dividing by phase space ・・・ – Λ c (2595): Q-value too small Σ c ++ π - : 1.7±0.6 MeV 、 Σ c + π 0 : 7.4±0.7 MeV Q may be < 0 （ Threshold effect on spectrum ） →Unmeasured Σ c + π 0 mode would be the main channel – Squared matrix element may be twice larger for Λ c (2595) Q-value1 MeV3 MeV5 MeV172 MeV Phase space （ relative ）

Λ c (2595) shape CLEO data fit with threshold effect considered. (PRD )  M(Λ c * )  M(Λ c ) = 305.6±0.3 MeV  ~3 MeV below  c 

Known things Λ(1405) analog states – Σπ resonance certainly exists. – DN bound state: candidate exists. Comparing partial decay rates, it seems Λ c (2595) has a stronger coupling to Σ c π Λ c (2765) has too many unknowns, and the quality of data Λ c (2595) is not enough.

What we want to know Is Λ c (2765) really the ND bound state and can be considered as a Λ(1405) analog state? Key measurements – Spin-parity:  Many controversial predictions – Decay width, branching ratios Λ c (2595) needs more data, too. – Need to consider threshold effect. Σ c + π 0 mode would be a key. Need help from theory side – Threshold effect for Λ c (2595) – Discussion from partial widths – Determination of parity (which was the case for Λ c (2880))

BELLE data PRL98 (2007) This paper’s main subject is Λ c (2880), but Λ(2765) was clearly seen, too. Black: via Σ c π Red ： sideband background （ scaled ） Width ： 73±5 MeV (Not used in PDG)

Possibility at BELLE Decay widths seem feasible – Is Λ c (2595)→Σ c + π 0 possible? Determination of spin – angular distribution of Λ c →Σ c π – Done for Λ c (2880) Parity – Most difficult – Λ c (2880) parity was determined from BR of Σ c π and Σ c *π using model (heavy quark symmetry)

Summary Charmed analog of Λ(1405) – Σπ resonance ： Λ c (2595) – DN bound state: Λ c (2765)? We want to know the nature of Λ c (2765) – Spin-parity (1/2  ?) – Decay width measurements would help, too. B-factory data contains huge statistics → analysis seems feasible