Observation of a Narrow Charm-Strange MesonDsJ+(2632)→Ds+ηand

A. Evdokimov¹,

U. Akgun²,

G. Alkhazov³

et al.

Abstract

We report the first observation of a charm-strange meson D(+)(sJ)(2632) at a mass of 2632.5+/-1.7 MeV/c(2) in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D(+)(s)eta and D0K+. In the D(+)(s)eta decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4+/-3.3 MeV/c(2). There is a corresponding peak of 21 events over a background of 6.9 at 2631.5+/-2.0 MeV/c(2) in the decay mode D0K+. The decay width of this state is <17 MeV/c(2) at 90% confidence level. The relative branching ratio Gamma(D0K+)/Gamma(D(+)(s)eta) is 0.14+/-0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D(+)(s)eta decay mode.

D_s meson spectroscopy

“…In addition there are a number of states which have been observed more recently. These are [1] the D ⋆ s1 (2710) the D ⋆ sJ (2860) the D ⋆ sJ (3040)) and an unconfirmed state previously observed by SELEX [2], the D ⋆ sJ (2632). While the D ⋆ s1 (2710) is commonly believed to have quantum numbers J P = 1 − , there are several possibilities for the other states which are not ruled out by experiment.…”

Possible2Sand1Dcharmed and charmed-strange mesons

“…Its existence has not yet been confirmed by other collaborations. D sJ ð2632Þ þ is another puzzling state first observed by SELEX [5]. It has not been observed by other collaborations either.…”

“…1 3 D 3 or [1Dð3 À ; 5 2 Þ] D Ã ð2760Þ and D Ã sJ ð2860Þ AE are very possibly the 1 3 D 3 D and D s , respectively. D Ã ð2760Þ 0 was observed in the decay channel D þ À and was suggested to be a D-wave charmed meson [18].…”

“…The two states in the doublet 1Dð2 À ; 3 À Þ [1Dð2 À ; 5 2 Þ and 1Dð3 À ; 5 2 Þ] have masses close to each other while their mass splitting is comparable to the uncertainty of their masses, it will be difficult to distinguish these two states through the channel of D and D Ã . In this case, the partial width of D Ã observed by experiment is the total one of Dð2750Þ 0 and D Ã ð2760Þ 0 .…”

“…In this case, the partial width of D Ã observed by experiment is the total one of Dð2750Þ 0 and D Ã ð2760Þ 0 . However, the state 1Dð2 À ; 5 2 Þ decays through the P wave and the F wave while the state 1Dð3 À ; 5 2 Þ can only decay through the F wave. Therefore, the widths of decay channels D and D!…”