J. C. Chen

Measurement of the mass and full width of the {eta}{sub c} meson

In a sample of 7.8 million J/{psi} decays collected in the Beijing Spectrometer, the process J/{psi}{yields}{gamma}{eta}{sub c} is observed for five different {eta}{sub c} decay channels: K{sup +}K{sup -}{pi}{sup +}{pi}{sup -}, {pi}{sup +}{pi}{sup -}{pi}{sup +}{pi}{sup -}, K{sup {+-}}K{sub S}{sup 0}{pi}{sup {+-}} (with K{sub S}{sup 0}{yields}{pi}{sup +}{pi}{sup -}), {phi}{phi} (with {phi}{yields}K{sup +}K{sup -}) and K{sup +}K{sup -}{pi}{sup 0}. From these signals, we determine the mass of {eta}{sub c} to be 2976.6{+-}2.9{+-}1.3 MeV. Combining this result with a previously reported result from a similar study using {psi}(2S){yields}{gamma}{eta}{sub c} detected in the same spectrometer gives m{sub {eta}{sub c}}=2976.3{+-}2.3{+-}1.2 MeV. For the combined samples, we obtain {gamma}{sub {eta}{sub c}}=11.0{+-}8.1{+-}4.1 MeV. (c) 2000 The American Physical Society.

Measurement of psi(2S) decays to baryon pairs

A sample of 3.95M {psi}(2S) decays registered in the BES detector are used to study final states containing pairs of octet and decuplet baryons. We report branching fractions for {psi}(2S){yields}p{bar p}, {Lambda}{bar {Lambda}}, {Sigma}{sup 0}{bar {Sigma}}{sup 0}, {Xi}{sup -}{bar {Xi}}{sup +}, {Delta}{sup ++}{bar {Delta}}{sup --}, {Sigma}{sup +}(1385){bar {Sigma}}{sup -}(1385), {Xi}{sup 0}(1530){bar {Xi}}{sup 0}(1530), and {Omega}{sup -}{bar {Omega}}{sup +}. These results are compared to expectations based on the SU(3)-flavor symmetry, factorization, and perturbative QCD.

Observation of a Charged (D(D)over-bar*)(+/-) Mass Peak in e(+)e(-) -> pi D(D)over-bar* at root s=4.26 GeV

We report on a study of the process e+e- --> pi+(D D*bar)- at Ecm=4.26 GeV using a 525 /pb data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the (DD*bar)- invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner lineshape, the pole mass and width are determined to be M_pole=(3883.9 +- 1.5 +- 4.2) MeV and Gamma_pole=(24.8 +- 3.3 +- 11.0) MeV. The mass and width of the structure, which we refer to as Z_c(3885), are 2sigma and 1sigma, respectively, below those of the Z_c(3900) --> pi+J/psi peak observed by BESIII and Belle in pi+pi-J/psi final states produced at the same center-of-mass energy. The angular distribution of the pi Z_c(3885) system favors a JP=1+ quantum number assignment for the structure and disfavors 1- or 0-. The Born cross section times the DD*bar branching fraction of the Z_(3885) is measured to be sigma(e+e- --> pi+ Z_c(3885)-) x Bf(Z_c(3885)-->DD*bar)=(83.5 +-6.6 +- 22.0) pb. Assuming the Z_c(3885) --> DD*bar signal reported here and the Z_c(3900) --> pi J/psi signal are from the same source, the partial width ratio Gamma(Z_c(3885) --> DD*bar)/Gamma(Z_c(3900) -->pi J/psi)=6.2 +- 1.1 +- 2.7 is determined.

Measurements of the Mass and Width of the eta(c) Using the Decay psi (3686) -> gamma eta(c)

The mass and width of the lowest-lying S-wave spin singlet charmonium state, the η(c), are measured using a data sample of 1.06×10(8) ψ(3686) decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates full interference between the signal reaction, ψ(3686)→γη(c), and a nonresonant radiative background to describe the line shape of the η(c) successfully. We measure the η(c) mass to be 2984.3±0.6±0.6 MeV/c(2) and the total width to be 32.0±1.2±1.0 MeV, where the first errors are statistical and the second are systematic.

{psi}(2S){yields}{pi}{sup +}{pi}{sup -}J/{psi} decay distributions

Using a sample of 3.8 M psi(2S) events accumulated with the BES detector, the process psi(2S) --> pi(+) pi(r)-J/psi is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some D wave amplitude, as well as S wave. On the other hand, the J/psi-(pi(+)pi(-)) relative angular momentum is consistent with being pure S wave. The decay distributions have been fit to heavy quarkonium models, including the Novikov-Shifman model. This model, which is written in terms of the parameter kappa, predicts that D wave pions should be present. We determine kappa = 0.183 +/- 0.002 +/- 0.003 based on the joint m(pi pi)-cos theta(pi)* distribution. The fraction of D wave amplitude as a function of m(pi pi) is found to decrease with increasing m(pi pi), in agreement with the model. We have also fit the Mannel-Yan model, which is another model that allows D wave pions.Using a sample of 3.8 M psi(2S) events accumulated with the BES detector, the process psi(2S) -> pi^+ pi^- J/psi is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some D-wave, as well as S-wave. On the other hand, the J/psi-(pi pi) relative angular momentum is consistent with being pure S-wave. The decay distributions have been fit to heavy quarkonium models, including the Novikov-Shifman model. This model, which is written in terms of the parameter kappa, predicts that D-wave should be present. We determine kappa = 0.183 +/- 0.002 +/- 0.003 based on the joint dipion mass - cos theta distribution. The fraction of D-wave as a function of the dipion mass is found to decrease with increasing dipion mass, in agreement with the model. We have also fit the Mannel-Yan model, another model that allows D-wave.

Direct measurement of B(D{sup 0}{yields}{phi}X{sup 0}) and B(D{sup +}{yields}{phi}X{sup +})

The first measurement of B(D{sup 0}{yields}{phi}X{sup 0}) and an upper limit for B(D{sup +}{yields}{phi}X{sup +}) are determined from 22.3 pb{sup -1} of e{sup +}e{sup -} annihilation data at a c.m. energy of 4.03 GeV. The data were recorded by the Beijing Spectrometer (BES) at BEPC. A recoil charge method is applied to charm threshold data to determine the charge of the D meson in the recoil from 9054{+-}309{+-}416 reconstructed D{sup 0}, D{sup +} mesons. The branching fractions B(D{sup 0}{yields}{phi}X{sup 0})=(1.71{sub -0.71}{sup +0.76}{+-}0.17)%, and B(D{sup +}{yields}{phi}X{sup +})<1.8% are determined from 10 events with a reconstructed D and a recoiling {phi}. In addition, a 90% C.L. upper limit of B(D{sup +}{yields}{phi}e{sup +}X{sup 0})<1.6% is determined from a search for semileptonic decays of the D{sup +}. (c) 2000 The American Physical Society.The first measurement of B(0->phi X0) and an upper limit for B(D+->phi X+) are determined from 22.3 pb-1 of e+e- annihilation data at a C. M. energy of 4.03 GeV. The data were recorded by the Beijing Spectrometer (BES) at BEPC. A recoil charge method is applied for the first time to charm threshold data to determine the charge of the D meson in the recoil from 9054+-309+-416 reconstructed D0, D+ mesons. The branching fractions B(D->phiX0) =(1.71+0.76-0.71+-0.17)%, and B(D+->phiX+) phi e+X0)<1.6% is determined from a search for semileptonic decays of the D+.

Measurement of the branching fraction of [Formula presented] inclusive semileptonic decay [Formula presented]

The absolute inclusive semileptonic branching fraction of the D{sub s} meson has been measured based on 22.3 pb{sup {minus}1} of e{sup +}e{sup {minus}} collision data collected with the Beijing Spectrometer at {radical} (s) =4.03GeV. At this energy, the D{sub s} are produced in pairs: e{sup +}e{sup {minus}}{r_arrow}D{sub s}{sup +}D{sub s}{sup {minus}}. We reconstructed 171{plus_minus}21{plus_minus}15 D{sub s} events in five hadronic decay modes. In the recoil system of these events, several D{sub s} inclusive semileptonic decays were observed and the branching fraction is estimated to be B(D{sub s}{sup +}{r_arrow}e{sup +}X)=(7.7{sub {minus}4.3{minus}2.1}{sup +5.7+2.4}){percent}. {copyright} {ital 1997} {ital The American Physical Society}Author(s): Bai, JZ; Bardon, O; Bian, JG; Blum, I; Breakstone, A; Burnett, T; Chai, ZW; Chen, GP; Chen, HF; Chen, J; Chen, JC; Chen, SM; Chen, Y; Chen, YB; Chen, YQ; Cheng, BS; Cowan, RF; Cui, XZ; Ding, HL; Du, ZZ; Dunwoodie, W; Fan, XL; Fang, J; Fero, M; Gao, CS; Gao, ML; Gao, SQ; Gratton, P; Gu, JH; Gu, SD; Gu, WX; Gu, YF; Guo, YN; Han, SW; Han, Y; Harris, FA; He, J; He, JT; He, M; Hitlin, DG; Hu, GY; Hu, JL; Hu, QH; Hu, T; Hu, XQ; Huang, XP; Huang, YZ; Izen, JM; Jia, QP; Jiang, CH; Jin, S; Jin, Y; Jones, L; Kang, SH; Ke, ZJ; Kelsey, MH; Kim, BK; Kong, D; Lai, YF; Lan, HB; Lang, PF; Lankford, A; Li, J; Li, PQ; Li, Q; Li, RB; Li, W; Li, WD; Li, WG; Li, XH; Li, XN; Lin, SZ; Lu, F; Liu, HM; Liu, J; Liu, JH; Liu, Q; Liu, RG; Liu, Y; Liu, ZA; Lou, XC; Lowery, B; Lu, JG; Lu, JY; Luo, SQ | Abstract: The absolute inclusive semileptonic branching fraction of the [Formula presented] meson has been measured based on [Formula presented] of [Formula presented] collision data collected with the Beijing Spectrometer at [Formula presented] At this energy, the [Formula presented] are produced in pairs: [Formula presented] We reconstructed [Formula presented] [Formula presented] events in five hadronic decay modes. In the recoil system of these events, several [Formula presented] inclusive semileptonic decays were observed and the branching fraction is estimated to be [Formula presented]