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Phys Rev Lett. 2004 Sep 10;93(11):112002. Epub 2004 Sep 10.

Observation of a threshold enhancement in the plambda invariant-mass spectrum.

Ablikim M1, Bai JZ, Ban Y, Bian JG, Cai X, Chang JF, Chen HF, Chen HS, Chen HX, Chen JC, Chen J, Chen J, Chen ML, Chen YB, Chi SP, Chu YP, Cui XZ, Dai HL, Dai YS, Deng ZY, Dong LY, Du SX, Du ZZ, Fang J, Fang SS, Fu CD, Fu HY, Gao CS, Gao YN, Gong MY, Gong WX, Gu SD, Guo YN, Guo YQ, Guo ZJ, Harris FA, He KL, He M, He X, Heng YK, Hu HM, Hu T, Huang GS, Huang L, Huang XP, Ji XB, Jia QY, Jiang CH, Jiang XS, Jin DP, Jin S, Jin Y, Lai YF, Li F, Li G, Li HH, Li J, Li JC, Li QJ, Li RB, Li RY, Li SM, Li WG, Li XL, Li XQ, Li XS, Liang YF, Liao HB, Liu CX, Liu F, Liu F, Liu HM, Liu JB, Liu JP, Liu RG, Liu ZA, Liu ZX, Lu F, Lu GR, Lu JG, Luo CL, Luo XL, Ma FC, Ma JM, Ma LL, Ma QM, Ma XY, Mao ZP, Mo XH, Nie J, Nie ZD, Olsen SL, Peng HP, Qi ND, Qian CD, Qin H, Qiu JF, Ren ZY, Rong G, Shan LY, Shang L, Shen DL, Shen XY, Sheng HY, Shi F, Shi X, Sun HS, Sun SS, Sun YZ, Sun ZJ, Tang X, Tao N, Tian YR, Tong GL, Varner GS, Wang DY, Wang JX, Wang JZ, Wang K, Wang L, Wang LS, Wang M, Wang P, Wang PL, Wang SZ, Wang WF, Wang YF, Wang Z, Wang Z, Wang Z, Wang ZY, Wei CL, Wei DH, Wu N, Wu YM, Xia XM, Xie XX, Xin B, Xu GF, Xu H, Xu Y, Xue ST, Yan ML, Yang F, Yang HX, Yang J, Yang SD, Yang YX, Ye M, Ye MH, Ye YX, Yi LH, Yi ZY, Yu CS, Yu GW, Yuan CZ, Yuan JM, Yuan Y, Yue Q, Zang SL, Zeng Y, Zeng Y, Zhang BX, Zhang BY, Zhang CC, Zhang DH, Zhang HY, Zhang J, Zhang JY, Zhang JW, Zhang LS, Zhang QJ, Zhang SQ, Zhang XM, Zhang XY, Zhang YJ, Zhang YY, Zhang Y, Zhang ZP, Zhang ZQ, Zhao DX, Zhao JB, Zhao JW, Zhao MG, Zhao PP, Zhao WR, Zhao XJ, Zhao YB, Zhao ZG, Zheng HQ, Zheng JP, Zheng LS, Zheng ZP, Zhong XC, Zhou BQ, Zhou GM, Zhou L, Zhou NF, Zhu KJ, Zhu QM, Zhu YC, Zhu YS, Zhu Y, Zhu ZA, Zhuang BA, Zou BS; BES Collaboration.

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Institute of High Energy Physics, Beijing 100039, People's Republic of China.


An enhancement near the m(p)+M(Lambda) mass threshold is observed in the combined pLambda and pLambda invariant-mass spectrum from J/psi-->pK(-)Lambda;+c.c. decays. It can be fit with an S-wave Breit-Wigner resonance with a mass m=2075+/-12(stat)+/-5(syst) MeV and a width of Gamma=90+/-35(stat)+/-9(syst) MeV; it can also be fit with a P-wave Breit-Wigner resonance. Evidence for a similar enhancement is also observed in psi(')-->pK(-)Lambda;+c.c. decays. The analysis is based on samples of 5.8x10(7)J/psi and 1.4x10(7)psi(') decays accumulated in the BES II detector at the Beijing Electron-Positron Collider.

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