| In the quark model,hadrons are classifies as meson which contains a pair of positive and negative charged quarks and baryon which contain three quarks.In fact,quantum chromodynamics also allows the existence of other hadron structure beyond the above classification,such as multi-quark state,molecular state and gluon ball.It has been a hot topic to search for such new hadron states in particle physics experiment.Recently,Numerous resonance states found in the study of charmonium spectrum can not be classified,such as X(3872).Y(4140).Y(4260),Y(4660),and Zc(3900).Since these resonance states usually decays to low-level charmo-nium state,and also have the similar nature with charmonium state,they are called charmonium-like states,which are named as "XYZ" state.For the nature of charmonium-like states,there is still no definitive conclusion so far.How-ever,charmonium-like states are in the ?-charm energy region which transit from non-perturbative to perturbative QCD,therefore,it is very important to study the nature of charmonium-like states for improving charmonium spectrum and understanding quantum chromodynamics.Using a data sample collected with the BESIII detector operating at the BEPCII storage ring at a center-of-mass energy of 4.600 GeV,we search for the production of e+e-???c0,1,2.A search is also performed for the charrmonium-like state Y(4140)in the radiative transition e+e-??Y(4140)with Y(4140)subsequently decaying into ?J/?.The processes e+e-? ??c1 and ??c2 are ob-served for the first time,each with a statistical significance of more than 10?,and the Born cross sections are measured to be(4.2-1.0+1.7±0.3)pb and(6.7-1.7+3.4±0.5)pb,respectively,where the first uncertainties are statistical and the second system-atic.No significant signals are observed for e+e-???c0 and e+e-?Y(4140)and upper limits on the Born cross sections at 4.600 GeV at 90%confidence level are measured to be 5.4 and 1.2 pb,respectively.The cross sections of other decay modes at this energy point,such as e+e-??+?-J/?,e+e-???c0,1,2,e+e-??J/?,are all at the level of a few pb.The upper limit of the Born cross section for e+e-??Y(4140)at 4.600 GeV is higher than those measured at 4.230,4.260,and 4.360 GeV,due to the non-trivial backgrounds from ee ? ??c2.Using about 11.6 fb-1 data samples collected with the BESe? detector oper-ating at the BEPCII storage ring at 15 energy points from 4.009 to 4.600 GeV,we also search for the production of e+e-???c0,1,2.The processes e+e-???c1 and ??c2 are observed at 4.180 GeV for the first time,with statistical signifi-cance of 9.9? and 7.3?,respectively.The Born cross sections are measured to be(3.20-0.42+0.44)pb and(4.30-0.72+0.76)pb,respectively,where the uncertainties are only statistical and the systematic uncertainty need to be further studied.Only ev-idences are found at several other energy points for the processes e+e-???c1 and ??c2 because of the statistic of data samples and the production rate of event.No obvious signals are observed for e+e???c0 at all energy points.Since the statistic of the data sample at 4.180 is largest,upper limit on the Born cross sections for the process e+e-???c0 at this energy point at 90%confidence level are given to be 3.02 pb. |
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