The beam energy measurement system is of great importance for both BEPC-Ⅱ accelerator and BES-III detector. The system is based on measuring the energies of Compton back-scattered photons. In order to meet the requirements of data taking and improve the measurement accuracy, the system has continued to be upgraded, which involves the updating of laser and optics subsystems, replacement of a view-port of the laser to the vacuum insertion subsystem, the use of an electric cooling system for a high purity germanium detector, and improvement of the data acquisition and processing subsystem. The upgrade system guarantees the smooth and efficient measurement of beam energy at BEPC-II and enables accurate offline energy values for further physics analysis at BES-Ⅲ.
To investigate the nature of the Ψ(3770) resonance and to measure the cross section for e^+e^-→DD, a cross-section scan data sample, distributed among 41 center-of-mass energy points from 3.73 to 3.89 GeV, was taken with the BESIII detector operated at the BEPCII collider in the year 2010. By analyzing the large angle Bhabha scattering events, we measure the integrated luminosity of the data sample at each center-of-mass energy point. The total integrated luminosity of the data sample is 76.16±0.04±0.61 pb^(-1), where the first uncertainty is statistical and the second systematic.
An exclusive event generator is designed for e+e-scan experiments,including initial state radiation effects up to the second order correction.The generator is coded within the framework of BesEvtGen.There are seventy hadronic decay modes available,with effective center-of-mass energy coverage from the two pion mass threshold up to about 6 GeV.The accuracy achieved for the initial state radiation correction reaches the level achieved by the KKMC generator.The uncertainty associated with the calculation of the correction factor to the initial state radiation is dominated by the measurements of the energy-dependent Born cross section.
The exclusive Born cross sections of the production of D^0, D^+ and D_s^+ smesons in e^+e^- annihilation at 13 energy points between 3.970 and 4.260 Ge V are obtained by applying corrections for initial state radiation and vacuum polarization to the observed cross sections measured by the CLEO-c experiment. Both the statistical and the systematic uncertainties for the obtained Born cross sections are estimated.
Data sets were collected with the BES detector at the BEPC collider at the center-of-mass energy of√s=3.650 GeV during May 2009 and at√s=3.773 GeV from January 2010 to May 2011.By analyzing the large angle Bhabha scattering events,the integrated luminosities of the two data sets are measured to be(44.49±0.02±0.44)pb 1and(2916.94±0.18±29.17)pb 1,respectively,where the first error is statistical and the second error is systematic.
To study the nature of the state Y(2175),a dedicated data set of e~ + e^-collision data was collected at the center-of-mass energy of 2.125 GeV with the BESⅢ detector at the BEPCⅡ collider.By analyzing large-angle Bhabha scattering events,the integrated luminosity of this data set is determined to be 108.49±0.02±0.85 pb^(-1),where the first uncertainty is statistical and the second one is systematic.In addition,the center-of-mass energy of the data set is determined with radiative dimuon events to be 2126.55±0.03±0.85 MeV,where the first uncertainty is statistical and the second one is systematic.
The cross sections of e+e-→π+π-hc at center-of-mass energies from 3.90 to 4.42 GeV were measured by the BES and the CLEO-c experiments. Resonant structures are evident in the e+e-→π+π-hc line shape. The fit to the line shape results in a narrow structure at a mass of(4216±18) MeV/c2and a width of(39±32) MeV, and a possible wide structure of mass(4293±9) MeV/c2and width(222±67) MeV. Here, the errors are combined statistical and systematic errors. This may indicate that the Y(4260) state observed in e+e-→π+π-J/ψ has a fine structure in it.
We report new measurements of the cross sections for the production of DD final states at theψ(3770)resonance.Our data sample consists of an integrated luminosity of 2.93 fb^(-1)of e^+e^-annihilation data produced by the BEPCⅡ collider and collected and analyzed with the BESⅢ detector.We exclusively reconstruct three D^0and six D^+hadronic decay modes and use the ratio of the yield of fully reconstructed DD events("double tags")to the yield of all reconstructed D or D mesons("single tags")to determine the number of D^0 D^0and D^+D^-events,benefiting from the cancellation of many systematic uncertainties.Combining these yields with an independent determination of the integrated luminosity of the data sample,we find the cross sections to beσ(e^+e^-→D^0D^0)=(3.615±0.010±0.038)nb andσ(e^+e^-→D^+D^-)=(2.830±0.011±0.026)nb,where the uncertainties are statistical and systematic,respectively.
The numbers of ψ(3686) events accumulated by the BESⅢ detector for the data taken during 2009 and2012 are determined to be(107.0±0.8)×10~6 and(341.1±2.1)×10~6, respectively, by counting inclusive hadronic events,where the uncertainties are systematic and the statistical uncertainties are negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of ψ(3686) events for the two data taking periods is(448.1±2.9)×10~6.
