| This thesis contains two parts,search for the D semileptonic decays of D0?d0(980)-e+ve and +? a0(980)0e+ve,and the branching fractions measurement of the radiative decays D0??K*0 and D0???.The classification of the light scalar mesons below 1 GeV/c2 is a long-standing puzzle in particle physics.Many experimental results are in favor of the nontrivial nature of these mesons.Many suggestions are discussed,such as the conventional qq mesons,tetra-quark states,meson-meson bound states and even scalar glueballs.Besides,the mixing between different contents makes the situation more complex.Semileptonic decay is an ideal test-bed to study the inner structure of the light scalar mesons,due to its clear production mechanism and limited final state interactions.However,because of the lack of statistics and high backgrounds,measurements of these interesting decays have not been reported yet.In 2010 and 2011,BES?has collected an e+e-collision data sample of 2.93 fb-1 at a center-of-mass energy of 3.773 GeV,which is the sample of the highest statistic lev-el at this energy point recently.These DD threshold data provides an ideal environment to study the decays of D mesons.Using these data and the D-tagging technique,we re-port the first observation of D0? a0(980)-e+ve and evidence for D0?a0(980)0e+ve with significance of 6.4? and 2.9?,respectively.The absolute branching fractions are determined to be:B(D0?a0(980)-e+ve)× B(a0(980)-???-)?(1.33+0.33-0.29 ± 0.09)× 10-4B(D+ ? a0(980)0e+ve)× B(a0(980)0???-)=(1.66-0.66+0.81± 0.11)x 10-4 where the first uncertainties are statistical and the second are systematic.Consid-ering the un-well measured branching fraction of the sub-mode decay ao(980)???,the product branching fractions are reported.Due to the limited signal significance,an upper limit of B(D+? a0(980)0e+ve)× B(a0(980)0???0)<3.0 × 10-4 is also determined at the 90%confidence level.These results will provide the information of the qq contribution,originated from the isovector combination of u or d quark with their anti-quark partners,in the ao(980)wave function.Along with the theoretical analysis and the other experimental results,our measurement will contribute a lot to the classification of the light scalar mesons.In the charm sector,the radiative of D? ?V(V refers to vector mesons)are dominated by the nonperturbative long-range process.The contributions to the ra-diative decay are expected to increase the branching fractions to the order of 10-5,whereas the short-range contributions are predicted to yield rates at the order of 10-8.As a result,the charm radiative decays provide a prominent environment for a better understanding of QCD and QCD-based calculations.The decay modes of D0 ??K*0 and D0??? have been observed with a significance larger than 5a by the Belle and BABAR collaborations.In 2017,Belle reported a result of the branching fractions with better precisions.However,the latest result of the branching fraction of D0??K*0 from Belle is not well-consistent with the result reported by the BABAR collaboration within their uncertainties.As a result,the cross check from an independent measurement turns out to be a necessity.Using data collected at a center-of-mass energy of 3.773 GeV by BES?,we mea-sure the branching fractions of D0??K*0 and D0??? with the DD threshold data for the first time.To better reduce the uncertainties from non-D decays,the D-tagging technique is applied.The measured branching fractions are B(D0??k*0)=(4.22± 0.68 ± 0.19)×10-4 and 3(D0???)=(3.53 ± 1.32 ± 0.16)x 10-5Due to the lack of statistics,our results turn out to have large statistical uncer-tainties.But it is still an important reference for the branching fraction of the decay of D0??K*0.Our measured branching fraction of D0??? is consistent with the previously reported results within the uncertainties. |
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