We report the first observation of D+→τ+ντ with a significance of 5.1σ. We measure B(D+→τ+ντ)=(1.20±0.24stat±0.12syst)×10−3. Taking the world average B(D+→μ+νμ)=(3.74±0.17)×10−4, we obtain ...Rτ/μ=Γ(D+→τ+ντ)/Γ(D+→μ+νμ)=3.21±0.64stat±0.43syst., which is consistent with the standard model expectation of lepton flavor universality. Using external inputs, our results give values for the D+ decay constant fD+ and the Cabibbo-Kobayashi-Maskawa matrix element |Vcd| that are consistent with, but less precise than, other determinations.
The cross section for the process
e
+
e
−
→
ηK
+
K
−
wasmeasured at c.m. energies in the range between 1.56 and 2.00 GeV in an experiment with the SND detector at the VEPP-2000
e
+
e
−
collider. The ...invariant-mass distribution of kaon pairs is consistent with the hypothesis that the transition through the
ηφ
intermediate state makes a dominant contribution to the transition in question.
By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the ...absolute branching fraction of the D+ → ημ+νμ decay to be BD+→ημ+νμ = ( 10.4 ± 1.0stat ± 0.5syst) × 10−4. Using the world averaged value of BD+ → ηe+νe, the ratio of the two branching fractions is determined to be BD+ → ημ+νμ/BD+ → ηe+νe = 0.91 ± 0.13(stat+syst), which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor f+η(0) and the c → d Cabibbo-Kobayashi-Maskawa matrix element |Vcd| to be fη+(0) |Vcd| = 0.087 ± 0.008stat ± 0.002syst. Taking the input of |Vcd| from the global fit in the standard model, we determine fη+(0) = 0.39 ± 0.04stat ± 0.01syst. On the other hand, using the value of fη+(0) calculated in theory, we find |Vcd| = 0.242 ± 0.022stat ± 0.00 6 syst ± 0.033theory.
The process Formula omitted is studied in the experiment at the VEPP-2000 Formula omitted collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) ...electromagnetic calorimeter is used to select Formula omitted events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.
Abstract
The integrated luminosities of data samples collected in the BESIII experiment in 2016–2017 at center-of-mass energies between 4.19 and 4.28 GeV are measured with a precision better than 1% ...by analyzing large-angle Bhabha scattering events. The integrated luminosities of old datasets collected in 2010–2014 are updated by considering corrections related to detector performance, offsetting the effect of newly discovered readout errors in the electromagnetic calorimeter, which can haphazardly occur.
Using an e+e− collision data sample of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of D0→a0(980)−e+νe and evidence for ...D+→a0(980)0e+νe with significances of 6.4σ and 2.9σ, respectively. The absolute branching fractions are determined to be B(D0→a0(980)−e+νe)×B(a0(980)−→ηπ−)=1.33−0.29+0.33(stat)±0.09(syst)×10−4 and B(D+→a0(980)0e+νe)×B(a0(980)0→ηπ0)=1.66−0.66+0.81(stat)±0.11(syst)×10−4. This is the first time the a0(980) meson has been measured in a D0 semileptonic decay, which would open one more interesting page in the investigation of the nature of the puzzling a0(980) states.
Recent results on
annihilation to hadrons below 2 GeV obtained at the SND experiment at the VEPP-2000 collider are presented. In particular, we discuss measurements of the
and
cross sections, and ...study of the processes
,
,
,
,
, and
.
We present the first amplitude analysis of the decay Ds+→π+π0η. We use an e+e− collision data sample corresponding to an integrated luminosity of 3.19 fb−1 collected with the BESIII detector at a ...center-of-mass energy of 4.178 GeV. We observe for the first time the W-annihilation dominant decays Ds+→a0(980)+π0 and Ds+→a0(980)0π+. We measure the absolute branching fraction B(Ds+→a0(980)+(0)π0(+),a0(980)+(0)→π+(0)η)=(1.46±0.15stat±0.23sys)%, which is larger than the branching fractions of other measured pure W-annihilation decays by at least one order of magnitude. In addition, we measure the branching fraction of Ds+→π+π0η with significantly improved precision.
We report the first observation of a$0\atop{0}$(980)-f0(980) mixing in the decays of J/$\psi$ → Φf0(980) → Φa$0\atop{0}$(980) → Φηπ0 and χc1 → a$0\atop{0}$(980)π0 → f0(980)π0 → π+ π- π0, using data ...samples of 1.31 × 109 J/$\psi$ events and 4.48 × 108 $\psi$(3686) events accumulated with the BESIII detector. The signals of f0(980) → a$0\atop{0}$(980) and a$0\atop{0}$(980) → f0(980) mixing are observed with a statistical significance of 7.4σ and 5.5σ, respectively. The corresponding branching fractions and mixing intensities are measured, and the constraint regions on the coupling constants, ga0K+K- and gf0K+K-, are estimated. The results improve the understanding of the nature of a$0\atop{0}$(980) and f0(980).
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