The electromagnetic process e+e−→pp¯ is studied with the initial-state-radiation technique using 7.5 fb−1 of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. ...The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/c2 using the pp¯ invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.
The Born cross sections of the e+e−→Σ+Σ¯− and e+e−→Σ−Σ¯+ processes are determined for center-of-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be ...described properly by a pQCD function and the resulting ratio of effective form factors for the Σ+ and Σ− is consistent with 3. In addition, ratios of the Σ+ electric and magnetic form factors, |GE/GM|, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the Σ± form factors require more theoretical discussions for the hyperons.
We search for an axion-like particle (ALP) a through the process ψ(3686)→π+π−J/ψ, J/ψ→γa, a→γγ in a data sample of (2.71±0.01)×109ψ(3686) events collected by the BESIII detector. No significant ALP ...signal is observed over the expected background, and the upper limits on the branching fraction of the decay J/ψ→γa and the ALP-photon coupling constant gaγγ are set at 95% confidence level in the mass range of 0.165≤ma≤2.84GeV/c2. The limits on B(J/ψ→γa) range from 8.3×10−8 to 1.8×10−6 over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for 0.165≤ma≤1.468GeV/c2.
Born cross sections for the processes e+e−→ωη and e+e−→ωπ0 have been determined for center-of-mass energies between 2.00 and 3.08 GeV with the BESIII detector at the BEPCII collider. The results ...obtained in this work are consistent with previous measurements but with improved precision. Two resonant structures are observed. In the e+e−→ωη cross sections, a resonance with a mass of (2176±24±3)MeV/c2 and a width of (89±50±5)MeV is observed with a significance of 6.2σ. Its properties are consistent with the ϕ(2170). In the e+e−→ωπ0 cross sections, a resonance denoted Y(2040) is observed with a significance of more than 10σ. Its mass and width are determined to be (2034±13±9)MeV/c2 and (234±30±25)MeV, respectively, where the first uncertainties are statistical and the second ones are systematic.
In the framework of detector development, Monte Carlo simulations play a key role in the evaluation of the expected performance and the full understanding of the behavior in beam conditions. In ...particular, a software which simulates the response of the detector to the particle passage is mandatory to test different setups and solutions, like geometries, fields, voltages, etc. and to understand the test beam data. For gas trackers, existing softwares, as GARFIELD, perform a very detailed simulation of the physical processes but are CPU time consuming. For the new cylindrical GEM tracker of BESIII, a faster code which models the results obtained from GARFIELD and adapts them to the experimental data, collected in several test beams, was written. It reproduces the behavior of a planar triple-GEM in different working conditions and, when completed, it will be inserted in the official BESIII code. A description of the procedure, based on different components (ionization, diffusion, magnetic field, avalanche multiplication, signal induction and readout) will be given and its results will be compared to the GARFIELD simulations and to the experimental data.
We report the first measurement of the absolute branching fraction for Λc+→Λμ+νμ. This measurement is based on a sample of e+e− annihilation data produced at a center-of-mass energy s=4.6 GeV, ...collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb−1. The branching fraction is determined to be B(Λc+→Λμ+νμ)=(3.49±0.46(stat)±0.27(syst))%. In addition, we calculate the ratio B(Λc+→Λμ+νμ)/B(Λc+→Λe+νe) to be 0.96±0.16(stat)±0.04(syst).
We report a search for a dark photon using 14.9 fb−1 of e+e− annihilation data taken at center-of-mass energies from 4.13 to 4.60 GeV with the BESIII detector operated at the BEPCII storage ring. The ...dark photon is assumed to be produced in the radiative annihilation process of e+e− and to predominantly decay into light dark matter particles, which escape from the detector undetected. The mass range from 1.5 to 2.9 GeV is scanned for the dark photon candidate, and no significant signal is observed. The mass dependent upper limits at the 90% confidence level on the coupling strength parameter ϵ for a dark photon coupling with an ordinary photon vary between 1.6×10−3 and 5.7×10−3.
We search for the semi-leptonic decays Λc+→Λπ+π−e+νe and Λc+→pKS0π−e+νe in a sample of 4.5fb−1 of e+e− annihilation data collected in the center-of-mass energy region between 4.600GeV and 4.699GeV by ...the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Λc+→Λπ+π−e+νe)<3.9×10−4 and B(Λc+→pKS0π−e+νe)<3.3×10−4 at the 90% confidence level, respectively.
The Born cross sections of the processes $e^+e^–$ → $ωπ^0$ and $e^+e^–$ → $ωη$ are measured at center-of-mass energies between 3.773 and 4.701 GeV using a total integrated luminosity of 22.7 fb–1 ...collected with the BESIII detector operating at the BEPCII collider. A simple $s^{-n}$ dependence for the continuum process can describe the measured Born cross sections. No significant contributions from the ψ(4160), Y(4230), Y(4360), ψ(4415), Y(4660) resonances are found, which indicates relative small branching fractions for these resonances into the $ωπ^0$ and $ωη$ final states.
Search for the decay $h_c$ → $π^0J/ψ Bai, X. H.; Bai, Y.; Bakina, O. ...
The journal of high energy physics,
05/2022, Letnik:
2022, Številka:
5
Journal Article
Recenzirano
Odprti dostop
A search for the decay $h_c$ → $π^0J/ψ$ is performed using a sample of hc produced in the reaction $e^+e^-$ → $π^+π^-h_c$. The data samples were collected with the BESIII detector at center-of-mass ...energies between 4.189 and 4.437 GeV, corresponding to a total integrated luminosity of 11 fb-1. No significant signal is observed. Upper limits on the branching ratio $\mathcal{B}$($h_c$ →$π^oJ/ψ$)/$\mathcal{B}$($h_c$ →$γη_c$ →$γK^+K_-π^o$) and on the branching fraction $\mathcal{B}$($h_c$ →$π^oJ/ψ$) are determined to be 7.5 x 10-2 and 4.7 x 10-4 at 90% confidence level, respectively. The latter is derived from the former using the measured branching fraction of the normalization channel. This is the first determination of the upper limit of the decay $h_c$ → $π^0J/ψ$
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