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We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− are observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data was collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− is observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
We study the direct production of the JPC=1++ charmonium state χc1(1P) in electron-positron annihilation by carrying out an energy scan around the mass of the χc1(1P). The data were collected with the BESIII detector at the BEPCII collider. An interference pattern between the signal process e+e−→χc1(1P)→γJ/ψ→γμ+μ− and the background processes e+e−→γISRJ/ψ→γISRμ+μ− and e+e−→γISRμ+μ− are observed by combining all the data samples. The χc1(1P) signal is observed with a significance of 5.1σ. This is the first observation of a C-even state directly produced in e+e− annihilation. The electronic width of the χc1(1P) resonance is determined to be Γee=(0.12+0.13−0.08) eV, which is of the same order of magnitude as theoretical calculations.
Based on 10 billion J/ψ events collected at the BESIII experiment, a search for CP violation in Λ decay is performed in the difference between CP-odd decay parameters α− for Λ→pπ− and α+ for Λ¯→p¯π+ by using the process e+e−→J/ψ→ΛΛ¯. With a five-dimensional fit to the full angular distributions of the daughter baryon, the most precise values for the decay parameters are determined to be α−=0.7519±0.0036±0.0024 and α+=−0.7559±0.0036±0.0030, respectively. The Λ and Λ¯ averaged value of the decay parameter is extracted to be αavg=0.7542±0.0010±0.0024 with unprecedented accuracy. The CP asymmetry ACP=(α−+α+)/(α−−α+) is determined to be −0.0025 ± 0.0046 ± 0.0012, which is one of the most precise measurements in the baryon sector. The reported results for the decay parameter will play an important role in the studies of the polarizations and CP violations for the strange, charmed and beauty baryons.