291 research outputs found

    Measurement of polarization transfer in the quasi-elastic 40Ca(e,ep)^{40}{\rm Ca}(\vec{e},e' \vec{p}) process

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    Polarization transfer to a bound proton in polarized electron knock-out reactions, A(e,ep)\mathrm{A}(\vec{e},e^{\prime}\vec{p}), is a powerful tool to look for in-medium modification of the bound proton. It requires comparison to calculations which consider the many-body effects accompanying the quasi-free process. We report here measured components PxP_x^{\prime}, PzP_z^{\prime}, and their ratio Px/PzP_x^{\prime}/P_z^{\prime}, of polarization transfer to protons bound in 40Ca^{40}\mathrm{Ca}, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations which cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio GE/GMG_E/G_M. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, (Px/Pz)A/(Px/Pz)H(P_x^{\prime}/P_z^{\prime})_{\rm A}/(P_x^{\prime}/P_z^{\prime})_{\rm H}, and its dependence on the bound-proton virtuality

    First Observation of the Direct Production of the χc1 in e+e− Annihilation

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    Observation of J/ψJ/\psi decays to e+ee+ee^{+}e^{-}e^{+}e^{-} and e+eμ+μe^{+}e^{-}\mu^{+}\mu^{-}

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    Using a data sample of 4.481×1084.481\times 10^8 ψ(3686)\psi(3686) events collected with the BESIII detector, we report the first observation of the four-lepton-decays J/ψe+ee+eJ/\psi\to e^+e^-e^+e^- and J/ψe+eμ+μJ/\psi\to e^+e^-\mu^+\mu^- utilizing the process ψ(3686)π+πJ/ψ\psi(3686)\to \pi^+\pi^- J/\psi. The branching fractions are determined to be [4.32±0.26 (stat)±0.19 (syst)]×105[4.32\pm0.26~(\rm stat)\pm0.19~(\rm syst)]\times 10^{-5} and [2.45 ±0.21 (stat)±0.10 (syst)]×105[2.45~\pm0.21~(\rm stat)\pm0.10~(\rm syst)]\times 10^{-5}, respectively. The results deviate from theoretical predictions, by 2.8 and 5.2 σ\sigma, respectively. No significant signal is observed for J/ψμ+μμ+μJ/\psi\to \mu^+\mu^-\mu^+\mu^-, and an upper limit on the branching fraction is set at 1.6×1061.6\times 10^{-6} at the 90%\% confidence level. A CP asymmetry observable is constructed for the first two channels, which is measured to be (0.019±0.067±0.025)(-0.019\pm0.067\pm0.025) and (0.016±0.081±0.003)(-0.016\pm0.081\pm0.003), respectively. No evidence for CP violation is observed in this process.Comment: 9 pages, 1 figur

    Measurement of Branching Fractions of Singly Cabibbo-suppressed Decays Λc+Σ0K+\Lambda_c^+ \rightarrow \Sigma^{0} K^+ and Σ+KS0\Sigma^{+} K_{S}^0

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    Based on a sample of 4.4 fb1\mathrm{fb}^{-1} of e+ee^{+}e^{-} annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays Λc+Σ0K+\Lambda_c^+ \rightarrow \Sigma^0 K^+ and Λc+Σ+KS0\Lambda_{c}^{+} \rightarrow \Sigma^+ K_{S}^0 are studied. The ratio of the branching fraction B(Λc+Σ0K+)\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^0 K^+) relative to B(Λc+Σ0π+)\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^0 \pi^+) is measured to be 0.0361±0.0073(stat.)±0.0005(syst.)0.0361 \pm 0.0073(\mathrm{stat.}) \pm 0.0005(\mathrm{syst.}), and the ratio of B(Λc+Σ+KS0)\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^+ K_{S}^0) relative to B(Λc+Σ+π+π)\mathcal{B}(\Lambda_{c}^{+} \rightarrow \Sigma^+ \pi^+ \pi^-) is measured to be 0.0106±0.0031(stat.)±0.0004(syst.)0.0106 \pm 0.0031(\mathrm{stat.}) \pm 0.0004(\mathrm{syst.}). After taking the world-average branching fractions of the reference decay channels, the branching fractions B(Λc+Σ0K+)\mathcal{B}(\Lambda_c^+ \rightarrow \Sigma^0 K^+) and B(Λc+Σ+KS0)\mathcal{B}(\Lambda_{c}^{+} \rightarrow \Sigma^+ K_{S}^0) are determined to be (4.7±0.9(stat.)±0.1(syst.)±0.3(ref.))×104(4.7\pm 0.9(\mathrm{stat.})\pm 0.1(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4} and (4.8±1.4(stat.)±0.2(syst.)±0.3(ref.))×104(4.8\pm 1.4(\mathrm{stat.})\pm 0.2(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}, respectively. The branching fraction of the Λc+Σ+KS0\Lambda_{c}^{+} \rightarrow \Sigma^+ K_{S}^0 decay is measured for the first time.Comment: 13 pages, 4 figure

    Observation of χcJΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta

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    By analyzing (448.1±2.9)×106(448.1\pm2.9)\times10^6 ψ(3686)\psi(3686) events collected with the BESIII detector operating at the BEPCII collider, the decays of χcJΛΛˉη\chi_{cJ} \to \Lambda\bar \Lambda \eta (J=0J=0, 1 and 2) are observed for the first time with statistical significances of 13.9σ13.9\sigma, 6.7σ6.7\sigma, and 8.2σ8.2\sigma, respectively. The product branching fractions of ψ(3686)γχcJ\psi(3686)\to\gamma\chi_{cJ} and χcJΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta are measured. Dividing by the world averages of the branching fractions of ψ(3686)γχcJ\psi(3686)\to\gamma\chi_{cJ}, the branching fractions of χcJΛΛˉη\chi_{cJ}\to \Lambda\bar \Lambda \eta decays are determined to be (2.31±0.30±0.21)×104(2.31\pm0.30\pm0.21)\times10^{-4}, (5.86±1.38±0.68)×105(5.86\pm1.38\pm0.68)\times10^{-5}, and (1.05±0.21±0.15)×104(1.05\pm0.21\pm0.15)\times10^{-4} for J=0J=0, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.Comment: 9 pages, 4 figure

    Measurement of branching fractions of singly Cabibbo-suppressed decays Λc+→Σ0K+ and Σ+KS0

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    Study of η(1405)/η(1475)\eta(1405)/\eta(1475) in J/ψγKS0KS0π0J/\psi\to\gamma K^{0}_{S} K^{0}_{S}\pi^{0} decay

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    Using a sample of (10.09±0.04)×109(10.09\pm0.04)\times10^{9} J/ψJ/\psi decays collected with the BESIII detector, partial wave analyses of the decay J/ψγKS0KS0π0J/\psi\to\gamma K^{0}_{S} K^{0}_{S}\pi^{0} are performed within the KS0KS0π0K^{0}_{S} K^{0}_{S}\pi^{0} invariant mass region below 1.6 GeV/c2{\textrm{GeV}/c^2}. The covariant tensor amplitude method is used in both mass independent and mass dependent approaches. Both analysis approaches exhibit dominant pseudoscalar and axial vector components, and show good consistency for the other individual components. Furthermore, the mass dependent analysis reveals that the KS0KS0π0K^{0}_{S} K^{0}_{S}\pi^{0} invariant mass spectrum for the pseudoscalar component can be well described with two isoscalar resonant states, i.e.{\it i.e.}, the η(1405)\eta(1405) with a mass of 1391.7±0.70.3+11.31391.7\pm0.7_{-0.3}^{+11.3} MeV/c2\textrm{MeV}/c^2 and a width of 60.8±1.212.0+5.560.8\pm1.2_{-12.0}^{+5.5} MeV\textrm{MeV}, and the η(1475)\eta(1475) with a mass of 1507.6±1.632.2+15.51507.6\pm1.6_{-32.2}^{+15.5} MeV/c2\textrm{MeV}/c^2 and a width of 115.8±2.410.9+14.8115.8\pm2.4_{-10.9}^{+14.8} MeV\textrm{MeV}. The first and second uncertainties are statistical and systematic, respectively. Alternate models for the pseudoscalar component are also tested, but the description of the KS0KS0π0K^{0}_{S} K^{0}_{S}\pi^{0} invariant mass spectrum deteriorates significantly.Comment: 20 pages, 6 figures, 6 table

    Observation of the Y(4230)Y(4230) and evidence for a new vector charmonium-like state Y(4710)Y(4710) in e+eKS0KS0J/ψe^{+}e^{-}\to K_{S}^{0} K_{S}^{0} J/\psi

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    Cross sections for the process e+eKS0KS0J/ψe^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/\psi at center-of-mass energies from 4.1284.128 to 4.9504.950 GeV are measured using data samples with a total integrated luminosity of 21.2 fb1^{-1} collected by the BESIII detector operating at the BEPCII storage ring. The Y(4230)Y(4230) state is observed in the energy dependence of the e+eKS0KS0J/ψe^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/\psi cross section for the first time with a statistical significance of 26.0σ\sigma. In addition, an enhancement around 4.7104.710 GeV, called the Y(4710)Y(4710), is seen with a statistical significance of 4.2σ\sigma. There is no clear structure around 4.4844.484 GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the Y(4230)Y(4230) state to be 4226.9±6.6±21.94226.9 \pm 6.6 \pm 21.9 MeV/c2c^{2} and 71.7±16.2±31.471.7 \pm 16.2 \pm 31.4 MeV, respectively, and the mass and width of the Y(4710)Y(4710) state to be 4704.0±52.3±69.54704.0 \pm 52.3 \pm 69.5 MeV/c2c^{2} and 183.2±114.0±90.8183.2 \pm 114.0 \pm 90.8 MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of e+eKS0KS0J/ψe^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/\psi to e+eK+KJ/ψe^{+} e^{-} \to K^{+} K^{-} J/\psi is measured to be 0.3880.028+0.035±0.0160.388_{-0.028}^{+0.035}\pm0.016, or 0.4260.031+0.038±0.0180.426_{-0.031}^{+0.038}\pm0.018 if three-body phase space is considered.Comment: Update draft based the comments from PRD refere

    Precise Measurements of Decay Parameters and CPCP Asymmetry with Entangled ΛΛˉ\Lambda-\bar{\Lambda} Pairs

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    Based on 10 billion J/ψJ/\psi events collected at the BESIII experiment, a search for CPCP violation in Λ\Lambda decay is performed in the difference between CPCP-odd decay parameters α\alpha_{-} for Λpπ\Lambda \rightarrow p\pi^- and α+\alpha_{+} for Λˉpˉπ+\bar\Lambda \rightarrow \bar{p}\pi^+ by using the process e+eJ/ψΛΛˉe^+e^- \to J/\psi \rightarrow \Lambda \bar\Lambda . 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\alpha_{-} = 0.7519 \pm 0.0036 \pm 0.0024 and α+=0.7559±0.0036±0.0030\alpha_{+} = -0.7559 \pm 0.0036 \pm 0.0030, respectively. The Λ\Lambda and Λˉ\bar{\Lambda} averaged value of the decay parameter is extracted to be αavg=0.7542±0.0010±0.0024\alpha_{\rm{avg}} = 0.7542 \pm 0.0010 \pm 0.0024 with unprecedented accuracy. The CPCP asymmetry ACP=(α+α+)/(αα+)A_{CP}=(\alpha_{-}+\alpha_{+})/(\alpha_{-}-\alpha_{+}) is determined to be 0.0025±0.0046±0.0012-0.0025 \pm 0.0046 \pm 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 CPCP violations for the strange, charmed and beauty baryons

    Observation of the hindered electromagnetic Dalitz decay ψ(3686)e+eηc\psi(3686) \to e^+ e^- \eta_c

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    Using a data sample of (448.1±2.9)×106 ψ(3686)(448.1 \pm 2.9)\times10^6 ~\psi(3686) decays collected at an e+ee^+ e^- center-of-mass energy of 3.686 GeV3.686~\rm{GeV} by the BESIII detector at BEPCII, we report an observation of the hindered electromagnetic Dalitz decay ψ(3686)e+eηc\psi(3686) \to e^+ e^- \eta_c with a significance of 7.9σ7.9\sigma. The branching fraction is determined to be B(ψ(3686)e+eηc)=(3.77±0.40stat.±0.18syst.)×105\mathcal{B} (\psi(3686) \to e^+ e^- \eta_c) = (3.77 \pm 0.40_{\rm stat.} \pm 0.18_{\rm syst.})\times 10^{-5}, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the ψ(3686)\psi(3686) and the ηc\eta_c, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ηc\eta_c decays.Comment: 8 pages, 2 figure
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