arXiv subjects

T. T. Chang

Publications and source records attributed to T. T. Chang.

At least 181 records · Page 10Linked to original sources

arXiv2023

Improved measurement of the branching fractions for $J/ψ\toγπ^0$, $γη$ and $γη^\prime$

Using a data sample of $(1.0087\pm 0.0044)\times 10^{10}$ $J/ψ$ events collected with the BESIII detector, the decays of $J/ψ\toγπ^{0} (η, η^\prime)\toγγγ$ are studied. Newly measured branching fractions are $\mathcal{B}$$(J/ψ\toγπ^{0})$=$(3.34\pm 0.02\pm 0.09)\times 10^{-5}$, $\mathcal{B}$$(J/ψ\toγη)$=$(1.096\pm 0.001\pm0.019)\times 10^{-3}$ and $\mathcal{B}$$(J/ψ\toγη^\prime)$=$(5.40\pm 0.01\pm0.11)\times 10^{-3}$, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world average values within two standard deviations. The ratio of partial widths $Γ(J/ψ\toγη^\prime)/Γ(J/ψ\toγη)$ is measured to be $4.93 \pm 0.13$. The singlet-octet pseudoscalar mixing angle $θ_P$ is determined to be $θ_P = -(22.11 \pm0.26)^\circ$ or $-(19.34 \pm 0.34)^\circ$ with two different phenomenological models.

hep-ex↗

arXiv2023

Measurement of $e^{+}e^{-}\toϕπ^{+}π^{-}$ cross sections at center-of-mass energies from 2.00 to 3.08 GeV

Using data corresponding to an integrated luminosity of $651~\mathrm{pb}^{-1}$ accumulated at 22 center-of-mass energies from 2.00 to 3.08 GeV by the BESIII experiment, the process $e^{+}e^{-}\toϕπ^{+}π^{-}$ is studied. The cross sections for $e^{+}e^{-}\toϕπ^{+}π^{-}$ are consistent with previous results, but with improved precision. To measure the mass and width of the structure observed in the cross section line shape, a combine fit is performed after enhancing the contribution from $ϕf_{0}(980)$. The fit reveals a structure with the mass of $M=2178\pm20\pm5~{\rm MeV}/c^2$ and the width of $\varGamma=140\pm36\pm16~{\rm MeV}$, where the first uncertainties are statistical and the second ones are systematic.

hep-ex↗

arXiv2023

Tests of $CP$ symmetry in the entangled $Ξ^0-\barΞ^0$ Pairs

The $J/ψ\to Ξ^0 \barΞ^{0}$ process and subsequent decays are investigated using $(10087 \pm 44)\times 10^6$ $J/ψ$ events collected at the BESIII experiment. The decay parameters of $Ξ^0$ and $\barΞ^0$ are measured with greatly improved precision over previous measurements to be $α_Ξ = -0.3750 \pm 0.0034 \pm 0.0016$, $\barα_Ξ = 0.3790 \pm 0.0034 \pm 0.0021$, $ϕ_Ξ = 0.0051 \pm 0.0096 \pm 0.0018$~rad, $\barϕ_Ξ = -0.0053 \pm 0.0097 \pm 0.0019$~rad, where the first and the second uncertainties are statistical and systematic, respectively. From these measurements, precise $CP$ symmetry tests in $Ξ^0$ decay are performed, and $A^Ξ_{CP} = (-5.4 \pm 6.5 \pm 3.1) \times 10^{-3}$ and $Δϕ^Ξ_{CP} = (-0.1 \pm 6.9 \pm 0.9) \times 10^{-3}$~rad are consistent with $CP$ conservation. The sequential decay also enables a separation of weak and strong phase differences, which are found for the first time to be $ξ_{P}-ξ_{S} = (0.0 \pm 1.7 \pm 0.2) \times 10^{-2}$~rad and $δ_{P}-δ_{S} = (-1.3 \pm 1.7 \pm 0.4)\times 10^{-2}$~rad, respectively. In addition, we measure the $Λ$ decay parameters and test $CP$ symmetry in $Λ$ decays.

hep-ex↗

arXiv2023

Search for the lepton number violation decay $ϕ\to π^+ π^+ e^- e^-$ via $J/ψ\to ϕη$

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we search for the lepton number violation decay $ϕ\to π^+ π^+ e^- e^-$ via $J/ψ\to ϕη$. No signal is found and the upper limit on the branching fraction of $ϕ\to π^+ π^+ e^- e^-$ is set to be $9.7\times10^{-6}$ at the 90\% confidence level.

hep-ex↗

arXiv2023

Measurement of the $e^+e^- \to Λ\barΣ^0 + c.c.$ cross sections at $\sqrt{s}$ from 2.3094 to 3.0800 GeV

The Born cross sections and effective form factors of the process $e^+e^-\toΛ\barΣ^0 + c.c.$ are measured at 14 center-of-mass energy points from 2.3094 to 3.0800 GeV, based on data corresponding to an integrated luminosity of $(478.5 \pm 4.8)\ \text{pb}^{-1}$ collected with the BESIII detector. A non-zero Born cross section is observed at the center-of-mass energy of 2.3094 GeV with a statistical significance of more than five standard deviations, and the cross sections at other energies are obtained with improved precision compared to earlier measurements from the BaBar Collaboration. The Born cross-section lineshape is described better by a shape with a plateau near the threshold than by a pQCD motivated functional form.

hep-ex↗

arXiv2023

Amplitude analysis and branching fraction measurement of the decay $D^{+} \to K_S^0π^+π^0π^0$

Using 2.93 $\rm{fb}^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at the center-of-mass energy 3.773\,GeV, we perform the first amplitude analysis of the decay $D^+\to K_S^0π^+π^0π^0$ and determine the relative magnitudes and phases of different intermediate processes. The absolute branching fraction of $D^+\to K_S^0π^+π^0π^0$ is measured to be $(2.888\pm0.058_{\rm stat.}\pm0.069_{\rm syst.})\%$. The dominant intermediate processes are $D^+\to K_S^0a_1(1260)^+(\to ρ^+π^0)$ and $D^+\to \bar{K}^{*0}ρ^+$, with branching fractions of $(8.66\pm1.04_{\rm stat.}\pm1.39_{\rm syst.})\!\times \!10^{-3}$ and $(9.70\pm0.81_{\rm stat.}\pm0.53_{\rm syst.})\!\times \!10^{-3}$, respectively.

hep-ex↗

arXiv2023

Observation of the decay $J/ψ\to e^+ e^- η(1405)$ with $η(1405) \to π^0 f_0(980)$

Using a data sample of $(10087\pm44)\times 10^6$ $J/ψ$ events collected by the BESIII detector in 2009, 2012, 2018 and 2019, the electromagnetic Dalitz process $J/ψ\to e^+ e^- η(1405)$ is observed via the decay $η(1405) \to π^0 f_0(980)$, $f_0(980) \to π^+ π^-$, with a significance of about $9.6σ$. The branching fraction of this decay is measured to be ${\mathcal B}(J/ψ\to e^+ e^- π^0 η(1405) \to e^+ e^- π^0 f_0(980) \to e^+ e^- π^0 π^+ π^-)=(2.02\pm0.24(\rm{stat.})\pm0.09(\rm{syst.}))\times 10^{-7}$. The branching-fraction ratio ${\mathcal B}(J/ψ\to e^+ e^- η(1405))$/${\mathcal B}(J/ψ\to γη(1405))$ is determined to be $(1.35\pm0.19(\rm{stat.})\pm0.06(\rm{syst.}))\times10^{-2}$. Furthermore, an $e^+e^-$ invariant-mass dependent transition form factor of $J/ψ\to e^+ e^-η(1405)$ is presented for the first time. The obtained result provides input for different theoretical models, and is valuable for the improved understanding the intrinsic structure of the $η(1405)$ meson.

hep-ex↗

arXiv2023

Studies of the decay $D^+_s\to K^+K^- μ^+ ν_μ$

The $D^+_s\to K^+K^-μ^+ν_μ$ decay is studied based on 7.33 fb$^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at center-of-mass energies in the range from 4.128 to 4.226 GeV. The absolute branching fraction is measured as ${\mathcal B}(D^+_s\to ϕμ^+ν_μ) = (2.25\pm 0.09 \pm 0.07) \times10^{-2}$, the most precise measurement to date. Combining with the world average of ${\mathcal B}(D^+_s\to ϕe^+ν_e)$, the ratio of the branching fractions obtained is$\frac{{\mathcal B}(D^+_s\to ϕμ^+ν_μ)}{{\mathcal B}(D^+_s\to ϕe^+ν_e)} = 0.94\pm0.08$, in agreement with lepton universality. By performing a partial wave analysis, the hadronic form factor ratios at $q^{2}=0$ are extracted, finding $r_{V}=\frac{V(0)}{A_{1}(0)}=1.58\pm0.17\pm0.02$ and $r_{2}=\frac{A_{2}(0)}{A_{1}(0)}=0.71\pm0.14\pm0.02$, where the first uncertainties are statistical and the second are systematic. No significant $S$-wave contribution from $f_0(980)\to K^+K^-$ is found. The upper limit $\mathcal{B}(D_s^+\to f_0(980)μ^{+}ν_μ) \cdot{\mathcal B}(f_0(980)\to K^+K^-) < 5.45 \times 10^{-4}$ is set at 90\% confidence level.

hep-ex↗

arXiv2023

Measurement of the Energy-Dependent Electromagnetic Form Factors of a Charmed Baryon

We study the process $e^{+}e^{-}\toΛ_{c}^{+}\barΛ_c^{-}$ at twelve center-of-mass energies from $4.6119$ to $4.9509~\mathrm{GeV}$ using data samples collected by the BESIII detector at the BEPCII collider. The Born cross sections and effective form factors ($|G_{\mathrm{eff}}|$) are determined with unprecedented precision after combining the single and double-tag methods based on the decay process $Λ_{c}^{+}\to pK^{-}π^{+}$. Flat cross sections around $4.63~\mathrm{GeV}$ are obtained and no indication of the resonant structure $Y(4630)$, as reported by Belle, is found. In addition, no oscillatory behavior is discerned in the $|G_{\mathrm{eff}}|$ energy-dependence of $Λ_{c}^{+}$, in contrast to what is seen for the proton and neutron cases. Analyzing the cross section together with the polar-angle distribution of the $Λ_{c}^{+}$ baryon at each energy point, the moduli of electric and magnetic form factors ($|G_{E}|$ and $|G_{M}|$) are extracted and separated. For the first time, the energy-dependence of the form factor ratio $|G_{E}/G_{M}|$ is observed, which can be well described by an oscillatory function.

hep-ex↗

arXiv2023

First simultaneous measurement of $Ξ^0$ and $\barΞ^0$ asymmetry parameters in $ψ(3686)$ decay

The $Ξ^0$ asymmetry parameters are measured using entangled quantum $Ξ^0$-$\barΞ^0$ pairs from a sample of $(448.1 \pm 2.9) \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at BEPCII. The relative phase between the transition amplitudes of the $Ξ^0 \barΞ^0$ helicity states is measured to be $ΔΦ= -0.050 \pm 0.150 \pm 0.020$~rad, which implies that there is no obvious polarization at the current level of statistics. The decay parameters of the $Ξ^0$ hyperon $(α_{Ξ^0}, α_{\barΞ^0}, ϕ_{Ξ^0}, ϕ_{\barΞ^0})$ and the angular distribution parameter $(α_{ψ(3686)})$ and $ΔΦ$ are measured simultaneously for the first time. In addition, the $CP$ asymmetry observables are determined to be $A^{Ξ^0}_{CP} = (α_{Ξ^0} + α_{\barΞ^0})/(α_{Ξ^0} - α_{\barΞ^0})$ $= -0.007$ $\pm$ 0.082 $\pm$ 0.025 and $Δϕ^{Ξ^0}_{CP} = (ϕ_{Ξ^0} + ϕ_{\barΞ^0})/2$ $= -0.079$ $\pm$ 0.082 $\pm$ 0.010 rad, which are consistent with $CP$ conservation.

hep-ex↗

arXiv2023

Measurement of $e^+e^-\to pK^-\barΛ+c.c.$ cross sections between 4.009 GeV and 4.951 GeV

Using $e^+e^-$ collision datasets corresponding to total integrated luminosity of 21.7 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider at center-of-mass energies ranging from 4.009 GeV to 4.951 GeV, the energy-dependent cross sections of $e^+e^-\to pK^-\barΛ+c.c.$ are measured for the first time. By fitting these energy-dependent cross sections, we search for the excited $ψ$ states $ψ(4160)$ and $ψ(4415)$, and the vector charmonium-like states $ψ(4230)$, $ψ(4360)$, and $ψ(4660)$. No evidence for these is observed and the upper limits on the branching fractions of these states decaying into $pK^-\bar Λ+c.c.$ are set at the 90\% confidence level.

hep-ex↗

arXiv2023

Search for the semi-leptonic decays $Λ_c^+ \to Λπ^+ π^- e^+ ν_e$ and $Λ_c^+ \to p K_S^0 π^- e^+ ν_e$

We search for the semi-leptonic decays $Λ_c^+ \to Λπ^+ π^- e^+ ν_e$ and $Λ_c^+ \to p K_S^0 π^- e^+ ν_e$ in a sample of 4.5 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV 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 $\mathcal{B}(Λ_c^+ \to Λπ^+ π^- e^+ ν_e)<3.9\times10^{-4}$ and $\mathcal{B}(Λ_c^+ \to p K_S^0 π^- e^+ ν_e)<3.3\times10^{-4}$ at the 90% confidence level, respectively.

hep-ex↗

arXiv2023

Study of $Λ_c^+\rightarrow Λμ^+ν_μ$ and Test of Lepton Flavor Universality with $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ Decays

The measurement of the Cabibbo-favored semileptonic decay $Λ_c^+\rightarrow Λμ^+ν_μ$ is reported using $4.5~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at center-of-mass energies ranging from 4.600~GeV to 4.699~GeV. The branching fraction of the decay is measured to be $\mathcal{B}(Λ_c^+\rightarrow Λμ^+ν_μ)=(3.48\pm0.14_{\rm stat.}\pm0.10_{\rm syst.})\%$, three times more precise than the prior world average result. Tests of lepton flavor universality using $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ ($\ell=e, μ$) decays are reported for the first time, based on measurements of the differential decay rates and the forward-backward asymmetries in separate four-momentum transfer regions. The results are compatible with Standard Model predictions. Furthermore, we improve the determination of the form-factor parameters in $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ decays, which provide stringent tests and calibration for lattice quantum chromodynamics (LQCD) calculations.

hep-ex↗

arXiv2023

First study of reaction $Ξ^{0}n\rightarrowΞ^{-}p$ using $Ξ^0$-nucleus scattering at an electron-positron collider

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring, the process $Ξ^{0}n\rightarrowΞ^{-}p$ is studied, where the $Ξ^0$ baryon is produced in the process $J/ψ\rightarrowΞ^0\barΞ^0$ and the neutron is a component of the $^9\rm{Be}$, $^{12}\rm{C}$ and $^{197}\rm{Au}$ nuclei in the beam pipe. A clear signal is observed with a statistical significance of $7.1σ$. The cross section of the reaction $Ξ^0+{^9\rm{Be}}\rightarrowΞ^-+p+{^8\rm{Be}}$ is determined to be $σ(Ξ^0+{^9\rm{Be}}\rightarrowΞ^-+p+{^8\rm{Be}})=(22.1\pm5.3_{\rm{stat}}\pm4.5_{\rm{sys}})$ mb at the $Ξ^0$ momentum of $0.818$ GeV/$c$, where the first uncertainty is statistical and the second is systematic. No significant $H$-dibaryon signal is observed in the $Ξ^-p$ final state. This is the first study of hyperon-nucleon interactions in electron-positron collisions and opens up a new direction for such research.

hep-ex↗

arXiv2023

Determination of spin and parity of $D^{*}_{(s)}$ mesons

The spin and parity of the charmed mesons $D_{s}^{*+}$, $D^{*0}$ and $D^{*+}$ are determined for the first time to be $J^P=1^{-}$ with significances greater than 10$σ$ over other hypotheses of $2^{+}$ and $3^{-}$, using an $e^+e^-$ collision data sample with an integrated luminosity of 3.19 fb$^{-1}$ collected by the BESIII detector at a center-of-mass energy of 4.178 GeV. Different spin-parity hypotheses for $D_{s}^{*+}$, $D^{*0}$, and $D^{*+}$ mesons are tested via a helicity amplitude analysis of the processes $e^+e^-\to D^{*+}_{s}D^{-}_{s}$, $D^{*0}D^{0}$ and $D^{*+}D^{-}$, with $D^{*+}_{s}\to D^{+}_{s} γ$, $D^{*0}\to D^{0}π^{0}$, and $D^{*+}\to D^{+}π^{0}$. The results confirm the quark model predictions.

hep-ex↗

arXiv2023

Precision Measurement of the Decay $Σ^{+} \rightarrow pγ$ in the Process $J/ψ\rightarrow Σ^{+}\barΣ^{-}$

Using $(10\:087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, the radiative hyperon decay $Σ\rightarrow pγ$ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be $\left(0.996 \pm 0.021_{\rm stat.}\pm 0.018_{\rm syst.}\right)\times 10^{-3}$, which is lower than its world average value by $4.2$ standard deviations. Its decay asymmetry parameter is determined to be $-0.652 \pm 0.056_{\rm stat.}\pm 0.020_{\rm syst.}$. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by $78\%$ and $34\%$, respectively.

hep-ex↗

arXiv2023

Precision measurement of the matrix elements for $η\toπ^+π^-π^0$ and $η\toπ^0π^0π^0$ decays

A precision measurement of the matrix elements for $η\toπ^+π^-π^0$ and $η\toπ^0π^0π^0$ decays is performed using a sample of $(10087\pm44)\times10^6$ $J/ψ$ decays collected with the BESIII detector. The decay $J/ψ\to γη$ is used to select clean samples of 631,686 $η\toπ^+π^-π^0$ decays and 272,322 $η\toπ^0π^0π^0$ decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The non-zero $gX^2Y$ term for the decay mode $η\toπ^+π^-π^0$ is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the $η\toπ^+π^-π^0$ decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the $η\toπ^0π^0π^0$ decay, and no obvious structure around the $π^+π^-$ mass threshold is observed.

hep-ex↗

arXiv2023

Search for baryon and lepton number violating decays of $Ξ^{0}$ hyperons

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays $Ξ^{0} \rightarrow K^{-} e^{+}$ with $Δ(B-L)=0$ and $Ξ^{0} \rightarrow K^{+} e^{-}$ with $|Δ(B-L)|=2$, where $B$ ($L$) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to $\mathcal B(Ξ^{0} \rightarrow K^{-} e^{+})<3.6\times10^{-6}$ and $\mathcal B(Ξ^{0} \rightarrow K^{+} e^{-})<1.9\times10^{-6}$ at the 90\% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.

hep-ex↗