Based on a sample of $2.7\times10^{9}$ $\psi(3686)$ events collected by the BESIII detector operating at the BEPCII collider, the decay $\psi(3686)\to\gamma\chi_{cJ}, \chi_{cJ}\to\eta\eta\eta^{\prime}$ is analyzed. The decay modes $\chi_{c1}$ and $\chi_{c2}\to\eta\eta\eta^{\prime}$ are observed for the first time, and their corresponding branching fractions are determined to be ${\cal{B}}(\chi_{c1}\to\eta\eta\eta^{\prime}) = $ $ (1.40\, \pm 0.13\, (\text{stat.}) \pm 0.09\, (\text{sys.})) \times 10^{-4}$ and ${\cal{B}}(\chi_{c2}\to\eta\eta\eta^{\prime}) = (4.18\, \pm 0.84\, (\text{stat.}) \pm 0.48\, (\text{sys.})) \times 10^{-5}$ . An upper limit on the branching fraction of $\chi_{c0}\to\eta\eta\eta^{\prime}$ is set as $2.59 \times 10^{-5}$ at a 90% confidence level (CL). A partial wave analysis (PWA) of the decay $\chi_{c1}\to\eta\eta\eta^{\prime}$ is performed to search for the $1^{-+}$ exotic state $\eta_1(1855)$ . The PWA result indicates that the structure in the $\eta\eta^{\prime}$ mass spectrum is attributed to $f_0(1500)$ , while in the $\eta\eta$ mass spectrum, it is attributed to the $0^{++}$ phase space. The upper limit of ${\cal{B}}(\chi_{c1}\to\eta_{1}(1855)\eta) \cdot {\cal{B}}(\eta_{1}(1855)\to\eta\eta^{\prime}) \lt $ $ 9.79 \times 10^{-5}$ is set based on the PWA at 90% CL.

China

M. Ablikim

Russia

M.N. Achasov

Sweden

P. Adlarson

X.C. Ai

Germany

R. Aliberti

Italy

A. Amoroso

Q. An

Y. Bai

O. Bakina

Y. Ban

H.R. Bao

Poland

V. Batozskaya

Mongolia

K. Begzsuren

N. Berger

M. Berlowski

M. Bertani

D. Bettoni

F. Bianchi

E. Bianco

A. Bortone

I. Boyko

United States

R.A. Briere

A. Brueggemann

H. Cai

M.H. Cai

X. Cai

A. Calcaterra

G.F. Cao

N. Cao

Türkiye

S.A. Cetin

X.Y. Chai

J.F. Chang

G.R. Che

Y.Z. Che

C.H. Chen

Chao Chen

G. Chen

H.S. Chen

H.Y. Chen

M.L. Chen

S.J. Chen

S.L. Chen

S.M. Chen

T. Chen

X.R. Chen

X.T. Chen

X.Y. Chen

Y.B. Chen

Y.Q. Chen

Z. Chen

Z.J. Chen

Z.K. Chen

S.K. Choi

X. Chu

G. Cibinetto

F. Cossio

United Kingdom

J. Cottee-Meldrum

J.J. Cui

H.L. Dai

J.P. Dai

A. Dbeyssi

R.E. de Boer

D. Dedovich

C.Q. Deng

Z.Y. Deng

A. Denig

I. Denysenko

M. Destefanis

F. De Mori

B. Ding

X.X. Ding

Y. Ding

Y.X. Ding

J. Dong

L.Y. Dong

M.Y. Dong

X. Dong

M.C. Du

S.X. Du

Y.Y. Duan

P. Egorov

G.F. Fan

J.J. Fan

Y.H. Fan

J. Fang

S.S. Fang

W.X. Fang

Y.Q. Fang

R. Farinelli

L. Fava

F. Feldbauer

G. Felici

C.Q. Feng

J.H. Feng

L. Feng

Q.X. Feng

Search for $\textit{η}$ $_{1}$(1855) in $\textit{χ}$ $\textit{cJ}$ → $\textit{ηηη}$′ decays * Supported in part by National Key R&D Program of China (2023YFA1606000, 2023YFA1606704); National Natural Science Foundation of China (NSFC) (11635010, 11935015, 11935016, 11935018, 12025502, 12035009, 12035013, 12061131003, 12192260, 12192261, 12192262, 12192263, 12192264, 12192265, 12221005, 12225509, 12235017, 12361141819); the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; CAS (YSBR-101); 100 Talents Program of CAS; The Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; Agencia Nacional de Investigación y Desarrollo de Chile (ANID), Chile (ANID PIA/APOYO AFB230003); German Research Foundation DFG (FOR5327); Istituto Nazionale di Fisica Nucleare, Italy; Knut and Alice Wallenberg Foundation (2021.0174, 2021.0299); Ministry of Development of Turkey (DPT2006K-120470); National Research Foundation of Korea ( NRF-2022R1A2C1092335); National Science and Technology fund of Mongolia; National Science Research and Innovation Fund (NSRF) via the Program Management Unit for Human Resources Institutional Development, Research and Innovation of Thailand ( B50G670107); Polish National Science Centre (2024/53/B/ST2/00975); Swedish Research Council (2019.04595); U. S. Department of Energy (DE-FG02-05ER41374)

Based on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> annihilation data collected with the BESIII detector at the BEPCII collider, searches for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msub><mi mathvariant="normal">Σ</mi><mi>c</mi></msub><msub><mover accent="true"><mi mathvariant="normal">Σ</mi><mo stretchy="false">¯</mo></mover><mi>c</mi></msub></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi mathvariant="normal">Σ</mi><mi>c</mi><mo>+</mo></msubsup><msubsup><mover accent="true"><mi mathvariant="normal">Σ</mi><mo stretchy="false">¯</mo></mover><mi>c</mi><mo>−</mo></msubsup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mi>c</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msubsup><mrow><mover accent="true"><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow><mrow><mn>0</mn></mrow></msubsup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>+</mo><mo>+</mo></mrow></msubsup><msubsup><mrow><mover accent="true"><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow><mrow><mo>−</mo><mo>−</mo></mrow></msubsup></mrow></math>) processes, as well as for the process <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup><msubsup><mover accent="true"><mi mathvariant="normal">Σ</mi><mo stretchy="false">¯</mo></mover><mi>c</mi><mo>−</mo></msubsup></math>, are conducted for the first time at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>4.750</mn></math>, 4.781, 4.843, 4.918, and 4.951 GeV. As no signals are observed for all the above channels, the upper limits on their Born cross sections at the 90% confidence level are reported. The obtained upper limits of cross sections for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msub><mi mathvariant="normal">Σ</mi><mi>c</mi></msub><msub><mover accent="true"><mi mathvariant="normal">Σ</mi><mo stretchy="false">¯</mo></mover><mi>c</mi></msub></math> are more than 2 orders of magnitude smaller than those for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msubsup><mi mathvariant="normal">Λ</mi><mi>c</mi><mo>+</mo></msubsup><msubsup><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi>c</mi><mo>−</mo></msubsup></math> near the threshold. In contrast, such suppression is absent in hyperon pair production (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi mathvariant="normal">Λ</mi><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Σ</mi><mover accent="true"><mi mathvariant="normal">Σ</mi><mo stretchy="false">¯</mo></mover></math>), suggesting distinct underlying dynamics in charmed baryon production.

JINR

G. Chelkov

South Korea

Z.H. Duan

Measurements of the cross sections of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><msub><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mi>c</mi></mrow></msub><msub><mrow><mover accent="true"><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow></msub></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>+</mo></mrow></msubsup><msubsup><mrow><mover accent="true"><mrow><mi mathvariant="normal">Σ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow><mrow><mo>−</mo></mrow></msubsup></mrow></math> near kinematic thresholds

Based on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>12.0</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collision data samples collected by the BESIII detector at center-of-mass energies from 4.1271 to 4.3583 GeV, a partial wave analysis is performed for the process <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></math>. The cross sections for the subprocesses <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><msup><mo stretchy="false">)</mo><mo>−</mo></msup><mo>+</mo><mi mathvariant="normal">c</mi><mo>.</mo><mi mathvariant="normal">c</mi><mo>.</mo><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>980</mn><mo stretchy="false">)</mo><mo stretchy="false">(</mo><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mo stretchy="false">)</mo><mi>J</mi><mo>/</mo><mi>ψ</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msub><mo stretchy="false">)</mo><mrow><mi mathvariant="normal">S</mi><mtext>−</mtext><mrow><mi>wave</mi></mrow></mrow></msub><mi>J</mi><mo>/</mo><mi>ψ</mi></math> are measured for the first time. The mass and width of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><msup><mo stretchy="false">)</mo><mo>±</mo></msup></math> are determined to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3884.6</mn><mo>±</mo><mn>0.7</mn><mo>±</mo><mn>3.3</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>37.2</mn><mo>±</mo><mn>1.3</mn><mo>±</mo><mn>6.6</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, respectively. The first errors are statistical and the second systematic. The final state <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">(</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><msub><mo stretchy="false">)</mo><mrow><mi mathvariant="normal">S</mi><mtext>−</mtext><mrow><mi>wave</mi></mrow></mrow></msub><mi>J</mi><mo>/</mo><mi>ψ</mi></math> dominates the process <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></math>. By analyzing the cross sections of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mo>±</mo></msup><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><msup><mo stretchy="false">)</mo><mo>∓</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>0</mn></msub><mo stretchy="false">(</mo><mn>980</mn><mo stretchy="false">)</mo><mi>J</mi><mo>/</mo><mi>ψ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Y</mi><mo stretchy="false">(</mo><mn>4220</mn><mo stretchy="false">)</mo></math> has been observed. Its mass and width are determined to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4225.7</mn><mo>±</mo><mn>4.1</mn><mo>±</mo><mn>3.4</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>/</mo><msup><mi>c</mi><mn>2</mn></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>57.5</mn><mo>±</mo><mn>9.4</mn><mo>±</mo><mn>12.1</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>, respectively.

O. Afedulidis

I. Balossino

C. Chen

Z.Y. Chen

Y. Fang

Y.T. Feng

M. Fritsch

C.D. Fu

J.L. Fu

Y.W. Fu

H. Gao

X.B. Gao

Y.N. Gao

Partial wave analysis of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup><mi>J</mi><mo>/</mo><mi>ψ</mi></math> and cross section measurement of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><msup><mi>π</mi><mo>±</mo></msup><msub><mi>Z</mi><mi>c</mi></msub><mo stretchy="false">(</mo><mn>3900</mn><msup><mo stretchy="false">)</mo><mo>∓</mo></msup></math> from 4.1271 to 4.3583 GeV

Using $\textit{e}$ $\textit{e}$ collision data corresponding to a total integrated luminosity of 20 fb collected with the BESIII detector at the BEPCII collider, we present a measurement of the Born cross section for the process $$ {e}^{+}{e}^{-}\to p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ at 39 center-of-mass energies between 3.5 and 4.9 GeV with a partial reconstruction technique. By performing a fit to the dressed cross section of $$ {e}^{+}{e}^{-}\to p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ with a power law function for continuum production and one resonance at a time for the $\textit{ψ}$(3770), $\textit{ψ}$(4040), $\textit{ψ}$(4160), $\textit{ψ}$(4230), $\textit{ψ}$(4360), $\textit{ψ}$(4415) or $\textit{ψ}$(4660), respectively, the upper limits for the product of partial electronic width and branching fraction into the final state $$ p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ for these resonances are determined at the 90% confidence level.

M. Achasov

X. Ai

R. Briere

M. Cai

G. Cao

S. Cetin

X. Chai

J. Chang

G. Che

Y. Che

H. Chen

M. Chen

S. Chen

X. Chen

Y. Chen

S. Choi

J. Cui

H. Dai

J. Dai

R. Boer

C. Deng

Z. Deng

F. Mori

X. Ding

L. Dong

M. Dong

M. Du

S. Du

Y. Duan

Z. Duan

G. Fan

J. Fan

Y. Fan

S. Fang

W. Fang

C. Feng

J. Feng

Measurement of the Born cross section for $$ {e}^{+}{e}^{-}\to p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ at $$ \sqrt{s}=3.5\hbox{--} 4.9 $$ GeV

The first direct measurement of the relative phase between the strong and electromagnetic amplitudes for a $\textit{J/ψ}$ decaying into a vector-pseudoscalar final state is performed using 26 energy points of $\textit{e}$ $\textit{e}$ annihilation data between 3$\textit{.}$00 GeV and 3.12 GeV. The data sets were collected by the BESIII detector with a total integrated luminosity of 452 pb . By investigating the interference pattern in the cross section lineshape of $\textit{e}$ $\textit{e}$ $\textit{→ ϕη}$, the relative phase between the strong and electromagnetic amplitudes of $\textit{J/ψ}$ decay is determined to be within [133$\textit{°,}$ 228$\textit{°}$] at 68% confidence level.

Y. Feng

C. Fu

J. Fu

Y. Fu

X. Gao

Measurement of the phase between strong and electromagnetic amplitudes in the decay $\textit{J/ψ → ϕη}$

By analyzing $\textit{e}$ $\textit{e}$ collision data taken at center-of-mass energies $$ \sqrt{s} $$ between 4.600 and 4.699 GeV with the BESIII detector at the BEPCII collider, corresponding to an integrated luminosity of 4.5 fb , we study the hadronic decays $$ {\Lambda}_c^{+}\to {\Sigma}^{+}\eta $$ and $$ {\Lambda}_c^{+}\to {\Sigma}^{+}{\eta}^{\prime } $$ using the single-tag method. The branching fraction ratio of $$ {\Lambda}_c^{+}\to {\Sigma}^{+}\eta $$ relative to $$ {\Lambda}_c^{+}\to {\Sigma}^{+}{\pi}^0 $$ is determined to be 0.305 $\textit{±}$ 0.046 $\textit{±}$ 0.007 , and that of $$ {\Lambda}_c^{+}\to {\Sigma}^{+}{\eta}^{\prime } $$ relative to $$ {\Lambda}_c^{+}\to {\Sigma}^{+}\omega $$ is 0.336 $\textit{±}$ 0.094 $\textit{±}$ 0.037 . The ratio of $$ \frac{\mathcal{B}\left({\Lambda}_c^{+}\to {\Sigma}^{+}{\eta}^{\prime}\right)}{\mathcal{B}\left({\Lambda}_c^{+}\to {\Sigma}^{+}\eta \right)} $$ is determined to be 1.73 $\textit{±}$ 0.22 $\textit{±}$ 0.16 . These results enrich our knowledge of charmed baryon decays.

Y. Gao

Measurement of branching fractions of $$ {\Lambda}_c^{+} $$ decays to Σ

With data collected in a dedicated energy scan from 2.3864 up to 3.0800 GeV, the BESIII Collaboration provides the first complete energy-dependent measurements of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math> electromagnetic form factors in the timelike region. By combining double-tag and single-tag events from the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><mi mathvariant="normal">Λ</mi><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mo stretchy="false">→</mo><mi>p</mi><msup><mrow><mi>π</mi></mrow><mrow><mo>−</mo></mrow></msup><mover accent="true"><mrow><mi>p</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></math> reaction, we achieve a complete decomposition of the spin structure of the reaction at five energy points, with high statistical and systematic precision. Our data reveal that while the modulus of the ratio between the electric and magnetic form factor, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>R</mi><mo stretchy="false">(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy="false">)</mo><mo>=</mo><mo stretchy="false">|</mo><msub><mrow><mi>G</mi></mrow><mrow><mi>E</mi></mrow></msub><mo stretchy="false">(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy="false">)</mo><mo>/</mo><msub><mrow><mi>G</mi></mrow><mrow><mi>M</mi></mrow></msub><mo stretchy="false">(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy="false">)</mo><mo stretchy="false">|</mo></mrow></math>, remains fairly constant across the considered energy range, the relative phase <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">Δ</mi><mi mathvariant="normal">Φ</mi><mo stretchy="false">(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy="false">)</mo><mo>=</mo><msub><mrow><mi mathvariant="normal">Φ</mi></mrow><mrow><mi>E</mi></mrow></msub><mo stretchy="false">(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy="false">)</mo><mo>−</mo><msub><mrow><mi mathvariant="normal">Φ</mi></mrow><mrow><mi>M</mi></mrow></msub><mo stretchy="false">(</mo><msup><mrow><mi>q</mi></mrow><mrow><mn>2</mn></mrow></msup><mo stretchy="false">)</mo></mrow></math> changes by more than 90° between 2.396 and 2.6544 GeV. Using a fit to our data based on dispersion relations, the complex form factor ratio is determined as a function of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>q</mi><mn>2</mn></msup></math>, and the preferred solution has multiple zero-crossings in the complex plane. From the derivative of the ratio at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>q</mi><mn>2</mn></msup><mo>=</mo><mn>0</mn></math>, the root-mean-squared charge radius of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math> is obtained. The two most probable solutions yield a negative root-mean-squared charge radius, indicating an asymmetric charge distribution where the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi><mi>s</mi></math> quark pair lies close to the center of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math> hyperon.

J. Biernat

Unraveling the Structure of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math> Hyperons with Polarized <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">Λ</mi><mover accent="true"><mrow><mi mathvariant="normal">Λ</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow></math> Pairs

Using 20.3 fb of $\textit{e}$ $\textit{e}$ collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we present the measurements of the absolute branching fractions of the doubly Cabibbo-suppressed decays $\textit{D}$ → $\textit{K}$ $\textit{π}$ , $\textit{D}$ → $\textit{K}$ $\textit{η}$ and $\textit{D}$ → $\textit{K}$ $\textit{η′}$ with the double-tag method, with significantly improved precision compared to the previous measurements. The statistical significance of each signal decay exceeds 10$\textit{σ}$. The branching fractions are determined to be ℬ($\textit{D}$ → $\textit{K}$ $\textit{π}$ ) = (1.45 ± 0.06 ± 0.08) × 10 , ℬ($\textit{D}$ → $\textit{K}$ $\textit{η}$) = (1.17 ± 0.10 ± 0.03) × 10 and ℬ($\textit{D}$ → $\textit{K}$ $\textit{η′}$) = (1.88 ± 0.15 ± 0.11) × 10 , where the first uncertainties are statistical and the second systematic. The branching fractions of $\textit{D}$ $\textit{→ K}$ $\textit{η}$ and $\textit{D}$ $\textit{→ K}$ $\textit{η′}$ are consistent with the world average values. The reported branching fraction of $\textit{D}$ $\textit{→ K}$ $\textit{π}$ deviates with the world average value by 3$\textit{σ}$.

Q. Feng

Measurements of the absolute branching fractions of the doubly Cabibbo-suppressed decays $\textit{D}$

We report a study of the semileptonic decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>+</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mo>ℓ</mo></mrow></msub></mrow></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>ℓ</mo><mo>=</mo><mi>e</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>μ</mi></mrow></math>) based on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>20.3</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub></mrow></math> decay is observed for the first time, with a branching fraction of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>0.896</mn><mo>±</mo><mn>0.01</mn><msub><mrow><mn>7</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.00</mn><msub><mrow><mn>8</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo stretchy="false">)</mo><mo>%</mo></mrow></math>, and the branching fraction of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mi>e</mi></mrow></msub></mrow></math> is determined with the improved precision as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>0.943</mn><mo>±</mo><mn>0.01</mn><msub><mrow><mn>2</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.01</mn><msub><mrow><mn>0</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo stretchy="false">)</mo><mo>%</mo></mrow></math>. From the analysis of the dynamics, we observe that the dominant <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mover accent="true"><mi>K</mi><mo stretchy="false">¯</mo></mover><mo>*</mo></msup><mo stretchy="false">(</mo><mn>892</mn><msup><mo stretchy="false">)</mo><mn>0</mn></msup></math> component is accompanied by an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math>-wave contribution, which accounts for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>7.10</mn><mo>±</mo><mn>0.6</mn><msub><mrow><mn>8</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.4</mn><msub><mrow><mn>1</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo stretchy="false">)</mo><mo>%</mo></mrow></math> of the total decay rate of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>μ</mi><mo>+</mo></msup></math> channel and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>6.39</mn><mo>±</mo><mn>0.1</mn><msub><mrow><mn>7</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.1</mn><msub><mrow><mn>4</mn></mrow><mrow><mi>syst</mi></mrow></msub><mo stretchy="false">)</mo><mo>%</mo></mrow></math> of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup></math> channel. Assuming a single-pole dominance parametrization, the hadronic form factor ratios are extracted to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>r</mi></mrow><mrow><mi>V</mi></mrow></msub><mo>=</mo><mi>V</mi><mo stretchy="false">(</mo><mn>0</mn><mo stretchy="false">)</mo><mo>/</mo><msub><mrow><mi>A</mi></mrow><mrow><mn>1</mn></mrow></msub><mo stretchy="false">(</mo><mn>0</mn><mo stretchy="false">)</mo><mo>=</mo><mn>1.42</mn><mo>±</mo><mn>0.0</mn><msub><mrow><mn>3</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.0</mn><msub><mrow><mn>2</mn></mrow><mrow><mi>syst</mi></mrow></msub></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>r</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>=</mo><msub><mrow><mi>A</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy="false">(</mo><mn>0</mn><mo stretchy="false">)</mo><mo>/</mo><msub><mrow><mi>A</mi></mrow><mrow><mn>1</mn></mrow></msub><mo stretchy="false">(</mo><mn>0</mn><mo stretchy="false">)</mo><mo>=</mo><mn>0.75</mn><mo>±</mo><mn>0.0</mn><msub><mrow><mn>3</mn></mrow><mrow><mi>stat</mi></mrow></msub><mo>±</mo><mn>0.0</mn><msub><mrow><mn>1</mn></mrow><mrow><mi>syst</mi></mrow></msub></mrow></math>. Based on the first comprehensive angular and the decay-rate <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> asymmetry analysis, the full set of averaged angular and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> asymmetry observables are measured as a function of the momentum-transfer squared; they are consistent with expectations from the standard model. No evidence for violation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>μ</mi><mo>−</mo><mi>e</mi></math> lepton-flavor universality is observed in either the full range or the five chosen bins of momentum-transfer squared.

Observation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub></mrow></math>, Test of Lepton Flavor Universality, and First Angular Analysis of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mover accent="true"><mrow><mi>K</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></mrow><mrow><mo>*</mo></mrow></msup><mo stretchy="false">(</mo><mn>892</mn><msup><mrow><mo stretchy="false">)</mo></mrow><mrow><mn>0</mn></mrow></msup><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>+</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mo>ℓ</mo></mrow></msub></mrow></math>

The study of meson pairs produced with quantum correlations gives direct access to parameters that are challenging to measure in other systems. In this Letter, the existence of quantum correlations due to charge-conjugation symmetry <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math> are demonstrated in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover></math> pairs produced through the processes <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mrow><mi>D</mi><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mrow><msup><mi>D</mi><mo>*</mo></msup><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mrow><msup><mi>D</mi><mo>*</mo></msup><mrow><msup><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover><mo>*</mo></msup></mrow></mrow></math>, where the lack of charge superscripts refers to an admixture of neutral-charm-meson particle and antiparticle states, using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>7.13</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> collision data collected by the BESIII experiment between center-of-mass energies of 4.13–4.23 GeV. Processes with either <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math>-even or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math>-odd constraints are identified and separated. A procedure is presented that harnesses the entangled production process to enable measurements of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mn>0</mn></msup></math>-meson hadronic parameters. This Letter provides the first confirmation of quantum correlations in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi>X</mi><mrow><mi>D</mi><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover></mrow></math> processes and the first observation of a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math>-even constrained <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover></math> system. The procedure is applied to measure <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>δ</mi><mrow><mi>K</mi><mi>π</mi></mrow><mi>D</mi></msubsup></math>, the strong phase between the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>D</mi></mrow><mrow><mn>0</mn></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><msup><mrow><mover accent="true"><mrow><mi>D</mi></mrow><mrow><mo stretchy="true">¯</mo></mrow></mover></mrow><mrow><mn>0</mn></mrow></msup></mrow><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></math> decay amplitudes, which results in the determination of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>δ</mi></mrow><mrow><mi>K</mi><mi>π</mi></mrow><mrow><mi>D</mi></mrow></msubsup><mo>=</mo><mo stretchy="false">(</mo><msubsup><mrow><mn>192.8</mn></mrow><mrow><mo>−</mo><mn>12.4</mn><mo>−</mo><mn>2.4</mn></mrow><mrow><mo>+</mo><mn>11.0</mn><mo>+</mo><mn>1.9</mn></mrow></msubsup><mo stretchy="false">)</mo><mo>°</mo></mrow></math>. The potential for measurements of other hadronic decay parameters and charm mixing with these and future datasets is also discussed.

First Observation of Quantum Correlations in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo stretchy="false">→</mo><mi>X</mi><mi>D</mi><mover accent="true"><mi>D</mi><mo stretchy="true">¯</mo></mover></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math>-Even Constrained <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>D</mi><mover accent="true"><mrow><mi>D</mi></mrow><mrow><mo stretchy="true">¯</mo></mrow></mover></mrow></math> Pairs