TY - JOUR

T1 - Unraveling the Structure of Λ Hyperons with Polarized ΛΛ[over ¯] Pairs

AU - BESIII Collaboration

AU - Ablikim, M.

AU - Achasov, M. N.

AU - Adlarson, P.

AU - Ai, X. C.

AU - Aliberti, R.

AU - Amoroso, A.

AU - An, Q.

AU - Bai, Y.

AU - Bakina, O.

AU - Ban, Y.

AU - Bao, H. R.

AU - Batozskaya, V.

AU - Begzsuren, K.

AU - Berger, N.

AU - Berlowski, M.

AU - Bertani, M.

AU - Bettoni, D.

AU - Bianchi, F.

AU - Bianco, E.

AU - Biernat, J.

AU - Bortone, A.

AU - Boyko, I.

AU - Briere, R. A.

AU - Brueggemann, A.

AU - Cai, H.

AU - Cai, M. H.

AU - Cai, X.

AU - Calcaterra, A.

AU - Cao, G. F.

AU - Cao, N.

AU - Cetin, S. A.

AU - Chai, X. Y.

AU - Chang, J. F.

AU - Che, G. R.

AU - Che, Y. Z.

AU - Chelkov, G.

AU - Chen, C. H.

AU - Chen, Chao

AU - Chen, G.

AU - Chen, H. S.

AU - Chen, H. Y.

AU - Chen, M. L.

AU - Chen, S. J.

AU - Chen, S. L.

AU - Chen, S. M.

AU - Chen, T.

AU - Chen, X. R.

AU - Chen, X. T.

AU - Chen, Y. B.

AU - Мучной, Николай Юрьевич

AU - Nikolaev, I. B.

N1 - The BESIII Collaboration thanks the staff of BEPCII [48] and the IHEP computing center for their strong support. This work is supported in part by National Key R&D Program of China under Contracts No. 2020YFA0406300, No. 2020YFA0406400, and No. 2023YFA1606000; National Natural Science Foundation of China (NSFC) under Contracts No. 11635010, No. 11735014, No. 11935015, No. 11935016, No. 11935018, No. 12025502, No. 12035009, No. 12035013, No. 12061131003, No. 12192260, No. 12192261, No. 12192262, No. 12192263, No. 12192264, No. 12192265, No. 12221005, No. 12225509, No. 12235017, and No. 12361141819; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics (CCEPP); Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contract No. U1832207; CAS under Contract No. YSBR-101; 100 Talents Program of CAS; The Institute of Nuclear and Particle Physics (INPAC) and Shanghai Key Laboratory for Particle Physics and Cosmology; German Research Foundation DFG under Contract No. FOR5327; Istituto Nazionale di Fisica Nucleare, Italy; Knut and Alice Wallenberg Foundation under Contracts No. 2021.0174 and No. 2021.0299; Ministry of Development of Turkey under Contract No. DPT2006K-120470; National Research Foundation of Korea under Contract No. 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 under Contract No. B50G670107; Polish National Science Centre under Contract No. 2019/35/O/ST2/02907; Swedish Research Council under Contracts No. 2019.04595 and No. 2021.04567; The Swedish Foundation for International Cooperation in Research and Higher Education under Contract No. CH2018-7756; U.S. Department of Energy under Contract No. DE-FG02-05ER41374.

PY - 2025/11/4

Y1 - 2025/11/4

N2 - 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 Λ electromagnetic form factors in the timelike region. By combining double-tag and single-tag events from the e^{+}e^{-}→ΛΛ[over ¯]→pπ^{-}p[over ¯]π^{+} 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, R(q^{2})=|G_{E}(q^{2})/G_{M}(q^{2})|, remains fairly constant across the considered energy range, the relative phase ΔΦ(q^{2})=Φ_{E}(q^{2})-Φ_{M}(q^{2}) 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 q^{2}, and the preferred solution has multiple zero-crossings in the complex plane. From the derivative of the ratio at q^{2}=0, the root-mean-squared charge radius of the Λ is obtained. The two most probable solutions yield a negative root-mean-squared charge radius, indicating an asymmetric charge distribution where the ds quark pair lies close to the center of the Λ hyperon.

AB - 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 Λ electromagnetic form factors in the timelike region. By combining double-tag and single-tag events from the e^{+}e^{-}→ΛΛ[over ¯]→pπ^{-}p[over ¯]π^{+} 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, R(q^{2})=|G_{E}(q^{2})/G_{M}(q^{2})|, remains fairly constant across the considered energy range, the relative phase ΔΦ(q^{2})=Φ_{E}(q^{2})-Φ_{M}(q^{2}) 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 q^{2}, and the preferred solution has multiple zero-crossings in the complex plane. From the derivative of the ratio at q^{2}=0, the root-mean-squared charge radius of the Λ is obtained. The two most probable solutions yield a negative root-mean-squared charge radius, indicating an asymmetric charge distribution where the ds quark pair lies close to the center of the Λ hyperon.

UR - https://www.scopus.com/pages/publications/105022761516

UR - https://www.mendeley.com/catalogue/64f7eb90-3e15-3764-a1d8-07ba5e94d979/

U2 - 10.1103/9f1h-fl4k

DO - 10.1103/9f1h-fl4k

M3 - Article

C2 - 41269939

VL - 135

JO - Physical Review Letters

JF - Physical Review Letters

SN - 0031-9007

IS - 19

M1 - 191902

ER -