TY - JOUR

T1 - Observation of transverse polarization and determination of psionic form factors of the Λ hyperon at √s = 3.773 GeV

AU - BESIII Collaboration

AU - Ачасов, Михаил Николаевич

AU - Мучной, Николай Юрьевич

AU - Николаев, Иван Борисович

N1 - The BESIII Collaboration thanks the staff of BEPCII ([61]) and the IHEP computing center for their strong support. This work is supported in part by the Fundamental Research Funds for the Central Universities under Contracts No. lzujbky-2025-ytA05, No. lzujbky-2025-it06, No. lzujbky-2024-jdzx06; Guangdong Provincial Key Laboratory of Advanced Particle Detection Technology No. 2024B1212010005; Guangdong Provincial Key Laboratory of Gamma-Gamma Collider and Its Comprehensive Applications No. 2024KSYS001; National Key R&D Program of China under Contracts No. 2023YFA1606000, No. 2023YFA1606704; National Natural Science Foundation of China (NSFC) under Contracts No. 12075107, No. 12247101, No. 11635010, 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, No. 12361141819; the Natural Science Foundation of Gansu Province No. 22JR5RA389, No. 25JRRA799; by the “111 Center” under Grant No. B20063; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; 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, 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 and Institutional Development, Research and Innovation of Thailand under Contract No. B50G670107; Polish National Science Centre under Contract No. 2024/53/B/ST2/00975; Swedish Research Council under Contract No. 2019.04595; U.S. Department of Energy under Contract No. DE-FG02-05ER41374.

PY - 2025/9/24

Y1 - 2025/9/24

N2 - Using a data sample of e + e − collision data corresponding to an integrated luminosity of 20.3 fb − 1 collected by the BESIII detector at the BEPCII collider, we present an observation of transverse polarization and a complete determination of the psionic form factors of the Λ hyperon in e + e − → Λ Λ ¯ decay with the entangled Λ − Λ ¯ pair at s = 3.773 GeV . The relative phase between the psionic form factors is determined to be Δ Φ = ( 1.53 ± 0.36 ± 0.03 ) rad with a significance of 5.5 σ taking into account systematic uncertainty. This result indicates a nonzero phase between the transition amplitudes of the Λ Λ ¯ helicity states. Additionally, we measure the angular distribution parameter and the modulus of the ratio between the psionic form factors to be η = 0.86 ± 0.05 ± 0.03 and R ( s ) = | G E ( s ) / G M ( s ) | = 0.47 ± 0.08 ± 0.05 , where the first uncertainty is statistical and the second systematic.

AB - Using a data sample of e + e − collision data corresponding to an integrated luminosity of 20.3 fb − 1 collected by the BESIII detector at the BEPCII collider, we present an observation of transverse polarization and a complete determination of the psionic form factors of the Λ hyperon in e + e − → Λ Λ ¯ decay with the entangled Λ − Λ ¯ pair at s = 3.773 GeV . The relative phase between the psionic form factors is determined to be Δ Φ = ( 1.53 ± 0.36 ± 0.03 ) rad with a significance of 5.5 σ taking into account systematic uncertainty. This result indicates a nonzero phase between the transition amplitudes of the Λ Λ ¯ helicity states. Additionally, we measure the angular distribution parameter and the modulus of the ratio between the psionic form factors to be η = 0.86 ± 0.05 ± 0.03 and R ( s ) = | G E ( s ) / G M ( s ) | = 0.47 ± 0.08 ± 0.05 , where the first uncertainty is statistical and the second systematic.

KW - Hadron production

KW - Hyperons

KW - Form factors

KW - Polarization

UR - https://www.webofscience.com/wos/woscc/full-record/WOS:001606789600001

UR - https://www.mendeley.com/catalogue/167ad4e6-4537-3ab0-880b-2f652f517c24/

U2 - 10.1103/qqw4-wnnt

DO - 10.1103/qqw4-wnnt

M3 - Article

VL - 112

JO - Physical Review D

JF - Physical Review D

SN - 2470-0010

IS - 5

M1 - L051102

ER -