TY - JOUR

T1 - Improved measurements of the Dalitz decays η/η′→γe+e−

AU - BESIII Collaboration

AU - Ablikim, M.

AU - Achasov, M. n.

AU - Николаев, Иван Борисович

AU - Мучной, Николай Юрьевич

PY - 2024/4/3

Y1 - 2024/4/3

N2 - Based on a data sample of 10 billion J/ψ events collected with the BESIII detector, improved measurements of the Dalitz decays η/η′→γe+e- are performed, where the η and η′ are produced through the radiative decays J/ψ→γη/η′. The branching fractions of η→γe+e- and η′→γe+e- are measured to be (7.07±0.05±0.23)×10-3 and (4.83±0.07±0.14)×10-4, respectively. Within the single-pole model, the parameter of electromagnetic transition form factor for η→γe+e- is determined to be Λη=(0.749±0.027±0.007) GeV/c2. Within the multipole model, we extract the electromagnetic transition form factors for η′→γe+e- to be Λη′=(0.802±0.007±0.008) GeV/c2 and γη′=(0.113±0.010±0.002) GeV/c2. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the η and η′ are calculated to be (0.645±0.023±0.007) fm and (0.596±0.005±0.006) fm, respectively. In addition, we search for the dark photon in η/η′→γe+e-, and the upper limits of the branching fractions as a function of the dark photon are given at 90% confidence level.

AB - Based on a data sample of 10 billion J/ψ events collected with the BESIII detector, improved measurements of the Dalitz decays η/η′→γe+e- are performed, where the η and η′ are produced through the radiative decays J/ψ→γη/η′. The branching fractions of η→γe+e- and η′→γe+e- are measured to be (7.07±0.05±0.23)×10-3 and (4.83±0.07±0.14)×10-4, respectively. Within the single-pole model, the parameter of electromagnetic transition form factor for η→γe+e- is determined to be Λη=(0.749±0.027±0.007) GeV/c2. Within the multipole model, we extract the electromagnetic transition form factors for η′→γe+e- to be Λη′=(0.802±0.007±0.008) GeV/c2 and γη′=(0.113±0.010±0.002) GeV/c2. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the η and η′ are calculated to be (0.645±0.023±0.007) fm and (0.596±0.005±0.006) fm, respectively. In addition, we search for the dark photon in η/η′→γe+e-, and the upper limits of the branching fractions as a function of the dark photon are given at 90% confidence level.

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85190639442&origin=inward&txGid=1f295e53cbb73ed4cb97d1426ba7fa7d

U2 - 10.1103/PhysRevD.109.072001

DO - 10.1103/PhysRevD.109.072001

M3 - Article

VL - 109

JO - Physical Review D

JF - Physical Review D

SN - 2470-0010

IS - 7

M1 - 072001

ER -