In:
Journal of High Energy Physics, Springer Science and Business Media LLC, Vol. 2024, No. 7 ( 2024-07-16)
Abstract:
With a sample of (10087 ± 44) × 10 6 J/ψ events accumulated with the BESIII detector, we analyze the decays η ′ → π + π − l + l − ( l = e, μ ) via the process J/ψ → γη ′. The branching fractions are measured to be $$ \mathcal{B} $$ B ( η ′ → π + π − e + e − ) = (2 . 45 ± 0 . 02(stat . ) ± 0 . 08(syst . )) × 10 − 3 and $$ \mathcal{B} $$ B ( η ′ → π + π − μ + μ − ) = (2 . 16 ± 0 . 12(stat . ) ± 0 . 06(syst . )) × 10 − 5 , and the ratio is $$ \frac{\mathcal{B}\left({\eta}^{\prime}\to {\pi}^{+}{\pi}^{-}{e}^{+}{e}^{-}\right)}{\mathcal{B}\left({\eta}^{\prime}\to {\pi}^{+}{\pi}^{-}{\mu}^{+}{\mu}^{-}\right)}=113.4\pm 0.9\left(\textrm{stat}.\right)\pm 3.7\left(\textrm{syst}.\right) $$ B η ′ → π + π − e + e − B η ′ → π + π − μ + μ − = 113.4 ± 0.9 stat . ± 3.7 syst . . In addition, by combining the η ′ → π + π − e + e − and η ′ → π + π − μ + μ − decays, the slope parameter of the electromagnetic transition form factor is measured to be b η ′ = 1.30 ± 0.19 (GeV /c 2 ) − 2 , which is consistent with previous measurements from BESIII and theoretical predictions from the VMD model. The asymmetry in the angle between the π + π − and l + l − decay planes, which has the potential to reveal the CP -violation originating from an unconventional electric dipole transition, is also investigated. The asymmetry parameters are determined to be $$ {\mathcal{A}}_{CP}\left({\eta}^{\prime}\to {\pi}^{+}{\pi}^{-}{e}^{+}{e}^{-}\right)=\left(-0.21\pm 0.73\left(\textrm{stat}.\right)\pm 0.01\left(\textrm{syst}.\right)\right)\% $$ A CP η ′ → π + π − e + e − = − 0.21 ± 0.73 stat . ± 0.01 syst . % and $$ {\mathcal{A}}_{CP}\left({\eta}^{\prime}\to {\pi}^{+}{\pi}^{-}{\mu}^{+}{\mu}^{-}\right)=\left(0.62\pm 4.71\left(\textrm{stat}.\right)\pm 0.08\left(\textrm{syst}.\right)\right)\% $$ A CP η ′ → π + π − μ + μ − = 0.62 ± 4.71 stat . ± 0.08 syst . % , implying that no evidence of CP -violation is observed at the present statistics. Finally, an axion-like particle is searched for via the decay η ′ → π + π − a, a → e + e − , and upper limits of the branching fractions are presented for the mass assumptions of the axion-like particle in the range of 0 − 500 MeV /c 2 .
Type of Medium:
Online Resource
ISSN:
1029-8479
DOI:
10.1007/JHEP07(2024)135
Language:
English
Publisher:
Springer Science and Business Media LLC
Publication Date:
2024
detail.hit.zdb_id:
2027350-2
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