We analyze the decays \eta \rightarrow {\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}(l=e,μ) via J/\psi \rightarrow \gamma {\eta }^{\prime }and {\eta }^{\prime }\rightarrow {\pi }^{+}{\pi }^{-}\eta , based on \left(10087\pm 44\right)\times {10}^{6}J/\psi events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of \eta \rightarrow {\mu }^{+}{\mu }^{-}is measured to be \mathcal{B}\left(\eta \rightarrow {\mu }^{+}{\mu }^{-}\right)=\left(5.8\pm {1.0}_{\mathrm{stat}}\pm {0.2}_{\mathrm{syst}}\right)\times {10}^{-6}, which is consistent with previous measurements and theoretical expectations. In addition, no significant \eta \rightarrow e^{+}e^{-}signal is observed in the e^{+}e^{-}invariant mass spectrum, and an improved upper limit of \mathcal{B}\left(\eta \rightarrow e^{+}e^{-}\right)\lt 2.2\times {10}^{-7} is set at the 90% confidence level.
Measurement of the branching fraction of η → μ + μ − and search for η → e + e −
Garzia, I.;Melendi, F. M.;
2026
Abstract
We analyze the decays \eta \rightarrow {\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}(l=e,μ) via J/\psi \rightarrow \gamma {\eta }^{\prime }and {\eta }^{\prime }\rightarrow {\pi }^{+}{\pi }^{-}\eta , based on \left(10087\pm 44\right)\times {10}^{6}J/\psi events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of \eta \rightarrow {\mu }^{+}{\mu }^{-}is measured to be \mathcal{B}\left(\eta \rightarrow {\mu }^{+}{\mu }^{-}\right)=\left(5.8\pm {1.0}_{\mathrm{stat}}\pm {0.2}_{\mathrm{syst}}\right)\times {10}^{-6}, which is consistent with previous measurements and theoretical expectations. In addition, no significant \eta \rightarrow e^{+}e^{-}signal is observed in the e^{+}e^{-}invariant mass spectrum, and an improved upper limit of \mathcal{B}\left(\eta \rightarrow e^{+}e^{-}\right)\lt 2.2\times {10}^{-7} is set at the 90% confidence level.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
