Measurement of η meson decays into lepton-antilepton pairs (original) (raw)

Measurement of eta meson decays into lepton-antilepton pairs

2007

A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta->e+e-e+e- events are reported with a background of 1.3+/-0.2 events. This allows to set an upper limit to the branching ratio of 9.7E-5 (90% CL). The branching ratio for the decay eta->e+e-gamma is determined to (7.8+/-0.5

Measurement of the branching ratio for the decay η→μ+μ−

Physical Review D, 1994

A new measurement of the branching ratio for the decay,.,-+ JJ+ JJ-, made at tile SATURNE II proton synchrotron, resulted in f(,.,-+ JJ+ JJ-)lf(,.,-+ all) = 15.7 ± 0.7 (stat.)±0.5 (syst.)) x 10-8. The reaction pd-+ l He ,., close to threshold yielded 800 S-I tagged ,.,'s in a narrow momentum band around 257 MeV Ic. Muon pairs were detected in two range telescopes. The data obtained consist of 114 events ,.,-+ JJ+ JJ-on a background of 14 events. The new value for the branching ratio is 1.3 ± 0.2 times the unitarity lower limit, consistent with most quark and Vector Meson Dominance models which describe th~ decay as an electromagnetic transition with a two-photon intermediate state. The result resolves the discrepancy between the two previous measurements of this

Prepared for submission to JHEP η and η ′ decays into lepton pairs

2018

In this work, we calculate the branching ratios for the η(η′)→ `` decays, where ` = e, μ. These processes have tiny rates in the Standard Model due to spin flip, loop and electromagnetic suppressions, which could make them sensitive to New Physics effects. In order to provide a reliable input for the Standard Model, we exploit the general analytical properties of the amplitude. For that purpose, we invoke the machinery of Canterbury approximants, which provides a systematic description of the underlying hadronic physics in a data-driven fashion. Given the current experimental discrepancies, we discuss in detail the role of the resonant region and comment on the reliability of χPT calculations. Finally, we discuss the kind of new physics which we think would be relevant to account for them. ar X iv :1 51 2. 09 29 2v 2 [ he pph ] 1 9 Se p 20 16

Measurement of the decay branching ratio

Physics Letters B, 2007

The reaction pd → 3 Heη at threshold was used to provide a clean source of η mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay η → π + π − e + e − is measured to be (4.3 ± 1.3 ± 0.4) × 10 −4 .

Η and Η ′ Decays Into Lepton Pairs

Journal of High Energy Physics, 2016

In this work, we calculate the branching ratios for the η(η) → decays, where = e, µ. These processes have tiny rates in the Standard Model due to spin flip, loop and electromagnetic suppressions, which could make them sensitive to New Physics effects. In order to provide a reliable input for the Standard Model, we exploit the general analytical properties of the amplitude. For that purpose, we invoke the machinery of Canterbury approximants, which provides a systematic description of the underlying hadronic physics in a data-driven fashion. Given the current experimental discrepancies, we discuss in detail the role of the resonant region and comment on the reliability of χPT calculations. Finally, we discuss the kind of new physics which we think would be relevant to account for them.

Search for Rare and Forbidden η′ Decays

Physical Review Letters, 2000

We have searched for the rare decays η ′ → e + e − η , η ′ → e + e − π 0 , η ′ → e + e − γ, and η ′ → eµ in hadronic events at the CLEO II detector. The search is conducted on 4.80 fb −1 of e + e − collisions at 10.6 GeV center-of-mass energy at the Cornell Electron Storage Ring (CESR). We find no signals in any of these modes, and set 90% confidence level upper limits on their branching fractions: B(η ′ → e + e − η) < 2.4 × 10 −3 , B(η ′ → e + e − π 0) < 1.4 × 10 −3 , B(η ′ → e + e − γ) < 0.9 × 10 −3 , and B(η ′ → eµ) < 4.7 × 10 −4. We also investigated the Dalitz plot of the common decay mode η ′ → π + π − η. We fit the matrix element with the Particle Data Group parameterization |M| 2 =A| 1 + αy | 2 , where y is a linear function of the kinetic energy of the η, and find Re(α) = −0.021 ± 0.025.

Novel approach to measure the leptonicη(′)→μ+μ−decays via charmed meson decays

Physical Review D, 2016

In this article, we propose a novel approach to measure the branching ratios of the leptonic η () → µ + µ − decays by using charmed meson decays, namely, D + (s) → π + η () (→ µ + µ −) and D 0 → K − π + η () (→ µ + µ −). We advocate that the data available at LHCb can already yield a new measurement of Br(η → µ + µ −) with accuracy competitive with the current world average. We also estimate that using the data collected by LHCb between 2015 and 2018 in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.0 fb −1 , the relative uncertainties to this branching ratio can be reduced down to ∼ 10%. We also show that the first observation of Br(η → µ + µ −) may be possible with the Upgrade of the LHCb experiment.