Physics of η[sup ʹ]→π[sup +]π[sup −]η and η[sup ʹ]→π[sup +]π[sup −]π[sup 0] decays (original) (raw)

Observation of η′ Decays to π+π-π0 and π+π-e+e

Physical Review Letters, 2009

Using ψ(2S)→π + π − J/ψ, J/ψ → γη ′ events acquired with the CLEO-c detector at the CESR e + e − collider, we make the first observations of the decays η ′ → π + π − π 0 and η ′ → π + π − e + e − , measuring absolute branching fractions (37 +11 − 9 ± 4) × 10 −4 and (25 +12 − 9 ± 5) × 10 −4 , respectively. For η ′ → π + π − π 0 , this result probes the mechanism of isospin violation and the roles of π 0 /η/η ′mixing and final state rescattering in strong decays. We also set upper limits on branching fractions for η ′ decays to π + π − µ + µ − , 2(π + π −), π + π − 2π 0 , 2(π + π −)π 0 , 3(π + π −), and invisible final states.

Measurement of the decay distribution of η′ → π+π−γ and evidence for the box anomaly

Physics Letters B, 1997

The distribution of m(π+π−) in the decay η′ → π+π−γ has been measured with the Crystal Barrel detector. The results are based on a total of 7392 observed η′ decays. The box anomaly constant is extracted from this and its value is found to agree well with theoretical expectations. The pseudoscalar nonet parameters (f1, f8 and θPS) are determined. Finally,

P o S ( C D 1 2 ) 0 3 5 A first calculation of the η ′ → π 0 γγ and η ′ → ηγγ decays

2013

The branching ratio of the η ′→ π0γγ and η ′→ ηγγ electromagnetic rare decays are calculated within the frameworks of the Linear Sigma Model and Vector Meson Dominance for the corresponding scalar and vector meson exchange contributions. The measured η → π0γγ process serves as a test of our approach while the non yet measured η ′ → (π0,η)γγ reactions are predicted for the first time. Our prediction for the η → π0γγ decay agrees with recent experimental reported values, thus supporting the validity of our framework. Therefore, our predictions for the η ′ → π0γγ and η ′ → ηγγ decays should be taken as a first indication of the possible values of the associated branching ratios. We hope these predictions to be interesting and useful for experiments such as KLOE-2, Crystal Ball, WASA, and BES-III where these processes are expected to be measured in the next future.

Amplitude analyses of the decays χ_{c1}→ηπ^{+}π^{-} and χ_{c1}→η^{′}π^{+}π^{-}

Physical Review D, 2011

Using a data sample of 2.59 × 10 7 ψ(2S) decays obtained with the CLEO-c detector, we perform amplitude analyses of the complementary decay chains ψ(2S) → γχ c1 ; χ c1 → ηπ + π − and ψ(2S) → γχ c1 ; χ c1 → η π + π −. We find evidence for an exotic P-wave η π amplitude, which, if interpreted as a resonance, would have parameters consistent with the π 1 (1600) state reported in other production mechanisms. We also make the first observation of the decay a 0 (980) → η π and measure the ratio of branching fractions B(a 0 (980) → η π)/B(a 0 (980) → ηπ) = 0.064 ± 0.014 ± 0.014. The ππ spectrum produced with a recoiling η is compared to that with η recoil.

New-physics signatures via CP violation in η(′) → π0μ+μ− and η′ → ημ+μ− decays

Journal of High Energy Physics

In this work we investigate the prospect of observing new-physics signatures via CP violation in η(′) → π0μ+μ− and η′ → ημ+μ− decays at the REDTOP experiment. We make use of the SMEFT to parametrise the new-physics CP-violating effects and find that the projected REDTOP statistics are not competitive with respect to nEDM experiments. This reasserts the η → μ+μ− process as the most promising channel to find CP-violation at this experimental facility.

Observation of D^{+}→K^{+}η^{(}′^{)} and Search for CP Violation in D^{+}→π^{+}η^{(}′^{)} Decays

Physical Review Letters, 2011

We report the first observation of the doubly Cabibbo-suppressed decays D + → K + η (′) using a 791 fb −1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e − collider. The ratio of the branching fractions of doubly Cabibbo-suppressed relative to singly Cabibbosuppressed D + → π + η (′) decays are B(D + → K + η)/B(D + → π + η) = (3.06 ± 0.43 ± 0.14)% and B(D + → K + η ′)/B(D + → π + η ′) = (3.77 ± 0.39 ± 0.10)%. From these, we find that the relative final-state phase difference between the tree and annihilation amplitudes in D + decays, δT A, is (72 ± 9) • or (288 ± 9) •. We also report the most precise measurements of CP asymmetries to date: A D + →π + η CP = (+1.74 ± 1.13 ± 0.19)% and A D + →π + η ′ CP = (−0.12 ± 1.12 ± 0.17)%.

Models of η^{0}→ π^{0}+ 2γ Decay

Physical Review, 1967

Recent experimental results on the zt'-+ zr'2v decay indicate that the branching ratio 8=P"(zr'2y)/ P"(zr zr p) is of the order of (or compatible with) 1. Using the vector-meson-dominant model, we have computed the width and the pion energy spectrum of the zt'z zr'2y decay, using the relevant SU(3)-symmetric coupling constants, including the zo-d mixing hypothesis as given by the static SU(6) theory, which demands Pe(zr'y) =0. We have then studied the effect of varying the mixing angle and the effective coupling constant fe &"ar ound the static SU(6) value over a wide range compatible with the present experimental information, using as input the experimental P (zr'y) as before. The model gives 8=0.331&&10 ' at the static SU(6) value, which increases by a factor of 10 at the mixing angle of 20'. It therefore appears that unless there is a drastic decrease in the experimental branching ratio, the vector-meson-dominant model cannot provide a dominant mechanism for the p~2 1-02' decay. A remark is also made about the relation between the value of the cop mixing angle and the ratios of various observed decay rates. We also study an alternative simple mechanism for the &-+ 21-'2p decay which may be suggested by the tadpole model of the electromagnetic mass difference of hadrons. We assume the existence of the I = 1, normal 0+ (rzzr) resonance c and consider the intermediary of the e meson go~woeo-+ 21 02'. Some consequences of this model are discussed.