THE CP-VIOLATING ASYMMETRY IN η → π+ π-e+e-

Gao, Dao-Neng

doi:10.1142/s0217732302007739

Cited by 43 publications

(39 citation statements)

References 29 publications

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“…The upper limit for Eq. 5 predicted by theory is ∼ 1% [18]. The current measured result for A Φ has been found by KLOE [19]: A Φ = (−0.6 ± 2.5 stat ± 1.8 sys ) · 10 −2 .…”

supporting

confidence: 56%

Studyingη-Meson Decays with WASA-at-COSY

Lersch

2016

EPJ Web Conf.

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Abstract. The η-meson is a unique tool in a way that it provides access to (rare) decay processes, which allow to probe symmetry breaking phenomena, determine transition form factors, or to explore the anomalous sector of QCD. Those decays have been studied with the WASA-at-COSY experiment. Two data sets with different η-production mechanisms have been acquired. The analysis of those data sets are restricted to: The investigation of the isospin violating decay η → π + π − π 0 ; Exploring the box anomaly inThe determination of the electromagnetic transition form factor via the reactions: η → e + e − γ and η → e + e − e + e − ; Testing the CP-violation in η → π− . An overview of the analysis of those decays will be given in the following. The WASA-at-COSY FacilityThe different η-decays are measured and reconstructed within the 4π wide angle shower apparatus (WASA) (see Fig. 1), which is located at the cooler synchrotron (COSY) at the Jülich Research Center in Germany. A proton beam, provided by COSY, is impinged on a liquid deuterium / hydrogen target producing η-mesons via: pd → 3 Heη and pp → ppη. The scattered projectiles are detected in the forward part of WASA, where the angular information is provided by tracking detectors and the kinetic energy is reconstructed by a range hodoscope (see Fig. 1). The decay products are detected in the central part of WASA. Charged particles are reconstructed within a drift chamber in combination with a ∼ 1 T magnetic solenoid field. Additional plastic scintillators and an electromagnetic calorimeter allow for the distinction between pions and electrons. Neutral particles are reconstructed within the electromagnetic calorimeter. The Data SetsA first iteration of measurements was done using the pd → 3 Heη reaction (∼ 3 · 10 7 η-mesons have been detected) for the study of the more abundant η-decay channels (such as η → π + π − π 0 ) and to setup the framework for a common analysis. The rare η-decay modes (e.g. η → e + e − e + e − ) are studied by using the high-statistics pp → ppη data set (∼ 10 9 η-mesons have been produced). The η-mesons are reconstructed via their missing mass, which is defined as: Missing mass = (P in − P out ) 2 , where P in is the four momentum of all incoming particles (i.e. beam and target) and P out is the corresponding four momentum of all scattered projectiles. A plot of the missing mass distribution for the two data

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“…The upper limit for Eq. 5 predicted by theory is ∼ 1% [18]. The current measured result for A Φ has been found by KLOE [19]: A Φ = (−0.6 ± 2.5 stat ± 1.8 sys ) · 10 −2 .…”

supporting

confidence: 56%

Studyingη-Meson Decays with WASA-at-COSY

Lersch

2016

EPJ Web Conf.

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“…These decays probe the structure of the η meson [25] and test the theoretical predictions of the branching ratio [39][40][41][42]. Moreover, the π + π − e + e − final state could reveal CP violation beyond the prediction of the Standard Model by measuring the angular asymmetry A φ between pions and electrons decay planes [43]. KLOE has already measured the first two processes of Tab.…”

Section: Perspectives From E + E − Interactions With Kloe-2 Datamentioning

confidence: 76%

KLOE Results on Hadron Physics and Perspectives for KLOE-2

Giovannella

2018

EPJ Web Conf.

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“…In fact, CP violation produces an asymmetry in the distribution of the angle between the π + π − and e + e − planes in the η reference frame. Such an asymmetry can be produced by a 4 fermions operator [12] and is not constrained by other CP sensitive measurements. In particular we measure:…”

Section: Thementioning

confidence: 96%

KLOE results on light meson properties

Micco¹

2010

Proceedings of European Physical Society Europhysics Conference on High Energy Physics — PoS(EPS-HEP 2009)

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for the KLOE collaboration † We present KLOE results on hadronic physics. We show results on the φ → a 0 (980)γ decay, with a 0 → ηπ 0 , which provides the a 0 (980) couplings to ηπ and K + K − and we discuss their relation with the a 0 structure; we also show the final measurement for the search of the φ → K 0K0 γ decay, which proceeds through f 0 (980)/a 0 (980) γ. Results for the upper limit on the branching ratio are presented with the full KLOE statistics, which allow to test most of the available theoretical models. Here we update our measurement of the gluonium content of the η that indicated a 3 σ 's evidence. Other SU(3) relations were added in the fit, further allowing the extraction of other parameters, such as the vector mixing angle and the SU(3) breaking parameter. Finally we show final results for the BR of the η → π + π − e + e − decay, for the CP violating asymmetry in the angular distribution between the π + π − and the e + e − decay planes in the η rest frame, whose observation could test unexpected mechanism of CP violation, thus providing an hint of new physics beyond the Standard Model. The upper limit on the strength of the new interaction is also evaluated. [8] for references), the KLOE allowed region has been computed using the a 0 , f 0 parameters measured by KLOE.

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THE CP-VIOLATING ASYMMETRY IN η → π⁺ π^-e⁺e^-

Cited by 43 publications

References 29 publications

Studyingη-Meson Decays with WASA-at-COSY

Studyingη-Meson Decays with WASA-at-COSY

KLOE Results on Hadron Physics and Perspectives for KLOE-2

KLOE results on light meson properties

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