0000000000315853
AUTHOR
Eryk Czerwiński
Observation of the rare η→e+e−e+e− decay with the KLOE experiment
Abstract We report the first observation of the rare η → e + e − e + e − ( γ ) decay based on 1.7 fb − 1 collected by the KLOE experiment at the DAΦNE ϕ-factory. The selection of the e + e − e + e − final state is fully inclusive of radiation. We have identified 362 ± 29 events resulting in a branching ratio of ( 2.4 ± 0.2 stat + bckg ± 0.1 syst ) × 10 − 5 .
Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy
We present new data for angular distributions and on the cross section ratio of the p + d -> 3He + eta reaction at excess energies of Q = 48.8 MeV and Q = 59.8 MeV. The data have been obtained at the WASA-at-COSY experiment (Forschungszentrum J\"ulich) using a proton beam and a deuterium pellet target. While the shape of obtained angular distributions show only a slow variation with the energy, the new results indicate a distinct and unexpected total cross section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the variation of the production mechanism within this energy interval.
Spin dependence of {\eta} meson production in proton-proton collisions close to threshold
Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high degree of the polarized proton beam of COSY, the reaction pp{\to} pp{\eta} has been measured close to threshold to explore the analyzing power Ay. The angular distribution of Ay is determined with the precision improved by more than one order of magnitude with respect to previous results allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q = 15 MeV signaling s wave production with no evidence for higher partial waves. At Q = 72 MeV the data reveals strong interference of P s and P p partial waves …
Physics with the KLOE-2 experiment at the upgraded DAFNE
Investigation at a $\phi$--factory can shed light on several debated issues in particle physics. We discuss: i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled kaon states, iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and eta/eta$^\prime$ mesons, iv) the contribution to understand the nature of light scalar mesons, and v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We…
Determination of theη′-Proton Scattering Length in Free Space
Taking advantage of both the high mass resolution of the COSY-11 detector and the high energy resolution of the low-emittance proton beam of the cooler synchrotron COSY, we determine the excitation function for the $pp\ensuremath{\rightarrow}pp{\ensuremath{\eta}}^{\ensuremath{'}}$ reaction close to threshold. Combining these data with previous results, we extract the scattering length for the ${\ensuremath{\eta}}^{\ensuremath{'}}$-proton potential in free space to be $\mathrm{Re}({a}_{p{\ensuremath{\eta}}^{\ensuremath{'}}})=0\ifmmode\pm\else\textpm\fi{}0.43\text{ }\text{ }\mathrm{fm}$ and $\mathrm{Im}({a}_{p{\ensuremath{\eta}}^{\ensuremath{'}}})={0.37}_{\ensuremath{-}0.16}^{+0.40}\text{ }\t…
A new limit on the CP violating decay KS→3π0 with the KLOE experiment
We have carried out a new direct search for the CP violating decay K-S -> 3 pi(0) with 1.7 fb(-1) of e(+)e(-) collisions collected by the KLOE detector at the Phi-factory DA Phi NE. We have searched for this decay in a sample of about 5.9 x 10(8) KSKL events tagging the K-S by means of the K-L interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake K-S tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of …