A. Kupsc

Double-pionic fusion of nuclear systems and the "ABC" effect: approaching a puzzle by exclusive and kinematically complete measurements.

The ABC effect-a puzzling low-mass enhancement in the pipi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn-->dpi;{0}pi;{0} at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pipi)_{I=L=0} channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a DeltaDelta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.

The WASA Detector Facility at CELSIUS

The WASA 4 pi multidetector system, aimed at investigating light meson production in light ion collisions and eta meson rare decays at the CELSIUS storage ring in Uppsala is presented. A unique fea ...

Measurement of eta meson decays into lepton-antilepton pairs

A search for rare lepton decays of the η meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay η→e+e-e+e- events are reported with a background of 1.3±0.2 e ...

Higher partial waves in p p ---> p p eta near threshold

Abstract Exclusive measurements of the production of η -mesons in the pp → ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η -meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the η -meson and also of the final proton-proton pair, probably to be associated with D -waves in this system interfering with the dominant S -wave term. The sign of the η angular anisotropy suggests that ρ -exchange is important for this reaction.

Test of CPT and Lorentz symmetry in entangled neutral kaons with the KLOE experiment

Neutral kaon pairs produced in phi decays in anti-symmetric entangled state can be exploited to search for violation of CPT symmetry and Lorentz invariance. We present an analysis of the CP-violating process phi -> KSKL -> pi(+)pi(-)pi(+)pi(-) based on 1.7 fb(-1) of data collected by the KLOE experiment at the Frascati phi-factory DA Phi NE. The data are used to perform a Measurement of the CPT-violating parameters Delta a(mu) for neutral kaons in the context of the Standard Model Extension framework. The parameters measured in the reference frame of the fixed stars are: Delta a(0) = (-6.0 +/- 7.7(stat)+/- 3.1(syst)) X 10(-18) GeV, Delta a(x) = (0.9 +/- 1.5(stat)+/- 0.6(syst)) X 10(-18) GeV, Delta a(y) = (-2.0 +/- 1.5(stat)+/- 0.5(syst)) X 10(-18) GeV, Delta a(z) = (3.1 +/- 1.7(stat)+/- 0.5(syst)) X 10(-18) GeV. These are presently the most precise measurements in the quark sector of the Standard Model Extension

Measurement of the slope parameter for the eta ---> 3pi0 decay in the pp->pp eta reaction

The CELSIUS-WASA setup is used to measure the 3π0 decay of η mesons produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV. The efficiency-corrected Dalitz plot and density distributions for this decay are shown, together with a fit of the quadratic slope parameter α yielding α = −0.026 ± 0.010(stat) ± 0.010(syst). This value is compared to recent experimental results and theoretical predictions.

Measurement of the slope parameter for the η → 3π0 decay in the pp → ppη reaction

The CELSIUS-WASA setup is used to measure the 3π0 decay of η mesons produced in pp interactions with beam kinetic energies of 1.36 and 1.45 GeV. The efficiency-corrected Dalitz plot and density distributions for this decay are shown, together with a fit of the quadratic slope parameter α yielding α = −0.026 ± 0.010(stat) ± 0.010(syst). This value is compared to recent experimental results and theoretical predictions.

Spectator tagging in quasi-free proton–neutron interactions in deuterium using an internal cluster-jet target at a storage ring

Abstract Low-energy spectator protons (p s ) from quasi-free proton–neutron interactions on deuterium have been measured for the pd→dπ 0 p s and pd→pnπ 0 p s reactions at the CELSIUS storage ring of the The Svedberg Laboratory. The experiment used 320 MeV protons incident on a deuterium cluster-jet target. The spectator protons were detected inside the scattering chamber using a silicon detector system which is compatible with a high vacuum. The low target density allows the spectator proton emerge without undergoing significant secondary scattering. Its measurement is therefore a useful tag upon such reactions, allowing cross-sections for quasi-free reactions to be deduced at well-defined centre-of-mass energies. The comparison with the simulation for the pd→dπ 0 p s reaction shows that the energy dependence of the pn→dπ 0 cross-section can be extracted near the threshold. The method greatly improves the experimental resolution achievable in quasi-free p–n reaction studies.

Pionic D-wave effects in pp→ppπ0 near threshold

The angular distribution of neutral pions produced in the pp --> pp pi(0) reaction has been measured at a beam energy of 310 MeV. Significant deviations from isotropy are found, which increase f ...

Measurement of the φ→π0e+e- transition form factor with the KLOE detector

Abstract A measurement of the vector to pseudoscalar conversion decay ϕ → π 0 e + e − with the KLOE experiment is presented. A sample of ∼9500 signal events was selected from a data set of 1.7 fb −1 of e + e − collisions at s ∼ m ϕ collected at the DAΦNE e + e − collider. These events were used to perform the first measurement of the transition form factor | F ϕ π 0 ( q 2 ) | and a new measurement of the branching ratio of the decay: BR ( ϕ → π 0 e + e − ) = ( 1.35 ± 0.05 − 0.10 + 0.05 ) × 10 − 5 . The result improves significantly on previous measurements and is in agreement with theoretical predictions.