The ABC Effect in Double-Pionic Nuclear Fusion and a pn Resonance as its Possible Origin

The ABC effect -- a long-standing puzzle in double-pionic fusion -- has been reexamined by the first exclusive and kinematically complete measurements of solid statistics for the fusion reactions $pn \to d\pi^0\pi^0$, $pd \to ^3$He$\pi\pi$ and $dd \to ^4$He$\pi\pi$ using the WASA detector, first at CELSIUS and recently at COSY -- the latter with a statistics increased by another two orders of magnitude. In all cases we observe a huge low-mass enhancement in the $\pi\pi$-invariant mass accompanied by a pronounced $\Delta\Delta$ excitation. For the most basic fusion reaction, the $pn \to d\pi^0\pi^0$ reaction, we observe in addition a very pronounced resonance-like energy dependence in the total cross section with a maximum 90 MeV below the $\Delta\Delta$ mass and a width of only 50 MeV, which is five times smaller than expected from a conventional $t$-channel $\Delta\Delta$ excitation. This reveals the ABC effect to be the consequence of a s-channel resonance with the formfactor of this dibaryonic state being reflected in the low-mass enhancement of the $\pi\pi$-invariant mass. From the fusion reactions to $^3$He and $^4$He we learn that this resonance is robust enough to survive even in nuclei.Comment: conference proceedings PANIC 0

Anisotropy in the pion angular distribution of the reaction pp -> pp pi0 at 400 MeV

The reaction pp -> pp pi0 was studied with the WASA detector at the CELSIUS storage ring. The center of mass angular distribution of the pi0 was obtained by detection of the gamma decay products together with the two outgoing protons, and found to be anisotropic with a negative second derivative slope, in agreement with the theoretical predictions from a microscopic calculation.Comment: Revtex 4 style, 5 pages 7 figures, PACS numbers:13.60.Le, 13.75.Cs, 21.45.+v, 25.10.+

Exclusive Measurements of pp -> dpi+pi0: Double-Pionic Fusion without ABC Effect

Exclusive measurements of the reaction pp -> dpi+pi0 have been carried out at T_p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The isovector pi+pi0 channel exhibits no enhancement at low invariant pipi masses, i. e. no ABC effect. The differential distributions are in agreement with the conventional t-channel Delta-Delta excitation process, which also accounts for the observed energy dependence of the total cross section. This is an update of a previously published version -- see important note at the end of the article

Double-Pionic Fusion of Nuclear Systems and the ABCEffect -- Aproaching a Puzzle by Exclusive and Kinematically Complete Measurements

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

Polarisation of the omega meson in the pd-->3He+omega reaction at 1360 and 1450 MeV

The tensor polarisation of omega mesons produced in the pd-->3He+omega reaction has been studied at two energies near threshold. The 3He nuclei were detected in coincidence with the pi0pi+pi- or pi0gamma decay products of the omega. In contrast to the case of phi meson production, the omega mesons are found to be unpolarised. This brings into question the applicability of the Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low energy hadronic reactions.Comment: 11 pages, 4 figure

The Effects of Reputation and Ethics on Budgetary Slack

This experimental study tests the effects on budgetary slack of two potential controls for opportunistic self-interestóreputation and ethics. I manipulate the level of information asymmetry between the subordinate and the superior regarding productive capability and measure the subordinateís reputation and ethical concerns regarding budgetary slack. In this setting, I examine how information asymmetry affects reputation and ethical concerns, and test the effects of these concerns on budgetary slack. Consistent with prior findings, subordinates restrict the slack in their budgets to well below the maximum under a slackinducing pay scheme, even after five periods of experience. Budgetary slack is negatively associated with a measure of ethical responsibility from a pre-experiment personality questionnaire as well as reputation and ethical concerns expressed in an exit questionnaire. Subordinates express lower reputation concerns as information asymmetry regarding productive capability increases, thereby reducing the superiorís ability to monitor the slack in their budget. Ethical concerns, however, are not diminished with increases in information asymmetry. These results suggest that reputation is a socially mediated control, whereas ethics is an internally mediated control for opportunistic self-interest