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We report on a measurement of hard photons (Eg>30 MeV) in the reaction Ar+Ca at 180A MeV at an energy in which photons from the decay of pi0 mesons are dominating. Simultaneous measurement with the TAPS spectrometer of the photon spectrum and photon-photon coincidences used for the identification of pi0 enabled the subtraction of pi0 contribution. The resulting photon spectrum exhibits an exponential shape with an inverse slope of E0=(53+-0.03(stat)-5+8(syst)) MeV. The photon multiplicity, equal to (1.21+-0.03(stat)+0.3-0.2(syst))10E0-2, is roughly one order of magnitude larger than the value extrapolated from existing systematics. This enhancement of the hard photon production is attributed to a strong increase in the contribution of secondary np collisions to the total photon yield. We conclude that, on average, the number of np collisions which contribute to the hard photon production is 7 times larger than the number of first chance np collisions in the reaction Ar+Ca at 180A MeV.
Exclusive data on the reactions pp -> ppK+K- and pp -> pK+ Lambda/Sigma0 have been taken at the cooler synchrotron COSY close to threshold. At equal excess energies, an enhancement of the Lambda/Sigma0 ratio by one order of magnitude has been observe
We review hadron production in heavy ion collisions with emphasis on pion and kaon production at energies below 2 AGeV and on partonic collectivity at RHIC energies.
The ultra-relativistic heavy-ion programs at the Relativistic Heavy Ion Collider and the Large Hadron Collider have evolved into a phase of quantitative studies of Quantum Chromodynamics at very high temperatures. The charm and bottom hadron producti
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
This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the proton and nucleus structure at high energy to deconfine