Resonance production at SPS energies: CERES and NA49

O Busch

doi:10.1051/epjconf/20123600005

Abstract

We present results on resonance production by the NA49 and CERES col- laborations. The measurement of the differential yields and spectral distributions of the K ∗ (892), Δ(1232), ρ, φ and Λ(1520) resonances from their leptonic and hadronic decay channels at different C.M.S. energies and for various colliding systems allows us to study in-medium modifications of the resonance mass, width and yield and constrains the prop- erties of the hadronic phase. For K ∗ (892) 0 , a strong system size dependence of the yield relative to kaon production is found. The production of the Δ(1232) resonance is consis- tent with thermal model expectations. φ meson spectra and yields reconstructed in the leptonic and hadronic decay channels are in agreement. Low-mass dilepton spectra indi- cate significant regeneration of the ρ meson and a strong modification of the ρ spectral function.

Highlights

Lattice QCD calculations predict a transition from confined hadronic matter to a chirally symmetric state of deconfined quarks and gluons at an energy density around 0.7 GeV/fm3 [1] and a transition temperature of about 150-170 MeV [2]
We present results on resonance production by the NA49 and CERES collaborations
An analysis of the apparent yield relative to the expectation at chemical freeze-out constrains the properties of the hadronic phase

Summary

Introduction

Lattice QCD calculations predict a transition from confined hadronic matter to a chirally symmetric state of deconfined quarks and gluons at an energy density around 0.7 GeV/fm3 [1] and a transition temperature of about 150-170 MeV [2]. The φ meson was reconstructed by CERES simultaneously in the hadronic and leptonic decay channel in Pb-Au collisions at 158 AGeV, and the NA49 collaboration has studied the beam energy dependence of φ production at SPS. The NA49 experimental apparatus [14] at CERN is based on a fixed-target hadron spectrometer using heavy-ion beams from SPS accelerator It consists of four large-volume time projection chambers (TPCs) for charged-particle tracking, two of which (VTPC) operate inside the magnetic field of two superconducting dipole magnets providing an excellent momentum measurement. In the momentum range covered by the measurement, no indication for resonance absorption or regeneration or rescattering is found

Low-mass electron-positron pairs from CERES

Summary and discussion

Methods