Deep sub-threshold K*(892)0 production in collisions of Ar + KCl at 1.76 A GeV

G Agakishiev,M Destefanis,P Zumbruch,P Salabura,E Morinière,D Kirschner,A Ivashkin,J L Boyard,H Ströbele,K Teilab,C Wendisch,R Holzmann,C Gilardi,J Wüstenfeld,T Hennino,A Tarantola,E Schwab,A Mangiarotti,B W Kolb,R Bassini,J Pietraszko,A Blanco,J Friese,W Kühn,I Fröhlich,V Pechenov,C Sturm,B Ramstein,L Naumann,J Markert,J A Garzón,V Metag,A Dybczak,S Spataro,T Christ,A Sadovsky,L Maier,T Galatyuk,V Wagner,P Huck,J Siebenson,A Rustamov,D Belver,I Iori,S Yurevich,B Michalska,E Castro,Y Parpottas,B Sailer,P Fonte,P Cabanelas,L Lopes,D González-Díaz,M Gumberidze,M Böhmer,M Traxler,H Tsertos,R Krücken,J Michel,J S Lange,O Pechenova,C Müntz,Yu G Sobolev,B Spruck,F Dohrmann,T Eberl,T Pérez Cavalcanti,K Lapidus,M Golubeva,T Liu,M Roy‐Stéphan ,T Karavicheva,Y Pachmayer ,M Pałka ,R Trębacz ,A Kurepin,А Куглер ,M Weber,S Lang,A Schmah,F Křížek ,A Reshetin,M Lorenz,R Kötte ,S Chernenko,Y Zanevsky ,P Tlustý ,Julio Pérez Díaz ,Manuel Heilmann ,Tomasz Wójcik ,W Przygoda,A Belyaev ,A Gil,D Mishra,P Finocchiaro,J Stroth,J Mousa,W Koenig,F Guber,M Wiśniowski ,I Köenig ,B Kämpfer,E Epple,T Heinz,J Otwinowski,A Bałanda ,R Gernhäuser,L Fabbietti,K Kanaki,O Fateev ,M Jurkovič

doi:10.1140/epja/i2013-13034-7

Abstract

Results on the deep sub-threshold production of the short-lived hadronic resonance K*(892)0 are reported for collisions of Ar + KCl at 1.76A GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The K*(892)0 production probability per central collision of \( P_{K^{*0}}=(4.4\pm 1.1 \pm 0.5)\times 10^{-4}\) and the K*(892)0/K0 ratio of \( P_{K^{*0}}/P_{K^0}=(1.9\pm 0.5\pm 0.3)\times 10^{-2}\) are determined at the lowest energy so far (i.e. deep below the threshold for the corresponding production in nucleon-nucleon collisions, \( \sqrt{s_{NN}}-\sqrt{s_{thr}}=-340\) MeV). The K*0/K0 ratio is compared with results of other experiments and with the predictions of the UrQMD transport approach and of the statistical hadronization model. The experimental K*0 yield and the K*0/K0 ratio are overestimated by the transport model by factors of about five and two, respectively. In a chemically equilibrated medium the ratio corresponds to a temperature of the thermalized system being systematically lower than the value determined by the yields of the stable and long-lived hadrons produced in Ar + KCl collisions. From the present measurement, we conclude that sub-threshold K* production either cannot be considered to proceed in a system being in thermal equilibrium or these short-lived resonances appear undersaturated, for example as a result of the rescattering of the decay particles in the ambient hadronic medium.

Highlights

The short-lived resonance K∗(892)0 can serve as a tool to study properties of the dense and hot nuclear matter produced in heavy-ion collisions
The experiment was performed with the High Acceptance Di-Electron Spectrometer (HADES) at the Schwerionensynchrotron SIS18 at GSI, Darmstadt
(This value includes the branching ratio of 2/3 for the decay K∗0 → K+π−.) The statistical error in (2) reflects the K∗0 yield left after the whole analysis of the simulation data, while the systematic error follows from the variation of the fireball temperature and the polar asymmetry in Pluto, similar to our previous studies of deep sub-threshold Ξ− production [21]

Summary

Introduction

The short-lived resonance K∗(892)0 (mass M = 896 MeV, decay width Γ = 50 MeV corresponding to a mean livetime τ = 4 fm/c [1]) can serve as a tool to study properties of the dense and hot nuclear matter produced in heavy-ion collisions. It has been conjectured [2] that the K∗ yields reconstructed from hadronic decay products are sensitive to the thermal history of the fireball.

The experiment

Analysis of experimental data

Analysis of simulation data

Findings

Discussion

Summary