Exploring time like tranistions in pp, πp and AA reactions with HADES

S Maurus,J Adamczewski-Musch,I Fröhlich,S Harabasz,P Zumbruch,L Lopes,S Spies,B Kardan,R Greifenhagen,W Esmail,L Ritman,L Naumann,R Holzmann,J Dreyer,V Pechenov,P Salabura,A Lebedev,I Kres,A Blanco,J Stumm,F Seck,M Traxler,A Rost,M Böhmer,O Golosov,T Matulewicz,T Galatyuk,J Friese,N Rathod,G Kornakov,A Ivashkin,L Chlad,H Ströbele,R Lalik,J Kuboś,F Kornas,A Belounnas,C Höhne,M Gumberidze,P Fonte,F Scozzi,C Müntz,V Metag,D Dittert,B Ramstein,V Wagner,P Wintz,A Kozela,J Markert,C Ungethüm,O Petukhov,S Fateev,A Prozorov,K Pysz,I Shabanov,J Förtsch,S Linev,O Pechenova,B Arnoldi-Meadows,J Pietraszko,C Wendisch,O Vazquez-Doce,A Malige,J Michel,R Hensch,P Kulesa,O Svoboda,I Ciepał,Michael Dürr ,L Fabbietti,A.A Weber,С И Борисенко ,A Reshetin,R Gernhäuser,M G Wiebusch ,А Куглер ,M Golubeva,W Koenig,S Lebedev,S V Morozov ,P Rodríguez-Ramos ,I Köenig ,T Mahmoud,W Przygoda,J Wirth,Vikas Patel ,J.-H Otto ,M Szala,C Blume,I Selyuzhenkov,Krzysztof Piasecki ,J Smyrski,R Kötte ,Christian Pauly ,A Belyaev,V P Ladygin ,P Tlustý ,G I Lykasov ,A Zhilin,A Ierusalimov,F Guber,M Lorenz,K.h Kampert ,U Singh ,B Kämpfer,P Chudoba ,K Nowakowski,D Pfeifer,J Stroth,Holger Huck

doi:10.1051/epjconf/202024101013

Abstract

Radiative transition of an excited baryon to a nucleon with emission of a virtual massive photon converting to dielectron pair (Dalitz decays) provides important information about baryon-photon coupling at low q2 in timelike region. A prominent enhancement in the respective electromagnetic transition Form Factors (etFF) at q2 near vector mesons ρ/ω poles has been predicted by various calculations reflecting strong baryon-vector meson couplings. The understanding of these couplings is also of primary importance for the interpretation of the emissivity of QCD matter studied in heavy ion collisions via dilepton emission. Dedicated measurements of baryon Dalitz decays in proton-proton and pion-proton scattering with HADES detector at GSI/FAIR are presented and discussed. The relevance of these studies for the interpretation of results obtained from heavy ion reactions is elucidated on the example of the HADES results.

Highlights

QCD describes nucleons as colorless states of three nearly massless quarks confined to a small volume due to the strong force
The order parameter of the chiral symmetry breaking is the non vanishing expectation value of the quark-anti quark condensate related to the pion decay constant by the Gell-Mann-Oaknes-Renner relation
Lattice calculations performed in the limit of vanishing baryo-chemical potential predict a crossover phase transition from the hadron gas to the quark-gluon plasma at a pseudo-critical temperature Tc 155MeV [2],[3] which is accompanied by the chiral symmetry restoration

Summary

Introduction

QCD describes nucleons as colorless states of three nearly massless quarks confined to a small volume due to the strong force. The hadronic models do not include explicitly quantities characterizing QCD vacuum properties like quark or gluon condensates but the connection between the splitting of spectral functions of the chiral partners ρ − a1 and the quark condensate and the pion decay constant is provided, as for example by the Weinberg sum rules [10]. Using the results of the hadronic models for the ρ meson in-medium spectral function and lattice results on the quark condensate evolution as a function of the temperature merging of the two spectral function has been demonstrated at T = Tc and vanishing μb [11] This signals the behaviour expected for the chiral symmetry restoration. These decays are being investigated, for the first time, by HADES by studies of exclusive dielectron channels in proton and pion induced reactions, as described in this contribution

Baryon transition form-factors

HADES experiment

Radiation from N-N collsions

Pion beams in HADES

Summary and outlook