Studying hadron properties in baryonic matter with HADES „Nuclear matter at High densities” Hirschegg Hirschegg P. Salabura Jagiellonian University/GSI for the HADES collaboration

P.Salabura Study of hadron properties in dense and hot nuclear matter Dense matterFreeze-out 1-2 AGeV HADES case: Probes: dielectrons penetrating probes-direct access to in medium hadron masses : vector mesons (  /  e+e-) strangeness production ( , K  , ) EOS(see C.Sturm talk), K-N potentials Strategy: Systematic spectroscopy in proton, pion and heavy ion induced reactions T C ~170 MeV BB SIS Nucleus temperature Quark Matter Hadron Resonance Gas Bevelac CERES, NA60 (SPS) T 940 MeV baryon chemical potential thermal freeze out chemical freeze out KEK,JLAB, TAPS PHENIX (RHIC) CBM/FAIR Goal: learn about properties of dense matter in collision zone new forms of matter ? properties of hadrons in matter e+ e- 1

Gross properties of the baryonic matter (from transport models) P.Salabura freeze-out Au+Au 1-2 AGeV : moderate densities but long system life time Baryonic matter:  /  N = 1-3, T< 80 MeV,  ~12-14 fm/c nucleons, baryonic resonances (~30%)  33 mesons(π 0 )~10% “resonance matter” abundances reach maximum at ~2-3  B long lived sources π 0 /  decay outside fireball short lived resonances  /  (c  1.3 fm/c) – absorption (N  NN or N  Nπ)! dielectron emission over full history of coll…. „ALL – freeze-out”= in-medium Sub-threshold production of heavy mesons : Multi-step processes (K - ), Resonance decays ,N *  N  /  for dielectrons x BR ~10 -4 ! S.Vogel et al. (URQMD) arXiv: v2 E.Bratkovskaya W. Cassing (HSD) 2

Pair excess in URHIC collisions P.Salabura D. Adamova, et al., subm. to PLB, nucl-ex/ large pair excess over yield from the “freeze-out” Main source (not for RHIC !) π + π -  e+e-(  +  - ) in-medium  spectral functions What about baryon rich matter? (pion densities 5-6 lower as compared to SPS!)  s NN= 17.4 GeV submitted to Phys. Lett.B arXiv:

P.Salabura Pair excess at low energies? Pair excess at low energies? low mass (0.14<M ee < 0.6 GeV/c 2 ) pair 1AGeV ("DLS" puzzle") Calculation: E.L.Bratkovskaya et al. Phys. Lett. B445 (1999) 265 Calculation: Ernst et al. Phys. Rev. C58 (1998) AGeV Calculation: C. Fuchs et al. Phys. Rev. C68 (2003) DLS Data: R.J. Porter et al.: Phys.Rev.Lett. 79 (1997) 1229 Status before HADES era: no explanation for pair excess in light and medium HI systems! 4

Side View START FW 5 High Acceptance Di-Electron Spectrometer  Beams from SIS18: pions, protons, nuclei  Spectrometer with high invariant mass resolution (2% at  /  mass) and powerful PID capabilities : p/π/K/e   Versatile detector for rear particle decays : dielectrons (e+,e-) strangeness: , K ,0,  Geometry Full azimuth, polar angles 18  - 85  e+e- pair acceptance  0.35 ~ channels, segmented solid or LH 2 targets 1 m P.Salabura

6 Experimental campaigns p+p 1.25 GeV (2006) 2.2 GeV (2002) 3.5 GeV (2007) d+p C+C 2.0 AGeV (2002) 1.0 AGeV (2004) 1.25 GeV (2007) Ar+KCl 1.75 GeV (2005) p+Nb 3.5 GeV (2008) p+p „ Anomalous” excess of e+e- pairs in 0.15 < M ee < 0.5 GeV/c 2 NN-Bremsstrahlung and  Dalitz decays vector mesons  /  in-medium p+p Resonance ( ,N * ) production Form-factors and studies of  /  Dalitz decays (helicity angles) Strangeness: , K ±,0,  production in HI P.Salabura

N+NN+N      e+e+ e-e- e+e+ e-e-  e+e+ e-e- e+e+ e-e- 7  Cocktail A („background”) “long-lived sources at freeze-out”  π 0 → e + e - , η → e + e -  Dalitz  ω → e + e - (direct), ω →e + e - π 0 (dalitz)  π 0 /  yield fixed by measurement(TAPS) Cocktail B: Cocktail A + Δ + ρ = “short-lived” resonances = “short-lived” resonances  Δ → e + e - N (Dalitz decay) – fixed to „freeze-out” abund. N(Δ) =3/2 N( π 0 ) – fixed to „freeze-out” abund.  ρ → e + e - (direct) Definition of „pair excess” cocktail: thermal source PLUTO event generator I. Froehlich et al. I. Froehlich et al.,arXiv: Excess – pair yield above A -> medium AND first chance coll. -> medium AND first chance coll P.Salabura

P.Salabura Inclusive e+e- from C+C collisions Inclusive e+e- from C+C collisions A. Agakichiev Phys.Rev. Lett 98(2007) A. Agakichiev Phys. Lett. B 663 (2008) 43 NORMALIZATION: N  ± from the same data sample  (M ee )~9% at M ee ~0.8 GeV/c 2 syst. error (27%) syst. error (21%) 8

P.Salabura Beam energy dependence of the excess enhancement scales like pions ! enhancement scales like pions ! Baryon resonance decays? N-N bremsstrahlung? Baryon resonance decays? N-N bremsstrahlung? 0.3(  sys) F(2.0) = 1.9 ± 0.2(stat) ± 0.3(sys) ± 0.3(  sys) 2.0(  sys) F(1.0) = 6.8 ± 0.6(stat) ± 1.3(sys) ± 2.0(  sys) TAPS TAPS collab. Z.Phys. A 359 (1997) 65 Phys.Rev. C 56 (1997) R2920 9

P.Salabura N-N Bremsstrahlung E.L. Bratkovskaya and W. Cassing arXiv: v1 NN ("quasielastic")-non resonant Strong + electromagnetic process (OBE models) 1 2 e+ e- + = resonant -baryon resonances (  ) collection of results from E.L Bratkovskaya & W. Cassing: Nucl.Phys A 807, 214 (2008). bremsstrahlung OBE calculations: Kaptari & Kämpfer, NPA 764 (2006) 338:  K&K OBE calculation: pn bremsstrahlung 4 larger (simplified picture!) 10

P.Salabura Comparison with up-to-date HSD M [GeV/c²] HSD: E.L. Bratkovskaya and W. Cassing Nucl.Phys A 807, 214 (2008). New treatment of Bremsstrahlung: L.P. Kaptari and B. Kämpfer, Nucl.Phys. A 764 (2006) 338 DLS Data: R.J. Porter et al. Phys.Rev.Lett. 79 (1997) 1229 M [GeV/c²] Does Δ and Bremsstrahlung explain excess?  verification in NN collisions is needed 11

Reference reaction: dielectrons from pp and “quasi-free” 1.25 AGeV P.Salabura Model Calculations: a) NN-bremsstrahlung Kaptari & Kämpfer (K&K) b) ,  yield constraint by data.  Dalitz decay Krivoruchenko et al. Phys. Rev. D 65 (2001) VMD form-factor (Q. Wan and F. Iachello, Int. J. Mod. Phys. A 20 (2005) 1846) pn data are not described by calculations ! 12

13 1 AGeV – pp & 1.25 GeV Dielectron spectrum from C+C given as superposition of NN collisions ! no indications for in-medium effects ! (at least for C+C ) What about larger systems ? spectra normalized to  0 yield in C+C and NN Absolute scale: 1 AGeV /A part = ± (A)GeV /A part  but for 1.00 (A)GeV /A part  P.Salabura

AGeV 1.75 AGeV 15 centrality : LVL1 = 3.5 fm Number of participating nucl.  38.5 ±4 Thermal source model Transport (HSD) N  =3/2 N  0 for  propagation in matter accounted estimate of  at freeze-out (much larger yield)  m T scaling NN bremsstrahlung : not important at this energy PRELIMINARY E.L. Bratkovskaya and W. Cassing Nucl.Phys A 807, 214 (2008) P.Salabura

Excess vs beam energy and system size 15 Excess scales with (A part ) ,  >1 (~2) multistep processes? NN->N ,  ->N ,  N->  Resonance radiation is the dominant source of e+e- yield! PRELIMINARY A part dependence need more studies : 1 AGeV vs 1AGeV (2010) 1.93 AGeV – dilepton mass dependence inclusive meson production (TAPS data) (min. bias) e+e- pair excess HADES DLS ArkCl = 19 vs. CC = P.Salabura

P.Salabura Vector mesons in medium 16

Vector mesons in medium P.Salabura Na60: R. Arnaldi et al., PRL 96 (2006) calculations: H. van Heesand R. Rapp, PRL 99 (2006) , R. Rapp, J. WambachEPJA 6 (1999) 415 CERES D. Adamova et al. nucl-ex/ SPS energies :  broadening due to interactions with hadronic medium (baryons are more important !) What is the situation at lower energies? No unique evidence for in medium modifications from p+A or  +A reactions (CLAS/KEK/CBTAPS) 17

Vector mesons  /  at SIS p+p at 3.5 GeV PRELIMINARY    Ar+ 38 KCl 1.75 AGeVp+ 92 Nb 3.5 GeV  “on-line spectrum!” Data are available! No quick answer to the question on in-medium  /  spectral function ! Only comprehensive analysis (in progress) of the pp/p+A/and A+A can give full picture resonance contribution?

What is K-N potential ? P.Salabura K + potential seems to be slightly repulsive -> confirmed also by K 0 pt distributions) Precise data on K - /K 0 flow can be provided by FOPI, HADES (2009,2010) 18

K - Production at SIS energies K - Production in HI reactions Similar scaling of K + and K - Mesons as a function of A part  correlated production via strangeness-exchange or Strangeness Exchange? belived to be dominant (KAOS data) non-resonant resonant (  ->K + K - ) important to clarify for prediction of in-medium effects on K ± production ( rates, flow phenomena) sub-threshold in NN (E threshold  2.6 GeV) ! secondary reactions (in-medium) B.Kampfer et. al Phys. G: Nucl. Part. Phys. 28 (2002) 2133–2136, P.Salabura

K + K -,  differential production rates P.Salabura for the first time measured in the same (large) acceptance  /K - =0.34  0.13 ~17% K - comes from  ! … but there is also non-resonant part! M  =1017,8 ± 0.9 MeV/c 2  = 6.2 MeV/c 2 20

K-/  ratio P.Salabura Statistical model K. Redlich, H. Oeschler-priv.comm For NN at threshold  /K - = 1.02±0.1 ANKE coll. PHYS. REV. C 77, (2008)  /K - in Ar+KCl is ~ 3 smaller -> more K - thanks to medium (i.e strangeness exchange ) … but reactions of the type NN->NN  and NN->NNK + K - (non-resonat) is important,too ! Agreement with Kaon systematics 21

P.Salabura 22 Outlook: future exp. Upgrade RPC, DAQ, MDC1, EM Calorimeter (for SIS100) 2008/9/10 Hades goes to FAIR ( 8 AGeV) > 2013 (SIS100) 2011  + N,  + A resonance ( , N * ) radiative decays, strangeness 2010 Ni + Au+Au dielectrons (  /  ), strangeness (K - K +  ) SIS18 increase of Mul(  /  ) by 2 orders of magnitue !! CBM HADES

P.Salabura Outlook and summary: Radiation from nuclear matter at 1-2 AGeV : at low energy (  1 AGeV) first chance NN colisions are important source of pairs (pn- bremsstrahlung? strong isospin effect pp vs pn!) small systems (i.e C+C) can be described by superposition of NN collisions for larger systems (i.e Ar+KCl) and larger energies strong contribution from „resonance matter”” (  ) visible with non-linear A part dependence In medium masses strong (broadenning) modification of  meson spectral function at SPS energies vector mesons observed for a first time at SIS/Bevalac energy regime  /  region measured with good precision – possibility to search for in-medium modifications of v.m. spectral functions K - in medium mass accessible only via indirect observables (flow,rates)- reaction mechanism must be known accurately (strangeness exchange) Outlook > HI collisions (Au+Au/Ni+Ni) at SIS18 and pion physics > HADES at FAIR Conference

P.Salabura26 The Collaboration GSI SIS  Catania (INFN - LNS), Italy  Cracow (Univ.), Poland  Darmstadt (GSI), Germany  Dresden (FZD), Germany  Dubna (JINR), Russia  Frankfurt (Univ.), Germany  Giessen (Univ.), Germany  Milano (INFN, Univ.), Italy  München (TUM), Germany  Moscow (ITEP,MEPhI,RAS), Russia  Nicosia (Univ.), Cyprus  Orsay (IPN), France  Rez (CAS, NPI), Czech Rep.  Sant. de Compostela (Univ.), Spain  Valencia (Univ.), Spain  Coimbra (Univ.), LIP, Portugal

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