HADES experiments investigating in- medium hadron properties P. Salabura Jagiellonian University for the HADES collaboration

Study of hadron properties in dense and hot nuclear matter Rear Probes: dielectrons penetrating probes  emissivity and in medium hadron masses : vector mesons (  /  e+e-)  chiral sym. strangeness production : , K  ,  (1321) EOS, K in-medium potentials, … Strategy: Reference measurements in N +N and A+A at 1-2 AGeV (<2015) and in future at SIS AGeV (FAIR) Goal: to cover interesting and not fully covered region of baryonic matter at low T „emissivity” of compressed matter hadron properties in matter e+ e- K+K+ K-K-  experiment: chemical freeze-out RHIC BES Na61 CBM Fair HADES FAIR L. McLerran, R.D. Pisarski 2007

Side View START FW High Acceptance Di-Electron Spectrometer  Beams from SIS18: protons, nuclei, pions  Spectrometer with high invariant mass resolution - 2% at  /   Versatile detector for rear probes : dielectrons (e+,e-) strangeness: , K ,0,  -  Upgrade(2010): new DAQ (  20 KHz, Tof- RPC (  tof ~80 ps) Geometry Full azimuth, polar angles 18  - 85  e+e- pair acceptance  0.35 ~ channels, segmented solid or LH 2 targets 1 m RPC (from 2010)

HADES programme (so far) HADES programme (so far) pp reactions (1.25, 2.2, 3.5 GeV) dp reactions (1.25 GeV) nucleus + nucleus C+C, Ar+KCl Au+Au (2012) p + nucleus 3.5 GeV) e+e- production in N+N – reference reactions for A+A single and double  production (barion resonances in N+N) , ,  production- hadr.channels and rear  e+e- decays (new UL in PDG)  (1405),  (1385) (new PDG entry) K 0 production low mas e+e- „excess” : (DLS puzzle, emissivity,..) kaon production : K 0 s Hyperon production; , ,  (1321)  production  -p, p-p, , correlations  /  mesons in cold nuclear matter strangeness production K, 

Low mass e+e- excess : „DLS puzzle” DLS data: R.J. Porter et al.: PRL. 79 (1997) 1229 Calculation: E.L.Bratkovskaya et al. PLB445 (1999) 265 before HADES (< 2008)HADES data projected in DLS acceptance HADES data: Agakishiev et al., PLB 663 (2008) 43  HADES fully confirms DLS results What about „excess” ? Is it true in-medium effect ? or not understood elementary process?

N+N reference (I): e+e- in p+p N+N reference (I): e+e- in p+p Important source:  pe+e- Dalitz decay Time Like (q 2 >0)  ( J=3/2 ) ->N ( J=1/2 )  * transition: Calculations: Vector Meson Dominance Krivoruchenko et al. PRD 65 (2001) G. Ramalho and T. Pena arxiv: v1 (2012) F. Dohrmann et al., Eur. Phys. J. A 45, 401 (2010) G(q 2 ) ? el. Transition Form Factors : extented baryon structure ! complemenary to  (space like) N   ( data: JLAB/Mainz/Bates) HADES: PLB690 (2010)118 q q q e-e- e+e+ pion cloud e+ e- G M (q 2 ) VMD ++ p e+e+ ** p p p  e+e-   pe+e-

N+N reference (II): e+e- in n+p N+N reference (II): e+e- in n+p calculations: R. Shyam and U. Mosel Phys. Rev. C 82:062201, 2010 data: HADES  production – fixed by COSY, WASA data bremsstrahlung pn  pne+e- (non resonant), why it is so much different from pp? R. Shyam and U. Mosel Phys. Rev. C 82:062201, 2010 charge pion exchange & pion eFormFactor ~2   DLS Large isospin effect at 1-2 AGeV! p n n p ++ for example: e+e- yield ratio dp/pp

CC compared to NN reference. CC compared to NN reference.  NN and C+C normalized to the individual N(  0 )  C+C data (1 and 2 AGeV !) reproduced (within 20%) by superposition of NN interactions (reference) – no room (within error bars) for in-medium effects data: HADES PLB690 (2010)118  contribution subtracted PRL98(2007) ratio CC/NN cocktail: „long lived sources”-freeze out baryons

Vector mesons in medium- motivation    p - beams SIS 18 SIS 200 T [MeV] 300 LHC RHIC SPS G.E. Brown / M. Rho: Scaling of masses with  -condensate ( PRL 1989, 1991 ) T. Hatsuda / S. Lee: QCD sum rules PRC46(1992)R34 how it begun..  second graph is related to elementary process: hadronic many body interactions- spectral functions..  - meson at 2 x  N S. Leupold et al. NPA 741 (2004) 81, NPA 780 (2006) 187 Dalitz decay prefered by data Data : Na60 EPJC 59 (2009) 607 calculations: Hess/Rapp: NPA806(2008)339.

Vector mesons in cold matter- experiments    217 MeV CLAS PRL 99 (2007) direct :  meson line shape no mass shift  broadenning  mass shift m * /m 0 = 1 – 0.09  N /  0 KEK-E325 PRL 96 (2006) CLAS: PRL 105 (2010) CBTAPS: PRL 100 (2008)  absorption indirect: transparency  large  absorption   * tot,   210 MeV !   meson (SPRING8, ANKE)   * ~ MeV   *  N v   VN  +A GeV p+Cu 12 GeV

p+p vs 3.5 GeV p+p vs 3.5 GeV large acceptance at small M e+e- and p (<1 GeV/c) ( first measurement at low p !) p+p cockail : based on known sources fixed to data  0 /  /  / ,  with constant eTFF underestimeted e+e- yield below VM pole  missing component? -> higher resonances ( , N * ) pp data scaled by „A part ” scaling „fast” p e+e- >0.8 GeV/c„fast” p e+e- < 0.8 GeV/c Nuclear modification factor data: arXiv: submitted to PRL

Fixing resonance contribution : exclusive channels in 3.5 GeV pn  + pp  0 ppe+ e- Preliminary …many differential distribution studied for pp  0, pn  +, pp , pp  R  Ne+e- constant eTFF M. Zetenyi et. al. Heavy Ion Phys. 17 (2003) 27 no off shell coupling to VM assumed  lower limit for e+e- emission   /  from data (hadronic dec.) missing yield related to low mass resonances and off shell VM !

e+e- excess in p+Nb e+e- excess in p+Nb „excess over pp reference”„slow” (p<0.8 GeV/c) pairs  clear excess in p+A below VM pole  - secondary reactions :  +N   (1720,..)(N * (1520),..)  N  Ne+e- ? el. TFF important !  constraint from ppe+e- …… work in progress - in medium  modification ? answer only after understanding of the p+p reference  R pA (vs p) – increase at small momenta : largest for the „  -region” BUT NOT for  peak  strong  absorption consistent with CBTAPS (  +A) results! R pa vs momentum M e+e

e+e- pairs from Cocktail with „freeze-out” comp.  first  ->e+e- observation at SIS18 energies  first evidence for „true” excess  Excess yield scales with system size ~ A part 1.4  multistep processes?  component subtracted data PRC84(2001)014902

15 Transport model results for Ar+KCl Transport models: not consistent picture  don’t describe (yet) pn data  „excess” region dominated by  but different predictions !  M e+e- >0.60  dominates complicated vacumm structure !  Are in-medium effects needed? Not clear yet… systematic studies needed new Au +Au data are essential! E.L. Bratkovskaya, W. Cassing, NPA 807 (2008) 214 GiBUU: J. Weil at al., arXiv: v1

 and  /  ratio in Ar + KCl   meson plays important role (~18%) in K - production at SIS18 energies Statistical model describe  rates with no suppression (i.e OZI rules) !  R  /  A+A : enhanced  production and  absorption?   K + K -   e + e - R  /  A+A >> R  /  in NN and πN reactions w.r.t N-N threshold

Double strange  - (1321) in Ar+KCl P.Salabura 640 MeV below NN threshold ! data: PRL 103 (2009) data: EPJA 47 (2011) 21 SHM: S. Wheaton, J. Cleymans, Comp. Phys. Comm. 180 (2009) 84   production significantly larger then transport model (UrQMD) and statistical model predictions  Note that also  is enhanced and  is not suppressed at all  all have ss(bar) content !..to be continued with Ag+Ag

Kaons in nuclear matter G.E Brown et.al NPA 567 (1994) 937, T. Waas, e al. PLB 379 (1996) 34 J. Schaffner-Bielich, et al.. NPA 625 (1997),.. indirect measurements : K+/K 0 considered as good quasiparticle at SIS K+  5 fm (weak absorption) repulsion from spectator matter : flow out of plane ( KAOS data PRL.95 (2005) ,FOPI-> Y. Leifels talks this afternoon ) reduced yield at low p t (p): ( FOPI, ANKE data PRL102(2009)183591) Acta Phys. Hung. A  (1405) K-K- K-K- N -1 K - in medium: more complicated  spectral function  (1405) physics : entry to K - in medium properties, kaonic clusters ppK -.., kaonic atoms,..

K 0 s in medium potential and  (1405) K 0 s in GeV data: PRC 82 (2010) IQMD : repulsive U KN  38 MeV  (1405) –bound K - N system?  (1405) pole pole shift? intereference with non. res  ? importnat bench mark for theory Preliminary new data will come from p+A..and Au+Au (+ flow measurement)

Au+Au run (finished 3 weeks ago) at 1.23 AGeV Thank to essential HADES upgrade (DAQ,MDC,RPC_TOF)  Ready for campaigns at FAIR SIS100! on line PID vertex reconstruction

Summary:  Low mass pair production in light systems (C+C) explained by known  0  cross sections and baryonic sources fixed from the NN reference reactions: pn- bremsstrahlung +  Dalitz are the essential e+ e- sources explaining „DLS” puzzle  OBE models come closer to pp/pn data : further studies are on-going  for larger systems, Ar+KCl, evidence for onset of pair excess over NN reference : radiation from „resonance ( , N * ) matter”: New Au+Au data are of key importance !  in-medium effects on  (A+A and p+A) are not clear yet : determination of  -meson shape in N-N collisions (vacumm) is far from trivial and requires better understanding of  /N * -  couplings  el.Transition Form Factors, work is in progress  absorption of  and enhanced  production in nuclear matter can be explain large R  /   new K 0 S data support repulsive KN in-medium potential ;  (1405) is crucial for antykaon properties in nuclear matter  Large production yields (above SHM predictions) of double strange  (1321)

Outlook: HI collisions (Au+Au/Ag+Ag) at SIS18 with upgraded HADES continuation of dielectrons + strangeness programme (also K +,K -, e+e-, flow measurements) > in discussion: pion beams : el.TFF of baryon resonances, pion, strangeness production > HADES at FAIR (SIS100) - zero day experiment- part of CBM physics programme HADES CBM stay tuned: lot of new interesting results are expected !

P.Salabura23 The Collaboration GSI SIS  Cracow (Univ.), Poland  Darmstadt (GSI), Germany  Dresden (FZD), Germany  Dubna (JINR), Russia  Frankfurt (Univ.), Germany  Giessen (Univ.), Germany  München (TUM), Germany  Moscow (ITEP,RAS), Russia  Nicosia (Univ.), Cyprus  Orsay (IPN), France  Rez (CAS, NPI), Czech Rep.  Sant. de Compostela (Univ.), Spain  LIP, Portugal

Gross properties of the baryonic matter 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 ( , N * ) matter” Sub-threshold production of ( , , K - K+,  ) : confined to high density zone Multi-step processes ~ Apart  >1 S.Vogel et al. (URQMD) arXiv: v2 Rapp & Wambach Adv. Nucl. Phys. 25 (2000) N+N->N ,  +N  N +N +  ex:  production SIS AGS SPS  K+K+ K-K- // P  /  e+e-  !

Upcoming experiments : Au+Au and Ag+Ag ( ) simulation: 4 weeks of beam (no in-medium effects included) ½(pp+pn) maximum excess (intermdediate mass) High statistics differential studies of excess centrality, dN/dm t, angular distributions countscounts Ag+Ag : maximal density  VM (  /  ) production rate at SIS18 High stat. spectroscopy of VM region Strangeness programme

Resonance reconstruction strangeness  ->  +  - Ar AGeV: excellent rec. capabilities  ->p+  - K 0 s ->  + +  -  ->K + + K - GeV/c 2 first observation at SIS