The Experimental Quest for In-Medium Effects Romain Holzmann GSI Helmholtzzentrum für Schwerionenphysik, Darmstadt at 23 rd Indian-Summer School of Physics and 6 th HADES Summer School: FAIR October 3-7, 2011 in Rez/Prague, Czech Republic  Lecture I: Pedestrian’s approach  Lecture II: Experiments galore  Lecture III: HADES at GSI

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 2 Lecture III: Investigating dense matter with HADES at GSI: Present and future

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 3 Physics we are after with HADES (High Acceptance DiElectron Spectrometer) In very general terms: Medium modifications of hadrons (e.g. vector mesons)  chiral symmetry restoration vs. hadronic effects  enhanced dilepton yields → emissivity of hot & dense hadronic matter  in-medium spectral functions  systematic dilepton spectroscopy in AA, pA and  A (ρ/ρ 0  1-3)

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 4 S. Vogel et al. Phys. Rev. C78 (2008) GeV 30 Exploring the phase diagram at high μ B Probing nuclear matter at SIS:  densities:  max /  0   temperature: T  MeV  N resonances become important Andronic et al., Nucl. Phys. A 837 (2010) 65 Trajectories from Ivanov et al., PRC 73 (2006) HADES operates here! UrQMD Au+Au Rapp & Wambach Adv. Nucl. Phys. 25 (2000) thermal model at  =  0 System stays above ground state density for   fm/c

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 5 The situation at SIS  few GeV/u regime Probing nuclear matter at:  densities:  max /  0   temperature: T  MeV System stays above ground state density for   fm/c A regime of “Resonance Matter”:   densities ~10 lower than at SPS  matter dominated by baryons (resonances up to 30% !)   fireball  10 ·  resonance Composition of a hot  N gas vs. T: S. Vogel et al. Phys. Rev. C (2008) Evolution of average  B vs.  system : UrQMD Rapp & Wambach Adv. Nucl. Phys. 25 (2000)

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 6 Hadron production & spectroscopy  meson and baryon production  coupling of  and  to N*    pn vs.  pp  strangeness production  form factors of    and   systematic dilepton (and hadron) spectroscopy in pp, pn and  p (ρ/ρ 0 = 0) Physics we are after with HADES → needed to model p+A & A+A (High Acceptance DiElectron Spectrometer) In very general terms: Medium modifications of hadrons (e.g. vector mesons)  chiral symmetry restoration vs. hadronic effects  enhanced dilepton yields → emissivity of hot & dense hadronic matter  in-medium spectral functions  systematic dilepton spectroscopy in AA, pA and  A (ρ/ρ 0  1-3) π 0 & η prod. in p+p

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 7 Dilepton sources in HI collisions Reminder: Dileptons are emitted in all phases of the collisions… first chance collisions elementary N-N collisions e+ e-e+ e- e+ e-e+ e- e+ e-e+ e- hot and dense phase multistep production of resonances and mesons freeze –out decays of long-lived mesons:    R N N N N R R   N N N  e-e- e+e+ N      e+ e- e+ e-   

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 8 HADES convention ! About low and high masses… low high 0.55 Intermediate 0.15 – 0.55 GeV accessible at SIS18 High-energy convention !

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 9 ECT* Dileptons September 13-17, 2010 R. Holzmann, GSI Darmstadt 9 The HADES detector at GSI  azimuth. symmetry  large coverage: y =  hadron & lepton PID  2% mass resolution  LVL2 lepton trigger  plastic forward wall Physics accessible with HADES: 1.Dielectrons in NN: p+p and n+p 2.Dielectrons in HI: from C+C to Au+Au 3.Vector mesons in cold matter: p+Nb 4.Strangeness production: p+p, p+A, A+A 5.Pion-induced reactions: ( ) 6.SIS100: (>2017) / RPC Technical paper: G. Agakishiev et al. Eur. Phys. J. A41, 243 (2009) General documentation:

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 10 HADES at SIS18 Unilac SIS18 ESR HADES π production target

Measure its:  velocity β :  momentum p :  energy loss in matter dE/dx:  Cherenkov (or transition) radiation:  calorimetry ► total energy E This needs a sophisticated detector, e.g. HADES How to identify a particle?  p = m ∙ βc ►mass  B B A primer for theorists ►Z►Z ►e - vs. hadrons

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 12 Detector components “RICH” (electron ID, hadron-blind) “TOF” (  ) “Pre-Shower” (electron ID) “MDC” (tracking,  )

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 13 Spectrometer concept Geometry  Full azimuth, polar angles 18 o - 85 o  Pair acceptance  0.30 Fast particle identification  RICH CsI solid photo cathode, N o  80, C 4 F 10 radiator (γ>18)  TOF scintillator rods (for θ>45 o )  RPC (for θ<45 o )  Pre-Shower 18 pad chambers & lead converters Momentum measurement  superconducting toroidal magnet B  = 0.36 Tm  MDC multi-wire drift chamber, single-cell resolution  100  m 1 m RPC

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 14 Technical layout of HADES Pre-Shower TOF outer MDC RPC He pipe Start + target Cryostat beam outer MDC inner MDC B field region inner MDC RICH readout HADES cave HADES sector

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 15 The RICH: a hadron-blind detector hadron-blind, but...  e+e+ e-e- 00  ~ %  0 Dalitz  e+e+ e-e-  ~ % γ conversion ► use segmented target γ > 18

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 16 Segmented target Example: 3.5 GeV p+Nb  93 Nb material  12 pellets of Ø = 1.25 mm  Δz = 4.5 mm  2.8% interaction prob. ~ 55 mm beam

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 17 IPN Orsay FZR LHE Dubna GSI wire planes: 10 o,-20 o,0 o,0 o,20 o,-10 o ORSAY plane Tracking: the Multiwire Drift Chambers  4 MDC/sector  total 33 m 2 area, cells   y<0.1 mm resolution  Ar-iC 4 H 10 [60-40] gas and low-Z material

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 18 Tracking: superconducting toroidal magnet B max = 0.8 Tesla (mid-plane) bending power = 0.36 Tm (typically operated at 70% - 90% of max. field) field map + tracking planes Runge-Kutta track fit

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 19 Hit matching & track reconstruction 3 matching stages I II III magnetic field

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 20 Electron/positron identification e-e-e-e- e-e- e+e+ velocity vs. momentum ++ RICH pattern MDC hit finder & hit/track matching Pre-Shower condition Momentum * charge [MeV/C] Data Monte Carlo e-e- e+e+

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 21 Lepton pair reconstruction  RICH rings lepton/baryon p1p1 e+e+e+e+ e-e- p2p2 Pair reconstruction   00 e-e- e+e+ e-e- e+e+  00 e-e- e+e+ uncorrelated pairs Combinatorial background subtraction From:  like-sign pairs  or event mixing Signal: S + - = N e+e - - CB + -

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 22 HADES e + e - pair acceptance Opening angle > 9 o Accepted rapidity bin =

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 23 The HADES Collaboration on tour Cyprus: Department of Physics, University of Cyprus Czech Republic: Nuclear Physics Institute, Academy of Sciences of Czech Republic France: IPN (UMR 8608), Université Paris Sud Germany: GSI, Darmstadt FZ Dresden-Rossendorf IKF, Goethe-Universität Frankfurt II.PI, Justus Liebig Universität Giessen PD E12, Technische Universität München Italy: Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud Istituto Nazionale di Fisica Nucleare, Sezione di Milano Poland: Smoluchowski Institute of Physics, Jagiellonian University of Cracow Portugal: LIP-Laboratório de Instrumentação e Física Experimental de Partículas 17 institutions 120+ members Russia: INR, Russian Academy of Science Joint Institute of Nuclear Research ITEP Spain: Departamento de Física de Partículas, University of Santiago de Compostela Instituto de Física Corpuscular, Universidad de Valencia-CSIC

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 24 First HADES data: e + e - production in C+C Efficiency-corrected di-electron spectra, normalized to the number of neutral pions: Phys.Rev. Lett 98(2007) Phys. Lett. B 663 (2008) 43 Cocktail generated with PLUTO  Checking on DLS: Is there excess e+e- yield?  How does the excess evolve with bombarding energy?  And with system size? – or – Is there physics beyond free NN?

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 25 1 AGeV C+C: HADES confirms DLS π 0, η acceptance HADES >> DLS π 0 π 0 →e + e – γ Hades DLS DLS mid-rapidity η→e + e – γ Hades DLS DLS mid-rapidity vs. ► HADES fully confirms highly controversial DLS findings in C+C: Porter et al., PRL 79 (1997) 1229 Agakishiev et al., PLB 690 (2010) 118 HADES DLS

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 26 e + e - production in GeV/u Ar+KCl  Again, strong overshoot above the cocktail of long-lived sources!  First ω peak seen at SIS energies! ► M LVL1 (ω) = (6.5 ± 2.8) ·10 -3 Cocktail of long-lived sources: π 0, η, and ω ~ 40 counts ±20 % sys.

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 27 Tagging quasi-free np reactions in HADES p+p: Cut View FW  > 7 o d p sp p prpr OBE calculations reproduce pp, but not (yet) np ! d+p: quasi-free np

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 28 pp and quasi-free pn data vs. OBE models p+p data : Pluto simulation inspired by OBE (coherent sum of  and NN bremsstrahlung terms à la K&K [L.P. Kaptari, B. Kämpfer, NPA 764 (2006) 338] ) comes out too high, “Δ only” scenario fits the data. n+p data : Data cannot (yet) be described well by OBE calculations.   COSY/CESIUS  Efficiency corrected data, normalized to pp elastic events  data: H. Calén et al. PRC 58, 1998  e.m. FF: Wan & Iachello, Int. J. Mod. Phys. A20(2005) 1846 OBE = One Boson Exchange np >> pp

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 29 Comparing C+C data with N+N data C+C data reproduced (within 20%) by superposition of NN interactions Pair excess observed in C+C data has been traced back to enhanced pair production in n+p collisions No true medium effects observed in C+C !  Data on heavier systems needed! Comparison of C+C data to average of pp and np collisions: Normalized to N π

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 30 Preparing a “reference” for A+A Compare excess over η in Ar+KCl with excess over η in reference Definition of a ”reference” based on pp and np data: x  η contributions subtracted !  yield normalized to M(π 0 ) ►► Excess over free NN!

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 31 “Excess” vs. beam energy and system size  baryonic contrib. in Ar+KCl >> C+C  scales with E beam like π production  scales with A part stronger than linear  ≈ 1.4 e + e - continuum pairs : HADES (LVL1) DLS (min. bias) π 0 and η from TAPS (min. bias) R R  N N  N N N N  R e-e- e+e+ N N ► multistep processes! Yield/A part N+N TAPS

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 32 Transport model predictions for Ar+KCl Transport models do  fine for M ee < 0.6 GeV  overshoot ω/ρ peak  Are in-medium effects needed? Not clear yet… vacuum calculationvacuum vs. in-medium HSD model (status 2008) E.L. Bratkovskaya, W. Cassing, Nucl.Phys.A 807 (2008) UrQMD model K. Schmidt et al. arXiv 0811:4073v2

Excess dilepton yield in HIC SPS RHIC SIS Low-mass dilepton excess present at all energies, although quite different processes contribute… ► Excitation function of the dilepton yield still largely unknown: HADES & CBM will provide this information at FAIR.

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 34 Strangeness production in Ar+KCl HADES has  high mom resolution  high acceptance  good particle ID  vertexing 1.76 GeV/u Ar+KCl PID based on dE/dx and TOF  →K + K - Ξ - → Λπ - T B = 84 PRC 80 (2009) PRL 103 (2009) PRC 82 (2010) EPJA 44 (2010) etc.

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 35 Comparison with statistical hadronization models THERMUS statistical model T, μ B and R C fitted to HADES yields Vector meson yields (ω and  ) are described well by THERMUS. in particular from ω → e + e - ϕ → K + K - Ξ - → Λπ - Ξ - yield missed by > order of magnitude !

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 36 Kinetic vs. thermal freeze-out at AGeV π 0 and η from TAPS

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 37  ratio: OZI in Ar+KCl vs. N+N Using the HADES yields:   → K + K - : (2.6 ± 0.7) ·10 -4   → e + e - : (6.5 ± 2.8) ·10 -3 ► >> R  /  in NN and πN reactions ! In HI, production is subthreshold - yet, many more channels can and might contribute… >> OZI allowed

Kaon (K 0,+ ) in-medium potential Ar+KCl data vs. IQMD (SUBATECH Nantes) consistent with V 0 = 39 MeV at  =  0 extrapolation from high density to  0 (IQMD)  +A & p+A data (FOPI & ANKE) consistent with V 0 = 20  5 MeV at  =  0 extrapolation from low density to  0 (HSD) Needs further studies! e.g. flow…

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 39 ω in cold nuclear matter: p+Nb vs. p+p  Do p+p to have “in-vacuum” reference  Do p+Nb and compare with p+p  However, from photoproduction data, ω is seen to be broadened (x8-x16) in the medium ► use transparency ratio T A ! On-going analysis… N ee normalized to respective π yield Ratio p+Nb / p+p

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 40 The Hades upgrade project (2010/11) Meta detector,  < 45 deg. Time res: 350 ps. PreShower pos. res: 1.5 cm Limitation: multihit capability RPC performance (beam test) Efficiency above 95 % Time res ps Negligible crosstalk < 1% List of HADES upgrade subprojects: RPC - Resistive Plate Chamber FINISHED  Time res ps, high granularity Forward Wall FINISHED   range 0.2 – 7 degrees, centrality, reaction plane DAQ-Upgrade FINISHED  goal 20 kHz for Au+Au LVL1 MDC I rebuild  system stability Commissioning Summer 2011: commissioned with Au beam 1 RPC sector

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture I: 41 Next runs at SIS18: 1.25 GeV/u Au+Au HADES upgrade nearly completed  new MDC inner tracking plane  new RPC timing detectors  new and faster readout electronics  Forward Wall installed ► Getting ready for Au run 2 nd Q 2012 Simulated counts for 4 weeks beam 1.25 GeV Au+Au Expected pair rates/day + plenty of strangeness!

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 42 Experiments with pion beams: The GSI secondary pion beam line Momentum of the beam particles reconstructed with precision of 0.3%  Tracking in the beam line: silicon strip detector  Diamond in front of the target for background rejection Q doublet defines acceptance  = 2.3 msr Momenta up to 2.8 GeV/c,  p/p = 8% Beam spot at the HADES focal point: 3σ x – 2.0 cm, 3σ y – 1.8 cm H1, H2 & H3 for beam momentum reconstruction (fiber/silicon det.)  p/p = 0.3% 7.5 o dispersive plane

Particle production in the HSD transport model Thermal Cassing & Bratkovskaya calculations for FAIR central Au+Au SIS100

Thermal model predictions Thermal models à la PBM and à la Cleymans underestimate grossly the η yield at E < 10 AGeV. Private communication: A. Andronic TAPS WA80 FAIR η/π 0 ≈ 0.1

A Photon Calorimeter for HADES Adding a calorimeter to HADES offers: Better lepton ID Neutral mesons in p+A & A+A Direct photons in p+A & A+A Hadron zoo in p+p & π+p Photon decays: π 0 → γγ η → γγ η’ → γγ ω → π 0 γ → γγγ + Dalitz decays

Neutral meson detection in A+A  large photon combinatorial background  small signal/background ratios  needs a high-resolution EM calorimeter S/B=0.07 % WA80 S/B=2.7 % TAPS 0.8 AGeV Au+Au 200 AGeV S+Au CB-subtracted m γγ spectra A. Wolf et al. PRL 69 (98) 5281 R. Albrecht et al. PLB 361 (95) AGeV Au+Au PHENIX S/B = 0.2% – 5% 158 AGeV Pb+Pb WA98 S/B < 0.5%

Eta Dalitz reconstruction in simulation η → γ e + e - measured in HADES + calorimeter: ► Potentially interesting, but needs to be explored in simulations! S/B >1

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: : HADES goes underground HADES in the CBM cave

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 49 The HADES roadmap: The present planning foresees:  2012: Au+Au run at 1.25 AGeV (dileptons + strangeness)  2013: first pion beam run (physics goals still being discussed)  2014: Ag+Ag run at 1.65 AGeV (dileptons + strangeness)  2015: another pion beam run ??  2016: move HADES to CBM cave at SIS100  2018: first beams from SIS100 ???

The next years …  No η data available in the FAIR energy range  Can we trust models in describing correctly the yields?  Transport models lack input on pp, pn, πN, etc.  Beyond the η, CALO can potentially give more (photons, Σ 0 → Λγ, η’ → e + e - γ, etc.)  Hadron spectroscopy in p+p and π+p could profit  Need realistic simulations to decide which cases are feasible with HADES + CALO

Rez The Experimental Quest for In-Medium Effects - R. Holzmann, GSILecture III: 51 HADES 2 – 8 GeV/u CBM 8 – 45 GeV/u Conclusions and outlook Understanding pp, np & πN processes is essential for A+A !!!  In Ar+KCl onset of “medium” effects  strong baryonic contribution to e + e -  first observation of vector mesons  2 nd focus on strangeness production  Upgraded HADES will investigate  heavy systems up to Au+Au  πN and πA reactions  + strong strangeness program  Move to SIS100 planned for 2016/17  add lead glass calorimeter  do physics at 2 – 8 AGeV