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The Experimental Quest for In-Medium Effects

The Experimental Quest for In-Medium Effects. Romain Holzmann GSI Helmholtzzentrum f ü r Schwerionenphysik, Darmstadt at 23 rd Indian-Summer School of Physics and 6 th HADES Summer School: Physics @ FAIR October 3-7, 2011 in Rez/Prague, Czech Republic.

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The Experimental Quest for In-Medium Effects

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

  2. Lecture III:Investigating dense matter with HADES at GSI:Present and future Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  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 pA (ρ/ρ0  1-3) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  4. S. Vogel et al. Phys. Rev. C78 (2008) 044909 30 11 2 GeV Rapp & Wambach Adv. Nucl. Phys. 25 (2000) Exploring the phase diagram at high μB Andronic et al., Nucl. Phys. A 837 (2010) 65 Trajectories from Ivanov et al., PRC 73 (2006) 044904 • Probing nuclear matterat SIS: • densities: max/r0 2 - 3 • temperature: T  50 -100 MeV • N resonances become important System stays above ground state density for   10 - 15 fm/c UrQMD Au+Au thermal model at r =r0 HADES operates here! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  5. π0 & η prod. in p+p 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 pA (ρ/ρ0  1-3) • Hadron production & spectroscopy • meson and baryon production • coupling of rand to N* • spn vs. spp • strangeness production • form factors of , f, D, 0and L • systematic dilepton (and hadron) spectroscopy in pp, pn and pp (ρ/ρ0 = 0) → needed to model p+A & A+A Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  6. The HADES detector at GSI Physics accessible with HADES: Dielectrons in NN: p+p and n+p Dielectrons in HI: from C+C to Au+Au Vector mesons in cold matter: p+Nb Strangeness production: p+p, p+A, A+A Pion-induced reactions: (2012-2016) SIS100: (>2017) Technical paper: G. Agakishiev et al. Eur. Phys. J. A41, 243 (2009) General documentation: http://www-hades.gsi.de • azimuth. symmetry • large coverage: y = 0 - 2 • hadron & lepton PID • 2% mass resolution • LVL2 lepton trigger • plastic forward wall /RPC Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI 9 R. Holzmann, GSI Darmstadt ECT* Dileptons September 13-17, 2010

  7. SIS18 Unilac π production target ESR HADES HADES at SIS18 Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  8. B A primer for theorists p = m∙ βc►mass How to identify a particle? ►Z ►e- vs. hadrons 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

  9. “TOF”( ) “RICH” (electron ID, hadron-blind) “Pre-Shower” (electron ID) “MDC” (tracking, ) Detector components Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  10. TOF Cryostat Pre-Shower outer MDC outer MDC RPC B field region inner MDC He pipe beam Start + target Technical layout of HADES HADES cave HADES sector inner MDC RICH readout Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  11. 20% p0 Dalitz 60% γ conversion g g e+ p0 e+ Q~ 15.20 Q~ 2.20 e- e- The RICH: a hadron-blind detector • γ > 18 hadron-blind, but... ► use segmented target Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  12. ~ 55 mm Segmented target • Example: 3.5 GeV p+Nb • 93Nb material • 12 pellets of Ø = 1.25 mm • Δz = 4.5 mm • 2.8% interaction prob. beam Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  13. IPN Orsay LHE Dubna FZR GSI Tracking: the Multiwire Drift Chambers • 4 MDC/sector • total 33 m2area, 27000 cells • y<0.1mmresolution • Ar-iC4H10 [60-40]gas and low-Z material ORSAY plane wire planes: 10o,-20o,0o,0o,20o,-10o Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  14. field map + tracking planes Runge-Kutta track fit Tracking: superconducting toroidal magnet Bmax = 0.8 Tesla (mid-plane) bending power = 0.36 Tm (typically operated at 70% - 90% of max. field) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  15. e- velocity vs. momentum e+ e- Electron/positron identification MDC hit finder & hit/track matching RICH pattern Pre-Shower condition + + Data Monte Carlo e- e+ Momentum * charge [MeV/C] Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  16. Pair reconstruction Combinatorial background subtraction 0 e- e- e- e+  From: • like-sign pairs • or event mixing e+ e+ 0  e- p1 q RICH rings e+ p2 Signal: S+-= Ne+e- - CB+- lepton/baryon Lepton pair reconstruction uncorrelated pairs Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  17. The HADES Collaboration on tour 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 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 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 17 institutions 120+ members Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  18. First HADES data: e+e- production in C+C 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? Efficiency-corrected di-electron spectra, normalized to the number of neutral pions: Cocktail generated with PLUTO Phys. Lett. B 663(2008)43 Phys.Rev. Lett 98(2007) 052302 Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  19. HADES DLS π0→e+e–γ η→e+e–γ Hades DLS Hades DLS mid-rapidity mid-rapidity 1 AGeV C+C: HADES confirms DLS • π0, η acceptance • HADES >> DLS 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 Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  20. e+e- production in 1.756 GeV/u Ar+KCl • Again, strong overshoot above the cocktail of long-lived sources! • First ω peak seen at SIS energies! ~ 40 counts Cocktail of long-lived sources: π0, η, and ω • ► MLVL1(ω) = (6.5 ± 2.8) ·10-3 ±20% sys. Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  21. Cut View pr psp FWq > 7o p d Tagging quasi-free np reactions in HADES p+p: d+p: quasi-free np OBE calculations reproduce pp, but not (yet) np ! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  22. Preparing a “reference” for A+A Definition of a ”reference” based on pp and np data: • Compare excess over η in Ar+KCl • with excess over η in reference x2.5 - 3 • η contributions subtracted ! • yield normalized to M(π0) ►► Excess over free NN! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

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

  24. Strangeness production in Ar+KCl  →K+K- • HADES has • high mom resolution • high acceptance • good particle ID • vertexing 1.76 GeV/u Ar+KCl PID based on dE/dx and TOF Ξ-→ Λπ- TB = 84 PRC 80 (2009) 025209 PRL 103 (2009) 132310 PRC 82 (2010) 021901 EPJA 44 (2010) etc. Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  25. The Hades upgrade project (2010/11) • List of HADES upgrade subprojects: •  RPC - Resistive Plate Chamber FINISHED •  Time res. 50-80 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 • Meta detector,  < 45 deg. • Time res: 350 ps. • PreShower pos. res: 1.5 cm • Limitation: multihit capability 1 RPC sector • RPC performance (beam test) •  Efficiency above 95 % •  Time res. 50-80 ps •  Negligible crosstalk < 1% Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  26. Simulated counts for 4 weeks beam 1.25 GeV Au+Au 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 2nd Q 2012 Expected pair rates/day + plenty of strangeness! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  27. dispersive plane 7.5o Experiments with pion beams:The GSI secondary pion beam line • Q doublet defines acceptance •  = 2.3 msr • Momenta up to 2.8 GeV/c , p/p = 8% • Beam spot at the HADES focal point: • 3σx – 2.0 cm, 3σy – 1.8 cm • H1, H2 & H3 for beam momentum • reconstruction (fiber/silicon det.) • p/p = 0.3% 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 Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

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

  29. 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: π0 →γγ η →γγ η’ →γγ ω→π0γ→γγγ + Dalitz decays

  30. 0.8 AGeV Au+Au TAPS S/B=2.7 % 158 AGeV Pb+Pb 100+100 AGeV Au+Au PHENIX WA98 WA80 S/B=0.07 % S/B = 0.2% – 5% S/B < 0.5% CB-subtracted mγγ spectra • large photon combinatorial background • small signal/background ratios •  needs a high-resolution EM calorimeter A. Wolf et al. PRL 69 (98) 5281 Neutral meson detection in A+A 200 AGeV S+Au R. Albrecht et al. PLB 361 (95) 14

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

  32. 2017: HADES goes underground HADES in the CBM cave Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  33. The HADES roadmap: 2012-2018 • 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 ??? Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  34. CBM 8 – 45 GeV/u HADES 2 – 8 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 • 2nd 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 Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

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