Dilepton and strangeness production studied with HADES Romain

Dilepton and strangeness production studied with HADES Romain Holzmann, GSI Helmholzzentrum für Schwerionenforschung, for the HADES collaboration § Probing hadronic matter with HADES: dileptons and strangeness § e+e- pairs - from N+N to A+A § HADES, a strangeness detector § The future: short- and mid-term projects CBM Physics Workshop, April 2010 CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt

Exploring the phase diagram at high μB Andronic et al. in ar. Xiv: 0911. 4806 v 3 Probing nuclear matter at SIS: § densities: max/ 0 2 - 3 § temperature: T 50 -100 Me. V à System stays above ground state density for 10 - 15 fm/c S. Vogel et al. Phys. Rev. C 78 044909 (2008) 30 A regime of “Resonance Matter”: 11 § matter dominated by baryons (up to 30% resonances!) 2 Ge. V § fireball 10 · resonance HADES operates here! CBM Physics Workshop April 14, 2010 Rapp & Wambach Adv. Nucl. Phys. 25 (2000) R. Holzmann, GSI Darmstadt 2

The HADES experiment at GSI § azimuth. symmetry § large coverage: y = 0 - 2 § hadron & lepton PID § 2% mass resolution § LVL 2 lepton trigger Dilepton studies with HADES: 1. 2. 3. 4. CBM Physics Workshop April 14, 2010 Confirmed DLS excess yield! C+C Origin of these pairs: p+p and n+p Move to larger systems: e+e- and strangeness in Ar+KCl Vector mesons in cold matter: p+Nb R. Holzmann, GSI Darmstadt 5

1) Inclusive e+e- production in C+C Phys. Rev. Lett 98(2007) 052302 Cocktail generated with PLUTO Phys. Lett. B 663 (2008) 43 Efficiency-corrected di-electron spectra, normalized to the number of neutral pions: § 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? CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 6

HADES vs. DLS: a direct comparison Project HADES data into DLS acceptance and compare … DLS Data: R. J. Porter et al. : PRL 79 (1997) 1229 J. Carroll at International Workshop on Soft Dilepton Production August 20 -22, 1997, LBNL HADES and DLS data agree ! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 7

The pair “excess” in C+C quantified Excess pair yield over cocktail of long-lived sources vs. Ebeam: TAPS data Enhancement scales like Mπ Hinting at Δ resonance decays and/or NN bremsstrahlung! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt R N N 8

2) Virtual photons from free NN collisions Measured 1. 25 Ge. V/u p+p and d+p Ø Check vs. microscopic calculations of NN processes Ø Compare NN with C+C Typical OBE diagrams for N N S N N e+ : e- + ISI + FSI Compilation by E. L Bratkovskaya & W. Cassing in Nucl. Phys A 807, 214 (2008). Main active players: exchange terms CBM Physics Workshop April 14, 2010 contact terms Kaptari & Kämpfer, Mosel & Shyam R. Holzmann, GSI Darmstadt 9

Tagging quasi-free np reactions in HADES p+p: Cut View pr psp d p FW q > 7 o d+p: quasi-free np OBE calculations reproduce pp, but not (yet) np ! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 10

Comparing C+C data with N+N data Comparison of C+C data to average of pp and np collisions: § C+C data reproduced (within 20%) by superposition of NN interactions § Pair “excess” observed in C+C data can be traced back to enhanced pair production in n+p collisions § How about yet heavier systems? All normalized to Nπ CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 11

3) Moving on to heavier systems: Ar+KCl § Again, strong overshoot above the trivial cocktail! § First ω peak seen at SIS energies! ~ 40 counts ► MLVL 1(ω) = (6. 7± 2. 7) · 10 -3 CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 12

“Excess” vs. beam energy and system size Yield/Apart § baryonic contrib. in Ar+KCl >> C+C § scales with Ebeam like π production Ca+Ca Ar+KCl § scales with Apart stronger than linear C+C ≈ <Apart>1. 4 N N N π0 and η from TAPS (min. bias) e+ e- continuum pairs : HADES (LVL 1) DLS (min. bias) CBM Physics Workshop April 14, 2010 N R N. . . R N N R g* N e+ e- ► multistep processes! R. Holzmann, GSI Darmstadt 13

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 x 2. 5 - 3 § η contributions subtracted ! § yield normalized to M(π0) ►► Excess over free NN! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 14

Transport model predictions for Ar+KCl vacuum calculation vacuum vs. in-medium HSD model (status 2008) E. L. Bratkovskaya, W. Cassing, Nucl. Phys. A 807 (2008) 214 -250 Ur. QMD model K. Schmidt et al. ar. Xiv 0811: 4073 v 2 Transport models do § fine for Mee< 0. 6 Ge. V § overshoot ω/ρ peak Are in-medium effects needed? Not clear yet… CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 15

Ar+KCl in HSD (Nov 09 release) retuned § M /Mπ0 = 0. 0019 (exp = 0. 0020) § for M>0. 65 Ge. V: ω+ρ = 70% CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 16

Strange, stranger, strangeness! HADES has 1. 76 Ge. V/u Ar+KCl § high mom resolution § high acceptance § good particle ID § vertexing PID based on d. E/dx and TOF Ξ- → Λπ →K+K- + more in N+N CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt e. g. Λ(1405), Σ(1385) 17

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

/ ratio: OZI in Ar+KCl vs. NN Using yields from § → K+K- : (2. 6 ± 0. 7) · 10 -4 § → e+ e- : (6. 7 ± 2. 7) >> OZI allowed · 10 -3 ► >> R / in NN and πN reactions ! Yet can be described in a statistical model (THERMUS): CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 19

Comparison with a statistical model THERMUS calculation (T, μB and RC fit to HADES data) ω and described in statistical model, but… from TAPS CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 20

Definition of mass slices for d. N/dmt low mid mostly 3 -body ! CBM Physics Workshop April 14, 2010 high mostly 2 -body ? R. Holzmann, GSI Darmstadt

Transverse-mass spectra: Mee< 0. 15 Ge. V (efficiency and acceptance corrected) A+A vs. ► Low-mass bin is well described by π0 Dalitz 1. 25 Ge. V N+N ► 1. 25 Ge. V/u NN reference CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt

Transverse mass: 0. 15 < Mee< 0. 50 Ge. V A+A vs. 1. 25 Ge. V ► Mid-mass bin: T of baryonic component changes only weakly with Ebeam ! N+N ► 1. 25 Ge. V/u NN reference … ? CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt

Transverse mass: Mee> 0. 50 Ge. V ► Large slopes: Tee >> Tchem = 75 Me. V CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt

More mass cuts in Ar. KCl… Mee = 0. 35 – 0. 50 – 0. 65 3 -body (!) CBM Physics Workshop April 14, 2010 >0. 65 Ge. V 2 -body (? ) decays R. Holzmann, GSI Darmstadt 25

Comparison with in-medium HSD vs. Ar+KCl at 1. 76 Ge. V/u § low-mass bin is well described, except for mt >800 Me. V § at mid-mass, slope is fine, but no selectivity § high-mass slope reproduced by neither ρ/ω, nor Δ ! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 26

Systematics of slopes at 1. 76 Ge. V/u π0 and η from TAPS Why are slopes of ρ/ω and so different ? CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 27

Momentum-dependant ω reabsorption § ωN → πN § ωN → π π N § ωN → ρN § etc. Lykasov et al. HSD calculation EJP A 6 (1999) 71 OBE calc. Large absorption cross sections (>50 mbarn) are supported by transparency ratio (TA) measurements in photoproduction (at MAMI C and ELSA) mt slope: 77 Me. V → 130 Me. V Also: slope(ω) >> slope( ) CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 28

4) 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 known to be broadened (x 16) in the medium ► use transparency ratio TA! On-going analysis… Nee normalized to respective π yield CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt Ratio p+Nb / p+p 29

5) HADES next runs at SIS 18 HADES upgrade nearly completed § § new MDC inner tracking plane new RPC timing detectors new and faster readout electronics Forward Wall installed Simulated counts for 4 weeks beam 1. 25 Ge. V Au+Au ► Getting ready for Au run in fall 2010 Expected pair rates/day + plenty of strangeness! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 30

Conclusions and outlook § Understanding pp and np 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 CBM 8 – 45 Ge. V/u § Upgraded HADES will investigate § heavy systems up to Au+Au § πN and πA reactions § + strong strangeness program § Move to SIS 100 planned for 2016/17 HADES 2 – 8 Ge. V/u CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 31

2016: HADES goes underground The HADES Collaboration CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 32

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 E 12, Technische Universität München CBM Physics Workshop April 14, 2010 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 R. Holzmann, GSI Darmstadt 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 33

Cavalry to the rescue! CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 34

HADES in CBM cave (design by W. Niebur) CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 35

Neutral Kaon Prodcution and the IQMD Model Absolute normalization (b < 6 fm) Normalized to pt > 450 Me. V/c Pr An repulsive KN potential effects both the production yield (reduction) and the pt-slope (blue-shift) ! Potential can be adjusted independently from systematic uncertainties in the yield. Manuel Lorenz Bormio 2010 C. Hartnack, A. Schmah, L. Fabbietti y ar in in im im el el Pr IQMD potential scan

6) HADES at SIS 100: beyond the 2 Ge. V limit! CBM 8 – 45 Ge. V/u 1. 0 AGe. V Simulations on-going … HADES 2 – 8 Ge. V/u CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 37

Time table for move to CBM cave CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 38

Cost table CBM Physics Workshop April 14, 2010 R. Holzmann, GSI Darmstadt 39