Dilepton production with HADES at 1 3 5

Dilepton production with HADES at 1 -3. 5 Ge. V kinetic energy Anar Rustamov GSI Helmholtzzentrum für Schwerionenforschung 1 Anar Rustamov, GSI Darmstadt, Germany

Outline Ø Ø Ø dilepton production main physics goal experimental approach HADES spectrometer pair spectra Ø Ø comparison with models Ø Ø Ø 2 cross sections PLUTO HSD Ur. QMD p. A data AA data summary Anar Rustamov, GSI Darmstadt, Germany

Dilepton spectra A. Drees Sources of dileptons: Ø Ø Ø Drell-Yan process charmonimum QGP dileptons resonances particles from freeze-out stage ü low mass part: 3 study of Chiral symmetry restoration Anar Rustamov, GSI Darmstadt, Germany

Physics motivation Hadrons in medium Chiral symmetry: SU(2)L x SU(2) R N*(1520) r r N-1 +. . . Spontaneously broken in vacuum by Partial Restoration in medium (melting of ) QCD sum rules dispersion relation QCD part: T. Hatsuda, S. H. Lee, Phys. Rev. C 46 (1992) R 34 Probing the matter with vector mesons 4 Anar Rustamov, GSI Darmstadt, Germany

Experimental approach Mass distribution of the hadrons inside medium: p 1, p 2: 4 -momenta Ø Hadrons should be short lived (ρ, ω, Φ) Ø p 1, p 2 should be detected undistorted (leptons) ρ(m) - spectral function, Г - width Experimental challenge: small branching ratios high background 5 Mass [Me. V] ct [fm] Г/Гtot->ee r 770 1. 3 4. 7× 10 -5 w 782 23. 4 7. 07× 10 -5 F 1020 44. 4 2. 97× 10 -4 Anar Rustamov, GSI Darmstadt, Germany

HADES spectrometer Ø Acceptance Ø Ø Momentum resolution Ø Ø Ø Ø RICH Time of flight Pre-Shower MDC (for hadrons) Trigger Ø Ø 6 Magnet: 0. 1 -0. 34 Tm MDC: 24 drift chambers σm~ 2% at ρ/ω region Particle identification Ø Ø φ ~ 2π 15 o < θ < 85 o pair ~ 30% LVL 1 - charged particle mult. LVL 2 - single electron trigger Anar Rustamov, GSI Darmstadt, Germany

Pair spectra for pp at 3. 5 Ge. V Not efficiency corrected. Inside HADES acceptance Ø Close partner cut Ø Momentum cut 80 < P [Me. V/c] < 2000 Ø Track fitting quality cut θpair > 90 Combinatorial background (CB) uncorrelated 7 correlated CB = N++ + N- Anar Rustamov, GSI Darmstadt, Germany

Absolute normalization Elastic scattering Kinematic constraints: Kammerud et al. Phys. Rev. D 4 (1971), 5 8 Anar Rustamov, GSI Darmstadt, Germany

Pair spectra Efficiency corrected. Inside HADES acceptance Signal CB σω ~ 16 Me. V/c 2 high S/CB ratio θpair > 90 9 Number of pairs: Ø All : ~ 6. 1*104 Ø M <0. 15 : ~ 5. 5*104 Ø 0. 6 < M < 0. 82 : ~ 451 Anar Rustamov, GSI Darmstadt, Germany

Cross sections Inclusive cross sections from pair spectra σπo = 15 mb ± 4 mb from Consistent with Resonance model S. Teis et al. Z. Phys. A 356, 421 -435 (1997) lines are from HSD pp → π + X pp → π - X pp → π o X (HADES) 10 H. Weber et al. , PRC 67 (2003) 014904 and references therein Anar Rustamov, GSI Darmstadt, Germany

Resonance model Δ (1232) sum over N* states higher 3/2 states ~ 13 mb 11 S. Teis et al. Z. Phys. A 356, 421 -435 (1997) and refernces therein Anar Rustamov, GSI Darmstadt, Germany

Cocktail simulation with PLUTO Ø particle production Ø phase space ( but 1 π exchange for the Δ ) Fröhlich et al, arxiv: 0708. 2382 Ø particle decays Ø form factors Ø mass dep. Width Ø cross sections [mb] Ø πo : 15 Ø Δ : from isospin coeff. Ø η : 1. 04 Ø ω : 0. 28 Ø ρ : 0. 36 12 Anar Rustamov, GSI Darmstadt, Germany

ρ/ω cross sections Cross sections were obtained from simulated cocktail by changing the ρ/ω ratio until simulation fits the data 13 W. Cassing, E. Bratkovskaya, Physics Reports 308 (1999) 65 -233 Anar Rustamov, GSI Darmstadt, Germany

Comparison with HSD 14 Anar Rustamov, GSI Darmstadt, Germany

Comparison with Ur. QMD 15 Anar Rustamov, GSI Darmstadt, Germany

Cocktail subtracted data πo, η and ω contributions are subtracted Particle production ØHSD Ø Lund String Model W. Cassing, E. Bratkovskaya , Physics Reports 308 (1999) 65 -233 Ø Ur. QMD Ø Through Resonances K. Schmidt, et al. Phys. Rev. C 79, 064908 (2009) m N N 16 N* , Δ N N Ø Missing higher resonances in PLUTO Ø Overestimation of ρ in Ur. QMD Ø HSD from new calculations Anar Rustamov, GSI Darmstadt, Germany

p. Nb data at the same kinetic energy of protons ( 3. 5 Ge. V ) p. Nb data Signal Online spectra: Ø preliminary calibrations Ø preliminary alignment pair momenta in ρ/ω region shape of ρ/ω as a function of their momenta can be studied 17 Anar Rustamov, GSI Darmstadt, Germany

AA collisions normalization Enhancement factor ( 0. 15 < M < 0. 5) F(2. 0) = 1. 9 ± 0. 2(stat) ± 0. 3(sys) ± 0. 3( sys) F(1. 0) = 6. 8 ± 0. 6(stat) ± 1. 3(sys) ± 2. 0( sys) 18 PRL 98, 052302 (2008) PLB 663 (2008) 43 -48 Anar Rustamov, GSI Darmstadt, Germany

Excess yield DLS data HADES data π0 and η mutlt. from TAPS data Excess scales with: Ø Ebeam: like π production Ø Apart : more than linear 19 Anar Rustamov, GSI Darmstadt, Germany

Excess yield thesis: T. Galatyuk, K. Lapidus 20 thesis: T. F. Krizek, S. Lang, M. Jurkovic …. § C+C data reproduced (within 20%) by superposition of NN interactions § Ar+KCl data overshoots the NN data by a factor of ~2. 5; Anar Rustamov, GSI Darmstadt, Germany

Summary I l l l 21 Meson production is investigated in pp reactions at Tkin = 3. 5 Ge. V For the first time inclusive cross sections for the π0, η, ω and ρ mesons are reconstructed Comparison of the data to transport models is shown The investigation of production mechanisms of the vector mesons are ongoing Reference spectra for the p. Nb run at the same beam kinetic energy is obtained Anar Rustamov, GSI Darmstadt, Germany

Summary II l l l Excess observed in DLS is confirmed by HADS experimentally The observed excess scales with energy like pion production and more than linear with Apart The excess in light system ( C+C ) is reproduced by superposition of NN interactions – 22 The observed enhancement in DLS data already exists in elementary reactions, and is not connected with any kind of medium effects Anar Rustamov, GSI Darmstadt, Germany

Comparison with Ur. QMD PT distributions for different mass bins 23 Anar Rustamov, GSI Darmstadt, Germany

Pair spectra All SS e+e- = = e+e- + +CB All CB e+ee+e 0 θpair> >9 90 Particle identification: Ø RICH-MDC matching Ø Time of flight cuts Ø Shower cuts Background rejection: Ø close track cut Ø opening angle cut Ø track fitting quality cut Combinatorial background (CB) uncorrelated CB = N++ + N- - 24 Anar Rustamov, GSI Darmstadt, Germany

AA data HADES data in DLS acceptance … DLS Data: R. J. Porter et al. : PRL 79 (1997) 1229 HADES and DLS data agree ! 25 Anar Rustamov, GSI Darmstadt, Germany

Comparison with the models Normalized to π peak 26 W. Cassing, E. Bratkovskaya, Physics Reports 308 (1999) 65 -233 K. Schmidt, et al. Phys. Rev. C 79, 064908 (2009) Anar Rustamov, GSI Darmstadt, Germany