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Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV

Michael Weber for the HADES collaboration. Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV. Technische Universität München. Introduction HADES experiment Effects in cold nuclear matter Relative to p 0 Cross sections Comparison with transport models

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Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV

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  1. Michael Weber for the HADES collaboration Inclusive e+e- pair production in p+p and p+Nb collisions at E = 3.5 GeV Technische Universität München • Introduction • HADES experiment • Effects in cold nuclear matter • Relative to p0 • Cross sections • Comparison with transport models • Conclusions WWND 2011

  2. Phase diagram • Learn about properties of QCD matter at different (T,r) • EM structure of matter • hadrons in matter http://www.ice.csic.es/en/graphics/phase.jpg WWND 2011

  3. o,  w,r o, e+ e- g* e+ e- w,r,f g* Phase diagram • Learn about properties of QCD matter at different (T,r) • EM structure of matter • hadrons in matter • Penetrating probe: • Dielectrons • Direct coupling of g* to VM (JP=1-) w,r,f http://www.ice.csic.es/en/graphics/phase.jpg WWND 2011

  4. e+ e- e+ e- e+ e- e+ e- Dense and hot matter • Accessible in: A+ A reactions LHC RHIC SPS FAIR SIS e+ e- Dense matter at SIS: J. Stroth http://www.ice.csic.es/en/graphics/phase.jpg WWND 2011

  5. e+ e- Cold nuclear matter • Accessible in: p + A / g + A / p + A WWND 2011

  6. Cold nuclear matter r meson • Accessible in: p + A / g + A / p + A • Medium effects: mass shift/ (collisional) broadening/ reabsorption/ regeneration • Measure: Spectral shape / Cross sections/ Attenuation • BUT: NON conlusive experimental results P.Mühlich et al., NPA 780 (2006), 187 WWND 2011

  7. HADESI HADES [ EPJ A41 243] Production of strangeness: L. Fabbietti 21.08.2014 WWND 2011

  8. HADESII HADES [ EPJ A41 243] High purity e+e- pair reconstruction A = 1 A = 93 • Beam: p • Ekin= 3.5 GeV • I ~ 6 · 106 1/s • Target : p • 4 cm LH2 • ~1% reaction prob. • 3.5 · 109 collisions • Beam: p • Ekin= 3.5 GeV • I ~ 2 · 106 1/s • Target :93Nb • 12 x 0.45 mm • ~3% reaction prob. • 9.2 · 109 collisions 21.08.2014 WWND 2011

  9. e+e- pair reconstruction • Signal to BG ratio • Comb. Background: • same event e-e- e+e+ • correlated BG from p0 / h decays WWND 2011

  10. e+e- sources in p + p • particle production • π via resonance decays (D,N*) • η, ω, ρ via phase space • Δ through 1 π exchange • particle decays • form factors • mass dep. Width PLUTO, Fröhlich et al, arxiv:0708.2382 • cross sections in 4π (mb) • π: 16 ± 2.6 (from data) • Δ: 7.5 PYTHIA • η: 0.93 ± 0.2 (fit to data) • ω: 0.25 ± 0.05 (fit to data) • ρ: 0.38 ± 0.07 (fit to data) σω ~ 16 MeV/c2 Δ FF is fixed at the photon point WWND 2011 Analysis by Anar Rustamov

  11. e+e- sources in p + p D - N transition form factor Space like: q2 < 0 Measured in electroproduction N D g* e- e+ Two–component VDM type model: Wan/Iachello, IJMP A20, 2005 only r relevant for D exclusive analysis NOT Measured Time like: q2 > 0 WWND 2011 Analysis by Anar Rustamov

  12. h e+e- No direct decay (same for p + Nb):  reduce BR (2.7 x 10-5) at least by factor of 3 WWND 2011 Analysis by Anar Rustamov

  13. e+e- in p + Nb Scaling to same yield in p0 peak Yield/p0 (p+Nb/p+p) • IM: 1.51 • HM: 1.37 • In w region 1.13 → diff. production and/or absorption mechansims for diff. sources → kinematic observables for diff. mass regions LM IM HM p0 h, D r,w,f WWND 2011

  14. pNb vs. pp: pT and y yCM, NN LM LM Transverse momentum pT2 = px2 + py2 Rapidity y = ½ ln (E+pz)/ (E+pz ) yCM, NN = 1.12 WWND 2011

  15. pNb vs. pp: pT and y For both mass bins: • Higher yield • At high pt • Shift to target rap.  add. slow source IM IM HM HM WWND 2011

  16. Fast and slow e+e- sources • Decays inside nucleus • In – Medium effects p cut HSD Simulation for HADES proposal WWND 2011

  17. Fast and slow e+e- sources HM p cut p+Nb Ekin= 3.5 GeV HADES: Significant e+e- yield with low pair momenta ( ~ 35 % in HM) WWND 2011

  18. Fast and slow sources in other Exp. KEK: p + A @ 12 GeV JLAB: g + A @ 0.6 -3.8 GeV S.Leupold, V.Metag and U.Mosel, nucl-th 0907.2388 R.Muto et al., PRL 98 (2007) 042501 WWND 2011

  19. Fast and slow e+e- sources Low p High p • High p: free p+p production • Low p: overshoot over p+p different for r, w, and f WWND 2011

  20. Cross sections • p+p: • X sect from spp, elastic • p+Nb: • X sect from sp-,acc comp to HARP • Bolshakova et al., EPJC (1997) 1865 • Isospin: • spd = 2 spp ( DLS: Ekin > 2 GeV ) • Wilson et al., PRC 57(1997) 1865 • A Scaling: • Black disc: a = 2/3 Glauber model: a ~ 0.8 • W.Cassing et al., PLB 238 (1990) 25 WWND 2011

  21. RpNb vs. p LM HM IM a~0.7 • High p: free NN prod. + same absorption for all sources WWND 2011

  22. RpNb vs. p LM HM IM a~0.7 • High p: free NN prod. + same absorption for all sources • Low p : enhanced prod. (secondary processes) and/or lower absorption in IM and HM WWND 2011

  23. A scaling for vector mesons Fit with Gaussians: • High p: apNb,w = 0.69 ± 0.27 apNb,f = 1.04 ± 2.50 • Low p: apNb,w = 0.62 ± 0.36 Data : p+A @ 12. GeV KEK E325  = 0.710 ± 0.021(stat) ± 0.037(syst)  = 0.937 ± 0.049(stat) ± 0.018(syst) • w: momentum dependent absorption ? • f: production in whole nucleus volume (statistics!) ? T. Tabaru et al.. Phys.Rev. C 74(2006) WWND 2011

  24. Transport models - M Different D, h, r contributions ! GiBUU UrQMD HSD WWND 2011

  25. Transport models - pT Different D, h, r contributions !  Constrain models ? GiBUU UrQMD HSD WWND 2011

  26. Slow and fast sources (GiBUU) Collisional width in GiBUU for w • momentum dependent • 20 – 90 MeV ( 2 – 11 x Gvac) WWND 2011

  27. Summary • e+e- - pair production p+p and p+Nb at E = 3.5 GeV ( M, pT and y) • clear w signal observed (sw/Mw ~ 2%) • significant e+e- - yield with low pair momenta (p < 800 MeV/c) • Additional prod. w.r.t p+p at intermediate masses ( hard pT and target rapidity ) • A scaling of differential cross sections: (p+Nb/p+p) ~ Aa • High p : all masses a ~ 0.7 • Low p : p0 region: a ~ 0.7 h, Dregion: a ~ 0.82 r,w,f region: a ~ 0.86 BUT w a ~ 0.62  in - medium omega width • Comparison with transport models  Better understanding of sources in p + p WWND 2011

  28. Outlook • e+e- - pair production in HI reactions • Regeneration of VM • Higher densities • HADES upgrade • in p- induced reactions • Large X – sections • VM „at rest“ • Beam particle tracking WWND 2011

  29. The HADES collaboration Thank you WWND 2011

  30. EXTRA SLIDES WWND 2011

  31. e+e- sources in p + p WWND 2011

  32. Collisional width of w in GiBUU free width WWND 2011 Priv. Comm. Janus Weil

  33. p + p normalization Elastic scattering Kinematic constraints: Kammerud et al. Phys. Rev. D 4 (1971), 5 WWND 2011 Analysis by Anar Rustamov

  34. p + Nb normalization p- yield in HADES acceptance: Systematic uncertainty Fit to HARP data: pT > 300 MeV/c WWND 2011

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