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50 th International Winter Meeting on Nuclear Physics, Bormio, January 23-27, 2012

Study of hadron properties in cold nuclear matter with HADES Pavel Tlust ý, Nuclear Physics Institute, Řež, Czech Republic for the HADES Collaboration.  ,  . p - beams. W. Weise. Modification of hadronic properties in nuclear matter

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50 th International Winter Meeting on Nuclear Physics, Bormio, January 23-27, 2012

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  1. Study of hadron properties in cold nuclear matter with HADES Pavel Tlustý, Nuclear Physics Institute, Řež, Czech Republic for the HADES Collaboration , . p - beams W. Weise Modification of hadronic properties in nuclear matter predicted by theory – already at normal nuclear density: • AA and cold matter experiments: Ceres, NA60, Phenix • KEK-E325, Clas, CBELSA/TAPS • results mostly consistent with broadening of mass distribution, • no indication of mass shift (except KEK-E325) • some experiments not sensitive to low monenta mesons • - no complete picture yet Experimental method: reconstruction of the w/r vector meson (VM) mass distribution from their e+e- pair decay + no final state interaction - low yields Electron pair production in “cold” nuclear matter: 50th International Winter Meeting on Nuclear Physics, Bormio, January 23-27, 2012 Partial decay branch might be suppressed by collisional broadening: Advantage over nucleus-nucleus collisions (AA): No density evolution in “cold” nuclear matter, controlled conditions Indirect measurements of ω: CBELSA/TAPS:gA reaction strong broadening (factor ≈16) M.Nanova arXiv:1109.4029 [nucl-ex] • HADES direct mass measurement : • measures e+e- pairs from p,p,and heavy-ion induced reactions • with large acceptance in solid angle and momentum • important for reconstruction of low momenta mesons

  2. Dileptons from p+p and p+Nb at 3.5 GeV Results: “Slow” pairs: Zoom to VM mass: pNb scaled to pp: Preliminary Preliminary Preliminary Preliminary Momentum dependence of RpA of various sources: Conclusion: Preliminary • pions show flat behavior • higher invariant mass regions rise with decreasing • momentum → feeding due to secondary reactions ω-mesons: identified ω's show also a flat behavior No feeding from secondary collisions due to strong broadening and decreased partial branching ratio..? ρ-mesons: No strong decrease of the partial branching ratio expected since it is already broad in vacuum

  3. Chargedpmesons from p+Nb at 3.5 GeV HADES measures particle multiplicities per reaction, which have to be recalculated to cross sections to compare data from pp and pA systems. Measured charged pion multiplicity is matched to pion cross section from existing pA data. Scaling constant is the total reaction cross section sp = Mp * stot Measured data contribute to the results from systematic studies of the pion production in the proton-nucleus collisions. Multiplicity of p- measured in various polar angle regions Statistical errors are negligible, systematic errors are 15% (not shown): Scalingof our data to HARP-CDP pA cross sections: Bolshakova A. et al. HARP-CDP Collaboration EPJ C63 (2009) 549, EPJ C64 (2009) 181. Preliminary Preliminary stot = 848 ± 14 mb (stat.) ± 127 (syst.)

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