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 m [GeV] q [GeV] A T [GeV -2 ] M. Post et al., NPA 741 (2004) 81 e- e+e+  Partial decay branch might be suppressed by collisional broadening: HIC 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  line shape results of KEK-E325 - some experiments (Clas, KEK-E325) not sensitive to low monenta mesons - no complete picture yet Dileptons from p+p and p+Nb at 3.5 GeV Charged  mesons from p+Nb at 3.5 GeV Motivation and Method Modification of hadronic properties in nuclear matter predicted by theory – already at normal nuclear density: Effect most prominent at low momenta –  spectral function : Experimental method: reconstruction of the  vector meson (VM) mass distribution from their e + e - pair decay + no final state interaction - low yields Advantage over nucleus-nucleus collisions (HIC): No density evolution in “cold” nuclear matter, controlled conditions Direct measurements of the ρ: NA60, nucleus-nucleus collisions centrality dependent broadening, no shift R.Arnaldi et al. PRL 96 (2006) Indirect measurements of ω-width: CBELSA/TAPS:  N reaction  yield not affected by secondaries strong broadening (factor ≈16) M.Nanova arXiv: [nucl-ex] HADES - operates on beam of SIS18 heavy-ion synchrotron at GSI Darmstadt - measures e + e - pairs from p, ,and heavy-ion induced reactions with large acceptance in solid angle and momentum - important for reconstruction of low momenta mesons where (1) medium modifications are predicted (2) most mesons decay inside the nucleus - p+Nb at 3.5 Gev measured, with p+p at the same energy as a reference Momentum cut important: Largest effect expected at low momenta (see above). Low momenta mesons decay mostly inside nucleus where the change of the line shape is expected: HADES acceptance allows cut on low momenta, even in the VM mass region! : Momentum cut Preliminary Scaling of pp and pNb data: two methods consistent method 1 – reaction cross section * number of participants method 2 –  0 yield Invariant mass distributions:  meson peak at GeV clearly identified Scaled data: no obvious difference Measured data Preliminary HSDcalculations : Fast pairsSlow pairs Preliminary “fast” pairs - the distribution for pp and pNb is the same. “slow” pairs - visible difference, see zoomed picture on the right side: Fast Slow Slow zoomed into VM region: additional broad contribution below the  peak (bands represent sys. errors) Invariant mass distributions for low (p 0.8 GeV) momenta pairs Preliminary - pions (M ee <0.15 GeV/c 2 ) show flat behavior - higher invariant mass regions rise with decreasing momentum → feeding due to secondary reactions - omega : no dependence on momentum 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 Due to the ρ coupling to baryonic resonances a solid theoretical description needed to extract possible broadening or mass shifts Preliminary Momentum dependence of various sources Conclusion HADES data:    =    tot, scaling constant to HARP-CDP data is  tot = 848 ± 14 mb Normalization to HARP-CDP data Motivation HADES measures particle multiplicities per reaction, which have to be recalculated to cross sections to compare data from pp and pA systems. p+p reaction: measured pp elastic scattering yield is matched to known cross section. p+A reaction: measured charged pion multiplicity is matched to pion cross section from existing pA data scaling constant is the total reaction cross section    =    t tot Measured data contribute to the results from systematic studies of the pion production in the proton-nucleus collisions, and can be used for tuning of transport models (see e.g. K.Gallmeister, U.Mosel, arXiv: [hep-ex] ), in the region of transition of the pion source from simple NN collisions to emission of thermalized pions from a baryonic matter, when increasing the atomic number of the target nucleus. Summary 200 < p < 1000 MeV/c 30  <  < 90  closest system to p+Nb at 3.5 GeV p+A at 3,5,8,12 GeV/c Bolshakova A. et al. HARP-CDP Collaboration EPJ C63 (2009) , EPJ C64 (2009) Existing data:  cross sections from pA 4 closest system to p+Nb at 3.5 GeV were used to compare with our data: p+Cu and p+Ta at 3 and 5 GeV/c (see below). Before the comparison, the HARP-CDP cross sections from these 4 systems were rescaled to expected values for p+Nb at 3 GeV via interpolation in 2D energy – atomic number space. same as on the left side, in the log scale: Multiplicities of charged pions from p+Nb at 3 GeV were measured. From comparison with the HARP-CDP data the p+Nb total cross section was extracted as  tot = 848 mb, with systematic error of 15%. This allows for an absolute normalization of the measured data, including dilepton production. Measured data together with results of systematic studies of pion production in p+p and p+A can be used for adjusting of transport models in the region between elementary p+p and proton-nucleus collisions. Preliminary Electron pair production in “cold” nuclear matter: Measured data Multiplicity of  - measured in various polar angle regions Statistical errors are negligible, systematic errors are 15% (not shown). Preliminary