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We report on the event-by-event multiplicity fluctuations of identified particles in central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. Employing a novel approach we unfolded the moments of the unknown multiplicity distributions of protons (p), kaons (K), pions (π) and electrons. Using these moments we reconstructed an excitation function of the fluctuation measure νdyn[A;B], with A and B denoting different particle types. Specifically, we reconstructed νdyn for the [p, π], [p, K] and [K, π] pairs. The energy dependence of νdyn is in agreement with previously published NA49 results on the related measure σdyn. Moreover, for [K; p] and [K;p] pairs, we discovered a dependence of the fluctuation measure νdyn on the phase space coverage (acceptance). Interestingly for the [p,π] case no significant acceptance dependence was observed. These observations provide a likely explanation of the reported differences between measurements of NA49 and those of STAR in central Au+Au collisions.
Ramstein, Béatrice ; Adamczewski-Musch, Jörn ; Arnold, Oliver Werner ; Atomssa, Ermias T. ; Behnke, Claudia ; Berger-Chen, Jia-Chii ; Biernat, Jacek ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Bordalo, Paula ; Chernenko, Sergey P. ; Deveaux, Christina Anna ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fateev, Oleg ; Fonte, Paulo ; Franco, Celso ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Hlaváč, Stanislav ; Höhne, Claudia ; Holzmann, Romain ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Kardan, Behruz ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Kuc, Hubert ; Kugler, Andrej ; Kunz, Tobias ; Kurepin, Alexander ; Kurilkin, Aleksey K. ; Kurilkin, Pavel ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lapidus, Kirill ; Lebedev, Alexei ; Lopes, Luis Alberto Vieira ; Lorenz, Manuel ; Mahmoud, Tariq ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Parpottas, Yannis ; Pechenov, Vladimir ; Pechenova, Olga ; Petousis, Vlasios ; Pietraszko, Jerzy ; Przygoda, Witold ; Rehnisch, Laura ; Reshetin, Andrey ; Rost, Adrian ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schmidt-Sommerfeld, Korbinian ; Schuldes, Heidi ; Sellheim, Patrick ; Siebenson, Johannes Stephan ; Silva, Luis ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian Thomas ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Wendisch, Christian ; Wirth, Joana ; Wüstenfeld, Jörn ; Zanevsky, Yuri V. ; Zumbruch, Peter W.
Przygoda, Witold ; Adamczewski-Musch, Jörn ; Arnold, Oliver Werner ; Atomssa, Ermias T. ; Behnke, Claudia ; Berger-Chen, Jia-Chii ; Biernat, Jacek ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Bordalo, Paula ; Chernenko, Sergey P. ; Deveaux, Christina Anna ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fateev, Oleg ; Fonte, Paulo ; Franco, Celso ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Hlaváč, Stanislav ; Höhne, Claudia ; Holzmann, Romain ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Kardan, Behruz ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Kuc, Hubert ; Kugler, Andrej ; Kunz, Tobias ; Kurepin, Alexander ; Kurilkin, Aleksey K. ; Kurilkin, Pavel ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lapidus, Kirill ; Lebedev, Alexei ; Lopes, Luis Alberto Vieira ; Lorenz, Manuel ; Mahmoud, Tariq ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Parpottas, Yannis ; Pechenov, Vladimir ; Pechenova, Olga ; Petousis, Vlasios ; Pietraszko, Jerzy ; Ramstein, Béatrice ; Rehnisch, Laura ; Reshetin, Andrey ; Rost, Adrian ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schmidt-Sommerfeld, Korbinian ; Schuldes, Heidi ; Sellheim, Patrick ; Siebenson, Johannes Stephan ; Silva, Luis ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian Thomas ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Wendisch, Christian ; Wirth, Joana ; Wüstenfeld, Jörn ; Zanevsky, Yuri V. ; Zumbruch, Peter W.
n this paper we report on the investigation of baryonic resonance production in proton-proton collisions at the kinetic energies of 1.25 GeV and 3.5 GeV, based on data measured with HADES. Exclusive channels npπ+ and ppπ0 as well as ppe+e− were studied simultaneously in the framework of a one-boson exchange model. The resonance cross sections were determined from the one-pion channels for Δ(1232) and N(1440) (1.25 GeV) as well as further Δ and N* resonances up to 2 GeV/c2 for the 3.5 GeV data. The data at 1.25 GeV energy were also analysed within the framework of the partial wave analysis together with the set of several other measurements at lower energies. The obtained solutions provided the evolution of resonance production with the beam energy, showing a sizeable non-resonant contribution but with still dominating contribution of Δ(1232)P33. In the case of 3.5 GeV data, the study of the ppe+e− channel gave the insight on the Dalitz decays of the baryon resonances and, in particular, on the electromagnetic transition form-factors in the time-like region. We show that the assumption of a constant electromagnetic transition form-factors leads to underestimation of the yield in the dielectron invariant mass spectrum below the vector mesons pole. On the other hand, a comparison with various transport models shows the important role of intermediate ρ production, though with a large model dependency. The exclusive channels analysis done by the HADES collaboration provides new stringent restrictions on the parameterizations used in the models.
Pietraszko, Jerzy ; Agakishiev, Geydar ; Behnke, Claudia ; Belver, Daniel ; Belyaev, Alexei V. ; Berger-Chen, Jia-Chii ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Cabanelas Eiras, Pablo ; Chernenko, Sergey P. ; Dritsa, Christina ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fateev, Oleg ; Fonte, Paulo ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; González-Díaz, Diégo ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Höhne, Claudia ; Holzmann, Romain ; Huck, Patrick ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Krizek, Filip ; Kuc, Hubert ; Kugler, Andrej ; Kurepin, Alexander ; Kurilkin, Aleksey K. ; Kurilkin, Pavel ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lang, Simon Martin ; Lapidus, Kirill ; Lebedev, Alexei ; Lopes, Luis Alberto Vieira ; Lorenz, Manuel ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Parpottas, Yannis ; Pechenov, Vladimir ; Pechenova, Olga ; Przygoda, Witold ; Ramstein, Béatrice ; Rehnisch, Laura ; Reshetin, Andrey ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schuldes, Heidi ; Siebenson, Johannes Stephan ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian Thomas ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Weber, Michael ; Wendisch, Christian ; Wüstenfeld, Jörn ; Yurevich, Sergey ; Zanevsky, Yuri V.
Many QCD based and phenomenological models predict changes of hadron properties in a strongly interacting environment. The results of these models differ significantly and the experimental determination of hadron properties in nuclear matter is essential. In this paper we present a review of selected physics results obtained at GSI Helmholtzzentrum für Schwerionenforschung GmbH by HADES (High-Acceptance Di-Electron Spectrometer). The e+e− pair emission measured for proton and heavy-ion induced collisions is reported together with results on strangeness production. The future HADES activities at the planned FAIR facility are also discussed.
Lorenz, Manuel ; Agakishiev, Geydar ; Behnke, Claudia ; Belver, Daniel ; Belyaev, Alexei V. ; Berger-Chen, Jia-Chii ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Cabanelas Eiras, Pablo ; Dritsa, Christina ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fonte, Paulo ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; González-Díaz, Diégo ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Holzmann, Romain ; Huck, Patrick ; Höhne, Claudia ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Krizek, Filip ; Kuc, Hubert ; Kugler, Andrej ; Kurepin, Alexander ; Kurilkin, Aleksey K. ; Kurilkin, Pavel ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lang, Simon Martin ; Lapidus, Kirill ; Lebedev, Alexei ; Lopes, Luis Alberto Vieira ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Parpottas, Yannis ; Pechenov, Vladimir ; Pechenova, Olga ; Pietraszko, Jerzy ; Przygoda, Witold ; Ramstein, Béatrice ; Rehnisch, Laura ; Reshetin, Andrey ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schuldes, Heidi ; Siebenson, Johannes Stephan ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian Thomas ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Weber, Michael ; Wendisch, Christian ; Wüstenfeld, Jörn ; Yurevich, Sergey ; Zanevsky, Yuri V.
The knowledge of baryonic resonance properties and production cross sections plays an important role for the extraction and understanding of medium modifications of mesons in hot and/or dense nuclear matter. We present and discuss systematics on dielectron and strangeness production obtained with HADES on p+p, p+A and A+A collisions in the few GeV energy regime with respect to these resonances.
Lorenz, Manuel ; Agakishiev, Geydar ; Behnke, Claudia ; Belver, Daniel ; Belyaev, Alexei V. ; Berger-Chen, Jia-Chii ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Cabanelas Eiras, Pablo ; Chernenko, Sergey P. ; Dritsa, Christina ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fateev, Oleg ; Fonte, Paulo ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; González-Díaz, Diégo ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Höhne, Claudia ; Holzmann, Romain ; Huck, Patrick ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Krizek, Filip ; Kuc, Hubert ; Kugler, Andrej ; Kurepin, Alexander ; Kurilkin, Aleksey K. ; Kurilkin, Pavel ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lang, Simon Martin ; Lapidus, Kirill ; Lebedev, Alexei ; Lopes, Luis Alberto Vieira ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Parpottas, Yannis ; Pechenov, Vladimir ; Pechenova, Olga ; Pietraszko, Jerzy ; Przygoda, Witold ; Ramstein, Béatrice ; Rehnisch, Laura ; Reshetin, Andrey ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schuldes, Heidi ; Siebenson, Johannes Stephan ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian Thomas ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Weber, Michael ; Wendisch, Christian ; Wüstenfeld, Jörn ; Yurevich, Sergey ; Zanevsky, Yuri V.
The High Acceptance DiElectron Spectrometer HADES [1] is installed at the Helmholtzzentrum für Schwerionenforschung (GSI) accelerator facility in Darmstadt. It investigates dielectron emission and strangeness production in the 1-3 AGeV regime. A recent experiment series focusses on medium-modifications of light vector mesons in cold nuclear matter. In two runs, p+p and p+Nb reactions were investigated at 3.5 GeV beam energy; about 9·109 events have been registered. In contrast to other experiments the high acceptance of the HADES allows for a detailed analysis of electron pairs with low momenta relative to nuclear matter, where modifications of the spectral functions of vector mesons are predicted to be most prominent. Comparing these low momentum electron pairs to the reference measurement in the elementary p+p reaction, we find in fact a strong modification of the spectral distribution in the whole vector meson region.
Kurilkin, Pavel ; Agakishiev, Geydar ; Behnke, Claudia ; Belver, Daniel ; Belyaev, Alexei V. ; Berger-Chen, Jia-Chii ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Cabanelas Eiras, Pablo ; Chernenko, Sergey P. ; Dritsa, Christina ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fateev, Oleg ; Fonte, Paulo J. R. ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; González-Díaz, Diégo ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Holzmann, Romain ; Huck, Patrick ; Höhne, Claudia ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Krizek, Filip ; Kuc, Hubert ; Kugler, Andrej ; Kurepin, Alexander ; Kurilkin, Aleksey K. ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lang, Simon Martin ; Lapidus, Kirill ; Lebedev, Alexei ; Lopes, Luis Alberto Vieira ; Lorenz, Manuel ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Parpottas, Yannis ; Pechenov, Vladimir ; Pechenova, Olga ; Pietraszko, Jerzy ; Przygoda, Witold ; Ramstein, Béatrice ; Rehnisch, Laura ; Reshetin, Andrey ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schuldes, Heidi ; Siebenson, Johannes Stephan ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian Thomas ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Weber, Michael ; Wendisch, Christian ; Wüstenfeld, Jörn ; Yurevich, Sergey ; Zanevsky, Yuri V.
New results on the differential cross section in deuteron-proton elastic scattering are obtained at the deuteron kinetic energy of 2.5 GeV with the HADES spectrometer. The angular range of 69° – 125° in the center of mass system is covered. The obtained results are compared with the relativistic multiple scattering model calculation using the CD-Bonn deuteron wave function. The data at fixed scattering angles in the c.m. are in qualitative agreement with the constituent counting rules prediction.
Kurilkin, Aleksey K. ; Arnold, Oliver ; Atomssa, Ermias T. ; Behnke, Claudia ; Belyaev, Alexei V. ; Berger-Chen, Jia-Chii ; Biernat, Jacek ; Blanco, Alberto ; Blume, Christoph ; Böhmer, Michael ; Bordalo, Paula ; Chernenko, Sergey ; Deveaux, Christina Anna ; Dybczak, Adrian ; Epple, Eliane ; Fabbietti, Laura ; Fateev, Oleg ; Fonte, Paulo ; Franco, Celso ; Friese, Jürgen ; Fröhlich, Ingo ; Galatyuk, Tetyana ; Garzón, Juan A. ; Gill, Katharina ; Golubeva, Marina ; González-Díaz, Diégo ; Guber, Fedor ; Gumberidze, Malgorzata ; Harabasz, Szymon ; Hennino, Thierry ; Höhne, Claudia ; Holzmann, Romain ; Ierusalimov, Alexander P. ; Ivashkin, Alexander ; Jurkovič, Martin ; Kämpfer, Burkhard ; Karavicheva, Tatiana L. ; Kardan, Behruz ; Koenig, Ilse ; Koenig, Wolfgang ; Kolb, Burkhard W. ; Korcyl, Grzegorz ; Kornakov, Georgy ; Kotte, Roland ; Krása, Antonin ; Krebs, Erik ; Krizek, Filip ; Kuc, Hubert ; Kugler, Andrej ; Kunz, Tobias ; Kurepin, Alexei ; Kurilkin, Pavel ; Ladygin, Vladimir P. ; Lalik, Rafał Tomasz ; Lang, Simon Martin ; Lapidus, Kirill ; Lebedev, Alexander ; Lopes, Luis Alberto Vieira ; Lorenz, Manuel ; Maier, Ludwig W. ; Mangiarotti, Alessio ; Markert, Jochen ; Metag, Volker ; Michel, Jan ; Müntz, Christian ; Münzer, Robert Helmut ; Naumann, Lothar ; Palka, Marek ; Pechenov, Vladimir ; Pechenova, Olga ; Petousis, Vlasios ; Pietraszko, Jerzy ; Przygoda, Witold ; Ramstein, Béatrice ; Rehnisch, Laura ; Reshetin, Andrey ; Rost, Adrian ; Rustamov, Anar ; Sadovsky, Alexander ; Salabura, Piotr ; Scheib, Timo ; Schmidt-Sommerfeld, Korbinian ; Schuldes, Heidi ; Sellheim, Patrick ; Siebenson, Johannes Stephan ; Silva, Luis ; Sobolev, Yuri G. ; Spataro, Stefano ; Ströbele, Herbert ; Stroth, Joachim ; Strzempek, Paweł ; Sturm, Christian ; Svoboda, Ondřej ; Tarantola Peloni, Attilio ; Teilab, Khaled ; Tlustý, Pavel ; Traxler, Michael ; Tsertos, Haralabos ; Vasiliev, Taras A. ; Wagner, Vladimir ; Wendisch, Christian ; Wirth, Joana ; Wüstenfeld, Jörn ; Yurevich, Sergey ; Zanevsky, Yuri V.
We present the results of two-pion production in tagged quasi-free np collisions at a deutron incident beam energy of 1.25 GeV/c measured with the High-Acceptance Di-Electron Spectrometer (HADES) installed at GSI. The specific acceptance of HADES allowed for the first time to obtain high-precision data on π+π− and π−π0 production in np collisions in a region corresponding to large transverse momenta of the secondary particles. The obtained differential cross section data provide strong constraints on the production mechanisms and on the various baryon resonance contributions (∆∆, N(1440), N(1520), ∆(1600)). The invariant mass and angular distributions from the np → npπ+π −and np → ppπ−π0 reactions are compared with different theoretical model predictions.
Within the statistical model, the net strangeness conservation and incomplete total strangeness equilibration lead to the suppression of strange particle multiplicities. Furthermore, suppression effects appear to be stronger in small systems. By treating the production of strangeness within the canonical ensemble formulation we developed a simple model which allows to predict the excitation function of K+/π+ ratio in nucleus–nucleus collisions. In doing so we assumed that different values of K+/π+, measured in p + p and Pb + Pb interactions at the same collision energy per nucleon, are driven by the finite size effects only. These predictions may serve as a baseline for experimental results from NA61/SHINE at the CERN SPS and the future CBM experiment at FAIR.
In this paper a new method of experimental data analysis, the Particle-Set Identification method, is presented. The method allows to reconstruct moments of multiplicity distribution of identified particles. The difficulty the method copes with is due to incomplete particle identification – a particle mass is frequently determined with a resolution which does not allow for a unique determination of the particle type. Within this method the moments of order k are calculated from mean multiplicities of k-particle sets of a given type. The Particle-Set Identification method remains valid even in the case of correlations between mass measurements for different particles. This distinguishes it from the Identity method introduced by us previously to solve the problem of incomplete particle identification in studies of particle fluctuations.