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Jagiellonian University Repository

# Resonance production and decays in nucleon-nucleon collisions with HADES

 dc.contributor.author Przygoda, Witold [SAP11016049] pl dc.date.accessioned 2018-05-11T13:18:07Z dc.date.available 2018-05-11T13:18:07Z dc.date.issued 2018 pl dc.identifier.isbn 978-83-60391-99-0 pl dc.identifier.uri https://ruj.uj.edu.pl/xmlui/handle/item/54251 dc.language eng pl dc.rights Udzielam licencji. Uznanie autorstwa 3.0 Polska * dc.rights.uri http://creativecommons.org/licenses/by/3.0/pl/legalcode * dc.title Resonance production and decays in nucleon-nucleon collisions with HADES pl dc.type Book pl dc.pubinfo Kraków : Jagiellonian University pl dc.description.physical [4], VI, 202 pl dc.description.additional Bibliogr. s. 181-202 pl dc.abstract.en The High Acceptance Di-Electron Spectrometer (HADES), installed at GSI, allows to study both hadron and rare dilepton production in a fixed target experiments in the beam energy range of a few GeV per nucleon, reaching up to 4.5 GeV for a proton beam and 1.5 GeV/nucleon for a heavy-ion beam. The present interpretation of dilepton spectra measured in heavy-ion reactions at various energies is based on hadronic models. They predict in-medium modifications of the $\rho$−meson spectral function due to its coupling to resonance-hole states. In the energy range of the HADES experiments, the $\rho$−meson can be produced in primary NN or secondary $\pi$ N collisions. The measurement of a dielectron emission in elementary reactions opens the possibility to constrain the interpretation of medium effects and better understand the relation between the couplings of the baryonic resonances to the $\rho$−meson. The Dalitz decay of baryonic resonances $(R \rightarrow Ne^{+}e^{-})$ gives access to the electromagnetic structure of baryonic transitions in a timelike region at small positive values of the squared fourmomentum transferred, where couplings to light vector $\rho /\omega$ mesons are expected. In this monograph the systematic studies of resonance excitation and decays, measured in NN collisions with the increasing energy, are presented. First, the pp collisions at 1.25 GeV allowed to measure exclusive channels with one-pion in the final state. They were put to extended studies based on various observables in one-pion exchange models and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The obtained $\Delta$ (1232) production cross section was further used for the first experimental extraction of the $\Delta$ Dalitz decay and compared to the models of the electromagnetic transition form factors. The branching ratio of this decay, achieved in the exclusive $pp \rightarrow ppe^{+}e^{-}$ channel, has been included in the 2018 Review of Particle Physics. In quasi-free np collisions at 1.25 GeV, two-pion production was studied to conclude on double−$\Delta$, N(1440), and $\Delta$ (1600) excitation with the aim of studying the production of the $\rho$−meson in the isospin I = 1 channel. In addition, this analysis provided an independent verification of the existence of the $d^{\ast }$(2370) resonance observed by the WASA Collaboration. Furthermore, a strong excess of the dielectron yield, in comparison to the pp reaction at 1.25 GeV, was observed in the $e^{+}e^{-}$ inclusive channel. This reaction is well suited for studies of the np bremsstrahlung with strong isospin effects effects predicted by one-boson-exchange models. The excess was confirmed also in the $e^{+}e^{-}$ exclusive channel and the data were compared with the models explaining the enhancement at large invariant masses due to the off-shell $\rho$−meson production. The exclusive hadronic channels with one-pion and rho−meson were identified in pp collisions at 2.2 GeV. The $\pi ^{0}$ and eta exclusive production cross sections were extracted and compared to the predictions of a resonance model. Further, the analysis of the $ppe^{+}e^{-}$ exclusive channel allowed for the reconstruction of $\pi ^{0}$ and $\eta$ Dalitz decays. The angular distributions of $e^{+} or e^{−}$ in the $\gamma^{\ast }$ rest frame were determined to be in agreement with the QED prediction for pseudoscalar mesons. In the pp collisions measured at energy T = 3.5 GeV, a peak corresponding to direct $\omega$ decays, with 2% mass resolution, was reconstructed. The inclusive production cross sections for $\omega$ and $\rho$ mesons were determined from dielectron experimental data for the first time at this energy. In addition, the upper bound for the direct $\eta \rightarrow e^{+}e^{-}$ decay was defined. The exclusive one pion production $(pp \rightarrow pp\pi ^{0}$ and $pp \rightarrow np\pi ^{+})$ and dielectron $(pp \rightarrow ppe^{+}e^{-})$ channels were used to extract the $N^{\ast }$ and $\Delta$ resonance production cross sections. The $e^{+}e^{-}$ emission from baryonic decays was identified with the dielectron invariant mass distribution strongly modified by the intermediate rho−meson. This observation has been interpreted within the Vector Dominance Model of the resonance electromagnetic transition form factor. Comparison with various transport models (PYTHIA, GiBUU/SMASH, HSD, UrQMD) unraveled the ambiguities of the model descriptions and the important role of the intermediate rho production. To tackle this problem a systematic investigation focused on the role of N(1520) production and decay in pion-induced reactions was started. Data at four different pion beam momenta (656, 690, 748 and 800 MeV/c) were collected in $\pi ^{−}p$ collisions. In the outlook, exclusive channels with one pion $(\pi ^{−} p)$, two pions $(n\pi ^{+} \pi ^{−})$ and dileptons $(ne^{+} e^{−})$ in the final state were discussed, with a special interest for the rhoN channel, since it has a direct impact on the in-medium distortions of the $\rho$−meson spectral function. Pion beam experiments will be continued in GSI in the next years, then the HADES experimental program will be pursued using the proton and ion beams at FAIR. This monograph has been extended by Appendices covering details on dielectron production channels as well as the models of the electromagnetic transition form factors for baryon resonance Dalitz decays. The HADES spectrometer and the analysis strategy were described, too. The author hopes that this book will serve not only as a report on the scientific achievements but also as a source of information on resonance production and decays in nucleon-nucleon collisions at energies of a few GeV. pl dc.subject.pl rezonanse barionowe pl dc.subject.pl mezony pl dc.subject.pl rozpady barionów pl dc.subject.pl rozpady mezonów pl dc.subject.pl rozpad Dalitza pl dc.subject.pl modele rezonansowe pl dc.subject.pl analiza fal parcjalnych pl dc.subject.pl algorytmy identyfikacji sygnału pl dc.subject.en baryon resonances pl dc.subject.en mesons pl dc.subject.en baryon decays pl dc.subject.en meson decays pl dc.subject.en Dalitz decay pl dc.subject.en resonance model pl dc.subject.en partial wave analysis pl dc.subject.en algorithms of signal identification pl dc.description.publication 14 pl dc.participation Przygoda, Witold: 100%; pl dc.affiliation Wydział Fizyki, Astronomii i Informatyki Stosowanej : Instytut Fizyki im. Mariana Smoluchowskiego pl dc.subtype Monography pl dc.rights.original CC-BY; otwarte repozytorium; ostateczna wersja wydawcy; przed opublikowaniem; 0 pl dc.publisher.ministerial Uniwersytet Jagielloński w Krakowie pl