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Register a new userStudy of the $pp to nppi^+$ reaction at 1.25 GeV with HADES
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T. Liu
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In pp collisions at 1.25 GeV kinetic energy, the HADES collaboration aimed at investigating the di-electron production related to $Delta$ (1232) Dalitz decay ($Delta^+ to pe^+e^-$). In order to constrain the models predicting the cross section and the production mechanisms of $Delta$ resonance, the hadronic channels have been measured and studied in parallel to the leptonic channels. The analyses of $ppto nppi^+$ and $ppto pppi^0$ channels and the comparison to simulations are presented in this contribution, in particular the angular distributions being sensitive to $Delta$ production and decay. The accurate acceptance corrections have been performed as well, which could be tested in all the phase space region thanks to the high statistic data. These analyses result in an overall agreement with the one-$pi$ exchange model and previous data.
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Inclusive production of e+e--pairs in pp and dp collisions at a kinetic beam energy of 1.25 GeV/u has been studied with the HADES spectrometer. In the latter case, the main goal was to obtain data on pair emission in quasi-free np collisions. To select this particular reaction channel the HADES experimental setup was extended with a Forward Wall hodoscope, which allowed to register spectator protons. Here, the measured invariant mass distributions demonstrate a strong enhancement of the pair yield for M > 140 MeV/c2 in comparison to pp data.
We present measurements of exclusive pi^{+,0} and eta production in pp reactions at 1.25 GeV and 2.2 GeV beam kinetic energy in hadron and dielectron channels. In the case of pi^+ and pi^0, high-statistics invariant-mass and angular distributions are obtained within the HADES acceptance as well as acceptance corrected distributions, which are compared to a resonance model. The sensitivity of the data to the yield and production angular distribution of Delta(1232) and higher lying baryon resonances is shown, and an improved parameterization is proposed. The extracted cross sections are of special interest in the case of pp to pp eta, since controversial data exist at 2.0 GeV; we find sigma =0.142 pm 0.022 mb. Using the dielectron channels, the pi^0 and eta Dalitz decay signals are reconstructed with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance corrected helicity angle distributions are found in good agreement with model predictions.
The tagged quasi-free $np to nppi^+pi^-$ reaction has been studied experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI at a deuteron incident beam energy of 1.25 GeV/nucleon ($sqrt s sim$ 2.42 GeV/c for the quasi-free collision). For the first time, differential distributions for $pi^{+}pi^{-}$ production in $np$ collisions have been collected in the region corresponding to the large transverse momenta of the secondary particles. The invariant mass and angular distributions for the $nprightarrow nppi^{+}pi^{-}$ reaction are compared with different models. This comparison confirms the dominance of the $t$-channel with $DeltaDelta$ contribution. It also validates the changes previously introduced in the Valencia model to describe two-pion production data in other isospin channels, although some deviations are observed, especially for the $pi^{+}pi^{-}$ invariant mass spectrum. The extracted total cross section is also in much better agreement with this model. Our new measurement puts useful constraints for the existence of the conjectured dibaryon resonance at mass M$sim$ 2.38 GeV and with width $Gammasim$ 70 MeV.
We report on the investigation of $Delta$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $ppe^{+}e^{-}$ and $ppe^{+}e^{-}gamma$ have been studied and compared with the partial wave analysis of the hadronic $pppi^{0}$ channel. They allow to access both $Delta^+ to ppi^0(e^+e^-gamma)$ and $Delta^+ to pe^+e^-$ Dalitz decay channels. The perfect reconstruction of the well known $pi^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $Delta$ Dalitz decay is identified for the first time and the sensitivity to N-$Delta$ transition form factors is tested. The $Delta$(1232) Dalitz decay branching ratio is also determined for the first time; our result is (4.19 $pm$ 0.62 syst. $pm$ 0.34 stat.) $times $ 10$^{-5}$, albeit with some model dependence.
Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25 GeV is investigated. The multi-differential data were measured by the HADES collaboration. Exclusive channels with one pion in the final state ($nppi^{+}$ and $pppi^{0}$) were put to extended studies based on various observables in the framework of a one-pion exchange model and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The results of the PWA confirm the dominant contribution of the $Delta$(1232), yet with a sizable impact of the $N$(1440) and non-resonant partial waves.
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