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Register a new userInclusive dielectron spectra in p+p collisions at 3.5 GeV
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We present the inclusive invariant-mass, transverse momentum and rapidity distributions of dielectrons (e$^{+}$e$^{-}$ pairs) in p+p interactions at 3.5 GeV beam kinetic energy. In the vector-meson mass region, a distinct peak corresponding to direct $omega$ decays is reconstructed with 2% mass resolution. The data is compared to predictions from three model calculations. Due to the large acceptance of the HADES apparatus for $e^{+}e^{-}$ invariant masses above 0.2 GeV/$c^{2}$ and for transverse pair momenta p$_{t}$ $ <$ 1 GeV/$c$, acceptance corrections are to a large extent model independent. This allows us to extract from dielectron data for the first time at this energy the inclusive production cross sections for light vector mesons. Inclusive production cross sections for $pi^o$ and $eta$ mesons are also reported. The obtained results will serve as an important reference for the study of vector meson production in proton-nucleus and heavy-ion collisions. Furthermore, using this data, an improved value for the upper bound of the branching ratio for direct $eta$ decays into the electron-positron channel is obtained.
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Data on inclusive pion and eta production measured with the dielectron spectrometer HADES in the reaction p+93Nb at a kinetic beam energy of 3.5 GeV are presented. Our results, obtained with the photon conversion method, supplement the rather sparse information on neutral meson production in proton-nucleus reactions existing for this bombarding energy regime. The reconstructed e+e-e+e- transverse-momentum and rapidity distributions are confronted with transport model calculations, which account fairly well for both pi0 and eta production.
Measurements of dielectron production in p+p and p+d collisions with beam kinetic energies from 1.04 to 4.88 GeV are presented. The differential cross section is presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the mass spectra and their evolution with beam energy provide information about the relative importance of the various dielectron production mechanisms in this energy regime. The p+d to p+p ratio of the dielectron yield is also presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the transverse momentum and rapidity spectra from the p+d and p+p systems are found to be similar to one another for each of the beam energies studied. The beam energy dependence of the integrated cross sections is also presented.
An exclusive analysis of the 4-body final states $mathrm{Lambda + p + pi^{+} + K^{0}}$ and $mathrm{Sigma^{0} + p + pi^{+} + K^{0}}$ measured with HADES for p+p collisions at a beam kinetic energy of 3.5 GeV is presented. The analysis uses various phase space variables, such as missing mass and invariant mass distributions, in the four particle event selection (p, $pi^+$, $pi^+$, $pi^-$) to find cross sections of the different production channels, contributions of the intermediate resonances $mathrm{Delta^{++}}$ and $mathrm{Sigma(1385)^{+}}$ and corresponding angular distributions. A dominant resonant production is seen, where the reaction $mathrm{Lambda + Delta^{++} + K^{0}}$ has an about ten times higher cross section ($mathrm{29.45pm0.08^{+1.67}_{-1.46}pm2.06,mu b}$) than the analogous non-resonant reaction ($mathrm{2.57pm0.02^{+0.21}_{-1.98}pm0.18,mu b}$). A similar result is obtained in the corresponding $Sigma^{0}$ channels with $mathrm{9.26pm0.05^{+1.41}_{-0.31}pm0.65, mu b}$ in the resonant and $mathrm{1.35pm0.02^{+0.10}_{-1.35}pm0.09,mu b}$ in the non-resonant reactions.
The inclusive production of {Lambda} hyperons in proton-proton collisions at $sqrt{s}$ = 3.18 GeV was measured with HADES at the GSI Helmholtzzentrum fur Schwerionenforschung in Darmstadt. The experimental data are compared to a data-based model for individual exclusive {Lambda} production channels in the same reaction. The contributions of intermediate resonances such as {Sigma}(1385), {Delta}++ or N* are considered in detail. In particular, the result of a partial wave analysis is accounted for the abundant pK$^+${Lambda} final state. Model and data show a reasonable agreement at mid rapidities, while a difference is found for larger rapidities. A total {Lambda} production cross section in p+p collisions at $sqrt{s}$ = 3.18 GeV of {sigma}(pp $to$ {Lambda} + X) = 207.3 $pm$ 1.3 +6.0 -7.3 (stat.) $pm$ 8.4 (syst.) +0.4 -0.5 (model) {mu}b is found.
Results on the production of the double-strange cascade hyperon $mathrm{Xi^-}$ are reported for collisions of p,(3.5~GeV),+,Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time, subthreshold $mathrm{Xi^-}$ production is observed in proton-nucleus interactions. Assuming a $mathrm{Xi^-}$ phase-space distribution similar to that of $mathrm{Lambda}$ hyperons, the production probability amounts to $P_{mathrm{Xi^-}}=(2.0,pm0.4,mathrm{(stat)},pm 0.3,mathrm{(norm)},pm 0.6,mathrm{(syst)})times10^{-4}$ resulting in a $mathrm{Xi^-/(Lambda+Sigma^0)}$ ratio of $P_{mathrm{Xi^-}}/ P_{mathrm{Lambda+Sigma^0}}=(1.2pm 0.3,mathrm{(stat)}pm0.4,mathrm{(syst)})times10^{-2}$. Available model predictions are significantly lower than the estimated $mathrm{Xi^-}$ yield.
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