arXiv subjects

K. Piasecki

Publications and source records attributed to K. Piasecki.

30 records · Page 2Linked to original sources

arXiv2019

Wide acceptance measurement of the K$^-$/K$^+$ ratio from Ni+Ni collisions at 1.91A GeV

The FOPI Collaboration at the GSI SIS-18 synchrotron measured charged kaons from central and semi-central collisions of Ni+Ni at a beam energy of 1.91A GeV. We present the distribution of the K$^-$\K$^+$ ratio on the energy vs polar angle plane in the nucleon-nucleon center-of-mass frame, with and without subtraction of the contribution of $ϕ$(1020) meson decays to the K$^-$ yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The ratio of K$^-$ to K$^+$ energy spectra is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate that after inclusion of the $ϕ$ meson decay contribution to the K$^-$ production no difference between the slopes of the K$^-$ and K$^+$ energy spectra is observed within uncertainties. For our data a linear fit to this ratio obtained after subtraction of the $ϕ$ meson contribution still shows a decrease with kinetic energy, although a constant value cannot be rejected. The contribution of $Λ(1520) \rightarrow p\text{K}^-$ decays estimated from fitting the thermal model to the experimental yields appears to be another factor of moderate relevance.

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arXiv2018

Determination of N* amplitudes from associated strangeness production in p+p collisions

We present the first determination of the energy-dependent production amplitudes of N$^{*}$ resonances with masses between 1650 MeV/c$^{2}$ and 1900 MeV/c$^{2}$ for an excess energy between $0$ and $600$ MeV. A combined Partial Wave Analysis of seven exclusively reconstructed data samples for the reaction p+p $\rightarrow pKΛ$ measured by the COSY-TOF, DISTO, FOPI and HADES collaborations in fixed target experiments at kinetic energies between 2.14 and 3.5 GeV is used to determine the amplitude of the resonant and non-resonant contributions.

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arXiv2017

Nuclear medium modifications of properties of kaons measured around threshold with FOPI

We report on the investigation of modifications of basic properties of K$^+$ and K$^-$ mesons emitted from collisions of Ni+Ni at beam energy of 1.91A GeV. Experimental K$^-$/K$^+$ ratio are presented in a wide range of phase space parameterized by kinetic energy and emission angle in the nucleon-nucleon centre of mass. The $v_1$ component of the azimuthal distribution was extracted as a function of rapidity and transverse momentum for central, and semi-peripheral collisions. A comparison of these patterns with the HSD transport model favours the existence of the kaon-nucleon in-medium potential. For the IQMD model, this interaction scenario is confirmed in case of K$^-$, whereas for K$^+$ the picture is less clear.

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arXiv2016

Centrality dependence of subthreshold $ϕ$ meson production in Ni+Ni collisions at 1.9A GeV

We analysed the $ϕ$ meson production in central Ni+Ni collisions at the beam kinetic energy of 1.93A GeV with the FOPI spectrometer and found the production probability per event of $[8.6 ~\pm~ 1.6 ~(\text{stat}) \pm 1.5 ~(\text{syst})] \times 10^{-4}$. This new data point allows for the first time to inspect the centrality dependence of the subthreshold $ϕ$ meson production in heavy-ion collisions. The rise of $ϕ$ meson multiplicity per event with mean number of participants can be parameterized by the power function with exponent $α= 1.8 \pm 0.6$. The ratio of $ϕ$ to $\text{K}^-$ production yields seems not to depend within the experimental uncertainties on the collision centrality, and the average of measured values was found to be $0.36 \pm 0.05$.

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arXiv2016

Strange meson production in Al+Al collisions at 1.9A GeV

The production of K$^+$, K$^-$ and $φ$(1020) mesons is studied in Al+Al collisions at a beam energy of 1.9A GeV which is close or below the production threshold in NN reactions. Inverse slopes, anisotropy parameters, and total emission yields of K$^{\pm}$ mesons are obtained. A comparison of the ratio of kinetic energy distributions of K$^-$ and K$^+$ mesons to the HSD transport model calculations suggests that the inclusion of the in-medium modifications of kaon properties is necessary to reproduce the ratio. The inverse slope and total yield of $ϕ$ mesons are deduced. The contribution to K$^-$ production from $ϕ$ meson decays is found to be [17 $\pm$ 3 (stat) $^{+2}_{-7}$ (syst)] %. The results are in line with previous K$^{\pm}$ and $ϕ$ data obtained for different colliding systems at similar incident beam energies.

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arXiv2014

Influence of $ϕ$ mesons on negative kaons in Ni+Ni collisions at 1.91A GeV beam energy

$ϕ$ and K$^-$ mesons from Ni+Ni collisions at the beam energy of 1.91A GeV have been measured by the FOPI spectrometer, with a trigger selecting central and semi-central events amounting to 51% of the total cross section. The phase space distributions, and the total yield of K$^-$, as well as the kinetic energy distribution and the total yield of $ϕ$ mesons are presented. The $ϕ$\K$^-$ ratio is found to be $0.44 \pm 0.07(\text{stat}) ^{+0.18}_{-0.12} (\text{syst})$, meaning that about 22% of K$^-$ mesons originate from the decays of $ϕ$ mesons, occurring mostly in vacuum. The inverse slopes of direct kaons are up to about 15 MeV larger than the ones extracted within the one-source model, signalling that a considerable share of gap between the slopes of K$^+$ and K$^-$ could be explained by the contribution of $ϕ$ mesons to negative kaons.

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arXiv2014

Azimuthal Emission Patterns of $K^{+}$ and of $ K^{-} $ Mesons in Ni + Ni Collisions near the Strangeness Production Threshold

Azimuthal emission patterns of $K^\pm$ mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum $p_{T}$ integrated directed and elliptic flow of $K^{+}$ and $K^{-}$ mesons as well as the centrality dependence of $p_{T}$ - differential directed flow of $K^{+}$ mesons are compared to the predictions of HSD and IQMD transport models. The data exhibits different propagation patterns of $K^{+}$ and $K^{-}$ mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for $K^{+}$ mesons and attractive for $K^{-}$ mesons.

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arXiv2011

Systematics of azimuthal asymmetries in heavy ion collisions in the 1 A GeV regime

Using the large acceptance apparatus FOPI, we study central and semi-central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include directed and elliptic flow. The data are compared to earlier data where possible and to transport model simulations. A stiff nuclear equation of state is found to be incompatible with the data. Evidence for extra-repulsion of neutrons in compressed asymmetric matter is found.

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arXiv2010

Systematics of central heavy ion collisions in the 1A GeV regime

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations.

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arXiv2010

Measurement of $K^*(892)^0$ and $K^0$ mesons in Al+Al collisions at 1.9$A$ GeV

New measurement of sub-threshold $K^*(892)^0$ and $K^0$ production is presented. The experimental data complete the measurement of strange particles produced in Al+Al collisions at 1.9$A$ GeV measured with the FOPI detector at SIS/GSI. The $K^*(892)^0$ / $K^0$ yield ratio is found to be $0.0315\pm 0.006 (\mathrm{stat.})\pm 0.012 (\mathrm{syst.})$ and is in good agreement with the UrQMD model prediction. These measurements provide information on in-medium cross section of $K^+$ - $π^-$ fusion which is the dominant process on sub-threshold $K^*(892)^0$ production.

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arXiv2010

Emission patterns of neutral pions in 40 A MeV Ta+Au reactions

Differential cross sections of neutral pions emitted in 181Ta + 197Au collisions at a beam energy of 39.5A MeV have been measured with the photon spectrometer TAPS. The kinetic energy and transverse momentum spectra of neutral pions cannot be properly described in the framework of the thermal model, nor when the reabsorption of pions is accounted for in a phenomenological model. However, high energy and high momentum tails of the pion spectra can be well fitted through thermal distributions with unexpectedly soft temperature parameters below 10 MeV.

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arXiv2009

Measurement of the in-medium K0 inclusive cross section in pi- -induced reactions at 1.15 GeV/c

The K0 meson production by pi- mesons of 1.15 GeV/c momentum on C, Al, Cu, Sn and Pb nuclear targets was measured with the FOPI spectrometer at the SIS accelerator of GSI. Inclusive production cross-sections and the momentum distributions of K0 mesons are compared to scaled elementary production cross-sections and to predictions of theoretical models describing the in-medium production of kaons. The data represent a new reference for those models, which are widely used for interpretation of the strangeness-production in heavy-ion collisions. The presented results demonstrate the sensitivity of the kaon production to the reaction amplitudes inside nuclei and point to the existence of a repulsive KN-potential of 20+-5 MeV at normal nuclear matter density.

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