82 research outputs found

    Novel low resistivity glass: MRPC detectors for ultra high rate applications

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    Abstract Multigap Resistive Plate Chambers (MRPCs) are often used as time-of-flight (TOF) detectors for high-energy physics and nuclear experiments thanks to their excellent time accuracy. For the Compressed Baryonic Matter (CBM) TOF system, MRPCs are required to work at particle fluxes on the order of 1-10 kHz/ c m 2 for the outer region and 10-25 kHz/ c m 2 for the central region. Better time resolution will allow particle identification with TOF techniques to be performed at higher momenta. From our previous studies, a time resolution of 25 ps has been obtained with a 20-gap MRPC of 140 μ m gap size with enhanced rate capbability. By using a new type of commercially available thin low-resistivity glass, further improvement MRPC rate capability is possible. In order to study the rate capability of the 10-gap MRPC built with this new low-resistivity glass, we have performed tests using the continuous electron beam at ELBE. This 10-gap MRPC, with 160 μ m gaps, reaches 97% efficiency at 19.2 kV and a time resolution of 36 ps at particle fluxes near 2 kHz/ c m 2 . At a flux of 100 kHz/ c m 2 , the efficiency is still above 95% and a time resolution of 50 ps is obtained, which would fulfil the requirement of CBM TOF system

    Measurement of global polarization of {\Lambda} hyperons in few-GeV heavy-ion collisions

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    The global polarization of {\Lambda} hyperons along the total orbital angular momentum of a relativistic heavy-ion collision is presented based on the high statistics data samples collected in Au+Au collisions at \sqrt{s_{NN}} = 2.4 GeV and Ag+Ag at 2.55 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at GSI, Darmstadt. This is the first measurement below the strangeness production threshold in nucleon-nucleon collisions. Results are reported as a function of the collision centrality as well as a function of the hyperon transverse momentum (p_T) and rapidity (y_{CM}) for the range of centrality 0--40%. We observe a strong centrality dependence of the polarization with an increasing signal towards peripheral collisions. For mid-central (20--40%) collisions the polarization magnitudes are (%) = 6.0 \pm 1.3 (stat.) \pm 2.0 (syst.) for Au+Au and (%) = 4.6 \pm 0.4 (stat.) \pm 0.5 (syst.) for Ag+Ag, which are the largest values observed so far. This observation thus provides a continuation of the increasing trend previously observed by STAR and contrasts expectations from recent theoretical calculations predicting a maximum in the region of collision energies about 3 GeV. The observed polarization is of a similar magnitude as predicted by 3D fluid dynamics and the UrQMD plus thermal vorticity model and significantly above results from the AMPT model.Comment: 8 pages, 4 figure

    Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions

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    In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pion–pion momentum correlations is investigated in Au + Au collisions at SNN\sqrt{^{S}NN} = 2.4 GeV. We show that the low-mt_{t} region (mt_{t} < 0.2 GeV / c2^{2}) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a Apart2/3A_{part}^{2/3} scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields

    Inclusive e+^+e^- production in collisions of pions with protons and nuclei in the second resonance region of baryons

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    Inclusive e+^+e^- production has been studied with HADES in π\pi^- + p, π\pi^- + C and π+CH2\pi^- + \mathrm{CH}_2 reactions, using the GSI pion beam at sπp\sqrt{s_{\pi p}} = 1.49 GeV. Invariant mass and transverse momentum distributions have been measured and reveal contributions from Dalitz decays of π0\pi^0, η\eta mesons and baryon resonances. The transverse momentum distributions are very sensitive to the underlying kinematics of the various processes. The baryon contribution exhibits a deviation up to a factor seven from the QED reference expected for the dielectron decay of a hypothetical point-like baryon with the production cross section constrained from the inverse γ\gamma nπ\rightarrow \pi^- p reaction. The enhancement is attributed to a strong four-momentum squared dependence of the time-like electromagnetic transition form factors as suggested by Vector Meson Dominance (VMD). Two versions of the VMD, that differ in the photon-baryon coupling, have been applied in simulations and compared to data. VMD1 (or two-component VMD) assumes a coupling via the ρ\rho meson and a direct coupling of the photon, while in VMD2 (or strict VMD) the coupling is only mediated via the ρ\rho meson. The VMD2 model, frequently used in transport calculations for dilepton decays, is found to overestimate the measured dielectron yields, while a good description of the data can be obtained with the VMD1 model assuming no phase difference between the two amplitudes. Similar descriptions have also been obtained using a time-like baryon transition form factor model where the pion cloud plays the major role.Comment: (HADES collaboration

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    Review

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    Review

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    Zur Kenntnis und Bestimmung der Kohlenhydrate

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    Kohlehydrate

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