1,323 research outputs found

    Electron Collision Cross Sections in Tetrafluoropropene HFO1234ze(E) for Gas Mixtures in Resistive Plate Chambers

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    In recent years, there has been growing interest in tetrafluoropropene HFO1234ze(E) (C3_{3}H2_{2}F4_{4}) for Resistive Plate Chambers (RPCs). This novel gas is considered a promising alternative to the standard mixtures currently used in RPCs, thanks to its low global warming potential. The knowledge of electron collision cross sections in C3_{3}H2_{2}F4_{4} enables reliable predictions of electron transport coefficients and reaction rates in C3_{3}H2_{2}F4_{4}-based gas mixtures. This allows for optimizing the C3_{3}H2_{2}F4_{4}-based gas mixtures to achieve the desired performance in RPCs. From measurements of electron transport coefficients and reaction rates, a complete set of scattering cross sections for electrons in C3_{3}H2_{2}F4_{4} has been derived. Validation of the electron collision cross sections is achieved through systematic comparisons of electron swarm parameters with experimental data in both pure C3_{3}H2_{2}F4_{4} and C3_{3}H2_{2}F4_{4}/CO2_{2} gas mixtures. Given the influence of electron attachment in C3_{3}H2_{2}F4_{4} by the gas density, this work also includes precise calculations of the critical electric field strength in such mixtures. This set of cross sections has been further utilized to compute the effective ionization Townsend coefficient in gas mixtures containing C3_{3}H2_{2}F4_{4}, potentially applicable for RPCs.Comment: Added section "Tetrafluoropropene-based Gas Mixtures for Resistive Plate Chambers

    On the electromagnetic energy resolution of Cherenkov-fiber calorimeters

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    Electromagnetic calorimeters which sample the Cherenkov radiation of shower particles in optical fibers operate in a markedly different manner from calorimeters which rely on the dE/dx of shower particles. The well-understood physics of electromagnetic shower development is applied to the case of Cherenkov-fiber calorimetry (also known as quartz fiber calorimetry) and the results of systematically performed studies are considered in detail to derive an understanding of the critical parameters involved in energy measurement using such calorimeters. A quantitative parameterization of Cherenkov-fiber calorimetry electromagnetic energy resolution is proposed and compared with existing experimental results

    Quartz fiber calorimetry

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    The fundamentals of a new electromagnetic and hadronic sampling calorimetry based on the detection of Cherenkov light generated in quartz optical fibers are presented. Optical fibers transport light only in a selected angular range which results in a non-obvious and absolutely unique characteristic for this new technique: showers of very narrow visible energy. In addition, the technique is characterized by radiation resistance measured in Gigarads and nanosecond signal duration. Combined, these properties make quartz fiber calorimetry a very promising technique for high intensity heavy ion experiments and for the high pseudorapidity regions of high intensity collider experiments. The results of beam tests and simulations are used to illustrate the basic properties and peculiar characteristics of this recent development

    The ALICE Zero Degree Calorimeters

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    In the ALICE experiment at Cern LHC, a set of hadron calorimeters will be used to determine the centrality of the Pb-Pb collision. The spectator protons and neutrons, will be separated from the ion beams, using the separator magnet (D1) of the LHC beam optics and respectively detected by a proton (ZP) and a neutron (ZN) "Zero-degree Calorimeter" (ZDC). The detectors will be placed in front of the separator D2 magnet, 115 meters away from the beam intersection point. The ZDCs are quartz-fiber spaghetti calorimeters that exploit the Cherenkov light produced by the shower particles in silica optical fibers.This technique offers the advantages of high radiation hardness (up to several Grad), fast response and reduced lateral dimension of the detectable shower. In addition, quartz-fiber calorimeters are intrinsically insensitive to radio-activation background, which produces particles below the Cherenkov threshold.The ALICE ZDC should have an energy resolution comparable with the intrinsic energy fluctuations, which range from about 20 0.000000or central events to about 5 0.000000or peripheral ones, according to simulations that use HIJING as event generator. The fiber-to-absorber filling ratio must be chosen as a good compromise between the required energy resolution and the fiber cost.The design of the proposed calorimeter will be discussed, together with the expected performances. Whenever possible, the simulated results will be compared with the experimental ones, obtained with the built prototypes and with the NA50 ZDC, which can be considered as a working prototype for the ALICE neutron calorimeter
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