111 research outputs found

    Characteristic properties of Planacon MCP-PMTs

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    A systematic investigation of Planacon MCP-PMTs was performed using 64 XP85002/ FIT-Q photosensors. These devices are equipped with microchannel plates of reduced resistance. Results of a study of their gain stability over time and saturation level in terms of the average anode current are presented. This information allows one to determine the lower limit of the MCP resistance for stable Planacon operation. The spread of the electron multiplication characteristics for the entire production batch is also presented, indicating the remarkably low voltage requirements of these MCP-PMTs. Detection efficiency and noise characteristics, such as dark count rate and afterpulsing level, are also reviewed.Peer reviewe

    Status of the GAMMA-400 Project

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    The preliminary design of the new space gamma-ray telescope GAMMA-400 for the energy range 100 MeV - 3 TeV is presented. The angular resolution of the instrument, 1-2{\deg} at E{\gamma} ~100 MeV and ~0.01^{\circ} at E{\gamma} > 100 GeV, its energy resolution ~1% at E{\gamma} > 100 GeV, and the proton rejection factor ~10E6 are optimized to address a broad range of science topics, such as search for signatures of dark matter, studies of Galactic and extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission, gamma-ray bursts, as well as high-precision measurements of spectra of cosmic-ray electrons, positrons, and nuclei.Comment: 6 pages, 1 figure, 1 table, submitted to Advances in Space Researc

    Elliptic flow of charged particles at midrapidity relative to the spectator plane in Pb–Pb and Xe–Xe collisions

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    Measurements of the elliptic flow coefficient relative to the collision plane defined by the spectator neutrons v2{ SP} in collisions of Pb ions at center-of-mass energy per nucleon–nucleon pair √ 2.76 TeV and Xe ions at √ sNN = sNN =5.44 TeV are reported. The results are presented for charged particles produced at midrapidity as a function of centrality and transverse momentum for the 5–70% and 0.2–6 GeV/c ranges, respectively. The ratio between v2{ SP} and the elliptic flow coefficient relative to the participant plane v2{4}, estimated using four-particle correlations, deviates by up to 20% from unity depending on centrality. This observation differs strongly from the magnitude of the corresponding eccentricity ratios predicted by the TRENTo and the elliptic power models of initial state fluctuations that are tuned to describe the participant plane anisotropies. The differences can be interpreted as a decorrelation of the neutron spectator plane and the reaction plane because of fragmentation of the remnants from the colliding nuclei, which points to an incompleteness of current models describing the initial state fluctuations. A significant transverse momentum dependence of the ratio v2{ SP}/v2{4} is observed in all but the most central collisions, which may help to understand whether momentum anisotropies at low and intermediate transverse momentum have a common origin in initial state f luctuations. The ratios of v2{ SP} and v2{4} to the corresponding initial state eccentricities for Xe–Xe and Pb–Pb collisions at similar initial entropy density show a difference of (7.0 ±0.9)%with an additional variation of +1.8% when including RHIC data in the TRENTo parameter extraction. These observations provide new experimental constraints for viscous effects in the hydrodynamic modeling of the expanding quark–gluon plasma produced in heavy-ion collisions at the LHC

    First measurement of Ωc0 production in pp collisions at s=13 TeV

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    The inclusive production of the charm–strange baryon 0 c is measured for the first time via its hadronic √ decay into −π+ at midrapidity (|y| <0.5) in proton–proton (pp) collisions at the centre-of-mass energy s =13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2 < pT < 12 GeV/c. The pT dependence of the 0 c-baryon production relative to the prompt D0-meson and to the prompt 0 c-baryon production is compared to various models that take different hadronisation mechanisms into consideration. In the measured pT interval, the ratio of the pT-integrated cross sections of 0 c and prompt + c baryons multiplied by the −π+ branching ratio is found to be larger by a factor of about 20 with a significance of about 4σ when compared to e+e− collisions

    Performance of the cost-effective Planacon Âź MCP-PMTs in strong magnetic fields

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    We present the behavior of the cost-effective Planacon MCP-PMTs with pore diameter in the presence of axial magnetic fields up to 0.5 T. Having a batch of 62 devices of the same type, two MCP-PMTs were selected and their gain variation measured in different magnetic fields. These two otherwise identical devices satisfied the selection criteria by requiring the lowest (1.15 kV) and one of the highest (1.4 kV) bias voltage values to achieve a given gain. Both MCP-PMTs have a nearly identical tolerance of the strong magnetic field despite the significant difference in the bias voltage. This clarifies the mechanism of the B-field influence on the MCP-PMT gain, emphasizing the importance of the intrinsic parameters of the MCP emissive coating rather than external parameters, such as the total bias voltage. By evaluating the dependence of both gain and timing parameters on the magnetic field strength, we confirm the operability of such MCP-PMTs in strong magnetic fields in spite of the relatively large pore diameter and low bias voltage required for a given gain.peerReviewe

    Luminosity determination in ALICE with T0 and V0 detectors

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    The contributions of the two ALICE forward detectors, V0 and T0, to the luminosity and multiplicity study, and beam diagnostics are discussed. Already the runs during the LHC commissioning period should provide sufficient data for luminosity and multiplicity determination and for establishing the position of the interaction point along longitudinal and transverse axis. Precise determination of the relative luminosity and its monitoring is required as it enters to the cross section calculations of all physics processes. The goal is to keep the systematic error of the relative luminosity in ALICE within 5 %
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