412 research outputs found

    Design and Performance of Fast, a Tracker for Antiproton Physics

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    The antiproton annihilation cross section on different nuclei was measured by the OBELIX collaboration at LEAR (CERN) during the '80s and '90s; its dependence on the atomic mass number A, in the momenta range 200-800 MeV/c, was found to be A^2/3. Low statistics measurements at lower energies (60 MeV/c) showed some anomalies that suggested the need for new experiments to investigate about them and to increase statistics. For these reasons, a new pbar cross section experiment has been proposed at the end of 2004, and a scintillating fiber tracker (FAST, Fiber Antiproton Scintillating Tracker) has been built to perform a direct annihilation cross section measurement at the Antiproton Decelerator (AD) at CERN. This thesis work decribes the design and the development of the detector, its assembly and commissioning phase results. The tests with a prototype and the comparisons with a Montecarlo simulation are reported too. In the last part, the data taking setups of September 2006 and July 2007 are presented

    Optical Channeling of Low Energy Antiprotons in Thin Crystal Targets

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    A relevant aspect of the interactions between charged fermions and crystal targets is coherence, which can exist at both classical and quantum levels. In the case of antiprotons crossing crystal targets, there are theories and measurements of classical-level coherence effects, in particular, channeling effects. For the present study, we assume the existence of a low-energy regime where the electrostatic interactions between an antiproton and the crystal atoms lead to a local loss in the beam flux as their leading effect. We expect this assumption to be well-justified for antiproton (p over bar ) energies below 100 eV, with a progressive transition to a standard "Rutherford regime" in the energy range 100-1000 eV. Under these conditions, the target can be treated as an optical absorber with a periodical structure, which can be simplified by considering a multi-layer planar structure only. As in standard optics, wave absorption is accompanied by interference and diffraction. Assuming sub-nanometer ranges for the relevant parameters and a realistic angular spread for the antiproton beam, we find narrow-angle focusing effects that reproduce the classical channeling effect at a qualitative level. We also find that diffraction dominates over interference, although this may strongly depend on the target details

    A hydrogen beam to characterize the ASACUSA antihydrogen hyperfine spectrometer

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    The antihydrogen programme of the ASACUSA collaboration at the antiproton decelerator of CERN focuses on Rabi-type measurements of the ground-state hyperfine splitting of antihydrogen for a test of the combined Charge-Parity-Time symmetry. The spectroscopy apparatus consists of a microwave cavity to drive hyperfine transitions and a superconducting sextupole magnet for quantum state analysis via Stern-Gerlach separation. However, the small production rates of antihydrogen forestall comprehensive performance studies on the spectroscopy apparatus. For this purpose a hydrogen source and detector have been developed which in conjunction with ASACUSA's hyperfine spectroscopy equipment form a complete Rabi experiment. We report on the formation of a cooled, polarized, and time modulated beam of atomic hydrogen and its detection using a quadrupole mass spectrometer and a lock-in amplification scheme. In addition key features of ASACUSA's hyperfine spectroscopy apparatus are discussed.

    Antiparticle cloud temperatures for antihydrogen experiments

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    An analysis of positron and antiproton cloud temperatures under condition similar to those found in antihydrogen experiments.Some simple general trends are brought out in the analysis, which includes the effects of cloud expansion for the first time

    Intravenous thrombolysis in the emergency department for the treatment of acute ischaemic stroke

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    BACKGROUND AND AIMS: Thrombolytic therapy with intravenous recombinant tissue plasminogen activator (rt-PA) improves outcome in patients with ischaemic stroke treated within 3 h of symptom onset, but its extended implementation is limited. A pilot study was designed to verify whether evaluation of patients with acute ischaemic stroke and their treatment with intravenous rt-PA in the emergency department (ED), followed by transportation to a semi-intensive stroke care unit, offers a safe and effective organisational solution to provide intravenous thrombolysis to acute stroke patients when a stroke unit (SU) is not available. METHODS: After checking for inclusion and exclusion criteria, ED doctors contacted the stroke team with a single page, located family members and urgently obtained computed tomography scan and laboratory tests. A stroke team investigator clinically assessed the patient, obtained written informed consent and supervised intravenous rt-PA in the ED. After treatment, the patient was transferred to the SU for rehabilitation and treatment of complications, under supervision of the same stroke team investigator. RESULTS: 52 patients were treated with intravenous rt-PA within 3 h of symptom onset. 20 patients (38%) improved neurologically after 24 h, the number increased to 30 (58%) after one week. At 3 months 22 patients had a favourable outcome (43%). The 3-month mortality rate was 12%. Symptomatic cerebral haemorrhage was observed in two patients (4%). CONCLUSIONS: Intravenous rt-PA administration in the ED is an effective organisational solution for acute ischaemic stroke when an SU is not established

    Strong Reduction of the Effective Radiation Length in an Axially Oriented Scintillator Crystal

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    We measured a considerable increase of the emitted radiation by 120 GeV/c electrons in an axially oriented lead tungstate scintillator crystal, if compared to the case in which the sample was not aligned with the beam direction. This enhancement resulted from the interaction of particles with the strong crystalline electromagnetic field. The data collected at the external lines of the CERN Super Proton Synchrotron were critically compared to Monte Carlo simulations based on the Baier-Katkov quasiclassical method, highlighting a reduction of the scintillator radiation length by a factor of 5 in the case of beam alignment with the [001] crystal axes. The observed effect opens the way to the realization of compact electromagnetic calorimeters or detectors based on oriented scintillator crystals in which the amount of material can be strongly reduced with respect to the state of the art. These devices could have relevant applications in fixed-target experiments, as well as in satellite-borne Îł telescopes

    A high-performance custom photodetection system to probe the light yield enhancement in oriented crystals

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    Scintillating homogeneous detectors represent the state of the art in electromagnetic calorimetry. Moreover, the currently neglected crystalline nature of the most common inorganic scintillators can be exploited to achieve an outstanding performance boost in terms of compactness and energy resolution. In fact, it was recently demonstrated by the AXIAL/ELIOT experiments that a strong reduction in the radiation length inside PWO, and a subsequent enhancement in the scintillation light emitted per unit thickness, are attained when the incident particle trajectory is aligned with a crystal axis within ∌1∘\sim 1^\circ. A SiPM-based system has been developed to directly probe this remarkable effect by measuring the scintillation light emitted by a PWO sample. The same concept could be applied to full-scale detectors that would feature a design significantly more compact than currently achievable and unparalleled resolution in the range of interest for present and future experiments