1,721,137 research outputs found
Search for the X(17) particle in the 7Li(p, e+e−)8Be reaction with the MEG II detector
No full textA recent measurement of the Internal Pair Creation in the 7Li(p,e+e-)8Be reaction performed at the Atomki laboratory in Hungary showed an unexpected excess in their angular distribution. The significance of the observed bump is ~7 standard deviations, and following measurements of the same reaction but with an upgraded experimental apparatus showed analogous results. Moreover, a measurement of the 3H(p,e+e-)4He reaction showed another significant excess at a different angle. Both these observations can be explained by the creation of a new physics boson with a 17 MeV mass called X(17). The MEG II experiment was designed to search for Charged Lepton Flavor Violation in the mu o e gamma decay, but its detectors are able to measure the 7Li(p,e+e-)8Be reaction as well. The experiment is in fact equipped with a photon detector and a magnetic spectrometer, and has access to a Cockroft-Walton accelerator for the photon detector calibrations. The accelerator can be used to generate the necessary proton beam, and the magnetic spectrometer can be used to measure the decay products of the reaction. An independent measurement with an experiment that guarantees a better invariant mass resolution and a larger angular acceptance can confirm that the anomaly observed at Atomki is not an artifact of the detector geometry, but a real anomaly not explained by any known nuclear physics effect. This measurement is possible only through a redesign of the target region of the CW accelerator used for MEG II calibrations, which was carefully selected after thermomechanical and physics simulations. The signal and background simulations, modeled on the state of the art knowledge of the IPC theory, showed that the MEG II experiment can perform the 7Li(p,e+e-)8Be measurement with a resolution on the invariant mass of 504 keV and reach a sensitivity of 5 in few days of data acquisition. A first prototype of this experimental setup, different from the final design, was built in such a way to not interfere with the MEG II data taking. It was used to take some preliminary data during the 2021 MEG II engineering run to test the CDCH reconstruction algorithms and to find the optimal trigger strategy for the final measurement. The construction of the definitive target region is underway and will be ready for the beginning of 2022, when the X(17) measurement at MEG II will begin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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