1,721,364 research outputs found
Exclusive eta Meson Reconstruction in Proton-Proton Collisions at 2.2 GeV with the HADES Spectrometer and High Resolution Tracking
No full textHADES (High Acceptance DiElectron Spectrometer) is a unique apparatus currently assembled at heavy-ion synchrotron SIS at GSI, Darmstadt. The main part of the HADES physics program is focused on in-medium properties of the light vector mesons ρ(770), ω(783) and φ(1020), but also concerns several important problems of hadron physics like: validity of the Vector meson Dominance Model (VDM) in the description of meson and baryon Dalitz decays and of the electromagnetic form-factor of the nucleon in time-like region. In the framework of the present thesis a detailed study of the exclusive η meson reconstruction in proton-proton collisions at 2.2 GeV kinetic energy of the incident proton beam is presented. The exclusive measurement of the η mesons has been performed for two electromagnetic decay channels (η→ π+π-π0 and η→ e+e-γ), the relative branching ratios of which are known. In order to obtain better tracking resolution, an algorithm of kinematic fit has been developed and tested. The main goal of the kinematic fit is to improve the reconstruction resolution by using physical constraints governing the process. Studied results have been used to evaluate the dielectron detection efficiency of the HADES experiment. The kinematic fit algorithm has been used for above mentioned analysis as well. Apart from these studies, using the kinematics of the elastic scattering channel, the spectrometer performance has been studied in terms of reconstruction resolution and detector alignments. From a technical point of view, a new method for momentum reconstruction, using a cubic spline track model in the magnetic field region of the HADES spectrometer, has been developed. An algorithm for matching of different hits belonging to one track reconstructed by the spectrometer systems has also been developed. Both algorithms have been used for the data analysis described in this work. The phase-space distributions of η→ π+π-π0 and η→ e+e-γ decay channels being different, the relative branching ratio of these decay channels will differ from that obtained for full phase space. Therefore the simulation data has been generated in order to find out the relative branching ratios of the above mentioned decay channels inside the HADES acceptance. We have done different types of simulations in order to compare with the data. In particular, the anisotropy in the angular distributions of the η mesons, observed by the DISTO experiment, have been included in the simulation and compared with our data. According to the VDM, the photon interacts with the hadron of interest not only directly, but also through vector mesons. In particular for the η meson, which is a neutral pseudoscalar meson, the Dalitz decay goes in two steps, where in a first step it emits two photons (real plus virtual), and in a second step the virtual photon decays into a e+e- pair. The validity of the VDM model in describing the Dalitz decay of the η meson has been investigated by comparing the experimentally reconstructed invariant-mass distribution of the e+e- pairs with the VDM model predictions. To investigate the production mechanism of the η meson, their angular distributions in the center-of-mass system have been studied. This thesis is divided into two parts: In the first part a brief introduction to the physics program of the HADES experiment is given. A description of the detector systems of the spectrometer and the detailed explanation of track reconstruction algorithm of the HADES experiment is given in this part as well. The second part mainly concerns the analysis of the proton-proton data and the discussion of the results
Recent results from NA61/SHINE and NA49
No full textPreliminary results on particle spectra and fluctuations in inelastic p+p interactions measured by NA61/SHINE at the CERN SPS are presented and its future ion program is discussed. We also show results on the excitation functions of event-by-event particle ratio fluctuations in central Pb+Pb collisions from NA49 using a novel approach. We found a dependence of the results on phase space coverage which appears to explain the reported difference between measurements of NA49 and those of STAR in central Au+Au collisions.Preliminary results on particle spectra and fluctuations in inelastic p+p interactions measured by NA61/SHINE at the CERN SPS are presented and its future ion program is discussed. We also show results on the excitation functions of event-by-event particle ratio fluctuations in central Pb+Pb collisions from NA49 using a novel approach. We found a dependence of the results on phase space coverage which appears to explain the reported difference between measurements of NA49 and those of STAR in central Au+Au collisions.Preliminary results on particle spectra and fluctuations in inelastic p+p interactions measured by NA61/SHINE at the CERN SPS are presented and its future ion program is discussed. We also show results on the excitation functions of event-by-event particle ratio fluctuations in central Pb+Pb collisions from NA49 using a novel approach. We found a dependence of the results on phase space coverage which appears to explain the reported difference between measurements of NA49 and those of STAR in central Au+Au collisions
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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