1,720,975 research outputs found
Hole in the Deuteron
Full text linkWe introduce a new observable, , that allows to isolate the node in the S-partial wave distribution of the deuteron in high electro-disintegration processes with tensor polarized target. The node is a signature of nuclear repulsive core and represents a crucial test of its strength, size as well as the role of the relativistic and non-nucleonic effects in a deeply bound state. Within plane wave impulse approximation the node immitates a ``hole through which incoming probe passes through without interaction. It is demonstrated that high electro-disintegration processes due to their strong anisotropy of final state interaction effects, allow to gain an unprecedented access to the node, opening up a new venue in probing elusive dynamics of the nuclear repulsive core.5 pages and 6 figure
Tagged spectator deep-inelastic scattering off the deuteron as a tool to study neutron structure
No full textWe give an overview of a model to describe deep-inelastic scattering (DIS) off the deuteron with a spectator proton, based on the virtual nucleon approximation (VNA). The model accounts for the final-state interactions (FSI) of the DIS debris with the spectator proton. Values of the rescattering cross section are obtained by fits to high-momentum spectator data. By using the so-called “pole extrapolation” method, free neutron structure functions can be obtained by extrapolating low-momentum spectator proton data to the on-shell neutron pole. We apply this method to the BONuS data set and find a surprising Bjorken x dependence, indicating a possible rise of the neutron to proton structure function ratio at high x
Protons in High Density Neutron Matter
No full textWe discuss the possible implication of the recent predictions of two new properties of high momentum distribution of nucleons in asymmetric nuclei for neutron star dynamics. The first property is about the approximate scaling relation between proton and neutron high momentum distributions weighted by their relative fractions (xp and xn) in the nucleus. The second is the existence of inverse proportionality of the high momentum distribution strength of protons and neutrons to xp/n. Based on these predictions we model the high momentum distribution functions for asymmetric nuclei and demonstrate that it describes reasonably well the high momentum characteristics of light nuclei. We also extrapolate our results to heavy nuclei as well as infinite nuclear matter and calculate the relative fractions of protons and neutrons with momenta above kF. Our results indicate that for neutron stars starting at {\em three} nuclear saturation densities the protons with xp=19 will populate mostly the high momentum tail of the momentum distribution while only 2% of the neutrons will do so. Such a situation may have many implications for different observations of neutron stars which we discus
Model independent method for determination of the DIS structure of free neutron
No full textAbstractWe present a model independent procedure for extracting deep-inelastic structure function of “free” neutron from the electron–deuteron scattering with protons produced in the target fragmentation region of the reaction. This procedure is based on the extrapolation of t, which describes the invariant momentum transfered to the proton, to the unphysical region corresponding to the mass of the struck neutron. We demonstrate that the impulse approximation diagram of the reaction has a pole at this limit with a residue being proportional to the “free” neutron structure function. The method is analogous to that of Chew and Low for extraction of the “free” pion–pion and neutron–neutron cross sections from p(π,p)X and d(n,n)pn reactions, respectively. We demonstrate that in the extrapolation the final state interaction amplitudes are smooth functions of t and have negligible contribution in the extracted “free” nucleon structure function. We also estimate the range of the recoil nucleon momenta which could be used for successful extrapolation procedure
High-x structure function of the virtually free neutron
No full textThe pole extrapolation method is applied to the semi-inclusive inelastic electron scattering off the deuteron with tagged spectator protons to extract the high-x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the spectator proton to the nonphysical pole of the bound neutron in the deuteron. The advantage of the method is in the possibility of suppression of the nuclear effects in a maximally model-independent way. The neutron structure functions obtained in this way demonstrate a surprising x dependence at x≥0.6 and 1.6≤Q2≤3.38GeV2, indicating a possible rise of the neutron-to-proton structure functions ratio. If the observed rise is valid in the true deep inelastic region then it may indicate new dynamics in the generation of high-x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton
Possible Universal Limit for Valence Parton Distributions
Full text linkWe report the observation of the existence of a possible universal limit for
valence parton distributions that should exist once partonic degrees of freedom
are relevant for high energy scattering from strongly interacting bound systems
like a nucleon, meson or a few nucleon system at very short distances. Our
observation is based on the notion that the Bjorken x weighted valence parton
distribution function has a peak, , that characterizes the average
momentum fraction carried out by the valence quarks in the system. Within the
residual mean-field model of the valence quark distribution we found that
has an upper limit: , where is the number of
valence quarks which can be considered in the cluster embedded in the strongly
interacting environment of the bound system. The existence of such a limit
imposes a new constraint on choosing the starting resolution scale for
PDFs. Our prediction for the nucleon is that ,
which is in agreement with all the available valence PDFs that employ the
standard approach for selecting starting . We also demonstrate how the
existence of this limit can be used to check the onset of quark-clusters in
short range nucleon correlations in nuclei.Comment: Main article 9 pages with 5 figure
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
Tagged spectator deep-inelastic scattering off the deuteron as a tool to study neutron structure
Full text linkWe give an overview of a model to describe deep-inelastic scattering (DIS) off the deuteron with a spectator proton, based on the virtual nucleon approximation (VNA). The model accounts for the final-state interactions (FSI) of the DIS debris with the spectator proton. Values of the rescattering cross section are obtained by fits to high-momentum spectator data. By using the so-called “pole extrapolation” method, free neutron structure functions can be obtained by extrapolating low-momentum spectator proton data to the on-shell neutron pole. We apply this method to the BONuS data set and find a surprising Bjorken x dependence, indicating a possible rise of the neutron to proton structure function ratio at high x
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