arXiv subjects
Publications and source records attributed to Evangelos Matsinos.
It is generally believed that the $ρ^0 - ω$ interference is the dominant mechanism underlying the violation of the isospin invariance in the $N N$ system. Assessed in this paper is the role which the mechanism might play in a potential departure from the isospin symmetry in the two $π^\pm p$ elastic-scattering reactions.
We investigate the description of the pion-nucleon experimental data at low energy (i.e., below pion laboratory kinetic energy of $100$ MeV) on the basis of the current SAID solution (WI08). We demonstrate that, in a self-consistent analysis scheme, the scale factors of the fits based on the Arndt-Roper formula come out independent of the beam energy and `cluster' around the expectation value of $1$. We report systematic effects in the low-energy behavior of the WI08 solution. These effects indicate that at least one of the three following assumptions, underlying the WI08 analysis, does \emph{not} hold, namely that: a) the bulk of the data is reliable, b) the electromagnetic effects are correctly accounted for, and c) the isospin invariance in the strong interactions of the $πN$ system is valid.
The interactions of the neutrini and antineutrini amongst themselves, as well as the interactions of these particles with the electrons and the positrons, are of interest in simulations of the early Universe and in studies of the processes involving compact stars. The objective in this paper is to create a reliable source of information regarding the differential and total cross sections of these interactions; expressions for these observables will be obtained using standard methodology. A number of relevant discrepancies in the literature will be addressed.
In the present paper, details are given on the implementation of a wavelet-based analysis tailored to the processing of acoustical signals. The family of the suitable wavelets (`Reimann wavelets') are obtained in the time domain from a Fourier transform, extracted in Ref.~\cite{r1} after invoking theoretical principles and time-frequency localisation constraints. A scheme is set forth to determine the optimal values of the parameters of this type of wavelet on the basis of the goodness of the reproduction of a $30$-s audio file containing harmonic signals corresponding to six successive $A$ notes of the chromatic musical scale, from $A_2$ to $A_7$. The quality of the reproduction over about six and a half octaves is investigated. Finally, details are given on the incorporation of the re-assignment method in the analysis framework, as the means a) to determine the important contributions of the wavelet transforms and b) to suppress noise present in the signal.
In a previous paper, we reported the results of a partial-wave analysis of the pion-nucleon ($πN$) differential cross sections (DCSs) of the CHAOS Collaboration and came to the conclusion that the angular distribution of their $π^+ p$ data sets is incompatible with the rest of the modern (meson-factory) database. The present work, re-addressing this issue, has been instigated by a number of recent improvements in our analysis, namely regarding the inclusion of the theoretical uncertainties when investigating the reproduction of experimental data sets on the basis of a given `theoretical' solution, modifications in the parameterisation of the form factors of the proton and of the pion entering the electromagnetic part of the $πN$ amplitude, and the inclusion of the effects of the variation of the $σ$-meson mass when fitting the ETH model of the $πN$ interaction to the experimental data. The new analysis of the CHAOS DCSs confirms our earlier conclusions and casts doubt on the value for the $πN$ $Σ$ term, which Stahov, Clement, and Wagner have extracted from these data.
In the present paper, we investigate the propagation of a massive spin-$\frac{3}{2}$ field, aiming at a direct application in hadronic models of the pion-nucleon ($πN$) interaction. Suitable expressions for the contributions to the standard invariant amplitudes $A$ and $B$ are derived, applicable in the general case of isospin decomposition. We first deal with the details of the lengthy calculation involving the Rarita-Schwinger propagator and confirm the validity of the expressions which had appeared in the literature in the early 1970s. We subsequently derive the corresponding contributions when following two other approaches, one featuring the Williams propagator, the other being known as Pascalutsa's method.
The ETH model of the pion-nucleon ($πN$) interaction contains $t$-channel $σ$- and $ρ$-exchange graphs, as well as the $s$- and $u$-channel contributions with the well-established $s$ and $p$ baryon states with masses below $2$ GeV as virtual particles; the model amplitudes obey crossing symmetry and isospin invariance. In the present work, we give the analytical expressions for the model contributions to the $K$-matrix elements up to (and including) the $f$ waves. We also extract a new phase-shift solution after performing a partial-wave analysis of meson-factory $π^\pm p$ elastic-scattering data below $100$ MeV; included in our results now are also the effects of the variation of the $σ$-meson mass in the interval which is currently recommended by the Particle-Data Group. Finally, we revisit the subject of the $πN$ $Σ$ term and, using the model amplitudes, obtain $Σ= 72.4 \pm 3.1$ MeV. Our prediction agrees well with the result extracted with Olsson's method, after a few flaws in his paper [Phys. Lett. B 482 (2000) 50] were corrected.
The value of $59 \pm 12$ MeV for the pion-nucleon ($πN$) $Σ$ term, which Stahov, Clement, and Wagner recently extracted from the differential cross sections (DCSs) of the CHAOS Collaboration, does not match well the expectation of an enhanced (more positive) isoscalar component in the $πN$ interaction at low energies, which the rest of the modern (meson-factory) data favour. However, we have already demonstrated that the angular distribution of the CHAOS $π^+ p$ DCSs is not compatible in shape with the rest of the modern low-energy $π^+ p$ data. This problem must be addressed and resolved by the CHAOS Collaboration prior to the extrapolation of their partial-wave amplitudes into the unphysical region.
We analyse the charge-exchange (CX) measurements $π^- p\rightarrow π^0 n$ below pion laboratory kinetic energy of 100 MeV. After the removal of five degrees of freedom from the initial database, we combine it with the truncated $π^+ p$ database of Ref. \cite{mrw1} and fit the ETH model \cite{glmbg} to the resulting data. The set of the parameter values of the ETH model, as well as the predictions derived on their basis for the hadronic phase shifts and for the low-energy $πN$ constants, are significantly different from the results obtained in the analysis of the truncated $π^\pm p$ elastic-scattering databases. The main difference in the hadronic phase shifts occurs in $\tildeδ_{0+}^{1/2}$. We discuss the implications of these findings in terms of the violation of the isospin invariance in the hadronic part of the $πN$ interaction. The effect observed amounts to the level of $7-8 %$ in the CX scattering amplitude below 70 MeV. The results and conclusions of this study agree well with those obtained in the mid 1990s, when the isospin invariance was first tested by using $πN$ experimental data, and disagree with the predictions obtained within the framework of the heavy-baryon Chiral-Perturbation Theory.
This paper presents the results of an analysis of the low-energy $π^\pm p$ differential cross sections, acquired by the CHAOS Collaboration at TRIUMF \cite{chaos,denz}. We first analyse separately the $π^+ p$ and the $π^- p$ elastic-scattering measurements on the basis of standard low-energy parameterisations of the $s$- and p-wave $K$-matrix elements. After the removal of the outliers, we subject the truncated $π^\pm p$ elastic-scattering databases into a common optimisation scheme using the ETH model \cite{glmbg}; the optimisation failed to produce reasonable values for the model parameters. We conclude that the problems we have encountered in the analysis of these data are due to the shape of the angular distributions of their $π^+ p$ differential cross sections.
The present document aims at developing the formalism needed in order to describe the two-dimensional motion of a vehicle with Mecanum wheels, including the effects of resistive friction. The description of recently-acquired experimental data, on the basis of this model, is found satisfactory.
We report the results of a phase-shift analysis (PSA) of the low-energy $π^\pm p$ elastic-scattering data. Following the method which we had set forth in our previous PSA (Matsinos et al., 2006), we first investigate the self-consistency of the low-energy $π^\pm p$ elastic-scattering databases, via two separate analyses of (first) the $π^+ p$ and (subsequently) the $π^- p$ elastic-scattering data. There are two main differences to our previous PSA: a) we now perform only one test for the acceptance of each data set (based on its contribution to the overall $χ^2$) and b) we adopt a more stringent acceptance criterion in the statistical tests. We show that it is possible to obtain self-consistent databases after removing a very small amount of the data (4.57% of the initial database). We subsequently fit the ETH model (Goudsmit et al. 1994) to the truncated $π^\pm p$ elastic-scattering databases. The model-parameter values show reasonable stability when subjected to different criteria for the rejection of single data points and entire data sets. Our result for the pseudovector $πN N$ coupling constant is $0.0726 \pm 0.0014$. We extract the scattering lengths and volumes, as well as the s- and p-wave hadronic phase shifts up to T=100 MeV. Large differences in the s-wave part of the interaction can be seen when comparing our hadronic phase shifts with the current SAID solution (WI08); there is general agreement in the p waves, save for the $\tildeδ_{1-}^{1/2}$ hadronic phase shift.
This is a technical note aiming at the re-examination of the phenomenon of the steady-state cracking in the two-layer system. The method of Suo and Hutchinson, as introduced in their 1989 paper, is followed. Our solution is compared with the one appearing in that paper for the substrate-to-film thickness ratio $λ_0=10$. We obtain results at three $λ_0<10$ values. Combined with the results for $λ_0=10$, the new sets of values cover thickness ratios between 1 and 10, sufficient for determining crack initiation and propagation in almost every relevant problem. We present our results in tables (and figures), thus facilitating their implementation and use.
The well-known Bragg-Kleeman rule RCSDA = A dot E0p has become a pioneer work in radiation physics of charged particles and is still a useful tool to estimate the range RCSDA of approximately monoenergetic protons with initial energy E0 in a homogeneous medium. The rule is based on the continuous-slowing-down-approximation (CSDA). It results from a generalized (nonrelativistic) Langevin equation and a modification of the phenomenological friction term. The complete integration of this equation provides information about the residual energy E(z) and dE(z)/dz at each position z (0 <= z <= RCSDA). A relativistic extension of the generalized Langevin equation yields the formula RCSDA = A dot (E0 +E02/2M dot c2)p. The initial energy of therapeutic protons satisfies E0 << 2M dot c2 (M dot c2 = 938.276 MeV), which enables us to consider the relativistic contributions as correction terms. Besides this phenomenological starting-point, a complete integration of the Bethe-Bloch equation (BBE) is developed, which also provides the determination of RCSDA, E(z) and dE(z)/dz and uses only those parameters given by the BBE itself (i.e., without further empirical parameters like modification of friction). The results obtained in the context of the aforementioned methods are compared with Monte-Carlo calculations (GEANT4); this Monte-Carlo code is also used with regard to further topics such as lateral scatter, nuclear interactions, and buildup effects. In the framework of the CSDA, the energy transfer from protons to environmental atomic electrons does not account for local fluctuations.
The present paper pertains to corrections which are due to the presence of beam-limiting and beam-shaping devices in proton planning. Two types of corrections are considered: those which are due to the nonzero thickness of such devices (geometrical effects) and those relating to the scattering of beam particles off their material. The application of these two types of corrections is greatly facilitated by decomposing the physical effects (i.e., the contribution to the fluence) of two-dimensional objects (i.e., of the apertures of the devices) into one-dimensional, easily-calculable contributions. To minimise the time requirements in the derivation of the scattering corrections, a two-step process is introduced. The first step occurs at beam-configuration phase and comprises the analysis of half-block fluence measurements and the extraction of the one parameter of the model which is used in the description of the beamline characteristics; subsequently, a number of Monte-Carlo runs lead to the determination of the parameters of a convenient parameterisation of the relevant fluence contributions. The second step involves (at planning time) the reconstruction of the parameters (which are used in the description of the scattering contributions) via simple interpolations, performed on the results obtained during the beam-configuration phase. It is shown that the inclusion of the scattering effects leads to substantial improvement in the reproduction of the experimental data. The contributions from the block-thickness and block-scattering effects have been presented separately in the case of a simple water phantom. In this example, the maximal contribution of the block-relating effects amounts to a few percent of the prescribed dose.
We propose a method to achieve the geometric calibration of cone-beam imaging and delivery systems in radiation therapy; our approach applies to devices where an X-ray source and a flat-panel detector, facing each other, move in circular orbits around the irradiated object. In order to extract the parameters of the geometry from the data, we use a light needle phantom which is easy to manufacture. A model with ten free parameters (spatial lengths and distortion angles) has been put forth to describe the geometry and the mechanical imperfections of the units being calibrated; a few additional parameters are introduced to account for residual effects (small effects which lie beyond our model). The values of the model parameters are determined from one complete scan of the needle phantom via a robust optimisation scheme. The application of this method to two sets of five counterclockwise (ccw) and five clockwise (cw) scans yielded consistent and reproducible results. A number of differences have been observed between the ccw and cw scans, suggesting a dissimilar behaviour of the devices calibrated in the two rotation modes. The description of the geometry of the devices was achieved at the sub-pixel level.
Varian Medical Systems has manufactured and recently put into operation a clinically-applicable solution for image-guided radiation therapy. Cone-beam CT imaging, one of the operation modes of the imaging unit of this device, aims at high-quality volumetric reconstruction. To boost the image quality, the dual-gain mode, a successful means for enhancing the dynamic range of the flat-panel detectors and obtaining better results in the contrast of the reconstructed image, was developed and successfully tested during the last few years. The important steps in the calibration of this mode involve a correction to the pulse widths associated with the X-ray production, the assessment of the detector signal above which nonlinear effects become significant and the determination of some properties of the detector pixels, namely, of dark fields, flatness corrections, etc. Finally, the defect-pixel map is obtained, containing dead and flickering pixels, as well as pixels with properties which are sufficiently `out of range'. An effect observed in the offset correction of raw images seems to originate in the mismatch between the measured and extrapolated values of the dark field; a correction scheme is proposed to take account of this effect. In the data processing, which is achieved on the basis of the files produced in the calibration of the mode, the high-gain signal is used whenever meaningful; otherwise, it is substituted by the low-gain signal, properly scaled. Defect pixels are interpolated from their good neighbours; a procedure achieving a correction in case of small defect-pixel clusters is outlined.
We describe a method aiming at increasing the dynamic range of X-ray detectors. Two X-ray exposures of an object are acquired at different dose levels and constitute the only input data. The values of the parameters which are needed to process these images are determined from information contained in the images themselves; the values of two parameters are extracted from the input data. The two input images are finally merged in such a way as to create one image containing useful information in all its entirety. This selective use of parts of each image allows both the contour of the irradiated object to be visible and the high-attenuation areas to retain their image quality corresponding to the information contained in the high-dose image. The benefits of the method are demonstrated with an example involving a head phantom.