Measurement of the Transverse-Longitudinal Cross Sections in the p (e,e'p)pi0 Reaction in the Delta Region

Accurate measurements of the p(e,e?p)pi0 reaction were performed at Q^2=0.127(GeV/c)^2 in the Delta resonance energy region. The experiments at the MIT-Bates Linear Accelerator used an 820 MeV polarized electron beam with the out of plane magnetic spectrometer system (OOPS). In this paper we report the first simultaneous determination of both the TL and TL? (``fifth" or polarized) cross sections at low Q^{2} where the pion cloud contribution dominates the quadrupole amplitudes (E2 and C2). The real and imaginary parts of the transverse-longitudinal cross section provide both a sensitive determination of the Coulomb quadrupole amplitude and a test of reaction calculations. Comparisons with model calculations are presented. The empirical MAID calculation gives the best overall agreement with this accurate data. The parameters of this model for the values of the resonant multipoles are |M_{1+}(I=3/2)|= (40.9 \pm 0.3)10^{-3}/m_pi, CMR= C2/M1= -6.5 \pm 0.3%, EMR=E2/M1=-2.2 \pm 0.9%, where the errors are due to the experimental uncertainties.Comment: 10 pages, 3 figures, minor corrections and addition

Nucleon deformation: A status report

The conjectured deformation of hadrons and its experimental verification offer a particularly fertile ground for understanding the intricate dynamics of their constituents and QCD at the confiment scale. The detailed study of the N → Δ transition is viewed as the preferred method of experimental investigation of this central issue in hadronic physics. A brief overview of the field is presented, followed by a presentation of the most recent results from Bates N → Δ program. The new Bates/OOPS data at Q2 = 0.127(GeV/c)2 yield RSM = (-6.27 ± 0.326 stat+sys ± 0.10model)% and REM = (-2.00 ± 0.40stat+sys ± 0.27model)% and they exclude a spherical nucleon and/or Δ. The magnitude and the origin of the deformation is the focus of the ongoing and planned investigations

Colloquium: The shape of hadrons

This Colloquium addresses the issue of the shape of hadrons and, in particular, that of the proton. The concept of shape in the microcosm is critically examined. Special attention is devoted to properly define the meaning of shape for bound-state systems of near massless quarks. The ideas that lead to the expectation of nonsphericity in the shape of hadrons, the calculations that predict it, and the experimental information obtained from recent high-precision measurements are examined. Particular emphasis is given to the study of the electromagnetic transition between the nucleon and its first excited state, the Δ(1232) resonance. The experimental evidence is critically examined and compared with lattice calculations, as well as with effective-field theories and phenomenological models. © 2012 American Physical Society

Sensitivity of multipoles to phase variations in pion photo- and electro-production analyses

We use the Athens Model Independent Analysis Scheme (AMIAS) to examine the validity of using the Fermi–Watson theorem in the multipole analyses of pion photoproduction and electroproduction data. A standard practice in this field is to fix the multipoles’ phases from πN scattering data, making use of the Fermi–Watson theorem. However, these phases are known with limited accuracy and the effect of this uncertainty on the obtained multipole extraction has not been fully explored yet. Using AMIAS we constrain the phases within their experimentally determined uncertainty. We first analyze sets of photoproduction pseudodata of increasing statistical precision and subsequently we apply the methodology for a re-analysis of the Bates/Mainz electroproduction data. It is found that the uncertainty induced by the πN phases uncertainty to the extracted solutions would be significant only in the analysis of data with much higher precision than the current available experimental data. © 2020, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature

Novel analysis method for excited states in lattice QCD: The nucleon case

We employ a novel method to analyze Euclidean correlation functions entering the calculation of hadron energies in lattice QCD. The method is based on the sampling of all possible solutions allowed by the spectral decomposition of the hadron correlators. We demonstrate the applicability of the method by studying the nucleon excited states in the positive- and negative-parity channels over a pion mass range of about 400 to 150 MeV. The results are compared to the standard variational approach routinely used to study excited states within lattice QCD. The main advantage of our new approach is its ability to unambiguously determine all excited states to which the Euclidean time correlation function is sensitive. © 2015 American Physical Society

Examining an image reconstruction method in infrared emission tomography

We present and evaluate the application of the “Reconstructed Image from Simulations Ensemble” (RISE), a novel tomographic image reconstruction method, in infrared tomography. We demonstrate that established methods of photon emission tomography, widely used with penetrating ionizing radiation, are applicable to infrared radiation. RISE, the method of choice, employs statistical physics concepts and utilizes Monte Carlo techniques to construct the imaged object from its infrared planar projections. The validity of the InfraRed Emission Tomographic (IRET) method is demonstrated, and the efficacy of RISE is evaluated with (A) simulated data and (B) experimental sets of infrared projections obtained from a thermal phantom with an infrared camera. For the simulation studies presented, the reconstructed images obtained with RISE and the well - known Algebraic Reconstruction Technique (ART) and Maximum Likelihood Expectation Maximization (MLEM) method were evaluated using well-established metrics. © 2019 Elsevier B.V

Study of the optical properties of continuous and pixelated scintillation crystals

The principal goal of this study is to characterize the width of the light distribution for a given number of initial optical photons and to try to express it as a function of the Depth of Interaction (DOI) in the crystal, where the initial optical photons are produced, the size of the initial volume the optical photons occupy before starting the transmission and the geometrical properties of the optical medium that guides the light to the photomultiplier surface. Monte Carlo runs based on the optical simulation package DETECT2000 have been performed. The results indicate that in the case of continuous crystal there is an apparent correlation of the DOI and the width of the light distribution. In the case of pixelated crystals the width of the light distribution seems to be independent of the DOI when the source is located deep in the crystal but there is a strong dependence as the source approaches the PSPMT's entrance window. This correlation of the DOI and the light distribution is not affected by the transverse dimensions of the continuous crystal but in the case of pixelated crystals this correlation is strongly depended on the crystal's aspect ratio. Through this study it also became clear that there is no dependence of the light distribution on the shape of the source. © 2009 IOP Publishing Ltd and SISSA

A correction method of the spatial distortion in planar images from γ-Camera systems

A methodology for correcting spatial distortions in planar images for small Field Of View (FOV) γ-Camera systems based on Position Sensitive Photomultiplier Tubes (PSPMT) and pixelated scintillation crystals is described. The process utilizes a correction matrix whose elements are derived from a prototyped planar image obtained through irradiation of the scintillation crystal by a 60Co point source and without a collimator. The method was applied to several planar images of a SPECT experiment with a simple phantom construction at different detection angles. The tomographic images are obtained using the Maximum-Likelihood Expectation-Maximization (MLEM) reconstruction technique. Corrected and uncorrected images are compared and the applied correction methodology is discussed. © 2009 IOP Publishing Ltd and SISSA

Design and development of a position-sensitive γ-camera for SPECT imaging based on PCI electronics

A position-sensitive γ-camera is being currently designed at IASA. This camera will be used experimentally (development mode) in order to obtain an integrated knowledge of its function and perhaps to improve its performance in parallel with an existing one, which has shown a very good performance in phantom, small animal, SPECT technique and is currently being tested for clinical applications. The new system is a combination of a PSPMT (Hamamatsu, R2486-05) and a PMT for simultaneous or independent acquisition of energy and position information, respectively. The resistive chain technique resulting in two signals at each (X,Y) direction will perform the readout of the PSPMT's anode signals; the system is based on PCI electronics. Status of the system's development and the ongoing progress is presented. © 2004 Elsevier B.V. All rights reserved