Numerical models indicate that collective animal behavior may emerge from simple local rules of interaction among the individuals. However, very little is known about the nature of such interaction, ...so that models and theories mostly rely on aprioristic assumptions. By reconstructing the three-dimensional positions of individual birds in airborne flocks of a few thousand members, we show that the interaction does not depend on the metric distance, as most current models and theories assume, but rather on the topological distance. In fact, we discovered that each bird interacts on average with a fixed number of neighbors (six to seven), rather than with all neighbors within a fixed metric distance. We argue that a topological interaction is indispensable to maintain a flock's cohesion against the large density changes caused by external perturbations, typically predation. We support this hypothesis by numerical simulations, showing that a topological interaction grants significantly higher cohesion of the aggregation compared with a standard metric one.
The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and ...progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton’s electromagnetic form factors; and phenomenology suggests that diquark correlations might be critical to the formation of exotic tetra- and penta-quark hadrons. A broad spectrum of such information is evaluated herein, with a view to consolidating the facts and therefrom moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play.
The strong interaction is not well understood at low energies or for interactions with low momentum transfer. Chiral perturbation theory gives testable predictions for the nucleonic generalized ...polarizabilities, which are fundamental quantities describing the nucleon’s response to an external field. We report a measurement of the proton’s generalized spin polarizabilities extracted with a polarized electron beam and a polarized solid ammonia target in the region where chiral perturbation theory is expected to be valid. The investigated structure function g2 characterizes the internal spin structure of the proton. From its moments, we extract the longitudinal–transverse spin polarizability δLT and twist-3 matrix element and polarizability d2¯. Our results provide discriminating power between existing chiral perturbation theory calculations and will help provide a better understanding of this strong quantum chromodynamics regime.Measurements of the proton’s generalized spin polarizabilities provide discriminating power between effective descriptions of the strong interaction at low energy.
The CLAS12 large area RICH detector Contalbrigo, M.; Cisbani, E.; Rossi, P.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2011, Letnik:
639, Številka:
1
Journal Article
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A large area RICH detector is being designed for the CLAS12 spectrometer as part of the 12
GeV upgrade program of the Jefferson Lab Experimental Hall-B. This detector is intended to provide excellent ...hadron identification from 3
GeV/
c up to momenta exceeding 8
GeV/
c and to be able to work at the very high design luminosity-up to 10
35
cm
2
s
−1. Detailed feasibility studies are presented for two types of radiators, aerogel and liquid C
6F
14 freon, in conjunction with a highly segmented light detector in the visible wavelength range. The basic parameters of the RICH are outlined and the resulting performances, as defined by preliminary simulation studies, are reported.
A method to calibrate measurement instruments through the fulfillment of physical laws is described. This method is particularly well suited to determine and/or improve magnetic spectrometer optics ...databases as well as to establish the best resolution achievable with them. This method was applied to obtain the best resolution achievable in the excitation and binding energy spectra of several hypernuclei produced in the experiment E94-107 performed at JLab, allowing us to obtain sub-MeV resolutions.
This paper presents the experimental results on the Terapia Oncologica con Protoni-Intensity Modulated Proton Linear Accelerator (TOP-IMPLART) beam that is currently accelerated up to 35 MeV, with a ...final target of 150 MeV. The TOP-IMPLART project, funded by the Innovation Department of Regione Lazio (Italy), is led by Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) in collaboration with the Italian Institute of Health and the Oncological Hospital Regina Elena-IFO. The accelerator, under construction and test at ENEA-Frascati laboratories, employs a commercial 425 MHz, 7 MeV injector followed by a sequence of 3 GHz accelerating modules consisting of side coupled drift tube linac (SCDTL) structures up to 71 MeV and coupled cavity linac structures for higher energies. The section from 7 to 35 MeV, consisting on four SCDTL modules, is powered by a single 10 MW klystron and has been successfully commissioned. This result demonstrates the feasibility of a “fully linear” proton therapy accelerator operating at a high frequency and paves the way to a new class of machines in the field of cancer treatment.
Microscopic simulations may bring a better understanding of the response of gaseous detectors. Such simulations are computationally demanding, due to the modelling of the low energy processes and to ...the high segmentation required for the 2D/3D field maps. In MPGD such maps can be much more complex than those of traditional multiwire chambers, due to the heterogeneous materials and more involute geometries, which break the simplifying symmetries featured in the latter. In order to investigate the performance of the triple GEM 2-dimensional tracking chambers being developed for high luminosity experiments with the Super BigBite Spectrometer at Jefferson Laboratory, we have set up a flexible and rather effcient multistep simulation processor based on either ANSYS or GMSH+ELMER for 3D CAD and electrostatic field modelling and then combined to Garfield++. Potential systematic effects from the 3D CAD modellers, the mesh generators and the electrostatic field solvers have been estimated with dedicated simulations; once these effects have been assessed, the results of the multistep approach have been compared to a simplified whole GEM chamber model.
This paper is about the Gas Electron Multiplier (GEM), a gas detector that will be installed on the new Super BigBite Spectrometer (SBS), under construction at Jefferson Laboratory in Newport News, ...VA, USA; the main interest of JLAB physics is the study of the fundamental interactions and constituents of hadronic matter and in particular the study of the electromagnetic Form Factors of the nucleons. The Italian group, JLAB12, is engaged in the construction, characterization and commissioning of two of the detectors that will be implemented in SBS: the GEM front tracker and the hadron calorimeter HCAL-J. A Gas Electron Multiplier is a gas detector useful to track the charged particles. It is composed of 2 layers of copper and a layer of Kapton, a dielectric material; all the layers together are inside a box with a mixture of gas:
of Argon an
of CO
. In each GEM foil there are a lot of biconical holes, and it is placed between a drift plane and a readout plane; when a charge particle crosses the gas, it loses energy creating couple ion-electron. If we apply a potential difference, the pairs are accelerated by the electric field, and they have enough energy to create an avalanche. The gain that we can reach with a single GEM foil is 1000. In JLAB's configuration for SBS, a TripleGEMs system will be used; a TripleGEM is composed of 3 GEM foil placed in cascade. The advantages of this technology are: the layers structure, so the primary ionization, the multiplication and the charge collection regions are separated, the high gain about 100,000, the flexibility of geometry, the good spatial resolution about 70 µm, low costs and small streamer or charging up phenomena. To verify GEMs performances and to optimize the digitalization model, we started simulations changing some physical and geometric parameters. In order to run the GEM's simulations, we used two different software: ANSYS Mechanical APDL to create the detector geometry, assign the materials, define the meshes in shape and size and the electric field, and Garfield++, a toolkit for detailed Monte Carlo simulation of a gaseous detector, to evaluate the distribution of the charged particles on the readout plane when we change some parameters like the type of the primary particle, its energy and its incident slope. In particular, we built two different models: a triple GEM model and a cascade model; we are comparing the simulations results with the real test that we did in Juelich (Germany) with a beam of 2.8 GeV protons.
This work reports on the Monte Carlo optimization studies of detection systems for Molecular Breast Imaging with radionuclides and Bremsstrahlung Imaging in nuclear medicine. Molecular Breast Imaging ...requires competing performances of the detectors: high efficiency and high spatial resolutions; in this direction, it has been proposed an innovative device which combines images from two different, and somehow complementary, detectors at the opposite sides of the breast. The dual detector design allows for spot compression and improves significantly the performance of the overall system if all components are well tuned, layout and processing carefully optimized; in this direction the Monte Carlo simulation represents a valuable tools. In recent years, Bremsstrahlung Imaging potentiality in internal radiotherapy (with beta-radiopharmaceuticals) has been clearly emerged; Bremsstrahlung Imaging is currently performed with existing detector generally used for single photon radioisotopes. We are evaluating the possibility to adapt an existing compact gamma camera and optimize by Monte Carlo its performance for Bremsstrahlung imaging with photons emitted by the beta- from 90Y.
The Intensity Modulated Proton Linear Accelerator for Cancer Therapy (TOP-IMPLART) is under development and construction by ENEA in collaboration with the Italian Institute of Health (ISS) and the ...Oncological Hospital Regina Elena-IFO with financial support of Regione Lazio. Its peculiar time structure (few microseconds pulse width) and very high peak intensity (≍ 109 proton/pulse) demand for ad hoc dose delivery monitors (DDM). The TOP-IMPLART DDM is based on ionization gas chambers. One segmented chamber prototype uses Micro Pattern Gaseous Detector technology for the 2-dimensional simultaneous x/y readout; the charge collected from each active segment (strips with pad-like shape) is readout by a dedicated gain-adaptable electronics. Two small, highly sensitive, integral ionization chambers, using the same electronics, complement the 2D chamber for the monitor of the single pulse beam charge, down to 1 pC/pulse. While under development and deployment of its accelerating modular cavities, the linear TOP-IMPLART beam is improved thanks also to the continuous monitoring and characterization by these devices, whose responses are periodically compared to calibrated dosimetric detectors such as real-time active microDiamond sensor, passive Alanine pellets, intrinsically stable integral Faraday Cup. Different calibration campaigns have been recently conducted to measure the recombination and dose-rate effects on the above ionization chambers. The outcome of these measurements shows clear electron-ion recombination in the chamber active volume, largely related to the high beam intensity and its small transverse cross section. Those effects can be taken into account and used to correct the actual measurement of the DDM. In this paper, the TOP-IMPLART project and the DDM devices are shortly presented and details of the above experimental studies are discussed.
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