Display of probability densities for data from a continuous distribution

Based on cumulative distribution functions, Fourier series expansion and Kolmogorov tests, we present a simple method to display probability densities for data drawn from a continuous distribution. It is often more efficient than using histograms.Comment: 5 pages, 4 figures, presented at Computer Simulation Studies XXIV, Athens, GA, 201

Measurement of the Generalized Polarizabilities of the Proton in Virtual Scattering at Q2=0.92 and 1.76 GeV2: I. Low Energy Expansion Analysis

Virtual Compton Scattering is studied at the Thomas Jefferson National Accelerator Facility at low Center-of-Mass energies, below pion threshold. Following the Low Energy Theorem for the $ep \to ep \gamma$ process, we obtain values for the two structure functions Pll-Ptt/epsilon and Plt at four-momentum transfer squared Q2=0.92 and 1.76 GeV2.Comment: 4 pages, 2 figures, to be submitted to PRL. Figs 1 and 2, lettering enlarge

Radiation tail in (e,e ` p) reactions and corrections to experimental data

We present a direct calculation of the cross section for the reaction He-3(e,e’p) including the radiation tail originating from bremsstrahlung processes. This calculation is compared to measured cross sections. The calculation is carried out from within a Monte Carlo simulation program so that acceptance-averaging effects, along with a subset of possible energy losses, are taken into account. Excellent agreement is obtained between our calculation and measured data, after a correction factor fur higher-order bremsstrahlung is devised and applied to the tail. Industry-standard radiative corrections fail fur these data, and we use the results of our calculation to dissect the failure. Implications for design and analysis of experiments in the Jefferson-Laboratory energy domain are discussed

Using model checking to analyze the system behavior of the LHC production grid

DIRAC (Distributed Infrastructure with Remote Agent Control) is the grid solution designed to support production activities as well as user data analysis for the Large Hadron Collider beauty experiment. It consists of cooperating distributed services and a plethora of light-weight agents delivering the workload to the grid resources. Services accept requests from agents and running jobs, while agents actively fulfill specific goals. Services maintain database back-ends to store dynamic state information of entities such as jobs, queues, or requests for data transfer. Agents continuously check for changes in the service states, and react to these accordingly. The logic of each agent is rather simple; the main source of complexity lies in their cooperation. These agents run concurrently, and communicate using the services’ databases as a shared memory for synchronizing the state transitions. Despite the effort invested in making DIRAC reliable, entities occasionally get into inconsistent states. Tracing and fixing such behaviors is difficult, given the inherent parallelism among the distributed components and the size of the implementation. In this paper we present an analysis of DIRAC with mCRL2, process algebra with data. We have reverse engineered two critical and related DIRAC subsystems, and subsequently modeled their behavior with the mCRL2 toolset. This enabled us to easily locate race conditions and livelocks which were confirmed to occur in the real system. We further formalized and verified several behavioral properties of the two modeled subsystems. Keywords: Model checking; Process algebra; Grid; LHC; Distributed system; Workflo

Property specification made easy : harnessing the power of model checking in UML designs

Developing correct concurrent software is challenging. Design errors can result in deadlocks, race conditions and livelocks, and discovering these is difficult. A serious obstacle for an industrial uptake of rigorous analysis techniques such as model checking is the learning curve associated to the languages — typically temporal logics — used for specifying the application-specific properties to be checked. To bring the process of correctly eliciting functional properties closer to software engineers, we introduce PASS, a Property ASSistant wizard as part of a UML-based front-end to the mCRL2 toolset. PASS instantiates pattern templates using three notations: a natural language summary, a µ-calculus formula and a UML sequence diagram depicting the desired behavior. Most approaches to date have focused on LTL, which is a state-based formalism. Conversely, µ-calculus is event-based, making it a good match for sequence diagrams, where communication between components is depicted. We revisit a case study from the Grid domain, using PASS to obtain the formula and monitor for checking the property

The He-4(e, e ' p) cross section at high missing energies

The He-4(e, e' p) reaction has been studied in a kinematic regime in which short-range correlations are expected to have a strong impact on the reaction strength. The measured cross sections exhibit a bump-shaped structure at missing energies corresponding to quasi-free knockout of two nucleons. The results of microscopic calculations, that account for meson-exchange currents, intermediate Delta -excitation and final-state interactions, reproduce the data satisfactorily. The calculations indicate that at small proton emission angles the cross section is dominated by knockout of a correlated nucleon pair.

Relativistic effects in the electrodisintegration of deuterium

The structure function R(LT) and the cross-section asymmetry A(phi) with respect to the direction of the momentum transfer in the reaction H-2(e, e'p) have been measured at a four-momentum transfer squared of 0.2 (GeV/c)(2), for missing momenta between 160 and 220 MeV/c at an invariant mass of 1050 MeV. For a proper description of these data calculations that include a relativistic form of the nucleon current operator are favoured. The absolute 2H(e, e'p) cross-section data favour a covariant calculation over non-relativistic calculations with relativistic corrections

Deuteron electrodisintegration at high missing momenta

The reaction (2)H(e, e'p) has been studied at an invariant mass W of 1050 MeV, i.e. well below the Delta(1232) resonance, Cross sections have been obtained at values of Q(2), the four-momentum transfer squared, of 0.10, 0.20, and 0.28 (GeV/c)(2), covering a missing-momentum range from 150 to 700 MeV/c. The data are compared to the results of covariant calculations of Tjon, and the results of calculations based on a Schrodinger formalism due to Laget and the Mainz group, respectively. The data are well described by the calculations of the Mainz group, whereas they are underestimated by Tjon's calculations at high missing momenta. The calculations of Laget, on the other hand, overestimate the data at low missing momenta, but give a good account of the data at high missing momenta. More detailed considerations reveal that the Delta(1232) contributions are dominant at high missing momenta. However, the lacking Delta(1232) contribution in Tjon's calculations is not enough to explain the large discrepancy between his calculation and the present (2)H(e, e'p) data at high missing momentum. Probably the deuteron wave function employed in the covariant calculations has a D-state contribution that is too small

Deuteron electrodisintegration in the Delta-resonance region

The differential cross section and the transverse-transverse interference structure function for the reaction H-2(e,e'p)n have been determined at an np invariant mass of 2.16 GeV. The data, covering a 40 degrees range in the proton emission angle, indicate that Delta excitation and subsequent N Delta interaction is the dominant reaction mechanism. Calculations performed within an N Delta coupled-channel approach reproduce the cross section data, but underestimate the f(TT) results by 30 to 40 percent

Proton detection with large-acceptance scintillator detection systems in electron-scattering environments

Two highly segmented plastic-scintillator arrays have been developed for proton detection in electron scattering experiments. The detectors subtend solid angles of 225 and 550 msr and cover energy ranges of 50-225 and 25-165 MeV, respectively. The charge and arrival time of each photomultiplier signal are digitized by flash ADCs and temporarily stored in a dual-port memory. The readout parameters are computer controlled, tuned, and monitored. These detectors have been employed in (e, e'p) and (e, e'pp) experiments for proton emission angles greater than 30 degrees and for luminosities up to 10(36) nucleons cm(-2) s(-1). The singles counting rates in the scintillator elements of the first layers were about 0.5 x 10(6) particles s(-1) and the trigger rate 1 MHz. The measured resolution in the excitation energy and timing spectra are 2.7% and 0.7 ns, respectively. (C) 1999 Elsevier Science B.V. All rights reserved