The Architecture of MEG Simulation and Analysis Software

MEG (Mu to Electron Gamma) is an experiment dedicated to search for the $\mu^+ \rightarrow e^+\gamma$ decay that is strongly suppressed in the Standard Model but predicted in several Super Symmetric extensions of it at an accessible rate. MEG is a small-size experiment ($\approx 50-60$ physicists at any time) with a life span of about 10 years. The limited human resource available, in particular in the core offline group, emphasized the importance of reusing software and exploiting existing expertise. Great care has been devoted to provide a simple system that hides implementation details to the average programmer. That allowed many members of the collaboration to contribute to the development of the software of the experiment with limited programming skill. The offline software is based on two frameworks: {\bf REM} in FORTRAN 77 used for the event generation and detector simulation package {\bf GEM}, based on GEANT 3, and {\bf ROME} in C++ used in the readout simulation {\bf Bartender} and in the reconstruction and analysis program {\bf Analyzer}. Event display in the simulation is based on GEANT 3 graphic libraries and in the reconstruction on ROOT graphic libraries. Data are stored in different formats in various stage of the processing. The frameworks include utilities for input/output, database handling and format conversion transparent to the user.Comment: Presented at the IEEE NSS Knoxville, 2010 Revised according to referee's remarks Accepted by European Physical Journal Plu

THE CAVES Project - Collaborative Analysis Versioning Environment System; THE CODESH Project - Collaborative Development Shell

A key feature of collaboration in science and software development is to have a {\em log} of what and how is being done - for private use and reuse and for sharing selected parts with collaborators, which most often today are distributed geographically on an ever larger scale. Even better if this log is {\em automatic}, created on the fly while a scientist or software developer is working in a habitual way, without the need for extra efforts. The {\tt CAVES} and {\tt CODESH} projects address this problem in a novel way, building on the concepts of {\em virtual state} and {\em virtual transition} to provide an automatic persistent logbook for sessions of data analysis or software development in a collaborating group. A repository of sessions can be configured dynamically to record and make available the knowledge accumulated in the course of a scientific or software endeavor. Access can be controlled to define logbooks of private sessions and sessions shared within or between collaborating groups.Comment: 4 pages, presented at the Meeting of the Division of Particles and Fields of the APS, Riverside, USA, August 200

Quantum state diffusion with a moving basis: computing quantum-optical spectra

Quantum state diffusion (QSD) as a tool to solve quantum-optical master equations by stochastic simulation can be made several orders of magnitude more efficient if states in Hilbert space are represented in a moving basis of excited coherent states. The large savings in computer memory and time are due to the localization property of the QSD equation. We show how the method can be used to compute spectra and give an application to second harmonic generation.Comment: 8 pages in RevTeX, 1 uuencoded postscript figure, submitted to Phys. Rev.

Extra Shared Entanglement Reduces Memory Demand in Quantum Convolutional Coding

We show how extra entanglement shared between sender and receiver reduces the memory requirements for a general entanglement-assisted quantum convolutional code. We construct quantum convolutional codes with good error-correcting properties by exploiting the error-correcting properties of an arbitrary basic set of Pauli generators. The main benefit of this particular construction is that there is no need to increase the frame size of the code when extra shared entanglement is available. Then there is no need to increase the memory requirements or circuit complexity of the code because the frame size of the code is directly related to these two code properties. Another benefit, similar to results of previous work in entanglement-assisted convolutional coding, is that we can import an arbitrary classical quaternary code for use as an entanglement-assisted quantum convolutional code. The rate and error-correcting properties of the imported classical code translate to the quantum code. We provide an example that illustrates how to import a classical quaternary code for use as an entanglement-assisted quantum convolutional code. We finally show how to "piggyback" classical information to make use of the extra shared entanglement in the code.Comment: 7 pages, 1 figure, accepted for publication in Physical Review

Soft X-ray emission in kink-unstable coronal loops

Solar flares are associated with intense soft X-ray emission generated by the hot flaring plasma. Kink unstable twisted flux-ropes provide a source of magnetic energy which can be released impulsively and account for the flare plasma heating. We compute the temporal evolution of the thermal X-ray emission in kink-unstable coronal loops using MHD simulations and discuss the results of with respect to solar flare observations. The model consists of a highly twisted loop embedded in a region of uniform and untwisted coronal magnetic field. We let the kink instability develop, compute the evolution of the plasma properties in the loop (density, temperature) without accounting for mass exchange with the chromosphere. We then deduce the X-ray emission properties of the plasma during the whole flaring episode. During the initial phase of the instability plasma heating is mostly adiabatic. Ohmic diffusion takes over as the instability saturates, leading to strong and impulsive heating (> 20 MK), to a quick enhancement of X-ray emission and to the hardening of the thermal X-ray spectrum. The temperature distribution of the plasma becomes broad, with the emission measure depending strongly on temperature. Significant emission measures arise for plasma at temperatures T > 9 MK. The magnetic flux-rope then relaxes progressively towards a lower energy state as it reconnects with the background flux. The loop plasma suffers smaller sporadic heating events but cools down conductively. The total thermal X-ray emission slowly fades away during this phase, and the high temperature component of emission measure distribution converges to the power-law distribution $EM\propto T^{-4.2}$. The amount of twist deduced directly from the X-ray emission patterns is considerably lower than the maximum magnetic twist in the simulated flux-ropes.Comment: submitted to A&

Impingement of Cloud Droplets on 36.5-Percent-Thick Joukowski Airfoil at Zero Angle of Attack and Discussion of Use as Cloud Measuring Instrument in Dye-Tracer Technique

The trajectories of droplets i n the air flowing past a 36.5-percent-thick Joukowski airfoil at zero angle of attack were determined. The amount of water i n droplet form impinging on the airfoil, the area of droplet impingement, and the rate of droplet impingement per unit area on the airfoil surface were calculated from the trajectories and cover a large range of flight and atmospheric conditions. With the detailed impingement information available, the 36.5-percent-thick Joukowski airfoil can serve the dual purpose of use as the principal element in instruments for making measurements in clouds and of a basic shape for estimating impingement on a thick streamlined body. Methods and examples are presented for illustrating some limitations when the airfoil is used as the principal element in the dye-tracer technique

Electronic and optical properties of graphene antidot lattices: Comparison of Dirac and tight-binding models

The electronic properties of graphene may be changed from semimetallic to semiconducting by introducing perforations (antidots) in a periodic pattern. The properties of such graphene antidot lattices (GALs) have previously been studied using atomistic models, which are very time consuming for large structures. We present a continuum model that uses the Dirac equation (DE) to describe the electronic and optical properties of GALs. The advantages of the Dirac model are that the calculation time does not depend on the size of the structures and that the results are scalable. In addition, an approximation of the band gap using the DE is presented. The Dirac model is compared with nearest-neighbour tight-binding (TB) in order to assess its accuracy. Extended zigzag regions give rise to localized edge states, whereas armchair edges do not. We find that the Dirac model is in quantitative agreement with TB for GALs without edge states, but deviates for antidots with large zigzag regions.Comment: 15 pages, 7 figures. Accepted by Journal of Physics: Condensed matte

Flux-tube geometry and solar wind speed during an activity cycle

The solar wind speed at 1 AU shows variations in latitude and in time which reflect the evolution of the global background magnetic field during the activity cycle. It is commonly accepted that the terminal wind speed in a magnetic flux-tube is anti-correlated with its expansion ratio, which motivated the definition of widely-used semi-empirical scaling laws relating one to the other. In practice, such scaling laws require ad-hoc corrections. A predictive law based solely on physical principles is still missing. We test whether the flux-tube expansion is the controlling factor of the wind speed at all phases of the cycle and at all latitudes using a very large sample of wind-carrying open magnetic flux-tubes. We furthermore search for additional physical parameters based on the geometry of the coronal magnetic field which have an influence on the terminal wind flow speed. We use MHD simulations of the corona and wind coupled to a dynamo model to provide a large statistical ensemble of open flux-tubes which we analyse conjointly in order to identify relations of dependence between the wind speed and geometrical parameters of the flux-tubes which are valid globally (for all latitudes and moments of the cycle). Our study confirms that the terminal speed of the solar wind depends very strongly on the geometry of the open magnetic flux-tubes through which it flows. The total flux-tube expansion is more clearly anti-correlated with the wind speed for fast rather than for slow wind flows, and effectively controls the locations of these flows during solar minima. Overall, the actual asymptotic wind speeds attained are also strongly dependent on field-line inclination and magnetic field amplitude at the foot-points. We suggest ways of including these parameters on future predictive scaling-laws for the solar wind speed.Comment: Accepted for publicaton on Astronomy & Astrophysic

Antiproton and Positron Signal Enhancement in Dark Matter Mini-Spikes Scenarios

The annihilation of dark matter (DM) in the Galaxy could produce specific imprints on the spectra of antimatter species in Galactic cosmic rays, which could be detected by upcoming experiments such as PAMELA and AMS02. Recent studies show that the presence of substructures can enhance the annihilation signal by a "boost factor" that not only depends on energy, but that is intrinsically a statistical property of the distribution of DM substructures inside the Milky Way. We investigate a scenario in which substructures consist of $\sim 100$ "mini-spikes" around intermediate-mass black holes. Focusing on primary positrons and antiprotons, we find large boost factors, up to a few thousand, that exhibit a large variance at high energy in the case of positrons and at low energy in the case of antiprotons. As a consequence, an estimate of the DM particle mass based on the observed cut-off in the positron spectrum could lead to a substantial underestimate of its actual value.Comment: 13 pages, 9 figures, minor changes, version accepted for publication in PR

Compatibility of quantum states

We introduce a measure of the compatibility between quantum states--the likelihood that two density matrices describe the same object. Our measure is motivated by two elementary requirements, which lead to a natural definition. We list some properties of this measure, and discuss its relation to the problem of combining two observers' states of knowledge.Comment: 4 pages, no figure