Majorana and the theoretical problem of photon-electron scattering

Relevant contributions by Majorana regarding Compton scattering off free or bound electrons are considered in detail, where a (full quantum) generalization of the Kramers-Heisenberg dispersion formula is derived. The role of intermediate electronic states is appropriately pointed out in recovering the standard Klein-Nishina formula (for free electron scattering) by making recourse to a limpid physical scheme alternative to the (then unknown) Feynman diagram approach. For bound electron scattering, a quantitative description of the broadening of the Compton line was obtained for the first time by introducing a finite mean life for the excited state of the electron system. Finally, a generalization aimed to describe Compton scattering assisted by a non-vanishing applied magnetic field is as well considered, revealing its relevance for present day research.Comment: latex, amsart, 10 pages, 1 figur

A study of the angular resolution of the ALICE HMPID CsI-RICH detector

In this report is presented an investigation of the Cherenkov angleresolution $\sigma_{\theta_c}$ achievable in the High MomentumParticle Identification (HMPID) CsI-RICH detector of ALICE.Two angle reconstruction procedures are described and the single contributions affecting the resolution are evaluated throughthe analytical treatment and the Monte Carlo simulation program{\em RICHSIM}. The $\sigma_{\theta_c}$ dependence on various detector parameters, namely the radiator thickness, the proximity gap thickness and the chamber gain, has been studied carrying out beam tests of CsI-RICH prototypes.A ring resolution of about 2 mrad has been achieved,for $\beta$=1 particles, in the optimal detector configuration (10 mm C$_6$F$_{14}$ radiator thickness, 103 mm proximity gap and 40 ADC channels single electron averagepulse height)

Interpretation of AMS-02 electrons and positrons data

We perform a combined analysis of the recent AMS-02 data on electrons, positrons, electrons plus positrons and positron fraction, in a self-consistent framework where we realize a theoretical modeling of all the astrophysical components that can contribute to the observed fluxes in the whole energy range. The primary electron contribution is modeled through the sum of an average flux from distant sources and the fluxes from the local supernova remnants in the Green catalog. The secondary electron and positron fluxes originate from interactions on the interstellar medium of primary cosmic rays, for which we derive a novel determination by using AMS-02 proton and helium data. Primary positrons and electrons from pulsar wind nebulae in the ATNF catalog are included and studied in terms of their most significant (while loosely known) properties and under different assumptions (average contribution from the whole catalog, single dominant pulsar, a few dominant pulsars). We obtain a remarkable agreement between our various modeling and the AMS-02 data for all types of analysis, demonstrating that the whole AMS-02 leptonic data admit a self-consistent interpretation in terms of astrophysical contributions.Comment: 33 pages, 26 figures and 4 tables, v2: accepted for publication in JCAP, minor changes relative to v

First observation of Cherenkov rings with a large area CsI-TGEM-based RICH prototype

We have built a RICH detector prototype consisting of a liquid C6F14 radiator and six triple Thick Gaseous Electron Multipliers (TGEMs), each of them having an active area of 10x10 cm2. One triple TGEM has been placed behind the liquid radiator in order to detect the beam particles, whereas the other five have been positioned around the central one at a distance to collect the Cherenkov photons. The upstream electrode of each of the TGEM stacks has been coated with a 0.4 micron thick CsI layer. In this paper, we will present the results from a series of laboratory tests with this prototype carried out using UV light, 6 keV photons from 55Fe and electrons from 90Sr as well as recent results of tests with a beam of charged pions where for the first time Cherenkov Ring images have been successfully recorded with TGEM photodetectors. The achieved results prove the feasibility of building a large area Cherenkov detector consisting of a matrix of TGEMs.Comment: Presented at the International Conference NDIP-11, Lyon,July201

Global Value Chains during the Great Trade Collapse: A Bullwhip Effect?

This paper analyzes the performance of global value chains during the trade collapse. To do so, it exploits a unique transaction-level dataset on French firms containing information on cross-border monthly transactions matched with data on worldwide intra-firm linkages as defined by property rights (multinational business groups, hierarchies of firms). This newly assembled dataset allows us to distinguish firm-level transactions among two alternative organizational modes of global value chains: internalization of activities (intra-group trade/trade among related parties) or establishment of supply contracts (arm’s length trade/trade among unrelated parties). After an overall assessment of the role of global value chains during the trade collapse, we document that intra-group trade in intermediates was characterized by a faster drop followed by a faster recovery than arm’s length trade. Amplified fluctuations in terms of trade elasticities by value chains have been referred to as the "bullwhip effect" and have been attributed to the adjustment of inventories within supply chains. In this paper we first confirm the existence of such an effect due to trade in intermediates, and we underline the role that different organizational modes can play in driving this adjustment.trade collapse, multinational firms, global value chains, hierarchies of firms, vertical integration.