1,722,006 research outputs found
Status and prospects of charged lepton flavor violation searches with the MEG-II experiment
No full textThe MEG experiment took data at the Paul Scherrer Institut (PSI) in the years 2009-2013 and published the most stringent limit on the charged lepton flavor violating decay μ → eγ: BR(μ → eγ) < 4.2 ×10−13 @90% C.L. The MEG detector is currently being upgraded in order to reach a sensitivity of ∼ 4 × 10−14, which corresponds to an improvement of one order of magnitude. The basic idea of MEG-II is to achieve the highest possible sensitivity by making the maximum use (7 × 107 muons/s) of the available muon intensity at PSI with an improved detector, keeping the background at a manageable level. The status of the MEG-II detector and the current schedule will be presented. MEG-II, together with the next generation charged lepton flavor violation experiments Mu3e (μ+ → e+e−e+) at PSI and Mu2e and COMET (μ → e conversion) at Fermilab and J-PARC respectively, will reach very high sensitivities in the next years. Accelerator upgrades are expected that will make muon beams with intensities of the order of 1010 muons/s feasible. At this extremely high beam rates, new detector concepts should be adopted in order to overcome the accidental background. Some future directions will be discussed
Future μ → eγ experiments
No full textExperiments with muons are a unique window to investigate the Standard Model of particle physics and to look for New Physics effects with high sensitivity. The search for the lepton flavor violating μ+ → e+γ decay will reach a sensitivity of few 10-14 within the next three years thanks to the MEG II experiment, presently taking data at the Paul Scherrer Institut, with a beam intensity of 4 × 107 muons/s. On the other hand, there is a world-wide effort to increase the muon beams intensity at present facilities by a factor 100. In order to exploit such intense muon beams a new generation of experiments has to be designed, since the present experimental concept is not adequate to deal with the expected increase in rate, radiation and background. An international study group has been recently set, the Study Group for Future μ → eγ search experiments, to organize this effort. This paper reviews the present main experimental directions identified, the results of simulations and R&D studies made so far
A novel dual-mode tracking device for online dose monitoring in hadron therapy
No full textHadron therapy is a technique for cancer treatment that exploits ion beams (mostly protons and carbons). Due to the shape of the hadron energy deposition pattern, dose releases are more localized with respect to radiotherapy. Hadron therapy is thus particularly suitable to treat tumors close to critical organs. A critical issue is the monitoring accuracy of the dose released by the beam to the patient. We present the design of a dual-tracking device capable of on-line dose monitoring through the detection of prompt photons and charged particles produced by the interactions of the beam in the patient tissues whose emission shapes are correlated to spatial dose release and to the Bragg peak. The dosimeter, whose design has been optimized using Monte Carlo simulations, is composed of a tracker made of six scintillating fiber stations followed by a layer of plastic scintillator (electron shield) and a lyso pixellated crystal to detect photons. A first tracker layer has been assembled and is under test. A complete simulation and reconstruction software has been developed to estimate the achievable spatial resolution. Charged particles are reconstructed using the fiber planes and those identified as protons are back-traced to determine the point of origin. Prompt photons are reconstructed exploiting their Compton interactions by combining the spatial and energy measurements from the tracker for the electron and from the lyso for the photon. For a real hadrotherapeutic treatment the achievable resolution is of the order of ten (few) millimeters using the neutral (charged) component
Combined readout of a triple-GEM detector
No full textOptical readout of GEM based devices by means of high granularity and low noise CMOS sensors allows to obtain very interesting tracking performance. Space resolution of the order of tens of μm were measured on the GEM plane along with an energy resolution of 20%÷30%. The main limitation of CMOS sensors is represented by their poor information about time structure of the event. In this paper, the use of a concurrent light readout by means of a suitable photomultiplier and the acquisition of the electric signal induced on the GEM electrode are exploited to provide the necessary timing informations. The analysis of the PMT waveform allows a 3D reconstruction of each single clusters with a resolution on z of 100 μm. Moreover, from the PMT signals it is possible to obtain a fast reconstruction of the energy released within the detector with a resolution of the order of 25% even in the tens of keV range useful, for example, for triggering purpose
The design of the MEG II experiment: MEG II Collaboration
No full textThe MEG experiment, designed to search for the μ+→ e+γ decay, completed data-taking in 2013 reaching a sensitivity level of 5.3 × 10- 13for the branching ratio. In order to increase the sensitivity reach of the experiment by an order of magnitude to the level of 6 × 10- 14, a total upgrade, involving substantial changes to the experiment, has been undertaken, known as MEG II. We present both the motivation for the upgrade and a detailed overview of the design of the experiment and of the expected detector performance
Gas distribution and monitoring for the drift chamber of the MEG II experiment
No full textThe reconstruction of the positron trajectory in the MEG II experiment searching for the μ+e+γ decay uses a cylindrical drift chamber operated with a helium-isobutane gas mixture. A stable performance of the detector in terms of its electron drift properties, avalanche multiplication, and with a gas mixture of controlled composition and purity has to be provided and continuously monitored. In this paper we describe the strategies adopted to meet the requirements imposed by the target sensitivity of MEG II, including the construction and commissioning of a small chamber for an online monitoring of the gas quality
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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