arXiv subjects

M. Velasco

Publications and source records attributed to M. Velasco.

24 records · Page 2Linked to original sources

arXiv2004

Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons

We present the first experimental results on the use of a thick aligned Si crystal acting as a quarter wave plate to induce a degree of circular polarisation in a high energy linearly polarised photon beam. The linearly polarised photon beam is produced from coherent bremsstrahlung radiation by 178 GeV unpolarised electrons incident on an aligned Si crystal, acting as a radiator. The linear polarisation of the photon beam is characterised by measuring the asymmetry in electron-positron pair production in a Ge crystal, for different crystal orientations. The Ge crystal therefore acts as an analyser. The birefringence phenomenon, which converts the linear polarisation to circular polarisation, is observed by letting the linearly polarised photons beam pass through a thick Si quarter wave plate crystal, and then measuring the asymmetry in electron-positron pair production again for a selection of relative angles between the crystallographic planes of the radiator, analyser and quarter wave plate. The systematics of the difference between the measured asymmetries with and without the quarter wave plate are predicted by theory to reveal an evolution in the Stokes parameters from which the appearance of a circularly polarised component in the photon beam can be demonstrated. The measured magnitude of the circularly polarised component was consistent with the theoretical predictions, and therefore is in indication of the existence of the birefringence effect.

hep-ex↗

arXiv2004

Measurement of Coherent Emission and Linear Polarization of Photons by Electrons in the Strong Fields of Aligned Crystals

We present new results regarding the features of high energy photon emission by an electron beam of 178 GeV penetrating a 1.5 cm thick single Si crystal aligned at the Strings-Of-Strings (SOS) orientation. This concerns a special case of coherent bremsstrahlung where the electron interacts with the strong fields of successive atomic strings in a plane and for which the largest enhancement of the highest energy photons is expected. The polarization of the resulting photon beam was measured by the asymmetry of electron-positron pair production in an aligned diamond crystal analyzer. By the selection of a single pair the energy and the polarization of individual photons could be measured in an the environment of multiple photons produced in the radiator crystal. Photons in the high energy region show less than 20% linear polarization at the 90% confidence level.

hep-ex↗

arXiv2002

Physics Potential at FNAL with Stronger Proton Sources

This document is the second in a series of reports on the exciting physics that would be accessible at Fermilab in the event of an upgraded proton source. Where the first report covered a broad range of topics, this report focuses specifically on three areas of study: there are brief discussions on the new measurements one could make in both the neutron and anti-proton sectors, and then a detailed discussion of what could be achieved in the neutrino oscillation sector using an upgraded proton source to supply the NuMI beamline with more protons. If one places a new detector optimized for $ν_e$ appearance at a new location slightly off the axis defined by the MINOS experiment, that new experiment would be ideal for making the next important steps in lepton flavor studies, namely, the search for $ν_μ\to ν_e$ at the atmospheric mass splitting, and CP violations. The report concludes with a summary of proton economics and demands for increased proton intensity for the Booster and Main Injector: what the proton source at Fermilab can currently supply, and what adiabatic changes could be implemented to boost the proton supply on the way from here to a proton driver upgrade.

hep-ex↗

arXiv2001

Results of the Survey on the Future of HEP

The Young Physicists Panel (YPP) summarizes results from their Survey on the Future of High Energy Physics, which was conducted from July 2 to July 15, 2001. Over 1500 physicists from around the world, both young and tenured, responded to the survey. We first describe the origin, design, and advertisement of the survey, and then present the demographics of the respondents. Following sections analyze the collected opinions on the desire for balance in the field, the impact of globalization, the necessity of outreach, how to build the field, the physics that drives the field, and the selection of the next big machine. Respondents' comments follow the survey analysis in an appendix.

hep-ex↗

arXiv2001

The Potential for Neutrino Physics at Muon Colliders and Dedicated High Current Muon Storage Rings

Conceptual design studies are underway for muon colliders and other high-current muon storage rings that have the potential to become the first true ``neutrino factories''. Muon decays in long straight sections of the storage rings would produce precisely characterized beams of electron and muon type neutrinos of unprecedented intensity. This article reviews the prospects for these facilities to greatly extend our capabilities for neutrino experiments, largely emphasizing the physics of neutrino interactions.

hep-ph↗

arXiv2000

Physics at a Neutrino Factory

In response to the growing interest in building a Neutrino Factory to produce high intensity beams of electron- and muon-neutrinos and antineutrinos, in October 1999 the Fermilab Directorate initiated two six-month studies. The first study, organized by N. Holtkamp and D. Finley, was to investigate the technical feasibility of an intense neutrino source based on a muon storage ring. This design study has produced a report in which the basic conclusion is that a Neutrino Factory is technically feasible, although it requires an aggressive R&D program. The second study, which is the subject of this report, was to explore the physics potential of a Neutrino Factory as a function of the muon beam energy and intensity, and for oscillation physics, the potential as a function of baseline.

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