Measurement of cosmic-ray low-energy antiproton spectrum with the first BESS-Polar Antarctic flight

The BESS-Polar spectrometer had its first successful balloon flight over Antarctica in December 2004. During the 8.5-day long-duration flight, almost 0.9 billion events were recorded and 1,520 antiprotons were detected in the energy range 0.1-4.2 GeV. In this paper, we report the antiproton spectrum obtained, discuss the origin of cosmic-ray antiprotons, and use antiprotons to probe the effect of charge sign dependent drift in the solar modulation.Comment: 18 pages, 1 table, 5 figures, submitted to Physics Letters

Measurements of Atmospheric Antiprotons

We measured atmospheric antiproton spectra in the energy range 0.2 to 3.4 GeV, at sea level and at balloon altitude in the atmospheric depth range 4.5 to 26 g/cm^2. The observed energy spectra, including our previous measurements at mountain altitude, were compared with estimated spectra calculated on various assumptions regarding the energy distribution of antiprotons that interacted with air nuclei.Comment: Accepted for publication in PL

Balloon Measurements of Cosmic Ray Muon Spectra in the Atmosphere along with those of Primary Protons and Helium Nuclei over Mid-Latitude

We report here the measurements of the energy spectra of atmospheric muons and of the cosmic ray primary proton and helium nuclei in a single experiment. These were carried out using the MASS superconducting spectrometer in a balloon flight experiment in 1991. The relevance of these results to the atmospheric neutrino anomaly is emphasized. In particular, this approach allows uncertainties caused by the level of solar modulation, the geomagnetic cut-off of the primaries and possible experimental systematics to be decoupled in the comparison of calculated fluxes of muons to measured muon fluxes. The muon observations cover the momentum and depth ranges of 0.3-40 GeV/c and 5-886 g/cmsquared, respectively. The proton and helium primary measurements cover the rigidity range from 3 to 100 GV, in which both the solar modulation and the geomagnetic cut-off affect the energy spectra at low energies.Comment: 31 pages, including 17 figures, simplified apparatus figure, to appear in Phys. Rev.

Interaction of quasilocal harmonic modes and boson peak in glasses

The direct proportionality relation between the boson peak maximum in glasses, $\omega_b$, and the Ioffe-Regel crossover frequency for phonons, $\omega_d$, is established. For several investigated materials $\omega_b = (1.5\pm 0.1)\omega_d$. At the frequency $\omega_d$ the mean free path of the phonons $l$ becomes equal to their wavelength because of strong resonant scattering on quasilocal harmonic oscillators. Above this frequency phonons cease to exist. We prove that the established correlation between $\omega_b$ and $\omega_d$ holds in the general case and is a direct consequence of bilinear coupling of quasilocal oscillators with the strain field.Comment: RevTex, 4 pages, 1 figur

Measurements of Proton, Helium and Muon Spectra at Small Atmospheric Depths with the BESS Spectrometer

The cosmic-ray proton, helium, and muon spectra at small atmospheric depths of 4.5 -- 28 g/cm^2 were precisely measured during the slow descending period of the BESS-2001 balloon flight. The variation of atmospheric secondary particle fluxes as a function of atmospheric depth provides fundamental information to study hadronic interactions of the primary cosmic rays with the atmosphere.Comment: 21 pages, 11 figures, 4 table

On possible interpretations of the high energy electron-positron spectrum measured by the Fermi Large Area Telescope

The Fermi-LAT experiment recently reported high precision measurements of the spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV. The spectrum shows no prominent spectral features, and is significantly harder than that inferred from several previous experiments. Here we discuss several interpretations of the Fermi results based either on a single large scale Galactic CRE component or by invoking additional electron-positron primary sources, e.g. nearby pulsars or particle Dark Matter annihilation. We show that while the reported Fermi-LAT data alone can be interpreted in terms of a single component scenario, when combined with other complementary experimental results, specifically the CRE spectrum measured by H.E.S.S. and especially the positron fraction reported by PAMELA between 1 and 100 GeV, that class of models fails to provide a consistent interpretation. Rather, we find that several combinations of parameters, involving both the pulsar and dark matter scenarios, allow a consistent description of those results. We also briefly discuss the possibility of discriminating between the pulsar and dark matter interpretations by looking for a possible anisotropy in the CRE flux.Comment: 29 pages, 12 figures. Final version accepted for publication in Astroparticle Physic

Propagation of secondary antiprotons and cosmic rays in the Galaxy

Recent measurements of the cosmic ray (CR) antiproton flux have been shown to challenge existing CR propagation models. It was shown that the reacceleration models designed to match secondary to primary nuclei ratios (e.g., B/C) produce too few antiprotons. In the present paper we discuss one possibility to overcome these difficulties. Using the measured antiproton flux AND B/C ratio to fix the diffusion coefficient, we show that the spectra of primary nuclei as measured in the heliosphere may contain a fresh local "unprocessed" component at low energies perhaps associated with the Local Bubble, thus decreasing the measured secondary to primary nuclei ratio. The independent evidence for SN activity in the solar vicinity in the last few Myr supports this idea. The model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni (Z<=28). Calculated isotopic distributions of Be and B are in perfect agreement with CR data. The abundances of three "radioactive clock" isotopes in CR, 10Be, 26Al, 36Cl, are all consistent and indicate a halo size z_h~4 kpc based on the most accurate data taken by the ACE spacecraft.Comment: 6 pages, 5 ps-figures, cospar.sty; Proc. of 34th COSPAR Scientific Assembly (Houston, 10-19 October 2002). Submitted to Advances in Space Research. More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm

Design, Commissioning and Performance of the PIBETA Detector at PSI

We describe the design, construction and performance of the PIBETA detector built for the precise measurement of the branching ratio of pion beta decay, pi+ -> pi0 e+ nu, at the Paul Scherrer Institute. The central part of the detector is a 240-module spherical pure CsI calorimeter covering 3*pi sr solid angle. The calorimeter is supplemented with an active collimator/beam degrader system, an active segmented plastic target, a pair of low-mass cylindrical wire chambers and a 20-element cylindrical plastic scintillator hodoscope. The whole detector system is housed inside a temperature-controlled lead brick enclosure which in turn is lined with cosmic muon plastic veto counters. Commissioning and calibration data were taken during two three-month beam periods in 1999/2000 with pi+ stopping rates between 1.3*E3 pi+/s and 1.3*E6 pi+/s. We examine the timing, energy and angular detector resolution for photons, positrons and protons in the energy range of 5-150 MeV, as well as the response of the detector to cosmic muons. We illustrate the detector signatures for the assorted rare pion and muon decays and their associated backgrounds.Comment: 117 pages, 48 Postscript figures, 5 tables, Elsevier LaTeX, submitted to Nucl. Instrum. Meth.

Stochastic Production Of Kink-Antikink Pairs In The Presence Of An Oscillating Background

We numerically investigate the production of kink-antikink pairs in a $(1+1)$ dimensional $\phi^4$ field theory subject to white noise and periodic driving. The twin effects of noise and periodic driving acting in conjunction lead to considerable enhancement in the kink density compared to the thermal equilibrium value, for low dissipation coefficients and for a specific range of frequencies of the oscillating background. The dependence of the kink-density on the temperature of the heat bath, the amplitude of the oscillating background and value of the dissipation coefficient is also investigated. An interesting feature of our result is that kink-antikink production occurs even though the system always remains in the broken symmetry phase.Comment: Revtex, 21 pages including 7 figures; more references adde

Comportamento à flexão de vigas eco-eficientes de ultra elevada durabilidade

Atualmente, o ecossistema mundial tem vindo a ser confrontado com problemas de grande importância, a elevada poluição do meio ambiente e a limitação dos recursos energéticos. Estes problemas têm contribuído para que a sustentabilidade da construção seja uma prioridade cada vez maior no presente e no futuro. A manutenção e a reabilitação do património construído surge como uma das medidas mais eficazes para prevenir ou reduzir o consumo de energia no setor da construção. No caso da construção nova, a tendência é para verificar-se um aumento da utilização de elementos estruturais pré-fabricados com partes betonadas em obra, obtendose uma maior rapidez de execução associada a um maior controlo de qualidade. O betão de ultra elevada durabilidade, reforçado com fibras metálicas, é considerado um material inovador desenvolvido nas últimas décadas, apresentando um conjunto de caraterísticas especiais, como a durabilidade, a facilidade de aplicação, as elevadas resistências mecânicas, tornando-o num produto particularmente atraente para a reabilitação e reforço de estruturas de betão. No entanto, este betão não deve ser produzido em grandes quantidades devido ao elevado consumo de cimento e adições, resultando em elevados custos económicos e ambientais. Considerando estas desvantagens é proposto que o betão de ultra elevada durabilidade seja usado apenas na camada de recobrimento, formando-se assim uma superskin que protege o elemento estrutural dos ambientes mais agressivos, isto é, aumenta a durabilidade das estruturas de betão sem que, no entanto, seja criado um impacte ambiental muito significativo (a quantidade de CO2 libertada para a atmosfera é menor devido ao menor consumo de cimento e adições). A presente dissertação pretende explorar o conceito de superskin do ponto de vista do comportamento estrutural, nomeadamente, estudar o comportamento de vigas sujeitas a esforços de flexão, compostas por uma camada exterior de betão de ultra elevada durabilidade, associado a um núcleo com betão eco-eficiente, com baixa dosagem de cimento, de modo a obter uma solução mais durável e ao mesmo tempo, ecologicamente mais eficiente. Foram realizadas oito vigas com diferentes taxas de armadura: quatro vigas produzidas apenas com betão com baixa dosagem de cimento (usadas como vigas de referência) e quatro vigas produzidas com um betão de ultra elevada durabilidade na camada de recobrimento e com um betão com baixa dosagem de cimento no núcleo. As diferentes taxas de armadura longitudinal permitem avaliar a influência da superskin em vigas com roturas dúcteis e frágeis. Com base nos dados recolhidos durante os ensaios experimentais estudou-se: (i) relação cargadeslocamento; (ii) os valores teóricos e experimentais do momento resistente; (iii) a evolução da curvatura nas secções críticas; (iv) a evolução da rigidez à flexão com a carga aplicada; (v) a ductilidade; e (vi) a fendilhação e o tipo de rotura. Da análise de resultados foi possível verificar que o recobrimento em betão de ultra elevada durabilidade é uma solução com aspetos muito positivos, nomeadamente, aumenta a resistência à flexão das vigas