Browsing by Author "Pimenta, M."
Now showing 1 - 10 of 22
Results Per Page
Sort Options
- A model for the transport of muons in extensive air showersPublication . Cazon, L.; Conceicao, R.; Pimenta, M.; Santos, E.In this article we identify the key elements that govern the propagation of muons from the production in extensive air showers to ground. We describe a model based on simple assumptions that propagates the muons starting from the few relevant distributions at production. We compare the results to the ground distributions given by a full air shower Monte Carlo. This study is motivated by the need of modeling the muon component in extensive air showers with the goal of experimentally reconstructing their distributions at production, which act as a footprint of the hadronic cascade.
- A search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (501 authors); Abreu, P.; Andringa, S.; Assis, P.; Brogueira, P.; Cazon, L.; Conceicao, R.; Diogo, F.; Espadanal, J.; Goncalves, P.; Pimenta, M.; Santo, C.E.; Santos, E.; Tome, B.Observations of cosmic ray arrival directions made with the Pierre Auger Observatory have previously provided evidence of anisotropy at the 99% CL using the correlation of ultra high energy cosmic rays (UHECRs) with objects drawn from the Veron-Cetty Veron catalog. In this paper we report on the use of three catalog independent methods to search for anisotropy. The 2pt-L, 2pt+ and 3pt methods, each giving a different measure of self-clustering in arrival directions, were tested on mock cosmic ray data sets to study the impacts of sample size and magnetic smearing on their results, accounting for both angular and energy resolutions. If the sources of UHECRs follow the same large scale structure as ordinary galaxies in the local Universe and if UHECRs are deflected no more than a few degrees, a study of mock maps suggests that these three methods can efficiently respond to the resulting anisotropy with a P-value = 1.0% or smaller with data sets as few as 100 events. Using data taken from January 1, 2004 to July 31, 2010 we examined the 20, 30,..., 110 highest energy events with a corresponding minimum energy threshold of about 49.3 EeV. The minimum P-values found were 13.5% using the 2pt-L method, 1.0% using the 2pt+ method and 1.1% using the 3pt method for the highest 100 energy events. In view of the multiple (correlated) scans performed on the data set, these catalog-independent methods do not yield strong evidence of anisotropy in the highest energy cosmic rays.
- A Search for Point Sources of EeV NeutronsPublication . Pierre Auger collaboration (509 authors); Abreu, P.; Andringa, S.; Assis, P.; Brogueira, P.; Cazon, L.; Conceicao, R.; Diogo, F.; Espadanal, J.; Goncalves, P.; Pimenta, M.; Santo, C.E.; Santos, E.; Tome, B.A thorough search of the sky exposed at the Pierre Auger Cosmic Ray Observatory reveals no statistically significant excess of events in any small solid angle that would be indicative of a flux of neutral particles from a discrete source. The search covers from -90 to +15 degrees in declination using four different energy ranges above 1 EeV (10^18 eV). The method used in this search is more sensitive to neutrons than to photons. The upper limit on a neutron flux is derived for a dense grid of directions for each of the four energy ranges. These results constrain scenarios for the production of ultra-high energy cosmic rays in the Galaxy.
- Constraints on the origin of cosmic rays above $10^{18}$ eV from large scale anisotropy searches in data of the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (513 authors); Abreu, P.; Andringa, S.; Assis, P.; Brogueira, P.; Cazon, L.; Conceicao, R.; Diogo, F.; Espadanal, J.; Goncalves, P.; Pimenta, M.; Santo, C.E.; Santos, E.; Tome, B.A thorough search for large scale anisotropies in the distribution of arrival directions of cosmic rays detected above $10^{18}$ eV at the Pierre Auger Observatory is reported. For the first time, these large scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above $10^{18}$ eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.
- Depth of maximum of air-shower profiles at the Pierre Auger Observatory. II. Composition implicationsPublication . Pierre Auger collaboration (485 authors); Abreu, P.; Andringa, S.; Assis, P.; Brogueira, P.; Cazon, L.; Conceicao, R.; Diogo, F.; Espadanal, J.; Goncalves, P.; Oliveira, M.; Pimenta, M.; Santo, C.E.; Santos, E.; Sarmento, R.; Tome, B.Using the data taken at the Pierre Auger Observatory between December 2004 and December 2012, we have examined the implications of the distributions of depths of atmospheric shower maximum (Xmax), using a hybrid technique, for composition and hadronic interaction models. We do this by fitting the distributions with predictions from a variety of hadronic interaction models for variations in the composition of the primary cosmic rays and examining the quality of the fit. Regardless of what interaction model is assumed, we find that our data are not well described by a mix of protons and iron nuclei over most of the energy range. Acceptable fits can be obtained when intermediate masses are included, and when this is done consistent results for the proton and iron-nuclei contributions can be found using the available models. We observe a strong energy dependence of the resulting proton fractions, and find no support from any of the models for a significant contribution from iron nuclei. However, we also observe a significant disagreement between the models with respect to the relative contributions of the intermediate components.
- Electroweak Measurements in Electron-Positron Collisions at W-Boson-Pair Energies at LEPPublication . ALEPH, DELPHI, L3, OPAL, LEP Electroweak collaboration (1644 authors); David, A.; Abreu, P.; Andringa, S.; Anjos, N.; Castro, N.; De Angelis, A.; Espirito Santo, M.C.; Goncalves, P.; Onofre, A.; Pimenta, M.; Tome, B.; Veloso, F.Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb$^{-1}$ collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, $M_W$ and $\Gamma_W$, the branching fraction of W decays to hadrons, $B(W\to\mathrm{had})$, and the trilinear gauge-boson self-couplings $g^Z_1$, $\kappa_\gamma$ and $\lambda_\gamma$ are determined to be: M_W = 80.376 \pm 0.033 ~GeV \Gamma_W = 2.195 \pm 0.083 ~GeV B(W\to\mathrm{had}) = 67.41 \pm 0.27 % g^Z_1 = 0.984 ^{+0.018}_{-0.020} \kappa_\gamma = 0.982 \pm 0.042 \lambda_\gamma = -0.022 \pm 0.019
- Highlights from the Pierre Auger ObservatoryPublication . Pierre Auger collaboration (496 authors); Abreu, P.; Andringa, S.; Assis, P.; Brogueira, P.; Cazon, L.; Conceicao, R.; Diogo, F.; Espadanal, J.; Goncalves, P.; Oliveira, M.; Pimenta, M.; Santo, C.E.; Santos, E.; Tome, B.The Pierre Auger Observatory is the world’s largest cosmic ray observatory. Our current exposure reaches nearly 40,000 km$^{2}$sr and provides us with an unprecedented quality data set. The performance and stability of the detectors and their enhancements are described. Data analyses have led to a number of major breakthroughs. Among these, we discuss the energy spectrum and the searches for large-scale anisotropies. We present analyses of our X$_{max}$ data and show how it can be interpreted in terms of mass composition. We also describe some new analyses that extract mass-sensitive parameters from the 100 % duty cycle surface detector (SD) data. A coherent interpretation of all these recent results opens new directions. The consequences regarding the cosmic ray composition and the properties of ultrahigh-energy cosmic ray (UHECR) sources are briefly discussed.
- Long term experience in Autonomous Stations and production quality controlPublication . Lopes, L.; Alves, A.B.; Assis, P.; Blanco, A.; Carolino, N.; Cerda, M.A.; Conceição, R.; Cunha, O.; Dobrigkeit, C.; Ferreira, M.; Fonte, P.; de Almeida, L.; Luz, R.; Martins, V.B.; Mendes, L.; Nogueira, J.C.; Pereira, A.; Pimenta, M.; Sarmento, R.; de Souza, V.; Tomé, B.
- Low-level laser therapy in neurosensory recovery : case series in dental and maxillofacial rehabilitationPublication . Nunes, T.; Alves, S.; Pimenta, M.; Rocha, S.; Caetano, C.; Corte-Real, A.
- MARTA: a high-energy cosmic-ray detector concept for high-accuracy muon measurementPublication . Abreu, P. et al. (45 authors); Andringa, S.; Assis, P.; Blanco, A.; Brogueira, P; Carolino, N.; Cazon, L.; Conceição, R.; Cunha, O; Diogo, F.; Espadanal, J.; Ferreira, M.; Ferreira, P.; Fonte, P.; Gonçalves, P.; Lopes, L.; Mendes, L.; Pereira, A.; Pimenta, M.; Sarmento, R.; Tomé, B.; Wolters, H.A new concept for the direct measurement of muons in air showers is presented. The concept is based on resistive plate chambers (RPCs), which can directly measure muons with very good space and time resolution. The muon detector is shielded by placing it under another detector able to absorb and measure the electromagnetic component of the showers such as a water-Cherenkov detector, commonly used in air shower arrays. The combination of the two detectors in a single, compact detector unit provides a unique measurement that opens rich possibilities in the study of air showers.
- «
- 1 (current)
- 2
- 3
- »