Efecto del rendimiento de fluorescencia atmosférica en la escala de energía del Observatorio Pierre Auger

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Atómica, Molecular y Nuclear, leída el 24-03-2015Más de 100 años después de su descubrimiento, existen todavía interrogantes abiertos sobre el origen y propagación de la radiación cósmica, especialmente en los llamados rayos cósmicos de ultra-alta energía (UHECRs por sus siglas en inglés). El escaso flujo de estas partículas hace necesaria la construcción de grandes instrumentos de detección como el Observatorio Pierre Auger. Este Observatorio emplea la técnica de fluorescencia, basada en la detección de la luz producida por las moléculas de nitrógeno de la atmósfera excitadas por la cascada de partículas generada por el rayo cósmico incidente. El rendimiento de fluorescencia atmosférica, Y, es un parámetro básico en esta técnica, puesto que mide el número de fotones producidos por unidad de energía depositada en la atmósfera. En los últimos años se han realizado nuevas medidas de este parámetro y sus diversas dependencias con la presión, temperatura y humedad.En esta tesis se ha realizado un estudio del efecto de Y en los parámetros reconstruidos de cascadas atmosféricas iniciadas por UHECRs. Para ello se han desarrollados dos métodos distintos: un método analítico que ofrece buenos resultados cuantitativos y cualitativos y un método más detallado que emplea el software de reconstrucción desarrollado por la colaboración Auger. En el primer caso se han analizado perfiles longitudinales típicos mientras que para el segundo se han empleado datos reales obtenidos por el Observatorio Auger.Aplicando ambos métodos se ha estudiado el efecto de incluir las dependencias de Y con la temperatura y la humedad, anteriormente ignoradas, en la reconstrucción de la energía del rayo cósmico y la profundidad de máximo desarrollo de la cascada, uno de los parámetros más importantes para determinar la composición másica de los UHECRs. Los dos procedimientos muestran que el efecto de dependencia con la humedad es más importante en cascadas que se desarrollan cerca del suelo, mientras que la dependencia con la temperatura afecta más a las que depositan la mayor parte de su energía en capas más elevadas de la atmósfera. El efecto neto de incluir ambas dependencias es un aumento de la energía reconstruida y una leve variación en la profundidad del máximo desarrollo de la cascada.Se ha estudiado también el efecto sobre la reconstrucción de los datos del Observatorio Pierre Auger al sustituir el valor absoluto del rendimiento de fluorescencia previamente utilizado por el valor medido recientemente por la colaboración AIRFLY. Este parámetro era hasta la fecha la principal fuente de incertidumbre en la escala de energía del observatorio. El estudio presentado en esta tesis, junto con otras mejoras realizadas por el grupo de trabajo de Reconstrucción Híbrida de la colaboración Auger, ha servido para actualizar la escala de energía del observatorio, así como reducir sustancialmente su error sistemático.Este nuevo valor de la escala de energía no resuelve las discrepancias existentes entre el espectro medido por el Observatorio Pierre Auger y el medido por el otro observatorio de UHECRs que opera en la actualidad, Telescope Array (TA). Estas discrepancias desaparecen al aplicar un factor de escala adecuado entre ambos espectros. En esta tesis se ha demostrado que las diferencias en los parámetros de fluorescencia usados en ambos experimentos dan cuenta de una fracción importante de la diferencia relativa en sus escalas de energía.Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

The AMY experiment: Microwave emission from air shower plasmas

You The Air Microwave Yield (AMY) experiment investigate the molecular bremsstrahlung radiation emitted in the GHz frequency range from an electron beam induced air-shower. The measurements have been performed at the Beam Test Facility (BTF) of Frascati INFN National Laboratories with a 510 MeV electron beam in a wide frequency range between 1 and 20 GHz. We present the apparatus and the results of the tests performed

Search for ultrarelativistic magnetic monopoles with the Pierre Auger observatory

We present a search for ultrarelativistic magnetic monopoles with the Pierre Auger observatory. Such particles, possibly a relic of phase transitions in the early Universe, would deposit a large amount of energy along their path through the atmosphere, comparable to that of ultrahigh-energy cosmic rays (UHECRs). The air-shower profile of a magnetic monopole can be effectively distinguished by the fluorescence detector from that of standard UHECRs. No candidate was found in the data collected between 2004 and 2012, with an expected background of less than 0.1 event from UHECRs. The corresponding 90% confidence level (C.L.) upper limits on the flux of ultrarelativistic magnetic monopoles range from 10(-1)9 (cm(2) sr s)(-1) for a Lorentz factor gamma = 10(9) to 2.5 x 10(-21) (cm(2) sr s)(-1) for gamma = 10(12). These results-the first obtained with a UHECR detector-improve previously published limits by up to an order of magnitude

Impact of atmospheric effects on the energy reconstruction of air showers observed by the surface detectors of the Pierre Auger Observatory

Atmospheric conditions, such as the pressure (P), temperature (T) or air density (rho proportional to P/T), affect the development of extended air showers initiated by energetic cosmic rays. We study the impact of the atmospheric variations on the reconstruction of air showers with data from the arrays of surface detectors of the Pierre Auger Observatory, considering separately the one with detector spacings of 1500m and the one with 750m spacing. We observe modulations in the event rates that are due to the influence of the air density and pressure variations on the measured signals, from which the energy estimators are obtained. We show how the energy assignment can be corrected to account for such atmospheric effects

A targeted search for point sources of EeV photons with the Pierre Auger Observatory

We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the 'ankle' at lg(E/eV) = 18.5-19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A > 4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth. (C) 2016 The Author(s). Published by Elsevier B.V

Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory (vol 4, 038, 2017) (Erratum)

© Iop Publishing. Artículo firmado por más de 10 autores.Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory

We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5.10(18) eV, i.e. the region of the all-particle spectrum above the so-called "ankle" feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show that uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results

Nanosecond-level time synchronization of autonomous radio detector stations for extensive air showers

To exploit the full potential of radio measurements of cosmic-ray air showers at MHz frequencies, a detector timing synchronization within 1 ns is needed. Large distributed radio detector arrays such as the Auger Engineering Radio Array (AERA) rely on timing via the Global Positioning System (GPS) for the synchronization of individual detector station clocks. Unfortunately, GPS timing is expected to have an accuracy no better than about 5 ns. In practice, in particular in AERA, the GPS clocks exhibit drifts on the order of tens of ns. We developed a technique to correct for the GPS drifts, and an independent method is used to cross-check that indeed we reach a nanosecond-scale timing accuracy by this correction. First, we operate a "beacon transmitter" which emits defined sine waves detected by AERA antennas recorded within the physics data. The relative phasing of these sine waves can be used to correct for GPS clock drifts. In addition to this, we observe radio pulses emitted by commercial airplanes, the position of which we determine in real time from Automatic Dependent Surveillance Broadcasts intercepted with a software-defined radio. From the known source location and the measured arrival times of the pulses we determine relative timing offsets between radio detector stations. We demonstrate with a combined analysis that the two methods give a consistent timing calibration with an accuracy of 2 ns or better. Consequently, the beacon method alone can be used in the future to continuously determine and correct for GPS clock drifts in each individual event measured by AERA