M. van den Akker

The L3+C detector, a unique tool-set to study cosmic rays

AbstractThe L3 detector at the CERN electron–positron collider, LEP, has been employed for the study of cosmic ray muons.The muon spectrometer of L3 consists of a set of high-precision drift chambers installed inside a magnet with avolume of about 1000 m 3 and a field of 0:5T: Muon momenta are measured with a resolution of a few percentat 50 GeV: The detector is located under 30 m of overburden. A scintillator air shower array of 54 m by 30 mis installed on the roof of the surface hall above L3 in order to estimate the energy and the core position of theshower associated with a sample of detected muons. Thanks to the unique properties of the L3þC detector, muonresearch topics relevant to various current problems in cosmic ray and particle astrophysics can be studied. r 2002Elsevier Science B.V. All rights reserved. PACS: 95.55.Vj; 98.70.Sa; 96.40.Tv; 95.85.RyKeywords: L3+C detector; Cosmic rays; Muon spectrum; Astroparticle physics 1. IntroductionThe L3þ C experiment (Figs. 1 and 2), installedat the Large Electron Positron collider (LEP) atCERN, Geneva, consists of two major parts:firstly, below ground, the L3 muon spectrometer[1], which is comprised of a large 0:5 T magnetwith a volume of 1000 m

The shape of the radio wavefront of extensive air showers as measured with LOFAR

Extensive air showers, induced by high energy cosmic rays impinging on the Earths atmosphere, produce radio emission that is measured with the LOFAR radio telescope. As the emission comes from a finite distance of a few kilometers, the incident wavefront is non-planar. A spherical, conical or hyperbolic shape of the wavefront has been proposed, but measurements of individual air showers have been inconclusive so far. For a selected high-quality sample of 161 measured extensive air showers, we have reconstructed the wavefront by measuring pulse arrival times to sub-nanosecond precision in 200 to 350 individual antennas. For each measured air shower, we have fitted a conical, spherical, and hyperboloid shape to the arrival times. The fit quality and a likelihood analysis show that a hyperboloid is the best parametrization. Using a non-planar wavefront shape gives an improved angular resolution, when reconstructing the shower arrival direction. Furthermore, a dependence of the wavefront shape on the shower geometry can be seen. This suggests that it will be possible to use a wavefront shape analysis to get an additional handle on the atmospheric depth of the shower maximum, which is sensitive to the mass of the primary particle.

Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFAR

Measuring radio emission from air showers offers a novel way to determine properties of the primary cosmic rays such as their mass and energy. Theory predicts that relativistic time compression effects lead to a ring of amplified emission which starts to dominate the emission pattern for frequencies above ∼100∼100 MHz. In this article we present the first detailed measurements of this structure. Ring structures in the radio emission of air showers are measured with the LOFAR radio telescope in the frequency range of 110–190 MHz. These data are well described by CoREAS simulations. They clearly confirm the importance of including the index of refraction of air as a function of height. Furthermore, the presence of the Cherenkov ring offers the possibility for a geometrical measurement of the depth of shower maximum, which in turn depends on the mass of the primary particle.

LORA: A scintillator array for LOFAR to measure extensive air showers

The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays, is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in the Netherlands. The main purpose of LORA is to measure the properties of air showers and to trigger the read-out of the LOFAR radio antennas to register extensive air showers. The experimental set-up of the array of scintillation detectors and its performance are described.

Measurement of the Shadowing of High-Energy Cosmic Rays by the Moon: A Search for TeV-Energy Antiprotons

The shadowing of high-energy cosmic rays by the Moon has been observed with a significance of 9.4 standard deviations with the L3 + C muon spectrometer at CERN. A significant effect of the Earth magnetic field is observed. Since no event deficit on the east side of the Moon has been observed, an upper limit at 90% confidence level on the antiproton to proton ratio of 0.11 is obtained for primary energies around 1 TeV.

NuMoon: Status of Ultra-High-Energy Cosmic Ray detection with LOFAR and improved limits with the WSRT.

LOFAR (Low Frequency Array) is a new distributed digital radio telescope built in the Netherlands and surrounding countries. It can be used to detect radio emission induced by cosmic rays as well as other transient signals, due to its design of stations of simple antennas. We will present LOFAR and how the NuMoon project plans to use the telescope to detect ultra-high-energy cosmic rays (> 10eV). The flux at these energies is very low, therefore, the Moon is chosen as target because of its large surface area of 10 km. When a cosmic ray hits the Moon surface it will produce a cascade of secondary particles with an excess of electrons. This causes radio emission, a process known as the Askaryan effect. Until recently, an unsolved problem was the possibility of formation-zone suppression of near-surface cascades, as produced by cosmic rays, which could prevent this radiation from being visible from Earth. We will show an analytic calculation that solves this problem. With this result we are able to set a limit on the flux of cosmic rays at the highest energies with data from the Westerbork Synthesis Radio Telescope and provide the expected sensitivity for LOFAR and the Square Kilometre Array.