arXiv subjects

H. Gemmeke

Publications and source records attributed to H. Gemmeke.

30 records · Page 2Linked to original sources

arXiv2013

Thunderstorm Observations by Air-Shower Radio Antenna Arrays

Relativistic, charged particles present in extensive air showers lead to a coherent emission of radio pulses which are measured to identify the shower initiating high-energy cosmic rays. Especially during thunderstorms, there are additional strong electric fields in the atmosphere, which can lead to further multiplication and acceleration of the charged particles and thus have influence on the form and strength of the radio emission. For a reliable energy reconstruction of the primary cosmic ray by means of the measured radio signal it is very important to understand how electric fields affect the radio emission. In addition, lightning strikes are a prominent source of broadband radio emissions that are visible over very long distances. This, on the one hand, causes difficulties in the detection of the much lower signal of the air shower. On the other hand the recorded signals can be used to study features of the lightning development. The detection of cosmic rays via the radio emission and the influence of strong electric fields on this detection technique is investigated with the LOPES experiment in Karlsruhe, Germany. The important question if a lightning is initiated by the high electron density given at the maximum of a high-energy cosmic-ray air shower is also investigated, but could not be answered by LOPES. But, these investigations exhibit the capabilities of EAS radio antenna arrays for lightning studies. We report about the studies of LOPES measured radio signals of air showers taken during thunderstorms and give a short outlook to new measurements dedicated to search for correlations of lightning and cosmic rays.

astro-ph.HE↗

arXiv2013

LOPES-3D, an antenna array for full signal detection of air-shower radio emission

To better understand the radio signal emitted by extensive air-showers and to further develop the radio detection technique of high-energy cosmic rays, the LOPES experiment was reconfigured to LOPES-3D. LOPES-3D is able to measure all three vectorial components of the electric field of radio emission from cosmic ray air showers. The additional measurement of the vertical component ought to increase the reconstruction accuracy of primary cosmic ray parameters like direction and energy, provides an improved sensitivity to inclined showers, and will help to validate simulation of the emission mechanisms in the atmosphere. LOPES-3D will evaluate the feasibility of vectorial measurements for large scale applications. In order to measure all three electric field components directly, a tailor-made antenna type (tripoles) was deployed. The change of the antenna type necessitated new pre-amplifiers and an overall recalibration. The reconfiguration and the recalibration procedure are presented and the operationality of LOPES-3D is demonstrated.

astro-ph.IM↗

arXiv2013

Cosmic Ray Measurements with LOPES: Status and Recent Results (ARENA 2012)

LOPES is a digital antenna array at the Karlsruhe Institute of Technology, Germany, for cosmic-ray air-shower measurements. Triggered by the co-located KASCADE-Grande air-shower array, LOPES detects the radio emission of air showers via digital radio interferometry. We summarize the status of LOPES and recent results. In particular, we present an update on the reconstruction of the primary-particle properties based on almost 500 events above 100 PeV. With LOPES, the arrival direction can be reconstructed with a precision of at least 0.65°, and the energy with a precision of at least 20 %, which, however, does not include systematic uncertainties on the absolute energy scale. For many particle and astrophysics questions the reconstruction of the atmospheric depth of the shower maximum, Xmax, is important, since it yields information on the type of the primary particle and its interaction with the atmosphere. Recently, we found experimental evidence that the slope of the radio lateral distribution is indeed sensitive to the longitudinal development of the air shower, but unfortunately, the Xmax precision at LOPES is limited by the high level of anthropogenic radio background. Nevertheless, the developed methods can be transferred to next generation experiments with lower background, which should provide an Xmax precision competitive to other detection technologies.

astro-ph.HE↗

arXiv2012

Experimental evidence for the sensitivity of the air-shower radio signal to the longitudinal shower development

We observe a correlation between the slope of radio lateral distributions, and the mean muon pseudorapidity of 59 individual cosmic-ray-air-shower events. The radio lateral distributions are measured with LOPES, a digital radio interferometer co-located with the multi-detector-air-shower array KASCADE-Grande, which includes a muon-tracking detector. The result proves experimentally that radio measurements are sensitive to the longitudinal development of cosmic-ray air-showers. This is one of the main prerequisites for using radio arrays for ultra-high-energy particle physics and astrophysics.

astro-ph.IM↗

arXiv2010

On noise treatment in radio measurements of cosmic ray air showers

Precise measurements of the radio emission by cosmic ray air showers require an adequate treatment of noise. Unlike to usual experiments in particle physics, where noise always adds to the signal, radio noise can in principle decrease or increase the signal if it interferes by chance destructively or constructively. Consequently, noise cannot simply be subtracted from the signal, and its influence on amplitude and time measurement of radio pulses must be studied with care. First, noise has to be determined consistently with the definition of the radio signal which typically is the maximum field strength of the radio pulse. Second, the average impact of noise on radio pulse measurements at individual antennas is studied for LOPES. It is shown that a correct treatment of noise is especially important at low signal-to-noise ratios: noise can be the dominant source of uncertainty for pulse height and time measurements, and it can systematically flatten the slope of lateral distributions. The presented method can also be transfered to other experiments in radio and acoustic detection of cosmic rays and neutrinos.

astro-ph.IM↗

arXiv2009

Lateral Distribution of the Radio Signal in Extensive Air Showers Measured with LOPES

The antenna array LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. The coincident measurements allow us to reconstruct the electric field strength at observation level in dependence of general EAS parameters. In the present work, the lateral distribution of the radio signal in air showers is studied in detail. It is found that the lateral distributions of the electric field strengths in individual EAS can be described by an exponential function. For about 20% of the events a flattening towards the shower axis is observed, preferentially for showers with large inclination angle. The estimated scale parameters R0 describing the slope of the lateral profiles range between 100 and 200 m. No evidence for a direct correlation of R0 with shower parameters like azimuth angle, geomagnetic angle, or primary energy can be found. This indicates that the lateral profile is an intrinsic property of the radio emission during the shower development which makes the radio detection technique suitable for large scale applications.

astro-ph.HE↗

arXiv2008

Third Level Trigger for the Fluorescence Telescopes of the Pierre Auger Observatory

The trigger system for the Auger fluorescence telescopes is implemented in hard- and software for an efficient selection of fluorescence light tracks induced by high-energy extensive air showers. The algorithm of the third stage uses the multiplicity signal of the hardware for fast rejection of lightning events with above 99% efficiency. In a second step direct muon hits in the camera and random triggers are rejected by analyzing the space-time correlation of the pixels. The trigger algorithm was tested with measured and simulated showers and implemented in the electronics of the fluorescence telescopes. A comparison to a prototype trigger without multiplicity shows the superiority of this approach, e.g. the false rejection rate is a factor 10 lower.

astro-ph↗

arXiv2005

Optical Relative Calibration and Stability Monitoring for the Auger Fluorescence Detector

The stability of the fluorescence telescopes of the Pierre Auger Observatory is monitored with the optical relative calibration setup. Optical fibers distribute light pulses to three different diffuser groups within the optical system. The total charge per pulse is measured for each pixel and compared with reference calibration measurements. This allows monitoring the short and long term stability with respect of the relative timing between pixels and the relative gain for each pixel. The designs of the LED calibration unit (LCU) and of the Xenon flash lamp used for relative calibration, are described and their capabilities to monitor the stability of the telescope performances are studied. We report the analysis of relative calibration data recorded during 2004. Fluctuations in the relative calibration constants provide a measure of the stability of the FD.

astro-ph↗

arXiv2003

Improved limits on nuebar emission from mu+ decay

We investigated mu+ decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for \nueb via the detection reaction p(\nueb,e+)n. No \nueb signal from LF violating mu+ decays was identified. We extract upper limits of the branching ratio for the LF violating decay mu+ -> e+ \nueb νcompared to the Standard Model (SM) mu+ -> e+ nue numub decay: BR < 0.9(1.7)x10^{-3} (90%CL) depending on the spectral distribution of \nueb characterized by the Michel parameter rho=0.75 (0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which \nueb emission from mu+ decay is allowed with considerable strength. The decay \mupdeb as source for the \nueb signal observed in the LSND experiment can be excluded.

hep-ex↗

arXiv2002

Upper limits for neutrino oscillations muon-antineutrino to electron-antineutrino from muon decay at rest

The KARMEN experiment at the spallation neutron source ISIS used \numub from \mup--decay at rest in the search for neutrino oscillations \numubnueb in the appearance mode, with p(\nueb,e+)n as detection reaction of \nueb. In total, 15 candidates fulfill all conditions for the \nueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta)<1.7x10e-3 for Dm^2>100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for \numubnueb.

hep-ex↗

arXiv1998

Measurement of the energy spectrum of ν_e from muon decay and implications for the Lorentz structure of the weak interaction

The KARMEN experiment uses the reaction 12C(ν_e,e-)12N to measure the energy distribution of ν_e emitted in muon decay at rest. The ν_e analog ω_l of the famous Michel parameter ρhas been derived from a maximum-likelihood analysis of events near the kinematic end point, E_max. The result, ω_l = (2.7^{+3.8}_{-3.3}\pm 3.1) * 10^{-2}, is in good agreement with the standard model prediction ω_l= 0. We deduce a 90% confidence upper limit of ω_l <= 0.113, which corresponds to a limit of |g^S_RL + 2 g^T_RL| <= 0.78 on the interference term between scalar and tensor coupling constants.

hep-ex↗

arXiv1998

KARMEN Limits on nu_e -> nu_tau Oscillations in 2-neutrino and 3-neutrino Mixing Schemes

The 56 tonne high resolution liquid scintillation calorimeter KARMEN at the beam stop neutrino source ISIS has been used to search for neutrino oscillations in the disappearance channel nu_e->x. The nu_e emitted in mu+ decay at rest are detected with spectroscopic quality via the exclusive charged current reaction 12-C(nu_e,e-)12-N_g.s. almost free of background. Analysis of the spectral shape of e- from the nu_e induced reaction as well as a measurement of the absolute nu_e flux allow to investigate oscillations of the type nu_e->nu_tau and nu_e->nu_mu . The flux independent ratio R(CC/NC) of charged current events 12-C(nu_e,e-)12-N_g.s. to neutral current events 12-C(nu,nu')12-C* provides additional information in the oscillation channel nu_e->x . All three analysis methods show no evidence for oscillations. For the nu_e->nu_tau channel 90%CL limits of sin^2(2t)<0.338 for dm^2>100eV^2 and dm^2<0.77eV^2 for maximal mixing in a simple 2 flavor oscillation formalism are derived. A complete 3 flavor analysis of the experimental data from five years of measurement with respect to nu_e<->nu_tau and nu_e<->nu_mu mixing is presented.

hep-ex↗