37,904 research outputs found
A Tracking Fiber Detector based on Silicon Photomultipliers for the Kaos Spectrometer
A tracking detector based on two meters long scintillating fibers read out by
silicon photomultipliers (SiPM) is being developed for the Kaos spectrometer at
the Mainz Microtron MAMI. Results from a prototype setup using 2 mm square
fibers and large area SiPM readout are presented. The detection efficiency of
such a combination was measured to be between 83 and 100% depending on the
threshold on the SiPM amplitude. A Monte Carlo simulation based on a physical
model was employed in order to extract the photon detection efficiency of the
SiPM devices.Comment: Contributed to 2008 IEEE Nuclear Science Symposium, 19-25 October
2008, Dresden, German
Power spectra in extended tachyon cosmologies
In the present work the power spectrum of a particular class of tachyon
fields is compared with the one corresponding to a cosmological constant model.
This is done for different barotropic indexes and the background
space time is assumed to be of the spatially flat Friedmann-Robertson-Walker
type. The differential equation describing the perturbations is solved
numerically and the power spectrum at the scale factor value is plotted
for each case. The result is that the power spectrum of the standard tachyon
field differs in many magnitude orders from the CDM. However, the one
with , which corresponds to a complementary tachyon field,
coincides fairly well with the concordance model. Therefore, we conclude that
the perturbed solutions constitute an effective method to distinguish between
the different values for the tachionization CDM model and
the fiducial model. The Statefinder parameters , measuring the
deviations of the analysed model from the concordance model, are also
explicitly calculated. Our result suggest that, depending on the value of
, these models can explain the observed expansion history or the
perturbation power spectrum of the universe, but they may have problems in
describing both features simultaneously.Comment: 7 pages, 7 figures, accepted for publication in General Relativity
and Gravitatio
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