6,073 research outputs found
Comparison between high-energy proton and charged pion induced damage in Lead Tungstate calorimeter crystals
A Lead Tungstate crystal produced for the electromagnetic calorimeter of the
CMS experiment at the LHC was cut into three equal-length sections. The central
one was irradiated with 290 MeV/c positive pions up to a fluence of (5.67 +-
0.46)x10^13 /cm^2, while the other two were exposed to a 24 GeV/c proton
fluence of (1.17 +- 0.11) x 10^13/ cm^2. The damage recovery in these crystals,
stored in the dark at room temperature, has been followed over two years. The
comparison of the radiation-induced changes in light transmission for these
crystals shows that damage is proportional to the star densities produced by
the irradiation.Comment: 7 pages, 4 figure
High-energy proton induced damage study of scintillation light output from PbWO4 calorimeter crystals
Eight PbWO4 crystals produced for the electromagnetic calorimeter of the CMS
experiment at LHC have been irradiated in a 20 GeV/c proton beam up to fluences
of 5.4 E13 p/cm2. The damage recovery in these crystals, stored in the dark at
room temperature, has been followed for over a year. Comparative irradiations
with 60Co photons have been performed on seven other crystals using a dose rate
of 1 kGy/h. The issue whether hadrons cause a specific damage to the
scintillation mechanism has been studied through light output measurements on
the irradiated crystals using cosmic rays. The correlation between light output
changes and light transmission changes is measured to be the same for
proton-irradiated crystals and for gamma-irradiated crystals. Thus, within the
precision of the measurements and for the explored range of proton fluences, no
additional, hadron-specific damage to the scintillation mechanism is observed.Comment: 7 pages, 4 figure
Towards a Precise Parton Luminosity Determination at the CERN LHC
A new approach to determine the LHC luminosity is investigated. Instead of
employing the proton-proton luminosity measurement, we suggest to measure
directly the parton-parton luminosity. It is shown that the electron and muon
pseudorapidity distributions, originating from the decay of W+, W- and Z0
bosons produced at 14 TeV pp collisions (LHC), constrain the x distributions of
sea and valence quarks and antiquarks in the range from about 3 x 10**-4 to
about 10**-1 at a Q**2 of about 10**4 GeV**2. Furthermore, it is demonstrated
that, once the quark and antiquark structure functions are constrained from the
W+,W- and Z0 production dynamics, other quark-antiquark related scattering
processes at the LHC like q-qbar --> W+W- can be predicted accurately. Thus,
the lepton pseudorapidity distributions provide the key to a precise parton
luminosity monitor at the LHC, with accuracies of about +-1% compared to the so
far considered goal of +-5%.Comment: plain tex, 14 pages, 5 figure
New allowed mSUGRA parameter space from variations of the trilinear scalar coupling A0
In minimal Supergravity (mSUGRA) models the lightest supersymmetric particle
(assumed to be the lightest neutralino) provides an excellent cold dark matter
(CDM) candidate. The supersymmetric parameter space is significantly reduced,
if the limits on the CDM relic density, obtained from WMAP data, are used.
Assuming a vanishing trilinear scalar coupling A0 and fixed values of
tan(beta), these limits result in narrow lines of allowed regions in the
m0-m1/2 plane, the so called WMAP strips. In this analysis the trilinear
coupling A0 has been varied within +/-4 TeV. A fixed non vanishing A0 value
leads to a shift of the WMAP strips in the m0-m1/2 plane.Comment: Typos corrected, Fig.1. updated, references adde
A study of high-energy proton induced damage in Cerium Fluoride in comparison with measurements in Lead Tungstate calorimeter crystals
A Cerium Fluoride crystal produced during early R&D studies for calorimetry
at the CERN Large Hadron Collider was exposed to a 24 GeV/c proton fluence
Phi_p=(2.78 +- 0.20) x 10EE13 cm-2 and, after one year of measurements tracking
its recovery, to a fluence Phi_p=(2.12 +- 0.15) x 10EE14 cm-2. Results on
proton-induced damage to the crystal and its spontaneous recovery after both
irradiations are presented here, along with some new, complementary data on
proton-damage in Lead Tungstate. A comparison with FLUKA Monte Carlo simulation
results is performed and a qualitative understanding of high-energy damage
mechanism is attempted.Comment: Submitted to Elsevier Science on May 6th, 2010; 11 pages, 8 figure
FACT - Long-term Monitoring of Bright TeV-Blazars
Since October 2011, the First G-APD Cherenkov Telescope (FACT) is operated
successfully on the Canary Island of La Palma. Apart from the proof of
principle for the use of G-APDs in Cherenkov telescopes, the major goal of the
project is the dedicated long-term monitoring of a small sample of bright TeV
blazars. The unique properties of G-APDs permit stable observations also during
strong moon light. Thus a superior sampling density is provided on time scales
at which the blazar variability amplitudes are expected to be largest, as
exemplified by the spectacular variations of Mrk 501 observed in June 2012.
While still in commissioning, FACT monitored bright blazars like Mrk 421 and
Mrk 501 during the past 1.5 years so far. Preliminary results including the Mrk
501 flare from June 2012 will be presented.Comment: 4 pages, 4 figures, presented at the 33rd ICRC (2013
FACT - Long-term stability and observations during strong Moon light
The First G-APD Cherenkov Telescope (FACT) is the first Cherenkov telescope
equipped with a camera made of silicon photon detectors (G-APD aka. SiPM).
Since October 2011, it is regularly taking data on the Canary Island of La
Palma. G-APDs are ideal detectors for Cherenkov telescopes as they are robust
and stable. Furthermore, the insensitivity of G-APDs towards strong ambient
light allows to conduct observations during bright Moon and twilight. This gain
in observation time is essential for the long-term monitoring of bright TeV
blazars. During the commissioning phase, hundreds of hours of data (including
data from the the Crab Nebula) were taken in order to understand the
performance and sensitivity of the instrument. The data cover a wide range of
observation conditions including different weather conditions, different zenith
angles and different light conditions (ranging from dark night to direct full
Moon). We use a new parmetrisation of the Moon light background to enhance our
scheduling and to monitor the atmosphere. With the data from 1.5 years, the
long-term stability and the performance of the camera during Moon light is
studied and compared to that achieved with photomultiplier tubes so far.Comment: 3 pages, 3 figures, FACT Contribution to the 33rd International
Cosmic Ray Conference (ICRC), Rio de Janeir
FACT - Threshold prediction for higher duty cycle and improved scheduling
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise
a higher photon detection efficiency, more robustness and higher precision than
photo-multiplier tubes. Being operated during different light-conditions, the
threshold settings of a Cherenkov telescope have to be adapted to feature the
lowest possible threshold but also an efficient suppression of triggers from
night-sky background photons. Usually this threshold is set either by
experience or a mini-ratescan. Since the measured current through the sensors
is directly correlated with the noise level, the current can be used to set the
best threshold at any time. Due to the correlation between the physical
threshold and the final energy threshold, the current can also be used as a
measure for the energy threshold of any observation. This presentation
introduces a method which uses the properties of the moon and the source
position to predict the currents and the corresponding energy threshold for
every upcoming observation allowing to adapt the observation schedule
accordingly
FACT - How stable are the silicon photon detectors?
The First G-APD Cherenkov telescope (FACT) is the first telescope using
silicon photon detectors (G-APD aka. SiPM). The use of Silicon devices promise
a higher photon detection efficiency, more robustness and higher precision than
photo-multiplier tubes. Since the properties of G-APDs depend on auxiliary
parameters like temperature, a feedback system adapting the applied voltage
accordingly is mandatory.
In this presentation, the feedback system, developed and in operation for
FACT, is presented. Using the extraction of a single photon-equivalent (pe)
spectrum as a reference, it can be proven that the sensors can be operated with
very high precision. The extraction of the single-pe, its spectrum up to
10\,pe, its properties and their precision, as well as their long-term behavior
during operation are discussed. As a by product a single pulse template is
obtained. It is shown that with the presented method, an additional external
calibration device can be omitted. The presented method is essential for the
application of G-APDs in future projects in Cherenkov astronomy and is supposed
to result in a more stable and precise operation than possible with
photo-multiplier tubes
Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope
The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of
the performance of silicon photo detectors in Cherenkov Astronomy. For more
than two years it is operated on La Palma, Canary Islands (Spain), for the
purpose of long-term monitoring of astrophysical sources. For this, the
performance of the photo detectors is crucial and therefore has been studied in
great detail. Special care has been taken for their temperature and voltage
dependence implementing a correction method to keep their properties stable.
Several measurements have been carried out to monitor the performance. The
measurements and their results are shown, demonstrating the stability of the
gain below the percent level. The resulting stability of the whole system is
discussed, nicely demonstrating that silicon photo detectors are perfectly
suited for the usage in Cherenkov telescopes, especially for long-term
monitoring purpose
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