204 research outputs found
MEG: Muon to Electron and Gamma
The possible existence of the \mu \rightarrow {e} \gammaμ→eγ
decay predicted by many new physics scenarios is investigated by
stopping positive muons in a very thin target and measuring emitted
photons and positrons with the best possible resolutions. Photons are
measured by a 2.7 ton ultra pure liquid xenon detector while positron
trajectories are measured in a specially designed gradient magnetic
field by low-mass drift chambers and precisely timed by scintillation
counters. A first phase of the experiment (MEG) ended in 2016, and
excluded the existence of the decay with branching ratios larger than
4.2 \times 10^{-13}4.2×10−13
(90% C.L.). This provides approximately 30~times stronger constraints on
a variety of new physics models than previous experiments. In the second
phase (MEG II), most of the detectors have been upgraded by adopting
up-to-date technologies to improve the search sensitivity by another
order of magnitude down to \mathcal{O}(10^{-14})(10−14).
MEG II will perform a search for physics beyond the Standard Model
complementary to high energy collider experiments with compatible or
even higher sensitivity
CTLA-4 and PD-1 ligand gene expression in epithelial thyroid cancers
The dysregulation of PD-1 ligands (PD-L1 and PD-L2) and CTLA-4 ligands (CD80 and CD86) represents a tumor strategy to escape the immune surveillance. Here, the expression of PD-L1, PD-L2, CD80 and CD86 was evaluated at mRNA level in 94 patients affected by papillary thyroid carcinoma (PTC) and 11 patients affected by anaplastic thyroid carcinoma (ATC). Variations in the mRNAs in PTC patients were then correlated with clinicopathological features.
The expression of all genes was deregulated in PTC and ATC tissues compared to normal tissues. In particular, the down-regulation of CD80 was observed in above all ATC. In addition, the increased expression of CD80 associated to longer disease-free survival in PTC. Higher expression of PD-L1 associated with the classical histological variant and with the presence of BRAFV600E mutation in PTC. The increased PD-L2 expression correlated with BRAFV600E mutation and lymph node metastasis, while its lower expression correlated with the follicular PTC variant. The latter was also associated with the CD80 down-regulation, which was also related to the absence of lymph node metastasis.
In conclusion, we documented the overall dysregulation of PD-1 and CTLA-4 ligands in PTC and ATC tissues and a possible prognostic value for CD80 gene expression in PTC
An X-ray Polarimeter for HXMT Mission
The development of micropixel gas detectors, capable to image tracks produced
in a gas by photoelectrons, makes possible to perform polarimetry of X-ray
celestial sources in the focus of grazing incidence X-ray telescopes. HXMT is a
mission by the Chinese Space Agency aimed to survey the Hard X-ray Sky with
Phoswich detectors, by exploitation of the direct demodulation technique. Since
a fraction of the HXMT time will be spent on dedicated pointing of particular
sources, it could host, with moderate additional resources a pair of X-ray
telescopes, each with a photoelectric X-ray polarimeter in the focal plane. We
present the design of the telescopes and the focal plane instrumentation and
discuss the performance of this instrument to detect the degree and angle of
linear polarization of some representative sources. Notwithstanding the limited
resources the proposed instrument can represent a breakthrough in X-ray
Polarimetry.Comment: 10 pages, 9 figure
LAMP: a micro-satellite based soft X-ray polarimeter for astrophysics
The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite
mission concept dedicated for astronomical X-ray polarimetry and is currently
under early phase study. It consists of segmented paraboloidal multilayer
mirrors with a collecting area of about 1300 cm^2 to reflect and focus 250 eV
X-rays, which will be detected by position sensitive detectors at the focal
plane. The primary targets of LAMP include the thermal emission from the
surface of pulsars and synchrotron emission produced by relativistic jets in
blazars. With the expected sensitivity, it will allow us to detect polarization
or place a tight upper limit for about 10 pulsars and 20 blazars. In addition
to measuring magnetic structures in these objects, LAMP will also enable us to
discover bare quark stars if they exist, whose thermal emission is expected to
be zero polarized, while the thermal emission from neutron stars is believed to
be highly polarized due to plasma polarization and the quantum electrodynamics
(QED) effect. Here we present an overview of the mission concept, its science
objectives and simulated observational results
Gas pixel detectors
Abstract With the Gas Pixel Detector (GPD), the class of micro-pattern gas detectors has reached a complete integration between the gas amplification structure and the read-out electronics. To obtain this goal, three generations of application-specific integrated circuit of increased complexity and improved functionality has been designed and fabricated in deep sub-micron CMOS technology. This implementation has allowed manufacturing a monolithic device, which realizes, at the same time, the pixelized charge-collecting electrode and the amplifying, shaping and charge measuring front-end electronics of a GPD. A big step forward in terms of size and performances has been obtained in the last version of the 0.18 μm CMOS analog chip, where over a large active area of 15×15 mm 2 a very high channel density (470 pixels/mm 2 ) has been reached. On the top metal layer of the chip, 105,600 hexagonal pixels at 50 μm pitch have been patterned. The chip has customable self-trigger capability and includes a signal pre-processing function for the automatic localization of the event coordinates. In this way, by limiting the output signal to only those pixels belonging to the region of interest, it is possible to reduce significantly the read-out time and data volume. In-depth tests performed on a GPD built up by coupling this device to a fine pitch (50 μm) gas electron multiplier are reported. Matching of the gas amplification and read-out pitch has let to obtain optimal results. A possible application of this detector for X-ray polarimetry of astronomical sources is discussed
PolarLight: a CubeSat X-ray Polarimeter based on the Gas Pixel Detector
The gas pixel detector (GPD) is designed and developed for high-sensitivity
astronomical X-ray polarimetry, which is a new window about to open in a few
years. Due to the small mass, low power, and compact geometry of the GPD, we
propose a CubeSat mission Polarimeter Light (PolarLight) to demonstrate and
test the technology directly in space. There is no optics but a collimator to
constrain the field of view to 2.3 degrees. Filled with pure dimethyl ether
(DME) at 0.8 atm and sealed by a beryllium window of 100 micron thick, with a
sensitive area of about 1.4 mm by 1.4 mm, PolarLight allows us to observe the
brightest X-ray sources on the sky, with a count rate of, e.g., ~0.2 counts/s
from the Crab nebula. The PolarLight is 1U in size and mounted in a 6U CubeSat,
which was launched into a low Earth Sun-synchronous orbit on October 29, 2018,
and is currently under test. More launches with improved designs are planned in
2019. These tests will help increase the technology readiness for future
missions such as the enhanced X-ray Timing and Polarimetry (eXTP), better
understand the orbital background, and may help constrain the physics with
observations of the brightest objects.Comment: Accepted for publication in Experimental Astronom
The WaveDAQ integrated Trigger and Data Acquisition System for the MEG II experiment
The WaveDAQ is a newly-designed digitization Trigger and Data AcQuisition
system (TDAQ) allowing Multi-gigasample waveform recording on a large amount of
channels (up to 16384) by using the DRS4 analog switched capacitor array as
downconverting ASIC. A high bandwidth, programmable input stage has been
coupled with a bias generator to allow SiPM operation without need of any other
external apparatus. The trigger generation is tightly coupled within the system
to limit the required depth of the analog memory, allowing faster digitization
speeds. This system has been designed for the MEG experiment upgrade but also
proved to be highly scalable and already found other applications.Comment: This manuscript is for conference record of the 21st IEEE Real Time
conference onl
X-ray polarimetry on-board HXMT
The development of micropixel gas detectors, capable to image tracks produced
in a gas by photoelectrons, makes possible to perform polarimetry of X-ray
celestial sources in the focus of grazing incidence X-ray telescopes. HXMT is a
mission by the Chinese Space Agency aimed to survey the Hard X-ray Sky with
Phoswich detectors, by exploitation of the direct demodulation technique. Since
a fraction of the HXMT time will be spent on dedicated pointing of particular
sources, it could host, with moderate additional resources a pair of X-ray
telescopes, each with a photoelectric X-ray polarimeter (EXP2, Efficient X-ray
Photoelectric Polarimeter) in the focal plane. We present the design of the
telescopes and the focal plane instrumentation and discuss the performance of
this instrument to detect the degree and angle of linear polarization of some
representative sources. Notwithstanding the limited resources, the proposed
instrument can represent a breakthrough in X-ray Polarimetry.Comment: 10 pages, 7 figure
Characterization of snowfall estimated by in situ and ground-based remote-sensing observations at Terra Nova Bay, Victoria Land, Antarctica
AbstractKnowledge of the precipitation contribution to the Antarctic surface mass balance is essential for defining the ice-sheet contribution to sea-level rise. Observations of precipitation are sparse over Antarctica, due to harsh environmental conditions. Precipitation during the summer months (November–December–January) on four expeditions, 2015–16, 2016–17, 2017–18 and 2018–19, in the Terra Nova Bay area, were monitored using a vertically pointing radar, disdrometer, snow gauge, radiosounding and an automatic weather station installed at the Italian Mario Zucchelli Station. The relationship between radar reflectivity and precipitation rate at the site can be estimated using these instruments jointly. The error in calculated precipitation is up to 40%, mostly dependent on reflectivity variability and disdrometer inability to define the real particle fall velocity. Mean derived summer precipitation is ~55 mm water equivalent but with a large variability. During collocated measurements in 2018–19, corrected snow gauge amounts agree with those derived from the relationship, within the estimated errors. European Centre for the Medium-Range Weather Forecasts (ECMWF) and the Antarctic Mesoscale Prediction System (AMPS) analysis and operational outputs are able to forecast the precipitation timing but do not adequately reproduce quantities during the most intense events, with overestimation for ECMWF and underestimation for AMPS
The silicon-strip tracker of the Gamma ray Large Area Space Telescope
Abstract The Gamma ray Large Area Space Telescope (GLAST) is an astro-particle mission that will study the mostly unexplored, high energy ( 20 MeV – 1 TeV ) spectrum of photons coming from active sources in the universe. Construction of the GLAST silicon tracker, by far the largest ever built for a space mission, is now well on the way, as it is scheduled for launch by NASA in autumn 2006. We report on the basic technology adopted for the silicon detectors, particularly in connection to their use in space, on the first results of sensors testing and on the status of tracker assembly
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