447 research outputs found
In vivo multiphoton microscopy beyond 1 mm in the brain
The ability to visualize deep brain structures in vivo with high spatial resolution is of rising interest to investigate neuronal physiology and cerebral vasculature. Optical imaging offers non-invasive, high-resolution in vivo microscopy techniques to observe brain tissue and its surrounding environment. Two-photon fluorescence laser- scanning microscopy (2PM) can overcome depth limitations by using nonlinear excitation. The ideal approach for deep imaging in brain is to use both high energy pulses and longer excitation wavelengths.
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Design of a high power production target for the Beam Dump Facility at CERN
The Beam Dump Facility (BDF) project is a proposed general-purpose facility
at CERN, dedicated to beam dump and fixed target experiments. In its initial
phase, the facility is foreseen to be exploited by the Search for Hidden
Particles (SHiP) experiment. Physics requirements call for a pulsed 400 GeV/c
proton beam as well as the highest possible number of protons on target (POT)
each year of operation, in order to search for feebly interacting particles.
The target/dump assembly lies at the heart of the facility, with the aim of
safely absorbing the full high intensity Super Proton Synchrotron (SPS) beam,
while maximizing the production of charmed and beauty mesons. High-Z materials
are required for the target/dump, in order to have the shortest possible
absorber and reduce muon background for the downstream experiment. The high
average power deposited on target (305 kW) creates a challenge for heat
removal. During the BDF facility Comprehensive Design Study (CDS), launched by
CERN in 2016, extensive studies have been carried out in order to define and
assess the target assembly design. These studies are described in the present
contribution, which details the proposed design of the BDF production target,
as well as the material selection process and the optimization of the target
configuration and beam dilution. One of the specific challenges and novelty of
this work is the need to consider new target materials, such as a molybdenum
alloy (TZM) as core absorbing material and Ta2.5W as cladding.
Thermo-structural and fluid dynamics calculations have been performed to
evaluate the reliability of the target and its cooling system under beam
operation. In the framework of the target comprehensive design, a preliminary
mechanical design of the full target assembly has also been carried out,
assessing the feasibility of the whole target system.Comment: 17 pages, 18 figure
Exclusion Limits on the WIMP-Nucleon Cross-Section from the First Run of the Cryogenic Dark Matter Search in the Soudan Underground Lab
The Cryogenic Dark Matter Search (CDMS-II) employs low-temperature Ge and Si
detectors to seek Weakly Interacting Massive Particles (WIMPs) via their
elastic scattering interactions with nuclei. Simultaneous measurements of both
ionization and phonon energy provide discrimination against interactions of
background particles. For recoil energies above 10 keV, events due to
background photons are rejected with >99.99% efficiency. Electromagnetic events
very near the detector surface can mimic nuclear recoils because of reduced
charge collection, but these surface events are rejected with >96% efficiency
by using additional information from the phonon pulse shape. Efficient use of
active and passive shielding, combined with the the 2090 m.w.e. overburden at
the experimental site in the Soudan mine, makes the background from neutrons
negligible for this first exposure. All cuts are determined in a blind manner
from in situ calibrations with external radioactive sources without any prior
knowledge of the event distribution in the signal region. Resulting
efficiencies are known to ~10%. A single event with a recoil of 64 keV passes
all of the cuts and is consistent with the expected misidentification rate of
surface-electron recoils. Under the assumptions for a standard dark matter
halo, these data exclude previously unexplored parameter space for both
spin-independent and spin-dependent WIMP-nucleon elastic scattering. The
resulting limit on the spin-independent WIMP-nucleon elastic-scattering
cross-section has a minimum of 4x10^-43 cm^2 at a WIMP mass of 60 GeV/c^2. The
minimum of the limit for the spin-dependent WIMP-neutron elastic-scattering
cross-section is 2x10^-37 cm^2 at a WIMP mass of 50 GeV/c^2.Comment: 37 pages, 42 figure
New Results from the Cryogenic Dark Matter Search Experiment
Using improved Ge and Si detectors, better neutron shielding, and increased
counting time, the Cryogenic Dark Matter Search (CDMS) experiment has obtained
stricter limits on the cross section of weakly interacting massive particles
(WIMPs) elastically scattering from nuclei. Increased discrimination against
electromagnetic backgrounds and reduction of neutron flux confirm
WIMP-candidate events previously detected by CDMS were consistent with neutrons
and give limits on spin-independent WIMP interactions which are >2X lower than
previous CDMS results for high WIMP mass, and which exclude new parameter space
for WIMPs with mass between 8-20 GeV/c^2.Comment: 4 pages, 4 figure
Exclusion limits on the WIMP-nucleon cross-section from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si
detectors to search for Weakly Interacting Massive Particles (WIMPs) via their
elastic-scattering interactions with nuclei while discriminating against
interactions of background particles. For recoil energies above 10 keV, events
due to background photons are rejected with >99.9% efficiency, and surface
events are rejected with >95% efficiency. The estimate of the background due to
neutrons is based primarily on the observation of multiple-scatter events that
should all be neutrons. Data selection is determined primarily by examining
calibration data and vetoed events. Resulting efficiencies should be accurate
to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed
fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent
with an earlier analysis with a more restrictive fiducial-volume cut.
Twenty-three WIMP candidate events are observed, but these events are
consistent with a background from neutrons in all ways tested. Resulting limits
on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude
unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}.
These limits border, but do not exclude, parameter space allowed by
supersymmetry models and accelerator constraints. Results are compatible with
some regions reported as allowed at 3-sigma by the annual-modulation
measurement of the DAMA collaboration. However, under the assumptions of
standard WIMP interactions and a standard halo, the results are incompatible
with the DAMA most likely value at >99.9% CL, and are incompatible with the
model-independent annual-modulation signal of DAMA at 99.99% CL in the
asymptotic limit.Comment: 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D;
v.2:clarified conclusions, added content and references based on referee's
and readers' comments; v.3: clarified introductory sections, added figure
based on referee's comment
A Testing Strategy for the Mass Production of CDMS II Detectors
The Cryogenic Dark Matter Search (CDMS) employs detectors which are capable of simultaneously measuring the ionization and phonon energies deposited by a particle collision. These detectors are 1-cm-thick, 7-cm-diameter crystals of either germanium or silicon with a thin film of aluminum and tungsten patterned on the surface. This presentation discusses the testing regimen that a typical CDMS detector undergoes before it gets approval for final installation at the CDMS II deep site in Soudan, MN which will come online in early 2002. Now that our technology is relatively stable, the main focus of our test facilities is to provide quality control for the mass production of our detectors. First, the critical temperatures of the tungsten and other basic quantities are measured in preparation for iron implantation, which will bring the Tc down to the desired range ( 70 mK). The same basic measurements are taken again after implantation to assure that the correct Tc was achieved. Finally, a detailed map of energy response as a function of position is made to calibrate residual inhomogeneities across th
RAAD: LIGHT-1 CubeSat's Payload for the Detection of Terrestrial Gamma-Ray Flashes
The Rapid Acquisition Atmospheric Detector (RAAD), onboard the LIGHT-1 3U
CubeSat, detects photons between hard X-rays and soft gamma-rays, in order to
identify and characterize Terrestrial Gamma Ray Flashes (TGFs). Three detector
configurations are tested, making use of Cerium Bromide and Lanthanum
BromoChloride scintillating crystals coupled to photomultiplier tubes or
Multi-Pixel Photon Counters, in order to identify the optimal combination for
TGF detection. High timing resolution, a short trigger window, and the short
decay time of its electronics allow RAAD to perform accurate measurements of
prompt, transient events. Here we describe the overview of the detection
concept, the development of the front-end acquisition electronics, as well as
the ground testing and simulation the payload underwent prior to its launch on
December 21st, 2021. We further present an analysis of the detector's in-orbit
system behavior and some preliminary results.Comment: 19 pages, 15 figure
A facility to Search for Hidden Particles (SHiP) at the CERN SPS
A new general purpose fixed target facility is proposed at the CERN SPS
accelerator which is aimed at exploring the domain of hidden particles and make
measurements with tau neutrinos. Hidden particles are predicted by a large
number of models beyond the Standard Model. The high intensity of the SPS
400~GeV beam allows probing a wide variety of models containing light
long-lived exotic particles with masses below (10)~GeV/c,
including very weakly interacting low-energy SUSY states. The experimental
programme of the proposed facility is capable of being extended in the future,
e.g. to include direct searches for Dark Matter and Lepton Flavour Violation.Comment: Technical Proposa
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