699 research outputs found
Spatial resolution and efficiency of prototype sensors for the LHCb VELO Upgrade
A comprehensive study of the spatial resolution and detection efficiency of
sensor prototypes developed for the LHCb VELO upgrade is presented. Data
samples were collected at the CERN SPS H8 beam line using a hadron mixture of
protons and pions with momenta of approximately 180 GeV/c. The sensor
performance was characterised using both irradiated and non-irradiated sensors.
Irradiated samples were subjected to a maximum fluence of
, of both protons and neutrons.
The spatial resolution is measured comparing the detected hits to the position
as predicted by tracks reconstructed by the Timepix3 telescope. The resolution
is presented for different applied bias voltages and track angles, sensor
thickness and implant size.Comment: 18 pages, 15 Figure
Timing performance of the LHCb VELO Timepix3 Telescope
We performed a detailed study of the timing performance of the LHCb VELO
Timepix3 Telescope with a 180 GeV/c mixed hadron beam at the CERN SPS. A
twofold method was developed to improve the resolution of single-plane time
measurements, resulting in a more precise overall track time measurement. The
first step uses spatial information of reconstructed tracks in combination with
the measured signal charge in the sensor to correct for a mixture of different
effects: variations in charge carrier drift time; variations in signal
induction, which are the result of a non-uniform weighting field in the pixels;
and lastly, timewalk in the analog front-end. The second step corrects for
systematic timing offsets in Timepix3 that vary from -2 ns to 2 ns. By applying
this method, we improved the track time resolution from 43816 ps to
2764 ps
Charge collection properties of prototype sensors for the LHCb VELO upgrade
An extensive sensor testing campaign is presented, dedicated to measuring the
charge collection properties of prototype candidates for the Vertex Locator
(VELO) detector for the upgraded LHCb experiment. The charge collection is
measured with sensors exposed to fluences of up to , as well as with nonirradiated prototypes. The results are
discussed, including the influence of different levels of irradiation and bias
voltage on the charge collection properties. Charge multiplication is observed
on some sensors that were nonuniformly irradiated with 24 GeV protons, to the
highest fluence levels. An analysis of the charge collection near the guard
ring region is also presented, revealing significant differences between the
sensor prototypes. All tested sensor variants succeed in collecting the minimum
required charge of 6000 electrons after the exposure to the maximum fluence
Resource Selection of Free-ranging Horses Influenced by Fire in Northern Canada
Free-ranging or feral horses (Equus ferus caballus) were important to the livelihood of First Nations and indigenous communities in Canada. The early inhabitants of the boreal region of British Columbia (BC) capitalized on naturally occurring wildfires and anthropogenic burning to provide forage for free-ranging horses and manage habitat for wildlife. This form of pyric herbivory, or grazing driven by fi re via the attraction to the palatable vegetation in recently burned areas, is an evolutionary disturbance process that occurs globally. However, its application to manage forage availability for free-ranging horses has not been studied in northern Canada. Across Canada, there are varying levels of governance for feral and free-ranging horses depending on the provincial jurisdiction and associated legislation. The BC Range Act (Act) allows range tenure holders to free-range horses that they own for commercial operations on Crown land. Big-game guide outfitters as range tenure holders are provided grazing licences or grazing permits under the Act with an approved range use plan. Guide outfitters and other range tenure holders have incorporated fi re ecology as part of their rangeland management in mountainous portions of the boreal forest of northeastern BC to promote mosaics of vegetation height and species composition across the landscape to meet nutritional requirements of their free-ranging horses. Using resource selection function models, we evaluated the influence of pyric herbivory on boreal vegetation and use by horse herds occupying 4 distinct landscapes. We found that horses preferentially selected recently burned areas and areas that burned more frequently when they were available. We also found that horses avoided steep slopes and forest cover types. Fire and the ecological processes associated with it, including pyric herbivory, are important considerations when managing boreal rangelands in northeastern BC. Because historical fi re regimes of the boreal region of Canada differ from the arid regions of the United States inhabited by feral horses, the role of pyric herbivory in altering horse distributions in the United States is limited
CH Cygni I: Observational Evidence for a Disk-Jet Connection
We investigate the role of accretion in the production of jets in the
symbiotic star CH Cygni. Assuming that the rapid stochastic optical variations
in CH Cygni come from the accretion disk, as in cataclysmic variables, we use
changes in this flickering to diagnose the state of the disk in 1997. At that
time, CH Cyg dropped to a very low optical state, and Karovska et al. report
that a radio jet was produced. For approximately one year after the jet
production, the amplitude of the fastest (time scales of minutes) variations
was significantly reduced, although smooth, hour-time-scale variations were
still present. This light curve evolution indicates that the inner disk may
have been disrupted, or emission from this region suppressed, in association
with the mass-ejection event. We describe optical spectra which support this
interpretation of the flickering changes. The simultaneous state change, jet
ejection, and disk disruption suggests a comparison between CH Cygni and some
black-hole-candidate X-ray binaries that show changes in the inner disk radius
in conjunction with discrete ejection events on a wide range of time scales
(e.g., the microquasar GRS 1915+105 and XTE J1550-564).Comment: 7 pages, 4 figures, to appear in the Ap
Observation of the Decay Λ0b→Λ+cτ−¯ν
The first observation of the semileptonic b-baryon decay Λb0→Λc+τ-ν¯τ, with a significance of 6.1σ, is reported using a data sample corresponding to 3 fb-1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ- lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+π-π+π-) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λb0→Λc+τ-ν¯τ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λb0→Λc+π-π+π-. The ratio of semileptonic branching fractions R(Λc+)B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+μ-ν¯μ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λb0→Λc+μ-ν¯μ contributes to the last term. This result is in agreement with the standard model prediction
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