122,910 research outputs found
Performance of the online track reconstruction and impact on hadronic triggers at the CMS High Level Trigger
The trigger systems of the LHC detectors play a crucial role in determining
the physics capabilities of the experiments. A reduction of several orders of
magnitude of the event rate is needed to reach values compatible with the
detector readout, offline storage and analysis capabilities. The CMS experiment
has been designed with a two-level trigger system: the Level 1 (L1) Trigger,
implemented on custom-designed electronics, and the High Level Trigger (HLT), a
streamlined version of the CMS reconstruction and analysis software running on
a computer farm. The software-base HLT requires a trade-off between the
complexity of the algorithms, the sustainable output rate, and the selection
efficiency. This is going to be even more challenging during Run II, with a
higher centre-of-mass energy, a higher instantaneous luminosity and pileup, and
the impact of out-of-time pileup due to the 25 ns bunch spacing. The online
algorithms need to be optimised for such a complex environment in order to keep
the output rate under control without impacting the physics efficiency of the
online selection. Tracking, for instance, will play an even more important role
in the event reconstruction. In this poster we will present the performance of
the online track and vertex reconstruction algorithms, and their impact on the
hadronic triggers that make use of b-tagging and of jets reconstructed with the
Particle Flow technique. We will show the impact of these triggers on physics
performance of the experiment, and the latest plans for improvements in view of
the Run II data taking in 2015.Comment: arXiv admin note: substantial text overlap with arXiv:1403.150
Gamma-Ray Spectroscopy of O and N Hypernuclei via the O reaction
he bound-state level structures of the O and
N hypernuclei were studied by -ray spectroscopy using
a germanium detector array (Hyperball) via the O ()
reaction. A level scheme for O was determined from the
observation of three -ray transitions from the doublet of states
(,) at MeV to the ground-state doublet (,). The
N hypernuclei were produced via proton emission from unbound
states in O . Three -rays were observed and the
lifetime of the state in N was measured by the
Doppler shift attenuation method. By comparing the experimental results with
shell-model calculations, the spin-dependence of the interaction is
discussed. In particular, the measured O ground-state doublet
spacing of 26.4 1.6 0.5 keV determines a small but nonzero strength
of the tensor interaction.Comment: 22 pages, 17 figure
Upgrade of the ALICE Inner Tracking System
During the Long Shutdown 2 of the LHC in 2018/2019, the ALICE experiment
plans the installation of a novel Inner Tracking System. It will replace the
current six layer detector system with a seven layer detector using Monolithic
Active Pixel Sensors. The upgraded Inner Tracking System will have
significantly improved tracking and vertexing capabilities, as well as readout
rate to cope with the expected increased Pb-Pb luminosity of the LHC. The
choice of Monolithic Active Pixel Sensors has been driven by the specific
requirements of ALICE as a heavy ion experiment dealing with rare processes at
low transverse momenta. This leads to stringent requirements on the material
budget of 0.3 per layer for the three innermost layers. Furthermore,
the detector will see large hit densities of on average for minimum-bias events in the
inner most layer and has to stand moderate radiation loads of 700 kRad TID and
1 MeV n NIEL at maximum. The
Monolithic Active Pixel Sensor detectors are manufactured using the TowerJazz
0.18 m CMOS Imaging Sensor process on wafers with a high-resistivity
epitaxial layer. This contribution summarises the recent R&D activities and
focuses on results on the large-scale pixel sensor prototypes.Comment: 10 pages, 8 figures, proceedings of VERTEX 2014, 15-19 September 201
Dynamic allometry in coastal overwash morphology
Allometry refers to a physical principle in which geometric (and/or metabolic) characteristics of an object or organism are correlated to its size. Allometric scaling relationships typically manifest as power laws. In geomorphic contexts, scaling relationships are a quantitative signature of organization, structure, or regularity in a landscape, even if the mechanistic processes responsible for creating such a pattern are unclear. Despite the ubiquity and variety of scaling relationships in physical landscapes, the emergence and development of these relationships tend to be difficult to observe - either because the spatial and/or temporal scales over which they evolve are so great or because the conditions that drive them are so dangerous (e.g. an extreme hazard event). Here, we use a physical experiment to examine dynamic allometry in overwash morphology along a model coastal barrier. We document the emergence of a canonical scaling law for length versus area in overwash deposits (washover). Comparing the experimental features, formed during a single forcing event, to 5 decades of change in real washover morphology from the Ria Formosa barrier system, in southern Portugal, we find differences between patterns of morphometric change at the event scale versus longer timescales. Our results may help inform and test process-based coastal morphodynamic models, which typically use statistical distributions and scaling laws to underpin empirical or semi-empirical parameters at fundamental levels of model architecture. More broadly, this work dovetails with theory for landscape evolution more commonly associated with fluvial and alluvial terrain, offering new evidence from a coastal setting that a landscape may reflect characteristics associated with an equilibrium or steady-state condition even when features within that landscape do not.Funding Agency
NERC Natural Environment Research Council
NE/N015665/2
Leverhulme Trust
RPG-2018-282info:eu-repo/semantics/publishedVersio
Direct measurement of sub-pixel structure of the EPIC MOS CCD on-board th e XMM/NEWTON satellite
We have used a mesh experiment in order to measure the sub-pixel structure of
the EPIC MOS CCDs on-board the XMM/NEWTON satellite. The EPIC MOS CCDs have 40
m-square pixels which have an open electrode structure in order to improve
the detection efficiency for low-energy X-rays. We obtained restored pixel
images for various X-ray event grades (e.g. split-pixel events, single pixel
events, etc.) at various X-ray energies.
We confirmed that the open electrode structure results in a distorted
horizontal pixel boundary. The open electrode region generates both single
pixel events and vertically split events, but no horizontally split events.
Because the single pixel events usually show the best energy resolution, we
discuss a method of increasing the fraction of single pixel events from the
open electrode region. Furthermore, we have directly measured the thickness of
the electrodes and dead-layers by comparing spectra from the open electrode
region with those from the other regions: electrodes, electrode finger and
channel stop. We can say that EPIC MOS CCDs are more radiation hard than
front-illumination chips of ACIS on-board Chandra X-ray Observatory because of
their extra absorption thickness above the charge transfer channel. We
calcurated the mean pixel response and found that our estimation has a good
agreement with that of the ground calibration of EPIC MOS CCD.Comment: 20pages including 2 tables, 10 figures,Accepted for publication in :
Nuclear Instruments and Methods in Physics Research
IceCube-Plus: An Ultra-High Energy Neutrino Telescope
While the first kilometer-scale neutrino telescope, IceCube, is under
construction, alternative plans exist to build even larger detectors that will,
however, b e limited by a much higher neutrino energy threshold of 10 PeV or
higher rather than 10 to 100 GeV. These future projects detect radio and
acoustic pulses as w ell as air showers initiated by ultra-high energy
neutrinos. As an alternative, we here propose an expansion of IceCube, using
the same strings, placed on a gri d with a spacing of order 500 m. Unlike other
proposals, the expanded detector uses methods that are understood and
calibrated on atmospheric neutrinos. Atmosp heric neutrinos represent the only
background at the energies under consideratio n and is totally negligible.
Also, the cost of such a detector is understood. We conclude that supplementing
the 81 IceCube strings with a modest number of addi tional strings spaced at
large distances can almost double the effective volume of the detector.
Doubling the number of strings on a 800 m grid can deliver a d etector that
this a factor of 5 larger for horizontal muons at modest cost.Comment: Version to be published in JCA
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