146 research outputs found
The multilevel trigger system of the DIRAC experiment
The multilevel trigger system of the DIRAC experiment at CERN is presented.
It includes a fast first level trigger as well as various trigger processors to
select events with a pair of pions having a low relative momentum typical of
the physical process under study. One of these processors employs the drift
chamber data, another one is based on a neural network algorithm and the others
use various hit-map detector correlations. Two versions of the trigger system
used at different stages of the experiment are described. The complete system
reduces the event rate by a factor of 1000, with efficiency 95% of
detecting the events in the relative momentum range of interest.Comment: 21 pages, 11 figure
Synthesis of Layered Organic-Inorganic Nanocomposites of Zinc and Copper by Laser Ablation in Liquid
The experimental data of studies of layered organic-inorganic nanocomposites (()-Zn(OH)2+DS) and (Cu2(OH)3+DS) which were produced in the result ablation of zinc and copper in aqueous solutions of surfactants—dodecyl sodium sulfate (SDS) and sodium bis-ethylhexyl succinate (AOT)—are presented. Dependence of the formation dynamics of these composites on an exposure time of radiation and on an aging time of colloids was studied by the absorption spectroscopy, by X-ray diffraction, by scanning electron (SEM), and atomic force microscopy (AFM). Composite (Cu2(OH)3+DS) with bilayered structure was produced by method of laser ablation of the copper metal target in liquid for the first time
KILT: a Benchmark for Knowledge Intensive Language Tasks.
Challenging problems such as open-domain question answering, fact checking, slot filling and entity linking require access to large, external knowledge sources. While some models do well on individual tasks, developing general models is difficult as each task might require computationally expensive indexing of custom knowledge sources, in addition to dedicated infrastructure. To catalyze research on models that condition on specific information in large textual resources, we present a benchmark for knowledge-intensive language tasks (KILT). All tasks in KILT are grounded in the same snapshot of Wikipedia, reducing engineering turnaround through the re-use of components, as well as accelerating research into task-agnostic memory architectures. We test both task-specific and general baselines, evaluating downstream performance in addition to the ability of the models to provide provenance. We find that a shared dense vector index coupled with a seq2seq model is a strong baseline, outperforming more tailor-made approaches for fact checking, open-domain question answering and dialogue, and yielding competitive results on entity linking and slot filling, by generating disambiguated text. KILT data and code are available at https://github.com/facebookresearc
First atom lifetime and scattering length measurements
The results of a search for hydrogen-like atoms consisting of
mesons are presented. Evidence for atom production
by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen
in terms of characteristic pairs from their breakup in the same target
() and from Coulomb final state interaction (). Using
these results the analysis yields a first value for the atom lifetime
of fs and a first model-independent measurement of
the S-wave isospin-odd scattering length
( for isospin ).Comment: 14 pages, 8 figure
Determination of scattering lengths from measurement of atom lifetime
The DIRAC experiment at CERN has achieved a sizeable production of
atoms and has significantly improved the precision on its lifetime
determination. From a sample of 21227 atomic pairs, a 4% measurement of the
S-wave scattering length difference
has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure
Investigation of pairs in the effective mass region near
The DIRAC experiment at CERN investigated in the reaction
the particle pairs and with relative momentum in the pair system less than 100 MeV/c.
Because of background influence studies, DIRAC explored three subsamples of
pairs, obtained by subtracting -- using time-of-flight (TOF) technique
-- background from initial distributions with sample fractions
more than 70\%, 50\% and 30\%. The corresponding pair distributions in and
in its longitudinal projection were analyzed first in a Coulomb model,
which takes into account only Coulomb final state interaction (FSI) and
assuming point-like pair production. This Coulomb model analysis leads to a
yield increase of about four at MeV/c compared to 100 MeV/c.
In order to study contributions from strong interaction, a second more
sophisticated model was applied, considering besides Coulomb FSI also strong
FSI via the resonances and and a variable distance
between the produced mesons. This analysis was based on three different
parameter sets for the pair production. For the 70\% subsample and with best
parameters, pairs was found to be compared to extracted by means of the Coulomb model. Knowing the efficiency
of the TOF cut for background suppression, the total number of detected
pairs was evaluated to be around , which agrees with
the result from the 30\% subsample. The pair number in the 50\%
subsample differs from the two other values by about three standard deviations,
confirming -- as discussed in the paper -- that experimental data in this
subsample is less reliable
DIRAC: A High Resolution Spectrometer for Pionium Detection
The DIRAC spectrometer has been commissioned at CERN with the aim of
detecting atoms produced by a 24 GeV/ high intensity proton
beam in thin foil targets. A challenging apparatus is required to cope with the
high interaction rates involved, the triggering of pion pairs with very low
relative momentum, and the measurement of the latter with resolution around 0.6
MeV/. The general characteristics of the apparatus are explained and each
part is described in some detail. The main features of the trigger system,
data-acquisition, monitoring and setup performances are also given.Comment: 49 pages, 37 figures. Figures 1, 2, 5 and 28 are removed because of
size limitations imposed by hep-ex. They don't offer essential information.
Latex class file 'elsart.cls' also provide
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