95 research outputs found
New Preshower detector for DIRAC Experiment
The Preshower (PSh) detector is a component of the DIRAC setup. It is
designed to improve rejection efficiency of e-e+ pairs background in the
{\pi}{\pi} and K{\pi} pair measurement. To increase the overall efficiency, a
new two-layer structure scintillator Preshower detector has been realized in
the region where the Nitrogen Cherenkov detector has been shortened to
introduce new detectors. The new Preshower-Cherenkov combination ensures the
electron rejection efficiency better than 99.9% in momentum region 1-7 GeV/c.Comment: to be published in NIM
Nonperturbative QED Processes at ELI-NP
The present paper analyses the current results and pursuits the main steps
required for the design of SF-QED experiments at High-Power Laser System (HPLS)
of ELI-NP in Magurele, Romania. After a brief analysis of the first experiment
(E-144 SLAC), which confirmed the existence of non-linear QED interactions of
the high energy electrons with the photons of a laser beam, we went on to
present fundamental QED processes possible to be studied at ELI-NP in a
multi-photon regime. The kinematics and characteristic parameters of the laser
beam interacting with electrons were presented. In the preparation of an
experiment at ELI-NP, the analysis of the kinematics and dynamics of the
non-linear QED interaction processes with the physical vacuum are required.
Initially, the linear QED processes and the corresponding Feynman diagrams that
allow to determine the amplitude of these processes are reviewed. Based on
these amplitudes, the cross sections of the processes can be obtained. For
multi-photon interactions it is necessary to adapt the technique of Feynman
diagrams from linear QED processes to the non-linear ones, by moving to the
quantum field description with dressed Dirac-Volkov states, for particles in
intense EM field. They then allow evaluation of the amplitude of the physical
processes and ultimately the determination of the corresponding cross section.
The SF-QED processes of multi-photon interactions with strong laser fields, can
be done taking into account the characteristics of the existing facilities at
ELI-NP in the context of the experimental production of electron-positron-pairs
and of energetic gamma-rays. We show also some upcoming experiments similar to
ours, in various stages of preparation.Comment: Presented at Bucharest University Meeting 2023
https://ssffb.fizica.unibuc.ro/SSFFB/Section.php?SectID=22
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
DIRAC Experiment and Test of Low-Energy QCD
The low-energy QCD predictions to be tested by the DIRAC experiment are revised. The experimental method, the setup characteristics and capabilities, along with first experimental results are reported. Preliminary analysis shows good detector performance: alignment error via mass measurement with , relative momentum resolution , and evidence for $\pi^
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
Detection of Pionium with DIRAC
The aim of the DIRAC experiment at CERN is to provide an accurate determination of S-wave pion-pion scattering lengths from the measurement of the lifetime of the pi+ pi- atom. The measurement will be done with precision comparable to the level of accuracy of theoretical predictions, formulated in the context of Chiral Perturbation Theory. Therefore, the understanding of chiral symmetry breaking of QCD will be submitted to a stringent test
Detection of atoms with the DIRAC spectrometer at CERN
The goal of the DIRAC experiment at CERN is to measure with high precision
the lifetime of the atom (), which is of order
s, and thus to determine the s-wave -scattering
lengths difference . atoms are detected through the
characteristic features of pairs from the atom break-up
(ionization) in the target. We report on a first high statistics atomic data
sample obtained from p Ni interactions at 24 GeV/ proton momentum and
present the methods to separate the signal from the background.Comment: 19 pages, 12 figures, 1 tabl
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