68 research outputs found
Charge Asymmetry in 1-1000 GeV Electromagnetic Showers and Possibility of Its Measurementnt
For the high energy electromagnetic showers the thickness dependence of a)
the development of electron and positron components, b) the difference between
the secondary electron and positron numbers, c) the charge asymmetry of high
energy electromagnetic showers, as well as d) the spectral distributions of the
components at the shower maxima for various energies of primary particle
energies,1 - 1000 GeV were investigated employing GEANT Monte Carlo simulation
package. Using these simulation results it is discussed the possibility of
observation and study of the charge asymmetry with the help of a magnetic
spectrometer which is important for the current and future experiments on the
detection of radiowaves produced by high energy neutrinos.Comment: TEX file and 4 figure
Improved Crystal Method for Photon Beam Linear Polarization Measurement at High Energies
A method for photon linear polarization determination based on the
measurement of the asymmetry of pairs produced by polarized photons in single
crystals within the optimal intervals of pair particles energies is proposed.
In difference to the well known methods the asymmetry in this case is
essentially larger. The optimal orientation of crystal is found which provides
the maximal values for analyzing power and figure of merit as well as minimal
measurement time.Comment: 8 pages, 5 figure
Spin physics at A Fixed-Target ExpeRiment at the LHC (AFTER@LHC)
We outline the opportunities for spin physics which are offered by a next
generation and multi-purpose fixed-target experiment exploiting the proton LHC
beam extracted by a bent crystal. In particular, we focus on the study of
single transverse spin asymetries with the polarisation of the target.Comment: Contributed to the 20th International Spin Physics Symposium,
SPIN2012, 17-22 September 2012, Dubna, Russia, 4 pages, LaTe
Prospectives for A Fixed-Target ExpeRiment at the LHC: AFTER@LHC
We argue that the concept of a multi-purpose fixed-target experiment with the
proton or lead-ion LHC beams extracted by a bent crystal would offer a number
of ground-breaking precision-physics opportunities. The multi-TeV LHC beams
will allow for the most energetic fixed-target experiments ever performed. The
fixed-target mode has the advantage of allowing for high luminosities, spin
measurements with a polarised target, and access over the full backward
rapidity domain --uncharted until now-- up to x_F ~ -1.Comment: 6 pages, 1 table, LaTeX. Proceedings of the 36th International
Conference on High Energy Physics (ICHEP2012), 4-11 July 2012, Melbourne,
Australi
Linear to Circular Polarisation Conversion using Birefringent Properties of Aligned Crystals for Multi-GeV Photons
We present the first experimental results on the use of a thick aligned Si
crystal acting as a quarter wave plate to induce a degree of circular
polarisation in a high energy linearly polarised photon beam. The linearly
polarised photon beam is produced from coherent bremsstrahlung radiation by 178
GeV unpolarised electrons incident on an aligned Si crystal, acting as a
radiator. The linear polarisation of the photon beam is characterised by
measuring the asymmetry in electron-positron pair production in a Ge crystal,
for different crystal orientations. The Ge crystal therefore acts as an
analyser. The birefringence phenomenon, which converts the linear polarisation
to circular polarisation, is observed by letting the linearly polarised photons
beam pass through a thick Si quarter wave plate crystal, and then measuring the
asymmetry in electron-positron pair production again for a selection of
relative angles between the crystallographic planes of the radiator, analyser
and quarter wave plate. The systematics of the difference between the measured
asymmetries with and without the quarter wave plate are predicted by theory to
reveal an evolution in the Stokes parameters from which the appearance of a
circularly polarised component in the photon beam can be demonstrated. The
measured magnitude of the circularly polarised component was consistent with
the theoretical predictions, and therefore is in indication of the existence of
the birefringence effect.Comment: 12 pages, 12 figures, 1 table, REVTeX4 two column, Version for
publicatio
Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence
The cross section for coherent pair production by linearly polarised photons
in the 20-170 GeV energy range was measured for photon aligned incidence on
ultra-high quality diamond and germanium crystals. The theoretical description
of coherent bremsstrahlung and coherent pair production phenomena is an area of
active theoretical debate and development. However, under our experimental
conditions, the theory predicted the combined cross section and polarisation
experimental observables very well indeed. In macroscopic terms, our experiment
measured a birefringence effect in pair production in a crystal. This study of
this effect also constituted a measurement of the energy dependent linear
polarisation of photons produced by coherent bremsstrahlung in aligned
crystals. New technologies for manipulating high energy photon beams can be
realised based on an improved understanding of QED phenomena at these energies.
In particular, this experiment demonstrates an efficient new polarimetry
technique. The pair production measurements were done using two independent
methods simultaneously. The more complex method using a magnet spectrometer
showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for
publicatio
Results on the Coherent Interaction of High Energy Electrons and Photons in Oriented Single Crystals
The CERN-NA-59 experiment examined a wide range of electromagnetic processes
for multi-GeV electrons and photons interacting with oriented single crystals.
The various types of crystals and their orientations were used for producing
photon beams and for converting and measuring their polarisation.
The radiation emitted by 178 GeV unpolarised electrons incident on a 1.5 cm
thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the
String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised
photon beams.
A new crystal polarimetry technique was established for measuring the linear
polarisation of the photon beam. The polarimeter is based on the dependence of
the Coherent Pair Production (CPP) cross section in oriented single crystals on
the direction of the photon polarisation with respect to the crystal plane.
Both a 1 mm thick single crystal of Germanium and a 4 mm thick multi-tile set
of synthetic Diamond crystals were used as analyzers of the linear
polarisation.
A birefringence phenomenon, the conversion of the linear polarisation of the
photon beam into circular polarisation, was observed. This was achieved by
letting the linearly polarised photon beam pass through a 10 cm thick Silicon
single crystal that acted as a "quarter wave plate" (QWP) as suggested by N.
Cabibbo et al.Comment: Presented at International workshop "Relativistic Channeling and
Related Coherent Phenomena", Frascati (Rome) 23-26 March 200
Performance of the ARIANNA Hexagonal Radio Array
Installation of the ARIANNA Hexagonal Radio Array (HRA) on the Ross Ice Shelf
of Antarctica has been completed. This detector serves as a pilot program to
the ARIANNA neutrino telescope, which aims to measure the diffuse flux of very
high energy neutrinos by observing the radio pulse generated by
neutrino-induced charged particle showers in the ice. All HRA stations ran
reliably and took data during the entire 2014-2015 austral summer season. A new
radio signal direction reconstruction procedure is described, and is observed
to have a resolution better than a degree. The reconstruction is used in a
preliminary search for potential neutrino candidate events in the data from one
of the newly installed detector stations. Three cuts are used to separate radio
backgrounds from neutrino signals. The cuts are found to filter out all data
recorded by the station during the season while preserving 85.4% of simulated
neutrino events that trigger the station. This efficiency is similar to that
found in analyses of previous HRA data taking seasons.Comment: Proceedings from the 34th ICRC2015, http://icrc2015.nl/ . 8 pages, 6
figure
A First Search for Cosmogenic Neutrinos with the ARIANNA Hexagonal Radio Array
The ARIANNA experiment seeks to observe the diffuse flux of neutrinos in the
10^8 - 10^10 GeV energy range using a grid of radio detectors at the surface of
the Ross Ice Shelf of Antarctica. The detector measures the coherent Cherenkov
radiation produced at radio frequencies, from about 100 MHz to 1 GHz, by
charged particle showers generated by neutrino interactions in the ice. The
ARIANNA Hexagonal Radio Array (HRA) is being constructed as a prototype for the
full array. During the 2013-14 austral summer, three HRA stations collected
radio data which was wirelessly transmitted off site in nearly real-time. The
performance of these stations is described and a simple analysis to search for
neutrino signals is presented. The analysis employs a set of three cuts that
reject background triggers while preserving 90% of simulated cosmogenic
neutrino triggers. No neutrino candidates are found in the data and a
model-independent 90% confidence level Neyman upper limit is placed on the all
flavor neutrino+antineutrino flux in a sliding decade-wide energy bin. The
limit reaches a minimum of 1.9x10^-23 GeV^-1 cm^-2 s^-1 sr^-1 in the 10^8.5 -
10^9.5 GeV energy bin. Simulations of the performance of the full detector are
also described. The sensitivity of the full ARIANNA experiment is presented and
compared with current neutrino flux models.Comment: 22 pages, 22 figures. Published in Astroparticle Physic
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