134 research outputs found
Transition Radiation Spectra of Electrons from 1 to 10 GeV/c in Regular and Irregular Radiators
We present measurements of the spectral distribution of transition radiation
generated by electrons of momentum 1 to 10 GeV/c in different radiator types.
We investigate periodic foil radiators and irregular foam and fiber materials.
The transition radiation photons are detected by prototypes of the drift
chambers to be used in the Transition Radiation Detector (TRD) of the ALICE
experiment at CERN, which are filled with a Xe, CO2 (15 %) mixture. The
measurements are compared to simulations in order to enhance the quantitative
understanding of transition radiation production, in particular the momentum
dependence of the transition radiation yield.Comment: 18 pages, 15 figures, submitted to Nucl. Instr. Meth. Phys. Res.
Chaos assisted tunnelling with cold atoms
In the context of quantum chaos, both theory and numerical analysis predict
large fluctuations of the tunnelling transition probabilities when irregular
dynamics is present at the classical level. We consider here the
non-dissipative quantum evolution of cold atoms trapped in a time-dependent
modulated periodic potential generated by two laser beams. We give some precise
guidelines for the observation of chaos assisted tunnelling between invariant
phase space structures paired by time-reversal symmetry.Comment: submitted to Phys. Rev. E ; 16 pages, 13 figures; figures of better
quality can be found at http://www.phys.univ-tours.fr/~mouchet
The K^*_0(800) scalar resonance from Roy-Steiner representations of pi K scattering
We discuss the existence of the light scalar meson K^*_0(800) (also called
kappa) in a rigorous way, by showing the presence of a pole in the pi K --> pi
K amplitude on the second Riemann sheet. For this purpose, we study the domain
of validity of two classes of Roy-Steiner representations in the complex energy
plane. We prove that one of them is valid in a region sufficiently broad in the
imaginary direction. From this representation, we compute the l=0 partial wave
in the complex plane with neither additional approximation nor model
dependence, relying only on experimental data. A scalar resonance with
strangeness S=1 is found with the following mass and width: E_kappa = 658 \pm
13 MeV and Gamma_kappa = 557 \pm 24 MeV.Comment: 16 pages, 8 figures. Domain of validity of a Roy-Steiner
representation corrected and enlarged, and features of the K^*_0(800) pole
discussed in more details. Conclusions unchange
A study of charged kappa in
Based on events collected by BESII, the decay
is studied. In the invariant mass
spectrum recoiling against the charged , the charged
particle is found as a low mass enhancement. If a Breit-Wigner function of
constant width is used to parameterize the kappa, its pole locates at MeV/. Also in this channel,
the decay is observed for the first time.
Its branching ratio is .Comment: 14 pages, 4 figure
Approximate Bisimulations for Sodium Channel Dynamics
Abstract. This paper shows that, in the context of the Iyer et al. 67-variable cardiac myocycte model (IMW), it is possible to replace the detailed 13-state continuous-time MDP model of the sodium-channel dy-namics, with a much simpler Hodgkin-Huxley (HH)-like two-state sodium-channel model, while only incurring a bounded approximation error. The technical basis for this result is the construction of an approximate bisim-ulation between the HH and IMW channel models, both of which are input-controlled (voltage in this case) continuous-time Markov chains. The construction of the appropriate approximate bisimulation, as well as the overall result regarding the behavior of this modified IMW model, in-volves: (1) The identification of the voltage-dependent parameters of the m and h gates in the HH-type channel, based on the observations of the IMW channel. (2) Proving that the distance between observations of the two channels never exceeds a given error. (3) Exploring the sensitivity of the overall IMW model to the HH-type sodium-channel approximation. Our extensive simulation results experimentally validate our findings, for varying IMW-type input stimuli
Evidence for kappa Meson Production in J/psi -> bar{K}^*(892)^0K^+pi^- Process
Based on 58 million BESII J/psi events, the bar{K}^*(892)^0K^+pi^- channel in
K^+K^-pi^+pi^- is studied. A clear low mass enhancement in the invariant mass
spectrum of K^+pi^- is observed. The low mass enhancement does not come from
background of other J/psi decay channels, nor from phase space. Two independent
partial wave analyses have been performed. Both analyses favor that the low
mass enhancement is the kappa, an isospinor scalar resonant state. The average
mass and width of the kappa in the two analyses are 878 +- 23^{+64}_{-55}
MeV/c^2 and 499 +- 52^{+55}_{-87} MeV/c^2, respectively, corresponding to a
pole at (841 +- 30^{+81}_{-73}) - i(309 +- 45^{+48}_{-72}) MeV/c^2.Comment: 17 pages, 5 figure
The CALorimetric Electron Telescope (CALET) for high-energy astroparticle physics on the International Space Station
The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF)
Measurement of the gamma ray background in the Davis Cavern at the Sanford Underground Research Facility
Deep underground environments are ideal for low background searches due to the attenuation of cosmic rays by passage through the earth. However, they are affected by backgrounds from γ-rays emitted by 40K and the 238U and 232Th decay chains in the surrounding rock. The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a liquid xenon TPC located within the Davis campus at the Sanford Underground Research Facility, Lead, South Dakota, at the 4,850-foot level. In order to characterise the cavern background, in-situ γ-ray measurements were taken with a sodium iodide detector in various locations and with lead shielding. The integral count rates (0--3300~keV) varied from 596~Hz to 1355~Hz for unshielded measurements, corresponding to a total flux in the cavern of 1.9±0.4~γ cm−2s−1. The resulting activity in the walls of the cavern can be characterised as 220±60~Bq/kg of 40K, 29±15~Bq/kg of 238U, and 13±3~Bq/kg of 232Th
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