arXiv subjects

J. Dolbeau

Publications and source records attributed to J. Dolbeau.

7 recordsLinked to original sources

arXiv2007

Absolute measurement of the nitrogen fluorescence yield in air between 300 and 430 nm

The nitrogen fluorescence induced in air is used to detect ultra-high energy cosmic rays and to measure their energy. The precise knowledge of the absolute fluorescence yield is the key quantity to improve the accuracy on the cosmic ray energy. The total yield has been measured in dry air using a 90Sr source and a [300-430 nm] filter. The fluorescence yield in air is 4.23 $\pm$ 0.20 photons per meter when normalized to 760 mmHg, 15 degrees C and with an electron energy of 0.85 MeV. This result is consistent with previous experiments made at various energies, but with an accuracy improved by a factor of about 3. For the first time, the absolute continuous spectrum of nitrogen excited by 90Sr electrons has also been measured with a spectrometer. Details of this experiment are given in one of the author's PhD thesis [32].

astro-ph↗

arXiv2006

MEMPHYS:A large scale water Cerenkov detector at Fréjus

A water Čerenkov detector project, of megaton scale, to be installed in the Fréjus underground site and dedicated to nucleon decay, neutrinos from supernovae, solar and atmospheric neutrinos, as well as neutrinos from a super-beam and/or a beta-beam coming from CERN, is presented and compared with competitor projects in Japan and in the USA. The performances of the European project are discussed, including the possibility to measure the mixing angle $θ_{13}$ and the CP-violating phase $δ$.

hep-ex↗

arXiv2005

UV Light Shower Simulator for Fluorescence and Cerenkov Radiation Studies

All experiments observing showers light use telescopes equipped with pixellised photodetectors. Monte-Carlo (MC) simulations of the apparatus operation in various situations (background light, shower energy, proximity of tracks...) are mandatory, but never enter into detector details like pulse shape, dead-time, or charge space effects which are finally responsible for the data quality. An apparatus where each pixel receives light from individual 370 nm UV LEDs through silica fibers is being built. The LEDs receive voltage through DACs, which get their input (which pixel, at what time, which amplitude) from a shower plus noise generator code. The typical time constant of a shower being one $/mu$s (300 m for light), the pulses are one $/mu$s wide. This is rather long compared to the intrinsic time constant (around 10 ns) of the light detectors, hence, these see "constant light" changing every $/mu$s. This is where important loading effects which are not included in MC code can be observed. The fibers illuminate the pixels through a diffuser, and each fiber illuminates only one pixel. The number of equipped pixels is such that it englobes a full shower (much less than the full focal surface). Finally, this equipment can be used also to calibrate the pixels.

physics.ins-det↗

arXiv2005

NOSTOS: a spherical TPC to detect low energy neutrinos

A novel low-energy ($\sim$few keV) neutrino-oscillation experiment NOSTOS, combining a strong tritium source and a high pressure spherical Time Projection Chamber (TPC) detector 10 m in radius has been recently proposed. The oscillation of neutrinos of such energies occurs within the size of the detector itself, potentially allowing for a very precise (and rather systematics-free) measure of the oscillation parameters, in particular, of the smaller mixing angle $θ_{13}$, which value could be determined for the first time. This detector could also be sensitive to the neutrino magnetic moment and be capable of accurately measure the Weinberg angle at low energy. The same apparatus, filled with high pressure Xenon, exhibits a high sensitivity as a Super Nova neutrino detector with extra galactic sensitivity. The outstanding benefits of the new concept of the spherical TPC will be presented, as well as the issues to be demonstrated in the near future by an ongoing R&D. The very first results of small prototype in operation in Saclay are shown.

hep-ex↗

arXiv2005

NOSTOS experiment and new trends in rare event detection

A novel low-energy neutrino-oscillation experiment NOSTOS, combining a strong tritium source and a high pressure spherical TPC detector (10 m in radius) has been recently proposed. The goal of the experiment is to measure the mixing angle $θ_{13}$, the neutrino magnetic moment and the Weinberg angle at low energy. The same apparatus, filled with high pressure Xenon, exhibits a high sensitivity as a Super Nova neutrino detector with extra galactic sensitivity. Results of a first prototype will be shown and a short-term experimental program will be discussed.

hep-ex↗

arXiv2001

A Preliminary Look at the Physics Reach of a Solar Neutrino TPC: Time-Independent Two Neutrino Oscillations

This paper will discuss the physics reach of a solar neutrino TPC containing many tons of He4 under high pressure. Particular attention is given to the LMA and SMA solutions, which are allowed by current data, and which are characterized by a lack of time-dependent phenomena (either summer-winter or day-night asymmetries). In this case, the physics of neutrino masses and mixing is all contained in the energy dependence of the electron neutrino survival probability, (or in its reciprocal, the electron neutrino disappearance probability).

hep-ph↗

arXiv1999

The solar neutrino project HELLAZ : status report on the hardware and the simulation

We report the status of the solar neutrino project called HELLAZ. In a high pressure and cooled TPC filled with helium, the detection of each ionisation electron of the track produced by the recoil electron from elastic scattering induced by solar neutrinos, will yield the low energy, high resolution solar neutrino spectrum. Two topics are presented ; test of Micromegas gas chambers giving a good discrimination between adjacent ionisation electrons and the preliminary test of the direction of the primary electron track from the cloud analysis. These two tests seem rather encouraging.

physics.ins-det↗