S. Maltezos

The Barrel Ring Imaging Cherenkov counter of DELPHI

Abstract A short explanation is given of the Barrel Ring Imaging CHerenkov (BRICH) detector and its performance. We discuss in brief some of the requirements to run this detector. Special attention is paid to the functioning of the Cherenkov photon detector — a photosensitive gas-filled drift chamber where the photoelectrons drift to a MWPC of special construction. We illustrate the BRICH performance with some preliminary results.

A VUV prism spectrometer for RICH radiator refractometry

Abstract A prism spectrometer has been developed to operate in the VUV wavelength range from 120 to 200 nm. It can be used as a pre-disperser in conjunction with a Fabry-Perot based gas refractometer. This instrument has also been used to measure the refractive index of the liquid radiator C6F14 in various spectral lines. This radiator is used in the RICH detectors of the DELPHI experiment and has been proposed for ALICE, and LHCb experiments. The spectral resolution of the system is improved as the wavelength decreases and the data are consistent with a wavelength accuracy about 0.4 nm at 140nm. The results for the dispersion curve of the above liquid are presented.

Precision measurements of gas refractivity by means of a Fabry–Perot interferometer illustrated by the monitoring of radiator refractivity in the DELPHI RICH detectors

Abstract With an updated, flexible, highly efficient and easily installed system we obtained accurate refractivity ( n −1) values. This system is a refractometer based on a Fabry–Perot interferometer and was used to monitor the refractivity of DELPHI RICH Cherenkov radiators near the VUV region. By using a Pt–Ne spectral lamp and improved alignment and temperature control, the refractivities of C 5 F 12 and C 4 F 10 have been monitored since 1996. With this light source, selected to have large coherence lengths, we can extract the refractivity at several wavelengths from one data set only. The estimated errors of the refractivity measurements are less than 1.2%, and depend on wavelength and the type of gas used. The various parameters affecting the accuracy of the refractometer are also discussed. Finally, results from special sample refractivity measurements of the liquid radiator (C 6 F 14 ) in its gas phase, are presented.

The ATLAS muon Micromegas R&D project: towards large-size chambers for the s-LHC

Detectors based on the bulk-Micromegas technology exhibit position resolution better than 100 μm at counting rates of up to several tens of kHz/cm2, along with trigger capabilities. These characteristics, combined with the detectors mechanical robustness and the possibility for cost-effective industrial production, makes them a promising candidate for the ATLAS Muon Spectrometer upgrade in a future luminosity enhancement of the LHC. The R&D project status will be presented together with the obtained results in the effort to define the baseline system specifications.

A system for monitoring the refractivities of fluids in the DELPHI RICH detectors in the VUV region

Abstract An overview of the instrumentation developed for the quality control of the optical properties of fluid components of RICH detectors is presented. An on-line data acquisition and control system for operation of a refractometer in the UV and VUV region is presented. The possibility of simultaneous measurement of transmittance and refractivity using a Fabry-Perot refractometer in the UV and VUV region is discussed. The accuracy of the refractometer in the n − 1 determination of atmospheric air is presently 0.3% at 255 nm and about 1% at 185 nm. It is expected to improve when measuring the refractivities of the fluorocarbons used as radiators in RICH detectors.

Extensive performance studies for the ATLAS BIS-MDT precision muon chambers with cosmic rays

ATLAS (A Toroidal LHC ApparatuS) is a general-purpose experiment, which will start its operation at the Large Hadron Collider (LHC) at CERN in 2007. The ATLAS detector is designed to explore numerous physics processes by measuring, recording, and investigating the products emerging from proton-proton collisions at energies up to 14 TeV. High-precision muon momentum measurement (dp/p-10% at p/sub T/=1 TeV/c) over large areas using Monitored Drift Tube (MDT) chambers is crucial for the ATLAS experiment. More than 1,200 MDT chambers, assembled from approximately 370,000 drift tubes operated at 3 bar pressure, will be used to provide for the total detector coverage of 5,500 m/sup 2/. Three Greek universities have taken the responsibility to construct 30,000 drift tubes of /spl sim/1.7 in length, to test them and finally assemble them into 120 BIS (Barrel Inner Small) chambers. The design of the muon drift tubes aims at high efficiency (>95%) and a spatial resolution of <80 /spl mu/m (single tube resolution). This paper describes the cosmic ray setup, which has been instrumented in order to verify. that the BIS chamber Module-0 fulfils its design requirements. The analysis of its data shows that the chamber meets these requirements; it has low noise levels, uniform drift properties, good spatial resolution and high particle detection efficiency.

The Fabry-Perot Interferometer for the DELPHI Ring Imaging Cherenkov Detector

The performance of a refractometer for operation in the DELPHI Ring Imaging Cherenkov detectors for operation in the far UV region is presented. Comparisons are made with performance in standard laboratory conditions. Data on absolute refractivities are given for reference samples of air, argon, Freon 12 as well as on gaseous C4F10 from the Forward RICH detector of DELPHI. The accuracy of the determination of the n-1 using this refractometer at the 253.7nm is estimated about 1% for C4 F10.

Energy estimation of ultra high energy cosmic particles by lateral distribution functions of extensive air showers

Energy is among the characteristics of Ultra High Energy Cosmic Rays (E > 5 ×1019eV) which could be estimated experimentally based on simulations. This paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of extensive air showers, vertical and inclined, are simulated to derive the lateral distribution functions of the shower particles. The scenario of simulations is adapted to the P. Auger Observatory site.

Multilayer filters for extending the duty cycle of optical telescopes in the highest energy cosmic ray experiments

Multilayer optical filters, appropriately designed to reject the optical noise emitted in the range between the main UV spectral lines of the atmospheric N, ’ fluorescence, induced by the Ultra High Energy Cosmic Rays (UHECR) via the effect of Extensive Air Showers (EAS), are presented in this work. For the design we used the method of simulated annealing, assuming 40 dielectric layers. A simplified model of the main optical noise components has been used for calculating the evolution of the trigger probability and the resulting duty cycle of a pixel detector. The method has been applied for the fluorescence telescope of the AUGER

The ring imaging Cherenkov detectors of DELPHI

A ring imaging Cherenkov (RICH) detector system has been built and is now in full operation within the DELPHI experiment. Large data samples of Z/sup 0/ decays are being collected with good resolution on the observed Cherenkov angles. Several studies of Z/sup 0/ decays using the RICH have already been performed on limited samples. Disturbance of the detector operation caused by shrinkage of polymeric construction materials and by migration of radiator substance is reported. These effects have been counteracted and do not endanger the quality of the data. >