R&D results on a CsI-TTGEM based photodetector

The very high momentum particle identification detector proposed for the ALICE upgrade is a focusing RICH using a C4F10 gaseous radiator. For the detection of Cherenkov photons, one of the options currently under investigation is to use a CsI coated Triple-Thick-GEM (CsI-TTGEM) with metallic or resistive electrodes. We will present results from the laboratory studies as well as preliminary results of beam tests of a RICH detector prototype consisting of a CaF2 radiator coupled to a 10x10 cm2 CsI-TTGEM equipped with a pad readout and GASSIPLEX-based front-end electronics. With such a prototype the detection of Cherenkov photons simultaneously with minimum ionizing particles has been achieved for the first time in a stable operation mode

The current progress of the ALICE Ring Imaging Cherenkov Detector

Recently, the last two modules (out of seven) of the ALICE High Momentum Particle Identification detector (HMPID) were assembled and tested. The full detector, after a pre-commissioning phase, has been installed in the experimental area, inside the ALICE solenoid, at the end of September 2006. In this paper we review the status of the ALICE/HMPID project and we present a summary of the series production of the CsI photo-cathodes. We describe the key features of the production procedure which ensures high quality photo-cathodes as well as the results of the quality assessment performed by means of a specially developed 2D scanner system able to produce a detailed map of the CsI photo-current over the entire photo-cathode surface. Finally we present our recent R&D efforts toward the development of a novel generation of imaging Cherenkov detectors with the aim to identify, in heavy ions collisions, hadrons up to 30 GeV/c.Comment: Presented at the Imaging-2006 Conference, Stockholm, Sweden, June 200

Investigations of fast neutron production by 190 GeV/c muon interactions on different targets

The production of fast neutrons (1 MeV - 1 GeV) in high energy muon-nucleus interactions is poorly understood, yet it is fundamental to the understanding of the background in many underground experiments. The aim of the present experiment (CERN NA55) was to measure spallation neutrons produced by 190 GeV/c muons scattering on carbon, copper and lead targets. We have investigated the energy spectrum and angular distribution of spallation neutrons, and we report the result of our measurement of the neutron production differential cross section.Comment: 19 pages, 11 figures ep

Leading-particle suppression in high energy nucleus-nucleus collisions

Parton energy loss effects in heavy-ion collisions are studied with the Monte Carlo program PQM (Parton Quenching Model) constructed using the BDMPS quenching weights and a realistic collision geometry. The merit of the approach is that it contains only one free parameter that is tuned to the high-pt nuclear modification factor measured in central Au-Au collisions at sqrt{s_NN} = 200 GeV. Once tuned, the model is coherently applied to all the high-pt observables at 200 GeV: the centrality evolution of the nuclear modification factor, the suppression of the away-side jet-like correlations, and the azimuthal anisotropies for these observables. Predictions for the leading-particle suppression at nucleon-nucleon centre-of-mass energies of 62.4 and 5500 GeV are calculated. The limits of the eikonal approximation in the BDMPS approach, when applied to finite-energy partons, are discussed.Comment: 28 pages, 14 figures, final version, accepted by Eur. Phys. J.

Recognition of Cherenkov patterns in high multiplicity environments

An algorithm for the recognition of Cherenkov patterns based on the Hough Transform Method (HTM), modified for signals with intrinsic width in presence of background, is presented. The method basically consists in a mapping of the pad coordinate space directly to the Cherenkov angle parameter space with a crucial increase of performance in the treatment of different pattern shapes and amount of background. The method has been developed in the framework of the ALICE experiment at CERN for the analysis of data taken in the HMPID (High Momentum Particle IDentification) RICH detector prototype test beam

Aging of large area CsI photocathodes for the ALICE HMPID prototypes

The ALICE HMPID RICH detector is equipped with CsI photocathodes in a MWPC for the detection of Cherenkov photons. The long term operational experience with large area CsI photocathodes will be described. The RICH prototypes have shown a very high stability of operation and performance, at a gain of 10 \5 and with rates up to 2x10 \4 cm-2 s-1. When exposure to air has been avoided, no degradation of the CsI quantum efficiency has been observed on photocathodes periodically exposed to test-beams over 7 years, corresponding to local integrated charge densities of ~ 1 mC cm-2. The results of limited exposures to oxygen and humidity will also be presented

First observation of Cherenkov rings with a large area CsI-TGEM-based RICH prototype

We have built a RICH detector prototype consisting of a liquid C6F14 radiator and six triple Thick Gaseous Electron Multipliers (TGEMs), each of them having an active area of 10x10 cm2. One triple TGEM has been placed behind the liquid radiator in order to detect the beam particles, whereas the other five have been positioned around the central one at a distance to collect the Cherenkov photons. The upstream electrode of each of the TGEM stacks has been coated with a 0.4 micron thick CsI layer. In this paper, we will present the results from a series of laboratory tests with this prototype carried out using UV light, 6 keV photons from 55Fe and electrons from 90Sr as well as recent results of tests with a beam of charged pions where for the first time Cherenkov Ring images have been successfully recorded with TGEM photodetectors. The achieved results prove the feasibility of building a large area Cherenkov detector consisting of a matrix of TGEMs.Comment: Presented at the International Conference NDIP-11, Lyon,July201

COSMOGRAIL: XVII. Time delays for the quadruply imaged quasar PG 1115+080

Indexación: Scopus.Acknowledgements. The authors would like to thank R. Gredel for his help in setting up the program at the ESO MPIA 2.2 m telescope, and the anonymous referee for his or her comments on this work. This work is supported by the Swiss National Fundation. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013, 2018) and the 2D graphics environment Matplotlib (Hunter 2007). K.R. acknowledge support from PhD fellowship FIB-UV 2015/2016 and Becas de Doctorado Nacional CONICYT 2017 and thanks the LSSTC Data Science Fellowship Program, her time as a Fellow has benefited this work. M.T. acknowledges support by the DFG grant Hi 1495/2-1. G. C.-F. C. acknowledges support from the Ministry of Education in Taiwan via Government Scholarship to Study Abroad (GSSA). D. C.-Y. Chao and S. H. Suyu gratefully acknowledge the support from the Max Planck Society through the Max Planck Research Group for S. H. Suyu. T. A. acknowledges support by the Ministry for the Economy, Development, and Tourism’s Programa Inicativa Científica Milenio through grant IC 12009, awarded to The Millennium Institute of Astrophysics (MAS).We present time-delay estimates for the quadruply imaged quasar PG 1115+080. Our results are based on almost daily observations for seven months at the ESO MPIA 2.2 m telescope at La Silla Observatory, reaching a signal-to-noise ratio of about 1000 per quasar image. In addition, we re-analyze existing light curves from the literature that we complete with an additional three seasons of monitoring with the Mercator telescope at La Palma Observatory. When exploring the possible source of bias we considered the so-called microlensing time delay, a potential source of systematic error so far never directly accounted for in previous time-delay publications. In 15 yr of data on PG 1115+080, we find no strong evidence of microlensing time delay. Therefore not accounting for this effect, our time-delay estimates on the individual data sets are in good agreement with each other and with the literature. Combining the data sets, we obtain the most precise time-delay estimates to date on PG 1115+080, with Δt(AB) = 8.3+1.5 -1.6 days (18.7% precision), Δt(AC) = 9.9+1.1 -1.1 days (11.1%) and Δt(BC) = 18.8+1.6 -1.6 days (8.5%). Turning these time delays into cosmological constraints is done in a companion paper that makes use of ground-based Adaptive Optics (AO) with the Keck telescope. © ESO 2018.https://www.aanda.org/articles/aa/abs/2018/08/aa33287-18/aa33287-18.htm