CsI(Tl) for WIMP dark matter searches

We report a study of CsI(Tl) scintillator to assess its applicability in experiments to search for dark matter particles. Measurements of the mean scintillation pulse shapes due to nuclear and electron recoils have been performed. We find that, as with NaI(Tl), pulse shape analysis can be used to discriminate between electron and nuclear recoils down to 4 keV. However, the discrimination factor is typically (10-15)% better than in NaI(Tl) above 4 keV. The quenching factor for caesium and iodine recoils was measured and found to increase from 11% to ~17% with decreasing recoil energy from 60 to 12 keV. Based on these results, the potential sensitivity of CsI(Tl) to dark matter particles in the form of neutralinos was calculated. We find an improvement over NaI(Tl) for the spin independent WIMP-nucleon interactions up to a factor of 5 assuming comparable electron background levels in the two scintillators.Comment: 16 pages, 8 figures, to be published in Nucl. Instrum. and Meth. in Phys. Res.

Neutron beam test of CsI crystal for dark matter search

We have studied the response of Tl-doped and Na-doped CsI crystals to nuclear recoils and $\gamma$'s below 10 keV. The response of CsI crystals to nuclear recoil was studied with mono-energetic neutrons produced by the $^3$H(p,n)$^3$He reaction. This was compared to the response to Compton electrons scattered by 662 keV $\gamma$-ray. Pulse shape discrimination between the response to these $\gamma$'s and nuclear recoils was studied, and quality factors were estimated. The quenching factors for nuclear recoils were derived for both CsI(Na) and CsI(Tl) crystals.Comment: 21pages, 14figures, submitted to NIM

SICANE: a Detector Array for the Measurement of Nuclear Recoil Quenching Factors using Monoenergetic Neutron Beam

SICANE is a neutron scattering multidetector facility for the determination of the quenching factor (ratio of the response to nuclear recoils and to electrons) of cryogenic detectors used in direct WIMP searches. Well collimated monoenergetic neutron beams are obtained with inverse (p,n) reactions. The facility is described, and results obtained for the quenching factors of scintillation in NaI(Tl) and of heat and ionization in Ge are presented.Comment: 30 pages, Latex, 11 figures. Submitted to NIM

Event categories in the EDELWEISS WIMP search experiment

Four categories of events have been identified in the EDELWEISS-I dark matter experiment using germanium cryogenic detectors measuring simultaneously charge and heat signals. These categories of events are interpreted as electron and nuclear interactions occurring in the volume of the detector, and electron and nuclear interactions occurring close to the surface of the detectors(10-20 mu-m of the surface). We discuss the hypothesis that low energy surface nuclear recoils,which seem to have been unnoticed by previous WIMP searches, may provide an interpretation of the anomalous events recorded by the UKDMC and Saclay NaI experiments. The present analysis points to the necessity of taking into account surface nuclear and electron recoil interactions for a reliable estimate of background rejection factors.Comment: 11 pages, submitted to Phys. Lett.

Background discrimination capabilities of a heat and ionization germanium cryogenic detector

The discrimination capabilities of a 70 g heat and ionization Ge bolometer are studied. This first prototype has been used by the EDELWEISS Dark Matter experiment, installed in the Laboratoire Souterrain de Modane, for direct detection of WIMPs. Gamma and neutron calibrations demonstrate that this type of detector is able to reject more than 99.6% of the background while retaining 95% of the signal, provided that the background events distribution is not biased towards the surface of the Ge crystal. However, the 1.17 kg.day of data taken in a relatively important radioactive environment show an extra population slightly overlapping the signal. This background is likely due to interactions of low energy photons or electrons near the surface of the crystal, and is somewhat reduced by applying a higher charge-collecting inverse bias voltage (-6 V instead of -2 V) to the Ge diode. Despite this contamination, more than 98% of the background can be rejected while retaining 50% of the signal. This yields a conservative upper limit of 0.7 event.day^{-1}.kg^{-1}.keV^{-1}_{recoil} at 90% confidence level in the 15-45 keV recoil energy interval; the present sensitivity appears to be limited by the fast ambient neutrons. Upgrades in progress on the installation are summarized.Comment: Submitted to Astroparticle Physics, 14 page

Technical design and performance of the NEMO3 detector

The development of the NEMO3 detector, which is now running in the Frejus Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun more than ten years ago. The NEMO3 detector uses a tracking-calorimeter technique in order to investigate double beta decay processes for several isotopes. The technical description of the detector is followed by the presentation of its performance.Comment: Preprint submitted to Nucl. Instrum. Methods A Corresponding author: Corinne Augier ([email protected]

Matière noire non baryonique: détecteurs à scintillation et bolomètres pour la recherche de WIMPs

ManoirParrmi les nombreux candidats à la masse manquante de l'Univers, les WIMPs (Particules Lourdes Interagissant Faiblement) sont des candidats d'autant plus sérieux que leur existence est prévue par les modèles supersymétriques. Dans le cadre de la mise en évidence des WIMPs, nous avons caractérisé deux types de détecteurs qui fonctionnent sur le principe de la détection du recul d'un noyau d'un cristal sous l'impact d'un WIMP, en donnant soit une impulsion de lumière dans un scintillateur soit une impulsion de chaleur dans un bolomètre maintenu à 10 mK dans un cryostat. Nous avons mis au point une méthode de mesure du facteur de quenching d'un scintillateur CsI(Tl) pour des énergies de recul très faibles (de l'ordre de 10 keV). Nous avons également caractérisé un bolomètre en saphir de très gros volume (1110 g) : la résolution obtenue est de 18 keV à mi-hauteur sur la raie du $^{57}$Co à 122 keV avec un seuil de 11 keV pour une température du senseur de 45 mK. Enfin nous proposons une méthode d'analyse des signaux basée sur la transformation en ondelettes, appliquée aussi bien aux données obtenues avec le cristal précédent qu'aux données obtenues par la collaboration EDELWEISS sur le détecteur double composante ionisation-chaleur installé au Laboratoire Souterrain de Modane

Détection directe de la matière noire non baryonique

Pas de résum

Remarques sur les techniques de construction de second art roman, à propos de Saint-André-de-Souvignargues (Gard)

The church in Saint-André de Souvignargues (Gard) built during the second Romanesque period, offers an exceptionnal architectural sectional view for understanding the techniques and building sites in that period. The major part of the geological resources is firstly exposed. Then the analysis of that construction reveals clearly the medieval trial and error proceedings to perfect the alternate disposition of the height of stones of the half dome vault, and more generally for the process of the stone cutting applied to the cylindrical assemblies with rayonnant joints. Studies of the tracings, of the carved ornaments and of the operation process from the point of view of stone work professionnals, open here new perpectives about the organisation of these still ill-known rural building sites. Many of these practices resuit from borrowings from the ancient monuments of the region, even for the stylistics, but the proper character of interpretation remains preponderant. One concern remains : will the current «restoration» be able to respect such a monument ?L'église Saint-André de Souvignargues (Gard), édifiée durant le second âge roman, offre un état d'écorché architectural tout à fait exceptionnel pour la connaissance des techniques et des chantiers de construction de cette période. Le rôle majeur des ressources géologiques locales est d'abord mis en évidence. Ensuite, l'analyse de cette construction révèle clairement les tâtonnements médiévaux pour la mise au point de l'appareil alterné, de la voûte en cul de four et, d'une manière plus générale, pour le traitement de la coupe des pierres appliquée aux ensembles cylindriques à joints rayonnants. L'étude des tracés, des ornements sculptés et de la mise en œuvre vue par des professionnels de la pierre, ouvre ici des perspectives inédites sur l'organisation de ces chantiers ruraux encore mal connus. Beaucoup de ces pratiques résultent d'emprunts aux monuments antiques de la région, il en est de même pour la stylistique mais le caractère propre de l'interprétation médiévale demeure prépondérant. La "restauration" en cours, saura-t-elle respecter un tel monument ? Un important problème d'éthique se pose ici.Bessac Jean-Claude, Pécourt Jacques. Remarques sur les techniques de construction de second art roman, à propos de Saint-André-de-Souvignargues (Gard). In: Archéologie du Midi médiéval. Tome 13, 1995. pp. 91-122