Results on Low-Mass Weakly Interacting Massive Particles from a 11 kg d Target Exposure of DAMIC at SNOLAB

Experimental efforts of the last decades have been unsuccessful in detecting WIMPs (Weakly Interacting Massive Particles) in the 10-to-104 GeV/c2 range, thus motivating the search for lighter dark matter. The DAMIC (DArk Matter In CCDs) at SNOLAB experiment aims for direct detection of light dark matter particles (mχ<10 GeV/c2) by means of CCDs (Charge-Coupled Devices). Fully-depleted 675 μm-thick CCDs are used to such end. The optimized readout noise and operation at cryogenic temperatures allow for a detection threshold of 50 eVee electron-equivalent energy. Focusing on nuclear and electronic scattering as potential detection processes, DAMIC has so far set competitive constraints on the detection of low mass WIMPs and hidden-sector particles. In this work, an 11 kg⋅ d exposure dataset is exploited to search for light WIMPs by building the first comprehensive radioactive background model for CCDs. Different background sources are discriminated making conjoint use of the spatial distribution and energy of ionization events, thereby constraining the amount of contaminants such as tritium from silicon cosmogenic activation and surface lead-210 from radon plate-out. Despite a conspicuous, statistically-significant excess of events below 200 eVee, this analysis places the strongest exclusion limit on the WIMP-nucleon scattering cross section with a silicon target for mχ< 9 GeV/c2

Skipper-CCD Sensors for the Oscura Experiment: Requirements and Preliminary Tests

Oscura is a proposed multi-kg skipper-CCD experiment designed for a dark matter (DM) direct detection search that will reach unprecedented sensitivity to sub-GeV DM-electron interactions with its 10 kg detector array. Oscura is planning to operate at SNOLAB with 2070 m overburden, and aims to reach a background goal of less than one event in each electron bin in the 2-10 electron ionization-signal region for the full 30 kg-year exposure, with a radiation background rate of 0.01 dru. In order to achieve this goal, Oscura must address each potential source of background events, including instrumental backgrounds. In this work, we discuss the main instrumental background sources and the strategy to control them, establishing a set of constraints on the sensors' performance parameters. We present results from the tests of the first fabricated Oscura prototype sensors, evaluate their performance in the context of the established constraints and estimate the Oscura instrumental background based on these results

Early Science with the Oscura Integration Test

Oscura is a planned light-dark matter search experiment using Skipper-CCDs with a total active mass of 10 kg. As part of the detector development, the collaboration plans to build the Oscura Integration Test (OIT), an engineering test experiment with 10% of the Oscura's total mass. Here we discuss the early science opportunities with the OIT to search for millicharged particles (mCPs) using the NuMI beam at Fermilab. mCPs would be produced at low energies through photon-mediated processes from decays of scalar, pseudoscalar, and vector mesons, or direct Drell-Yan productions. Estimates show that the OIT would be a world-leading probe for low-mass mCPs.Comment: 21 pages, 13 figure

Measurement of the D0 meson production in Pb-Pb collisions with the ALICE experiment at the LHC

The D0 is the lightest particle with a charm quark and is particularly well suited for the study of charm production and interaction with the Quark-Gluon Plasma (QGP). This phase of matter sees quarks in the asymptotic freedom regime and can form only when very high temperatures are reached. The ultra-relativistic lead-lead collisions studied at the LHC are one of such scenarios, allowing to investigate in-medium energy loss mechanisms for heavy quarks. The data collected by ALICE experiment during the latest 2018 run will allow the most precise measurement to date of such effects. In this thesis work, the D0 production in 2018 Pb-Pb collisions at Sqrt(sNN) = 5.02 TeV is assessed via the reconstruction of its decay into a charged pion and kaon. The aim is setting important boundaries for the understanding of the interaction of charm quarks with the high-temperature QCD medium, especially at transverse momenta in the 1-to-3 GeV/c range, where its relative yield is to be interpreted as stemming from the entanglement of several phenomena. The reconstruction is accomplished by studying the decay topology, in order to best exploit the excellent spatial resolution and particle-identification capabilities of the ALICE detector. In particular, a selection process discarding the so-called combinatorial background, distinctively abundant in the high-multiplicity environment of Pb-Pb collisions, is carried out. Each pair of tracks candidate to be considered as stemming from a D0 decay must fulfil a set of conditions, which are optimised through the maximisation of the statistical significance of the signal. In order to circumvent gross misestimations due to possible background fluctuations, the signal samples are produced through HIJING and PYTHIA Monte Carlo simulations. Subsequently, a study of the cut efficiency and of the systematic uncertainties associated to procedures such as yields evaluation and significance maximisation (usage of Monte Carlo simulations for the signal, choice of fit function for the background etc.) is performed. The overall goal is the extraction of the nuclear modification factor, denoted by RAA. This observable is the ratio of the transverse-momentum D0 production spectra obtained in the Pb-Pb and in the p-p colliding systems, where the latter is rescaled in the hypothesis that the heavy-ion collision be a superposition of independent nucleon-nucleon collisions. Whenever this hypothesis is correct, then RAA = 1 within uncertainties – this has been observed to be the case, for instance, in p-Pb collisions, where an extended volume of QGP matter is not expected to form. However, if so-called final-state interactions between the charm and the QGP take place, then a suppression of the nuclear modification factor for a specific transverse momentum interval is expected. The described tasks are carried out with state-of-the-art computational tools such as dedicated data analysis framework AliRoot and C++ programming language. Furthermore, Machine Learning techniques are to be employed. These are gaining increasing importance in science as they provide effective methods to deal with problems characterised by several degrees of freedom

Results on low-mass weakly interacting massive particles from a 11 kg d target exposure of DAMIC at SNOLAB

International audienceExperimental efforts of the last decades have been unsuccessful in detecting WIMPs (Weakly Interacting Massive Particles) in the 10-to-10$^4$ GeV/$c^2$ range, thus motivating the search for lighter dark matter. The DAMIC (DArk Matter In CCDs) at SNOLAB experiment aims for direct detection of light dark matter particles ($m_\chi<10$ GeV/$c^2$) by means of CCDs (Charge-Coupled Devices). Fully-depleted 675 $\mu$m-thick CCDs are used to such end. The optimized readout noise and operation at cryogenic temperatures allow for a detection threshold of 50 eV$_{ee}$ electron-equivalent energy. Focusing on nuclear and electronic scattering as potential detection processes, DAMIC has so far set competitive constraints on the detection of low mass WIMPs and hidden-sector particles.In this work, an 11 kg$\cdot$d exposure dataset is exploited to search for light WIMPs by building the first comprehensive radioactive background model for CCDs. Different background sources are discriminated making conjoint use of the spatial distribution and energy of ionization events, thereby constraining the amount of contaminants such as tritium from silicon cosmogenic activation and surface lead-210 from radon plate-out.Despite a conspicuous, statistically-significant excess of events below 200 $\text{eV}_{ee}$, this analysis places the strongest exclusion limit on the WIMP-nucleon scattering cross section with a silicon target for $m_\chi$ < 9 GeV/$c^2$

Recherche de matière noire légère et exploration du secteur caché avec les dispositifs à transfert de charges de DAMIC à SNOLAB et DAMIC-M

L'existence dans l’Univers de matière non baryonique électromagnétiquement inerte est étayée par une pléthore d'observations astrophysiques et cosmologiques. Ainsi, la matière noire devrait représenter plus de 80 % de la masse de l'Univers. Un vaste bestiaire de particules candidates a été théorisé, le paradigme des particules massives à interaction faible (WIMP) dominant le paysage. Les efforts expérimentaux des dernières décennies n'ont pas réussi à détecter les WIMP pour des masses entre 10 et 10^4 GeV/c2, motivant ainsi la recherche de matière noire plus légère. Les expériences DAMIC (DArk Matter In CCDs) visent à la détection directe de WIMP légers et de candidats du secteur caché au moyen de dispositifs à transfert de charges (CCD) en silicium épais. Le détecteur DAMIC de SNOLAB ~40 g se trouve sous un mort-terrain rocheux de 2070 m dans la mine de Vale Creighton au Canada. Ses CCD se caractérisent par un bruit de lecture de l’ordre d’un électron, un courant de fuite minimal (~1E-4 e-/pixel/jour) et une excellente résolution spatiale (~15 µm). Le détecteur DAMIC-M, avec une masse de l’ordre de 1 kg, sera hébergé au Laboratoire Souterrain de Modane (LSM), à 1700 m sous le pic du Fréjus, en France. Ses capteurs CCD comportent des amplificateurs skipper, qui permettent une résolution d’une fraction d’électron en réalisant mesures non destructives des charges. L'objectif de minimisation du bruit de fond de DAMIC-M est de 0,1 dru (0,1 événement par keV-kg-jour), une amélioration de deux ordres de grandeur par rapport à l'installation de SNOLAB. Ce travail de thèse s'articule autour de deux grands thèmes : la construction du premier modèle de bruit de fond CCD complet dans le cadre de DAMIC à SNOLAB, et les efforts de recherche et développement vers les objectifs scientifiques de DAMIC-M, notamment avec le déploiement de son détecteur prototype, la Low Background Chamber (LBC). Le modèle de bruit de fond de DAMIC à SNOLAB est construit à partir de simulations GEANT4 des contaminations radioactives dans une géométrie virtuelle du détecteur. Les activités sont contraintes à partir des mesure de dosages effectuées sur les différents composants du détecteur. Par ailleurs, une technique d'analyse de coïncidence spatiale unique aux CCD est exploitée pour quantifier les isotopes primordiaux et cosmogéniques distribués sur la surface et dans la masse du CCD. Certaines des mesures effectuées de cette manière surpassent largement les méthodes de dosage les plus courantes. Le modèle de fond est utilisé pour rechercher des WIMP légers à partir d’un ensemble de données correspondant à une exposition de 11 kg-jour. Malgré un excès statistiquement significatif d'événements d’énergie inférieure à 200 eV, cette analyse place la limite d'exclusion la plus forte sur la section efficace de diffusion WIMP-nucléon indépendante du spin avec un détecteur cible en silicium pour masses < 9 GeV/c2. DAMIC-M est sur le point de franchir des étapes technologiques importantes vers ses objectifs scientifiques. Le déploiement de CCD skipper avec une électronique développée au LPNHE abaissera les seuils de détection à moins d’une dizaine d’eV, permettant simultanément une caractérisation plus précise du détecteur. Des cryostats de tests sont mis en place pour effectuer des évaluations systématiques des CCD et concevoir un processus de sélection pour DAMIC-M. Au LPNHE, un cryostat a également été utilisé pour la mise en service de l'instrumentation de l'expérience prototype LBC au LSM. La LBC à été mise en service fin 2021. Le bruit électronique (~10 e-) et le courant de fuite (~1E-3 e-/pixel/jour) élevés mesurés par rapport aux détecteurs de SNOLAB, mettent en évidence deux revers potentiels pour DAMIC -M. Malgré tout le premier ensemble de données scientifiques acquis avec les CCD skipper de la LBC (~ 20 g) permettent de définir des limites d'exclusion de classe mondiale sur la section efficace de diffusion de la matière noire sur les électrons.The existence of electromagnetically inert non-baryonic matter in the universe is supported by a plethora of astrophysical and cosmological observations. Dark matter is expected to account for more than 80% of the mass of the universe. A vast bestiary of particle candidates have been theorized, with the Weakly Interacting Massive Particle (WIMP) paradigm dominating the landscape thanks to its desirable features. Experimental efforts of the last decades have been unsuccessful in detecting WIMPs with weak-scale masses (10-10^4 GeV/c2), thus motivating the search for lighter dark matter. The DAMIC (DArk Matter In CCDs) experiments aim for direct detection of light WIMPs and hidden sector candidates by means of thick silicon Charge-Coupled Devices (CCDs). DAMIC at SNOLAB ~40 g detector sits beneath a 2070 m rock overburden in the Vale Creighton Mine in Canada. Its CCDs are characterized by electron-order readout noise, minimal leakage current (~1E-4 e-/pixel/day) and exquisite spatial resolution (~15 µm). The DAMIC-M kg-scale detector will be hosted in the cleanroom facilities of the Laboratoire Souterrain de Modane (LSM), 1700 m below the Fréjus peak, in France. Its CCDs additionally feature skipper readout amplifiers, which enable sub-electron resolution by means of repeated non-destructive charge measurements. DAMIC-M background goal is 0.1 dru (0.1 events per keV-kg-day), which represents a two orders of magnitude leap relative to SNOLAB apparatus. This thesis work delves into two major themes: the construction of the first comprehensive CCD background model in the context of DAMIC at SNOLAB, and the research and development efforts towards DAMIC-M science goals, particularly with the deployment of its prototype detector, the Low Background Chamber (LBC). The DAMIC at SNOLAB background model is constructed by performing GEANT4 simulations of radioactive contaminants in a virtual detector geometry. Activities are constrained by means of different assay methods. Notably, the spatial coincidence analysis technique unique to Charge-Coupled Devices is leveraged to quantify notorious primordial and cosmogenic isotopes distributed over CCD surface and bulk. Some of the measurements conducted in this fashion vastly outperform more common assay methods. The background model is used to search for light WIMPs in a 11 kg-day exposure dataset. Despite a conspicuous, statistically-significant excess of events below 200 eV, this analysis places the strongest exclusion limit on the WIMP-nucleon spin-independent scattering cross section with a silicon target detector for masses < 9 GeV/c2. DAMIC-M is set to achieve important technological milestones on the way to its science goals. The deployment of skipper CCDs with custom electronics will lower detection thresholds down to ~10 eV, simultaneously enabling higher-precision detector characterization. Cryogenic test chambers are set up across institutions to conduct systematic CCD testing and design a selection process in view of DAMIC-M CCD production. A protocol is defined to establish detector grade and characterize detector performance. The test chamber constructed at LPNHE is additionally used to commission instrumentation for the LBC prototype experiment at LSM. The Low Background Chamber is commissioned for operations in late 2021. High electronic noise (~10 e-) and leakage current (~1E-3 e-/pixel/day) are measured with respect to SNOLAB detectors, highlighting two potential setbacks for DAMIC-M. Despite this, the first science dataset acquired with both LBC skipper CCDs (~20 g) is used to set world-class exclusion limits on the dark matter-electron scattering cross section

Platelet-Rich Plasma Combined with Hyaluronic Acid versus Leucocyte and Platelet-Rich Plasma in the Conservative Treatment of Knee Osteoarthritis. A Retrospective Study

Background and objectives: Knee osteoarthritis (KO) is one of the most common joint diseases, determining knee pain and reduction of mobility, with a negative effect on quality of life. Intra-articular injections of different formulations of platelet-rich plasma (PRP) are an increasingly common non-surgical treatment for KO. Recently, in order to combine the anti-inflammatory effect of platelet rich plasma and the viscosupplementation effect of hyaluronic acid, a formulation of PRP combined with hyaluronic acid (PRP + HA) has been proposed. The purpose of this study is to retrospectively compare the effectiveness of plasma with high concentration of platelets and leukocytes (L-PRP) with PRP + HA in patients with mild to moderate (Kellgren–Lawrence scale II-III grade) KO. Materials and Methods: Among the 51 patients included, 28 have been treated with L-PRP, while 23 with PRP + HA. A retrospective evaluation at baseline (T0), after 3 months (T1) and 1 year (T2) has been performed. The outcome analyzed are the Knee Society Score (KSS), the Visuo Analogic Scale (VAS) (at T0, T1, and T2) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) (T0 and T2). We evaluated change in mean scores within and between groups among different time points using repeated measures ANCOVA. Results: Although the two treatments have been both effective in reducing VAS, the group treated with PRP + HA showed a significantly lower KSS. Conclusions: Our results show that the use of both treatments may help to reduce pain in patients with mild to moderate KO. PRP + HA showed better results in improving knee mobility and function. These results should be considered only preliminary: Further research is needed to completely describe the clinical effectiveness of these formulations

Platelet-Rich Plasma Combined with Hyaluronic Acid versus Leucocyte and Platelet-Rich Plasma in the Conservative Treatment of Knee Osteoarthritis. A Retrospective Study

Background and objectives: Knee osteoarthritis (KO) is one of the most common joint diseases, determining knee pain and reduction of mobility, with a negative effect on quality of life. Intra-articular injections of different formulations of platelet-rich plasma (PRP) are an increasingly common non-surgical treatment for KO. Recently, in order to combine the anti-inflammatory effect of platelet rich plasma and the viscosupplementation effect of hyaluronic acid, a formulation of PRP combined with hyaluronic acid (PRP + HA) has been proposed. The purpose of this study is to retrospectively compare the effectiveness of plasma with high concentration of platelets and leukocytes (L-PRP) with PRP + HA in patients with mild to moderate (Kellgren–Lawrence scale II-III grade) KO. Materials and Methods: Among the 51 patients included, 28 have been treated with L-PRP, while 23 with PRP + HA. A retrospective evaluation at baseline (T0), after 3 months (T1) and 1 year (T2) has been performed. The outcome analyzed are the Knee Society Score (KSS), the Visuo Analogic Scale (VAS) (at T0, T1, and T2) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) (T0 and T2). We evaluated change in mean scores within and between groups among different time points using repeated measures ANCOVA. Results: Although the two treatments have been both effective in reducing VAS, the group treated with PRP + HA showed a significantly lower KSS. Conclusions: Our results show that the use of both treatments may help to reduce pain in patients with mild to moderate KO. PRP + HA showed better results in improving knee mobility and function. These results should be considered only preliminary: Further research is needed to completely describe the clinical effectiveness of these formulations