Search

International audience; The NEMO-3 experiment performed precise measurement of the double beta decay and searched for the neutrino-less double beta decay on seven isotopes, among which 100 Mo and 82 Se were the dominant ones. The detector, installed in the Laboratoire Souterrain de Modane, took data for 8 years before being decommissioned in 2011. The key feature of NEMO-3 was its unique capabil- ity to fully reconstruct the kinematics of the events, which allowed to reduce the backgrounds and to discriminate among different mechanisms beyond the neutrino-less double beta decay. No evi- dence of 0ν β β has been found with an exposure of 34.3 kg×y of 100 Mo, providing a limit for the light Majorana neutrino mass mechanism of T 0ν β β > 1.1 × 1024 y (90 % C.L.) which corresponds to an effective neutrino mass of |mβ β | < 0.33 − 0.62 eV, depending from the NME considered. Furthermore, no background events in the double electron channel has been found in the energy region 3.2 − 10 MeV after an exposure of 47 kg×y. The same experimental technique is adopted for the next generation experiment called SuperNEMO. The new detector has a modular design with the capability to measure different isotopes at the same time. 48 Ca, 82 Se and 150 Nd are currently under consideration. With 20 detection modules observing for 5 years 100 kg of 82 Se, the expected sensitivity should reach T 0ν > 1026 y (|mβ β | < 0.04 − 0.10 eV), competitive with other experiments. In order to demonstrate the feasibility of the full experiment, the first step is the imminent construction of a first demonstrator module containing 7 kg of 82 Se. With an expected sensitivity of T 0ν > 6.6 × 1024 y (|mβ β | < 0.2 − 0.4 eV) after 2.5 y, the demonstrator module will also be able to perform a competitive measurement.

A search was made at the CERN SPS for long-lived fractionally charged particles produced in deep inelastic muon interactions on a Be target using the existing muon beam line as a spectrometer. No such particles were found, leading to upper limits for the production cross section of the order of 10 −36 cm 2 for 200 GeV incident muon momentum and quark masses below 9 GeV for the 2 3 charge and 15 GeV for 1 3 charge.

International audience; The OPERA experiment, located in the Gran Sasso underground laboratory, has recently assessed the discovery of nu-tau neutrinos in the CNGS 730km long baseline muon neutrino beam with a significance larger than 5 sigma, thus successfully achieving its main goal.The data taking took place from 2008 to 2012, the detector is now undergoing decommissioning and the ongoing activity is aimed at the completion of the data analysis.In the first part of this talk the updated OPERA results will be presented including the search for nu-mu to nu-e oscillations.In this context, the second part of the talk will present a review of the actual disappearance and appearance oscillation measurements obtained up to now from the various long baseline neutrino-oscillation experiments.

International audience; Precision measurements of the Drell-Yan production of W and Z/gamma* bosons at the LHC provide a benchmark of our understanding of perturbative QCD and probe the proton structure in a unique way. The ATLAS collaboration has performed high precision measurements at center-of-mass energies of 7TeV and 8TeV, integrated and as a function of the rapidity and the Z/gamma* mass. New measurements at 7 TeV reach unprecedented accuracy in the resonance regions, while the 8 TeV measurements explore the high mass Z/gamma* domain. The measurements are compared to state-of-the-art calculations at NNLO in QCD, combined with various contemporary parton distribution functions and including higher-order electroweak effects. Strong constraints on the parton distribution functions are found.

Exotica review (ATLAS, CMS, LHCb) proceedings for the LHCSki 2016 Conference.

Searches for new resonances decaying into two photons in the ATLAS experiment at the LHC are described. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 3.2 fb$^{-1}$ at $\sqrt{s}$ = 13 TeV recorded in 2015. Two different searches are performed, one targeted for a spin-2 particle, using Randall-Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle. The most significant deviation from the background predictions is observed at a diphoton invariant mass around 750 GeV with local significances of 3.6 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 1.8 and 2.0 standard deviations. The consistency between the data collected at 13 TeV and 8 TeV is also evaluated. Limits on the production cross-section for the two benchmark resonances are reported.

International audience; Fast evacuation of avalanche ions in Micromegas makes these detectors capable of withstanding very high rates with no loss of gain. But this intrinsic high-rate capability is often compromised by sporadic sparking which introduces dead time and is potentially harmful for the readout. Resistive electrode designs, by limiting spark current and keeping voltage drop locally, provide an effective remedy. They are thus quite popular, but there is actually more to them than simply spark attenuation. We propose that the spark probability is also drastically reduced because of charge-up of the resistive electrode surface. The underlying mechanism is a progressive reduction of field (in the region where spark-initiating avalanches develop) by the charges successively incoming onto the surface. We predict that the time constant with which the surface potential is relaxed is crucial to the success of this quenching mechanism. Small prototypes with a time constant varying over 5 orders of magnitude were built to verify this model. During tests in a high intensity hadron beam, spark quenching was observed for time constants larger than roughly 1-10 ns, corresponding to the avalanche timescale in Micromegas. These findings shed light on the basic mechanism of spark quenching in resistive detectors. Of general interest to the gaseous detector community, they also open the way to an optimisation of the resistivity value for best rate capability and full spark suppression.

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The addition of a 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiment's sensitivity to lower energies, providing new opportunities for studies of Active Galactic Nuclei (AGNs) with soft intrinsic spectra and at high redshifts. The high-frequency peaked BL Lac objects PKS 2155-304 (z = 0.116) and PG 1553+113 (0.43 < z < 0.58) are among the brightest objects in the gamma-ray sky, both showing clear signatures of gamma-ray absorption at E > 100 GeV interpreted as being due to interactions with the extragalactic background light (EBL). Multiple observational campaigns of PKS 2155-304 and PG 1553+113 were conducted during 2013 using the full H.E.S.S. II array (CT1-5). To achieve the lowest energy threshold, a monoscopic analysis of the data taken with CT5 was developed along with an investigation into the systematic uncertainties on the spectral parameters which are derived from this analysis. The energy spectra were reconstructed down to energies of 80 GeV for PKS 2155-304, which transits near zenith, and 110 GeV for the more northern PG 1553+113. The measured spectra, well fitted in both cases by a log-parabola spectral model (with a 5 sigma statistical preference for non-zero curvature for PKS 2155-304 and 4.5 sigma for PG 1553+113), were found consistent with spectra derived from contemporaneous Fermi-LAT data, indicating a sharp break in the observed spectra of both sources at E ~ 100 GeV. When corrected for EBL absorption, the intrinsic spectrum of PKS 2155-304 was found to show significant curvature. For PG 1553+113, however, no significant detection of curvature in the intrinsic spectrum could be found within statistical and systematic uncertainties., 6 pages, 2 figures, to be appear in Proceedings of the 6th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2016), Heidelberg, Germany, July 11-15, 2016

International audience; The knowledge of (anti-)neutrino fluxes is one of the largest limitation in accelerator-based precision neutrino experiments. The main limitation arise from the poorly known production cross section of neutrino parents in hadron-nucleus interactions. Strategies used by neutrino experiment to constrain their fluxes using external hadroproduction data will be described and illustrated with an example of a tight collaboration between T2K and NA61/SHINE experiments. This enabled a reduction of the T2K neutrino flux uncertainty from ∼25% (without external constraints) down to ∼10%.On-going developments to further constrain the T2K (anti-)neutrino flux will be discussed and recent results from NA61/SHINE will be reviewed.As the next-generation long baseline experiments aim for a neutrino flux uncertainty at a level of a few percent, the future data-taking plans of NA61/SHINE will be discussed.

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International audience; Our knowledge of the quark-mixing matrix and of CP violation has been tremendously improved thanks to the B factories and Tevatron: the KM mechanism is the dominant source of CP violation at the electroweak scale. LHCb is one of the six experiments being constructed on the Large Hadron Collider accelerator at CERN. It is a next generation of flavor-physics experiments which will perform precision tests of CP violation and study rare phenomena to unveil physics beyond the Standard Model, if any, in the interactions of charm- and beauty-hadron decays. The current build status of the detector is given followed by selected topics of the expected physics reach.

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The seek of high precision analyses in $\gamma$-ray astronomy leads to the implementation of multivariate combination, benefiting from several reconstruction methods. Such analysis, called $X_{eff}$, was developed for the H.E.S.S. data using three shower reconstruction methods. This paper presents the improvement granted to this analysis by refining the distribution calculation of discriminant variables, considering observation conditions, and adding new variables in the $X_{eff}$ combination. The efficiency of the analysis is presented using simulations and real data. A comparison with the standard analysis (model++), for a typical set of sources, shows a significant gain in sensitivity., Comment: Contribution to the Proceedings of the 34th International Cosmic Ray Conference (ICRC 2015), The Hague, The Netherlands

International audience

For the current generation of Imaging Atmospheric Cherenkov Telescopes (IACTs), with their large mirrors and their cameras with fine segmentation of photodetectors, the focusing capability is a relevant issue. The optical system of an IACT has a limited depth of field. Therefore, focusing the telescopes close to the shower maximum in the atmosphere has a significant impact on the data acquisition and analysis. As the distance of the shower maximum to the telescope depends (among others) on the zenith angle, an adjustable focus would be desirable. The fifth Cherenkov telescope of the H.E.S.S. II array is equipped with a focus system which allows to adjust the position of the camera along the optical axis, possibly during data taking. This impact has been studied on gamma-ray Monte Carlo simulations, and the results in terms of gamma-ray trigger rate, energy reconstruction and gamma-ray effective area will be shown., In Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands

International audience; Interest in light sterile neutrinos has been recently revived by the so-called Gallium and reactor neutrino anomalies. In both of them, a deficit of detected neutrinos was observed with respect to the expectations. Both anomalies could be explained by the oscillations of a sterile neutrino introducing an additional Δm2 around 1 eV2. Such oscillations should cause a tell-tale distortion of the neutrino energy spectrum, with the known L/E dependence of neutrino oscillations. The STEREO experiment has been designed to exploit such a signature at short baselines, thus confirming or refuting the Δm2≃ 1 eV2 sterile neutrino hypothesis. The STEREO detector consists of six optically separated cells filled with Gd-loaded liquid scintillator, where reactor anti-neutrinos are detected through their inverse beta decay, surrounded by an external blanket of non-loaded liquid scintillator. The experiment will be placed in early 2016 at the Institut Laue-Langevin (ILL) at Grenoble, next to one of the most compact nuclear reactors in operation, with detector commissioning and data taking starting soon afterwards. We present the experiment design, which has been finalised, its sensitivity, and the status of its preparation.

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The last focusing magnets of the future Compact Linear Collider (CLIC) are critical elements needed to reach the desired luminosity. Designed to guide the nanometer sized focused beams, they need to be as stiff as possible to avoid any unwanted ground motion vibration amplification. Following our recent study concerning CLIC's ground motion mitigation techniques such as the active seismic isolator, the next step is to build a real scale prototype of the QD0. This mock-up is needed to validate experimentally the proposed control strategy. Such a prototype isn't yet available, hence this first study with a scale model of QD0. In this paper, modal analysis is used to analyze the dynamic characteristics of the structure of the prototype. This analysis identifies mode shapes, frequency and damping parameters. The purpose of this paper is to provide model verification by comparing experimental and theoretical modal analysis. The knowledge of these modes would later allow to validate experimentally ground motion vibration damping on that scale model of QD0, and finally on the real scale mock-up of QD0 by predicting the effect of design change.

International audience; An excellent electron and photon performance is crucial for precision results from high energy proton-proton collisions with electrons and photons in the final state.Identification, energy calibration, response uniformity and linearity for electrons and photons with the ATLAS detector during the LHC run I will be presented.Events with W and Z bosons and J/psi mesons are employed to benchmark these performance parameters. The uncertainties of the measured identification efficiencies are at the few per mil level for electron transverse energy greater than 30 GeV and in the range of 1-2% for high energy photons The achieved calibration for electrons from Z decays is typically accurate to 0.05% in most of the detector acceptance, rising to 0.2% in regions with large amounts of passive material and is on average 0.3% for photons. The stability of the electron energy response as a function of the mean number of interactions per bunch crossing and as a function of time show stability at the level of 0.05%.Early Run2 results will be presented if available.

The blazar PKS~2155-304 was the target of a multiwavelength campaign from June to October 2013 which widely improves our knowledge of its spectral energy distribution. This campaign involved the NuSTAR satellite (3-79 keV), the Fermi Large Area Telescope (LAT, 100~MeV-300~GeV) and the High Energy Stereoscopic System (H.E.S.S.) array phase II (with an energy threshold of few tens of GeV). While the observations with NuSTAR extend the X-ray spectrum to higher energies than before, H.E.S.S. phase II, together with the use of the LAT PASS 8, enhance the coverage of the $\gamma$-ray regime with an unprecedented precision. In this work, preliminary results from the multi-wavelength analysis are presented., Comment: 2014 Fermi Symposium proceedings - eConf C14102.1

International audience; The most massive stars appear grouped in giant molecular clouds. Their strong wind activity generates large structures known as super bubbles and induces collective effects which could accelerate particles up to the high energy and produce gamma-rays. The best objects to observe these effects are young massive star clusters in which no supernova explosion has occurred yet. Such star associations are typically still embedded in their parent molecular cloud, which can be traced by the emission due to ionization by the stellar light (HII region). Considering this region as a spherical leaky-box surrounding a central cosmic ray source, a phenomenological model has been developed to estimate cosmic-rays and gamma-rays production for several clusters. The expected gamma-ray flux have been finally compared to the present and future gamma-ray telescopes sensitivities.

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International audience; Decays of b-hadrons to three-body final states including an open-charmed meson provide a rich laboratory to constrain the unitarity triangle and search for new physics. Recent measurements in this sector are presented in these proceedings, including measurements of the properties of thenewly observed D(s) excited states, study of f0(500) and f0(980) substructures and final-state interactions in B!Dr system.

International audience; The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). It comprises a calorimeter system composed of four subdetectors: a Scintillating Pad Detector (SPD) and a Pre-Shower detector (PS) in front of an electromagnetic calorimeter (ECAL) which is followed by a hadron calorimeter (HCAL). They are used to select transverse energy hadron, electron and photon candidates for the first trigger level and they provides the identification of electrons, photons and hadrons as well as the measurement of their energies and positions. The calorimeter has been pre-calibrated before its installation in the pit. The calibration techniques have been tested with data taken in 2010 and used regularly during run 1. For run 2, new calibration methods have been devised to follow and correct online the calorimeter detector response. The design and construction characteristics of the LHCb calorimeter will be recalled. Strategies for monitoring and calibration during data taking will be detailed in all aspects. Scintillating fibres, plastics and photomultipliers suffer from ageing due to radiation damage or high currents. Different methods which are used to calibrate the detectors and to recover the initial performances will be presented. The performances achieved will be illustrated in selected channels of interest for B physics.

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The LHC will be the world next generation accelerator to be operational in 2007 at CERN. The UHV requirements force the installation of ion pumps in the experimental areas of ATLAS. Due to the unacceptable particle background that standards ion pumps may generate, a reduction in the amount of material constitutive of the pump body is required. Hence, an stainless steel 0.8 mm thick body annular triode ion pump has been designed. A pumping speed of ~ 20 l/s at 10-9 mbar is provided by 15 pumping elements. Finite elements analysis and destructive tests have been performed in its design. Final vacuum tests results are shown.