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Exclusive Meson Photoproduction with a Leading Neutron at HERA
No full text38 pages, 13 figures, 10 tables, submitted tp EPJC - see paper for full list of authorsInternational audienceA first measurement is presented of exclusive photoproduction of mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years and at a centre-of-mass energy of GeV and correspond to an integrated luminosity of pb. The mesons with transverse momenta , are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality GeV, the total energy of the photon-proton system GeV and the polar angle of the leading neutron mrad. The cross section of the reaction is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, , is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction
Discrete Hammersley's Lines with sources and sinks
No full textInternational audienceWe introduce two stationary versions of two discrete variants of Hammersley's process in a finite box, this allows us to recover in a unified and simple way the laws of large numbers proved by T. Seppäläinen for two generalized Ulam's problems. As a by-product we obtain an elementary solution for the original Ulam problem. We also prove that for the first process defined on Z, Bernoulli product measures are the only extremal and translation-invariant stationary measures
Upper bound on neutrino mass based on T2K neutrino timing measurements
No full textsee paper for full list of authorsInternational audienceThe Tokai to Kamioka (T2K) long-baseline neutrino experiment consists of a muon neutrino beam, produced at the J-PARC accelerator, a near detector complex and a large 295km distant far detector. The present work utilizes the T2K event timing measurements at the near and far detectors to study neutrino time of flight as function of derived neutrino energy. Under the assumption of a relativistic relation between energy and time of flight, constraints on the neutrino rest mass can be derived. The sub-GeV neutrino beam in conjunction with timing precision of order tens of ns provide sensitivity to neutrino mass in the few MeV/ range. We study the distribution of relative arrival times of muon and electron neutrino candidate events at the T2K far detector as a function of neutrino energy. The 90% C.L. upper limit on the mixture of neutrino mass eigenstates represented in the data sample is found to be m
Bayesian nonparametric dependent model for partially replicated data: the influence of fuel spills on species diversity
No full textInternational audienceWe introduce a dependent Bayesian nonparametric model for the probabilistic modeling of membership of subgroups in a community based on partially replicated data. The focus here is on species-by-site data, i.e. community data where observations at different sites are classified in distinct species. Our aim is to study the impact of additional covariates, for instance environmental variables, on the data structure, and in particular on the community diversity. To that purpose, we introduce dependence a priori across the covariates, and show that it improves posterior inference. We use a dependent version of the Griffiths-Engen-McCloskey distribution defined via the stick-breaking construction. This distribution is obtained by transforming a Gaussian process whose covariance function controls the desired dependence. The resulting posterior distribution is sampled by Markov chain Monte Carlo. We illustrate the application of our model to a soil microbial dataset acquired across a hydrocarbon contamination gradient at the site of a fuel spill in Antarctica. This method allows for inference on a number of quantities of interest in ecotoxicology, such as diversity or effective concentrations, and is broadly applicable to the general problem of communities response to environmental variables
An Adaptive Multipreconditioned Conjugate Gradient Algorithm
No full textThis article introduces and analyzes a new adaptive algorithm for solving symmetric positive definite linear systems in cases where several preconditioners are available or the usual preconditioner is a sum of contributions. A new theoretical result allows to select, at each iteration, whether a classical Preconditioned CG iteration is sufficient (i.e. the error decreases by a factor of at least some chosen ratio) or whether convergence needs to be accelerated by performing an iteration of Multi Preconditioned CG [4]. We first present this in an abstract framework with the one strong assumption being that a bound for the smallest eigenvalue of the preconditioned operator is available. Then, we apply the algorithm to the Balancing Domain Decomposition method and illustrate its behaviour numerically. In particular we observe that it is optimal in terms of local solves, both for well conditioned and ill conditioned test cases, which makes it a good candidate to be a default parallel linear solver
Evidence for exclusive gamma-gamma to W+ W- production and constraints on anomalous quartic gauge couplings at sqrt(s) = 7 and 8 TeV
No full textSubmitted to JHEP, see paper for full list of authorsInternational audienceA search for exclusive or quasi-exclusive gamma-gamma to W+W- production, via pp to p(*) W+W- p(*) to p(*) mu+/- e-/+ at sqrt(s)=8 TeV, is reported using data corresponding to an integrated luminosity of 19.7 inverse femtobarns. Events are selected by requiring the presence of an electron-muon pair with large transverse momentum pt(mu+/- e-/+>) 30 GeV, and no associated charged particles detected from the same vertex. The 8 TeV results are combined with the previous 7 TeV results (obtained for 5.05 inverse femtobarns of data). In the signal region, 13 (2) events are observed over an expected background of 3.9 +/- 0.6 (0.84 +/-0.15) events for 8 (7) TeV, resulting in a combined excess of 3.4 sigma over the background-only hypothesis. The observed yields and kinematic distributions are compatible with the standard model prediction for exclusive and quasi-exclusive gamma-gamma to W+W- production. Upper limits on the anomalous quartic gauge coupling operators a[W;0,C] (dimension-6) and f[M0,1,2,3] (dimension-8), the most stringent to date, are derived from the measured dilepton transverse momentum spectrum
Monitoring the water cycle in the UT/LS with Raman lidar
No full textInternational audienceRaman water vapor Lidar start to investigated 20 years ago on existing lidars in the frame of the NDACC network located in South of France (44°N, 6°E) and in Reunion Island (21°S, 55°E) with elasting scatter to register simultaneously cristal particules. From this experiment, a nex system have been designed to monitor the water vapor in the whole troposphere up to the lower stratosphere. Measurements have been validated with CFH and Vaisala radiosondes. Measuring quantities of a few ppmv in the lower stratosphere is achiveded. Calibration methodology have been developped and tested during the campaign MALICCA (MAïdo LIdar Calibration CAmpaign). The lidar water vapor profiles are calibrated with water vapor columns obtained from a collocated GNSS receiver. New methodologies of data averaging have been developped, for a long-term monitoring and studies of water transport around the tropopause. Few cases studies are presented to illustrated lidar capabilities
Influence of Venus topography on the zonal wind and albedo at cloud top level : The role of stationary gravity waves
No full textInternational audienceBased on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67±2 km) collected with VMC (Venus Monitoring Camera) on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°s) shows a con- spicuous variation (from -101 to -83 m/s) with geo- graphic longitude of Venus, correlated with the un- derlying relief of Aphrodite Terra. We interpret this pattern [1] as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to cloud top level, break there and transfer their momentum to the zonal flow
Brainhack: a collaborative workshop for the open neuroscience community
No full textInternational audienceBrainhack events offer a novel workshop format with participant-generated content that caters to the rapidly growing open neuroscience community. Including components from hackathons and unconferences, as well as parallel educational sessions, Brainhack fosters novel collaborations around the interests of its attendees. Here we provide an overview of its structure, past events, and example projects. Additionally, we outline current innovations such as regional events and post-conference publications. Through introducing Brainhack to the wider neuroscience community, we hope to provide a unique conference format that promotes the features of collaborative, open science
Localization and broadband follow-up of the gravitational-wave transient GW150914
No full textSubmitted to ApJL, see paper for full list of authorsInternational audienceA gravitational-wave transient was identified in data recorded by the Advanced LIGO detectors on 2015 September 14. The event candidate, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the gravitational wave data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network Circulars, giving an overview of the participating facilities, the gravitational wave sky localization coverage, the timeline and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the electromagnetic data and results of the electromagnetic follow-up campaign will be disseminated in the papers of the individual teams