Demonstration of event position reconstruction based on diffusion in the NEXT-white detector.

Noble element time projection chambers are a leading technology for rare event detection in physics, such as for dark matter and neutrinoless double beta decay searches. Time projection chambers typically assign event position in the drift direction using the relative timing of prompt scintillation and delayed charge collection signals, allowing for reconstruction of an absolute position in the drift direction. In this paper, alternate methods for assigning event drift distance via quantification of electron diffusion in a pure high pressure xenon gas time projection chamber are explored. Data from the NEXT-White detector demonstrate the ability to achieve good position assignment accuracy for both high- and low-energy events. Using point-like energy deposits from 83mKr calibration electron captures (E∼45 keV), the position of origin of low-energy events is determined to 2 cm precision with bias <1mm. A convolutional neural network approach is then used to quantify diffusion for longer tracks (E≥1.5 MeV), from radiogenic electrons, yielding a precision of 3 cm on the event barycenter. The precision achieved with these methods indicates the feasibility energy calibrations of better than 1% FWHM at Qßß in pure xenon, as well as the potential for event fiducialization in large future detectors using an alternate method that does not rely on primary scintillation.

Ba+2 ion trapping using organic submonolayer for ultra-low background neutrinoless double beta detector.

If neutrinos are their own antiparticles the otherwise-forbidden nuclear reaction known as neutrinoless double beta decay can occur. The very long lifetime expected for these exceptional events makes its detection a daunting task. In order to conduct an almost background-free experiment, the NEXT collaboration is investigating novel synthetic molecular sensors that may capture the Ba dication produced in the decay of certain Xe isotopes in a high-pressure gas experiment. The use of such molecular detectors immobilized on surfaces must be explored in the ultra-dry environment of a xenon gas chamber. Here, using a combination of highly sensitive surface science techniques in ultra-high vacuum, we demonstrate the possibility of employing the so-called Fluorescent Bicolor Indicator as the molecular component of the sensor. We unravel the ion capture process for these molecular indicators immobilized on a surface and explain the origin of the emission fluorescence shift associated to the ion trapping.

Neandertal roots: Cranial and chronological evidence from Sima de los Huesos.

Seventeen Middle Pleistocene crania from the Sima de los Huesos site (Atapuerca, Spain) are analyzed, including seven new specimens. This sample makes it possible to thoroughly characterize a Middle Pleistocene hominin paleodeme and to address hypotheses about the origin and evolution of the Neandertals. Using a variety of techniques, the hominin-bearing layer could be reassigned to a period around 430,000 years ago. The sample shows a consistent morphological pattern with derived Neandertal features present in the face and anterior vault, many of which are related to the masticatory apparatus. This suggests that facial modification was the first step in the evolution of the Neandertal lineage, pointing to a mosaic pattern of evolution, with different anatomical and functional modules evolving at different rates.

From the fetal liver to spleen and gut: the highway to natural antibody.

The film of sIgA lining the intestinal epithelium plays a role in the regulation of the commensal microflora and prevention of pathogen invasion. We show that, in the absence of intentional immunization, all sIgA in the gut is produced by B-1a B cells. We also show that B-1a B cells and sIgA derive from lineage-negative precursors found in the fetal liver and located in the spleen after birth. The splenic precursors do not generate B cells of the adaptive immune system in bone marrow, spleen, and lymph nodes, but efficiently replenish the cells producing the natural antibodies. Therefore, B-1a B cells with their splenic progenitors and their progeny of plasma cells fill the same function of the primordial immune system of lower vertebrates. The natural antibodies in the serum and on the intestinal epithelium may be an evolutionary ancient tool for the immediate protection against commensal and pathogenic bacteria.

Transcription factor AP-4 is a ligand for immunoglobulin-kappa promoter E-box elements.

Immunoglobulin (Ig)-kappa promoters from humans and mice share conserved sequences. The octamer element is common to all Ig promoters and pivotal for their function. However, other conserved sequence motifs, that differ between Ig variable gene families, are required for normal promoter function. These conserved motifs do not stimulate transcription in the absence of an octamer. One example is an E-box of the E47/E12 type (5'-CAGCTG-3'), which is found in all promoters of the human and murine Ig-kappa gene subgroups/families, with the exception of subgroups II and VI and their related murine families. In the present study we show that the ubiquitously expressed transcription factor AP-4, and not E47, interacts specifically with the kappa promoter E-boxes when tested in electrophoretic mobility-shift assays using nuclear extracts derived from human and murine B-cell lines. Furthermore, AP-4, unlike E47, did not act as a transactivator, which is in agreement with previous studies on intact kappa promoters, showing that transcription is absent when the octamer element has been mutated. Based on these data, and the conservation of the 5'-CAGCTG-3' motif among human and murine kappa promoters, we propose that AP-4 is the major ligand for Ig-kappa promoter E-boxes.