Single Vectorlike Quark Production at the LHC

A gluon resonance G of mass below 1 TeV could be the origin of the t\bar{t} forward-backward asymmetry observed at the Tevatron provided that new decay modes G->\bar{q}Q, with q a standard quark and Q its massive excitation, make G broad enough. We consider all the different cases, with q the top, the bottom or a light quark and dominant decay modes Q->Wq' or Q->Zq. We show that current experimental searches are unable to probe the model, but that minimal departures from these analyses can explore a large region of its parameter space for the current LHC luminosity. This includes the challenging case with the new quarks decaying mostly into light quark flavors. In some channels not only the heavy quark but also the massive gluon can be reconstructed, which would stablish the origin of the t\bar{t} asymmetry. Similar analyses can be applied to more general models with new massive gluons and vectorlike quarks.Comment: 17 pages, 8 figures. Version 2: references adde

Shaping the top asymmetry

We study different profiles of the distribution of the top forward-backward asymmetry, depending on the invariant mass of the t tbar pair. We show that they can be reproduced by one or more light colour octets, while keeping moderate departures of the t tbar cross section and invariant mass distributions with respect to the Standard Model predictions at Tevatron and LHC.Comment: LaTeX 14 pages. Final version to appear in PLB, with an enlarged discussion about dijet constraint

Most \u3cem\u3eCaenorhabditis elegans\u3c/em\u3e MicroRNAs are Individually Not Essential for Development or Viability

MicroRNAs (miRNAs), a large class of short noncoding RNAs found in many plants and animals, often act to post-transcriptionally inhibit gene expression. We report the generation of deletion mutations in 87 miRNA genes in Caenorhabditis elegans, expanding the number of mutated miRNA genes to 95, or 83% of known C. elegans miRNAs. We find that the majority of miRNAs are not essential for the viability or development of C. elegans, and mutations in most miRNA genes do not result in grossly abnormal phenotypes. These observations are consistent with the hypothesis that there is significant functional redundancy among miRNAs or among gene pathways regulated by miRNAs. This study represents the first comprehensive genetic analysis of miRNA function in any organism and provides a unique, permanent resource for the systematic study of miRNAs

Physiological-enzymatic characteristics and inoculation of mycelial strains of Descolea antarctica Sing. in Nothofagus seedlings

At present, reforestation has focused on native forests with anthropogenic intervention and eroded soils. There is interest in producing Nothofagus seedlings which can overcome adverse conditions encountered on reforestation sites. It is necessary to find new fungi that can be utilized as mycorrhizal inoculants and that enable the seedlings to increase their tolerance to adverse conditions. Two ectomycorrhizal strains of the fungus Descolea antarctica (D1 and D2) were cultured at different temperatures, pH levels and the activities of amylases, cellulases, and phosphatases were determined. In greenhouse and nursery trials, the growth responses of inoculated Nothofagus obliqua seedlings were evaluated. D1 and D2 exhibited the highest growth rates at 23\ubaC. Both strains grew at pH levels from 4 to 11. The highest enzymatic activities were registered for amylase (57.2 mg glucose/ml * g of mycelium * hr) and acid phosphatases (58.1 mg p-nitrophenol/ml * g of mycelium * hr) at 37\ubaC, and acid phospatases (1.720 mg p-nitrophenol/ml * g of mycelium * hr) and alkaline phosphatases (1.360 mg p-nitrophenol/ml * g of mycelium * hr) at pH 4 and pH 11, respectively. We conclude that suitable N. obliqua seedlings for use in reforestation were obtained using D2 as inoculant

HDE 245059: A Weak-Lined T Tauri Binary Revealed by Chandra and Keck

We present the Chandra High Energy Transmission Grating Spectrometer (HETGS) and Keck observations of HDE 245059, a young weak-lined T Tauri star (WTTS), member of the pre-main sequence group in the Lambda Orionis Cluster. Our high spatial resolution, near-infrared observations with Keck reveal that HDE 245059 a binary separated by 0.87". Based on this new information we have obtained an estimate of the masses of the binary components; 3M_{sun} and 2.5M_{sun} for the north and south components, respectively. We have estimated the age of the system to be ~2-3 Myr. We detect both components of the binary in the zeroth order Chandra image and in the grating spectra. Our fits to the spectrum of the binary have shown that the emission is dominated by a plasma between 8 and 15 MK, a soft component at 4 MK and a hard component at 50 MK are also detected. The value of the hydrogen column density was low, 8 x 10^{19} cm^{-2}, likely due to the clearing of the inner region of the Lambda Orionis cloud. The abundance pattern shows an inverse First Ionization Potential (FIP) effect for all elements from O to Fe, the only exception being Ca. A 3-T model was fitted to the individual zeroth order spectra using the abundances derived for the binary. We have also obtained several lines fluxes from the grating spectra. The fits to the triplets show no evidence of high densities. We conclude that the X-ray properties of the weak-lined T Tau binary HDE 245059 are similar to those generally observed in other weak-lined T Tau stars. Although its accretion history may have been affected by the clearing of the interstellar material around Lambda Ori, its coronal properties appears not to have been strongly modified.Comment: 12 pages, 10 figures Accepted for publication in Ap

Top quark forward-backward asymmetry in R-parity violating supersymmetry

The interaction of bottom squark-mediated top quark pair production, occurring in the R-parity violating minimal supersymmetric standard model (MSSM), is proposed as an explanation of the anomalously large $t\bar{t}$ forward-backward asymmetry (FBA) observed at the Tevatron. We find that this model can give a good fit to top quark data, both the inclusive and invariant mass-dependent asymmetries, while remaining consistent (at the 2-$\sigma$ level) with the total and differential production cross-sections. The scenario is challenged by strong constraints from atomic parity violation (APV), but we point out an extra diagram for the effective down quark-Z vertex, involving the same coupling constant as required for the FBA, which tends to weaken the APV constraint, and which can nullify it for reasonable values of the top squark masses and mixing angle. Large contributions to flavor-changing neutral currents can be avoided if only the third generation of sparticles is light.Comment: 24 pages, 7 figures. v3: included LHC top production cross section data; model still consistent at 2 sigma leve

ATLAS data quality operations and performance for 2015-2018 data-taking

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiereThe ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015-2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at s=13 TeV certified for physics analysi

The Large Aperture GRB Observatory

The Large Aperture GRB Observatory (LAGO) is aiming at the detection of the high energy (around 100 GeV) component of Gamma Ray Bursts, using the single particle technique in arrays of Water Cherenkov Detectors (WCD) in high mountain sites (Chacaltaya, Bolivia, 5300 m a.s.l., Pico Espejo, Venezuela, 4750 m a.s.l., Sierra Negra, Mexico, 4650 m a.s.l). WCD at high altitude offer a unique possibility of detecting low gamma fluxes in the 10 GeV - 1 TeV range. The status of the Observatory and data collected from 2007 to date will be presented.Comment: 4 pages, proceeding of 31st ICRC 200

Water Cherenkov Detectors response to a Gamma Ray Burst in the Large Aperture GRB Observatory

In order to characterise the behaviour of Water Cherenkov Detectors (WCD) under a sudden increase of 1 GeV - 1 TeV background photons from a Gamma Ray Burst (GRB), simulations were conducted and compared to data acquired by the WCD of the Large Aperture GRB Observatory (LAGO). The LAGO operates arrays of WCD at high altitude to detect GRBs using the single particle technique. The LAGO sensitivity to GRBs is derived from the reported simulations of the gamma initiated particle showers in the atmosphere and the WCD response to secondaries.Comment: 5 pages, proceeding of the 31st ICRC 200