Operational Experience of the ATLAS High Level Trigger with Single-Beam and Cosmic Rays

ATLAS is one of two general-purpose detectors at the LHC. Using fast reconstruction algorithms, the trigger system needs to efficiently reject a large rate of background events while keeping potentially interesting ones with high efficiency. After a first level trigger implemented in custom electronics, the trigger selection is made by software running on two processor farms (the High Level Trigger system), containing a total of around two thousand multi-core machines. To reduce the network data traffic and the processing time to manageable levels, the HLT uses seeded, step-wise event reconstruction, aiming at the earliest possible rejection of background events. The LHC start up and single-beam run periods in 2008 provided a "stress test" of the trigger system. Following this period, ATLAS continued to collect cosmic-ray events for detector alignment and calibration as well as for commissioning the trigger. These running periods allowed us to exercise the trigger system online, including its configuration and monitoring infrastructure, as well as reconstruction and selection algorithms. Several tracking, muon-finding, and calorimetry algorithms were commissioned under different running conditions. Frequent changes of the trigger configuration were required to cope with the parallel commissioning of the ATLAS sub-detectors. The experience gained while running the trigger system online was very valuable to design and implement a n optimal strategy for the collision data taking period of 2009. This paper focuses on the operational experience gained in running the trigger in the fast-changing environment of the detector commissioning with cosmic rays and single beam runs

El manejo del suelo salino usando arena afecta el crecimiento de raíces y la sobrevivencia de plántulas de Prosopis tamarugo Phil. (Fabaceae)

Natural regeneration of endemic tree Prosopis tamarugo in the Pampa del Tamarugal is almost absent. Soil salinity is probably an important barrier for tamarugo seedling establishment. Despite there are numerous techniques to manage soil salinity, substrates prepared using mix of saline soil and sand are poorly known. In the present study, the effect of different experimental substrates was evaluated on root growth and seedling survival of P. tamarugo. The experimental soils were prepared using natural soil and sand in equal proportion (1:1) and using a double proportion of sand (1:2). Saline soil used as control treatment. Bulk density (B.D.), electrical conductivity (E.C.) and sodium and chloride concentration was characterized for the three experimental soils. Seedling root growth was evaluated through length and root biomass, root/shoot ratio (R/S) and specific root length (SRL). Root biomass was also monitored during the study. Aerial growth was determined using leaf formation. Additionally, salt content in tissues and survival of seedlings were evaluated at the day 50 of initiated of experiment. The natural soil presented a E.C. (176 dS/m) and B.D. (0.9 g/cc) higher tan experimental soils 1:1 (132 dS/m and 1.1 g/cc) and 1:2 (140 dS/m and 1.4 g/cc). Sodium and chloride concentration decreased on average by 37 and 41% in 1:1 and 1:2 soils with sand amendment respectively in comparison with the natural saline soil. Seedlings grown in the two amendment soils showed significant growth in root length, root biomass, R/S and SRL and significantly increased their root biomass by day 30. They also exhibited a lower sodium and chloride concentration in their tissues, more number of pairs of leaves and a higher final survival compared with seedling growing on experimental natural saline soil. These results support the idea that amendment of saline soil with sand as a management technique promotes root growth and increases seedling survival of P. tamarugo.La regeneración natural del árbol endémico Prosopis tamarugo es casi inexistente en la Pampa del Tamarugal, probablemente la salinidad del suelo es una barrera para el establecimiento de plántulas. Aunque existen numerosas técnicas para manejar la salinidad del suelo, la creación de un sustrato en la que suelo salino es mezclado con arena es escasamente conocido. En el presente estudio se profundizó en el efecto de tres sustratos experimentales (suelo salino natural, suelo 1:1 y suelo 1:2) en el crecimiento de raíces y supervivencia de plántulas de P. tamarugo durante un período de 50 días. El suelo 1:1 fue creado mezclando suelo natural y arena en igual proporción y el suelo 1:2, aumentado la proporción de arena al doble. Para los tres suelos se caracterizó la densidad aparente (D.A.), conductividad eléctrica (C.E.) y la concentración de sodio y cloruro. El crecimiento radicular de las plántulas fue caracterizado midiendo al final del estudio la longitud y biomasa de raíces, cociente raíz/tallo (R/T) y longitud radicular específica (LRE), además se monitoreó la biomasa radicular durante el estudio. El crecimiento aéreo se midió a través de la formación de hojas. Finalmente fue determinado el contenido de sales en los tejidos y la sobrevivencia de plántulas en cada suelo experimental. El suelo natural presentó una C.E. (176 dS/m) y D.A. (0,9 g/cc) más alta comparada con el suelo 1:1 (132 dS/m y 1,1 g/cc) y suelo 1:2 (140 dS/m y 1,4 g/cc). La concentración de sodio y cloruro disminuyó en promedio un 37 y 41% en los suelos 1:1 y 1:2, respectivamente comparado con el suelo salino natural. Las plántulas que crecieron en estos dos suelos presentaron un crecimiento significativo en longitud y biomasa radicular, R/T y LRE e incrementaron notablemente su biomasa radicular a partir del día 30. También exhibieron un menor contenido de sodio y cloruro en sus tejidos, mayor número de pares de hojas y una alta sobrevivencia final. Estos resultados apoyan la idea que incorporando arena en suelo salino como técnica de manejo de la salinidad del suelo favorece el crecimiento de las raíces y aumenta la supervivencia de plántulas de P. tamarugo

Implementation and Performance of the ATLAS Second Level Jet Trigger

ATLAS is one of the four major LHC experiments, designed to cover a wide range of physics topics. In order to cope with a rate of 40 MHz and 25 interactions per bunch crossing, the ATLAS trigger system is divided in three different levels. The first one (LVL1, hardware based) identifies signatures in 2 microseconds that are confirmed by the the following trigger levels (software based). The Second Level Trigger (LVL2) only looks at a region of the space around the LVL1 signature (called Region of Interest or ROI), confirming/rejecting the event in about 10 ms, while the Event Filter (Third Level Trigger, EF) has potential full event access and larger processing times, of the order of 1 s. The jet selection starts at the LVL1 with dedicated processors that search for high ET hadronic energy depositions. At the LVL2, the jet signatures are verified with the execution of a dedicated, fast jet reconstruction algorithm. Given the fact that the main jet's background are jets,the energy calibration at the LVL2 is one of the major dificulties of this trigger, allowing to distinguish low/high energy jets. The algorithm for the calibration has been chosen to be fast and robust, with a good performance. The other major dificulty is the execution time of the algorithm,dominated by the data unpacking time due to the large sizes of the jet ROI. In order to reduce the execution time, three possible granularities have been proposed and are being evaluated: cell based (standard), energy sums calculated at each Fron-End Board (FEB) and the use of the LVL1 Trigger Towers. The FEB and Trigger Tower granularities are also being used/evaluated for the reconstruction of the missing ET triggers at the Event Filter, given the short times available to process the full event. In this presentation, the design and implementation of the jet trigger of ATLAS will be discussed in detail, emphasasing the major dificulties of each selection step. The performance of the jet algorithm, including timing, eficiencies and rates will also be shown, with detailed comparisons of the different unpacking modes

Attraction Basins as Gauges of Robustness against Boundary Conditions in Biological Complex Systems

One fundamental concept in the context of biological systems on which researches have flourished in the past decade is that of the apparent robustness of these systems, i.e., their ability to resist to perturbations or constraints induced by external or boundary elements such as electromagnetic fields acting on neural networks, micro-RNAs acting on genetic networks and even hormone flows acting both on neural and genetic networks. Recent studies have shown the importance of addressing the question of the environmental robustness of biological networks such as neural and genetic networks. In some cases, external regulatory elements can be given a relevant formal representation by assimilating them to or modeling them by boundary conditions. This article presents a generic mathematical approach to understand the influence of boundary elements on the dynamics of regulation networks, considering their attraction basins as gauges of their robustness. The application of this method on a real genetic regulation network will point out a mathematical explanation of a biological phenomenon which has only been observed experimentally until now, namely the necessity of the presence of gibberellin for the flower of the plant Arabidopsis thaliana to develop normally

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson

Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS

The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured

Measurement of the flavour composition of dijet events in pp collisions at root s=7 TeV with the ATLAS detector

This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at √s=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y|<2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions