The TileCal Energy Reconstruction for LHC Run2 and Future Perspectives

The TileCal is the main hadronic calorimeter of ATLAS and it covers the central part of the detector ($|\eta|$ < 1.6). The energy deposited by the particles in TileCal is read out by approximately 10,000 channels. The signal provided by the readout electronics for each channel is digitized at 40 MHz and its amplitude is estimated by an optimal filtering algorithm. The increase of LHC luminosity leads to signal pile-up that deforms the signal of interest and compromises the amplitude estimation performance. This work presents the proposed algorithm for energy estimation during LHC Run 2. The method is based on the same approach used during LHC Run 1, namely the Optimal Filter. The only difference is that the signal baseline (pedestal) will be subtracted from the received digitized samples, while in Run 1 this quantity was estimated on an event-by-event basis. The pedestal value is estimated through special calibration runs and it is stored in a data base for online and offline usage. Additionally, the background covariance matrix will also be used for the computation of the Optimal Filter weights for high occupancy channels. The use of such information reduces the bias and uncertainties introduced by signal pile-up. The performance of the Optimal Filter version used in Run 1 and Run 2 is compared using Monte Carlo data. The efficiency achieved by the methods is shown in terms of error estimation, when different conditions of luminosity and occupancy are considered. Concerning future work, a new method based on linear signal deconvolution has been recently proposed and it is under validation. It could be used for Run 2 offline energy reconstruction and future upgrades.Comment: 5 pages, 7 figures, LISHEP 2015, 2-9 August 2015, Manau

Calibration and Performance of the ATLAS Tile Calorimeter

The Tile Calorimeter (TileCal) is the hadronic calorimeter covering the most central region of the ATLAS experiment at the LHC. It is a key detector for the measurement of hadrons, jets, tau leptons and missing transverse energy. The TileCal calibration system comprises radioactive source, laser and charge injection elements and it allows to monitor and equalize the calorimeter response at each stage of the signal production, from scintillation light to digitization. This contribution presents a brief description of the different TileCal calibration systems as well as the latest results on their performance in terms of calibration factors, linearity and stability. The performance of the Tile Calorimeter with the cosmic muons and collision data is also presented, including the absolute energy scale, time resolution and associated stabilities.Comment: 4 pages, 7 figures, LISHEP 2013, 17-24 March 2013, Rio de Janeir

Desconvolução de sinais para estimação de energia em sistemas de calorimetria operando a alta taxa de eventos

This article aims to evaluate the performance of a method based on Signal Deconvolution for energy estimation in high-energy calorimeters. The study focuses on reconstructing signals produced by the readout channels of a calorimetry system resulting from atomic particle collisions. Data processing is performed in a continuous or sequential format (free-running), aligned with the operation of modern experiments characterized by high event rates and high luminosity. This context enables determining the optimal sample processing interval to enhance the efficiency of signal reconstruction by the readout channels. Additionally, the K-Fold cross-validation technique is employed for statistical error analysis. The study compares the efficiency of the proposed method with the linear technique currently used in modern calorimeters under different operating conditions. The findings identified the optimal intervals for the methods in amplitude estimation and highlighted the independence of the Deconvolution method from signal pile-up, making it advantageous in high-luminosity environments.Este artigo visa avaliar o desempenho de um método baseado na Desconvolução de Sinais para a estimação da energia em calorímetros de altas energias. O contexto do trabalho compreende a reconstrução dos sinais produzidos pelos canais de leitura de um sistema de calorimetria e advindos de colisões de partículas atômicas. O tratamento do conjunto de dados é realizado no formato contínuo ou sequenciado (free-running), conforme o funcionamento de experimentos modernos que operam em alta taxa de eventos e alta luminosidade. Esse cenário permite definir qual a quantidade de janelamento das amostras pode ser adotada como ideal, buscando aprimorar a eficiência da reconstrução do sinal adquirido pelos canais de leitura. Além disso, a técnica de validação cruzada K-Fold também é empregada para a análise estatística do erro de estimação. Dessa maneira, a comparação de eficiência do método proposto com a técnica linear atualmente utilizada em calorímetros modernos é apresentada considerando diferentes condições de operação. O estudo identificou os janelamentos ideais para os métodos comparados na estimação de amplitudes sob as condições analisadas, assim como revelou a independência do método de Desconvolução em relação ao empilhamento, tornando-o vantajoso em condições de alta luminosidade

Qualidade de dados baseada em probabilidades para reconstrução da energia em calorimetria de altas energias

In several engineering applications, the quality of the reconstruction of the information of interest directly interferes with the success of decision making. In modern high-energy physics experiments, the reconstruction of events is essential for the precise observation of particles and important discoveries for science. In this context, the signals from the calorimetry system provide information about the energy of the particles produced in collisions. Typically, the energy reconstruction quality is measured using the &nbsp;method. However, in experiments operating in high luminosity conditions, such an approach is not able to operate under signals pile-up conditions, being only able to detect the presence of pile-up effect in the received signal. Therefore, in this work, a new approach to evaluate the quality of energy reconstruction under pile-up conditions is presented. The proposed method relies on the calculation of probabilities regardless of the energy reconstruction algorithm employed. Using simulated data for a general calorimeter system operating under different signals pile-up conditions, the results show that the use of the proposed method increases signals selection efficiency.Em diversas aplicações de engenharia, a qualidade da reconstrução da informação de interesse interfere diretamente no sucesso da tomada de decisão. Em experimentos modernos de física de altas energias, a reconstrução dos eventos é essencial para a observação precisa de partículas e descobertas importantes para a ciência. Neste contexto, os sinais provenientes do sistema de calorimetria destes experimentos fornecem a informação sobre a energia das partículas produzidas nas colisões. Tipicamente, a qualidade da reconstrução da energia é medida utilizando-se o método do . Entretanto, em experimentos que operam em alta luminosidade, tal abordagem não é capaz de operar em condições de empilhamento de sinais, conseguindo somente detectar a presença do efeito do empilhamento no sinal recebido. Portanto, neste trabalho, uma nova abordagem para avaliar a qualidade da reconstrução da energia em condições de empilhamento de sinais é apresentada. O método proposto se apoia no cálculo de probabilidades e é independente do método de reconstrução empregado. Utilizando dados simulados para um sistema de calorimetria genérico operando em diferentes condições de empilhamento de sinais, os resultados mostram que o uso do método proposto aumenta a eficiência de seleção de sinais

Probing the W tb vertex structure in t-channel single-top-quark production and decay in pp collisions at s√=8 TeV with the ATLAS detector

To probe the W tb vertex structure, top-quark and W -boson polarisation observables are measured from t-channel single-top-quark events produced in proton-proton collisions at a centre-of-mass energy of 8 TeV. The dataset corresponds to an integrated luminosity of 20.2 fb−1, recorded with the ATLAS detector at the LHC. Selected events contain one isolated electron or muon, large missing transverse momentum and exactly two jets, with one of them identified as likely to contain a b-hadron. Stringent selection requirements are applied to discriminate t-channel single-top-quark events from background. The polarisation observables are extracted from asymmetries in angular distributions measured with respect to spin quantisation axes appropriately chosen for the top quark and the W boson. The asymmetry measurements are performed at parton level by correcting the observed angular distributions for detector effects and hadronisation after subtracting the background contributions. The measured top-quark and W -boson polarisation values are in agreement with the Standard Model predictions. Limits on the imaginary part of the anomalous coupling gR are also set from model-independent measurements.We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; SRNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, ERDF, FP7, Horizon 2020 and Marie Sklodowska-Curie Actions, European Union; Investissements d'Avenir Labex and Idex, ANR, Region Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; CERCA Programme Generalitat de Catalunya, Generalitat Valenciana, Spain; the Royal Society and Leverhulme Trust, United Kingdom.The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resoinfo:eu-repo/semantics/publishedVersio

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements