At the LHC, muons are produced in many final states and used in a variety of analysis, such as Standard Model precision measurements and searches for new physics. The B-physics programme in ATLAS includes the measurement of CP violating effects in B meson decays, the search for rare b decay signatures, as well as the study of the production cross sections. The ATLAS detector can identify muons with high purity in a transverse momentum ($p_{T}$) range from a few GeV to several TeV. In order to achieve a high trigger efficiency for low $p_{T}$ di-muon events and at the same time keep an acceptable trigger rate, dedicated trigger algorithms have been designed and implemented in the trigger menu since the 2010 data taking period. There are two categories of B-physics triggers, one topological and one non-topological. Both of these have been studied and their performance assessed using collision data at $\sqrt{s}$ = 7 TeV. The performance found with data has been verified with simulated events.
Muonic final states will provide clean signatures formany physics processes at the LHC. The two LHC experiments ATLAS and CMS will be able to identify muons with a high reconstruction efficiency above 96% and a high transverse momentum resolution better than 2% for transverse momenta below 400 GeV/c and about 10% at 1 TeV/c. The two experiments follow complentary concepts of muon detection. ATLAS has an instrumented air-toroid mangetic system serving as a stand-alone muon spectrometer. CMS relies on high bending power and momentum resolution in the inner detector, and uses an iron yoke to incr…
In 2012, the LHC is operated at sqrt(s) = 8 TeV in a mode leading up to 40 inelastic pp collisions per bunch crossing. The identification and reconstruction of muons produced in hard collisions is difficult in this challenging environment. Di-muon decays of Z bosons have been used to study the muon momentum resolution as well as the muon identification and reconstruction efficiencies of the ATLAS detector as a function of the muon transverse momentum from 15 GeV to 100 GeV and the number of inelastic collisions per event. These studies show that the muon momentum resolution, muon identificatio…
The ATLAS experiment identifies and reconstructs muons with two high precision tracking systems, the Inner Detector and the Muon Spectrometer, which provide independent measurements of the muon momentum. This paper summarizes the performance of the combined muon reconstruction in terms of reconstruction efficiency, momentum scale and resolution. Data-driven techniques are used to derive corrections to be applied to the simulation in order to reproduce the reconstruction efficiency, momentum scale and resolution observed in experimental data, and to assess systematic uncertainties on these quan…
The search for the Standard Model Higgs boson in the four lepton (electron and muon) final state with the ATLAS detector at the LHC is presented. The analysis strategy and the efficiency for selecting the signal and rejecting the background are discussed, focusing on the performance of the lepton identification that can be achieved with the first data of LHC expected in 2008.
The B physics programme of the ATLAS experiment includes measurements of production cross sections, searches for rare B-decay signatures which are sensitive to new physics at the TeV energy scale and studies of CP violation effects in B-events, such as $B_{s}^{0}\rightarrow J/ψϕ$ and $B_{d}^{0}\rightarrow J/ψK_{s}^{0}$. The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-$p_{T}$ di-muon events, whilst keeping an acceptable trigger rate. ATLAS developed two separate approaches for triggering on di-muon events from resonances such as $J/ψ$ and Ups…
Energetic primary cosmic rays entering the Earth's atmosphere generate flux of secondary particles including neutrinos. Muon neutrinos passed through the Earth and produced muons via the charged current reaction can be registered by experimental setups intended for the measurements with colliding beams. Due to large geometrical size and advanced muon detecting system such detectors as ATLAS and CMS on LHC have chance to contribute also into the neutrino physics. The estimation of possible rates of up-going muons produced by neutrinos is given.
The performance of the ATLAS muon trigger system is evaluated with proton-proton collision data collected in 2012 at the Large Hadron Collider at a centre-of-mass energy of 8 TeV. It is primarily evaluated using events containing a pair of muons from the decay of $Z$ bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum 25 < $p_T$ < 100 GeV, with a statistical uncertainty of less than 0.01% and a systematic uncertainty of 0.6%. The $p_T$ range for efficiency determination is extended by using muons from decays of $J/ψ$ mesons, $W$ bosons, and top quar…
Triggering on hadronic tau decays is essential for a wide variety of analyses of interesting physics processes at ATLAS. The ATLAS tau trigger combines information from the tracking detectors and calorimeters to identify the signature of hadronically decaying tau leptons. In Run 2 operation expected to start in 2015, the trigger strategies will become more important than ever before. In this paper, the tau trigger performance during Run 1 is summarized and also an overview of the developments of Run 2 tau trigger strategy is presented.
The measurement of the muon inclusive differential cross section dsigma/dpT in pp collisions at sqrt(s)=7 TeV with the ATLAS detector is presented. The analysis is performed in the pseudorapidity interval |eta|< 2.5 for muon of transverse momentum 4 < pT < 100 GeV and with an integrated luminosity of 1.4 pb-1. The result is compared with the next-to-leading order with next-to-leading log high pT resummation prediction for the heavy avour production and with MC@NLO prediction for W-Z bosons production. The measurement is sensitive for the first time to the next-to-leading log contribution to th…
With the high bunch-crossing and interaction rates and potentially large event sizes the experiments at the LHC challenge data acquisition and trigger systems. Within the ATLAS experiment, a multi-level trigger system based on hardware and software is employed to cope with the task of event-rate reduction. This review article gives an overview of the trigger of the ATLAS experiment highlighting the design principles and the implementation of the system and provides references to more detailed information. In addition, first trigger- performance studies and an outlook on the ATLAS event-selecti…
The status of the commissioning of the ATLAS experiment as of May 2008 is presented. The sub-detector integration in recent milestone weeks is described. Cosmic commissioning in milestone week M6 included simultaneous data-taking and combined track analysis of the muon detector and inner detector, as well as combined analysis of muon detector and muon trigger. The calorimeters have achieved near-full operation, and are integrated with the calorimeter trigger. The high-level-trigger infrastructure is being installed and algorithms tested in technical runs.
The ATLAS detector has been designed to have good muon momentum resolution up to momenta in the TeV range. The muon momentum resolution of the ATLAS spectrometer has been measured with p-p collision data recorded in 2011. The measurement combines the di-muon mass resolution in J/Ψ->μμand Z->μμdecays with measurements of the alignment accuracy of the detector based on straight muon tracks, which are acquired with special runs without magnetic field in the ATLAS detector.
This paper presents a study of the performance of the muon reconstruction in the analysis of proton-proton collisions at $\sqrt{s}$=7 TeV at the LHC, recorded by the ATLAS detector in 2010. This performance is described in terms of reconstruction and isolation efficiencies and momentum resolutions for different classes of reconstructed muons. The results are obtained from an analysis of J/$ψ$ meson and Z boson decays to dimuons, reconstructed from a data sample corresponding to an integrated luminosity of 40~$pb^{-1}$. The measured performance is compared to Monte Carlo predictions and deviati…
The early physics program at the ATLAS experiment includes measuring the basic properties of proton proton collisions, such as charged particle multiplicities, in order to constrain phenomenological models of soft interactions in the LHC energy regime. An inclusive and well understood trigger is crucial to minimize any possible bias in the event selection. The ATLAS experiment uses two complementary types of minimum bias triggers. A scintillator trigger sensitive to the forward regions of 2.1<|eta|<3.8 has been proven to efficiently select proton proton collisions, while a trigger based on cou…
A search is performed for collimated muon pairs displaced from the primary vertex produced in the decay of long-lived neutral particles in proton-proton collisions at sqrt(s) = 7 TeV centre-of-mass energy, with the ATLAS detector at the LHC. In a 1.9 fb-1 event sample collected during 2011, the observed data are consistent with the Standard Model background expectations. Limits on the product of the production cross section and the branching ratio of a Higgs boson decaying to hidden-sector neutral long-lived particles are derived as a function of the particles' mean lifetime.
We present a search for new high mass phenomena using the latest data collected by the ATLAS detector at the LHC, corresponding to 36.1 fb$^{-1}$ at $\sqrt{s}$ = 13 TeV. The search is conducted for both resonant and non-resonant new phenomena in dimuon final states. The dimuon invariant mass spectrum is the discriminating variable used in the search. No significant deviations from the Standard Model expectation are observed. Lower limits are set on the signal parameters of interest at 95% credibility level, using a Bayesian interpretation. In particular, a Sequential Standard Model Z' resonanc…
The muon spectrometer of the ATLAS experiment is one of the largest detectors ever built. At the LHC, new physics signs could appear through high momentun muons (1 TeV). Identification and precise momentum measurement of such muons are two of the main challenges of the ATLAS muon spectrometer. In order to get a good resolution for high energy muons (i.e. 10% at 1 TeV), the accuracy on the alignment of precision chambers must be of the order of 50 microns. Several procedures have been developed to reach such a precision. This document describes complementary techniques used to align the muon su…
A sophisticated trigger system, capable of real-time track reconstruction, is used in the ATLAS experiment to select interesting events in the proton-proton collisions at the Large Hadron Collider at CERN. A set of $b$-jet triggers was activated in ATLAS for the entire 2011 data-taking campaign and successfully selected events enriched in jets arising from heavy-flavour quarks. Such triggers were demonstrated to be crucial for the selection of events with no lepton signature and a large jet multiplicity. An overview of the track reconstruction and online $b$-jet selection with performance esti…
This letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range 4 < pT < 100 GeV and within pseudorapidity |eta| < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < pT < 26 GeV and within |eta| <2.0, excluding 1.37<|eta|<1.52. Integrated luminosities of 1.3 pb-1 and 1.4 pb-1 are used for the electron and muon measureme…
Proton-proton collisions at sqrt{s} = 7 TeV and heavy ion collisions at sqrt{s_NN} = 2.76 TeV were produced by the LHC and recorded using the ATLAS experiment's trigger system in 2010. The LHC is designed with a maximum bunch crossing rate of 40 MHz and the ATLAS trigger system is designed to record approximately 200 of these per second. The trigger system selects events by rapidly identifying signatures of muon, electron, photon, tau lepton, jet, and B meson candidates, as well as using global event signatures, such as missing transverse energy. An overview of the ATLAS trigger system, the ev…
A search for pair-produced vector-like quarks decaying into a $Z$ boson and a third generation quark using 2015 and 2016 $pp$ collision data at $\sqrt{s}~=~13~$TeV collected by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of $36.1~$fb$^{-1}$, is presented. No significant excess over the Standard Model expectation was found so lower exclusion limits at 95% confidence level were set on the vector-like quark masses at 1030 (1210) GeV for singlet (doublet) $T$ and 1010 (1140) GeV for singlet (doublet) $B$.
The momentum measurement capability of the ATLAS muon spectrometer relies fundamentally on the intrinsic single-hit spatial resolution of the monitored drift tube precision tracking chambers. Optimal resolution is achieved with a dedicated calibration program that addresses the specific operating conditions of the 354000 high-pressure drift tubes in the spectrometer. The calibrations consist of a set of timing offsets and drift time to drift distance transfer relations, and result in chamber resolution functions. This paper describes novel algorithms to obtain precision calibrations from data …
This article documents the muon reconstruction and identification efficiency obtained by the ATLAS experiment for 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV collected between 2015 and 2018 during Run 2 of the LHC. The increased instantaneous luminosity delivered by the LHC over this period required a reoptimisation of the criteria for the identification of prompt muons. Improved and newly developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of large samples of $Z\toμμ$ …
A new search signature for excited leptons is explored. Excited muons are sought in the channel $pp \to μμ^* \to μμ\textrm{ jet jet}$, assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb$^{-1}$ of $pp$ collision data at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV taken with the ATLAS detector at the Large Hadron Collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass $m_{μ^*}$. For $m_{μ^*}$ between 1.3 TeV and 3.0 TeV,…
The ATLAS muon spectrometer is designed to measure muon momenta with a resolution of 4% @ 100 GeV/c rising to 10% @ 1 TeV/c track momentum. The spectrometer consists of precision tracking and trigger chambers embedded in a 2T magnetic field generated by three large air-core superconducting toroids. The precision detectors provide 50 micron tracking resolution to a pseudo-rapidity of 2.7. The system also includes an optical monitoring system which measures detector positions with 40 micron precision. This paper reports on the calibration and performance of the ATLAS muon spectrometer.
The online event selection is crucial to reject most of the events containing uninteresting background collisions while preserving as much as possible the interesting physical signals. The b-jet selection is part of the trigger strategy of the ATLAS experiment and a set of dedicated triggers was contributing to the event selection for the 2011 running. The b-jets acceptance is increased and the background reduced by lowering jet transverse energy thresholds at the first trigger level and applying b-tagging techniques at the subsequent levels. Different physics channels, especially topologies c…
The performance of the three-level ATLAS muon trigger as evaluated by using LHC data is presented. Events have been selected by using only the hardware-based Level-1 trigger in order to commission and to subsequently enable the (software-based) selections of the High Level Trigger. Studies aiming at selecting prompt muons from J/ψ and at reducing non prompt muon contamination have been performed. A brief overview on how the muon triggers evolve with increasing luminosity is given.
A measurement of the cross section of top quark pair production in proton-proton collisions recorded with the ATLAS detector at the LHC at a centre-of-mass energy of 7 TeV is reported. The data sample used corresponds to an integrated luminosity of 2.05 fb^-1. Events with an isolated electron or muon and a tau lepton decaying hadronically are used. In addition, a large missing transverse momentum and two or more energetic jets are required. At least one of the jets must be identified as originating from a b quark. The measured cross section, sigma_ttbar = 186+/- 13 (stat) +/- 20 (syst) +/- 7 (…
A search is presented for pair-production of long-lived neutral particles using 33 fb$^{-1}$ of $\sqrt{s} = 13$ TeV proton-proton collision data, collected during 2016 by the ATLAS detector at the LHC. This search focuses on a topology in which one long-lived particle decays in the ATLAS inner detector and the other decays in the muon spectrometer. Special techniques are employed to reconstruct the displaced tracks and vertices in the inner detector and in the muon spectrometer. One event is observed that passes the full event selection, which is consistent with the estimated background. Limit…
The LHC copiously produces muons via different processes, and the muon sample will be large at the high-luminosity LHC (HL-LHC). In this work we propose to leverage this large muon sample and utilize the HL-LHC as a muon fixed-target experiment, with the ATLAS calorimeter as the target. We consider a novel analysis for the ATLAS detector, which takes advantage of the two independent muon momentum measurements by the inner detector and the muon system. We show that a comparison of the two measurements, before and after the calorimeters, can probe new force carriers that are coupled to muons and…
A set of three dedicated triggers designed to detect long-lived neutral particles decaying throughout the ATLAS detector to a pair of hadronic jets is described. The efficiencies of the triggers for selecting displaced decays as a function of the decay position are presented for simulated events. The effect of pile-up interactions on the trigger efficiencies and the dependence of the trigger rate on instantaneous luminosity during the 2012 data-taking period at the LHC are discussed.
In the first phase of LHC data-taking ATLAS will measure the charged-particle density at the initial center-of-mass energy of 10 TeV and then at 14 TeV. This will allow us improve our knowledge of soft QCD models and pin-down cross-sections of different classes of inelastic collisions at LHC energies. In particular, the dominant non-diffractive interaction is a key process to understanding QCD backgrounds when we reach higher luminosities. We highlight two minimum-bias triggers, sensitive to particles in complementary ranges in pseudo-rapidity, one based on signals from the Inner Detector, the…
The goals of the ongoing and planned ATLAS muon detector upgrades are to increase the acceptance for precision muon momentum measurement and triggering and to improve the rate capability of the muon chambers in the high-background regions corresponding to the increasing LHC luminosity. Smalldiameter Muon Drift Tube (sMDT) chambers have been developed for these purposes. With half the drift-tube diameter of the current ATLAS Muon Drift Tube (MDT) chambers with 30 mm drift tube diameter and otherwise unchanged operating parameters, the sMDT chambers share all the advantages of the MDTs, but have…
Large-scale computing in ATLAS is based on a grid-linked system of tiered computing centers. The ATLAS Great Lakes Tier-2 came online in September 2006 and now is commissioning with full capacity to provide significant computing power and services to the USATLAS community. Our Tier-2 Center also host the Michigan Muon Calibration Center which is responsible for daily calibrations of the ATLAS Monitored Drift Tubes for ATLAS endcap muon system. During the first LHC beam period in 2008 and following ATLAS global cosmic ray data taking period, the Calibration Center received a large data stream f…
During 2015 the ATLAS experiment recorded 3.8 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of 13 TeV. The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton--proton collision data.
A search is presented for a high mass neutral particle that decays directly to the emu final state. The data sample was recorded by the ATLAS detector in sqrt(s) = 7 TeV pp collisions at the LHC from March to June 2011 and corresponds to an integrated luminosity of 1.07 fb^-1. The data are found to be consistent with the Standard Model background. The high emu mass region is used to set 95% confidence level upper limits on the production of two possible new physics processes: tau sneutrinos in an R-parity violating supersymmetric model and Z'-like vector bosons in a lepton flavor violating mod…
A search for long-lived particles decaying into hadrons and at least one muon is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced vertex. The analyzed dataset of proton-proton collisions at $\sqrt{s} = 13$ TeV was collected with the ATLAS detector and corresponds to 136 fb$^{-1}$. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particle decays that occur in the ATLAS inner detector. Background estimates for Standard Model processes an…
A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 13$ TeV recorded in 2015-2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed…
The ATLAS detector at the LHC is used to search for excited electrons and excited muons in the channel pp -> ll* -> llgamma, assuming that excited leptons are produced via contact interactions. The analysis is based on 13 fb-1 of pp collisions at a centre-of-mass energy of 8 TeV. No evidence for excited leptons is found, and a limit is set at the 95% credibility level on the cross section times branching ratio as a function of the excited-lepton mass m_l*. For m_l* > 0.8 TeV, the respective upper limits on sigma*B(l* -> lgamma) are 0.75 fb and 0.90 fb for the e* and mu* searches. Limits on sig…
An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb^-1 of integrated luminosity collected in 2011 at sqrt(s) = 7 TeV with the ATLAS detector at the LHC. Muon pairs are selected by requiring two isolated muons of the same electric charge with pT > 20 GeV and abs(eta) < 2.5. Minimal requirements are placed on the rest of the event activity. The distribution of the invariant mass of the muon pair m(mumu) is found to agree well with the background expectation. Upper l…
In this talk I discuss the use of calorimeter timing both for detector commissioning and in searches for new physics. In particular I present real and simulated cosmic ray muons data results for the ATLAS Tile Calorimeter system. The analysis shows that several detector errors such as imperfect calibrations can be uncovered. I also demonstrate the use of ATLAS Tile Calorimeters excellent timing resolution in suppressing cosmic ray fake missing transverse energy in searches for supersymmetry.
This article documents the performance of the ATLAS muon identification and reconstruction using the first LHC dataset recorded at $\sqrt{s}$ = 13 TeV in 2015. Using a large sample of $J/ψ\toμμ$ and $Z\toμμ$ decays from 3.2 fb$^{-1}$ of $pp$ collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to $99\%$ over most of the covered phase space ($|η|<2.5$ and $5 < p_{T} < 100$ GeV). The isolation efficiency varies between $93\%$ and …
The ATLAS High Level Trigger (HLT) system provides software-based event selection after the initial LVL1 hardware trigger. It is composed of two stages, the LVL2 trigger and the Event Filter. The HLT is implemented as software tasks running on large processor farms. An essential part of the HLT is the supervision system, which is responsible for configuring, coordinating, controlling and monitoring the many hundreds of processes running in the HLT. A prototype implementation of the supervision system, using tools from the ATLAS Online Software system is presented. Results from scalability test…
A search for events with two displaced vertices from long-lived particles (LLP) pairs using data collected by the ATLAS detector at the LHC is presented. This analysis uses 139~fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of LLPs decaying to jets in the muon spectrometer displaced between 3 m and 14 m with respect to the primary interaction vertex. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined. For the Higgs boso…
Model (BSM). ATLAS and CMS concentrate on B decays that can be registered by a di-muon signature. B-hadrons decaying to J/psi(mumu) will statistically dominate B-physics analyses allowing high precision measurements, in particular a test of BSM effects in the CP violation of Bs-Jpsiphi. In the so-called rare B-decay sector, ATLAS and CMS will concentrate on a family of semi-muonic exclusive channels, b - s mumu and on the purely muonic decay Bs - mumu. After three years of LHC running at a luminosity of a few times 1033 cm-2 s-1 (corresponding to 30 fb-1), each of these two experiments can mea…
The ATLAS muon spectrometer uses drift-tube chambers for precision tracking. The performance of these chambers in the presence of magnetic field and high radiation fluxes is studied in this article using test-beam data recorded in the Gamma Irradiation Facility at CERN. The measurements are compared to detailed predictions provided by the Garfield drift-chamber simulation programme.
A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb$^{-1}$, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of $c$- or $b$-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquark…
Calibration of the discriminator threshold of the Amplifier-Shaper-Discriminator Chip for the Upgrade of the ATLAS Muon Drift-Tube Chambers for the High-Luminosity LHC
This paper presents the performance of the ATLAS muon reconstruction during the LHC run with $pp$ collisions at $\sqrt{s}=7-8$ TeV in 2011-2012, focusing mainly on data collected in 2012. Measurements of the reconstruction efficiency and of the momentum scale and resolution, based on large reference samples of $J/ψ\to μμ$, $Z\to μμ$ and $Υ\toμμ$ decays, are presented and compared to Monte Carlo simulations. Corrections to the simulation, to be used in physics analysis, are provided. Over most of the covered phase space (muon $|η|<2.7$ and $5 \lesssim p_{\mathrm{T}} \lesssim 100$ GeV) the effic…
The Monitored Drift Tubes, as a part of the ATLAS muon spectrometer, are precision drift chambers designed to provide excellent spatial resolution and high tracking efficiency independent of the track angle. Through the life of the LHC and ATLAS experiment, this detector has already demonstrated that they provide precise tracking over large areas. The aim of the ATLAS muon spectrometer upgrade is to increase the muon trigger efficiency, precise muon momentum measurement and to improve the rate capability of the muon system in the high-background regions during the High-Luminosity LHC runs. To …
The ATLAS muon spectrometer consists of several major components: Monitored Drift Tubes (MDTs) for precision measurements in the bending plane of the muons, supplemented by Cathode Strip Chambers (CSC) in the high eta region; Resistive Plate Chambers (RPCs) and Thin Gap Chambers (TGCs) for trigger and second coordinate measurement in the barrel and endcap regions, respectively; an optical alignment system to track the relative positions of all chambers; and, finally, the world's largest air-core magnetic toroid system. We will describe the status and commissioning of the muon system with cosmi…
This paper presents measurements from the ATLAS experiment of the forward-backward asymmetry in the reaction $pp\rightarrow Z/γ^{*}\rightarrow l^{+}l^{-}$, with $l$ being electrons or muons, and the extraction of the effective weak mixing angle. The results are based on the full set of data collected in 2011 in $pp$ collisions at the LHC at $\sqrt{s}$ = 7 TeV, corresponding to an integrated luminosity of 4.8 fb$^{-1}$. The measured asymmetry values are found to be in agreement with the corresponding Standard Model predictions. The combination of the muon and electron channels yields a value of…
The performance of the jet trigger for the ATLAS detector at the LHC during the 2011 data taking period is described. During 2011 the LHC provided proton-proton collisions with a centre-of-mass energy of 7 TeV and heavy ion collisions with a 2.76 TeV per nucleon-nucleon collision energy. The ATLAS trigger is a three level system designed to reduce the rate of events from the 40 MHz nominal maximum bunch crossing rate to the approximate 400 Hz which can be written to offline storage. The ATLAS jet trigger is the primary means for the online selection of events containing jets. Events are accept…
The ATLAS detector is intended to verify the standard model and to search for new physics at the Large Hadron Collider (LHC, CERN). In addition to this primary goal, it also allows detection of muons of cosmic rays. On the other hand, unusual bursts of the muon intensity, which correlate with powerful solar flares were recorded and investigated earlier at the Baksan Underground Scintillation Telescope (BUST, INR, Russia) in period from 1981 to 2006 (~2.5 solar cycles). The nature of the muon bursts and their probable relation to the solar cosmic rays is still not quite clear. ATLAS has an exce…
The Z to tau tau cross section is measured with the ATLAS experiment at the LHC in four different final states determined by the decay modes of the tau leptons: muon-hadron, electron-hadron, electron-muon, and muon-muon. The analysis is based on a data sample corresponding to an integrated luminosity of 36 pb^-1, at a proton-proton center-of-mass energy of sqrt(s) = 7 TeV. Cross sections are measured separately for each final state in fiducial regions of high detector acceptance, as well as in the full phase space, over the mass region 66 - 116 GeV. The individual cross sections are combined a…
The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the…
The ATLAS trigger has been used very successfully for the online event selection during the first part of the second LHC run (Run-2) in 2015/16 at a center-of-mass energy of 13 TeV. The trigger system is composed of a hardware Level-1 trigger and a software-based high-level trigger; it reduces the event rate from the bunch-crossing rate of 40 MHz to an average recording rate of about 1 kHz. The excellent performance of the ATLAS trigger has been vital for the ATLAS physics program of Run-2, selecting interesting collision events for a wide variety of physics signatures with high efficiency. Th…
