0000000001023526
AUTHOR
Dhiman Chakraborty
Search for pairs of highly collimated photon-jets in pp collisions at s=13 TeV with the ATLAS detector
Results of a search for the pair production of photon-jets - collimated groupings of photons - in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photonlike energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb-1, were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria …
Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in thelepton+jetsfinal state with ATLAS
A measurement is presented of the (tt) over bar inclusive production cross section in pp collisions at a center-ofmass energy of pffisffiffi root s = 8 TeV using data collected by the ATLAS detector at the CERN Large Hadron Collider. The measurement was performed in the lepton + jets final state using a data set corresponding to an integrated luminosity of 20.3 fb(-1). The cross section was obtained using a likelihood discriminant fit and b-jet identification was used to improve the signal-to-background ratio. The inclusive (tt) over bar production cross section was measured to be 260 +/- 1(stat)(-23)(+22)(stat) +/- 8(lumi) +/- 4(beam) pb assuming a top-quark mass of 172.5 GeV, in good agre…
Dijet azimuthal correlations and conditional yields in pp and p+Pb collisions at sNN=5.02TeV with the ATLAS detector
This paper presents a measurement of forward-forward and forward-central dijet azimuthal angular correlations and conditional yields in proton-proton (pp) and proton-lead (p + Pb) collisions as a p ...
Measurements of four-lepton production in pp collisions at s=8 TeV with the ATLAS detector
A search is presented for a high-mass Higgs boson in the , , , and decay modes using the ATLAS detector at the CERN Large Hadron Collider. The search uses proton-proton collision data at a centre-o ...
Study of jets produced in association with aWboson inppcollisions ats=7 TeVwith the ATLAS detector
We report a study of final states containing a W boson and hadronic jets, produced in proton-proton collisions at a center-of-mass energy of 7 TeV. The data were collected with the ATLAS detector at the CERN LHC and comprise the full 2010 data sample of 36 pb^-1. Cross sections are determined using both the electron and muon decay modes of the W boson and are presented as a function of inclusive jet multiplicity, N_jet, for up to five jets. At each multiplicity, cross sections are presented as a function of jet transverse momentum, the scalar sum of the transverse momenta of the charged lepton, missing transverse momentum, and all jets, the invariant mass spectra of jets, and the rapidity d…
Search for anomalous electroweak production of WW/WZ in association with a high-mass dijet system in pp collisions at s=8 TeV with the ATLAS detector
A search is presented for anomalous quartic gauge boson couplings in vector-boson scattering. The data for the analysis correspond to $20.2$ fb$^{-1}$ of $\sqrt{s}=8$ TeV $pp$ collisions, and were collected in 2012 by the ATLAS experiment at the Large Hadron Collider. The search looks for the production of $WW$ or $WZ$ boson pairs accompanied by a high-mass dijet system, with one $W$ decaying leptonically, and a $W$ or $Z$ decaying hadronically. The hadronically decaying $W/Z$ is reconstructed as either two small-radius jets or one large-radius jet using jet substructure techniques. Constraints on the anomalous quartic gauge boson coupling parameters $\alpha_4$ and $\alpha_5$ are set by fit…
Measurement of inclusive jet charged-particle fragmentation functions in Pb+Pb collisions at sNN=2.76 TeV with the ATLAS detector
Measurements of charged-particle fragmentation functions of jets produced in ultra-relativistic nuclear collisions can provide insight into the modification of parton showers in the hot, dense medi ...
Search for high-mass dilepton resonances using 139 fb−1 of pp collision data collected at s=13 TeV with the ATLAS detector
A search for high-mass dielectron and dimuon resonances in the mass range of 250 GeV to 6 TeV is presented. The data were recorded by the ATLAS experiment in proton–proton collisions at a centre-of-mass energy of s=13 TeV during Run 2 of the Large Hadron Collider and correspond to an integrated luminosity of 139 fb −1 . A functional form is fitted to the dilepton invariant-mass distribution to model the contribution from background processes, and a generic signal shape is used to determine the significance of observed deviations from this background estimate. No significant deviation is observed and upper limits are placed at the 95% confidence level on the fiducial cross-section times bran…
Search for Higgs bosons decaying toaain theμμττfinal state inppcollisions ats=8 TeVwith the ATLAS experiment
A search for the decay to a pair of new particles of either the 125 GeV Higgs boson (h) or a second charge parity (CP)-even Higgs boson (H) is presented. The data set corresponds to an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV recorded by the ATLAS experiment at the LHC in 2012. The search was done in the context of the next-to-minimal supersymmetric standard model, in which the new particles are the lightest neutral pseudoscalar Higgs bosons (a). One of the two a bosons is required to decay to two muons while the other is required to decay to two tau leptons. No significant excess is observed above the expected backgrounds in the dimuon invariant mass range fr…
Search for long-lived particles produced in pp collisions at s=13 TeV that decay into displaced hadronic jets in the ATLAS muon spectrometer
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 ...
Search for an excess of events with an identical flavour lepton pair and significant missing transverse momentum in root s=7 TeV proton-proton collisions with the ATLAS detector
Results are presented of a search for supersymmetric particles decaying into final states with significant missing transverse momentum and exactly two identical flavour leptons (e or mu) of opposite charge in sqrt{s}=7 TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corres…
Measurement of the transverse momentum distribution ofWbosons inppcollisions ats=7 TeVwith the ATLAS detector
This paper describes a measurement of the W boson transverse momentum distribution using ATLAS pp collision data from the 2010 run of the LHC at root s = 7 TeV, corresponding to an integrated lumin ...
Search for right-handed W bosons in top quark decay
We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This …
Search for light resonances decaying to boosted quark pairs and produced in association with a photon or a jet in proton–proton collisions at s=13TeV with the ATLAS detector
This Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high- pT photon or jet. The dataset consists of proton–proton collisions with an integrated luminosity of 36.1 fb −1 at a centre-of-mass energy of s=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector Z′ boson.
Properties of jet fragmentation using charged particles measured with the ATLAS detector in pp collisions at s=13 TeV
This paper presents a measurement of quantities related to the formation of jets from high-energy quarks and gluons (fragmentation). Jets with transverse momentum 100 GeV 500 MeV and vertical bar ...
Measurement of jet fragmentation in Pb+Pb and pp collisions at sNN=5.02 TeV with the ATLAS detector
This paper presents a measurement of jet fragmentation functions in 0.49 nb−1 of Pb+Pb collisions and 25 pb−1 of pp collisions at √sNN=5.02 TeV collected in 2015 with the ATLAS detector at the LHC. These measurements provide insight into the jet quenching process in the quark-gluon plasma created in the aftermath of ultrarelativistic collisions between two nuclei. The modifications to the jet fragmentation functions are quantified by dividing the measurements in Pb+Pb collisions by baseline measurements in pp collisions. This ratio is studied as a function of the transverse momentum of the jet, the jet rapidity, and the centrality of the collision. In both collision systems, the jet fragmen…
Search for the neutral Higgs bosons of the Minimal Supersymmetric Standard Model in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector
A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb[superscript −1] to 4.8 fb[superscript −1]. Higgs boson decays into oppositely-charged muon or τ lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits ar…
Search for a Structure in the Bs0π± Invariant Mass Spectrum with the ATLAS Experiment
A search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→B_{s}^{0}π^{±}, B_{s}^{0}→J/ψϕ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb^{-1} of pp collisions at 7 TeV and 19.5 fb^{-1} at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to B_{s}^{0} mesons, ρ_{X}, were determined at 95% confidence level. The results are N(X)<382 and ρ_{X}<0.015 for B_{s}^{0} mesons with transverse momenta above 10 GeV, and N(X)<356 and ρ_{X}<0.016 for transverse m…
Study of the hard double-parton scattering contribution to inclusive four-lepton production in pp collisions at s=8 TeV with the ATLAS detector
The inclusive production of four isolated charged leptons in pp collisions is analysed for the presence of hard double-parton scattering, using 20.2 fb(-1) of data recorded in the ATLAS detector at ...
Measurements ofWγandZγproduction inppcollisions ats=7 TeVwith the ATLAS detector at the LHC
The integrated and differential fiducial cross sections for the production of a W or Z boson in association with a high-energy photon are measured using pp collisions at root s = 7 TeV. The analyse ...
Measurements of the Total and Differential Higgs Boson Production Cross Sections Combining theH→γγandH→ZZ*→4ℓDecay Channels ats=8 TeVwith the ATLAS Detector
Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3 fb(-1) of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of root s = 8 TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H -> gamma gamma and H -> ZZ*. 4l event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be sigma(pp -> …
Search for Low-Mass Dijet Resonances Using Trigger-Level Jets with the ATLAS Detector in pp Collisions at s=13 TeV
Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, who ...
Search for Dilepton Resonances inppCollisions ats=7 TeVwith the ATLAS Detector
This Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at root s = 7 TeV at the Large Hadron Collider and correspond to a total integrated luminosity of 1.08 (1.21) fb(-1) in the e(+)e(-) (mu(+)mu(-)) channel. No statistically significant excess above the standard model expectation is observed and upper limits are set at the 95% C. L. on the cross section times branching fraction of Z' resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the sequential standard model Z' boson is set. A Randall-Sundrum…
Evidence for an anomalous like-sign dimuon charge asymmetry
We measure the charge asymmetry $A\equiv(N^{++} - N^{--})/(N^{++} + N^{--})$ of like-sign dimuon events in 6.1~fb$^{-1}$ of $p\bar{p}$ collisions recorded with the D0 detector at a center-of-mass energy $\sqrt{s}=1.96$~TeV at the Fermilab Tevatron collider. From $A$ we extract the like-sign dimuon charge asymmetry in semileptonic $b$-hadron decays: $\aslb=-0.00957\pm0.00251\thinspace({\rm stat})\pm0.00146\thinspace({\rm sys})$. It differs by 3.2~standard deviations from the standard model prediction $\aslb({\rm SM})=(-2.3^{+0.5}_{-0.6})\times10^{-4}$, and provides first evidence of anomalous $CP$ violation in the mixing of neutral $B$ mesons.
Search for pair production of Higgsinos in final states with at least three b -tagged jets in s=13 TeV pp collisions using the ATLAS detector
A search for pair production of the supersymmetric partners of the Higgs boson (higgsinos H˜) in gauge-mediated scenarios is reported. Each higgsino is assumed to decay to a Higgs boson and a gravitino. Two complementary analyses, targeting high- and low-mass signals, are performed to maximize sensitivity. The two analyses utilize LHC pp collision data at a center-of-mass energy s=13 TeV, the former with an integrated luminosity of 36.1 fb-1 and the latter with 24.3 fb-1, collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing missing transverse momentum and several energetic jets, at least three of which must be identified as b-quark jets. No sig…
Measurement of jet charge in dijet events froms=8 TeVppcollisions with the ATLAS detector
The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum ...
Luminosity determination in pp collisions at s=7 TeV using the ATLAS detector at the LHC
Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at s√=7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0<μ<2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, do…
Hard single diffraction in p̄p collisions at s=630 and 1800 GeV
Using the D empty set detector, we have studied events produced in (p) over barp collisions that contain large forward regions with very little energy deposition ("rapidity gaps") and concurrent jet production at center-of-mass energies of roots = 630 and 1800 GeV. The fraction of events with forward or central jets associated with rapidity gaps is compared to predictions for hard diffraction. We also extract the momentum loss for scattered protons in such processes. (C) 2002 Elsevier Science B.V. All rights reserved.
Search for resonant top quark plus jet production intt¯+jetsevents with the ATLAS detector inppcollisions ats=7 TeV
This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to (t)over-barq or tq, leading to a resonance within the t(t)over-bar + jets signature. The full 2011 ATLAS pp collision data set from the LHC (4.7 fb(-1)) is used to search for t(t)over-bar events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both W' boson and color tr…
Resolution of the ATLAS muon spectrometer monitored drift tubes in LHC Run 2
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 354 000 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 collected by ATLAS in LHC Run 2 and from a gas monitoring chamber, deployed in a dedicated gas fac…
Ratio of Isolated Photon Cross Sections in pp¯ Collisions at √s=630 and 1800 GeV
The inclusive cross section for production of isolated photons has been measured in p (p) over bar collisions at roots = 630 GeV with the DO detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E-T) range from 7-49 GeV and have pseudorapidity \eta\ s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E-T range.
Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector
A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb[superscript −1]. No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles.
Measurement of the t-channel single top quark production cross section
The D0 collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb^-1 of ppbar collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14 +0.94 -0.80 pb for the t-channel and 1.05 +…
Search for R-parity-violating supersymmetric particles in multi-jet final states produced in p–p collisions at s=13 TeV using the ATLAS detector at the LHC
Results of a search for gluino pair production with subsequent R-parity-violating decays to quarks are presented. This search uses 36.1 fb(-1) of data collected by the ATLAS detector in proton-prot ...
Measurement of the differential cross-section of highly boosted top quarks as a function of their transverse momentum ins=8 TeVproton-proton collisions using the ATLAS detector
The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV. The measur ...
Measurement of the nuclear modification factor for inclusive jets in Pb+Pb collisions at sNN=5.02 TeV with the ATLAS detector
Measurements of the yield and nuclear modification factor, R-AA, for inclusive jet production are performed using 0.49 nb(-1) of Pb+Pb data at root s(NN) = 5.02 TeV and 25 pb(-1) of Pb+Pb data at r ...
Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks inppcollisions ats=8 TeVwith the ATLAS detector
This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb(-1) of pp collisions at a center-of-m ...
Search for the standard model Higgs boson in tau final states
We present a search for the standard model Higgs boson using hadronically decaying tau leptons, in 1 inverse femtobarn of data collected with the D0 detector at the Fermilab Tevatron ppbar collider. We select two final states: tau plus missing transverse energy and b jets, and tau+ tau- plus jets. These final states are sensitive to a combination of associated W/Z boson plus Higgs boson, vector boson fusion and gluon-gluon fusion production processes. The observed ratio of the combined limit on the Higgs production cross section at the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of 115 GeV.
Electron and photon performance measurements with the ATLAS detector using the 2015-2017 LHC proton-proton collision data
This paper describes the reconstruction of electrons and photons with the ATLAS detector, employed for measurements and searches exploiting the complete LHC Run 2 dataset. An improved energy clustering algorithm is introduced, and its implications for the measurement and identification of prompt electrons and photons are discussed in detail. Corrections and calibrations that affect performance, including energy calibration, identification and isolation efficiencies, and the measurement of the charge of reconstructed electron candidates are determined using up to 81 fb−1 of proton-proton collision data collected at √s=13 TeV between 2015 and 2017.
Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using root s=7 TeV pp collisions with the ATLAS detector
Results are presented of a search for any particle(s) decaying to six or more jets in association with missing transverse momentum. The search is performed using 1.34fb−1 of s √ s = 7 TeV proton-proton collisions recorded by the ATLAS detector during 2011. Data-driven techniques are used to determine the backgrounds in kinematic regions that require at least six, seven or eight jets, well beyond the multiplicities required in previous analyses. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a supersymmetry model (MSUGRA/CMSSM) where they extend previous constraints.
Search for pair production of the scalar top quark in the electron-muon final state
We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tilde{\nu}$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tilde{\nu}}$) mass plane.
Search for WH production with a light Higgs boson decaying to prompt electron-jets in proton–proton collisions at \(\sqrt {s}=7\) TeV with the ATLAS detector
A search is performed for WH production with a light Higgs boson decaying to hidden-sector particles resulting in clusters of collimated electrons, known as electron-jets. The search is performed with 2.04 fb[superscript −1] of data collected in 2011 with the ATLAS detector at the Large Hadron Collider in proton–proton collisions at √s=7 TeV . One event satisfying the signal selection criteria is observed, which is consistent with the expected background rate. Limits on the product of the WH production cross section and the branching ratio of a Higgs boson decaying to prompt electron-jets are calculated as a function of a Higgs boson mass in the range from 100 to 140 GeV.
Measurement of Higgs boson production in the diphoton decay channel inppcollisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector
A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5 fb(-1) of proton-proton collisions data at root s = 7 TeV and 20.3 fb(-1) at root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be mu = 1.17 +/- 0.27 at the value of the Higgs boson mass measured by ATLAS, m(H) = 125.4 GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m(H). They are found to be mu(ggF) = 1.32…
The upgraded DO detector
The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of s…
Measurement of hard double-parton interactions inW(???) + 2-jet events at $\sqrt{s}\,=7$ TeV with the ATLAS detector
The production of W bosons in association with two jets in proton–proton collisions at a centre-of-mass energy of √s=7 TeV has been analysed for the presence of double-parton interactions using data corresponding to an integrated luminosity of 36 pb[superscript −1], collected with the ATLAS detector at the Large Hadron Collider. The fraction of events arising from double-parton interactions, f[superscript (D) over subscript DP], has been measured through the p[subscript T] balance between the two jets and amounts to f[superscript (D) over subscript DP] = 0.08 ± 0.01 (stat.) ± 0.02 (sys.) for jets with transverse momentum p[subscript T] > 20 GeV and rapidity |y| < 2.8. This corresponds to a …
Search for supersymmetry via associated production of charginos and neutralinos in final states with three leptons
A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a ppbar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a dataset corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching f…
Measurements of spin correlation in top-antitop quark events from proton-proton collisions ats=7 TeVusing the ATLAS detector
Measurements of spin correlation in top quark pair production are presented using data collected with the ATLAS detector at the LHC with proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 4.6 fb(-1). Events are selected in final states with two charged leptons and at least two jets and in final states with one charged lepton and at least four jets. Four different observables sensitive to different properties of the top quark pair production mechanism are used to extract the correlation between the top and antitop quark spins. Some of these observables are measured for the first time. The measurements are in good agreement with the Stan…
Search for dark photons from supersymmetric hidden valleys
We search for a new light gauge boson, a dark photon, with the D0 experiment. In the model we consider, supersymmetric partners are pair produced and cascade to lightest neutralinos that can decay into the hidden sector state plus either a photon or a dark photon. The dark photon decays through its mixing with a photon into fermion pairs. We therefore investigate a previously unexplored final state that contains a photon, two spatially close leptons, and large missing transverse energy. We do not observe any evidence for dark photons and set a limit on their production.
Search for heavy vector-like quarks coupling to light quarks in proton–proton collisions at s=7 TeV with the ATLAS detector
This letter presents a search for singly produced vector-like quarks, Q, coupling to light quarks, q. The search is sensitive to both charged current (CC) and neutral current (NC) processes, p p --> Q q --> W q q' and p p --> Q q --> Z q q' with a leptonic decay of the vector gauge boson. In 1.04/fb of data taken in 2011 by the ATLAS experiment at a center-of-mass energy sqrt(s) = 7 TeV, no evidence of such heavy vector-like quarks is observed above the expected Standard Model background. Limits on the heavy vector-like quark production cross section times branching ratio as a function of mass m_Q are obtained. For a coupling kappa_(qQ) = v/m_Q, where v is the Higgs vacuum expectation value…
Search for contact interactions in dimuon events fromppcollisions ats=7 TeVwith the ATLAS detector
A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at root s = 7 TeV. The data sample corresponds to an integrated ...
Search for a Heavy Neutral Particle Decaying toeμ,eτ, orμτinppCollisions ats=8 TeVwith the ATLAS Detector
This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, e(+/-) mu(-/+), e(+/-) tau(-/+), or mu(+/-) tau(-/+) using 20.3 fb(-1) of pp collision data at root s = 8 TeV collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the standard model expectations. Limits are set on the cross section of new phenomena in two scenarios: the production of (nu) over tilde (tau) in R-parity-violating supersymmetric models and the production of a lepton-flavor-violating Z' vector boson.
Measurement of the W±Z production cross section and limits on anomalous triple gauge couplings in proton–proton collisions at s=7 TeV with the ATLAS detector
This Letter presents a measurement of W(+/-)Z production in 1.02 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected w ...
Search for squarks and gluinos in final states with hadronically decaying τ -leptons, jets, and missing transverse momentum using pp collisions at s=13 TeV with the ATLAS detector
A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying τ-lepton is presented. Two exclusive final states with either exactly one or at least two τ-leptons are considered. The analysis is based on proton-proton collisions at s=13 TeV corresponding to an integrated luminosity of 36.1 fb-1 delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair pr…
Search for a right-handed gauge boson decaying into a high-momentum heavy neutrino and a charged lepton in pp collisions with the ATLAS detector at s=13 TeV
A search for a right-handed gauge boson WR, decaying into a boosted right-handed heavy neutrino NR, in the framework of Left-Right Symmetric Models is presented. It is based on data from proton–proton collisions with a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015, 2016 and 2017, corresponding to an integrated luminosity of 80 fb$^{−1}$. The search is performed separately for electrons and muons in the final state. A distinguishing feature of the search is the use of large-radius jets containing electrons. Selections based on the signal topology result in smaller background compared to the expected signal. No significant d…
Search for scalar leptoquarks in pp collisions at $\sqrt{s}$=13 TeV with the ATLAS experiment
An inclusive search for a new-physics signature of lepton-jet resonances has been performed by the ATLAS experiment. Scalar leptoquarks, pair-produced in pp collisions at s √s = 13 TeV at the large hadron collider, have been considered. An integrated luminosity of 3.2 fb-1, corresponding to the full 2015 dataset was used. First (second) generation leptoquarks were sought in events with two electrons (muons) and two or more jets. The observed event yield in each channel is consistent with Standard Model background expectations. The observed (expected) lower limits on the leptoquark mass at 95% confidence level are 1100 and 1050 GeV (1160 and 1040 GeV) for first and second generation leptoqua…
Search for excited leptons in proton-proton collisions ats=7 TeVwith the ATLAS detector
The ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel l* -> l gamma. Results are presented based on the analysis of pp collisions at a center-of ...
Measurement of the b-hadron production cross section using decays to D⁎+μ−X final states in pp collisions at s=7 TeV with the ATLAS detector
The b-hadron production cross section is measured with the ATLAS detector in pp collisions at root s = 7 TeV, using 3.3 pb(-1) of integrated luminosity, collected during the 2010 LHC run. The b-had ...
Evidence for production of single top quarks
We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron ppbar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top quark partner that is always produced from strong coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top quark production has been searched for in ever larger datasets. In this analysis, we select events from a 0.9 fb-1 dataset that have an electron or muon and missing transverse energy from the decay of a W boson from the top quark decay, and two, three, …
Measurement of the cross-section for W boson production in association with b-jets in pp collisions at root s=7 TeV with the ATLAS detector
This paper reports a measurement of the W +b-jets (W +b+ X and W + b[¯ over b] +X) production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC. These results are based on data corresponding to an integrated luminosity of 4.6 fb[superscript −1], collected with the ATLAS detector. Cross-sections are presented as a function of jet multiplicity and of the transverse momentum of the leading b-jet for both the muon and electron decay modes of the W boson. The W +b-jets cross-section, corrected for all known detector effects, is quoted in a limited kinematic range. Combining the muon and electron channels, the fiducial cross-section for W +b-jets is measured…
Search for a Resonance Decaying intoWZBoson Pairs inpp¯Collisions
We present the first search for an electrically charged resonance W' decaying to a WZ boson pair using 4.1 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron p (p) over bar collider. The WZ pairs are reconstructed through their decays into three charged leptons (l = e, mu). A total of 9 data events is observed in good agreement with the background prediction. We set 95% C.L. limits on the W'WZ coupling and on the W' production cross section multiplied by the branching fractions. We also exclude W' masses between 188 and 520 GeV within a simple extension of the standard model and set the most restrictive limits to date on low-scale technicolor models.
Underlying event characteristics and their dependence on jet size of charged-particle jet events inppcollisions at(s)=7 TeVwith the ATLAS detector
Distributions sensitive to the underlying event are studied in events containing one or more charged-particle jets produced in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector at the Large Hadron Collider (LHC). These measurements reflect 800 inverse microbarns of data taken during 2010. Jets are reconstructed using the antikt algorithm with radius parameter R varying between 0.2 and 1.0. Distributions of the charged-particle multiplicity, the scalar sum of the transverse momentum of charged particles, and the average charged-particle pT are measured as functions of pT^JET in regions transverse to and opposite the leading jet for 4 GeV < pT^JET < 100 GeV. In addition, the R-dependen…
Measurement of top quark pair differential cross sections in the dilepton channel in pp collisions at s=7 and 8 TeV with ATLAS
Measurements of normalized differential cross-sections of top quark pair ($t\bar t$) production are presented as a function of the mass, the transverse momentum and the rapidity of the $t\bar t$ system in proton-proton collisions at center-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV. The dataset corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at 7 TeV and 20.2 fb$^{-1}$ at 8 TeV, recorded with the ATLAS detector at the Large Hadron Collider. Events with top quark pair signatures are selected in the dilepton final state, requiring exactly two charged leptons and at least two jets with at least one of the jets identified as likely to contain a $b$-hadron. The measured distributi…
Measurement of upsilon production in 7 TeV pp collisions at ATLAS
Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM
Search for new fermions ("quirks") at the Fermilab Tevatron Collider
We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in $2.4$ fb$^{-1}$ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron $p\bar{p}$ collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like {\it SU(N)} sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107 ~GeV for the mass of a charged quirk with strong dynamics scale $\Lambda$ in the range from 10 keV to 1 MeV.
Combination of Searches for Invisible Higgs Boson Decays with the ATLAS Experiment
Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for H → invisible decays where H is produced according to the standard model via vector boson fusion, Z(ℓℓ)H, and W/Z(had)H, all performed with the ATLAS detector using 36.1 fb⁻¹ of pp collisions at a center-of-mass energy of √s = 13 TeV at the LHC. In combination with the results at √s = 7 and 8 TeV, an exclusion limit on the H → invisible branching ratio of 0.26(0.17-0.05+0.07) at 95% confidence level is observed (expected).
Search for third generation scalar leptoquarks decaying into tau b
We have searched for third generation leptoquarks (LQ3) using 1.05 inverse femtobarns of data collected with the D0 detector at the Fermilab Tevatron Collider operating at sqrt(s)=1.96 TeV. We set a 95% C.L. lower limit of 210 GeV on the mass of a scalar LQ3 state decaying solely to a b quark and a tau lepton.
Search for Supersymmetry inppCollisions ats=7 TeVin Events with Two Photons and Missing Transverse Energy
A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36 pb(-1) recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squa…
Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions atsNN=2.76 TeVwith the ATLAS Detector at the LHC
By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymme…
Search for charged Higgs bosons in decays of top quarks
We present a search for charged Higgs bosons in decays of top quarks, in the mass range $80 < m_{H^{\pm} < 155$ GeV, assuming the subsequent decay $H^{+} \to ��^{+} ��_��$ (and its charge conjugate). Using 0.9 fb$^{-1}$ of lepton+jets data collected with the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider, operating at a center of mass energy $\sqrt{s}=1.96$ TeV, we find no evidence for a $H^{\pm}$ signal. Hence, we exclude branching ratios $B(t \to H^+b) > 0.24$ for $m_{H^{\pm}=80$ GeV, and $B(t \to H^+b) > 0.19$ for $m_{H^{\pm}=155$ GeV, at the 95% C.L.
Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in pp collisions at s=13 TeV with the ATLAS detector
A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energ ...
Search for heavy charged long-lived particles in proton–proton collisions at s=13TeV using an ionisation measurement with the ATLAS detector
This Letter presents a search for heavy charged long-lived particles produced in proton-proton collisions at root s= 13 TeV at the LHC using a data sample corresponding to an integrated luminosity ...
Measurement of the tt¯Z and tt¯W cross sections in proton-proton collisions at s=13 TeV with the ATLAS detector
A measurement of the associated production of a top-quark pair (tt) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb-1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The ttZ and ttW production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σttZ=0.95±0.08stat±0.10syst…
Simultaneous measurements of thett¯,W+W−, andZ/γ*→ττproduction cross-sections inppcollisions ats=7 TeVwith the ATLAS detector
Simultaneous measurements of the t (t) over bar, W+W-, and Z/gamma* -> tau tau production cross-sections using an integrated luminosity of 4.6 fb(-1) of pp collisions at root s = 7 TeV collected ...
ATLAS data quality operations and performance for 2015-2018 data-taking
The 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 ev…
Measurement of the muon charge asymmetry from W boson decays
We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb^{-1} of data collected at \sqrt{s}=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron ppbar Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.
Search for lepton-flavor-violating decays of the Z boson into a τ lepton and a light lepton with the ATLAS detector
Direct searches for lepton flavor violation in decays of the Z boson with the ATLAS detector at the LHC are presented. Decays of the Z boson into an electron or muon and a hadronically decaying r l ...
Measurement of inclusive jet and dijet production inppcollisions ats=7 TeVusing the ATLAS detector
Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using jets clustered with the anti-kT algorithm with parameters R=0.4 and R=0.6. These measurements are based on the 2010 data sample, consisting of a total integrated luminosity of 37 inverse picobarns. Inclusive jet double-differential cross sections are presented as a function of jet transverse momentum, in bins of jet rapidity. Dijet double-differential cross sections are studied as a function of the dijet invariant mass, in bins of half the rapidity separation of the two leading …
Search for heavy long-lived multicharged particles in proton-proton collisions at s=13 TeV using the ATLAS detector
A search for heavy long-lived multicharged particles is performed using the ATLAS detector at the LHC. Data with an integrated luminosity of 36.1 fb(-1) collected in 2015 and 2016 from proton-proto ...
Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector
Physics letters / B 784, 173 - 191 (2018). doi:10.1016/j.physletb.2018.07.035
Measurements of the charge asymmetry in top-quark pair production in the dilepton final state ats=8 TeVwith the ATLAS detector
Measurements of the top--antitop quark pair production charge asymmetry in the dilepton channel are presented using data corresponding to an integrated luminosity of 20.3 fb−1 from pp collisions at a center-of-mass energy of s√=8 TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the tt¯ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: AllC based on the selected leptons and Att¯C based on the reconstructed tt¯ final state. The inclusive asymmet…
Search for Pair Production of a Heavy Up-Type Quark Decaying to aWBoson and abQuark in thelepton+jetsChannel with the ATLAS Detector
A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming subsequent decay to a W boson and a b quark, t'(t) over bar' -> W(+)bW(-)(b) over bar. The search is based on 1.04 fb(-1) of proton-proton collisions at root s = 7 TeV collected by the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton + jets final state, characterized by a high transverse momentum isolated electron or muon, high missing transverse momentum, and at least three jets. No significant excess of events above the background expectation is observed. A 95% C.L. lower limit of 404 GeV is set for the mass of the t' quark.
Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb final state in pp collisions at s=13 TeV with the ATLAS detector
A search for a heavy neutral Higgs boson, A, decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 36.1 fb(-1) from ...
Search for heavy charged long-lived particles in the ATLAS detector in 36.1 fb−1 of proton-proton collision data at s=13 TeV
A search for heavy charged long-lived particles is performed using a data sample of 36.1 fb−1 of proton-proton collisions at s=13 TeV collected by the ATLAS experiment at the Large Hadron Collider. The search is based on observables related to ionization energy loss and time of flight, which are sensitive to the velocity of heavy charged particles traveling significantly slower than the speed of light. Multiple search strategies for a wide range of lifetimes, corresponding to path lengths of a few meters, are defined as model independently as possible, by referencing several representative physics cases that yield long-lived particles within supersymmetric models, such as gluinos/squarks …
Search for the Standard Model Higgs boson in the decay channel H→ZZ(⁎)→4ℓ with 4.8 fb−1 of pp collision data at s=7 TeV with ATLAS
This Letter presents a search for the Standard Model Higgs boson in the decay channel H -> ZZ((*)) -> l(+)l(-)l(-)+l(')-, where l,l' = e or mu, using proton-proton collisions at root s = 7 TeV recorded with the ATLAS detector and corresponding to an integrated luminosity of 4.8 fb(-1). The four-lepton invariant mass distribution is compared with Standard Model background expectations to derive upper limits on the cross section of a Standard Model Higgs boson with a mass between 110 GeV and 600 GeV. The mass ranges 134-156 GeV, 182-233 GeV, 256-265 GeV and 268-415 GeV are excluded at the 95% confidence level. The largest upward deviations from the background-only hypothesis are observed for …
Search for Higgs boson decays into pairs of light (pseudo)scalar particles in the γγjj final state in pp collisions at s=13TeV with the ATLAS detector
This Letter presents a search for exotic decays of the Higgs boson to a pair of new (pseudo)scalar particles, H→aa , where the a particle has a mass in the range 20–60 GeV, and where one of the a bosons decays into a pair of photons and the other to a pair of gluons. The search is performed in event samples enhanced in vector-boson fusion Higgs boson production by requiring two jets with large invariant mass in addition to the Higgs boson candidate decay products. The analysis is based on the full dataset of pp collisions at s=13TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.7 fb −1 . The data are in a…
Search for new phenomena in final states with an energetic jet and large missing transverse momentum inppcollisions ats=13 TeVusing the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses proton-proton collision data corresponding to an inte ...
A novel method for modeling the recoil in W boson events at hadron collider
We present a new method for modeling the hadronic recoil in W->lnu events produced at hadron colliders. The recoil is chosen from a library of recoils in Z->ll data events and overlaid on a simulated W->lnu event. Implementation of this method requires that the data recoil library describe the properties of the measured recoil as a function of the true, rather than the measured, transverse momentum of the boson. We address this issue using a multidimensional Bayesian unfolding technique. We estimate the statistical and systematic uncertainties from this method for the W boson mass and width measurements assuming 1 fb-1 of data from the Fermilab Tevatron. The uncertainties are found…
Search for quark contact interactions in dijet angular distributions in pp collisions at s=7 TeV measured with the ATLAS detector
Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
Search for lepton-flavor violation in different-flavor, high-mass final states in pp collisions at s=13 TeV with the ATLAS detector
A search is performed for a heavy particle decaying into different-flavor, dilepton pairs (e mu, e tau or mu tau), using 36.1 fb(-1) of proton-proton collision data at root s = 13 TeV collected in ...
Search for TeV-scale gravity signatures in final states with leptons and jets with the ATLAS detector at s=7 TeV
A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb−1 of proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at √s = 13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.
Determination of the width of the top quark
We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -> W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -> W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |Vtb'| < 0.63 at 95% C.L.
Search for charged Higgs bosons in top quark decays
We present a search for charged Higgs bosons in top quark decays. We analyze the \eplus, \muplus, $ee$, $e\mu$, $\mu\mu$, \etau and \mutau final states from top quark pair production events, using data from about 1${\text{fb}}^{-1}$ of integrated luminosity recorded by the \dzero experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a $\tau$ lepton and a $\tau$ neutrino and a third one where both decays appear. We extract limits on the branching ratio $B(t\to H^+ b)$ for all these models. We use two method…
Electron and photon energy calibration with the ATLAS detector using 2015-2016 LHC proton-proton collision data
Artículo realizado por muchos autores. Solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración y los autores que firman como pertenecientes a la UAM
Search for charged Higgs bosons through the violation of lepton universality in t(t)over-bar events using pp collision data at root s=7 TeV with the ATLAS experiment
In several extensions of the Standard Model, the top quark can decay into a bottom quark and a light charged Higgs boson H [superscript +], t → bH [superscript +], in addition to the Standard Model decay t → bW. Since W bosons decay to the three lepton generations equally, while H [superscript +] may predominantly decay into τν, charged Higgs bosons can be searched for using the violation of lepton universality in top quark decays. The analysis in this paper is based on 4.6 fb[superscript −1] of proton-proton collision data at √s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider. Signatures containing leptons (e or μ) and/or a hadronically decaying τ (τ [subscript had])…
Two-particle azimuthal correlations in photonuclear ultraperipheral Pb+Pb collisions at 5.02 TeV with ATLAS
We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. 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 and ANID, Chile, CAS, MOST, and NSFC, China, COLCIENCIAS, Colombia, MSMT CR, MPO CR, and VSC CR, Czech Republic, DNRF and DNSRC, Denmark, IN2P3-CNRS and CEA-DRF/IRFU, France, SRNSFG, Georgia, BMBF, HGF, and MPG, Germany, GSRT, Greece, RGC and Hong Kong SAR, China, ISF and Benoziyo Center, Israel, INFN, Italy, MEXT and JSPS, Japan, CNR…
Search for chargino-neutralino production using recursive jigsaw reconstruction in final states with two or three charged leptons in proton-proton collisions at s=13 TeV with the ATLAS detector
A search for electroweak production of supersymmetric particles is performed in two-lepton and three-lepton final states using recursive jigsaw reconstruction, a technique that assigns reconstructed objects to the most probable hemispheres of the decay trees, allowing one to construct tailored kinematic variables to separate the signal and background. The search uses data collected in 2015 and 2016 by the ATLAS experiment in s=13 TeV proton-proton collisions at the CERN Large Hadron Collider corresponding to an integrated luminosity of 36.1 fb-1. Chargino-neutralino pair production, with decays via W/Z bosons, is studied in final states involving leptons and jets and missing transverse mome…
Observation of Long-Range Elliptic Azimuthal Anisotropies ins=13and 2.76 TeVppCollisions with the ATLAS Detector
ATLAS has measured two-particle correlations as a function of relative azimuthal-angle, $\Delta \phi$, and pseudorapidity, $\Delta \eta$, in $\sqrt{s}$=13 and 2.76 TeV $pp$ collisions at the LHC using charged particles measured in the pseudorapidity interval $|\eta|$<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at $\Delta \phi \sim 0$ that extends over a wide range of $\Delta\eta$, which has been referred to as the "ridge". Per-trigger-particle yields, $Y(\Delta \phi)$, are measured over 2<$|\Delta\eta|$<5. For both collision energies, the $Y(\Delta \phi)$ distribution in all multiplicity …
Search for Heavy Particles Decaying into Electron-Positron Pairs inpp¯Collisions
We present results of searches for technirho (rho (T)), techniomega (omega (T)), and Z' particles, using the decay channels rho (T), omega (T), Z' --> e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the DO detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes p (p) over bar --> rho (T), omega (T), Z' - e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho (T) and omega (T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermi…
Beam-induced and cosmic-ray backgrounds observed in the ATLAS detector during the LHC 2012 proton-proton running period
This paper discusses various observations on beam-induced and cosmic-ray backgrounds in the ATLAS detector during the LHC 2012 proton-proton run. Building on published results based on 2011 data, the correlations between background and residual pressure of the beam vacuum are revisited. Ghost charge evolution over 2012 and its role for backgrounds are evaluated. New methods to monitor ghost charge with beam-gas rates are presented and observations of LHC abort gap population by ghost charge are discussed in detail. Fake jets from colliding bunches and from ghost charge are analysed with improved methods, showing that ghost charge in individual radio-frequency buckets of the LHC can be resol…
Comparison between simulated and observed LHC beam backgrounds in the ATLAS experiment at E beam =4 TeV
Results of dedicated Monte Carlo simulations of beam-induced background (BIB) in the ATLAS experiment at the Large Hadron Collider (LHC) are presented and compared with data recorded in 2012. During normal physics operation this background arises mainly from scattering of the 4 TeV protons on residual gas in the beam pipe. Methods of reconstructing the BIB signals in the ATLAS detector, developed and implemented in the simulation chain based on the FLUKA Monte Carlo simulation package, are described. The interaction rates are determined from the residual gas pressure distribution in the LHC ring in order to set an absolute scale on the predicted rates of BIB so that they can be compared qua…
Observation of Single Top Quark Production
We report observation of the electroweak production of single top quarks in ppbar collisions at sqrt(s) = 1.96 TeV based on 2.3 fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(ppbar -> tb + X, tqb + X) = 3.94 +- 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10^-7, corresponding to a 5.0 standard deviation significance for the observation.
Search for the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment
A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH→ℓ+ℓ−c¯c is studied. A data set with an integrated luminosity of 36.1 fb−1 of pp collisions at √s=13TeV recorded by the ATLAS experiment at the LHC is used. The H→c¯c signature is identified using charm-tagging algorithms. The observed (expected) upper limit on σ(pp→ZH)×B(H→c¯c) is 2.7 (3.9+2.1−1.1) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the standard model value is 26 fb.
Measurement of the top quark mass in final states with two leptons
We present measurements of the top quark mass in ttbar candidate events with two final state leptons using 1 inverse fb of data collected by the D0 experiment. Our data sample is selected by requiring two fully identified leptons or by relaxing one lepton requirement to an isolated track if at least one jet is tagged as a b jet. The top quark mass is extracted after reconstructing the event kinematics under the ttbar hypothesis using two methods. In the first method, we integrate over expected neutrino rapidity distributions, and in the second we calculate a weight for the possible top quark masses based on the observed particle momenta and the known parton distribution functions. We analyz…
Search for stable hadronising squarks and gluinos with the ATLAS experiment at the LHC
Hitherto unobserved long-lived massive particles with electric and/or colour charge are predicted by a range of theories which extend the Standard Model. In this Letter a search is performed at the ATLAS experiment for slow-moving charged particles produced in proton–proton collisions at 7 TeV centre-of-mass energy at the LHC, using a data-set corresponding to an integrated luminosity of 34 pb[superscript −1]. No deviations from Standard Model expectations are found. This result is interpreted in a framework of supersymmetry models in which coloured sparticles can hadronise into long-lived bound hadronic states, termed R-hadrons, and 95% CL limits are set on the production cross-sections of…
Search for four-top-quark production in the single-lepton and opposite-sign dilepton final states in pp collisions at s=13 TeV with the ATLAS detector
A search for four-top-quark production, tttt, is presented. It is based on proton-proton collision data with a center-of-mass energy s=13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1. Data are analyzed in both the single-lepton and opposite-sign dilepton channels, characterized by the presence of one or two isolated electrons or muons with high-transverse momentum and multiple jets. A data-driven method is used to estimate the dominant background from top-quark pair production in association with jets. No significant excess above the Standard Model expectation is observed. The result i…
First measurement of the forward-backward charge asymmetry in top quark pair production
We present the first measurement of the integrated forward-backward charge asymmetry in top-antitop quark pair (ttbar) production in proton-antiproton collisions in the lepton plus jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming ttbar+X production and decay, a sample of 0.9fb-1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on ttbar+X production via a Z' resonance.
Observation of top-quark pair production in association with a photon and measurement of thett¯γproduction cross section inppcollisions ats=7TeV using the ATLAS detector
A search is performed for top-quark pairs (t (t) over bar) produced together with a photon (gamma) with transverse energy greater than 20 GeV using a sample of t (t) over bar candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t (t) over bar gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 +/- 26 and 120 +/- 39 non-t (t) over bar gamma background events,…
Observation of an Excited $B^{\pm}_c$ Meson State with the ATLAS Detector
A search for excited states of the B±c meson is performed using 4.9 fb-1 of 7 TeV and 19.2 fb-1 of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decay B±c→J/ψπ±. The state appears in the m(Bc±π+π-)-m(Bc±)-2m(π±) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842±4±5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the B±c meson, B±c(2S).
Femtoscopy with identified charged pions in proton-lead collisions at sNN=5.02 TeV with ATLAS
Bose-Einstein correlations between identified charged pions are measured for $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV using data recorded by the ATLAS detector at the LHC corresponding to a total integrated luminosity of $28$ $\mathrm{nb}^{-1}$. Pions are identified using ionization energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of collision centrality as well as the average transverse momentum ($k_{\mathrm{T}}$) and rapidity ($y^{\star}_{\pi\pi}$) of the pair. Pairs are selected with a rapidity $-2 < y^{\star}_{\pi\pi} < 1$ and with an average transverse momentum $0.1 < k_{\mathrm{T}} <…
Measurement of the Inclusive Jet Cross Section inpp¯Collisions ats=1.96 TeV
We report on a measurement of the inclusive jet cross section in p (p) over bar collisions at a center-of-mass energy root s = 1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0: 70 fb(-1). The data cover jet transverse momenta from 50 to 600 GeV and jet rapidities in the range -2.4 to 2.4. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.
Measurements of Higgs boson properties in the diphoton decay channel with 36 fb−1 of pp collision data at s=13 TeV with the ATLAS detector
Properties of the Higgs boson are measured in the two-photon final state using 36.1 fb-1 of proton? proton collision data recorded at ffiffi √s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon-gluon fusion, vectorboson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of 0.99 ± 0.14 improves on the precision of the ATLAS measurement at √s = 7 and 8 TeV by a factor of two. …