Measurement of inclusive and differential cross sections in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector
Inclusive and differential fiducial cross sections of Higgs boson production in proton-proton collisions are measured in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel. The proton-proton collision data were produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. The inclusive fiducial cross section in the $H \rightarrow ZZ^* \rightarrow 4\ell$ decay channel is measured to be 3.62 $\pm$ 0.50 (stat) $^{+0.25}_{-0.20}$ (sys) fb, in agreement with the Standard Model prediction of 2.91 $\pm$ 0.13 fb. The cross section is also extrapolated to the total phase space including all Standard Model Higgs boson decays. Several differential fiducial cross sections are measured for observables sensitive to the Higgs boson production and decay, including kinematic distributions of jets produced in association with the Higgs boson. Good agreement is found between data and Standard Model predictions. The results are used to put constraints on anomalous Higgs boson interactions with Standard Model particles, using the pseudo-observable extension to the kappa-framework.
Latest results on inclusive top-quark pair production cross-sections are presented using collision data collected by ATLAS and CMS experiments at the LHC. Inclusive and differential measurements of top-quark pair production cross-sections from ATLAS and CMS are presented in the resolved and boosted kinematic regions. The cross-sections are measured as a function of various kinematic observables of the top quarks, the jets and leptons of the event final state.
This Thesis presents the measurement of the inclusive jet cross section using the full 2010 data set, corresponding to 37 pb^{-1} collected by ATLAS. Jets with p_{T} > 20 GeV and |y| < 4.4 are considered in this analysis. The measurement of the jet shapes using the first 3 pb^{-1} is also presented, for jets with p_{T} > 30 GeV and |y| < 2.8. Both measurements are unfolded back to the particle level. Results are compared to theoretical predictions, showing the potential of the measurements to test QCD, and its importance in the search for new physics.
Several electroweak precision measurements are performed by the ATLAS and CMS collaborations at the LHC. The main ones are carried out using Drell-Yan production of single W and Z boson. They regard the measurement of the production cross sections of W and Z bosons, the mass of the W boson, and $\sin^2θ_W$. The results of the $\sin^2θ_W$ measurements have an accuracy of approximately twice that reached at LEP and SLD. Other measurements reported are about the Drell-Yan differential production cross section.
The properties of the Higgs boson measured in bosonic decay channels ($H \rightarrow γγ$, $H \rightarrow ZZ^* \rightarrow 4\ell$, $H \rightarrow WW^{*} \rightarrow \ellν\ellν$, $H \rightarrow Zγ$) with 25 fb$^{-1}$ of pp collision data from the Large Hadron Collider run-1 collected by the ATLAS experiment are presented. The results include an improved measurement of the mass of the Higgs boson from a combined fit to the invariant mass spectra of the decay channels $H \rightarrow γγ$ and $H \rightarrow ZZ^* \rightarrow 4\ell$, which yields $m_H = 125.36 \pm 0.37$ (stat) $\pm 0.18$ (syst) GeV = …
The mass of the Higgs boson is measured in the $H\rightarrow ZZ^* \rightarrow 4\ell$ and in the $H\rightarrow γγ$ decay channels with 36.1 fb$^{-1}$ of proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the $H\rightarrow ZZ^* \rightarrow 4\ell$ channel is $m_{H}^{ZZ^{*}} = 124.79 \pm 0.37$ GeV, while the measured value in the $H\rightarrow γγ$ channel is $m_{H}^{γγ} = 124.93 \pm 0.40$ GeV. Combining these results with the ATLAS measurement based on 7 TeV and 8 TeV proton-proton …
The results of the most recent measurements of the inclusive $\mathrm{t\bar{t}}$ cross section performed by the ATLAS and CMS experiments at the CERN LHC are summarized. These include results obtained in proton-proton collisions at different centre-of-mass energies, and the first observation of $\mathrm{t\bar{t}}$ production in proton-lead collisions. A new result at $\sqrt{s} = 13~\mathrm{TeV}$ by the CMS Collaboration is presented for the first time at this conference. In this analysis, the total cross section is determined both for a fixed top quark mass value in the simulation of $m_{\math…
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…
The latest results on the direct experimental search for a Standard Model Higgs boson decaying to a pair of Z bosons are presented. Three distinct final states are considered: $H\rightarrow ZZ^{(*)}\rightarrow \ell\ell\ell\ell$, $H\rightarrow ZZ\rightarrow \ell\ellνν$, and $H\rightarrow ZZ\rightarrow \ell\ell qq$, where $\ell = e, μ$. A dataset of more than 1fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 7$ TeV collected by the ATLAS detector at the CERN LHC during the on-going 2011 run is used. In this model and for these final states, Higgs boson masses in the ranges 192 GeV $< m_H < $…
The inclusive jet cross-section has been measured in proton-proton collisions at sqrt(s)=2.76 TeV in a dataset corresponding to an integrated luminosity of 0.20pb-1 collected with the ATLAS detector at the Large Hadron Collider in 2011. Jets are identified using the anti-kt algorithm with two radius parameters of 0.4 and 0.6. The inclusive jet double-differential cross-section is presented as a function of the jet transverse momentum pT and jet rapidity y, covering a range of 20 <= pT < 430 GeV and |y| < 4.4. The ratio of the cross-section to the inclusive jet cross-section measurement at sqrt…
Inclusive isolated-photon production in $pp$ collisions at a centre-of-mass energy of 13 TeV is studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 3.2 fb$^{-1}$. The cross section is measured as a function of the photon transverse energy above 125 GeV in different regions of photon pseudorapidity. Next-to-leading-order perturbative QCD and Monte Carlo event-generator predictions are compared to the cross-section measurements and provide an adequate description of the data.
An improved measurement of the mass of the Higgs boson is derived from a combined fit to the invariant mass spectra of the decay channels $H\rightarrow γγ$ and $H \rightarrow ZZ^{*} \rightarrow 4\ell$. The analysis uses the $pp$ collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at center-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 25 fb$^{-1}$. The measured value of the Higgs boson mass is $m_H$ = 125.36 $\pm$ 0.37 (stat) $\pm$ 0.18 (syst) GeV. This result is based on improved energy-scale calibrations for photons, el…
We present the measurement of the inclusive electron spectrum in proton-proton collisions at a centre-of-mass energy of 7 TeV, using 1.3 pb-1 of data collected by the ATLAS experiment at the Large Hadron Collider. Signal electrons in the transverse momentum range 7 < pt < 26 GeV and within |eta| <2.0, excluding 1.37<|eta|<1.52, are extracted from the dominant hadron and conversion backgrounds. After subtraction of the small W/Z/gamma* contribution, the cross-section as a function of pt is found to be in good agreement with theoretical predictions for heavy flavour production from Fixed Order N…
An inclusive search for the non-Standard Model production of two isolated leptons of the same electrical charge is presented. The search was performed with 2010 collision data in the ATLAS detector at the Large Hadron Collider for ee, eμ, and μμ channels. With 34 pb-1 of integrated luminosity, no disagreement with the Standard Model prediction was found, and limits on the fiducial cross section for generic same-sign production as well as four model-dependent limits for models of new physics were set. An updated same sign analysis with 1.6 fb-1 is underway and nearly complete for the μμ channel…
The inclusive $t\bar{t}$ production cross-section is measured in the lepton+jets channel using 20.2 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and $b$-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the W+jets process is modelled using Z+jets events in a data-based approach. The inclusive $t\bar{t}$ cross-section is m…
Inclusive jet and dijet double-differential cross sections have been measured in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector at the LHC. The cross sections were measured using jets clustered with the anti-kt algorithm. The measurements are performed in the jet rapidity range |y| < 4.4, covering jet transverse momenta from 20 GeV to 1.5 TeV and dijet invariant masses from 70 GeV to 5 TeV. The data are compared to expectations based on next-to-leading order QCD calculations corrected for non-perturbative effects, as well as to next-to-leading order Monte…
Recent results on inclusive charmless semileptonic decays of B mesons are reviewed. Emphasis is given to measurements on the recoil of fully reconstructed B mesons, which allow to exploit several regions of phase space. Preliminary averages of the CKM matrix element $|V_{ub}|$ from the Heavy Flavour Working Group are shown, using four different theoretical calculations.
The inclusive as well as differential cross section of the associated production of top-antitop quark pairs and a $Z$ boson ($t\bar{t}Z$) is measured in final states with exactly three or four isolated leptons (electrons or muons). For this purpose, the full LHC Run 2 dataset of proton-proton collisions recorded by the ATLAS detector from $2015$ to $2018$, which corresponds to an integrated luminosity of $139\,\text{fb}^{-1}$, is used. The inclusive production cross section is measured to be $σ_{t\bar{t}Z}=1.05\pm0.05\,(\text{stat.})\,\pm0.09\,(\text{syst.})\,\text{pb}$, which is in agreement …
A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a centre-of-mass energy sqrt(s) = 7TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<|eta|<1.81 in the transverse energy range 15 < E_T <100 GeV. The results are based on an integrated luminosity of 880 nb-1, collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based…
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 $\sqrt{s} = 8$ TeV and recorded by the ATLAS detector. Cross sections are obtained from measured $H \rightarrow γγ$ and $H \rightarrow ZZ ^{*}\rightarrow 4\ell$ 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, num…
We present a measurement of two-particle angular correlations in proton-proton collisions at sqrt(s) = 900 GeV and 7 TeV. The collision events were collected during 2009 and 2010 with the ATLAS detector at the Large Hadron Collider using a single-arm minimum bias trigger. Correlations are measured for charged particles produced in the kinematic range of transverse momentum pT > 100 MeV and pseudorapidity |eta| < 2.5. A complex structure in pseudorapidity and azimuth is observed at both collision energies. Results are compared to Pythia 8 and Herwig++ as well as to the AMBT2B, DW and Perugia 20…
A first measurement of the ttgamma cross section in pp collisions at the LHC using 1.04 fb^-1 of data taken with the ATLAS detector is presented. A total of 122 candidate events were identified in the single electron and single muon channels. The contributions from background processes with prompt photons, and with electrons or hadrons misidentified as photons were estimated reducing the dependence on simulations by the use of data-driven techniques. The resulting cross section times branching ratio into the single lepton and dilepton decay channels for photons with pt > 8 GeV reads σ_ttgamma …
The production cross sections of the inclusive Drell-Yan processes W to l nu and Z/gamma to ll (l=e,mu) are measured in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector. The cross sections are reported integrated over a fiducial kinematic range, extrapolated to the full range and also evaluated differentially as a function of the W decay lepton pseudorapidity and the Z boson rapidity, respectively. Based on an integrated luminosity of about 35 pb^-1 collected in 2010, the precision of these measurements reaches a few per cent. The integrated and the differential W+- and Z/ga…
A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and th…
A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb$^{-1}$ of 13 TeV proton-proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured $H \rightarrow γγ$ and $H \rightarrow ZZ^* \rightarrow 4\ell$ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0$^{+6.0}_{-5.9}$ (stat.) $^{+4.0}_{-3.3}$ (syst.) pb, in…
This paper describes the concept, technical realisation and validation of a largely data-driven method to model events with $Z\rightarrowττ$ decays. In $Z\rightarrowμμ$ events selected from proton--proton collision data recorded at $\sqrt{s}=8$ TeV with the ATLAS experiment at the LHC in 2012, the $Z$ decay muons are replaced by $τ$ leptons from simulated $Z\rightarrowττ$ decays at the level of reconstructed tracks and calorimeter cells. The $τ$ lepton kinematics are derived from the kinematics of the original muons. Thus, only the well-understood decays of the $Z$ boson and $τ$ leptons as wel…
Despite the absence of experimental evidence, weak scale supersymmetry remains one of the best motivated and studied Standard Model extensions. This report summarises recent ATLAS results on inclusive searches for supersymmetric squarks and gluinos, including third generation squarks produced in the decay of gluinos. Results are presented for both R-parity conserving and R-parity violating scenarios, with final states containing jets with and without missing transverse momentum, light leptons, taus or photons.
Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb$^{-1}$ recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-${k_t}$ algorithm with a radius parameter value of $R=0.4$. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to $|y|=3$. The double-differential dijet produ…
A measurement of charged-particle distributions sensitive to the properties of the underlying event is presented for an inclusive sample of events containing a Z-boson , decaying to an electron or muon pair. The measurement is based on data collected using the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 7 TeV with an integrated luminosity of $4.6$ fb$^{-1}$. Distributions of the charged particle multiplicity and of the charged particle transverse momentum are measured in regions of azimuthal angle defined with respect to the Z-boson direction. The measur…
This document presents a search for a $W'$ boson, decaying to a top quark and a $b$ quark in an effective coupling approach, using a multivariate method based on boosted decision trees. It reports exclusion limits on the $W'\rightarrow tb$ cross-section times branching ratio and effective couplings as a function of the $W'$-boson mass. The search covers $W'$-boson masses between 0.5 and 3.0 TeV, for right-handed or left-handed $W'$-boson, with 20.3 fb$^{-1}$ of proton-proton collision data produced by the LHC in 2012, at a center-of-mass energy of 8 TeV and collected by the ATLAS detector.
Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb-1 recorded at the Large Hadron Collider. The anti-kt algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidit…
Measurement of the muon charge asymmetry in inclusive $pp$$\rightarrow$$W(μν)$ + X at $\sqrt{s}$ = 8 TeV is presented. The data sample corresponds to an integrated luminosity of 18.8 $fb^{-1}$ recorded with the CMS detector at the LHC. With a sample of more than a hundred million $W$$\rightarrow$$μ$$ν$ events, the statistical precision is greatly improved in comparison to previous measurements. This new result can provide additional constraints on the parton distribution functions of the proton. This measurement is used together with the cross sections for inclusive deep inelastic ep scatterin…
An observation of the $Λ_b^0 \rightarrow ψ(2S) Λ^0$ decay and a comparison of its branching fraction with that of the $Λ_b^0 \rightarrow J/ψΛ^0$ decay has been made with the ATLAS detector in proton--proton collisions at $\sqrt{s}=8\,$TeV at the LHC using an integrated luminosity of $20.6\,$fb$^{-1}$. The $J/ψ$ and $ψ(2S)$ mesons are reconstructed in their decays to a muon pair, while the $Λ^0\rightarrow pπ^-$ decay is exploited for the $Λ^0$ baryon reconstruction. The $Λ_b^0$ baryons are reconstructed with transverse momentum $p_{\rm T}>10\,$GeV and pseudorapidity $|η|<2.1$. The measured bran…
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 the LHC at centre-of-mass energy $\sqrt{s}$ = 8 TeV. In the four-lepton invariant-mass range of $80<m_{4\ell}<1000$ GeV, an artificial neural network is used to enhance the separation between single- and double-parton scattering based on the kinematics of the four leptons in the final state. An upper limit on the fraction of events originating from double-parton scattering is determined at 95% …
Jet shapes have been measured in inclusive jet production in proton-proton collisions at sqrt(s) = 7 TeV using 3 pb^{-1} of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30 GeV < pT < 600 GeV and rapidity in the region |y| < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measure…
The ratio of the cross section for $p\bar{p}$ interactions producing a $Z$ boson and at least one $b$ quark jet to the inclusive $Z+{\rm jet}$ cross section is measured using $4.2\ {\rm fb}^{-1}$ of $p\bar{p}$ collisions collected with the \dzero\ detector at the Fermilab Tevatron collider at $\sqrt{s}=1.96$ TeV. The $Z\rightarrow\ell^+\ell^-$ candidate events with at least one $b$ jet are discriminated from $Z+$ charm and light jet(s) events by a novel technique that exploits the properties of the tracks associated to the jet. The measured ratio is $0.0193\pm0.0027$ for events having a jet wi…
The inclusive cross-section for jet production in association with a Z boson decaying into an electron-positron pair is measured as a function of the transverse momentum and the absolute rapidity of jets using 19.9 fb$^{-1}$ of $\sqrt s = 8$ TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The measured Z + jets cross-section is unfolded to the particle level. The cross-section is compared with state-of-the-art Standard Model calculations, including the next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations, correcte…
This paper presents combinations of inclusive and differential measurements of the charge asymmetry ($A_{\mathrm{C}}$) in top quark pair ($\mathrm{t}\overline{\mathrm{t}}$) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centre-of-mass energies of 7 and 8 TeV corresponding to integrated luminosities of about 5 and 20 fb$^{-1}$ for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are $A_{\mathrm{C}}^{\mathrm{LHC7}} = 0.005 \pm0.007 \text{ (stat)}\pm0.006 \text{ (syst)…
An angular analysis of the decay $B^0_d \rightarrow K^{*}μ^+μ^-$ is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb$^{-1}$ of integrated luminosity collected during 2012 at centre-of-mass energy of $\sqrt{s}=8$ TeV. Measurements of the $K^{*}$ longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.
The production of exclusive $γγ\rightarrow μ^+ μ^-$ events in proton--proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC, using data corresponding to an integrated luminosity of 3.2 fb$^{-1}$. The measurement is performed for a dimuon invariant mass of 12 GeV $<m_{μ^+μ^-}<$ 70 GeV. The integrated cross-section is determined within a fiducial acceptance region of the ATLAS detector and differential cross-sections are measured as a function of the dimuon invariant mass. The results are compared to theoretical predictions that include corrections…
Using the angular correlation between the $π^+$ emitted in a $D^{*+} \rightarrow D^0 π^+$ decay and the $e^+$ emitted in the subsequent $D^0 \rightarrow Xe^+ν$ decay, we have measured the branching fraction for the inclusive semi-electronic decay of the $D^0$ meson to be: {\cal B}(D^0 \rightarrow X e^+ ν) = [6.64 \pm 0.18 (stat.) \pm 0.29 (syst.)] \%. The result is based on 1.7 fb$^{-1}$ of $e^+e^-$ collisions recorded by the CLEO II detector located at the Cornell Electron Storage Ring (CESR). Combining the analysis presented in this paper with previous CLEO results we find, \frac{{\cal B} (D…
Measurements of the muon charge asymmetry in inclusive $pp \rightarrow WX$ production at $\sqrt{s}=7$ TeV are presented. The data sample corresponds to an integrated luminosity of 4.7 $\mathrm{fb^{-1}}$ recorded with the CMS detector at the LHC. With a sample of more than twenty million $W \rightarrow μν$ events, the statistical precision is greatly improved in comparison to previous measurements. These new results provide additional constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable $x$ from $10^{-3}$ to $10^{-1}$. These measurements ar…
A measurement of the Higgs boson production cross sections via associated $WH$ and $ZH$ production using $H \rightarrow WW^{\ast} \rightarrow \ellν\ellν$ decays, where $\ell$ stands for either an electron or a muon, is presented. Results for combined $WH$ and $ZH$ production are also presented. The analysis uses events produced in proton-proton collisions collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The data correspond to an integrated luminosity of 36.1 fb$ ^{-1}$ recorded at a centre-of-mass energy of 13 TeV. The products of the $H \rightarrow WW^{\ast}$ b…
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…
Recent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb^-1 of pp collisions delivered by the LHC at sqrt(s) = 7 TeV. In a subsample of events with single pp collisions, measurementes corrected for detector efficiency and resolution are presented w…
The ATLAS detector at the Large Hadron Collider is used to search for the lepton flavor violating process $Z \rightarrow e μ$ in pp collisions using 20.3 $fb^{-1}$ of data collected at $\sqrt{s}$ = 8 TeV. An enhancement in the $e μ$ invariant mass spectrum is searched for at the Z boson mass. The number of Z bosons produced in the data sample is estimated using events of similar topology, $Z \rightarrow ee$ and $μμ$, significantly reducing the systematic uncertainty in the measurement. There is no evidence of an enhancement at the Z boson mass, resulting in an upper limit on the branching frac…
The energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range $10<p_\textrm{T}<300$ GeV. The measurement is performed using 139 $\textrm{fb}^{-1}$ of LHC proton-proton collision data at $\sqrt{s}=13$ TeV taken in Run 2 by the ATLAS detector. Charged pions originating from $τ$-lepton decays are used to provide a sample of high-$p_\textrm{T}$ isolated particles, where the composition is known, to test an energy regime that has not previously been probed by in situ single-particle measurements. The calorimeter response to single-pions is o…
The sensitivity of the ATLAS experiment to the top-quark rare decay via flavor-changing neutral currents $t \rightarrow Zq$ ($q$ represents $c$ and $u$ quarks) has been studied at $\sqrt{s}$=14 TeV in two decay modes: 1.The pure leptonic decay of gauge bosons: $t\bar{t} \rightarrow ZqWb \rightarrow l^{+} l^{-} j l^{\pm} νb$ , (l=e, $μ$). 2.The leptonic decay of Z bosons and hadronic decay of W bosons: $t\bar{t} \rightarrow ZqWb \rightarrow l^{+} l^{-} jjjb$ , (l=e, $μ$). The dominant backgrounds $Z+jets$, $WZ$ and $t\bar{t}$ have been analysed. The signal and backgrounds were generated via PYT…
A measurement of the cross section for the inclusive production of isolated prompt photons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 8$ TeV is presented. The measurement covers the pseudo rapidity ranges $|η^γ| < 1.37$ and $1.56 \leq |η^γ| < 2.37$ in the transverse energy range $25 < E_{\rm T}^γ < 1500$ GeV. The results are based on an integrated luminosity of 20.2 fb$^{-1}$, recorded by the ATLAS detector at the LHC. Photon candidates are identified by combining information from the calorimeters and the inner tracker. The background is subtracted using a data-drive…
We measure the ratio of cross sections, $σ(p\bar{p}\rightarrow Z+2~b~\text{jets})$/$σ(p\bar{p}\rightarrow Z+\text{2 jets})$, for associated production of a $Z$ boson with at least two jets with transverse momentum $p_T^{\rm jet} > 20$ GeV and pseudorapidity $|η^{\rm jet}| < 2.5$. This measurement uses data corresponding to an integrated luminosity of 9.7 fb$^{-1}$ collected by the \DO experiment in Run II of Fermilab's Tevatron \ppbar Collider at a center-of-mass energy of 1.96 TeV. The measured integrated ratio of $0.0236\pm0.0032\left(\mbox{stat}\right)\pm0.0035\left(\mbox{syst}\right)$ is i…
Measurements of the variation of inclusive jet suppression as a function of relative azimuthal angle, Delta phi, with respect to the elliptic event plane provide insight into the path-length dependence of jet quenching. ATLAS has measured the Delta phi dependence of jet yields in 0.14 nb^-1 of sqrt(s(NN))= 2.76 TeV Pb+Pb collisions at the LHC for jet transverse momenta p_T > 45 GeV in different collision centrality bins using an underlying event subtraction procedure that accounts for elliptic flow. The variation of the jet yield with Delta phi was characterized by the parameter, v_2^jet, and …
This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a $Z$ boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 13 TeV with an integrated luminosity of 3.2 fb$^{-1}$. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the $Z$ boson direction. The measured distributions are compared with the predictions of va…
Charged Higgs bosons heavier than the top quark and decaying via $H^{\pm} \rightarrow tb$ are searched for in proton--proton collisions measured with the ATLAS experiment at $\sqrt{s}=8$ TeV corresponding to an integrated luminosity of 20.3 fb$^{-1}$. The production of a charged Higgs boson in association with a top quark, $gb \rightarrow tH^{\pm}$, is explored in the mass range 200 to 600 GeV using multi-jet final states with one electron or muon. In order to separate the signal from the Standard Model background, analysis techniques combining several kinematic variables are employed. An exce…
Production of prompt isolated photons at hadron colliders provides a probe of perturbative QCD and can be used to study the gluon density function of the proton. The ATLAS collaboration has performed precise measurements of the inclusive production of isolated prompt photons in 20.2 fb${}^{-1}$ of data collected at $\sqrt{s}=8$ TeV and in 6.4 pb${}^{-1}$ of data collected at $\sqrt{s}=13$ TeV. The measurements are compared with state-of-the-art theory predictions at NLO in QCD and with predictions of several MC generators. Production of inclusive jets at hadron colliders also provides a probe …
Inclusive jet production cross-sections are measured in proton--proton collisions at a centre-of-mass energy of $\sqrt{s}=$8 TeV recorded by the ATLAS experiment at the Large Hadron Collider at CERN. The total integrated luminosity of the analysed data set amounts to $20.2$ fb$^{-1}$. Double-differential cross-sections are measured for jets defined by the anti-$k_{t}$ jet clustering algorithm with radius parameters of $R=0.4$ and $R=0.6$ and are presented as a function of the jet transverse momentum, in the range between 70 GeV and 2.5 TeV and in six bins of the absolute jet rapidity, between …
The search of the "hidden sector" via new neutral light bosons Z-dark ($Z_{d}$) could be revealed by the study of the decay of the discovered Higgs-like boson or any other undiscovered Higgs boson. After the LHC concluded a successful first period of running, the ATLAS Collaboration published its latest results on the $H\rightarrow Z_{d}Z_{d}\rightarrow 4l$ analysis using up to 20 fb$^{-1}$ of integrated luminosity at $\sqrt{s}=8$ TeV. In this proceeding I present a summary of the recent results on the search of the $Z_{d}$ in the signature $H\rightarrow Z_{d}Z_{d}\rightarrow 4l$ with the ATLA…
The differential cross section for isolated-photon production in $pp$ collisions is measured at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC using an integrated luminosity of 36.1 fb$^{-1}$. The differential cross section is presented as a function of the photon transverse energy in different regions of photon pseudorapidity. The differential cross section as a function of the absolute value of the photon pseudorapidity is also presented in different regions of photon transverse energy. Next-to-leading-order QCD calculations from JETPHOX and SHERPA as well as next-to-ne…
The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb^-1. The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. …
