Search for a new $Z'$ gauge boson via the $pp \rightarrow W^{\pm(*)} \rightarrow Z' μ^{\pm} ν\rightarrow μ^{\pm}μ^{\mp}μ^{\pm}ν$ process in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
A search for a new $Z'$ gauge boson predicted by $L_μ-L_τ$ models, based on charged-current Drell-Yan production, $pp \rightarrow W^{\pm(*)} \rightarrow Z' μ^{\pm} ν\rightarrow μ^{\pm}μ^{\mp}μ^{\pm}ν$, is presented. The data sample used corresponds to an integrated luminosity of 140 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} = 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. The search examines a final state of $3μ$ plus large missing transverse momentum. Upper limits are set on the $Z'$ production cross-section times branching ratio in the mass range of 5-81 GeV. After combining with the previous $Z'$ search using the neutral-current Drell-Yan production with a $4μ$ final state, the most stringent exclusion limits to date are achieved in the parameter space of the $Z'$ coupling strength and mass.
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 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 < $…
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…
Proceeding for LHCP2017 conference. Referencing the ATLAS publication note: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2017-005/
New measurements from ATLAS at the LHC are presented on the total cross section at $\sqrt{s}=8$ TeV from elastic scattering using the ALFA sub-detector and on the inelastic cross section at $\sqrt{s}=13$ TeV using the MBTS sub-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 $\sqrt{s} = 8$ 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…
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…
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.
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…
We report on the observation of the charm mesons D^\ast \pm, D^\pm and D_s ^\pm with 1.4 nb^-1 of data, and of the J/psi-->mu+mu- resonance with 78 nb-1 of data from the ATLAS detector in 7 TeV proton-proton collisions at the LHC. The resultant signals support the high performance of the ATLAS detector as predicted from simulation and prospects for future measurements in the charm and charmonium sector.
This document presents a measurement of WZ production in 1.02 fb-1 of pp collision data at CME of 7 TeV collected by the ATLAS experiment at LHC in 2011. The production cross-section is measured to be consistent with the Standard Model (SM) prediction. Limits on anomalous triple gauge boson couplings have been derived.
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…
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…
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…
The production of events with multiple high transverse momentum particles including charged leptons and jets is measured, using 1.04 fb-1 of proton-proton collision data recorded by the ATLAS detector during the first half of 2011 at sqrt(s) = 7 TeV. No excess beyond Standard Model expectations is observed, and upper limits on the fiducial cross sections for non-Standard Model production of these final states are set. Using models for string ball and black hole production and decay, exclusion contours are determined as a function of mass threshold and the fundamental gravity scale.
The ATLAS detector has been used to search for high mass ee or mumu resonances, such as new heavy neutral gauge bosons. Over 1 fb^{-1} of proton-proton collisions at s = 7 TeV recorded by the ATLAS experiment are used to search for a high mass state decaying to dilepton pairs. No excess over Standard Model expectations is observed, and limits are placed on benchmark models predicting spin-1 and spin-2 resonances.
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…
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 $χ$ 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 $χ$ distributions excludes quark contact interactions with a compositeness scale $Λ$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
We present the results of a search for neutralinos decaying at a significant distance from their production point into charged hadrons and a high momentum muon, forming displaced vertexes. The analysis was performed with 33 pb^-1 of pp collision data collected by the ATLAS experiment at the LHC in 2010 at sqrt{s}= 7 TeV. The poster will show some highlights of the analysis.
The ATLAS detector has been used to search for high-mass states decaying into a single high momentum lepton and missing transverse energy, such as new heavy charged gauge bosons. The latest search results for a W Prime boson decaying to lepton plus neutrino in 1.04 fb^-1 of proton-proton collisions at a center of mass energy of 7 TeV produced at the Large Hadron Collider are presented.
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 Stand…
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 luminosity determination for the ATLAS detector at the LHC during pp collisions at $\sqrt{s}$ = 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of dL/L = +/- 1.9% is obtained for the 22.7 fb$^{-1}$ of pp collision data delivered to ATLAS at $\sqrt{s}$ = 8 TeV in 2012.
We report the observation of energetic jet production in proton-proton collisions at sqrt(s) = 7 TeV, based on about 1 nb^-1 of integrated luminosity collected by the ATLAS detector. The anti-kT algorithm is used to reconstruct jets with pT > 30 GeV and |y| < 2.8. Jets with pT up to ~500 GeV and events with dijet mass up to ~1 TeV are observed. The jet shapes and charged particle flow confirm that the observed jet signal corresponds to collimated flows of particles in the final state.
Studies of the spin, parity and tensor couplings of the Higgs boson in the $H\rightarrow ZZ^*\rightarrow 4\ell$, $H\rightarrow WW^* \rightarrow eνμν$ and $H\rightarrow γγ$ decay processes at the LHC are presented. The investigations are based on $25$ fb$^{-1}$ of $pp$ collision data collected by the ATLAS experiment at $\sqrt{ s} = 7$ TeV and $\sqrt{ s }= 8$ TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers $J ^P=0^+$, is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal coupling…
A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in root(s) = 7 TeV proton-proton collisions by the Large Hadron Collider (LHC) and correspond to an integrated luminosity of 315 nb^-1 collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% CL the q* mass interval 0.30 < m(q*) < 1.26 TeV, extending the reach of previous experiments.
Searches for high-mass resonances decaying to pairs of standard model bosons using ATLAS and CMS detectors are presented. The searches use 15 - 36 $\textrm{fb}^{-1}$ of proton-proton collision data collected at the centre-of-mass energy of 13 TeV at the LHC. Many different final states have been considered and the results are interpreted in a range of theories beyond the standard model of particle physics, most common being heavy vector triplet and warped extra dimensions.
This letter reports a measurement of the muon charge asymmetry from $W$ bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The asymmetry is measured in the $W \rightarrow μν$ decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb$^{-1}$. The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the $u$ and $d$ quark momentum fractions in the proto…
Invariant mass distributions of jet pairs (dijets) produced in LHC proton-proton collisions at a centre-of-mass energy sqrt(s)=7 TeV have been studied using a data set corresponding to an integrated luminosity of 1.0 fb^-1 recorded in 2011 by ATLAS. Dijet masses up to ~4 TeV are observed in the data, and no evidence of resonance production over background is found. Limits are set at 95% CL for several new physics hypotheses: excited quarks are excluded for masses below 2.99 TeV, axigluons are excluded for masses below 3.32 TeV, and colour octet scalar resonances are excluded for masses below 1…
Two recent measurements of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV are presented. The results are based on data collected in 2010 with the ATLAS detector at the Large Hadron Collider. The measurements cover the pseudorapidity ranges |eta(gamma)|<1.37 and 1.52<|eta(gamma)|<2.37 and the transverse energy range 15 < ET(gamma) < 400 GeV. The measured cross sections are compared to predictions from next-to-leading-order perturbative QCD calculations.
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-mass energy of 7 TeV corresponding to an integrated luminosity of 2.05/fb. No evidence for excited leptons is found, and limits are set on the compositeness scale Lambda as a function of the excited lepton mass m_l*. In the special case where Lambda = m_l*, excited electron and muon masses below 1.87 TeV and 1.75 TeV are excluded at 95% C.L., respectively.
The search for physics beyond the Standard Model (BSM) is one of the most important goals for the general purpose detector ATLAS at the Large Hadron Collider at CERN. Already with early LHC data, the ATLAS experiment should be sensitive to discover physics beyond the Standard Model. This paper summarizes the prospects of the ATLAS experiment to find experimental evidence for Supersymmetry (SUSY) and Universal Extra Dimensions (UED) in channels with jets, leptons and missing transverse energy for an integrated luminosity of L = 200pb-1 at a centre-of-mass energy sqrt s = 10 TeV. Only a selectio…
We present a search for new high mass phenomena using the latest data collected by the ATLAS detector at the LHC, corresponding to 36.1 fb$^{-1}$ at $\sqrt{s}$ = 13 TeV. The search is conducted for both resonant and non-resonant new phenomena in dimuon final states. The dimuon invariant mass spectrum is the discriminating variable used in the search. No significant deviations from the Standard Model expectation are observed. Lower limits are set on the signal parameters of interest at 95% credibility level, using a Bayesian interpretation. In particular, a Sequential Standard Model Z' resonanc…
A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at sqrt(s) = 7 TeV. The data sample corresponds to an integrated luminosity of 42 pb-1. No significant deviation from the Standard Model is observed in the dimuon mass spectrum, allowing the following 95% C.L. limits to be set on the energy scale of contact interactions: Lambda > 4.9 TeV (4.5 TeV) for constructive (destructive) interference in the left-left isoscalar compositeness model. These limits are the most stringent to date for mumuqq contact interactions…
A review of the searches for the SM Higgs boson produced in association with a pair of top quarks, ${t\bar{t}H}$, using up to 13.3 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector at the LHC is presented. Searches in the diphoton, multilepton and $b\bar{b}$ decay channels are summarised. The combination of these searches yields a measured (expected) significance for the observation of the ${t\bar{t}H}$ production process of $2.8 σ$ ($1.8 σ$).
We present a search for high-mass l+l- resonances in pp collisions at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment in 2011. No statistically significant excess above the Standard Model expectation is observed in a dataset corresponding to an integrated luminosity of approximately 1/fb. Consequently, upper limits are set on the cross-section times branching ratio of resonances decaying to muon pairs as a function of the resonance mass. In particular, a Sequential Standard Model Z' is excluded for masses below 1.83 TeV, and a Randall-Sundrum Kaluza-Klein graviton with coupli…
The coupling properties of the Higgs boson are studied in the four-lepton decay channel using 36.1 fb$^{-1}$ of $pp$ collision data from the LHC at a centre-of-mass energy of 13 TeV collected by the ATLAS detector. Cross sections are measured for the four key production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for $H \rightarrow ZZ^*$ decay and for a Higgs boson absolute rapidity below 2.5 is measured to be $1.73^{+0.24}_{-0.23}$(stat.)$^{+0.10}_{-0.08}$(exp…
The luminosity calibration for the ATLAS detector at the LHC during pp collisions at sqrt(s) = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at sqrt(s) = 7 TeV. A luminosity uncertainty of Delta L/L = +/- 3.5% is obtained for the 47 pb-1 of data delivered to ATLAS in 2010, and an uncertainty of Delta L/L = +/- 1.8% is obtained for the 5.5 fb-1 delivered in 2011.
Models with extra gauge symmetry were well motivated extensions of the Standard Model. In this paper, we search for an excess of events in search of a heavy neutral gauge boson Z which is fermiophobic. We are looking at llbb final states where the dilepton channel provides the most stringent constraint on the fermiophobic (FB) model. Since Z is fermiophobic, the production of such particles can occur via vector boson fusion, with subsequent decays into WW or Zh. We observe no significant excess of events over the background-only hypothesis and are able to put the constraint on efficiency times…
This proceeding presents the latest studies on the Yukawa couplings of the Standard Model Higgs boson with 139 fb$^{-1}$ data collected using the ATLAS detector at a center-of-mass energy of 13 TeV. A first direct probe of $CP$ violation in the top-quark Yukawa coupling using events where the Higgs boson is produced in association with top quarks ($t\bar{t}H$ and $tH$), and decays into two photons ($H \rightarrow γγ$ ) is discussed. The latest results on the Higgs boson production in association with a $W$ or $Z$ boson ($VH$) in the $H \rightarrow b \bar{b}$ channel are depicted as well. Final…
Weak scale supersymmetry is one of the best motivated and studied Standard Model extensions. It predicts the existence of new heavy coloured particles called squarks and gluinos which are the supersymmetric partners of the quarks and gluons, respectively. The poster summarises results on inclusive searches for supersymmetric squarks and gluinos in events containing jets and missing transverse momentum without leptons. The searches use the full data sample recorded in 2012 at $\sqrt{s}$=8~TeV centre-of-mass energy by the ATLAS experiment at the LHC.
The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W'), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a centre-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.7 fb-1. No excess beyond Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95% credibility level for masses up to 2.55 TeV. Excited chiral bosons (W*) with equivalent coupling strength are excluded for masses up to 2.42 TeV.
The ATLAS detector is used to search for high-mass states, such as heavy charged gauge bosons (W', W*) decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 36 pb-1. No excess beyond standard model expectations is observed. A W' with sequential standard model couplings is excluded at 95% confidence level for masses below 1.49 TeV, and a W*(charged chiral boson) for masses below 1.47 TeV.
The search for the production of the Higgs boson associated with a pair of top quarks in the ATLAS experiment is presented. It focuses on Higgs bosons decaying to $b\bar{b}$ and events containing two leptons (electrons and/or muons). It uses 20.3 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 8 TeV collected with the ATLAS detector at the LHC in 2012. No significant excess of events is found and the 95% CL observed (expected) limit is 7.0xSM (4.3xSM). After combining with the single lepton final state an observed (expected) limit of 4.1xSM (2.6xSM) with a best fit of $μ=1.7\pm1.4$ is obtaine…
With an integrated luminosity of 2.47 fb$^{-1}$ recorded by the ATLAS experiment at the LHC, the exclusive decays $B_{s}^{0}\rightarrow J/ψϕ$ and $B_{d}^{0}\rightarrow J/ψK^{*0}$ of $B$ mesons produced in $pp$ collisions at $\sqrt{s}=7$ TeV are used to determine the ratio of fragmentation fractions $f_s/f_d$. From the observed $B_{s}^{0}\rightarrow J/ψϕ$ and $B_{d}^{0}\rightarrow J/ψK^{*0}$ yields, the quantity $\frac{f_s}{f_d}\frac{\mathcal{B}(B_{s}^{0} \rightarrow J/ψϕ)}{\mathcal{B}(B_{d}^{0} \rightarrow J/ψK^{*0})}$ is measured to be 0.199 $\pm$ 0.004(stat) $\pm$ 0.008(sys). Using a recent …
A search for new phenomena in LHC proton-proton collisions at a center-of-mass energy of $\sqrt{s}=8$ TeV was performed with the ATLAS detector using an integrated luminosity of 17.3 fb$^{-1}$. The angular distributions are studied in events with at least two jets; the highest dijet mass observed is 5.5 TeV. All angular distributions are consistent with the predictions of the Standard Model. In a benchmark model of quark contact interactions, a compositeness scale below 8.1 TeV in a destructive interference scenario and 12.0 TeV in a constructive interference scenario is excluded at 95 % CL; m…
We discuss the early performance of the reconstruction of electrons and photons at ATLAS with a center-of-mass energy of 7 TeV. Using a data sample of about 15 nb^-1, we present a measurement of the transverse momentum distribution of inclusive electrons, as well as an observation of prompt photons and a measurement of the purity of this sample. We also demonstrate the reconstruction of J/psi mesons with a data sample of 78 nb^-1.
We report a measurement of the WW production cross section in pp collisions at 7 TeV. The WW leptonic decay channels are analyzed using data corresponding to 1.02 /fb of integrated luminosity collected by the ATLAS detector during 2011 at the CERN Large Hadron Collider. With 414 observed WW candidate events and an estimated background of 170$\pm$28 events, the measured WW production cross section is $48.2 \pm 4.0 {\rm(stat)} \pm 6.4 {\rm(syst)} \pm 1.8 {\rm(lumi)}$ pb, in agreement with the Standard Model NLO prediction of 46$\pm$3 pb.
A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the Large Hadron Collider (LHC) and correspond to an integrated luminosity of 315 nb^-1 collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark (q*) production as a function of q* mass. These exclude at the 95% CL the q* mass interval 0.30 < mq* < 1.26 TeV, extending the reach of previous experiments.
A search for new phenomena in events featuring a high energy jet and large missing transverse momentum in proton-proton collisions at sqrt(s) = 7 TeV is presented using a dataset corresponding to an integrated luminosity of 33 pb^-1 recorded with the ATLAS detector at the Large Hadron Collider. The number of observed events is consistent with the Standard Model prediction and this result is interpreted in terms of limits on a model of Large Extra Dimensions.
The B physics programme of the ATLAS experiment includes measurements of production cross sections, searches for rare B-decay signatures which are sensitive to new physics at the TeV energy scale and studies of CP violation effects in B-events, such as $B_{s}^{0}\rightarrow J/ψϕ$ and $B_{d}^{0}\rightarrow J/ψK_{s}^{0}$. The key to the detection of these B signals in ATLAS is to achieve a high trigger efficiency for low-$p_{T}$ di-muon events, whilst keeping an acceptable trigger rate. ATLAS developed two separate approaches for triggering on di-muon events from resonances such as $J/ψ$ and Ups…
A search for $W'$-boson production in the $W' \rightarrow t\bar{b} \rightarrow q\bar{q}' b\bar{b}$ decay channel is presented using 36.1 fb$^{-1}$ of 13 TeV proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search is interpreted in terms of both a left-handed and a right-handed chiral $W'$ boson within the mass range 1-5 TeV. Identification of the hadronically decaying top quark is performed using jet substructure tagging techniques based on a shower deconstruction algorithm. No significant deviation from the Standard Model predicti…
Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, $H\rightarrowγγ$, $H\rightarrow ZZ^{*}\rightarrow 4 \ell$ and $H\rightarrow W W \rightarrow \ellν\ellν$. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of about 25 fb$^{-1}$. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Hig…
