A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at $\sqrt{s} = 13$ TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb$^{-1}$. Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed.
Determination of the strong coupling constant $α_s$ from transverse energy-energy correlations in multijet events at $\sqrt{s} = 8$ TeV using the ATLAS detector
Determination of the strong coupling constant from transverse energy$-$energy correlations in multijet events at $\sqrt{s} = 13$ TeV with the ATLAS detector
A search for singly produced vector-like $T/Y$ quark is performed in proton-proton collision data at a centre-of-mass energy of $13$ TeV corresponding to an integrated luminosity of $139.1 fb^{-1}$, recorded with the ATLAS detector at the LHC from 2015-18. The analysis focused on the hadronic channel of $T/Y \rightarrow Wb$ decay mode. The hadronic channel is not a clean channel, unlike the leptonic channel, because of the contribution coming from the QCD processes, which accounts for a significant background. The modelling of QCD processes is challenging due to their theoretical prediction an…
Measurement of the $t$-channel single top-quark and top-antiquark differential cross-sections in $pp$ collisions at $\sqrt{s} = 8~\textrm{TeV}$ with the ATLAS detector
At the Large Hadron Collider (LHC), the most abundant processes which take place in proton-proton collisions are the generation of multijet events. These final states rely heavily on phenomenological models and perturbative corrections which are not fully understood, and yet for many physics searches at the LHC, multijet processes are an important background to deal with. It is therefore imperative that the modelling of multijet processes is better understood and improved. For this reason, a study has been done with several state-of-the-art Monte Carlo event generators, and their predictions a…
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 ri…
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 factor of four increase in the LHC luminosity, from $0.5\times 10^{34}\,\textrm{cm}^{-2}\textrm{s}^{-1}$ to $2.0\times 10^{34}\textrm{cm}^{-2}\textrm{s}^{-1}$, and the corresponding increase in pile-up collisions during the 2015-2018 data-taking period, presented a challenge for ATLAS to trigger on missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achiev…
Inclusive and differential cross section measurements of $\textrm{t}\overline{\textrm{t}}$-associated processes are performed at the ATLAS and CMS Collaborations with high precision. In this contribution, a selection of recent measurements of inclusive and differential measurements of the $\textrm{t}\overline{\textrm{t}}γ$, $\textrm{t}\overline{\textrm{t}}\textrm{Z}$ and $\textrm{t}\overline{\textrm{t}}\textrm{W}$ processes are presented. Searches for $\textrm{t}\overline{\textrm{t}}\textrm{t}\overline{\textrm{t}}$ production are presented for both collaborations, providing evidence for the pr…
Dark matter particles, if sufficiently light, may be produced in decays of the Higgs boson. This Letter presents a statistical combination of searches for $H\to\textrm{invisible}$ decays where $H$ is produced according to the Standard Model via vector boson fusion, $Z(\ell\ell)H$, and $W\!/\!Z(\textrm{had})H$, all performed with the ATLAS detector using 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of $\sqrt s = 13$ TeV at the LHC. In combination with the results at $\sqrt s = 7$ and 8 TeV, an exclusion limit on the $H\to\textrm{invisible}$ branching ratio of $0.26 (0.17^{+0.07}…
Universal Extra Dimension (UED) is a well-motivated and well-studied scenario. One of the main motivations is the presence of a dark matter (DM) candidate namely, the lightest level-1 Kaluza-Klein (KK) particle (LKP), in the particle spectrum of UED. The minimal version of UED (mUED) scenario is highly predictive with only two parameters namely, the radius of compactification and cut-off scale, to determine the phenomenology. Therefore, stringent constraint results from the WMAP/PLANCK measurement of DM relic density (RD) of the universe. The production and decays of level-1 quarks and gluons …
A measurement of the mass of the $W$ boson is presented based on proton-proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb$^{-1}$ of integrated luminosity. The selected data sample consists of $7.8 \times 10^6$ candidates in the $W\rightarrow μν$ channel and $5.9 \times 10^6$ candidates in the $W\rightarrow e ν$ channel. The $W$-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the $W$ boson transverse mass in the electron and muon …
Measurements of jet production are sensitive to the strong coupling constant, high order perturbative calculations and parton distribution functions. In this talk we present the most recent ATLAS measurements in this area at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV. We present measurements of variables probing the properties of the multijet energy flow and of the Lund Plane using charged particles. We will also present new measurements sensitive to the strong coupling constant. For jet fragmentation, we present a measurement of the fragmentation properties of $b$-quark initiated jets, st…
A new measurement of elastic $pp$ scattering at $\sqrt{s} = 13$ TeV with the ATLAS-ALFA detector is presented. The measurement was performed using data recorded in a special run of the LHC with $β^\star = 2.5$ km. The elastic cross-section was measured differentially in the Mandelstam $t$ variable and from a fit to ${\textrm{d}}σ/\textrm{d}t$ the total cross section, the $ρ$-parameter and parameters of the nuclear slope are determined. The results for $σ_{\textrm{tot}}$ and $ρ$ are \begin{equation*} σ_{\textrm{tot}}(pp\rightarrow X) = \mbox{104.7} \; \pm 1.1 \; \mbox{mb} , \; \; ρ= \mbox{0.098…
Measurement of the top pair production cross-section in 8 TeV proton-proton collisions using kinematic information in the lepton+jets final state with ATLAS
Measurements of Higgs boson production via gluon-gluon fusion and vector-boson fusion using $H\rightarrow WW^\ast \rightarrow \ellν\ellν$ decays in $pp$ collisions with the ATLAS detector and their effective field theory interpretations
The production yield of $Z$ bosons is measured in the electron and muon decay channels in Pb+Pb collisions at $\sqrt{s_{\textrm{NN}}}$ = 5.02 TeV with the ATLAS detector. Data from the 2015 LHC run corresponding to an integrated luminosity of 0.49 $\textrm{nb}^{-1}$ are used for the analysis. The $Z$ boson yield, normalised by the total total number of minimum-bias events and the mean nuclear thickness function, is measured as a function of dilepton rapidity and event centrality. The measurements in Pb+Pb collisions are compared with similar measurements made in proton$-$proton collisions at t…
Measurements of the Higgs boson production, fiducial and differential cross-sections in the four lepton decay channel using 164 fb$^{-1}$ of data collected at $\sqrt{s}$ = 13.6 TeV with the ATLAS detector
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)（欧洲核子研究组织（CERN））
A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector-boson fusion process and the dominant Higgs boson decay into $b$-quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$=13 TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final-state signature is $1.3 \pm 1.0$ times the Standard Model prediction. The obs…
Measurement of the $ZZ$ production cross section in $pp$ collisions at $\sqrt{s}$ = 8 TeV using the $ZZ\to\ell^{-}\ell^{+}\ell^{\prime -}\ell^{\prime +}$ and $ZZ\to\ell^{-}\ell^{+}ν\barν$ channels with the ATLAS detector
A search is presented for new phenomena in events characterised by high jet multiplicity, no leptons (electrons or muons), and four or more jets originating from the fragmentation of $b$-quarks ($b$-jets). The search uses 139 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider during Run 2. The dominant Standard Model background originates from multijet production and is estimated using a data-driven technique based on an extrapolation from events with low $b$-jet multiplicity to the high $b$-jet multiplicities used in th…
Search for magnetic monopole pair production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{_\textrm{NN}}}=5.36$ TeV with the ATLAS detector at the LHC
Search for single production of a vector-like quark via a heavy gluon in the $4b$ final state with the ATLAS detector in $pp$ collisions at $\sqrt{s} = 8$ TeV
搜索进行的过程$pp \to G^* \to B_H\bar b/\bar B_H b \to H b \bar b \to b\bar bb\bar b$，预测在复合希格斯粒子的情况下，其中$G^*$是一个沉重的颜色八重矢量共振和$B_H$矢量夸克的电荷$-1/3$。这些数据是从$pp$碰撞中获得的，质心能量为8 TeV，对应的积分光度为19.5 fb $^{-1}$，由ATLAS探测器记录在LHC上。最大的背景，多射流生产，估计使用数据驱动的方法。没有观察到相对于标准模型预测的显著过量的事件，并且设定了生产横截面乘以分支比的上限。比较从一个特定的基准模型的预测，导致在二维质量平面的$m_{G^*}$与$m_{B_H}$的质量下限。
Measurement of coherent exclusive $J/ψ\toμ^+μ^-$ production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{\textrm{NN}}}=5.36$ TeV with the ATLAS detector
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN)（欧洲核子研究中心）
Measurement of the charge asymmetry in top-quark pair production in the lepton-plus-jets final state in $pp$ collision data at $\sqrt{s}=8$ TeV with the ATLAS detector
Search for charged-lepton-flavour violating $μτqt$ interactions in top-quark production and decay in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector at the LHC
This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, $H \rightarrow b\bar{b}$, for proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy $\sqrt{s}=13$ TeV. These decays are reconstructed from calorimeter jets found with the anti-$k_{t}$ $R = 1.0$ jet algorithm. To tag Higgs bosons, a combination of requirements is used: $b$-tagging of $R = 0.2$ track-jets matched to the large-$R$ calorimeter jet, and requirements on the jet mass and other jet substructu…
