A hypothetical dark Higgs boson was proposed in a dark matter (DM) model to explain the origin of mass in dark sector as well as to open up new annihilation channel relaxing the DM relic density constraint from cosmological observation. The search focusing on Majorana DM produced with a low mass dark Higgs boson decaying to two b-quarks is proposed and working in progress using the 139fb-1...
Dark Matter (DM) searches are of great importantance to the LHC program. In this talk, I will first present a DM search using the Higgs boson as a portal. This search targets events that contain large missing transverse momentum and either two $b$-tagged small-radius jets or a single large-radius jet associated with two $b$-tagged sub-jets. No significant excess with respect to the SM...
Extending the Standard Model (SM) with a new strongly coupled dark sector can generate models with both an experimentally accessible dark meson production mechanism and a viable dark matter candidate particle. A search for dark mesons is presented in an integrated luminosity of 139 $\mathrm{fb^{-1}}$ of proton-proton collision data at a center of mass energy of 13 TeV with the ATLAS detector...
Four top-quark production, a rare process in the Standard Model (SM) with a cross-section around 12 fb, is one of the heaviest final states produced at the LHC, and it is naturally sensitive to physics beyond the Standard Model (BSM). A data excess is observed with twice of the expectation. A follow-up analysis is the search for Heavy (pseudo)Higgs boson A/H produced in association with a...
New long-lived particles are a feature of many extensions to the Standard Model and may elude searches for promptly decaying particles. An analysis of data collected in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron Collider is described, focusing on identifying signatures of jets produced by long-lived particles decaying to Standard Model fermions within...
Vector-like quarks (VLQ) are predicted in many extensions to the
Standard Model (SM) as their vector-like nature allows them to extend
the SM while still being compatible with electroweak sector
measurements. Pair production of VLQ provides a model-independent
method of searching due to the QCD production of the particles. While
most searches have focused on VLQs that decay to an SM...
A search for a fermi-phobic heavy Higgs boson via the $pp \rightarrow W^{\pm}H \rightarrow W^{\pm}W^{\pm}W^{\mp}$ process with 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=13~\text{TeV}$ collected by the ATLAS detector is presented.
The heavy Higgs boson has potential dimension-6 effects in an effective field theory context, which can cause significant kinematic deviations from those...
Studies of Higgs boson pair production (hh) represent the next crucial step to constraining the Higgs sector and allow the chance to refine measurements of the Higgs boson self-coupling. While previous searches have focused on the hh production in the gluon-gluon fusion (ggF) and vector-boson fusion (VBF) modes, this analysis documents a new search, with 139 fb-1 of pp collisions at $\sqrt{s}$...
Top quark pair-production in association with one or two additional $b$-jets is one of the main backgrounds in the search for $t\bar{t}+H$ production, and in BSM physics searches involving top and bottom quarks in the final states. Precise measurement of $t\bar{t}+b$ and $t\bar{t}+bb$ differential cross sections will help to significantly reduce systematic and modeling uncertainties in future...
A measurement of the $B_s^0\rightarrow J/\psi\phi$ decay parameters using $80~\mathrm{fb}^{-1}$ of integrated luminosity collected with the ATLAS detector from $13~\mathrm{TeV}$ proton-proton collisions at the LHC is presented. The measured parameters include the $\textit{CP}$-violating phase $\phi_s$, the width difference $\Delta\Gamma_s$ between the $B_s^0$ meson mass eigenstates and the...
A comparison of three flavor scheme, four flavor scheme and five flavor scheme has been performed using top quark pair-production with additional charm jet $(t\bar{t}+c)$ events simulated by MadGraph and showered by Pythia8. Spectra of additional c-jets that do not originate from the top quark decay are compared in the three schemes. These studies are motivated by the upcoming $t\bar{t}+c$...
This talk will present a search strategy for Higgs boson pair-production in final states with three electrons or muons. The analysis is performed using an integrated luminosity of 139 fb$^{-1}$ of $pp$ collision at $\sqrt{s}= 13$ TeV collected by the ATLAS detector at the LHC. There are many decay modes of Higgs boson pairs that have low branching ratios, and many of these are not covered by...
A combination of searches for Higgs boson pair production is performed using up to 139 fb$^{-1}$ of proton-proton collision data at a center-of-mass energy $\sqrt{s} = 13$ TeV recorded with the ATLAS detector at the LHC. The combination exploits three analyses searching for $HH$ decays to $bb\gamma\gamma$, $bb\tau\tau$ and $bbbb$. Results are interpreted in the context of non-resonant and...
This unique analysis investigates the production of two photons in conjunction with heavy flavor quarks using the ATLAS detector at the Large Hadron Collider at CERN using the full Run 2 dataset with a center-of-mass energy of $\sqrt{s}= 13$ TeV. The $\gamma\gamma$ + heavy flavor jets process is a dominant background in at least two important analyses: the $HH\rightarrow\gamma\gamma bb$...
Searches for di-Higgs production are some of the most exciting new results at the LHC. This talk will present the latest ATLAS HH combination results with the full Run 2 dataset of 139/fb at $\sqrt{s}=13$ TeV. By combining results from three different complementary search channels, bbγγ, bbττ, and bbbb, the HH combination has high sensitivity in both non-resonant and resonant interpretations....
A measurement of the Higgs boson cross section using H -> tau tau decays is performed, with the result split into 4 production modes, with both hadronic and semi-hadronic decays considered. Data was taken by the ATLAS detector during Run 2 of CERN's Large Hadron Collider, with a center-of-mass energy of 13 TeV, resulting in 139 fb^{-1} of proton-proton collision data. Full unblinded results...
We present a prospect study on di-Higgs production in the $HH \rightarrow b\bar{b}\gamma\gamma$ decay channel with the ATLAS experiment at the High Luminosity LHC (HL-LHC). The results are obtained by extrapolating the results from the Run 2 measurement, with 139 fb$^{-1}$ of data at a center-of-mass energy of 13 TeV, to the conditions expected at the HL-LHC. While there is no sign of di-Higgs...
The Large Hadron Collider (LHC) will be upgraded to increase its luminosity by a factor of 7.5 relative to the design luminosity. The ATLAS detector will undergo a major upgrade to fully explore the physics opportunities provided by the upgraded LHC. In order to optimize trigger efficiencies at the High-Luminosity LHC (HL-LHC), the Muon Spectrometer will be upgraded by replacing the MDT...
The Large Hadron Collider is expected to reach an instantaneous luminosity of $5-7.5\times10^{34}cm^{-2}s^{-1}$ towards high-luminosity runs in the future. The ATLAS Phase-Ⅰ upgrade plans to replace the present innermost station of Muon Spectrometer in the forward region, Small Wheels, with the New Small Wheel (NSW) detector system in order to improve Level-1 muon trigger selectivity and...
The muon spectrometer of the ATLAS detector at the LHC consists of thousands of muon precision chambers. Precise muon track reconstruction is crucial in order to achieve the physics goals of the ATLAS experiment, but attaining the required level of precision is not trivial due to the size and nature of the muon detectors. To reach the 80 microns precision needed to obtain a 10% precision on 1...
New small Monitored Drift Tube (sMDT) chambers were developed by the Max Planck Institute (MPI) for the ATLAS muon spectrometer upgrade. The smaller tube size allows sMDT chambers to cope with the increased luminosity of the High Luminosity LHC (HL-LHC) and make space for additional Resistive Plate Chamber (RPC) layers. The University of Michigan will construct 48 sMDT chambers containing...
To accommodate the high trigger-rate conditions at the High Luminosity Large Hadron Collider (HL-LHC) in Run 4 and onwards, the Monitoring Drift Tube (MDT) chambers in the inner barrel layer of the ATLAS muon spectrometer will be replaced with new small-diameter MDTs. The upgrade will allow for better muon tracking resolution and for the installation of new Resistive Plate Chambers (RPCs) to...
The New Small Wheel (NSW) phase-I upgrade is an extremely challenging project for high-luminosity LHC operations to improve both tracking and trigger capability of the ATLAS muon spectrometer for discoveries at the LHC.
NSW consists of two types of new detectors, the small-strip Thin Gap Chambers (sTGCs) and the MicroMegas (MM) chambers, both are capable of precision tracking and fast...
In preparation for the high-luminosity LHC (HL-LHC), the ATLAS detector will be upgraded with a new silicon-strip charged-particle tracking detector (ITk strip detector) to satisfy the radiation, granularity and timing requirements. The AMACStar (Autonomous Monitor and Control) is one of three ITk application-specific integrated circuits (ASICs). It is designed to monitor and control...
The High-Luminosity Large Hadron Collider (HL-LHC) is expected to deliver 10 times the integrated luminosity as the previous three runs combined, with approximately 200 inelastic collisions per bunch crossing. This large increase in pileup imposes significant challenges on the ATLAS Trigger and Data Acquisition system hardware electronics. To meet this challenge, the Global Trigger is designed...
Tau decays are notoriously difficult to detect because many particles decay with a similar signature. When searching for taus, capturing data from tau-lookalikes has been an ongoing problem, and previous global tau trigger algorithms have only had access to coarse granularity data from the calorimeters. The upgrade of the ATLAS Trigger and Data Acquisition system for the High-Luminosity Large...
The increased radiation environment and data rate for the High Luminosity Large Hadron Collider (HL-LHC) require upgrades to the readout electronics for the Muon Spectrometer (MS) electronics. In this talk, I will present ongoing irradiation studies of a custom-built front-end electronics board, the chamber service module (CSM), which is responsible for multiplexing data read out from...
The ATLAS experiment is currently preparing for an upgrade of the inner tracking detector for High-Luminosity LHC operation, scheduled to start in 2027. The new detector, known as the Inner Tracker or ITk, employs an all-silicon design with five inner Pixel layers and four outer Strip layers. The staves are the building blocks of the ITk Strip barrel layers. Each stave consists of a...
We are exploring Hough Transform (HT) algorithms in FPGAs to identify charged particle trajectories in the ATLAS detector at the HL-LHC. The Inner Detector of the ATLAS experiment measures the trajectories of charged particles in a uniform magnetic field. Our approach is to perform the Hough transformation pattern identification in two steps. The “first-stage” HT uses parameter space in phi0...
The inner tracking detector of the ATLAS experiment at CERN is currently preparing for an upgrade to operate in the High Luminosity LHC, scheduled for the late 2020s. A complete replacement of the existing Inner Detector of ATLAS is required to cope with the expected luminosity and radiation damage. The all-silicon Inner Tracker (ITk) design under construction composes a mixture of Pixel and...
Reconstructing the type and energy of isolated pions from the ATLAS calorimeters is a key step in hadronic reconstruction. The existing methods were optimized early in the experiment lifetime. We recently showed that image-based deep learning can significantly improve the performance over these traditional techniques. This note presents an extension of that work using point cloud methods...
The separation of quark and gluon initiated jets(q/g jets) is crucial to enhance the reach of many new physics searches at the ATLAS experiment in the Large Hadron Collider. A tagger serving as a tool to distinguish quark and gluon jets is developed based on the Boosted Decision Tree using charged-particle track observables associated with the jet. However, quark-versus-gluon jet tagging is...
In the Standard Model of particle physics, the spontaneous symmetry breaking of the complex Higgs field gives rise to the massive Higgs boson and three Goldstone bosons, which represent the longitudinal degrees of freedom of the $W^{\pm}$ and $Z$ bosons. It is therefore critical to study the interactions of longitudinally-polarized $W^{\pm}$ and $Z$ bosons ($W^{\pm}_0$ and $Z_0$). Here, we...
The production of a single electroweak vector boson in association with jets (V+jets) is one of the fundamental processes at the Large Hadron Collider (LHC) experiment. The leptonic decay modes of this process provides a clean experimental signature for measuring the electroweak sector of the Standard Model and the perturbative QCD accuracy in multi-jets final states.
In the talk, we will...
The Standard Model predicts self interactions between gauge bosons, including triple gauge boson couplings (TGC) and quartic gauge boson couplings (QGC). In addition, the interactions between the Higgs boson and gauge bosons are also of interest. In ATLAS group, events with four leptons (electrons or muons) in the final state are used to search for the production of WWZ -> lvlvll. The total...
Measurements of multi-jet cross-section ratios are presented.
The measured quantities are the ratio of the four-jet and three-jet
cross-sections and the ratio of the four-jet and two-jet cross-sections.
The data were collected with the ATLAS detector in proton-proton
collisions at a center of mass energy of 13 TeV during 2015-2018.
The results are presented as a function of the transverse...
The cross-sections of prompt and non-prompt production of $J/\psi+W^{\pm}$ are being measured by the ATLAS Collaboration using the $139~\textrm{fb}^{-1}$ Run II 13 TeV $pp$ collision data set. The prompt production of $J/\psi$ associated with a $W^{\pm}$, where both particles are produced in a single parton-parton interaction, provides constraints on models of non-relativistic QCD, especially...
Measurements of the production rate of Z bosons in association with heavy quarks provide sensitive tests of perturbative quantum chromodynamics (pQCD) predictions, which are made at next-to-leading-order (NLO) accuracy using either a 4-flavor number scheme (4FNS) or 5-flavor number scheme (5FNS). In the 4FNS, b-quarks are not present in the parton distribution functions (PDFs) and only appear...
Supersymmetry is a natural solution to many phenomena left unexplained by the Standard Model, such as the hierarchy problem that arises due to quantum corrections to the Higgs boson mass. Models which allow for R-parity violation (RPV) are favored by recent lepton flavor anomalies and can provide insight into the neutrino mixing hierarchy. The direct pair ...
Higgsinos with compressed mass spectra and masses near the electroweak scale are highly motivated by naturalness considerations and consistent with cosmological evidence, yet still poorly constrained by the LHC. This search will focus on the neutralino mass splitting $Δm=m_{{\widetilde{χ}}_2^0}-m_{{\widetilde{χ}}_1^0}$, in the region of 0.3~2 GeV, which has not been covered by ATLAS analyses...
One of the challenges of the ATLAS missing transverse momentum trigger is understanding how the trigger rate will evolve with the number of proton collisions per bunch crossing, or pileup. In the past, the data have been fit to parametric functions and extrapolated to higher pileup values. In this poster, we present a new technique using machine learning regression models to describe the...
In Higgs portal models, it is predicted that the Higgs boson could decay into dark matter particles. We may be able to detect these processes with the ATLAS detector, located at the Large Hadron Collider in Geneva Switzerland. There are many different production modes of the Higgs boson that could be used in a search for these Higgs boson to invisible decays, and when used together they...
The most challenging ATLAS Phase I upgrade project during Long Shutdown 2 (2019-2021) is the New Small-Wheel (NSW) for Muon Spectrometer. The main purpose of the NSW upgrade is to improve the performance of muon triggering and precision tracking for the High-Luminosity Large-Hadron-Collider (HL-LHC), which will deliver 3,000 fb-1 of data at √s = 14 TeV. The NSW will feature two new detector...
The Monitored Drift Tube (MDT) provides precise tracking and momentum measurement in the ATLAS muon spectrometer. To accommodate higher event rates and provide better fake rejection in the High Luminosity LHC, a new integrated chamber with small-diameter MDT (sMDT) and thin Resistive Plate Chambers (tRPC) had been developed and will be installed into barrel inner layer of the muon detector for...
The ATLAS detector at the LHC is subject to millions of events per second. ATLAS employs a trigger system to select events of high-importance for offline storage. To ensure the triggers are working as expected, we use a software tool called xMon, which has been in operation in the ATLAS control room for a decade. xMon works by predicting the trigger rate based on offline fits from previous...
The ATLAS detector at the LHC is subject to millions of events per second. ATLAS employs a trigger system to select events of high importance for offline storage. To ensure the triggers are working as expected, we use a software tool called xMon, which has been in operation in the ATLAS control room for a decade. xMon works by predicting the trigger rate based on offline fits from previous...
A search for resonant Higgs boson pair production in the four b-jet final state is conducted. The analysis uses 139 fb$^{-1}$ of pp collision data at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector. The analysis is divided into two regimes, targeting Higgs boson decays which are reconstructed as pairs of b-tagged small-radius jets or as single large-radius jets associated with b-tagged...
Following the discovery of the Higgs boson in 2012 by both the ATLAS and CMS experiments, a wealth of papers have been published concerning measurements or observations of the Higgs' decay modes. However, the most dominant decay mode, $H→b\bar{b}$, proved to be an elusive and challenging search due to the low signal-to-background environment, and a diverse range of backgrounds arising from...
The Standard Model (SM) of particle physics explains many natural phenomena yet remains incomplete. Vector-like quarks (VLQs) lie at the heart of many extensions to the SM seeking to address the hierarchy problem. VLQs could be produced either singly or in pairs, and then decay to a SM boson and a third-generation quark. While single-production depends on the coupling of the VLQ to the SM...
The High-Luminosity Large Hadron Collider (HL-LHC) project, a planned upgrade to the Large Hadron Collider (LHC) at CERN, is scheduled to begin colliding protons at unprecedented instantaneous luminosity later this decade. The HL-LHC will deliver an unprecedented proton-proton collision dataset to the LHC experiments at a center-of-mass energy of 14 TeV. The experiments - ATLAS, CMS, LHCb, and...
WWW production was recently observed by the ATLAS collaboration using the full Run II data set with an integrated luminosity of 139 fb$^{-1}$ at $\sqrt{s} = 13$ TeV. These first observation and cross-section measurements are presented. Measurements are performed in two final states. Events with two same-sign electrons or muons in association with two jets as well as events with three charged...
Higgsinos with masses near the electroweak scale and within a compressed mass spectrum represent a poorly constrained region of the SUSY parameter space that is nonetheless strongly motivated by both naturalness and dark matter considerations. In this talk we develop a search for higgsinos in compressed scenarios by studying the production of the second lightest neutralino ($\tilde{\chi}^0_2$)...
