In pp collisions at LHC energies, the production of heavy quarks proceeds from the hard scattering and then these quarks hadronise in either open heavy-flavor hadrons or quarkonia (e.g. J/$\psi$, $\psi(2S)$, $\Upsilon$). The study of quarkonium production as a function of charged-particle multiplicity links soft and hard processes and allows to study their interplay. While a linear increase of...
The electronics of the CMS (Compact Muon Solenoid) DT (Drift Tubes) chambers will need to be replaced for the HL-LHC (High Luminosity Large Hadron Collider) operation due to the increase of occupancy and trigger rates in the detector, which cannot be sustained by present system. A system is being designed that will forward asynchronously the totality of the chambers signals to the control...
The powerful photon fluxes of relativistic nuclei provide the possibility to study photonuclear and two-photon interactions in ultra-peripheral collisions (UPC), where the nuclei do not overlap and no strong nuclear interactions occur. Within the Vector Meson Dominance Model (VDM), the rho0 contribution dominates the QCD part of the photon structure function. The gamma+A → rho0+A process in...
Liquid argon (LAr) sampling calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region |η| < 3.2, and for hadronic and forward calorimetry in the region from |η| = 1.5 to |η| = 4.9. In the first LHC run a total luminosity of 27 fb−1 has been collected at center-of-mass energies of 7-8 TeV. After detector consolidation during a long shutdown, Run-2...
The LHC is expected to increase its centre-of-mass energy to 14 TeV and to keep longer time with an instantaneous luminosity of about 2.0×10^34 cm^-2s^-1 for Run-3 scheduled from 2021 to 2024. In order to cope with the high event rate, upgrades of the ATLAS trigger system are required. The level-1 Endcap Muon trigger system identifies muons with high transverse momentum by combining data from...
Modern particle physics analysis is carried out using sophisticated programming and coding. How, therefore, can we genuinely introduce students to experimental particle physics analysis without an initial exposure to the coding behind? The answer from ATLAS Open Data is to build tools for interactive data visualisation. Web-based resources such as the “Histogram Analyser”, “ATLAS detector...
The ATLAS experiment at the Large Hadron Collider is collecting unprecedented amounts of proton–proton collision data. The ATLAS Collaboration analyses these data, seeking to give answers to questions that have puzzled particle physicists for many decades now. In this process, the Standard Model is being precisely measured and searches for new physics are performed in sophisticated and clever...
The Virtual Visit service run by the ATLAS Collaboration has been provided since 2010. The ATLAS Collaboration has used this popular and effective method to bring the excitement of scientific exploration and discovery into classrooms and other public places around the world. The programme, which uses a combination of video conferencing, webcasts, and video recording to communicate with remote...
The existing CMS endcap calorimeters will be replaced with a High Granularity Calorimeter (HGCAL) for operation at the High-Luminosity (HL) LHC. Radiation hardness and excellent physics performance will be achieved by utilising silicon pad sensors and SiPM-on-scintillator tiles with high transverse and longitudinal segmentation. One of the major challenges of the HL-LHC will be the high pileup...
The luminosity measurement of the CMS experiment is calibrated under special beam conditions with beam separation scans called Van der Meer (VdM) scans. In a VdM scan, the two proton beams are separated transversely and moved in steps across each other. From the rate measurement of a luminosity detector as function of the transverse beam separation, the absolute luminosity scale is inferred...
We study discovery prospects for a real triplet extension of the Standard Model scalar sector at the Large Hadron Collider (LHC) and a possible future 100TeV $pp$ collider. We focus on the scenario in which the neutral triplet scalar is stable and contributes to the dark matter relic density. When produced in $pp$ collisions, the charged triplet scalar decays to the neutral component plus a...
To meet new TDAQ buffering requirements and withstand the high expected radiation doses at the high-luminosity LHC, the ATLAS Liquid Argon Calorimeter readout electronics will be upgraded. The triangular calorimeter signals are amplified and shaped by analogue electronics over a dynamic range of 16 bits, with low noise and excellent linearity. Developments of low-power preamplifiers and...
We present in this poster the measurement of light neutral mesons, $\pi^{0}$ and $\eta$, in pp collisions at different center-of-mass energies obtained with the ALICE experiment at CERN. In pp collisions, neutral mesons are used to validate the pQCD predictions and also act as a baseline for their measurement in heavy-ion collisions. Neutral mesons have been reconstructed by invariant mass...
MATHUSLA is a proposed detector that will be placed above the CMS experiment to study long-lived particles (LLP) produced by the LHC. It is instrumented with a tracking system to observe LLP decays inside its empty volume, and it is composed of a modular array of detectors covering together (100 × 100) m2 × 25 m high. MATHUSLA, with a large detection area and good granularity tracking system,...
Measurements made recently by the STAR collaboration show that the Lambda hyperons produced in relativistic heavy-ion collisions are subject to global spin polarization with respect to an axis coincident with the axis of rotation of the produced matter. Recently formulated formalism of relativistic hydrodynamics with spin, which is a generalization of the standard hydrodynamics, is a natural...
Transverse missing momentum from non-interacting particles is one of the important characteristics for many analyses especially for Beyond Standard Model physics searches. To study these events at the Large Hadron Collider (LHC) with the ATLAS experiment an efficient trigger selection is needed. The ATLAS transverse missing momentum trigger uses calorimeter-based global energy sums together...
The High-Luminosity LHC will open an unprecedented window on the weak-scale nature of the universe, providing high-precision measurements of the Standard Model as well as searches for new physics beyond the standard model. The Compact Muon Solenoid (CMS) experiment is planning to replace entirely its trigger and data acquisition system to achieve this ambitious physics program. Efficiently...
The measurement of (anti)nuclei production in pp, p-A and A-A collisions at the ultrarelativistic energies of LHC is important to understand hadronization. The excellent tracking and particle identification capabilities of ALICE make it the most suited detector at the LHC to study light (anti)nuclei produced in high-energy hadronic collisions. (Anti)nuclei with mass numbers up to 4, such as...
The identification of jets coming from the hadronization of b-quarks (b-tagging) is instrumental for many physics analyses performed at the Large Hadron Collider. ATLAS has b-tagging capability starting at trigger level, where b-tagging algorithms are fed with tracks that are reconstructed at the High-Level Trigger stage. Physics analyses with b-jets in the final state, but no lepton or...
The Higgs boson decays to pairs of b-quarks were studied in associated production with a W or Z boson by the ATLAS Collaboration. The decay to b-quarks is of particular importance since it allows a direct measurement of the coupling of the Higgs boson to b-quarks. The highest sensitivity in this channel is obtained when the vector boson produced alongside the Higgs boson decays to leptons. The...
Recently, discrepancies of up to 4σ between the different determinations of the CKM element Vus have been observed. Modified neutrino couplings to Standard Model gauge bosons could explain this "Cabibbo-angle anomaly". However, this explanation necessarily affects also the EW fit and the other observables sensitive to LFU violation. Therefore, in order to assess the viability, a global fit of...
The discovery of a 125 GeV Higgs-boson at the Large Hadron Collider poses a significant challenge for the minimal supersymmetric standard model (MSSM). We present our phenomenological research on various Higgs allied processes in the light of the pre-existing data from several other experiments including the data on electroweak precision observables, B-physics and the data from dark matter...
The identification of heavy flavour jets (tagging) plays an important role in many
physics analyses at the ATLAS experiment. It is an essential tool for precision measurements as well as for searches for new physics phenomena. Significant progress has been made in the last few years to ensure the robust training of deep neural networks, requiring large training datasets.
The ATLAS deep...
The Run 2 ATLAS trigger system is comprised of two levels: a hardware level (L1) and a software higher level trigger (HLT). Between late 2018 and early 2021, the ATLAS trigger system is undergoing upgrades. Two major sets of upgrades to the ATLAS level 1 trigger system will be the increase in read-out granularity in the LAr detectors ("supercells") and the addition of new Feature EXtractors...
Precise luminosity calibration at bunched-beam hadron colliders like the Large Hadron Collider (LHC) is critical to determine fundamental parameters of the standard model and to constrain or to discover beyond-the-standard-model phenomena. The luminosity determination at the LHC interaction point 5 with the Compact Muon Solenoid (CMS) detector, using proton-proton, proton-nucleus, or...
Emil Gorm Nielsen (on behalf of the ALICE Collaboration)
Niels Bohr Institute, University of Copenhagen, Denmark
One of the main goals of ultra-relativistic nuclear collisions is to create a
new state of matter called quark-gluon plasma (QGP) and study its properties. One of the experimental observables is the anisotropic flow vn, defined
as correlation of azimuthal angle of each...
We propose to utilize the polarization information of the $Z$ bosons in $ZZ$ production, via the gluon-gluon fusion process $gg\to ZZ$, to probe the $Zt\bar{t}$ gauge coupling. The contribution of longitudinally polarized $Z$ bosons is sensitive to the axial-vector component ($a_t$) of the $Zt\bar{t}$ coupling. We demonstrate that the angular distribution of the charged lepton from $Z$ boson...
ATLAS electron and photon triggers covering transverse energies from 5 GeV to several TeV are essential to record signals for a wide variety of physics: from Standard Model processes to searches for new phenomena. During Run 3 (2021-2024) main triggers used for those physics studies will be a single-electron trigger with ET threshold around 25 GeV and a diphoton trigger with thresholds at 25...
Presence of non-holomorphic soft SUSY breaking terms is known to be a possibility in the popular setup of the Minimal Supersymmetric Standard Model (MSSM). It has been shown that such a scenario known as Non-Holomorphic Supersymmetric Standard Model (NHSSM) could remain ‘natural’ (i.e., not fine-tuned) even in the presence of a rather heavy higgsino-like LSP. In a first study of such a...
A search for heavy resonances decaying into WW, Z Z or W Z using proton–proton collision data at a centre-of-mass energy of √ s = 13 TeV. The data, corresponding to an integrated luminosity of 139 fb−1 , were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one W or Z boson decays leptonically, and the other W...
Events with a large number of high-pT b-jets are rare in the Standard Model (SM); an excess of events with such topology would be a signal of phenomena beyond the SM. One phenomenon where a large excess is expected is a variant of supersymmetry in which R-parity is violated, allowing baryon number violating decays of the super partners of the SM particles.
This analysis presents the search...
Most recent results on searches for supersymmetric (SUSY) particles decaying to final states containing high energy photon(s) are presented. The searches are based on data collected at the center-of-mass energy of 13 TeV in proton-proton collisions recorded by the CMS detector.
Many extensions to the Standard Model introduce a hidden or dark
sector to provide candidates for dark matter in the universe an
explanation to astrophysical observations such as the positron excess
observed in the cosmic radiation flux. this hidden sector could rise
from an additional U(1)d gauge symmetry. The gauge boson of the dark
sector would be either a massless or a massive dark...
The instantaneous luminosity of the Large Hadron Collider at CERN will be increased by about a factor of five with respect to the design value by undergoing an extensive upgrade program over the coming decade. The largest phase-1 upgrade project for the ATLAS Muon System is the replacement of the present first station in the forward regions with the New Small Wheels (NSWs) during the long-LHC...
We study new physics contributions to Wtb anomalous couplings in top-quark decay process t-> Wb at the partonic level. In particular, we compute the limits on anomalous couplings to Wtb vertex. Limits were obtained at 13 TeV LHC energy with an integrated luminosity of 36.1 fb^-1 and predictions for future circular colliders, namely, HL-LHC, HE-LHC and FCC-hh were given. For future colliders,...
For the High-Luminosity LHC, planned to start in 2027, the ATLAS experiment will be equipped with the Hardware Tracking for the Trigger (HTT) system, a dedicated hardware system able to reconstruct tracks in the silicon detectors with short latency. The evolved TDAQ system design consists of a two-level hardware trigger in which the HTT is used in a low-latency mode (L1Track), providing tracks...
The Inner Detector (ID) trigger plays an essential role in the ATLAS trigger system, enabling the high purity reconstruction of physics objects - electron, tau, muon, bjet candidates, providing access to regions of the phase space populated by these objects which span a wide range of kinematic regimes. These are essential for the core physics programme at ATLAS: Standard Model measurements;...
Muon triggers are essential for studying a variety of physics processes in the ATLAS experiment, including both standard model measurements and searches for new physics. The ATLAS muon trigger consists of a hardware-based system (Level-1), as well as a software-based reconstruction (High-Level Trigger). The muon triggers have been optimised during Run 2 to provide a high efficiency while...
The ATLAS experiment aims to record about 1 kHz of physics collisions. This is achieved by using a two-level trigger system to select interesting physics events while reducing the data rate from the 40 MHz LHC crossing frequency. Events are selected based on physics signatures such as the presence of energetic leptons, photons, jets or large missing energy. The wide physics programme carried...
In preparation for LHC Run 3 ALICE will upgrade its subsystems to cope with the increased interaction rate of 50 kHz in Pb-Pb and up to 1 MHz in other collision systems, resulting in the data throughput from the detector up to 3 TB/s. Storing and analyzing such amount of data is a significant challenge and therefore, the online event selection will be required.
The Fast Interaction Trigger...
ALICE (A Large Ion Collider Experiment) is one of the four main detectors at CERN LHC. In order to exploit the increased luminosity and interaction rate during the upcoming LHC Run 3 and 4, ALICE is now implementing a significant upgrade of its detectors and systems.
The minimum latency interaction trigger, luminosity monitoring, precision collision time, and determination of centrality and...
Although the Standard Model successfully explains most phenomena at the LHC, there are several outstanding questions, including the nature of dark matter, the origin of neutrino masses, and the asymmetry in matter and anti-matter abundances in the Universe. Located in the side tunnel TI12, FASER (Forward Search Experiment) will search for highly displaced signals from light and extremely...
The ATLAS level-1 calorimeter trigger (L1Calo) is a hardware-based system that identifies events containing calorimeter-based physics objects, including electrons, photons, taus, jets, and missing transverse energy. In preparation for Run 3, when the LHC is expected to run at higher energy and instantaneous luminosity, L1Calo is currently implementing a significant programme of planned...
A new method for identifying hints of possible beyond the standard model (BSM) signals with energetic high jet multiplicity final states is proposed. In particular, the QCD background is estimated in a data driven way. Based on the simplified picture where QCD multijet events are created from a 2$\to$2 process followed by cascade branching of the outcoming partons, the proposed “Two...
Ultraperipheral Collisions (UPC) occur when the interacting nuclei or protons have an impact parameter larger than the sum of their radii. They are mediated by virtual photon exchange. The photoproduction of heavy vector mesons is especially interesting because they couple to the photon.
The ALICE Collaboration has analysed both p-Pb and Pb--Pb UPC at the centre-of-mass energy of...
To compute cross sections in proton-proton collisions, parton distribution functions (PDFs) are used which describe the density of partons within the proton. In nuclear environments, such as heavy ions, these densities change and therefore PDFs must be modified to nuclear PDFs (nPDFs). Measurements of electroweak bosons help to constrain the nPDFs. This in turn allows to compute cross sections...
