Search for Dark Matter in events with missing transverse momentum and a Higgs boson decaying into bottom quarks with the ATLAS detector

Many astrophysical observations indicate the existence Dark Matter, which is not predicted by the Standard Model (SM) of particle physics. Many theories beyond the Standard Model (BSM) predict new heavy particles called WIMPs (Weakly Interacting Massive Particles). One way to search for WIMP dark matter is through its pair-production in collider experiments. A possible signature, in this case, is the associated production of a WIMP pair with a Higgs boson decaying to a pair of b-quarks. The WIMPs leave the detector without interacting, leading to events with a large amount of missing transverse momentum and two highly-energetic b-jets due to the decay of the Higgs boson. The search presented in this thesis uses such events based on data from proton-proton collisions recorded with the ATLAS detector from 2015 to 2018 at √s=13 TeV. A profile likelihood fit is performed to extract a possible signal. No significant excess above the SM predictions is observed, and the results are interpreted in terms of the Z'2HDM and 2HDM+a benchmark models. In addition, model-independent limits are set on the cross-section for new physics at 95% confidence level (CL). The thesis also presents a reinterpretation of the results in terms of the Dark-Higgs model. All physics analyses rely on the reconstruction of physics objects and the high-precision measurements of their energy and momentum. The outermost part of the ATLAS Inner Detector, Transition Radiation Tracker (TRT), contributes significantly to the momentum measurement of the charged particles by extending the length of the measured trajectories. This thesis describes studies of the drift-time calibration of the TRT. These studies examine the dependence of the calibration parameters on the transverse momentum of reconstructed tracks and pile-up using simulated events. Furthermore, the effect of additional drift-time corrections in straw tubes filled with Argon-based gas mixture is studied

The ATLAS Trigger System for LHC Run 3 and Trigger performance in 2022

The ATLAS trigger system is a crucial component of the ATLAS experiment at the LHC. It is responsible for selecting events in line with the ATLAS physics programme. This paper presents an overview of the changes to the trigger and data acquisition system during the second long shutdown of the LHC, and shows the performance of the trigger system and its components in the proton-proton collisions during the 2022 commissioning period as well as its expected performance in proton-proton and heavy-ion collisions for the remainder of the third LHC data-taking period (2022-2025)

A search for R-parity violating supersymmetric decays of the top squark to a b-jet and a lepton in √S = 13 TeV pp collisions with the ATLAS detector

A search is presented for direct pair production of the stop, the supersymmetric partner of the top quark, in a decay through an R-parity violating coupling to a charged lepton and a b-quark. The dataset corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions at a center-of-mass energy of √s = 13 TeV collected between 2015 and 2018 by the ATLAS detector at the LHC. The final state has two charged leptons (electrons or muons) and two b-jets. The results of the search are interpreted in the context of a Minimal Supersymmetric Standard Model with an additional B−L gauge symmetry that is spontaneously broken. No significant excess is observed over the Standard Model background and exclusion limits on stop pair production are set at 95% confidence level. The corresponding lower limits on the stop mass for 100% branching ratios to a b-quark and an electron, muon, or tau-lepton are 1.9 TeV, 1.8 TeV and 800 GeV, respectively, extending the reach of previous LHC searches

A search for R-parity-violating supersymmetry in final states containing many jets in pp collisions at √s=13TeV with the ATLAS detector

A search for R-parity-violating supersymmetry in final states with high jet multiplicity is presented. The search uses 140fb−1 of proton-proton collision data at √s=13TeV collected by the ATLAS experiment during Run 2 of the Large Hadron Collider. The results are interpreted in the context of R-parity-violating supersymmetry models that feature prompt gluino-pair production decaying directly to three jets each or decaying to two jets and a neutralino which subsequently decays promptly to three jets. No significant excess over the Standard Model expectation is observed and exclusion limits at the 95% confidence level are extracted. Gluinos with masses up to 1800 GeV are excluded when decaying directly to three jets. In the cascade scenario, gluinos with masses up to 2340 GeV are excluded for a neutralino with mass up to 1250 GeV

Search for pair production of boosted Higgs bosons via vector-boson fusion in the bb¯bb¯ final state using pp collisions at √s=13 TeV with the ATLAS detector

A search for Higgs boson pair production via vector-boson fusion is performed in the Lorentz-boosted regime, where a Higgs boson candidate is reconstructed as a single large-radius jet, using 140 fb−1 of proton-proton collision data at s√=13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Only Higgs boson decays into bottom quark pairs are considered. The search is particularly sensitive to the quartic coupling between two vector bosons and two Higgs bosons relative to its Standard Model prediction, κ2V. This study constrains κ2V to 0.55<κ2V<1.49 at 95% confidence level. The value κ2V=0 is excluded with a significance of 3.8 standard deviations with other Higgs boson couplings fixed to their Standard Model values. A search for new heavy spin-0 resonances that would mediate Higgs boson pair production via vector-boson fusion is carried out in the mass range of 1-5 TeV for the first time under several model and decay-width assumptions. No significant deviation from the Standard Model hypothesis is observed and exclusion limits at 95% confidence level are derived

Dark Matter search at the LHC

There are many astrophysical observations and cosmological evidence for the existence of dark matter (DM), but little is known of its particle nature. The Standard Model (SM) does not predict its existence, however numerous theories beyond the Standard Model (BSM) provide viable candidates for dark matter. Common candidates in many of these theoretical models are the weakly interacting massive particle (WIMP). One way to search for WIMP dark matter is through its production in collider experiments at the Large Hadron Collider (LHC). This talk covers a selection of the latest results of DM searches at the ATLAS, CMS and LHCb experiments

Breast lymphoma in a patient with B-cell Non Hodgkin Lymphoma: A case report study

INTRODUCTION: Breast involvement in Non Hodgkin Lymphoma is a rare entity as it accounts for 2.2% of all extranodal lymphomas. PRESENTATION OF CASE: A 59-year-old woman was referred to our Breast Unit because of two nodules of the right breast newly discovered during her annual mammography. Moreover, during the physical examination, a red-brown itchy lump of the scalp was discovered. The punch biopsies of the scalp lesion and ultrasound-guided core biopsies of both nodules of the right breast, revealed the presence of diffuse large B-cell Non Hodgkin Lymphoma in all tissue specimen sites. DISCUSSION: Breast lymphomas represent an uncommon form of localized extranodal lymphomas that can be classified as Primary (PBL) or Secondary (SBL) breast lymphomas. CONCLUSION: The value of preoperative diagnosis should be underlined as the patient avoids unnecessary surgical intervention and has earlier initiation of chemotherapy. (C) 2017 The Authors.Published by Elsevier Ltd on behalf of IJS Publishing Group Ltd