Suche nach Supersymmetrie in multi-leptonischen und tau-Paar-Endzuständen mit dem ATLAS-Experiment am LHC bei 13 TeV Schwerpunktsenergie

Supersymmetric (SUSY) extensions can solve several shortcomings of the Standard Model (SM) of particle physics by predicting new heavy particles which can be probed at the Large Hadron Collider. Several SUSY models with and without R-parity violation have been tested in pp collision events with at least four charged or a pair of τ leptons and compared to the SM prediction. Improved lower limits on the masses of the lightest SUSY particles are derived using data of the ATLAS detector at √ s =13 TeV.Supersymmetrische (SUSY) Erweiterungen können einige der offenen Fragen des Standard Modells (SM) der Teilchenphysik durch die Vorhersage neuer schwerer Teilchen erklären, die am Large Hadron Collider erzeugt werden können. Protonkollisionsdaten bei √ s=13 TeV vom ATLAS Detektor mit vier geladenen Leptonen oder einem τ Paar wurden auf die Vorhersage von SUSY-Modellen mit und ohne R-Paritätsverletzung untersucht und mit der SM-Vorhersage verglichen. Verbesserte untere Auschlussgrenzen für die leichtesten SUSY Teilchen wurden abgeleitet

Search for Supersymmetry with R-parity violation in leptonic final states with the ATLAS detector at 13 TeV center-of-mass energy

Supersymmetry with R-parity violation, where the lightest supersymmetric particle can decay into Standard Model particles is an attractive target for collider-based searches for physics beyond the Standard Model. In this thesis, four-lepton events are studied as a possible signature of R-parity-violating supersymmetry, using proton- proton collision events collected by the ATLAS experiment at $\sqrt{s}$ = 13 TeV. The event selection is optimized for events with low-mass collimated lepton pairs, and the viability of estimating the important $t\bar{t}Z$ background process from $t\bar{t}\gamma$ events is shown. Using the optimized selection, it is found that pair-produced charginos with masses above 1 TeV can be discovered with $3\sigma$ significance in $10~\text{fb}^{-1}$ of data

Searches for Supersymmetry in multi-leptonic and τ\tau pair final states with the ATLAS experiment at the LHC at s=13\sqrt{s}=13~TeV

Supersymmetry (SUSY) is an attractive framework for extension of the Standard Model of particle physics providing answers for several open questions such as the nature of Dark Matter and the explanation of the value of the Higgs boson mass at the electroweak scale. It postulates for each Standard Model particle a superpartner with the same quantum numbers but differing in spin by half. None of these particles have been observed yet, leading to the conclusion that the superpartners are much heavier and SUSY must be broken. At the Large Hadron Collider~(LHC), proton beams collide at a centre-of-mass energy of actually $\sqrt{s}=13$~TeV in order to test the Standard Model and to search for new physics processes including supersymmetric particles. In this thesis, two searches for Supersymmetry have been performed using data of the ATLAS experiment at the LHC at $\sqrt{s}=13$~TeV with an integrated luminosity of 139~\ifb . If R-parity is violated due to additional lepton number violating interactions, the lightest supersymmetric particle (LSP) which is assumed to be produced in pairs and electrically neutral, can decay into two charged leptons and a neutrino. A search for such SUSY scenarios exploits final states wit four or more charged leptons which are experimentally very clean with low background and high reconstruction efficiency. The low background contributions also allow for probing supersymmetric models with gauge mediated SUSY breaking where the LSP is a gravitino originating from higgsino decays together with a Z or Higgs boson. The measurements were in good agreement with the SM predictions and improved lower limits were set on the supersymmetric particle masses and their decay modes into SM particles in the framework of simplified signal models. An essential prerequisite for searches in multi-leptonic final states is the precise knowledge of the lepton reconstruction efficiencies and of additional selection criteria. In this thesis, the muon reconstruction and identification efficiency as well as the efficiencies of a muon to originate from the primary collision vertex or to be isolated from hadronic activity in the detector have been estimated from data of $Z\to\mu\mu$ and $J/\psi\to\mu\mu$ decays with unprecedented precision of better than 0.1\% using the so-called tag-and-probe method. The second search presented in this thesis concerns the pair production of the supersymmetric partner of the $\tau$ lepton, the stau slepton. Light staus could reconcile the theoretical predictions with the measurements of the anomalous magnetic moment of the muon and also provide a mechanism for generating the Dark Matter relic density observed in the universe. The signature of such models consists of two $\tau$ leptons and missing transverse momentum from the two escaping LSPs and the neutrinos from $\tau$ decays. This final state is challenging at the LHC due to the large hadronic background. Hence, the limits on the stau mass from the LEP experiments prevailed until the end of the $\sqrt{s}=13$~TeV data taking. Events in which both $\tau$ leptons decay hadronically are used to search for direct stau production. No excess above the SM expectation has been observed and lower limits are placed on the stau masses which significantly improve the previous results. Prospect studies for combination of these results using di-tau events where one of the $\tau$ leptons decay leptonically are also presented

Searches for R-Parity violating SUSY at ATLAS

Conference talk for ICHEP 202

Search for Supersymmetry in multileptonic final states

Poster for LHCP in Bologn

Performance of the ATLAS \\Muon Spectrometer at s=13\sqrt{s}=13~TeV

LHC poster for the MCP group

Machine Learning in High Energy Physics Community White Paper

peer reviewedMachine learning is an important research area in particle physics, beginning with applications to high-level physics analysis in the 1990s and 2000s, followed by an explosion of applications in particle and event identification and reconstruction in the 2010s. In this document we discuss promising future research and development areas in machine learning in particle physics with a roadmap for their implementation, software and hardware resource requirements, collaborative initiatives with the data science community, academia and industry, and training the particle physics community in data science. The main objective of the document is to connect and motivate these areas of research and development with the physics drivers of the High-Luminosity Large Hadron Collider and future neutrino experiments and identify the resource needs for their implementation. Additionally we identify areas where collaboration with external communities will be of great benefit

Observation of WWWWWW Production in pppp Collisions at s\sqrt s =13 TeV with the ATLAS Detector

International audienceThis Letter reports the observation of $WWW$ production and a measurement of its cross section using 139 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from $WWW$ production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive $WWW$ production cross section is measured to be $820 \pm 100\,\text{(stat)} \pm 80\,\text{(syst)}$ fb, approximately 2.6 standard deviations from the predicted cross section of $511 \pm 18$ fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy

Observation of WWWWWW Production in pppp Collisions at s\sqrt s =13 TeV with the ATLAS Detector

International audienceThis Letter reports the observation of $WWW$ production and a measurement of its cross section using 139 fb$^{-1}$ of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from $WWW$ production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive $WWW$ production cross section is measured to be $820 \pm 100\,\text{(stat)} \pm 80\,\text{(syst)}$ fb, approximately 2.6 standard deviations from the predicted cross section of $511 \pm 18$ fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy