Study of the Higgs boson discovery potential, produced by the vector boson fusion with the ATLAS detector and commissioning of calorimetric transverse missing energy.

The subject of this thesis is the evaluation of the discovery potential of the ATLAS detector at the Large Hadron Collider for the Standard Model Higgs boson in vector boson fusion (VBF) production and a subsequent decay into a $au$-lepton pair (H to tau tau). This is one of the most promising discovery channels in the low mass range, which is the mass range favored from precision measurements of the electroweak interaction. The decay modes where both $au$ leptons decay leptonically and where one $au$ lepton decays leptonically and the other one hadronically were studied. The characteristic vector boson fusion topology, which consists of two jets in the forward regions of the detector and the Higgs boson decay products in the central region, provides a unique signature allowing the suppression of background. In addition, since vector boson fusion is a purely electroweak process, no QCD activity is expected and thus no central jets are expected for signal events. This allows the central jet veto cut application to further reject background processes. A cut-oriented analysis was used, focusing on the central jet veto cut optimization. The main objective was to investigate the Higgs boson ATLAS discovery potential with an integrated luminosity of 30 fb$^{-1}$ in the mass range 115~GeV$le$mH$le$140~GeV, for an LHC energy at the center of mass $sqrt{s}$=14~TeV. After the application of all cuts, an excess above 5$sigma$ of sign al significance was found for the mass range 115~GeV$le$mH$le$125~GeV. %A maximum signal significance of 5.4$sigma$ was achieved for a Higgs mass of 120~GeV. In H to tau tau decay channel, transverse missing energy (EtMiss) resolution is of high importance since it affects directly the resolution of the Higgs boson mass. This was the initial motivation for performing and presenting in this thesis a calorimetric commissioning study based on EtMiss quantities, focused on the electronics noise etmiss ~contribution, measured with cosmics data of the period fall 2008. A Gaussian behavior of noise in all liquid argon calorimeters was found, whereas a region of non-Gaussian tails in scintillating tile calorimeter was high-lighted. For the latter, a new noise model was tested using a double Gaussian parameterization resulting in a more realistic description. Finally, this analysis provided a useful calorimeter commissioning tool, which allowed the observation and the correction of several features in the ATLAS calorimeter behavior

Localization for Involutions in Floer Cohomology

We consider Lagrangian Floer cohomology for a pair of Lagrangian submanifolds in a symplectic manifold M. Suppose that M carries a symplectic involution, which preserves both submanifolds. Under various topological hypotheses, we prove a localization theorem for Floer cohomology, which implies a Smith-type inequality for the Floer cohomology groups in M and its fixed point set. Two applications to symplectic Khovanov cohomology are included.National Science Foundation (U.S.) (grant DMS-0405516)National Science Foundation (U.S.) (grant DMS-065260)European Research Council (grant ERC-2007-StG-205349

Hadron beam test of a scintillating fibre tracker system for elastic scattering and luminosity measurement in ATLAS

A scintillating fibre tracker is proposed to measure elastic proton scattering at very small angles in the ATLAS experiment at CERN. The tracker will be located in so-called Roman Pot units at a distance of 240 m on each side of the ATLAS interaction point. An initial validation of the design choices was achieved in a beam test at DESY in a relatively low energy electron beam and using slow off-the-shelf electronics. Here we report on the results from a second beam test experiment carried out at CERN, where new detector prototypes were tested in a high energy hadron beam, using the first version of the custom designed front-end electronics. The results show an adequate tracking performance under conditions which are similar to the situation at the LHC. In addition, the alignment method using so-called overlap detectors was studied and shown to have the expected precision.Comment: 12 pages, 8 figures. Submitted to Journal of Instrumentation (JINST

The HEP.TrkX Project: deep neural networks for HL-LHC online and offline tracking

Particle track reconstruction in dense environments such as the detectors of the High Luminosity Large Hadron Collider (HL-LHC) is a challenging pattern recognition problem. Traditional tracking algorithms such as the combinatorial Kalman Filter have been used with great success in LHC experiments for years. However, these state-of-the-art techniques are inherently sequential and scale poorly with the expected increases in detector occupancy in the HL-LHC conditions. The HEP.TrkX project is a pilot project with the aim to identify and develop cross-experiment solutions based on machine learning algorithms for track reconstruction. Machine learning algorithms bring a lot of potential to this problem thanks to their capability to model complex non-linear data dependencies, to learn effective representations of high-dimensional data through training, and to parallelize easily on high-throughput architectures such as GPUs. This contribution will describe our initial explorations into this relatively unexplored idea space. We will discuss the use of recurrent (LSTM) and convolutional neural networks to find and fit tracks in toy detector data

Evidence for the h_b(1P) meson in the decay Upsilon(3S) --> pi0 h_b(1P)

Using a sample of 122 million Upsilon(3S) events recorded with the BaBar detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we search for the $h_b(1P)$ spin-singlet partner of the P-wave chi_{bJ}(1P) states in the sequential decay Upsilon(3S) --> pi0 h_b(1P), h_b(1P) --> gamma eta_b(1S). We observe an excess of events above background in the distribution of the recoil mass against the pi0 at mass 9902 +/- 4(stat.) +/- 2(syst.) MeV/c^2. The width of the observed signal is consistent with experimental resolution, and its significance is 3.1sigma, including systematic uncertainties. We obtain the value (4.3 +/- 1.1(stat.) +/- 0.9(syst.)) x 10^{-4} for the product branching fraction BF(Upsilon(3S)-->pi0 h_b) x BF(h_b-->gamma eta_b).Comment: 8 pages, 4 postscript figures, submitted to Phys. Rev. D (Rapid Communications

Search for direct stau production in events with two hadronic tau-leptons in root s=13 TeV pp collisions with the ATLAS detector

A search for the direct production of the supersymmetric partners ofτ-leptons (staus) in final stateswith two hadronically decayingτ-leptons is presented. The analysis uses a dataset of pp collisions corresponding to an integrated luminosity of139fb−1, recorded with the ATLAS detector at the LargeHadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected StandardModel background is observed. Limits are derived in scenarios of direct production of stau pairs with eachstau decaying into the stable lightest neutralino and oneτ-lepton in simplified models where the two staumass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidencelevel for a massless lightest neutralino

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13