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

A theorem of Tits type for compact Kahler manifolds

We prove a theorem of Tits type about automorphism groups for compact Kahler manifolds, which has been conjectured in the paper [KOZ].Comment: Inventiones Mathematicae (to appear), 11 page

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

Expected Performance of Tracking in CMS at the HL-LHC

During the Long Shutdown 3, scheduled from 2024 to mid 2026, CERN is planning an upgrade program in preparation of the High-Luminosity LHC (HL-LHC), which will bring the luminosity up to 5 × 1034 cm−2 s−1, almost five times the one envisaged for 2017. As a consequence, up to 200 inelastic collisions on average will be superimposed on the event of interest. In this high-occupancy environment, reconstructing charged particle momenta with high precision is one of the biggest challenges. In order to face this new scenario, called Phase 2, the Compact Muon Solenoid (CMS) experiment will build a completely new silicon tracking detector. New approaches to track finding will have to be implemented to exploit the capabilities of the new tracker in addition to the algorithms already in use. The expected performance of CMS tracking at the HL-LHC is presented in this contribution

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

Parameterization-based tracking for the P2 experiment

The P2 experiment in Mainz aims to determine the weak mixing angle θW at low momentum transfer by measuring the parity-violating asymmetry of elastic electronproton scattering. In order to achieve the intended precision of Δ(sin2 θW)/sin2θW = 0:13% within the planned 10 000 hours of running the experiment has to operate at the rate of 1011 detected electrons per second. Although it is not required to measure the kinematic parameters of each individual electron, every attempt is made to achieve the highest possible throughput in the track reconstruction chain. In the present work a parameterization-based track reconstruction method is described. It is a variation of track following, where the results of the computation-heavy steps, namely the propagation of a track to the further detector plane, and the fitting, are pre-calculated, and expressed in terms of parametric analytic functions. This makes the algorithm extremely fast, and well-suited for an implementation on an FPGA. The method also takes implicitly into account the actual phase space distribution of the tracks already at the stage of candidate construction. Compared to a simple algorithm, that does not use such information, this allows reducing the combinatorial background by many orders of magnitude, down to O(1) background candidate per one signal track. The method is developed specifically for the P2 experiment in Mainz, and the presented implementation is tightly coupled to the experimental conditions

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