1,063 research outputs found

    Higgs pair production: Choosing benchmarks with cluster analysis

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    New physics theories often depend on a significant number of parameters and the phenomenology of fundamental processes may vary drastically depending on their values. It is advantageous to categorize the resulting final state kinematics such that the investigation of a few typical points yields knowledge on a large area of the parameter space. Here it is showed how this can be done effectively with a cluster analysis, by considering as specific process the non-resonant Higgs boson pairs production in the context of Standard Model extensions to Higgs boson anomalous couplings

    Production of the new pixel detector for the upgrade of the CMS experiment and study of anomalous couplings in the non-resonant Higgs bosons pair production in p-p collisions at sqrt(s) = 13 TeV

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    The present thesis work has been carried out in the framework of the CMS collaboration, one of the experiment designed to study the physics of the proton-proton collisions at the Large Hadron Collider (LHC) at CERN. Experimentation at CMS (and at ATLAS) led to the discovery of a new particle in 2012 which has been identified as the Higgs boson, the missing brick of the Standard Model of the fundamental interactions. All the experiments at LHC are upgrading their detectors in order to fulfill the continuous increment of the LHC luminosity and the consequent increment of the per collision event rate. The CMS upgrade project foresees, inter alia, the production of a new pixel detector (CMS Phase 1 Pixel Upgrade) to be commissioned at the beginning of 2017. Crucial part of the upgrade is the new readout chip (ROC) for the silicon sensor, psi46digV2respin, designed at the Paul Scherrer Institute (PSI) with a 250 nm CMOS technology. This chip represents the state of the art in the readout electronics for the silicon detectors. The thesis concerns the study and the development of test procedures for this new readout chip. Thanks to a long stay at PSI, I could provide an important contribution to the debug phases of the first version of the ROC and TBM, the chip that handles the various ROCs in the pixel module, and to the development of the software used by the whole collaboration for the ROC and module testing. This experience allowed me to be the expert for the installation and commissioning of the ROC readout system in all the production centres in Italy. Furthermore, I managed the ROC wafers test from the early project phases. The ROCs are produced on silicon wafers and undergo various processes before being assembled on the modules, e.g., metal deposition on the pixel pads, thinning and dicing. These processes lead mechanical and thermal stresses that can damage the chips. The ROC wafers test has thus been performed following the same procedure before and after the processing. In order to minimize the failing ROCs fraction mounted on the modules. It has been measured that the processing introduces a 5.2 % reduction of the number of perfectly working ROCs. The pixel detector production line, the module qualification process and the ROC wafers test results are reported in this thesis. The modifications performed on the ROC-sensor connection technology are also described. The new pixel detector installation will allow an increase of the tracks reconstruction efficiency and a 10-15 um resolution to be maintained in the interaction vertices reconstruction, independently from the increment of the mean number of events per p-p interaction from the current 15 to 50-60 in 2017. The excellent performances of the new pixel vertex detector plus the planned increment of the luminosity (a factor 35 between 2017 and the current value) could allow access to physical processes with a low cross section and a high number of b quarks in the final states. For this purpose, a preliminary study on the non-resonant Higgs bosons pair production in the fully hadronic decay channel bbbb is here presented. The study has been performed analysing the data collected by the CMS experiment in 2015, equal to 2.19 fb-1. This process has a low cross section, accordingly to the SM, and its measurement in p-p collision at centre of mass energies of 13-14 TeV is forecast only with a high amount of data (ab-1). The data collected in 2015 do not allow to set a reasonable exclusion limit on the cross section of this process and the analysis will be completely developed in 2016 and following years. The study of the Higgs bosons pair production is relevant because the pairs can be produced also after couplings which are not allowed by the Standard Model (anomalous), such as the higgs-gloun contact interaction. These anomalous couplings lead to an increment of the cross section of the process and to differences in the kinematics of the final states. The process of Higgs bosons pair production via anomalous couplings is described by a Lagrangian with five free parameters. This implies a difficulty in the identification of parameters space point to be experimentally investigated. I developed an analysis technique which allows, by studying simulated samples, to divide the parameters space in kinematically similar regions and to identify a benchmark in each of them. The distance among different points of the parameters space has been defined through a binned likelihood ratio and an iterative algorithm has been developed to group them together. Twelve regions which are kinematically equivalent have been identified in a 5-D space. The results of this study, described in this thesis, are collected in an article which is under publication on JHEP and they will be considered as guideline for the searches of non-resonant Higgs bosons pair production at CMS

    Higgs Pair Production: Choosing Benchmarks With Cluster Analysis

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    New physics theories often depend on a large number of free parameters. The precise values of those parameters in some cases drastically affect the resulting phenomenology of fundamental physics processes, while in others finite variations can leave it basically invariant at the level of detail experimentally accessible. When designing a strategy for the analysis of experimental data in the search for a signal predicted by a new physics model, it appears advantageous to categorize the parameter space describing the model according to the corresponding kinematical features of the final state. A multi-dimensional test statistic can be used to gauge the degree of similarity in the kinematics of different models; a clustering algorithm using that metric may then allow the division of the space into homogeneous regions, each of which can be successfully represented by a benchmark point. Searches targeting those benchmark points are then guaranteed to be sensitive to a large area of the parameter space. In this document we show a practical implementation of the above strategy for the study of non-resonant production of Higgs boson pairs in the context of extensions of the standard model with anomalous couplings of the Higgs bosons. A non-standard value of those couplings may significantly enhance the Higgs pair production cross section, such that the process could be detectable with the data that the Large Hadron Collider will collect in Run 2.Comment: Editorial changes, improvements in figures and changes in the appendi

    LOFT - a Large Observatory For x-ray Timing

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    The high time resolution observations of the X-ray sky hold the key to a number of diagnostics of fundamental physics, some of which are unaccessible to other types of investigations, such as those based on imaging and spectroscopy. Revealing strong gravitational field effects, measuring the mass and spin of black holes and the equation of state of ultradense matter are among the goals of such observations. At present prospects for future, non-focused X-ray timing experiments following the exciting age of RXTE/PCA are uncertain. Technological limitations are unavoidably faced in the conception and development of experiments with effective area of several square meters, as needed in order to meet the scientific requirements. We are developing large-area monolithic Silicon Drift Detectors offering high time and energy resolution at room temperature, which require modest resources and operation complexity (e.g., read-out) per unit area. Based on the properties of the detector and read-out electronics that we measured in the lab, we developed a realistic concept for a very large effective area mission devoted to X-ray timing in the 2-30 keV energy range. We show that effective areas in the range of 10-15 square meters are within reach, by using a conventional spacecraft platform and launcher of the small-medium class.Comment: 13 pages, 8 figures, 1 table, Proceedings of SPIE Vol. 7732, Paper No. 7732-66, 201

    INTEGRAL survey of the Cassiopeia region in hard X rays

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    We report on the results of a deep 1.6 Ms INTEGRAL observation of the Cassiopeia region performed from December 2003 to February 2004. Eleven sources were detected with the imager IBIS-ISGRI at energies above 20 keV, including three new hard X-ray sources. Most remarkable is the discovery of hard X-ray emission from the anomalous X-ray pulsar 4U 0142+61, which shows emission up to \~150 keV with a very hard power-law spectrum with photon index Gamma = 0.73 +/- 0.17. We derived flux upper limits for energies between 0.75 MeV and 30 MeV using archival data from the Compton telescope COMPTEL. In order to reconcile the very hard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL upper limits, the spectrum has to bend or break between ~75 keV and ~750 keV. 1E 2259+586, another anomalous X-ray pulsar in this region, was not detected. INTEGRAL and COMPTEL upper limits are provided. The new INTEGRAL sources are IGR J00370+6122 and IGR J00234+6144. IGR J00370+6122 is a new supergiant X-ray binary with an orbital period of 15.665 +/- 0.006 days, derived from RXTE All-Sky Monitor data. Archival BeppoSAX Wide-Field Camera data yielded four more detections. IGR J00234+6144 still requires a proper identification. Other sources for which INTEGRAL results are presented are high-mass X-ray binaries 2S 0114+650, Gamma~Cas, RX J0146.9+6121 and 4U 2206+54, intermediate polar V709 Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each of these sources the hard X-ray spectra are fitted with different models and compared with earlier published results.Comment: 16 pages, 13 figures, accepted for publication in A&

    Differential cross section measurements for the production of a W boson in association with jets in proton‚Äďproton collisions at ‚ąös = 7 TeV

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    Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript ‚ąí1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

    Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an