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Title: Search for gluino and squark production in multi-jets plus missing transverse energy final states at the Tevatron using the CDF detector

Abstract

In this thesis, the results of the search for squarks and gluinos in multiple jets plus missing transverse energy final states have been presented. No evidence of these new particles have been found in 371 pb -1 of CDF Run II data. New limits have been set which exclude gluino masses below 220 GeV and, in the region where M $$\tilde{g}$$ ~ M $$\tilde{q}$$, masses below 380 GeV/c 2 are excluded. These limits are valid in a mSUGRA scenario with tan β = 5, A = 0 and μ < 0 assuming the lightest four squark flavours degenerate in mass. To obtain these results a careful study of the beam conditions and their contribution to events with E T final states has been performed. Special attention has been taken in studying the different SM backgrounds and their normalizations at NLO. Dedicated cuts have been introduced to remove the background processes and main discriminating variables have been optimized for different signal regions. The different systematic uncertainties have also been considered. This is the first time that this search is performed at CDF Run II and the results presented here show significant improvements with respect to the constraints from previous experiments. Thus, this analysis has established the procedure to continue searching for squarks and gluinos with the new data samples that CDF is collecting from Tevatron. Some improvements may also be implemented by considering other hadron final states with different jet multiplicities. This could help extending the sensitivity of the analysis to regions where gluino and squark masses are not similar. At the forthcoming LHC, the search for squarks and gluinos in this inclusive channel constitutes one of the first analyses to be performed. The E T and multiple jets final states are present in multiple decay modes of many models beyond the SM. The experience from Tevatron in working on an hadron collider environment will be useful for these kind of studies aiming to discover the presence of supersymmetric processes.

Authors:
 [1]
  1. Autonomous Univ. of Barcelona, Bellaterra (Spain). Inst. for High Energy Physics
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
902543
Report Number(s):
FERMILAB-THESIS-2007-02
TRN: US0702944
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; DECAY; FERMILAB COLLIDER DETECTOR; FERMILAB TEVATRON; HADRONS; PRODUCTION; SENSITIVITY; TRANSVERSE ENERGY; Experiment-HEP

Citation Formats

Portell i Bueso, Xavier. Search for gluino and squark production in multi-jets plus missing transverse energy final states at the Tevatron using the CDF detector. United States: N. p., 2007. Web. doi:10.2172/902543.
Portell i Bueso, Xavier. Search for gluino and squark production in multi-jets plus missing transverse energy final states at the Tevatron using the CDF detector. United States. doi:10.2172/902543.
Portell i Bueso, Xavier. Mon . "Search for gluino and squark production in multi-jets plus missing transverse energy final states at the Tevatron using the CDF detector". United States. doi:10.2172/902543. https://www.osti.gov/servlets/purl/902543.
@article{osti_902543,
title = {Search for gluino and squark production in multi-jets plus missing transverse energy final states at the Tevatron using the CDF detector},
author = {Portell i Bueso, Xavier},
abstractNote = {In this thesis, the results of the search for squarks and gluinos in multiple jets plus missing transverse energy final states have been presented. No evidence of these new particles have been found in 371 pb-1 of CDF Run II data. New limits have been set which exclude gluino masses below 220 GeV and, in the region where M$\tilde{g}$ ~ M$\tilde{q}$, masses below 380 GeV/c2 are excluded. These limits are valid in a mSUGRA scenario with tan β = 5, A = 0 and μ < 0 assuming the lightest four squark flavours degenerate in mass. To obtain these results a careful study of the beam conditions and their contribution to events with ET final states has been performed. Special attention has been taken in studying the different SM backgrounds and their normalizations at NLO. Dedicated cuts have been introduced to remove the background processes and main discriminating variables have been optimized for different signal regions. The different systematic uncertainties have also been considered. This is the first time that this search is performed at CDF Run II and the results presented here show significant improvements with respect to the constraints from previous experiments. Thus, this analysis has established the procedure to continue searching for squarks and gluinos with the new data samples that CDF is collecting from Tevatron. Some improvements may also be implemented by considering other hadron final states with different jet multiplicities. This could help extending the sensitivity of the analysis to regions where gluino and squark masses are not similar. At the forthcoming LHC, the search for squarks and gluinos in this inclusive channel constitutes one of the first analyses to be performed. The ET and multiple jets final states are present in multiple decay modes of many models beyond the SM. The experience from Tevatron in working on an hadron collider environment will be useful for these kind of studies aiming to discover the presence of supersymmetric processes.},
doi = {10.2172/902543},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Thesis/Dissertation:
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  • A model-independent signature-based search for physics beyond the Standard Model is performed in the photon + jets + missing transverse energy channel in \ppbar collisions at a center of mass energy of 1.96 TeV using the CDF II detector. Events with a photon + jets are predicted by the Standard Model and also by many theoretical models beyond the Standard Model. In the Standard Model, the main mechanisms for photon + jets production include quark-antiquark annihilation and quark-gluon scattering. No intrinsic missing transverse energy is present in any of these Standard Model processes. In this search, photon +more » $$\geq$$1 jet and photon + $$\geq$$2 jet events are analyzed with and without a minimum requirement on the missing transverse energy. Numerous mass distributions and kinematic distributions are studied and no significant excess over the background prediction is found. All results indicate good agreement with expectations of the Standard Model.« less
  • In the scope of the strong ongoing data analysis efforts of the CDF col- laboration at Fermilab, we present a search for the production of mas sive W1 bosons decaying to a top and a bottom quark in pmore » $$\bar{p}$$ collisions at √s = 1.96 TeV. To perform this search, we select events with large Missing Transverse Energy plus two or three jets, in which the W generated from top decays leptonically, and either the e or µ is lost or the τ is reconstructed as a jet. A complete study of the selected sample is discussed, including the creation and subsequent optimization of a Neural Network-based multivariate tool to reject the QCD multijet background from the signal region. Finally, we perform a likelihood-based multichannel Bayesian fit procedure on the invariant transverse mass of the Missing Transverse Energy and jets to extract 95% CL limits on σ(p$$\bar{p}$$ . → W') × B(W' → tb) for M W' = 200 GeV/c 2« less
  • In the first part of this work, we present a search for WW and WZ production in charged lepton, neutrino plus jets final states produced in pmore » $$\bar{p}$$ collisions with √s = 1.96 TeV at the Fermilab Tevatron, using 1.2 fb -1 of data accumulated with the CDF II detector. This channel is yet to be observed in hadron colliders due to the large singleWplus jets background. However, this decay mode has a much larger branching fraction than the cleaner fully leptonic mode making it more sensitive to anomalous triple gauge couplings that manifest themselves at higher transverse W momentum. Because the final state is topologically similar to associated production of a Higgs boson with a W, the techniques developed in this analysis are also applicable in that search. An Artificial Neural Network has been used for the event selection optimization. The theoretical prediction for the cross section is σ WW/WZ theory x Br(W → ℓv; W/Z → jj) = 2.09 ± 0.14 pb. They measured N Signal = 410 ± 212(stat) ± 102(sys) signal events that correspond to a cross section σ WW/WZ x Br(W → ℓv; W/Z → jj) = 1.47 ± 0.77(stat) ± 0.38(sys) pb. The 95% CL upper limit to the cross section is estimated to be σ x Br(W → ℓv; W/Z → jj) < 2.88 pb. The second part of the present work is technical and concerns the ATLAS SemiConductor Tracker (SCT) assembly phase. Although technical, the work in the SCT assembly phase is of prime importance for the good performance of the detector during data taking. The production at the University of Geneva of approximately one third of the silicon microstrip end-cap modules is presented. This collaborative effort of the university of Geneva group that lasted two years, resulted in 655 produced modules, 97% of which were good modules, constructed within the mechanical and electrical specifications and delivered in the SCT collaboration for assembly on the end-cap disks. The SCT end-caps and barrels consist of 4088 silicon modules, with a total of 6.3 million readout channels. The coherent and safe operation of the SCT during commissioning and subsequent operation is the essential task of the Detector Control System (DCS). The main building blocks of the DCS are the cooling system, the power supplies and the environmental system. The DCS has been initially developed for the SCT assembly phase and this system is described in the present work. Particular emphasis is given in the environmental hardware and software components, that were my major contributions. Results from the DCS testing during the assembly phase are also reported.« less