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During the period 2010-2012, we conducted particle physics research with the ATLAS and CDF experiments and developed new instrumentation for tracking fundamental particles.
The mass of the W boson is one of the most important parameters in the Standard Model. A precise measurement of the W boson mass, together with a precise measurement of the top quark mass, can constrain the mass of the undiscovered Higgs boson within the Standard Model framework or give a hint for physics beyond the Standard Model. This dissertation describes a measurement of the W boson mass through its decay into a muon and a neutrino using ~ 2.2 fb -1 of √ s = 1.96 TeV p$\bar{p}$ data taken with the CDF II detector at Fermilab. We measure the W boson mass to be (80.374 ± 0.015 stat . ± 0.016 syst. ) GeV/c 2 . This result, when combined with the W mass measurement in the electron channel, leads to the single most precise mW value and greatly constrains the possible mass range of the undiscovered Higgs boson. iv
This dissertation presents a search for heavy, long-lived, neutral particles that decay to photons in proton anti-proton collisions with a center of mass energy of 1.96 TeV at the Collider Detector at Fermilab (CDF) experiment. Such particles are typical of models of Gauge Mediated Supersymmetry Breaking (GMSB). We select events with a single photon, missing transverse energy, and little other activity in the detector. We model the photon arrival time for Standard Model and non-collision sources using a data-driven method and consider photons which have a time of arrival at the detector which is significantly delayed relative to predictions. Using 6.3 fb -1 of data collected from December 2004 to June 2010, we observe 322 events in the signal region compared to a background prediction of 287 ± 24 events. While the data are consistently above predictions, we report a model excess with a significance of 1.2 standard deviations from the null hypothesis.
A search for the rare decays of B$^0$$_s$→ μ + μ - and B$^0$$_d$ → + μ + μ - is presented in p$\bar{p}$ collisions at √s=1.96 TeV corresponding to 10 fb -1 of integrated luminosity collected by the CDF II detector. The observed number of B$^0$$_d$ candidates is consistent with background-only expectations and yields an upper limit on the branching fraction B(B$^0$$_d$ → μ + μ - ) of 4.2 x 10 -9 at 95% confidence level. An excess is observed for the B0s signal region. The probability that background processes alone could produce such an excess or larger is 0.94%. The probability that the combination of background and the expected standard model rate B$^0$$_s$ → μ + μ - could produce such an excess or larger is 6.8%. These data are used to determine a central value of B(B$^0$$_s$ → μ + μ - ) = (1:3 +0.9 -0.7 ) 10 -8 as well as a two sided limit at 90% C.L. of 2:2 10 -9 < B(B$^0$$_s$ → μ + μ - ) < 3.0 x 10 -8 .
This thesis describes a measurement of the lifetime of the B ± c meson in an exclusive decay channel B ± c → J/ ψ π ± , where the J/ψ decays as J/ψ → μ + μ - . The measurement uses a data sample with an integrated luminosity of 6.7 fb -1 collected at CDF. This is the first measurement of the B ± c meson lifetime in a hadronic channel and the measured lifetime, τ = 0.449 +0.054 -0.048 (stat:) ± 0.019(syst:) ps, is in good agreement with previous results obtained from semileptonic decay channel and confirms previous measurements and theoretical predictions.
The top quark pair production and decay into leptons with at least one being a τ lepton is studied in the framework of the CDF experiment at the Tevatron proton antiproton collider at Fermilab (USA). The selection requires an electron or a muon produced either by the τ lepton decay or by a W decay. The analysis uses the complete Run II data set i.e. 9.0 fb -1 , selected by one trigger based on a low transverse momentum electron or muon plus one isolated charged track. The top quark pair production cross section at 1.96 TeV is measured at 8.2 ± 1.7 +1.2 -1.1 ± 0.5 pb, and the top branching ratio into τ lepton is measured at 0.120 ± 0.027 +0.022 -0.019 ± 0.007 with statistical, systematics and luminosity uncertainties. These are up to date the most accurate results in this top decay channel and are in good agreement with the results obtained using other decay channels of the top at the Tevatron. The branching ratio is also measured separating the single lepton from the two leptons events with a log likelihood method. This is the first time these two signatures are separately identified. With a fit to data along the log-likelihood variable an alternative measurement of the branching ratio is made: 0.098 ± 0.022(stat:) ± 0.014(syst:); it is in good agreement with the expectations of the Standard Model (with lepton universality) within the experimental uncertainties. The branching ratio is constrained to be less than 0.159 at 95% con dence level. This limit translates into a limit of a top branching ratio into a potential charged Higgs boson.
A measurement of direct CP asymmetry is performed using 6fb -1 of p$\bar{p}$ collisions at √s = 1.96TeV from the CDF detector at the Fermi National Accelerator Laboratory. Approximately 80,000 B - → J/ K - (and charge conjugate) events were selected on the dimuon trigger and the yields were determined using a simultaneous mass and lifetime fit. After corrections, a measurement of ACP = 0.0034 ± 0.0043(stat.) ± 0.0060(syst.) is obtained, which is consistent with the SM prediction and previous measurements at DØ and the B factories.
In this thesis we study one of the last corners of the Standard Model to be thoroughly investigated in a hadron collider, the production of two simultaneous Z bosons. We analyze 6.1 fb -1 of data produced at Fermilab at a center-of-mass energy √s = 1.96 TeV and recorded by the CDF experiment. The predicted cross-section is 1.4 pb and we measured 2.18 +0.64 -0.63 pb (stat) 0:30 (syst) using 14 observed events. This is the largest set of candidate events in this channel yet found and with our estimated signal in the sample of 9.54 events provides the smallest percentage uncertainty on the ZZ cross-section to date. We also use this large set of events to yield kinematic plots and measure ZZ properties that will be of use in probing for new physics in the future.
This is the Closeout Report for the research grant in experimental elementary particle physics, carried out by the Duke University High Energy Physics (HEP) group. We re- port on physics results and detector development carried out under this grant, focussing on the recent three-year grant period (2010 to 2013). The Duke HEP group consisted of seven faculty members, two senior scientists, five postdocs and eight graduate students. There were three thrusts of the research program. Measurements at the energy frontier at CDF and ATLAS were used to test aspects of elementary particle theory described by the Stan- dard Model (SM) and to search for new forces and particles beyond those contained within the SM. The neutrino sector was explored using data obtained from a large neutrino detector located in Japan, and R & D was conducted on new experiments to be built in the US. The measurements provided information about neutrino masses and the manner in which neutri- nos change species in particle beams. Two years ago we have started a new research program in rare processes based on the Mu2E experiment at Fermilab. This research is motivated by the search for the {mu} {yields} e transition with unprecedented sensitivity, a transition forbidden in the standard model but allowed in supersymmetric and other models of new physics. The high energy research program used proton and antiproton colliding beams. The experiments were done at the Fermilab Tevatron (proton-antiproton collisions at a center of mass energy of 1.96 TeV) and at the CERN Large Hadron Collider (proton-proton collisions at 7-8 TeV). The neutrino program used data obtained from the Super-Kamiokande detector. This water-filled Cherenkov counter was used to detect and measure the properties of neutrinos produced in cosmic ray showers, and from neutrino beams produced from acceler- ators in Japan. The Mu2E experiment will use a special stopped muon beam to be built at Fermilab.
MCNP5/X has the capability to perform photon Doppler broadening to incorporate the effect of bound electrons on photon scattering. This effect is generally important if energy spectra or detector responses are desired for photons in the tens to hundreds of keY energy range. In the Fall of 2011, a diligent MCNP user noticed that the sampling routines in MCNP were inconsistent with t he data for sampling which atomic shell t he electron is bound. The data are provided in probability density function (PDF) format, whereas MCNP sampled the data as if they are in a cumulative density function (CDF) format, leading to erroneous results.
We developed new CDF and PDF methods for solving non-linear stochastic hyperbolic equations that does not rely on linearization approximations and allows for rigorous formulation of the boundary conditions.
The purpose of high energy physics is to improve our knowledge about the fundamental structure of matter, in particular about particles that constitute the world. One of these is the top quark, that was discovered in 1995 by the CDF and D0 collaborations at the Tevatron protons-antiprotons collider. One of the primary aim of the Tevatron has been then the fine study of the top quark properties, in particular the top-antitop production cross section. Different analysis have been performed in the leptons (μ,e,τ) + jets, dileptons, and all hadronic channels to determine accurately the values of these parameters, and thus to test the validity of the Standard Model. The main goal of this thesis is to verify one of the theoretical predictions of the Standard Model of particle physics, the top-antitop production cross section, at the Tevatron collider.
Understanding the microstructure of the financial market requires the processing of a vast amount of data related to individual trades, and sometimes even multiple levels of quotes. Analyzing such a large volume of data requires tremendous computing power that is not easily available to financial academics and regulators. Fortunately, public funded High Performance Computing (HPC) power is widely available at the National Laboratories in the US. In this paper we demonstrate that the HPC resource and the techniques for data-intensive sciences can be used to greatly accelerate the computation of an early warning indicator called Volume-synchronized Probability of Informed trading (VPIN). The test data used in this study contains five and a half year's worth of trading data for about 100 most liquid futures contracts, includes about 3 billion trades, and takes 140GB as text files. By using (1) a more efficient file format for storing the trading records, (2) more effective data structures and algorithms, and (3) parallelizing the computations, we are able to explore 16,000 different ways of computing VPIN in less than 20 hours on a 32-core IBM DataPlex machine. Our test demonstrates that a modest computer is sufficient to monitor a vast number of trading activities in real-time – an ability that could be valuable to regulators. Our test results also confirm that VPIN is a strong predictor of liquidity-induced volatility. With appropriate parameter choices, the false positive rates are about 7% averaged over all the futures contracts in the test data set. More specifically, when VPIN values rise above a threshold (CDF > 0.99), the volatility in the subsequent time windows is higher than the average in 93% of the cases.
Testing the Standard Model (SM) and looking for new phenomena have been the focus of generations of particle physicists in the last decades. Following this spirit, this thesis presents two searches. The first is the search for single top quark production from the exchange of an s-channel virtual W boson using events with an imbalance in the total transverse energy, b-tagged jets, and no identified leptons. Assuming the electroweak production of top quarks of mass 172.5 GeV/c 2 in the s-channel, a cross section of 1.12 +0.61 -0.57 (stat+syst) pb, with a significance of 1.9 standard deviations, is measured. This measurement is combined with the result obtained from events with an imbalance in total transverse momentum, b-tagged jets, and exactly one identified lepton, yielding a cross section of 1.36 +0.37 -0.32 2 (stat+syst) pb, with a significance of 4.2 standard deviations. The first observation of single-top-quark production in the s channel through the combination of the CDF and D0 measurements is also reported. The measured cross section is σs = 1.29 +0.26 -0.24 4 pb. The probability of observing a statistical fluctuation of the background to a cross section of the observed size or larger is 1.8 10 -10 , corresponding to a significance of 6.3 standard deviation. The second is the search for W'-like resonances decaying to tb. No significant excess above the SM prediction is found. Using a benchmark W' → tb left-right symmetric model, 95% C.L. mass-dependent upper limits are placed on the W0 boson production cross section times branching ratio to tb. Assuming a W' boson with SM-like couplings and allowed (forbidden) decay to leptons, W' → tb is excluded with 95% C.L. for W' boson masses below 860 (880) GeV/c 2 . Relaxing the hypothesis on SM-like couplings, we exclude W' boson coupling strength values as a function of the W' boson mass above 10% of the SM coupling strength for M W' = 300 GeV/c 2 . The constraints obtained with the present analysis are the most stringent for charged resonance masses below 570 GeV/c 2 decaying to a top and a bottom quark.
In this work we report a measurement of the Λ 0 b baryon lifetime using the exclusive decay Λ 0 b → J/ ΨΛ 0 . The B 0 meson lifetime is also measured in the topologically similar channel B 0 → J/ K 0 S , which provides a crosscheck of the measurement procedure, and allows a direct determination of the ratio of the Λ 0 b and the B 0 lifetimes. The data used in this analysis were collected with the DØ detector during the complete Run II of the Fermilab Tevatron Collider, from 2002 to 2011, and correspond to an integrated luminosity of 10.4 fb -1 of proton-antiproton collisions at a center of mass energy √s = 1.96 TeV. We obtain τ (Λ 0 b ) = 1.303 ± 0.075 (stat.) ± 0.035 (syst.) ps, τ (B 0 ) = 1.508±0.025 (stat.)±0.043 (syst.) ps and τ (Λ 0 b )/τ (B 0 ) = 0.864± 0.052 (stat.)±0.033 (syst.). These measurements supersede previous results of the DØ Collaboration using the same decay channels. Our measurement of the lifetime ratio is in excellent agreement with theoretical predictions and compatible with the current world-average, but differs with the latest measurement of the CDF Collaboration in more than 2 standard deviations.
The accidents at the Three Mile Island Unit 2 (TMI-2) and Fukushima Daiichi Units 1, 2, and 3 nuclear power plants demonstrate the critical importance of accurate, relevant, and timely information on the status of reactor systems during a severe accident. These events also highlight the critical importance of understanding and focusing on the key elements of system status information in an environment where operators may be overwhelmed with superfluous and sometimes conflicting data. While progress in these areas has been made since TMI-2, the events at Fukushima suggests that there may still be a potential need to ensure that critical plant information is available to plant operators. Recognizing the significant technical and economic challenges associated with plant modifications, it is important to focus on instrumentation that can address these information critical needs. As part of a program initiated by the Department of Energy, Office of Nuclear Energy (DOE-NE), a scoping effort was initiated to assess critical information needs identified for severe accident management and mitigation in commercial Light Water Reactors (LWRs), to quantify the environment instruments monitoring this data would have to survive, and to identify gaps where predicted environments exceed instrumentation qualification envelop (QE) limits. Results from the Pressurized Water Reactor (PWR) scoping evaluations are documented in this report. The PWR evaluations were limited in this scoping evaluation to quantifying the environmental conditions for an unmitigated Short-Term Station BlackOut (STSBO) sequence in one unit at the Surry nuclear power station. Results were obtained using the MELCOR models developed for the US Nuclear Regulatory Commission (NRC)-sponsored State of the Art Consequence Assessment (SOARCA) program project. Results from this scoping evaluation indicate that some instrumentation identified to provide critical information would be exposed to conditions that significantly exceeded QE limits for extended time periods for the low frequency STSBO sequence evaluated in this study. It is recognized that the core damage frequency (CDF) of the sequence evaluated in this scoping effort would be considerably lower if evaluations considered new FLEX equipment being installed by industry. Nevertheless, because of uncertainties in instrumentation response when exposed to conditions beyond QE limits and alternate challenges associated with different sequences that may impact sensor performance, it is recommended that additional evaluations of instrumentation performance be completed to provide confidence that operators have access to accurate, relevant, and timely information on the status of reactor systems for a broad range of challenges associated with risk important severe accident sequences.
CO2 sequestration in deep saline formations is increasingly being considered as a viable strategy for the mitigation of greenhouse gas emissions from anthropogenic sources. In this context, detailed numerical simulation based models are routinely used to understand key processes and parameters affecting pressure propagation and buoyant plume migration following CO2 injection into the subsurface. As these models are data and computation intensive, the development of computationally-efficient alternatives to conventional numerical simulators has become an active area of research. Such simplified models can be valuable assets during preliminary CO2 injection project screening, serve as a key element of probabilistic system assessment modeling tools, and assist regulators in quickly evaluating geological storage projects. We present three strategies for the development and validation of simplified modeling approaches for CO2 sequestration in deep saline formations: (1) simplified physics-based modeling, (2) statisticallearning based modeling, and (3) reduced-order method based modeling. In the first category, a set of full-physics compositional simulations is used to develop correlations for dimensionless injectivity as a function of the slope of the CO2 fractional-flow curve, variance of layer permeability values, and the nature of vertical permeability arrangement. The same variables, along with a modified gravity number, can be used to develop a correlation for the total storage efficiency within the CO2 plume footprint. Furthermore, the dimensionless average pressure buildup after the onset of boundary effects can be correlated to dimensionless time, CO2 plume footprint, and storativity contrast between the reservoir and caprock. In the second category, statistical “proxy models” are developed using the simulation domain described previously with two approaches: (a) classical Box-Behnken experimental design with a quadratic response surface, and (b) maximin Latin Hypercube sampling (LHS) based design with a multidimensional kriging metamodel fit. For roughly the same number of simulations, the LHS-based metamodel yields a more robust predictive model, as verified by a k-fold cross-validation approach (with data split into training and test sets) as well by validation with an independent dataset. In the third category, a reduced-order modeling procedure is utilized that combines proper orthogonal decomposition (POD) for reducing problem dimensionality with trajectory-piecewise linearization (TPWL) in order to represent system response at new control settings from a limited number of training runs. Significant savings in computational time are observed with reasonable accuracy from the PODTPWL reduced-order model for both vertical and horizontal well problems – which could be important in the context of history matching, uncertainty quantification and optimization problems. The simplified physics and statistical learning based models are also validated using an uncertainty analysis framework. Reference cumulative distribution functions of key model outcomes (i.e., plume radius and reservoir pressure buildup) generated using a 97-run full-physics simulation are successfully validated against the CDF from 10,000 sample probabilistic simulations using the simplified models. The main contribution of this research project is the development and validation of a portfolio of simplified modeling approaches that will enable rapid feasibility and risk assessment for CO2 sequestration in deep saline formations.
This thesis describes the search for the Standard Model Higgs boson decaying to tau lepton pairs, in the Tevatron proton-antiproton collisions at a center of mass energy $\sqrt{s}$ = 1.96 TeV. The search is based on approximately 2.3 fb$^{-1}$ of CDF Run II data and is performed by considering the following signal processes: WH($\rightarrow\tau\tau$), ZH($\rightarrow\tau\tau$), qHq'$\rightarrow$q$\tau\tau$q' and gg$\rightarrow$H$\rightarrow\tau\tau$. Events are selected by requiring an hadronic tau and one isolated electron or muon, coming from the leptonic decay of one of the two taus. In addition, at least one calorimeter jet must be present in the final state. We expect 921.8$\pm$48.9 background events in the 1 jet channel and 159.4$\pm$11.6 in the $\ge$ 2 jets channel, while in data we observe 965 and 166 events, respectively. In order to improve the search sensitivity we employ a multivariate technique, based on a set of Boosted Decision Trees trained to get the best sep aration between signal and the dominant sources of background. We observe no evidence for a Higgs boson signal and therefore we set a 95\% confidence level (C.L.) upper limit on the cross section relative to the SM predictions ($\sigma/\sigma_{\mathrm{SM}}$). Results are presented for the Higgs boson mass varying from M$_\mathrm{H}$ = 100 GeV/$c^2$ to M$_\mathrm{H}$ = 150 GeV/$c^2$. For the mass hypothesis of 120 GeV/c$^2$ the observed limit is 27.2, while the corresponding expected value is 23.4$^{+9.8}_{-6.4}$.