DOCSLIB.ORG

Analytic Solutions for Neutrino Momenta in Decay of Top Quarks

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Analytic Solutions for Neutrino Momenta in Decay of Top Quarks Analytic solutions for neutrino momenta in decay of top quarks Burton A. Betchart∗, Regina Demina, Amnon Harel Department of Physics and Astronomy, University of Rochester, Rochester, NY, United States of America Abstract We employ a geometric approach to analytically solving equations of constraint on the decay of top quarks involving leptons. The neutrino momentum is found as a function of the 4-vectors of the associated bottom quark and charged lepton, the masses of the top quark and W boson, and a single parameter, which constrains it to an ellipse. We show how the measured imbalance of momenta in the event reduces the solutions for neutrino momenta to a discrete set, in the cases of one or two top quarks decaying to leptons. The algorithms can be implemented concisely with common linear algebra routines. Keywords: top, neutrino, reconstruction, analytic 1. Introduction decay of the intermediate W boson falls outside experimental acceptance. Top quark reconstruction from channels containing one or more leptons presents a challenge since the neutrinos are not directly observed. The sum of neutrino momenta can be in- 2. Derivation ferred from the total momentum imbalance, but this quantity The kinematics of top quark decay constrain the W boson frequently has the worst resolution of all constraints on top momentum vector to an ellipsoidal surface of revolution about quark decays. Reconstruction at hadron colliders faces fur- an axis coincident with bottom quark momentum. Simultane- ther difficulties, since the longitudinal momentum is uncon- ously, the kinematics of W boson decay constrain the W boson strained. In a common approach to the single neutrino final momentum vector to an ellipsoidal surface of revolution about state at hadron colliders (e.g. [1]), constraining the invariant an axis coincident with the momentum of the resulting charged mass of the neutrino and associated charged lepton to the W lepton. The intersection of the two surfaces is an ellipse. The boson mass provides a quadratic equation for the unmeasured neutrino momentum is consequently constrained to a transla- longitudinal component of neutrino momentum, with zero so- tion of the ellipse, for which a parametric expression in the lab- lutions, or two solutions which can be further resolved heuris- oratory coordinate system is given. The measured momentum tically by consideration of additional constraints. We suggest imbalance further constrains solutions to a discrete set for the an alternative approach to analytic top quark reconstruction in cases of one or two top quark decays involving neutrinos. which the invariant mass constraints from the top quark and the W boson are both exact, and in which the solution set for each 2.1. Definitions neutrino momentum is an ellipse. For events with a single neu- trino, the ellipse is analytically reduced to a unique solution by A particle q is described by its mass mq, energy Eq, and application of the momentum imbalance constraint, taking its momentum 3-vector pq, with the dispersion relation uncertainty into account. The approach extends naturally to the 2 2 2 mq = Eq − pq: arXiv:1305.1878v2 [hep-ph] 2 Oct 2013 case of two neutrinos in the final state, allowing an alternative method for calculating the solution pairs previously described The magnitude of the momentum is p . Since there will be no by [2, 3, 4], and suggesting a most likely pair in the case of no q need to denote positions, the Cartesian coordinates of the mo- exact solution. mentum p in the laboratory coordinate system are represented The solutions for the one- and two-neutrino cases are de- q as (xq; yq; zq) in order to avoid double subscripts. In the labora- rived in Section 2. Their use in simulated Tevatron and LHC tory coordinate system, the azimuthal and polar angles of q are events, in the context of iterative kinematic fit procedures, is denoted φ and θ , and the relativistic speed and Lorentz factor discussed in Section 3. These results may also be useful for any q q are q event topology with similar kinematic constraints, including de- pq −1 mq 2 βq ≡ ; γq ≡ = 1 − βq: cays involving new physics with massive invisible particles, and Eq Eq hadronic decays of top quarks where one of the quarks from the For definiteness we consider the decay chain t ! bW ! bµν: a top quark (t) decays to a bottom quark (b) and a W boson ∗[email protected] (W), with subsequent decay of the W boson to a muon (µ) and Preprint submitted to Elsevier October 3, 2013 Incorporating relations (1) for the F0 coordinates, it is clear that pW is constrained to the surface 0 2 02 02 0 0 2 02 (x ˜ /γb) + y˜ + z˜ + 2βb x˜0 x˜ + mW − x˜0 = 0; (3) which is an ellipsoid of revolution about thex ˜0-axis. Particle W subsequently decays to particles µ and ν. This decay has the same kinematics as the decay t ! bW, with the substitutions b ! µ,W ! ν, and t ! W. We define the W decay analog of Equation 2, 1 2 2 2 x˜0 ≡ − mW − mµ − mν : 2Eµ In analogy to Equation 3 and using F coordinates, pν is con- strained to the surface (x ˜/γ )2 + y˜2 + z˜2 + 2β x˜ x˜ + m2 − x˜2 = 0; (4) Figure 1: The momenta of observed particles µ and b define the coordinate µ µ 0 ν 0 systems F and F0. A possible momentum of the W boson is drawn to show the angle θbW. which is an ellipsoid of revolution about thex ˜-axis. A congru- ent surface of solutions for pW is translated from the neutrino solutions (4) by +pµ along thex ˜-axis, a neutrino (ν). We assume established masses for all five parti- cles, for example from world average measurements[5]. Energy 2 2 2 2 h 2 2 2i (x ˜/γµ) + y˜ + z˜ + 2βµS x˜ x˜ + m − x˜ − = 0; (5) and momentum conservation for this system imply W 0 where for compactness and later use we have defined Et = Eb + EW = Eb + Eµ + Eν; pt = pb + pW = pb + pµ + pν: −2 2 S x˜ = x˜0βµ − pµγµ /βµ; (6) Momentum coordinate systems Ffx˜; y˜; z˜g and F0fx˜0; y˜0; z˜0g 2 −2 2 2 are defined in the laboratory reference frame to share a common = γµ mW − mν : z z0 F0 F axis ˜ = ˜ . Coordinate system is rotated relative to by the The solution set for p is the intersection of two simultaneous θ p p p x p W angle bµ between b and µ, with µ along the ˜-axis, and b surfaces of constraint, (3) and (5), imposed by the b measure- x0 p F0 along the ˜ -axis. Polar and Cartesian coordinates of W in ment and the masses (m , m ), and the µ measurement and the are related as t W masses (mW, mν), respectively. Figure 2 shows examples. For 0 0 02 02 2 02 relativistic particles µ and b, the surfaces limit on paraboloids, x˜ = pWC ; y˜ + z˜ = p S ; (1) W W W W 2 S x˜ limits onx ˜0, and limits on zero. 0 0 where S (C ) is the (co)sine of the angle θbW between pW and pb. Figure 1 shows the coordinate systems. 2.3. Extended Matrix Representation The use of homogeneous coordinates r = ( x y 1 )T or 2.2. Two surfaces for W momentum s = ( x y z 1 )T allows extended matrix representation of Energy and momentum are conserved in the decay t ! bW, various 2- or 3-dimensional geometric objects. In particular, hence the 1 × 3 row matrix L is the extended representation of the line 2 2 2 Lr = 0 in two dimensions. A 3 × 3 symmetric square matrix M mt = Et − pt is the extended representation of the conic section rT Mr = 0 in = (E + E )2 − (p + p )2 b W b W two dimensions. A quadric surface in three dimensions, like a 2 2 0 = mb + mW + 2EbEW − 2pb pWC : paraboloid or ellipsoid, can be represented as a 4 × 4 symmet- T For compactness we define ric square matrix A, with s As = 0. Extended representations are unique up to a multiplicative factor, and allow transforma- 0 1 2 2 2 tions like rotations and translations to be expressed by matrix x˜0 ≡ − mt − mW − mb : (2) 2Eb multiplication[6, 7, 8]. It follows that The ellipsoid defined by particle b (3) is represented for ho- mogeneous F0 coordinates by the matrix 0 0 0 = x˜0 + EW − βb pWC 0 −2 0 1 2 h 0 0i2 B γb 0 0x ˜0βb C 0 = E − x˜ − βb pWC B C W 0 0 B 0 1 0 0 C A˜ = B C : m2 − x02 β p C0 x0 p2 − β2C02 b B 0 0 1 0 C 0 = W ˜0 + 2 b W ˜0 + W 1 b @B AC x˜0 β 0 0 m2 − x˜02 2 02 0 0 2 −2 02 02 0 b W 0 0 = mW − x˜0 + 2βb pWC x˜0 + pW γb C + S : 2 F coordinates: P+ slice of ~z = ~z ′= 0 ~ ~ (x 1,y 1,0) ~z , ~z ′ Lab coordinates: b projections on z=0 µ ~y y χ2 = 4.6 100 GeV/c P ~ (Sx~,Sy~) x x F coordinates: P+ slice of ~z = ~z ′= 0 ~ ~ (x 1,y 1,0) ~z , ~z ′ b Lab coordinates: projections on z=0 µ ~y P (Sx~,Sy~) y χ2 = 6.3 100 GeV/c ~x x Figure 2: Reconstruction of neutrino momentum from the decay t ! bµν for two events, with θbµ large (top) and small (bottom).
Load more

Recommended publications
  • First Determination of the Electric Charge of the Top Quark
    First Determination of the Electric Charge of the Top Quark PER HANSSON arXiv:hep-ex/0702004v1 1 Feb 2007 Licentiate Thesis Stockholm, Sweden 2006 Licentiate Thesis First Determination of the Electric Charge of the Top Quark Per Hansson Particle and Astroparticle Physics, Department of Physics Royal Institute of Technology, SE-106 91 Stockholm, Sweden Stockholm, Sweden 2006 Cover illustration: View of a top quark pair event with an electron and four jets in the final state. Image by DØ Collaboration. Akademisk avhandling som med tillst˚and av Kungliga Tekniska H¨ogskolan i Stock- holm framl¨agges till offentlig granskning f¨or avl¨aggande av filosofie licentiatexamen fredagen den 24 november 2006 14.00 i sal FB54, AlbaNova Universitets Center, KTH Partikel- och Astropartikelfysik, Roslagstullsbacken 21, Stockholm. Avhandlingen f¨orsvaras p˚aengelska. ISBN 91-7178-493-4 TRITA-FYS 2006:69 ISSN 0280-316X ISRN KTH/FYS/--06:69--SE c Per Hansson, Oct 2006 Printed by Universitetsservice US AB 2006 Abstract In this thesis, the first determination of the electric charge of the top quark is presented using 370 pb−1 of data recorded by the DØ detector at the Fermilab Tevatron accelerator. tt¯ events are selected with one isolated electron or muon and at least four jets out of which two are b-tagged by reconstruction of a secondary decay vertex (SVT). The method is based on the discrimination between b- and ¯b-quark jets using a jet charge algorithm applied to SVT-tagged jets. A method to calibrate the jet charge algorithm with data is developed. A constrained kinematic fit is performed to associate the W bosons to the correct b-quark jets in the event and extract the top quark electric charge.
    [Show full text]
  • Searching for a Heavy Partner to the Top Quark
    SEARCHING FOR A HEAVY PARTNER TO THE TOP QUARK JOSEPH VAN DER LIST 5e Abstract. We present a search for a heavy partner to the top quark with charge 3 , where e is the electron charge. We analyze data from Run 2 of the Large Hadron Collider at a center of mass energy of 13 TeV. This data has been previously investigated without tagging boosted top quark (top tagging) jets, with a data set corresponding to 2.2 fb−1. Here, we present the analysis at 2.3 fb−1 with top tagging. We observe no excesses above the standard model indicating detection of X5=3 , so we set lower limits on the mass of X5=3 . 1. Introduction 1.1. The Standard Model One of the greatest successes of 20th century physics was the classification of subatomic particles and forces into a framework now called the Standard Model of Particle Physics (or SM). Before the development of the SM, many particles had been discovered, but had not yet been codified into a complete framework. The Standard Model provided a unified theoretical framework which explained observed phenomena very well. Furthermore, it made many experimental predictions, such as the existence of the Higgs boson, and the confirmation of many of these has made the SM one of the most well-supported theories developed in the last century. Figure 1. A table showing the particles in the standard model of particle physics. [7] Broadly, the SM organizes subatomic particles into 3 major categories: quarks, leptons, and gauge bosons. Quarks are spin-½ particles which make up most of the mass of visible matter in the universe; nucleons (protons and neutrons) are composed of quarks.
    [Show full text]
  • Three Lectures on Meson Mixing and CKM Phenomenology
    Three Lectures on Meson Mixing and CKM phenomenology Ulrich Nierste Institut f¨ur Theoretische Teilchenphysik Universit¨at Karlsruhe Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany I give an introduction to the theory of meson-antimeson mixing, aiming at students who plan to work at a flavour physics experiment or intend to do associated theoretical studies. I derive the formulae for the time evolution of a neutral meson system and show how the mass and width differences among the neutral meson eigenstates and the CP phase in mixing are calculated in the Standard Model. Special emphasis is laid on CP violation, which is covered in detail for K−K mixing, Bd−Bd mixing and Bs−Bs mixing. I explain the constraints on the apex (ρ, η) of the unitarity triangle implied by ǫK ,∆MBd ,∆MBd /∆MBs and various mixing-induced CP asymmetries such as aCP(Bd → J/ψKshort)(t). The impact of a future measurement of CP violation in flavour-specific Bd decays is also shown. 1 First lecture: A big-brush picture 1.1 Mesons, quarks and box diagrams The neutral K, D, Bd and Bs mesons are the only hadrons which mix with their antiparticles. These meson states are flavour eigenstates and the corresponding antimesons K, D, Bd and Bs have opposite flavour quantum numbers: K sd, D cu, B bd, B bs, ∼ ∼ d ∼ s ∼ K sd, D cu, B bd, B bs, (1) ∼ ∼ d ∼ s ∼ Here for example “Bs bs” means that the Bs meson has the same flavour quantum numbers as the quark pair (b,s), i.e.∼ the beauty and strangeness quantum numbers are B = 1 and S = 1, respectively.
    [Show full text]
  • Quarks and Their Discovery
    Quarks and Their Discovery Parashu Ram Poudel Department of Physics, PN Campus, Pokhara Email: [email protected] Introduction charge (e) of one proton. The different fl avors of Quarks are the smallest building blocks of matter. quarks have different charges. The up (u), charm They are the fundamental constituents of all the (c) and top (t) quarks have electric charge +2e/3 hadrons. They have fractional electronic charge. and the down (d), strange (s) and bottom (b) quarks Quarks never exist alone in nature. They are always have charge -e/3; -e is the charge of an electron. The found in combination with other quarks or antiquark masses of these quarks vary greatly, and of the six, in larger particle of matter. By studying these larger only the up and down quarks, which are by far the particles, scientists have determined the properties lightest, appear to play a direct role in normal matter. of quarks. Protons and neutrons, the particles that make up the nuclei of the atoms consist of quarks. There are four forces that act between the quarks. Without quarks there would be no atoms, and without They are strong force, electromagnetic force, atoms, matter would not exist as we know it. Quarks weak force and gravitational force. The quantum only form triplets called baryons such as proton and of strong force is gluon. Gluons bind quarks or neutron or doublets called mesons such as Kaons and quark and antiquark together to form hadrons. The pi mesons. Quarks exist in six varieties: up (u), down electromagnetic force has photon as quantum that (d), charm (c), strange (s), bottom (b), and top (t) couples the quarks charge.
    [Show full text]
  • Higgs Boson Production in Association with a Top Quark Pair at √ S = 13
    Higgs boson production in association with a top quark pair p at s = 13 TeV with the ATLAS detector Robert Wolff on behalf of the ATLAS Collaboration CPPM, Aix-Marseille Universit´eand CNRS/IN2P3, 163, avenue de Luminy - Case 902 - 13288 Marseille, France A search for the associated production of the Higgs boson with a top quark pair (ttH¯ ) is performed in multileptonic final states using a dataset corresponding to an integrated lumi- nosity of 36.1 fb1 of proton-proton collision data recorded by the ATLAS experiment at a p center-of-mass energy of s = 13 TeV at the Large Hadron Collider. Higgs boson decays to WW ∗, ττ and ZZ∗ are targeted. Seven final states, categorized by the number and flavour of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass close to 125 GeV and a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. Furthermore, the combination of this result with other ttH¯ searches from the ATLAS experiment using the Higgs boson decay modes to b¯b, γγ and ZZ∗ ! 4` is briefly reported. 1 Top quark Yukawa coupling at the LHC The Higgs boson has been discovered by the ATLAS and CMS experiments at the Run 1 of the Large Hadron Collider (LHC) with a mass close to 125 GeV1;2. Its measured properties like spin and interactions are consistent with those predicted for a Higgs boson by the Standard Model (SM) of particle physics.
    [Show full text]
  • Quark Masses 1 66
    66. Quark masses 1 66. Quark Masses Updated August 2019 by A.V. Manohar (UC, San Diego), L.P. Lellouch (CNRS & Aix-Marseille U.), and R.M. Barnett (LBNL). 66.1. Introduction This note discusses some of the theoretical issues relevant for the determination of quark masses, which are fundamental parameters of the Standard Model of particle physics. Unlike the leptons, quarks are confined inside hadrons and are not observed as physical particles. Quark masses therefore cannot be measured directly, but must be determined indirectly through their influence on hadronic properties. Although one often speaks loosely of quark masses as one would of the mass of the electron or muon, any quantitative statement about the value of a quark mass must make careful reference to the particular theoretical framework that is used to define it. It is important to keep this scheme dependence in mind when using the quark mass values tabulated in the data listings. Historically, the first determinations of quark masses were performed using quark models. These are usually called constituent quark masses and are of order 350MeV for the u and d quarks. Constituent quark masses model the effects of dynamical chiral symmetry breaking discussed below, and are not directly related to the quark mass parameters mq of the QCD Lagrangian of Eq. (66.1). The resulting masses only make sense in the limited context of a particular quark model, and cannot be related to the quark mass parameters, mq, of the Standard Model. In order to discuss quark masses at a fundamental level, definitions based on quantum field theory must be used, and the purpose of this note is to discuss these definitions and the corresponding determinations of the values of the masses.
    [Show full text]
  • 11. the Top Quark and the Higgs Mechanism Particle and Nuclear Physics
    11. The Top Quark and the Higgs Mechanism Particle and Nuclear Physics Dr. Tina Potter Dr. Tina Potter 11. The Top Quark and the Higgs Mechanism 1 In this section... Focus on the most recent discoveries of fundamental particles The top quark { prediction & discovery The Higgs mechanism The Higgs discovery Dr. Tina Potter 11. The Top Quark and the Higgs Mechanism 2 Third Generation Quark Weak CC Decays 173 GeV t Cabibbo Allowed |Vtb|~1, log(mass) |Vcs|~|Vud|~0.975 Top quarks are special. Cabibbo Suppressed m(t) m(b)(> m(W )) |Vcd|~|Vus|~0.22 |V |~|V |~0.05 −25 cb ts τt ∼ 10 s ) decays b 4.8GeV before hadronisation Vtb ∼ 1 ) 1.3GeV c BR(t ! W + b)=100% s 95 MeV 2.3MeV u d 4.8 MeV Bottom quarks are also special. b quarks can only decay via the Cabbibo suppressed Wcb vertex. Vcb is very small { weak coupling! Interaction b-jet point ) τ(b) τ(u; c; d; s) b Jet initiated by b quarks look different to other jets. b quarks travel further from interaction point before decaying. b-jet traces back to a secondary vertex {\ b-tagging". Dr. Tina Potter 11. The Top Quark and the Higgs Mechanism 3 The Top Quark The Standard Model predicted the existence of the top quark 2 +3e u c t 1 −3e d s b which is required to explain a number of observations. d µ− Example: Non-observation of the decay W − 0 + − 0 + − −9 K ! µ µ B(K ! µ µ ) < 10 u=c=t νµ The top quark cancels the contributions W + from the u and c quarks.
    [Show full text]
  • ELEMENTARY PARTICLES in PHYSICS 1 Elementary Particles in Physics S
    ELEMENTARY PARTICLES IN PHYSICS 1 Elementary Particles in Physics S. Gasiorowicz and P. Langacker Elementary-particle physics deals with the fundamental constituents of mat- ter and their interactions. In the past several decades an enormous amount of experimental information has been accumulated, and many patterns and sys- tematic features have been observed. Highly successful mathematical theories of the electromagnetic, weak, and strong interactions have been devised and tested. These theories, which are collectively known as the standard model, are almost certainly the correct description of Nature, to first approximation, down to a distance scale 1/1000th the size of the atomic nucleus. There are also spec- ulative but encouraging developments in the attempt to unify these interactions into a simple underlying framework, and even to incorporate quantum gravity in a parameter-free “theory of everything.” In this article we shall attempt to highlight the ways in which information has been organized, and to sketch the outlines of the standard model and its possible extensions. Classification of Particles The particles that have been identified in high-energy experiments fall into dis- tinct classes. There are the leptons (see Electron, Leptons, Neutrino, Muonium), 1 all of which have spin 2 . They may be charged or neutral. The charged lep- tons have electromagnetic as well as weak interactions; the neutral ones only interact weakly. There are three well-defined lepton pairs, the electron (e−) and − the electron neutrino (νe), the muon (µ ) and the muon neutrino (νµ), and the (much heavier) charged lepton, the tau (τ), and its tau neutrino (ντ ). These particles all have antiparticles, in accordance with the predictions of relativistic quantum mechanics (see CPT Theorem).
    [Show full text]
  • The Quark Model and Deep Inelastic Scattering
    The quark model and deep inelastic scattering Contents 1 Introduction 2 1.1 Pions . 2 1.2 Baryon number conservation . 3 1.3 Delta baryons . 3 2 Linear Accelerators 4 3 Symmetries 5 3.1 Baryons . 5 3.2 Mesons . 6 3.3 Quark flow diagrams . 7 3.4 Strangeness . 8 3.5 Pseudoscalar octet . 9 3.6 Baryon octet . 9 4 Colour 10 5 Heavier quarks 13 6 Charmonium 14 7 Hadron decays 16 Appendices 18 .A Isospin x 18 .B Discovery of the Omega x 19 1 The quark model and deep inelastic scattering 1 Symmetry, patterns and substructure The proton and the neutron have rather similar masses. They are distinguished from 2 one another by at least their different electromagnetic interactions, since the proton mp = 938:3 MeV=c is charged, while the neutron is electrically neutral, but they have identical properties 2 mn = 939:6 MeV=c under the strong interaction. This provokes the question as to whether the proton and neutron might have some sort of common substructure. The substructure hypothesis can be investigated by searching for other similar patterns of multiplets of particles. There exists a zoo of other strongly-interacting particles. Exotic particles are ob- served coming from the upper atmosphere in cosmic rays. They can also be created in the labortatory, provided that we can create beams of sufficient energy. The Quark Model allows us to apply a classification to those many strongly interacting states, and to understand the constituents from which they are made. 1.1 Pions The lightest strongly interacting particles are the pions (π).
    [Show full text]
  • Measurement of the Top Quark Mass with Lepton+Jets Final States Using Pp Collisions at Sqrt(S)
    EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-EP-2018-063 2018/11/06 CMS-TOP-17-007 Measurement of the top quark massp with lepton+jets final states using pp collisions at s = 13 TeV The CMS Collaboration∗ Abstract The mass of the top quark is measured using a samplep of tt events collected by the CMS detector using proton-proton collisions at s = 13 TeV at the CERN LHC. Events are selected with one isolated muon or electron and at least four jets from data corresponding to an integrated luminosity of 35.9 fb−1. For each event the mass is reconstructed from a kinematic fit of the decay products to a tt hypothesis. Us- ing the ideogram method, the top quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the mass of the W boson in qq0 decays. The measurement is calibrated on samples simulated at next-to-leading or- der matched to a leading-order parton shower. The top quark mass is found to be 172.25 ± 0.08 (stat+JSF) ± 0.62 (syst) GeV. The dependence of this result on the kine- matic properties of the event is studied and compared to predictions of different mod- els of tt production, and no indications of a bias in the measurements are observed. Published in the European Physical Journal C as doi:10.1140/epjc/s10052-018-6332-9. arXiv:1805.01428v2 [hep-ex] 5 Nov 2018 c 2018 CERN for the benefit of the CMS Collaboration. CC-BY-4.0 license ∗See Appendix A for the list of collaboration members 1 1 Introduction The top quark plays a key role in precision measurements of the standard model (SM) because of its large Yukawa coupling to the Higgs boson.
    [Show full text]
  • The Discovery of the Top Quark
    The discovery of the top quark Claudio Campagnari University of California, Santa Barbara, California 93106 Melissa Franklin Harvard University, Cambridge, Massachusetts 02138 Evidence for pair production of a new particle consistent with the standard-model top quark has been reported recently by groups studying proton-antiproton collisions at 1.8 TeV center-of-mass energy at the Fermi National Accelerator Laboratory. This paper both reviews the history of the search for the top quark in electron-positron and proton-antiproton collisions and reports on a number of precise electroweak measurements and the value of the top-quark mass that can be extracted from them. Within the context of the standard model, the authors review the theoretical predictions for top-quark production and the dominant backgrounds. They describe the collider and the detectors that were used to measure the pair-production process and the data from which the existence of the top quark is evinced. Finally, they suggest possible measurements that could be made in the future with more data, measurements that would confirm the nature of this particle, the details of its production in hadron collisions, and its decay properties. [S0034-6861(97)00101-3] CONTENTS 2. Z tt background 174 → 3. Drell-Yan background 174 4. WW background 175 I. Introduction 137 5. bb¯ and fake-lepton backgrounds 175 II. The Role of the Top Quark in the Standard Model 138 6. Results 175 III. Top Mass and Precision Electroweak Measurements 140 B. Lepton 1 jets + b tag 176 A. Measurements from neutral-current experiments 140 1. Selection of lepton 1 jets data before b 1.
    [Show full text]
  • Direct Measurement of the Top Quark Decay Width in the Muon+Jets Channel Using the CMS Experiment at the LHC
    Vrije Universiteit Brussel Faculteit Wetenschappen en Bio-ingenieurswetenschappen Departement Natuurkunde Direct measurement of the top quark decay width in the muon+jets channel using the CMS experiment at the LHC Lieselotte Moreels Promotor Prof. Dr. Petra Van Mulders Co-promotor Prof. Dr. Jorgen D’Hondt Proefschrift ingediend met het oog op het behalen van de academische graad Doctor in de Wetenschappen April 2018 Doctoral examination commission: Prof. Dr. Nick van Eijndhoven (Vrije Universiteit Brussel, chair ) Prof. Dr. Alberto Mariotti (Vrije Universiteit Brussel, secretary ) Prof. Dr. Petra Van Mulders (Vrije Universiteit Brussel, supervisor ) Prof. Dr. Jorgen D’Hondt (Vrije Universtiteit Brussel, advisor ) Prof. Dr. Dirk Ryckbosch (Universiteit Gent) Dr. Ivan Marchesini (Vrije Universiteit Brussel) Dr. Rebeca Gonzalez Suarez (University of Nebraska, USA) Prof. Dr. Philippe Claeys (Vrije Universiteit Brussel) Cover illustration: Fisheye view of the CMS detector. The barrel (front) and one of the endcaps (back) are connected by the beam pipe. Picture taken from CMS-doc-13419-v1. Cover kindly designed by Isis Van Parijs. ISBN: 978 94 923 1271 6 NUR: 924, 926 c 2018 Lieselotte Moreels All rights reserved. No parts of this book may be reproduced or transmitted in any form or by any means, electronic, mechanical, pho- tocopying, recording, or otherwise, without the prior written permission of the author. Contents Introduction 1 1 The Particle Universe 3 1.1 The Standard Model . .4 1.1.1 Particles and forces . .4 1.1.2 Mathematical framework . .7 1.1.3 Open questions . 10 1.2 The Top Quark Sector . 12 1.2.1 Production and decay . 13 1.2.2 Top quark mass .
    [Show full text]