60. Top Quark
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Decays of the Tau Lepton*
SLAC - 292 UC - 34D (E) DECAYS OF THE TAU LEPTON* Patricia R. Burchat Stanford Linear Accelerator Center Stanford University Stanford, California 94305 February 1986 Prepared for the Department of Energy under contract number DE-AC03-76SF00515 Printed in the United States of America. Available from the National Techni- cal Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22161. Price: Printed Copy A07, Microfiche AOl. JC Ph.D. Dissertation. Abstract Previous measurements of the branching fractions of the tau lepton result in a discrepancy between the inclusive branching fraction and the sum of the exclusive branching fractions to final states containing one charged particle. The sum of the exclusive branching fractions is significantly smaller than the inclusive branching fraction. In this analysis, the branching fractions for all the major decay modes are measured simultaneously with the sum of the branching fractions constrained to be one. The branching fractions are measured using an unbiased sample of tau decays, with little background, selected from 207 pb-l of data accumulated with the Mark II detector at the PEP e+e- storage ring. The sample is selected using the decay products of one member of the r+~- pair produced in e+e- annihilation to identify the event and then including the opposite member of the pair in the sample. The sample is divided into subgroups according to charged and neutral particle multiplicity, and charged particle identification. The branching fractions are simultaneously measured using an unfold technique and a maximum likelihood fit. The results of this analysis indicate that the discrepancy found in previous experiments is possibly due to two sources. -
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. -
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. -
Probing Light Gauge Bosons in Tau Neutrino Experiments
Probing Light Gauge Bosons in Tau Neutrino Experiments Felix Kling∗ SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA The tau neutrino is probably the least studied particle in the SM, with only a handful of interaction events being identified so far. This can in part be attributed to their small production rate in the SM, which occurs mainly through Ds meson decay. However, this also makes the tau neutrino flux measurement an interesting laboratory for additional new physics production modes. In this study, we investigate the possibility of tau neutrino production in the decay of light vector bosons. We consider four scenarios of anomaly-free U(1) gauge groups corresponding to the B−L, B−Lµ−2Lτ , B − Le − 2Lτ and B − 3Lτ numbers, analyze current constraints on their parameter spaces and explore the sensitivity of DONuT and as well as the future emulsion detector experiments FASERν, SND@LHC and SND@SHiP. We find that these experiments provide the leading direct constraints in parts of the parameter space, especially when the vector boson's mass is close to the mass of the ! meson. I. INTRODUCTION other neutrino flavors. This small SM production rate makes the tau neutrino flux measurement an interesting The standard model (SM) consist of 17 particles, out laboratory for additional beyond the SM (BSM) produc- tion modes. of which the tau neutrino ντ is the least experimentally constrained one. To detect the rare tau neutrino interac- One example of such new physics are light vector tions, an intense neutrino beam with a sufficiently large bosons V associated with additional gauge groups. -
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. -
J = Τ MASS Page 1
Citation: P.A. Zyla et al. (Particle Data Group), Prog. Theor. Exp. Phys. 2020, 083C01 (2020) J 1 τ = 2 + + τ discovery paper was PERL 75. e e− → τ τ− cross-section threshold behavior and magnitude are consistent with pointlike spin- 1/2 Dirac particle. BRANDELIK 78 ruled out pointlike spin-0 or spin-1 particle. FELDMAN 78 ruled out J = 3/2. KIRKBY 79 also ruled out J=integer, J = 3/2. τ MASS VALUE (MeV) EVTS DOCUMENT ID TECN COMMENT 1776..86 0..12 OUR AVERAGE ± +0.10 1776.91 0.12 1171 1 ABLIKIM 14D BES3 23.3 pb 1, Eee = ± 0.13 − cm − 3.54–3.60 GeV 1776.68 0.12 0.41 682k 2 AUBERT 09AK BABR 423 fb 1, Eee =10.6 GeV ± ± − cm 1776.81+0.25 0.15 81 ANASHIN 07 KEDR 6.7 pb 1, Eee = 0.23 ± − cm − 3.54–3.78 GeV 1776.61 0.13 0.35 2 BELOUS 07 BELL 414 fb 1 Eee =10.6 GeV ± ± − cm 1775.1 1.6 1.0 13.3k 3 ABBIENDI 00A OPAL 1990–1995 LEP runs ± ± 1778.2 0.8 1.2 ANASTASSOV 97 CLEO Eee = 10.6 GeV ± ± cm . +0.18 +0.25 4 Eee . 1776 96 0.21 0.17 65 BAI 96 BES cm= 3 54–3 57 GeV − − 1776.3 2.4 1.4 11k 5 ALBRECHT 92M ARG Eee = 9.4–10.6 GeV ± ± cm +3 6 Eee 1783 4 692 BACINO 78B DLCO cm= 3.1–7.4 GeV − We do not use the following data for averages, fits, limits, etc. -
Tau (Or No) Leptons in Top Quark Decays at Hadron Colliders
Tau (or no) leptons in top quark decays at hadron colliders Michele Gallinaro for the CDF, D0, ATLAS, and CMS collaborations Laborat´oriode Instrumenta¸c˜aoe F´ısicaExperimental de Part´ıculas LIP Lisbon, Portugal DOI: http://dx.doi.org/10.3204/DESY-PROC-2014-02/12 Measurements in the final states with taus or with no-leptons are among the most chal- lenging as they are those with the smallest signal-to-background ratio. However, these final states are of particular interest as they can be important probes of new physics. Tau identification techniques and cross section measurements in top quark decays in these final states are discussed. The results, limited by systematical uncertainties, are consistent with standard model predictions, and are used to set stringent limits on new physics searches. The large data samples available at the Fermilab and at the Large Hadron Collider may help further improving the measurements. 1 Introduction Many years after its discovery [1, 2], the top quark still plays a fundamental role in the program of particle physics. The study of its properties has been extensively carried out in high energy hadron collisions. The production cross section has been measured in many different final states. Deviation of the cross section from the predicted standard model (SM) value may indicate new physics processes. Top quarks are predominantly produced in pairs, and in each top quark pair event, there are two W bosons and two bottom quarks. From the experimental point of view, top quark pair events are classified according to the decay mode of the two W bosons: the all-hadronic final state, in which both W bosons decay into quarks, the “lepton+jet” final state, in which one W decays leptonically and the other to quarks, and the dilepton final state, in which both W bosons decay leptonically. -
Search for Rare Multi-Pion Decays of the Tau Lepton Using the Babar Detector
SEARCH FOR RARE MULTI-PION DECAYS OF THE TAU LEPTON USING THE BABAR DETECTOR DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Ruben Ter-Antonyan, M.S. * * * * * The Ohio State University 2006 Dissertation Committee: Approved by Richard D. Kass, Adviser Klaus Honscheid Adviser Michael A. Lisa Physics Graduate Program Junko Shigemitsu Ralph von Frese ABSTRACT A search for the decay of the τ lepton to rare multi-pion final states is performed + using the BABAR detector at the PEP-II asymmetric-energy e e− collider. The anal- 1 ysis uses 232 fb− of data at center-of-mass energies on or near the Υ(4S) resonance. + 0 In the search for the τ − 3π−2π 2π ν decay, we observe 10 events with an ex- ! τ +2:0 pected background of 6:5 1:4 events. In the absence of a signal, we calculate the − + 0 6 decay branching ratio upper limit (τ − 3π−2π 2π ν ) < 3:4 10− at the 90 % B ! τ × confidence level. This is more than a factor of 30 improvement over the previously established limit. In addition, we search for the exclusive decay mode τ − 2!π−ν ! τ + 0 +1:0 with the further decay of ! π−π π . We observe 1 event, expecting 0.4 0:4 back- ! − 7 ground events, and calculate the upper limit (τ − 2!π−ν ) < 5:4 10− at the B ! τ × 90 % confidence level. This is the first upper limit for this mode. -
Dstau: Study of Tau Neutrino Production with 400 Gev Protons from the CERN-SPS
Prepared for submission to JHEP DsTau: Study of tau neutrino production with 400 GeV protons from the CERN-SPS Shigeki Aoki,a Akitaka Ariga,b;1 Tomoko Ariga,b;c Sergey Dmitrievsky,d Elena Firu,e Dean Forshaw,b Tsutomu Fukuda,f Yuri Gornushkin,d Ali Murat Guler,g Maria Haiduc,e Koichi Kodama,h Masahiro Komatsu,f Muhtesem Akif Korkmaz,g Umut Kose,i Madalina Miloi,e Antonio Miucci,b Motoaki Miyanishi,f Mitsuhiro Nakamura,f Toshiyuki Nakano,f Alina Neagu,e Hiroki Rokujo,f Osamu Sato,f Elizaveta Sitnikova,d Yosuke Suzuki,f Tomoki Takao,f Svetlana Vasina,d Mykhailo Vladymyrov,b Thomas Weston,b Junya Yoshida,j Masahiro Yoshimoto.k The DsTau Collaboration aKobe University, Kobe, Japan bAlbert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern, Bern, Switzerland cKyushu University, Fukuoka, Japan dJoint Institute for Nuclear Research, Dubna, Russia eInstitute of Space Science, Bucharest, Romania f Nagoya University, Nagoya, Japan gMiddle East Technical University, Ankara, Turkey hAichi University of Education, Kariya, Japan iCERN, Geneva, Switzerland jAdvanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan kGifu University, Gifu, Japan E-mail: [email protected] Abstract: In the DsTau experiment at the CERN SPS, an independent and direct way to measure tau neutrino production following high energy proton interactions was proposed. As the main source of tau neutrinos is a decay of Ds mesons, produced in proton-nucleus arXiv:1906.03487v1 [hep-ex] 8 Jun 2019 interactions, the project aims at measuring a differential cross section of this reaction. The experimental method is based on a use of high resolution emulsion detectors for effective registration of events with short lived particle decays. -
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. -
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. -
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.