Particle Physics Handout 8 the Weak Force
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Fundamentals of Particle Physics
Fundamentals of Par0cle Physics Particle Physics Masterclass Emmanuel Olaiya 1 The Universe u The universe is 15 billion years old u Around 150 billion galaxies (150,000,000,000) u Each galaxy has around 300 billion stars (300,000,000,000) u 150 billion x 300 billion stars (that is a lot of stars!) u That is a huge amount of material u That is an unimaginable amount of particles u How do we even begin to understand all of matter? 2 How many elementary particles does it take to describe the matter around us? 3 We can describe the material around us using just 3 particles . 3 Matter Particles +2/3 U Point like elementary particles that protons and neutrons are made from. Quarks Hence we can construct all nuclei using these two particles -1/3 d -1 Electrons orbit the nuclei and are help to e form molecules. These are also point like elementary particles Leptons We can build the world around us with these 3 particles. But how do they interact. To understand their interactions we have to introduce forces! Force carriers g1 g2 g3 g4 g5 g6 g7 g8 The gluon, of which there are 8 is the force carrier for nuclear forces Consider 2 forces: nuclear forces, and electromagnetism The photon, ie light is the force carrier when experiencing forces such and electricity and magnetism γ SOME FAMILAR THE ATOM PARTICLES ≈10-10m electron (-) 0.511 MeV A Fundamental (“pointlike”) Particle THE NUCLEUS proton (+) 938.3 MeV neutron (0) 939.6 MeV E=mc2. Einstein’s equation tells us mass and energy are equivalent Wave/Particle Duality (Quantum Mechanics) Einstein E -
Exploring the Spectrum of QCD Using a Space-Time Lattice
ExploringExploring thethe spectrumspectrum ofof QCDQCD usingusing aa spacespace--timetime latticelattice Colin Morningstar (Carnegie Mellon University) New Theoretical Tools for Nucleon Resonance Analysis Argonne National Laboratory August 31, 2005 August 31, 2005 Exploring spectrum (C. Morningstar) 1 OutlineOutline z spectroscopy is a powerful tool for distilling key degrees of freedom z calculating spectrum of QCD Æ introduction of space-time lattice spectrum determination requires extraction of excited-state energies discuss how to extract excited-state energies from Monte Carlo estimates of correlation functions in Euclidean lattice field theory z applications: Yang-Mills glueballs heavy-quark hybrid mesons baryon and meson spectrum (work in progress) August 31, 2005 Exploring spectrum (C. Morningstar) 2 MonteMonte CarloCarlo methodmethod withwith spacespace--timetime latticelattice z introduction of space-time lattice allows Monte Carlo evaluation of path integrals needed to extract spectrum from QCD Lagrangian LQCD Lagrangian of hadron spectrum, QCD structure, transitions z tool to search for better ways of calculating in gauge theories what dominates the path integrals? (instantons, center vortices,…) construction of effective field theory of glue? (strings,…) August 31, 2005 Exploring spectrum (C. Morningstar) 3 EnergiesEnergies fromfrom correlationcorrelation functionsfunctions z stationary state energies can be extracted from asymptotic decay rate of temporal correlations of the fields (in the imaginary time formalism) Ht −Ht z evolution in Heisenberg picture φ ( t ) = e φ ( 0 ) e ( H = Hamiltonian) z spectral representation of a simple correlation function assume transfer matrix, ignore temporal boundary conditions focus only on one time ordering insert complete set of 0 φφ(te) (0) 0 = ∑ 0 Htφ(0) e−Ht nnφ(0) 0 energy eigenstates n (discrete and continuous) 2 −−()EEnn00t −−()EEt ==∑∑neφ(0) 0 Ane nn z extract A 1 and E 1 − E 0 as t → ∞ (assuming 0 φ ( 0 ) 0 = 0 and 1 φ ( 0 ) 0 ≠ 0) August 31, 2005 Exploring spectrum (C. -
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. -
1. Discovery of the W and Z Boson 1983 at CERN Spps Accelerator, √S≈540 Gev, UA-1/2 Experiments 1.1 Boson Production in Pp Interactions
Experimental tests of the Standard Model • Discovery of the W and Z bosons • Precision tests of the Z sector • Precision tests of the W sector • Electro-weak unification at HERA • Radiative corrections and prediction of the top and Higgs mass • Top discovery at the Tevatron • Higgs searches at the LHC 1. Discovery of the W and Z boson 1983 at CERN SppS accelerator, √s≈540 GeV, UA-1/2 experiments 1.1 Boson production in pp interactions − − p , q p ,q u W u Z ˆ ˆ d s ν u s +,q p , q p → → ν + → → + pp W X pp Z ff X σ (σ ) 10 nb W Z Similar to Drell-Yan: (photon instead of W) 1nb = ≈ sˆ xq xq s mit xq 12.0 2 1.0 nb = ≈ = 2 sˆ xq s .0 014 s 65( GeV ) → Cross section is small ! sˆ M 1 10 100 W ,Z 1.2 UA-1 Detector 1.3 Event signature: pp → Z → ff + X + p p − High-energy lepton pair: 2 2 2 m = (p + + p − ) = M Z ≈ MZ 91 GeV → → ν + 1.4 Event signature: pp W X Missing p T vector Undetected ν − ν Missing momentum p p High-energy lepton – Large transverse momentum p t How can the W mass be reconstructed ? W mass measurement In the W rest frame: In the lab system: • = = MW p pν • W system boosted 2 only along z axis T ≤ MW • p • p distribution is conserved 2 T −1 2 dN 2p M 2 Jacobian Peak: T ⋅ W − 2 ~ pT pT MW 4 dN dp T • Trans. -
Supersymmetry: What? Why? When?
Contemporary Physics, 2000, volume41, number6, pages359± 367 Supersymmetry:what? why? when? GORDON L. KANE This article is acolloquium-level review of the idea of supersymmetry and why so many physicists expect it to soon be amajor discovery in particle physics. Supersymmetry is the hypothesis, for which there is indirect evidence, that the underlying laws of nature are symmetric between matter particles (fermions) such as electrons and quarks, and force particles (bosons) such as photons and gluons. 1. Introduction (B) In addition, there are anumber of questions we The Standard Model of particle physics [1] is aremarkably hope will be answered: successful description of the basic constituents of matter (i) Can the forces of nature be uni® ed and (quarks and leptons), and of the interactions (weak, simpli® ed so wedo not have four indepen- electromagnetic, and strong) that lead to the structure dent ones? and complexity of our world (when combined with gravity). (ii) Why is the symmetry group of the Standard It is afull relativistic quantum ®eld theory. It is now very Model SU(3) ´SU(2) ´U(1)? well tested and established. Many experiments con® rmits (iii) Why are there three families of quarks and predictions and none disagree with them. leptons? Nevertheless, weexpect the Standard Model to be (iv) Why do the quarks and leptons have the extendedÐ not wrong, but extended, much as Maxwell’s masses they do? equation are extended to be apart of the Standard Model. (v) Can wehave aquantum theory of gravity? There are two sorts of reasons why weexpect the Standard (vi) Why is the cosmological constant much Model to be extended. -
Measurement of the W-Boson Mass in Pp Collisions at √ S = 7 Tev
EUROPEAN ORGANISATION FOR NUCLEAR RESEARCH (CERN) Eur. Phys. J. C 78 (2018) 110 CERN-EP-2016-305 DOI: 10.1140/epjc/s10052-017-5475-4 9th November 2018 Measurementp of the W-boson mass in pp collisions at s = 7 TeV with the ATLAS detector The ATLAS Collaboration A measurement of the mass of the W boson is presented based on proton–proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding to 4.6 fb−1 of integrated luminosity. The selected data sample consists of 7:8 × 106 candidates in the W ! µν channel and 5:9 × 106 candidates in the W ! eν channel. The W-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the W boson transverse mass in the electron and muon decay channels, yielding mW = 80370 ± 7 (stat.) ± 11 (exp. syst.) ± 14 (mod. syst.) MeV = 80370 ± 19 MeV; where the first uncertainty is statistical, the second corresponds to the experimental system- atic uncertainty, and the third to the physics-modelling systematic uncertainty. A meas- arXiv:1701.07240v2 [hep-ex] 7 Nov 2018 + − urement of the mass difference between the W and W bosons yields mW+ − mW− = −29 ± 28 MeV. c 2018 CERN for the benefit of the ATLAS Collaboration. Reproduction of this article or parts of it is allowed as specified in the CC-BY-4.0 license. 1 Introduction The Standard Model (SM) of particle physics describes the electroweak interactions as being mediated by the W boson, the Z boson, and the photon, in a gauge theory based on the SU(2)L × U(1)Y symmetry [1– 3]. -
Particle Physics: Problem Sheet 5 Weak, Electroweak and LHC Physics
2010 — Subatomic: Particle Physics 1 Particle Physics: Problem Sheet 5 Weak, electroweak and LHC Physics 1. Draw a quark level Feynman diagram for the decay K+ → π+π0. This + is a weak decay. K has strange quark number, Ns = −1. The final state has no strange quarks so Ns = 0. The number of strange quarks can only change when a W boson is exchanged. 2. Write down all possible decay modes of the W − boson into quarks and leptons. What is the strength of each of these vertices? Decay Strength − − W → e ν¯e gW − − W → τ ν¯τ gW − − W → µ ν¯µ gW − W → ¯us gW Vus − W → ¯ud gW Vud − W → ¯ub gW Vub − W → ¯cd gW Vcd − W → ¯cs gW Vcs − W → ¯cb gW Vcb − W → ¯t d gW Vtd − W → ¯t s gW Vts − W → ¯t b gW Vtb 3. By drawing the lowest order Feynman diagrams, show that both charged (W ± exchange) and neutral current (Z0 exchange) contribute to neutrino − − electron scattering: νe + e → νe + e . 2010 — Subatomic: Particle Physics 2 Charged current means exchange of the W ± boson, neutral current means exchange of the Z0 boson. Because we can draw both diagrams, whilst obeying all the conservation laws, it means that both are able to happen. When we observe an electron-neutrino scat- tering event we can never tell, on an event-by-event basis, whether the Z-boson or the W -boson was responsilbe. However by measuring the total cross section and comparing with predictions, we can show that both charged and neutral currents are involved. -
The Discovery of the W and Z Particles
June 16, 2015 15:44 60 Years of CERN Experiments and Discoveries – 9.75in x 6.5in b2114-ch06 page 137 The Discovery of the W and Z Particles Luigi Di Lella1 and Carlo Rubbia2 1Physics Department, University of Pisa, 56127 Pisa, Italy [email protected] 2GSSI (Gran Sasso Science Institute), 67100 L’Aquila, Italy [email protected] This article describes the scientific achievements that led to the discovery of the weak intermediate vector bosons, W± and Z, from the original proposal to modify an existing high-energy proton accelerator into a proton–antiproton collider and its implementation at CERN, to the design, construction and operation of the detectors which provided the first evidence for the production and decay of these two fundamental particles. 1. Introduction The first experimental evidence in favour of a unified description of the weak and electromagnetic interactions was obtained in 1973, with the observation of neutrino interactions resulting in final states which could only be explained by assuming that the interaction was mediated by the exchange of a massive, electrically neutral virtual particle.1 Within the framework of the Standard Model, these observations provided a determination of the weak mixing angle, θw, which, despite its large experimental uncertainty, allowed the first quantitative prediction for the mass values of the weak bosons, W± and Z. The numerical values so obtained ranged from 60 to 80 GeV for the W mass, and from 75 to 92 GeV for the Z mass, too large to be accessible by any accelerator in operation at that time. -
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. -
Higgs Bosons with Large Couplings to Light Quarks
YITP-SB-19-25 Higgs bosons with large couplings to light quarks Daniel Egana-Ugrinovic1;2, Samuel Homiller1;3 and Patrick Meade1 1C. N. Yang Institute for Theoretical Physics, Stony Brook University, Stony Brook, New York 11794, USA 2Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2L 2Y5, Canada 3Department of Physics, Brookhaven National Laboratory, Upton, New York 11973, USA Abstract A common lore has arisen that beyond the Standard Model (BSM) particles, which can be searched for at current and proposed experiments, should have flavorless or mostly third-generation interactions with Standard Model quarks. This theoretical bias severely limits the exploration of BSM phenomenology, and is especially con- straining for extended Higgs sectors. Such limitations can be avoided in the context of Spontaneous Flavor Violation (SFV), a robust and UV complete framework that allows for significant couplings to any up or down-type quark, while suppressing flavor- changing neutral currents via flavor alignment. In this work we study the theory and phenomenology of extended SFV Higgs sectors with large couplings to any quark generation. We perform a comprehensive analysis of flavor and collider constraints of extended SFV Higgs sectors, and demonstrate that new Higgs bosons with large arXiv:1908.11376v2 [hep-ph] 31 Dec 2019 couplings to the light quarks may be found at the electroweak scale. In particular, we find that new Higgses as light as 100 GeV with order ∼ 0.1 couplings to first- or second-generation quarks, which are copiously produced at the LHC via quark fusion, are allowed by current constraints. Furthermore, the additional SFV Higgses can mix with the SM Higgs, providing strong theory motivation for an experimental program looking for deviations in the light quark{Higgs couplings. -
The 21St-Century Electron Microscope for the Study of the Fundamental Structure of Matter
The Electron-Ion Collider The 21st-Century Electron Microscope for the Study of the Fundamental Structure of Matter 60 ) milner mit physics annual 2020 by Richard G. Milner The Electron-Ion Collider he Fundamental Structure of Matter T Fundamental, curiosity-driven science is funded by developed societies in large part because it is one of the best investments in the future. For example, the study of the fundamental structure of matter over about two centuries underpins modern human civilization. There is a continual cycle of discovery, understanding and application leading to further discovery. The timescales can be long. For example, Maxwell’s equations developed in the mid-nineteenth century to describe simple electrical and magnetic laboratory experiments of that time are the basis for twenty-first century communications. Fundamental experiments by nuclear physicists in the mid-twentieth century to understand spin gave rise to the common medical diagnostic tool, magnetic resonance imaging (MRI). Quantum mechanics, developed about a century ago to describe atomic systems, now is viewed as having great potential for realizing more effective twenty-first century computers. mit physics annual 2020 milner ( 61 u c t g up quark charm quark top quark gluon d s b γ down quark strange quark bottom quark photon ve vμ vτ W electron neutrino muon neutrino tau neutrino W boson e μ τ Z electron muon tau Z boson Einstein H + Gravity Higgs boson figure 1 THE STANDARD MODEL (SM) , whose fundamental constituents are shown sche- Left: Schematic illustration [1] of the fundamental matically in Figure 1, represents an enormous intellectual human achievement. -
Flavor Symmetries and Fermion Masses }
LBL-35586; UCB-PTH-94/10 April 1994 Flavor symmetries and fermion masses } Andrija Rasin 2 Ph. D. Dissertation Department of Physics, University of California, k '•keley, CA 94720 and Theoretical Physics Group, Lawrence Berkeley Laboratory University of California, Berkeley, CA 9J, 720 Abstract We introduce several ways in which approximate flavo; ymmetries act on fermions and which are consistent with observed fermion masses and mixings. Flavor changing interactions mediated by new scalars appear as a consequence of approximate flavor symmetries. We discuss the experimental limits on masses of the new scalars, and show that the masses can easily be of the order of weak scale. Some implications for neutrino physics are also discussed. Such flavor changing interactions would easily erase any primordial baryon asymmetry. We show that this situation can be saved by simply adding a new charged particle with its own asymmetry. The neutral ity of the Universe, together with sphaleron processes, then ensures a survival of baryon asymmetry. Several topics on flavor structure of the supersymmetric grand uni fied theories are discussed. First, we show that the successful predic tions for the Kobayashi-Maskawa mixing matrix elements, V^/V^ = i , . Jm^/mc and Vtd/Vu = Jm,ilm„ are a consequence of a large class of models, rather than specific properties of a few models. Second, we discuss how the recent observation of the decay b —» 57 constrains the parameter space when the ratio of the vacuum expectation values of the two Higgs doublets, tan/?, is large. Finally, we discuss the flavor structure of proton decay. We observe a surprising enhancement of the branching ratio for the muon mode in SO(10) models compared to the same mode in the SU(5) model.