DOCSLIB.ORG

Standard Modelmodel -- Electroweakelectroweak Interactionsinteractions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Standard Modelmodel -- Electroweakelectroweak Interactionsinteractions StandardStandard ModelModel -- ElectroweakElectroweak InteractionsInteractions OutlineOutline Weak Neutral Interactions Neutral Currents (NC) Electroweak Theory W± and Z0 and γ Discovery of W± and Z0 bosons Experimental Tests LEP Z0 Boson Mass and Width Number of Neutrinos W± Boson W± Pair Production Mass and Width Higgs Boson Mass, LHC Supersymmetry SUSY Unification Standard Model Summary Nuclear and Particle Physics Franz Muheim 1 WeakWeak NeutralNeutral InteractionsInteractions Weak Neutral Current (NC) Z0 boson couples to all fermions: neutrinos, charged leptons, quarks Weak NC is flavour conserving e.g µτZ0 vertex does not exist Coupling Strength Proportional to weak neutral charge g’W 0 Î For each Z vertex add factor g’W to matrix element How are g’W and weak charge gW related? Z0 Boson Propagator Neutral Current mediated by exchange of virtual Z0 boson 2 2 Î Add propagator term 1/(q –MZ ) to matrix element/amplitude At small q2 NC masked by electromagnetic interactions Are weak and electromagnetic force related? Discovery of Neutral Currents 1973 Bubble chamber Gargamelle at CERN 3 events in elastic νµ neutrino scattering e − − ν µ + e →ν µ + e Anti-νµ beam Very low background Nuclear and Particle Physics Franz Muheim 2 StandardStandard ModelModel ElectroweakElectroweak InteractionsInteractions Electroweak Unification Developed in 1960s by Glashow Weinberg Salam Quantum Theory of weak charged (CC) and neutral currents (NC) and electromagnetic interactions (QED) Surprise - QED and weak interactions are a unified force Electroweak Gauge Bosons Initially four massless bosons W+, W0, W- and B0 Neutral bosons mix Î Physical bosons W± and Z0 and γ ⎛ Z 0 ⎞ ⎛cosθ − sinθ ⎞ ⎛W 0 ⎞ ⎜ ⎟ = ⎜ W W ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ 0 ⎟ ⎝γ ⎠ ⎝ sinθ W cosθ W ⎠ ⎝ B ⎠ θW weak mixing (Weinberg) angle W± and Z0 acquire mass via Higgs Mechanism Electroweak Coupling Constants gW and g’W are related to electric charge e e = gW sin θW = g’W cos θW 2 2 ElectroweakElectroElectroweakweak TheoryTTheoryheory e GF gW αem = , = 2 , sinθW 3 fundamental parameters, e.g. 4π 2 8MW ± 0 2 2 2 Mass of W and Z related M Z 0 = MW / cos θW Predicts coupling strengths of W± and Z0 to quarks and leptons, self interaction couplings of W± and Z0 and γ Nuclear and Particle Physics Franz Muheim 3 WW andand ZZ BosonsBosons Virtual W± and Z0 Bosons Mediate weak interaction in scattering and decay of weakly interacting fermions − − 0 − + e.g. muon or meson decay, µ → e ν eν µ D → K µ ν µ − − − − v-e scattering ν e + e →ν e + e ν µ + e →ν µ + e Real W± and Z0 Bosons Produced in collisions if sufficient energy available + + + u + d → W → e ν e , µ ν µ − − − u + d → W → e ν e , µ ν µ u + u⎫ ⎬ → Z 0 → e +e − , µ + µ − d + d ⎭ Discovery of W± and Z0 Bosons at p-pbar collider at CERN in 1983 Energy E(p) =E(pbar) = 270 GeV W event UA1 experiment CERN − − e- W → e ν e Nuclear and Particle Physics Franz Muheim 4 ExperimentalExperimental TestsTests -- LEPLEP LEP - Large Electron Positron Collider Largest e+e- collider, 27 km circumference Centre-of-mass energy √s = 90 – 200 GeV Operational from 1989 to 2000 Four experiments: Aleph, Delphi, L3, OPAL e +e − → Z 0 → qq → hadrons Z0 Bosons at LEP Resonance production at √s = MZ ~4 million e+ e- → Z0 events/expt W± Bosons at LEP Production at √s ≥ 2 MW ~8000 e+ e- → W+ W- events/expt LEP Measurements Mass and width of Z0 and W± bosons Z0 and W± boson couplings to quarks and leptons Weak decays of heavy mesons QCD measurements Precision tests of Standard Model of Particle Physics Nuclear and Particle Physics Franz Muheim 5 ZZ0 ResonanceResonance e+ e- Annihilations → Hadrons at High Energies √s < 50 GeV exchange of γ dominates At larger energies √s ≥ 50 GeV Z0 and γ exchange diagram, also Z0/γ interference Z0 Boson Production 0 at energies √s ≈ MZ production of real Z boson diagram with Z0 boson dominates Z0 boson is Breit-Wigner Resonance Z0 boson decays very fast, lifetime τ ~ 10-25 s 0 Measure energy width of Z resonance ΓZ = ħ/τ Nuclear and Particle Physics Franz Muheim 6 ZZ0 MassMass andand WidthWidth Breit-Wigner Resonance Cross section for relativistic initial and final states 4π Γee Γ σ ()e +e − → Z 0 → f f = g ff s ⎡ 2 2 ⎤ ()s − M Z + ΓZ / 4 ⎣⎢ ⎦⎥ 0 Partial decay widths Γff = Γ(Z → f f ) Spin: average initial states 2J + 1 g = Z & sum final states ()2se− + 1 (2se+ + 1) Total Decay Width ΓZ Sum over all partial decay widths Γff Γ = Γ + Γ + Γ + Γ + Γ + Γ + Γ Z qq ee µµ ττ ν eν e ν µν µ ντντ Cross section at peak of resonance √s = MZ 0 + − 0 12π Γee Γff σ ff = σ ()e e → Z → f f = 2 2 M Z ΓZ Z0 Resonance Measure e+ e- → Hadrons at energies close to MZ QED corrections Shift: e+ e- → γ hadrons Mass and Width of Z0 MZ = 91.1876(21) GeV ΓZ = 2.49529(23) GeV Peak cross section 0 σ qq = 41.5409(37) nb Nuclear and Particle Physics Franz Muheim 7 ZZ0 PartialPartial DecayDecay WidthsWidths Cross Sections σ (e +e − → Z 0 → f f ) Measurements for all visible fermions Obtain partial decay widths using 0 peak cross section σ qq and MZ, ΓZ Note --- all resonance curves have width ΓZ ΓZ = 2495.2 ± 2.3 MeV Γ = 1744.4 ± 2.0 MeV qq Evidence for Ncolour = 3 Γll = Γee = Γµµ = Γττ = 83.984 ± 0.086 MeV Invisible Z0 Width 0 Decays Z →ν eν e ,ν µν µ ,ν τν τ Comparison of total and partial decay widths ΓZ = Γqq + Γee + Γµµ + Γττ + Nν Γνν Nν - number of Γ = Γ = Γ = Γ neutrino flavours νν ν eν e ν µν µ ντντ Number of Neutrino Flavours Prediction Γνν = 167 MeV Measurement NνΓνν = 499.0 ± 1.5 MeV Number of light neutrinos Nν = 2.994 ± 0.012 (with mass mν < MZ/2) Consistency also for e, µ, τ Lepton universality holds for Z0 →ee, µµ, ττ couplings Nuclear and Particle Physics Franz Muheim 8 WW+WW- PairPair ProductionProduction Standard Model Diagrams W± Boson Decays CC Universality for leptons and weak quark eigenstates − − − − − − 1 ± Γ(W → e ν e )= Γ(W → µ ν µ ) = Γ(W → τ ν τ )= 3 Γ(W → lν ) − − − − − Γ()W → d'u = Γ()W → s'c = N cΓ()W → e ν e Γ()W → b't = 0 ⇒ Γ()W ± → q'q = 2Γ(W ± → lν ) e+ e- → W+ W- at LEP Example L3 experiment + − + − − e e → W W → qqe ν e My 1st W± pair Cross Section vs Energy Agrees with SM prediction Confirms existence of Mass and Width of W± Boson W+ W- Z0 vertex MW = 80.425 ± 0.038 GeV Nuclear and Particle Physics Franz Muheim 9 ΓW = 2.124 ±.0.041 GeV HiggsHiggs andand UnificationUnification Electroweak Theory 2 Precise measurements of αem, GF, MZ, MW and sin θW Only 3 independent parameters Powerful constraints, corrections: higher order diagrams Higgs Mechanism Only missing particle in Standard Model Scalar, i.e Spin 0, Non-zero vacuum -> All particles acquire mass by Higgs interaction Peter Higgs Higgs coupling ∝ mass gHff = √(√2 GF ) mf Prof emeritus Direct Mass Limit MH > 114 GeV Univ of Edinburgh Require Large Hadron Collider (LHC) starts in 2007 Supersymmetry - SUSY SUSY Partners: Fermion ↔ Boson fermion ↔ sfermion Unification of electroweak boson ↔ …ino and strong interaction α1 = αem α2 = αW α3 = αS Nuclear and Particle Physics Franz Muheim 10 StandardStandard ModelModel ofof ParticleParticle PhysicsPhysics One-pageOne-page SummarySummary Fermions Gauge Bosons Quarks and Leptons Mediate interactions 3 Generations of Charge Inter- Gauge Charge Coupling action Goson Constant Leptons & Quarks [e] [e] Strong g 0 αS ≈ 0.2 νe νµ ντ 0 µ τ e- - - -1 Electro γ 0 αem ≈ 0.008 u c t +2/3 magnetic 0 d s b -1/3 Weak Z 0 αW ≈ 0.03 W± ±1 Electromagnetic (QED) Strong (QCD) γ couples to charge e g couple to colour conserves q, l flavour quark flavour conserved Weak Charged Current (CC) Neutral Current (NC) ± 0 W couples to weak charge gW Z couples to g’W Flavour changing for quarks conserves q, l flavour Nuclear and Particle Physics Franz Muheim 11 FeynmanFeynman DiagramsDiagrams One-Page Tutorial One-pageOne-page TutorialTutorial Scattering, annihilation or decays Only Standard Model vertices Initial and final states Write down quark/lepton/boson content for all initial and final state particles Interactions Try to find out which exchange bosons are responsible for reaction by checking conservation laws Conservation Laws For all interactions at each vertex Energy-momentum Electric charge, Baryon number For strong and electromagnetic interactions Quark and Lepton flavour, Parity, Isospin, Strangeness For weak charged interactions (CC) Quark flavour is not conserved, Lepton universality For weak neutral interaction (NC) Quark and lepton flavour are conserved Useful Hints Photon only interacts electromagnetically Neutrinos and Z0 only interact weakly Only Quarks and Gluons interact strongly If more than 1 possibility, faster reaction wins Keep it as simple as possible Nuclear and Particle Physics Franz Muheim 12.
Load more

Recommended publications
  • Quantum Field Theory*
    Quantum Field Theory y Frank Wilczek Institute for Advanced Study, School of Natural Science, Olden Lane, Princeton, NJ 08540 I discuss the general principles underlying quantum eld theory, and attempt to identify its most profound consequences. The deep est of these consequences result from the in nite number of degrees of freedom invoked to implement lo cality.Imention a few of its most striking successes, b oth achieved and prosp ective. Possible limitation s of quantum eld theory are viewed in the light of its history. I. SURVEY Quantum eld theory is the framework in which the regnant theories of the electroweak and strong interactions, which together form the Standard Mo del, are formulated. Quantum electro dynamics (QED), b esides providing a com- plete foundation for atomic physics and chemistry, has supp orted calculations of physical quantities with unparalleled precision. The exp erimentally measured value of the magnetic dip ole moment of the muon, 11 (g 2) = 233 184 600 (1680) 10 ; (1) exp: for example, should b e compared with the theoretical prediction 11 (g 2) = 233 183 478 (308) 10 : (2) theor: In quantum chromo dynamics (QCD) we cannot, for the forseeable future, aspire to to comparable accuracy.Yet QCD provides di erent, and at least equally impressive, evidence for the validity of the basic principles of quantum eld theory. Indeed, b ecause in QCD the interactions are stronger, QCD manifests a wider variety of phenomena characteristic of quantum eld theory. These include esp ecially running of the e ective coupling with distance or energy scale and the phenomenon of con nement.
    [Show full text]
  • Frstfo O Ztif
    FRStfo o ztif * CONNISSARIAT A L'ENERGIE ATOMIQUE CENTRE D'ETUDES NUCLEAIRES DE SACLAY CEA-CONF -- 8070 Service de Documentation F9119! GIF SUR YVETTE CEDEX L2 \ PARTICLE PHYSICS AND GAUGE THEORIES MOREL, A. CEA CEN Socloy, IRF, SPh-T Communication présentée à : Court* on poxticlo phytic* Cargos* (Franc*) 15-28 Jul 1985 PARTICLE PHYSICS AND GAUGE THEORIES A. MOREL Service de Physique Théorique CEN SACLA Y 91191 Gif-sur-Yvette Cedex, France These notes are intended to help readers not familiar with parti­ cle physics in entering the domain of gauge field theory applied to the so-called standard model of strong and electroweak interactions. They are mainly based on previous notes written in common with A. Billoire. With re3pect to the latter ones, the introduction is considerably enlar­ ged in order to give non specialists a general overview of present days "elementary" particle physics. The Glashow-Salam-Weinberg model is then treated,with the details which its unquestioned successes deserve, most probably for a long time. Finally SU(5) is presented as a prototype of these developments of particle physics which aim at a unification of all forces. Although its intrinsic theoretical difficulties and the. non- observation of a sizable proton decay rate do not qualify this model as a realistic one, it has many of the properties expected from a "good" unified theory. In particular, it allows one to study interesting con­ nections between particle physics and cosmology. It is a pleasure to thank the organizing committee of the Cargèse school "Particules et Cosmologie", and especially J. Audouze, for the invitation to lecture on these subjects, and M.F.
    [Show full text]
  • Lesson 46: Cloud & Bubble Chambers
    Lesson 46: Cloud & Bubble Chambers Imagine you're on a really stupid game show where they put a whole bunch of ping pong balls on the floor, turn off the lights, and then send you in to count them. How would you do it? • I'm thinking that your only chance is to get down on your hands and knees and try to touch them around you. • One of the problems is that in the very act of counting them (by reaching out), you change them by pushing them around, maybe even missing some of them. This is kind of the same problem that subatomic physicists have. They have to reach around “in the dark” to measure something that they can't see. • The amazing part is that methods have been developed to do this, and actually do it accurately. • This is the beginning of our journey into the modern subatomic realm of physics. Cloud Chambers In 1894 the Scottish physicist Charles Wilson was interested in the odd shadows that can sometimes be formed on cloud tops by mountain climbers (called Brocken Spectre). • To be able to study this further, he came up with a way water to build a device called a cloud chamber that would droplets allow him to make his own mini-clouds inside a glass chamber. ◦ To be able to do this he made his device so that he could keep the air inside supersaturated with water. ▪ Air can usually only hold a certain amount of path of vapour. Supersaturated means the air was charged particle holding more vapour than it would normally be Illustration 1: Water droplets condense able to at that pressure and temperature.
    [Show full text]
  • Weak Interaction Processes: Which Quantum Information Is Revealed?
    Weak Interaction Processes: Which Quantum Information is revealed? B. C. Hiesmayr1 1University of Vienna, Faculty of Physics, Boltzmanngasse 5, 1090 Vienna, Austria We analyze the achievable limits of the quantum information processing of the weak interaction revealed by hyperons with spin. We find that the weak decay process corresponds to an interferometric device with a fixed visibility and fixed phase difference for each hyperon. Nature chooses rather low visibilities expressing a preference to parity conserving or violating processes (except for the decay Σ+ pπ0). The decay process can be considered as an open quantum channel that carries the information of the−→ hyperon spin to the angular distribution of the momentum of the daughter particles. We find a simple geometrical information theoretic 1 α interpretation of this process: two quantization axes are chosen spontaneously with probabilities ±2 where α is proportional to the visibility times the real part of the phase shift. Differently stated the weak interaction process corresponds to spin measurements with an imperfect Stern-Gerlach apparatus. Equipped with this information theoretic insight we show how entanglement can be measured in these systems and why Bell’s nonlocality (in contradiction to common misconception in literature) cannot be revealed in hyperon decays. We study also under which circumstances contextuality can be revealed. PACS numbers: 03.67.-a, 14.20.Jn, 03.65.Ud Weak interactions are one out of the four fundamental in- systems. teractions that we think that rules our universe. The weak in- Information theoretic content of an interfering and de- teraction is the only interaction that breaks the parity symme- caying system: Let us start by assuming that the initial state try and the combined charge-conjugation–parity( P) symme- of a decaying hyperon is in a separable state between momen- C try.
    [Show full text]
  • Gravitational Interaction to One Loop in Effective Quantum Gravity A
    IT9700281 LABORATORI NAZIONALI Dl FRASCATI SIS - Pubblicazioni LNF-96/0S8 (P) ITHf 00 Z%i 31 ottobre 1996 gr-qc/9611018 Gravitational Interaction to one Loop in Effective Quantum Gravity A. Akhundov" S. Bellucci6 A. Shiekhcl "Universitat-Gesamthochschule Siegen, D-57076 Siegen, Germany, and Institute of Physics, Azerbaijan Academy of Sciences, pr. Azizbekova 33, AZ-370143 Baku, Azerbaijan 6INFN-Laboratori Nazionali di Frascati, P.O. Box 13, 00044 Frascati, Italy ^International Centre for Theoretical Physics, Strada Costiera 11, P.O. Box 586, 34014 Trieste, Italy Abstract We carry out the first step of a program conceived, in order to build a realistic model, having the particle spectrum of the standard model and renormalized masses, interaction terms and couplings, etc. which include the class of quantum gravity corrections, obtained by handling gravity as an effective theory. This provides an adequate picture at low energies, i.e. much less than the scale of strong gravity (the Planck mass). Hence our results are valid, irrespectively of any proposal for the full quantum gravity as a fundamental theory. We consider only non-analytic contributions to the one-loop scattering matrix elements, which provide the dominant quantum effect at long distance. These contributions are finite and independent from the finite value of the renormalization counter terms of the effective lagrangian. We calculate the interaction of two heavy scalar particles, i.e. close to rest, due to the effective quantum gravity to the one loop order and compare with similar results in the literature. PACS.: 04.60.+n Submitted to Physics Letters B 1 E-mail addresses: [email protected], bellucciQlnf.infn.it, [email protected] — 2 1 Introduction A longstanding puzzle in quantum physics is how to marry the description of gravity with the field theory of elementary particles.
    [Show full text]
  • Multidisciplinary Design Project Engineering Dictionary Version 0.0.2
    Multidisciplinary Design Project Engineering Dictionary Version 0.0.2 February 15, 2006 . DRAFT Cambridge-MIT Institute Multidisciplinary Design Project This Dictionary/Glossary of Engineering terms has been compiled to compliment the work developed as part of the Multi-disciplinary Design Project (MDP), which is a programme to develop teaching material and kits to aid the running of mechtronics projects in Universities and Schools. The project is being carried out with support from the Cambridge-MIT Institute undergraduate teaching programe. For more information about the project please visit the MDP website at http://www-mdp.eng.cam.ac.uk or contact Dr. Peter Long Prof. Alex Slocum Cambridge University Engineering Department Massachusetts Institute of Technology Trumpington Street, 77 Massachusetts Ave. Cambridge. Cambridge MA 02139-4307 CB2 1PZ. USA e-mail: [email protected] e-mail: [email protected] tel: +44 (0) 1223 332779 tel: +1 617 253 0012 For information about the CMI initiative please see Cambridge-MIT Institute website :- http://www.cambridge-mit.org CMI CMI, University of Cambridge Massachusetts Institute of Technology 10 Miller’s Yard, 77 Massachusetts Ave. Mill Lane, Cambridge MA 02139-4307 Cambridge. CB2 1RQ. USA tel: +44 (0) 1223 327207 tel. +1 617 253 7732 fax: +44 (0) 1223 765891 fax. +1 617 258 8539 . DRAFT 2 CMI-MDP Programme 1 Introduction This dictionary/glossary has not been developed as a definative work but as a useful reference book for engi- neering students to search when looking for the meaning of a word/phrase. It has been compiled from a number of existing glossaries together with a number of local additions.
    [Show full text]
  • The Weak Charge of the Proton Via Parity Violating Electron Scattering
    The Weak Charge of the Proton via Parity Violating Electron Scattering Dave “Dawei” Mack (TJNAF) SPIN2014 Beijing, China Oct 20, 2014 DOE, NSF, NSERC SPIN2014 All Spin Measurements Single Spin Asymmetries PV You are here … … where experiments are unusually difficult, but we don’t annoy everyone by publishing frequently. 2 Motivation 3 The Standard Model (a great achievement, but not a theory of everything) Too many free parameters (masses, mixing angles, etc.). No explanation for the 3 generations of leptons, etc. Not enough CP violation to get from the Big Bang to today’s world No gravity. (dominates dynamics at planetary scales) No dark matter. (essential for understanding galactic-scale dynamics) No dark energy. (essential for understanding expansion of the universe) What we call the SM is only +gravity part of a larger model. +dark matter +dark energy The astrophysical observations are compelling, but only hint at the nature of dark matter and energy. We can look but not touch! To extend the SM, we need more BSM evidence (or tight constraints) from controlled experiments4 . The Quark Weak Vector Charges p Qw is the neutral-weak analog of the proton’s electric charge Note the traditional roles of the proton and neutron are almost reversed: ie, neutron weak charge is dominant, proton weak charge is almost zero. This suppression of the proton weak charge in the SM makes it a sensitive way to: 2 •measure sin θW at low energies, and •search for evidence of new PV interactions between electrons and light quarks. 5 2 Running of sin θW 2 But sin θW is determined much better at the Z pole.
    [Show full text]
  • 1 Drawing Feynman Diagrams
    1 Drawing Feynman Diagrams 1. A fermion (quark, lepton, neutrino) is drawn by a straight line with an arrow pointing to the left: f f 2. An antifermion is drawn by a straight line with an arrow pointing to the right: f f 3. A photon or W ±, Z0 boson is drawn by a wavy line: γ W ±;Z0 4. A gluon is drawn by a curled line: g 5. The emission of a photon from a lepton or a quark doesn’t change the fermion: γ l; q l; q But a photon cannot be emitted from a neutrino: γ ν ν 6. The emission of a W ± from a fermion changes the flavour of the fermion in the following way: − − − 2 Q = −1 e µ τ u c t Q = + 3 1 Q = 0 νe νµ ντ d s b Q = − 3 But for quarks, we have an additional mixing between families: u c t d s b This means that when emitting a W ±, an u quark for example will mostly change into a d quark, but it has a small chance to change into a s quark instead, and an even smaller chance to change into a b quark. Similarly, a c will mostly change into a s quark, but has small chances of changing into an u or b. Note that there is no horizontal mixing, i.e. an u never changes into a c quark! In practice, we will limit ourselves to the light quarks (u; d; s): 1 DRAWING FEYNMAN DIAGRAMS 2 u d s Some examples for diagrams emitting a W ±: W − W + e− νe u d And using quark mixing: W + u s To know the sign of the W -boson, we use charge conservation: the sum of the charges at the left hand side must equal the sum of the charges at the right hand side.
    [Show full text]
  • Aalborg Universitet Photon-Graviton Interaction and CPH Theory Javadi
    Aalborg Universitet Photon-Graviton Interaction and CPH Theory Javadi, Hossein; Forouzbakhsh, Farshid; Daei Kasmaei, Hamed Published in: The General Science Journal Publication date: 2016 Document Version Accepted author manuscript, peer reviewed version Link to publication from Aalborg University Citation for published version (APA): Javadi, H., Forouzbakhsh, F., & Daei Kasmaei, H. (2016). Photon-Graviton Interaction and CPH Theory. The General Science Journal. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research. ? You may not further distribute the material or use it for any profit-making activity or commercial gain ? You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us at [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from vbn.aau.dk on: September 26, 2021 Photon-Graviton Interaction and CPH Theory H. Javadi 1, F. Forouzbakhsh 2 and H.Daei Kasmaei 3 1 Faculty of Science, Islamic Azad University, South Tehran Branch, Tehran, Iran [email protected] 2 Department of Energy Technology,
    [Show full text]
  • Introduction to Supersymmetry
    Introduction to Supersymmetry Pre-SUSY Summer School Corpus Christi, Texas May 15-18, 2019 Stephen P. Martin Northern Illinois University [email protected] 1 Topics: Why: Motivation for supersymmetry (SUSY) • What: SUSY Lagrangians, SUSY breaking and the Minimal • Supersymmetric Standard Model, superpartner decays Who: Sorry, not covered. • For some more details and a slightly better attempt at proper referencing: A supersymmetry primer, hep-ph/9709356, version 7, January 2016 • TASI 2011 lectures notes: two-component fermion notation and • supersymmetry, arXiv:1205.4076. If you find corrections, please do let me know! 2 Lecture 1: Motivation and Introduction to Supersymmetry Motivation: The Hierarchy Problem • Supermultiplets • Particle content of the Minimal Supersymmetric Standard Model • (MSSM) Need for “soft” breaking of supersymmetry • The Wess-Zumino Model • 3 People have cited many reasons why extensions of the Standard Model might involve supersymmetry (SUSY). Some of them are: A possible cold dark matter particle • A light Higgs boson, M = 125 GeV • h Unification of gauge couplings • Mathematical elegance, beauty • ⋆ “What does that even mean? No such thing!” – Some modern pundits ⋆ “We beg to differ.” – Einstein, Dirac, . However, for me, the single compelling reason is: The Hierarchy Problem • 4 An analogy: Coulomb self-energy correction to the electron’s mass A point-like electron would have an infinite classical electrostatic energy. Instead, suppose the electron is a solid sphere of uniform charge density and radius R. An undergraduate problem gives: 3e2 ∆ECoulomb = 20πǫ0R 2 Interpreting this as a correction ∆me = ∆ECoulomb/c to the electron mass: 15 0.86 10− meters m = m + (1 MeV/c2) × .
    [Show full text]
  • Fundamental Physical Constants: Looking from Different Angles
    1 Fundamental Physical Constants: Looking from Different Angles Savely G. Karshenboim Abstract: We consider fundamental physical constants which are among a few of the most important pieces of information we have learned about Nature after its intensive centuries- long studies. We discuss their multifunctional role in modern physics including problems related to the art of measurement, natural and practical units, origin of the constants, their possible calculability and variability etc. PACS Nos.: 06.02.Jr, 06.02.Fn Resum´ e´ : Nous ... French version of abstract (supplied by CJP) arXiv:physics/0506173v2 [physics.atom-ph] 28 Jul 2005 [Traduit par la r´edaction] Received 2004. Accepted 2005. Savely G. Karshenboim. D. I. Mendeleev Institute for Metrology, St. Petersburg, 189620, Russia and Max- Planck-Institut f¨ur Quantenoptik, Garching, 85748, Germany; e-mail: [email protected] unknown 99: 1–46 (2005) 2005 NRC Canada 2 unknown Vol. 99, 2005 Contents 1 Introduction 3 2 Physical Constants, Units and Art of Measurement 4 3 Physical Constants and Precision Measurements 7 4 The International System of Units SI: Vacuum constant ǫ0, candela, kelvin, mole and other questions 10 4.1 ‘Unnecessary’units. .... .... ... .... .... .... ... ... ...... 10 4.2 ‘Human-related’units. ....... 11 4.3 Vacuum constant ǫ0 andGaussianunits ......................... 13 4.4 ‘Unnecessary’units,II . ....... 14 5 Physical Phenomena Governed by Fundamental Constants 15 5.1 Freeparticles ................................... .... 16 5.2 Simpleatomsandmolecules . .....
    [Show full text]
  • TRIUMF & Canadian Scientists Help Measure Proton's Weak Charge
    Canada’s national laboratory for particle and nuclear physics Laboratoire national canadien pour la recherche en physique nucléaire et en physique des particules News Release | For Immediate Release | 17 Sep 2013, 5:00 p.m. PDT TRIUMF & Canadian Scientists Help Measure Proton’s Weak Charge (Newport News, VA, USA) --- An international team including Canadian researchers at TRIUMF has reported first results for the proton’s weak charge in Physical Review Letters (to appear in the October 18, 2013 issue) based on precise new data from Jefferson Laboratory, the premier U.S. electron-beam facility for nuclear and particle physics in Newport News, Virginia. The Q-weak experiment used a high-energy electron beam to measure the weak charge of the proton—a fundamental property that sets the scale of its interactions via the weak nuclear force. This is distinct from but analogous to its more familiar electric charge (Q), hence, the experiment’s name: ‘Q-weak.’ Following a decade of design and construction, Q-weak had a successful experimental run in 2010–12 in Hall C at Jefferson Laboratory. Data analysis has been underway ever since. “Nobody has ever attempted a measurement of the proton’s weak charge before,” says Roger Carlini, Q- weak’s spokesperson at Jefferson Laboratory, “due to the extreme technical challenges to reach the required sensitivity. The first 4% of the data have now been fully analyzed and already have an important scientific impact, although the ultimate sensitivity awaits analysis of the complete experiment.” The first result, based on Q-weak’s commissioning data set, is Q_W^p= 0.064 ± 0.012.
    [Show full text]