DOCSLIB.ORG

Lecture 16 - Electroweak Theory

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lecture 16 - Electroweak Theory Lecture 16 - Electroweak Theory Electroweak Unification • W and Z Boson masses and widths • Z production at LEP • Forward-backward asymmetries • W production at colliders • Precision tests of Electroweak theory • 1 SU(2) Isospin and U(1) Hypercharge The combined groups SU(2)L U(1) describe electroweak symmetry × SU(2)L describes weak isospin (I3) couplings to left-handed fermions (or right-handed antifermions) U(1) describes weak hypercharge (Y) couplings The weak charged currents are described by SU(2) matrices τ ±: + 1 0 1 − 1 0 0 τ = (τ1 +iτ2)= τ = (τ1 iτ2)= 2 0 0 2 − 1 0 + µ + − µ − J =χ ¯νe γ τ χe J =χ ¯eγ τ χνe These are the currents associated with W + and W − exchange 2 Electroweak Neutral Currents The third component of weak isospin describes a weak neutral current: 3 µ 1 µ µ 1 0 J =χγ ¯ τ3χ =χ ¯νe γ χνe χ¯eγ χe τ3 = 2 − 0 1 − The electromagnetic current couples to charge Q: J EM =χγ ¯ µQχ This can be rewritten in terms of I3 and Y: Y EM 3 1 Y Q = I3 + J = J + J 2 2 The EM current is a sum of weak isospin and hypercharge 3 Electroweak Unification The combined electroweak interaction has a Lagrangian: = gJ.~ W~ + g′J Y B L W~ is a triplet of vector bosons W 1,2,3 coupling to weak isospin currents J 1,2,3 with strength g B0 is a singlet vector boson coupling to the weak hypercharge current J Y with strength g′ The physical vector bosons are: 1 W ± = (W 1 iW 2) r2 ∓ 0 3 0 0 3 0 Z = W cos θW B sin θW A = W sin θW + B cos θW − where the neutral W 3 and B0 mix to give Z0 and photon A0 4 The Weinberg Angle The mixing angle θW is measured to be: 2 sin θW = 0.2221 The weak isospin, hypercharge and EM couplings are related by: ′ g sin θW = g cos θW = e The electroweak Lagrangian can be written out in terms of the physical weak and electromagnetic currents: g − + + − g 3 2 EM 0 EM 0 (J W + J W )+ (J sin θW J )Z + eJ A √2 cos θW − The first terms describe W ± couplings with strength g The last term describes photon couplings with strength e The middle term describes the neutral Z0 coupling. It has pieces from both J 3 and J EM ! 5 Masses of W and Z Bosons The mass of the W boson can be related to sin θW : 2 2 GF g e √2 37.4 = 2 MW = 2 = GeV √2 8MW s8GF sin θW sin θW The mass of the Z boson is related to the mass of the W boson: MW 75 MZ = = GeV cos θW sin2θW These are now very accurately measured: MW = 80.425 0.038 GeV MZ = 91.1876 0.0021 GeV ± ± The large masses of the W and Z compared to the zero mass of the photon break electroweak symmetry Leads to introduction of Higgs mechanism - see next lecture 6 Neutral Current Couplings of Z The Z boson has left-handed couplings from J 3 and J EM and right-handed couplings from J EM : 2 2 gL = I3 Qsin θW gR = Qsin θW − − Usually expressed as vector and axial-vector couplings cV and cA: 2 cV = gL + gR = I3 2Qsin θW cA = gL gR = I3 − − Lepton 2cV 2cA Quark 2cV 2cA 8 2 νe, νµ, ντ 1 1 u,c,t 1 sin θW 1 − 3 2 4 2 e, µ, τ 1+4sin θW -1 d,s,b 1+ sin θW -1 − − 3 Electroweak theory predicts the weak neutral current couplings which depend on fermion type! 7 Z Production at LEP (1989-1995) ] σ0 nb 0 [ 40 Large samples of Z were + − had ALEPH collected in e e collisions σ DELPHI L3 at ECM MZ 30 OPAL ≈ Note interference between Γ 0 Z γ (QED) and Z diagrams 20 measurements, error bars increased by factor 10 Width of the Z0 boson: 10 σ from fit QED unfolded ΓZ = 2.4952 0.0023 GeV ± MZ 86 88 90 92 94 [ ] Ecm GeV 8 Z Couplings to fermions The couplings of the Z0 to ff¯ are: 2 0 ¯ g 2 2 Γ(Z ff)= 2 (cV + cA)f MZ → 48π cos θW The couplings to charged leptons are: 2 0 ¯ g Γ(Z ℓℓ)= 2 MZ = 84 MeV → 192π cos θW Sum of all quark couplings gives ratio of hadron jets to leptons: Γ(Z0 hadrons) R = → = 20.767 0.025 Γ(Z0 leptons) ± → The couplings to neutrinos give the invisible width: Γ(Z0 νν¯)=166MeV Γ(Z0 invisible) = 499 1.5 MeV → → ± The total width requires 2.988 0.023 neutrinos with mν < MZ /2 ± 9 Universality of Z couplings to leptons -0.032 -0.035 e+e−, µ+µ−, τ +τ − mH couplings are same Vl g mt Note the sensitivity -0.038 of these couplings + − ∆α l l to the Higgs mass! + − e e µ+µ− τ+τ− 68% CL -0.041 -0.503 -0.502 -0.501 -0.5 gAl 10 Interference between photon and Z e+e− ff¯ is described by sum of Z0 and photon diagrams: → 2 √2GF MZ f µ f µ e µ e µ Z = [g f¯Rγ fR + g f¯Lγ fL][g e¯Rγ eR + g e¯Lγ eL] M s M 2 R L R L − Z 2 e µ µ γ = [fγ¯ f][¯eγ e] M s The cross-sections depend on fermion helicities: 2 dσ − − α (e e+ µ µ+)= (1 + cos θ)2 1+ rgµge 2 dΩ L R → L R 4s | L L| 2 dσ − − α (e e+ µ µ+)= (1 cos θ)2 1+ rgµ ge 2 dΩ L R → R L 4s − | R L| where r is ratio of coefficients of Z0 and photon amplitudes 11 Forward-Backward Asymmetries Combining all four possible helicity combinations: 2 dσ + − + − α 2 (e e µ µ )= [A0(1 + cos θ)+ A1 cos θ] dΩ → 4s 2 2 2 2 2 2 2 2 2 A0 =1+2Re[r]c + r (c + c ) A1 = 4Re[r]c + 8 r c c V | | V A A | | V A The cos θ term gives a forward-backward asymmetry F B 1 dσ 0 dσ AF B = − F = dΩ B = dΩ F + B dΩ − dΩ Z0 Z 1 2 3A1 3 2 3cAGF s AF B = AF B(s MZ )= Re(r)cA = 8A0 ≪ 2 − √2e2 AF B is small at low s where r 1 and photon dominates | | ≪ 0 AF B 0 at √s = MZ where Z dominates ≈ 12 0.15 s) √ ( FB LEP A Forward-Backward 0.1 Asymmetries at √s MZ ≈ 0.05 The heavy quark AF B are sensitive to 0 virtual H, t diagrams Ab FB Ac FB -0.05 89 90 91 92 93 94 √s [GeV] Leptons AF B(MZ ) Quarks AF B(MZ ) e+e− e+e− (1.45 0.25)% e+e− ss¯ (9.8 1.1)% → ± → ± e+e− µ+µ− (1.69 0.13)% e+e− cc¯ (7.04 0.36)% → ± → ± e+e− τ +τ − (1.88 0.17)% e+e− b¯b (10.01 0.17)% → ± → ± 13 W Boson Production The W and Z bosons were discovered in pp¯ collisions at CERN W ℓν decays to high pT lepton and high missing ET of ν → CDF Experiment (2007) UA1 experiment (1983) MW = 80.493 0.048 GeV ± ΓW = 2.115 0.105 GeV ± 14 W +W − Pair Production at LEP-2 From 1996-2001 LEP-2 produced W pairs at √s 200 GeV. ≈ 30 02/08/2004 LEP (pb) PRELIMINARY Cross-section is a sum of: WW σ νe exchange 20 (t-channel) + virtual photon 10 (s-channel) 0 YFSWW/RacoonWW + Z with trilinear no ZWW vertex (Gentle) only ν exchange (Gentle) e gauge coupling − 0 Z0W +W 160 180 200 √s (GeV) 15 Measurement Fit |Omeas−Ofit|/σmeas 0 1 2 3 ∆α(5) ± had(mZ) 0.02758 0.00035 0.02767 Summary of m [GeV] 91.1875 ± 0.0021 91.1874 Z electroweak Γ [ ] ± Z GeV 2.4952 0.0023 2.4965 σ0 [ ] ± measurements had nb 41.540 0.037 41.481 R 20.767 ± 0.025 20.739 l http://lepewwg. 0,l ± Afb 0.01714 0.00095 0.01642 ± web.cern.ch/ Al(Pτ) 0.1465 0.0032 0.1480 ± Rb 0.21629 0.00066 0.21562 LEPEWWG/ ± Rc 0.1721 0.0030 0.1723 0,b ± Good agreement with Afb 0.0992 0.0016 0.1037 0,c ± Afb 0.0707 0.0035 0.0742 electroweak theory A 0.923 ± 0.020 0.935 b b (apart from AF B?) ± Ac 0.670 0.027 0.668 ± Al(SLD) 0.1513 0.0021 0.1480 2θlept ± sin eff (Qfb) 0.2324 0.0012 0.2314 [ ] ± mW GeV 80.425 0.034 80.389 Γ [ ] ± W GeV 2.133 0.069 2.093 [ ] ± mt GeV 178.0 4.3 178.5 0 1 2 3 16.
Load more

Recommended publications
  • 12 from Neutral Currents to Weak Vector Bosons
    12 From neutral currents to weak vector bosons The unification of weak and electromagnetic interactions, 1973{1987 Fermi's theory of weak interactions survived nearly unaltered over the years. Its basic structure was slightly modified by the addition of Gamow-Teller terms and finally by the determination of the V-A form, but its essence as a four fermion interaction remained. Fermi's original insight was based on the analogy with elec- tromagnetism; from the start it was clear that there might be vector particles transmitting the weak force the way the photon transmits the electromagnetic force. Since the weak interaction was of short range, the vector particle would have to be heavy, and since beta decay changed nuclear charge, the particle would have to carry charge. The weak (or W) boson was the object of many searches. No evidence of the W boson was found in the mass region up to 20 GeV. The V-A theory, which was equivalent to a theory with a very heavy W , was a satisfactory description of all weak interaction data. Nevertheless, it was clear that the theory was not complete. As described in Chapter 6, it predicted cross sections at very high energies that violated unitarity, the basic principle that says that the probability for an individual process to occur must be less than or equal to unity. A consequence of unitarity is that the total cross section for a process with 2 angular momentum J can never exceed 4π(2J + 1)=pcm. However, we have seen that neutrino cross sections grow linearly with increasing center of mass energy.
    [Show full text]
  • Discovery of Weak Neutral Currents∗
    Discovery of Weak Neutral Currents∗ Dieter Haidt Emeritus at DESY, Hamburg 1 Introduction Following the tradition of previous Neutrino Conferences the opening talk is devoted to a historic event, this year to the epoch-making discovery of Weak Neutral Currents four decades ago. The major laboratories joined in a worldwide effort to investigate this new phenomenon. It resulted in new accelerators and colliders pushing the energy frontier from the GeV to the TeV regime and led to the development of new, almost bubble chamber like, general purpose detectors. While the Gargamelle collaboration consisted of seven european laboratories and was with nearly 60 members one of the biggest collaborations at the time, the LHC collaborations by now have grown to 3000 members coming from all parts in the world. Indeed, High Energy Physics is now done on a worldwide level thanks to net working and fast communications. It seems hardly imaginable that 40 years ago there was no handy, no world wide web, no laptop, no email and program codes had to be punched on cards. Before describing the discovery of weak neutral currents as such and the cir- cumstances how it came about a brief look at the past four decades is anticipated. The history of weak neutral currents has been told in numerous reviews and spe- cialized conferences. Neutral currents have since long a firm place in textbooks. The literature is correspondingly rich - just to point out a few references [1, 2, 3, 4]. 2 Four decades Figure 1 sketches the glorious electroweak way originating in the discovery of weak neutral currents by the Gargamelle Collaboration and followed by the series of eminent discoveries.
    [Show full text]
  • Introduction to Subatomic- Particle Spectrometers∗
    IIT-CAPP-15/2 Introduction to Subatomic- Particle Spectrometers∗ Daniel M. Kaplan Illinois Institute of Technology Chicago, IL 60616 Charles E. Lane Drexel University Philadelphia, PA 19104 Kenneth S. Nelsony University of Virginia Charlottesville, VA 22901 Abstract An introductory review, suitable for the beginning student of high-energy physics or professionals from other fields who may desire familiarity with subatomic-particle detection techniques. Subatomic-particle fundamentals and the basics of particle in- teractions with matter are summarized, after which we review particle detectors. We conclude with three examples that illustrate the variety of subatomic-particle spectrom- eters and exemplify the combined use of several detection techniques to characterize interaction events more-or-less completely. arXiv:physics/9805026v3 [physics.ins-det] 17 Jul 2015 ∗To appear in the Wiley Encyclopedia of Electrical and Electronics Engineering. yNow at Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723. 1 Contents 1 Introduction 5 2 Overview of Subatomic Particles 5 2.1 Leptons, Hadrons, Gauge and Higgs Bosons . 5 2.2 Neutrinos . 6 2.3 Quarks . 8 3 Overview of Particle Detection 9 3.1 Position Measurement: Hodoscopes and Telescopes . 9 3.2 Momentum and Energy Measurement . 9 3.2.1 Magnetic Spectrometry . 9 3.2.2 Calorimeters . 10 3.3 Particle Identification . 10 3.3.1 Calorimetric Electron (and Photon) Identification . 10 3.3.2 Muon Identification . 11 3.3.3 Time of Flight and Ionization . 11 3.3.4 Cherenkov Detectors . 11 3.3.5 Transition-Radiation Detectors . 12 3.4 Neutrino Detection . 12 3.4.1 Reactor Neutrinos . 12 3.4.2 Detection of High Energy Neutrinos .
    [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]
  • Measurement of Neutrino-Nucleon Neutral-Current Elastic Scattering Cross-Section at Sciboone
    Measurement of Neutrino-Nucleon Neutral-Current Elastic Scattering Cross-section at SciBooNE Hideyuki Takei Thesis submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Science at Tokyo Institute of Technology February, 2009 2 Abstract In this thesis, results of neutrino-nucleon neutral current (NC) elastic scattering analysis are presented. Neutrinos interact with other particles only with weak force. Measure- ment of cross-section for neutrino-nucleon reactions at various neutrino en- ergy are important for the study of nucleon structure. It also provides data to be used for beam flux monitor in neutrino oscillation experiments. The cross-section for neutrino-nucleon NC elastic scattering contains the 2 axial vector form factor GA(Q ) as well as electromagnetic form factors unlike electromagnetic interaction. GA is propotional to strange part of nucleon spin (∆ s) in Q2 → 0 limit. Measurement of NC elastic cross-section with smaller Q2 enables us to access ∆ s. NC elastic cross-sections of neutrino- nucleon and antineutrino-nucleon were measured earlier by E734 experiment at Brookheaven National Laboratory (BNL) in 1987. In this experiment, cross-sections were measured in Q2 > 0.4 GeV 2 region. Result from this experiment was the only published data for NC elastic scattering cross-section published before our experiment. SciBooNE is an experiment for the measurement of neutrino-nucleon scat- tering cross-secitons using Booster Neutrino Beam (BNB) at FNAL. BNB has energy peak at 0.7 GeV. In this energy region, NC elastic scattering, charged current elastic scattering, charged current pion production, and neutral cur- rent pion production are the major reaction branches.
    [Show full text]
  • 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.
    [Show full text]
  • 1989-1990 Eight College Teachers Participated in the Training
    SATYENDRA NATH BOSE NATIONAL CENTRE FOR BASIC SCIENCES Calcutta ANNUAL REPORT April 1, 1989 to March 31,1990 Objectives The objectives of the S N Bose National Centre for Basic Sciences established in June 1986 as a registered society functioning under the umbrella of the Department of Science & Technology, Government of India, are : To foster, encourage and promote the growth of advanced studies in selected branches of basic sciences ; To conduct original research in theoretical and mathematical sciences and other basic sciences in frontier areas, including challenging theoretical studies of future applications ; To provide a forum of personal contacts and intellectual interaction among scientists within the country and also between them and scientists abroad ; To train young scientists for research in basic sciences. Governing Body The present Governing Body of the Centre consists of the following members : 1 Dr V Gowariker Secretary Chairman Department of Science & Technology Government of India, New Delhi 2 Professor C N R Rao Direct or Member Indian Institute of Science Bangalore 3 Professor C S Seshadri Dean Member School of Mathematics SPIC, Science Foundation Madras Professor J V Narlikar Director Member Inter-Universit y Centre for Astronomy & Astrophysics Pune Shri B K Chaturvedi Joint Secretary & Financial Adviser Member Department of Science & Technology Government of India, New Delhi Shri T C Dutt Chief Secretary Member Government of West Bengal Calcutta Professor C K Mzjumdar Director Member S N Bose National Centre for Basic Sciences Calcutta Dr J Pal Chaud huri Administrative Officer Non-member-Secretary S N Bose National Centre for Basic Sciences Calcutta At the moment the Centre operates from a rented house located at DB 17, Sector I, Salt Lake City, Calcutta 700 064.
    [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]
  • Threshold Corrections in Grand Unified Theories
    Threshold Corrections in Grand Unified Theories Zur Erlangung des akademischen Grades eines DOKTORS DER NATURWISSENSCHAFTEN von der Fakult¨at f¨ur Physik des Karlsruher Instituts f¨ur Technologie genehmigte DISSERTATION von Dipl.-Phys. Waldemar Martens aus Nowosibirsk Tag der m¨undlichen Pr¨ufung: 8. Juli 2011 Referent: Prof. Dr. M. Steinhauser Korreferent: Prof. Dr. U. Nierste Contents 1. Introduction 1 2. Supersymmetric Grand Unified Theories 5 2.1. The Standard Model and its Limitations . ....... 5 2.2. The Georgi-Glashow SU(5) Model . .... 6 2.3. Supersymmetry (SUSY) .............................. 9 2.4. SupersymmetricGrandUnification . ...... 10 2.4.1. MinimalSupersymmetricSU(5). 11 2.4.2. MissingDoubletModel . 12 2.5. RunningandDecoupling. 12 2.5.1. Renormalization Group Equations . 13 2.5.2. Decoupling of Heavy Particles . 14 2.5.3. One-Loop Decoupling Coefficients for Various GUT Models . 17 2.5.4. One-Loop Decoupling Coefficients for the Matching of the MSSM to the SM ...................................... 18 2.6. ProtonDecay .................................... 21 2.7. Schur’sLemma ................................... 22 3. Supersymmetric GUTs and Gauge Coupling Unification at Three Loops 25 3.1. RunningandDecoupling. 25 3.2. Predictions for MHc from Gauge Coupling Unification . 32 3.2.1. Dependence on the Decoupling Scales µSUSY and µGUT ........ 33 3.2.2. Dependence on the SUSY Spectrum ................... 36 3.2.3. Dependence on the Uncertainty on the Input Parameters ....... 36 3.2.4. Top-Down Approach and the Missing Doublet Model . ...... 39 3.2.5. Comparison with Proton Decay Constraints . ...... 43 3.3. Summary ...................................... 44 4. Field-Theoretical Framework for the Two-Loop Matching Calculation 45 4.1. TheLagrangian.................................. 45 4.1.1.
    [Show full text]
  • Atomic Parity Violation, Polarized Electron Scattering and Neutrino-Nucleus Coherent Scattering
    Available online at www.sciencedirect.com ScienceDirect Nuclear Physics B 959 (2020) 115158 www.elsevier.com/locate/nuclphysb New physics probes: Atomic parity violation, polarized electron scattering and neutrino-nucleus coherent scattering Giorgio Arcadi a,b, Manfred Lindner c, Jessica Martins d, Farinaldo S. Queiroz e,∗ a Dipartimento di Matematica e Fisica, Università di Roma 3, Via della Vasca Navale 84, 00146, Roma, Italy b INFN Sezione Roma 3, Italy c Max-Planck-Institut für Kernphysik (MPIK), Saupfercheckweg 1, 69117 Heidelberg, Germany d Instituto de Física Teórica, Universidade Estadual Paulista, São Paulo, Brazil e International Institute of Physics, Universidade Federal do Rio Grande do Norte, Campus Universitário, Lagoa Nova, Natal-RN 59078-970, Brazil Received 7 April 2020; received in revised form 22 July 2020; accepted 20 August 2020 Available online 27 August 2020 Editor: Hong-Jian He Abstract Atomic Parity Violation (APV) is usually quantified in terms of the weak nuclear charge QW of a nucleus, which depends on the coupling strength between the atomic electrons and quarks. In this work, we review the importance of APV to probing new physics using effective field theory. Furthermore, we correlate our findings with the results from neutrino-nucleus coherent scattering. We revisit signs of parity violation in polarized electron scattering and show how precise measurements on the Weinberg’s angle give rise to competitive bounds on light mediators over a wide range of masses and interactions strengths. Our bounds are firstly derived in the context of simplified setups and then applied to several concrete models, namely Dark Z, Two Higgs Doublet Model-U(1)X and 3-3-1, considering both light and heavy mediator regimes.
    [Show full text]
  • 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.
    [Show full text]
  • 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].
    [Show full text]