DOCSLIB.ORG

Cross Sections for Neutral-Current Neutrino-Nucleus Interactions: Applications for 12C and 16O

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Cross Sections for Neutral-Current Neutrino-Nucleus Interactions: Applications for 12C and 16O PHYSICAL REVIEW C VOLUME 59, NUMBER 6 JUNE 1999 Cross sections for neutral-current neutrino-nucleus interactions: Applications for 12C and 16O N. Jachowicz,* S. Rombouts, K. Heyde,† and J. Ryckebusch Institute for Theoretical Physics, Vakgroep Subatomaire en Stralingsfysica, Proeftuinstraat 86, B-9000 Gent, Belgium ~Received 29 September 1998; revised manuscipt received 4 February 1999! We study quasielastic neutrino-nucleus scattering on 12C and 16O within a continuum random phase ap- proximation ~RPA! model. The RPA equations are solved using a Green’s function approach with an effective Skyrme ~SkE2! two-body interaction. Besides a comparison with existing calculations, we carry out a detailed study using various methods ~Tamm-Dancoff approximation and RPA! and different forces ~SkE2 and Landau- Migdal!. We evaluate cross sections that may be relevant for neutrino nucleosynthesis. @S0556-2813~99!01606-4# PACS number~s!: 25.30.Pt, 24.10.Eq, 26.30.1k I. INTRODUCTION function approach in which the polarization propagator is approximated by an iteration of the first-order contribution Neutrinos are extremely well-suited probes to provide de- @14#. The unperturbed wave functions are generated using tailed information about the structure and properties of the either a Woods-Saxon potential or a HF calculation using a weak interaction, as they are only interacting via the weak Skyrme force. The latter approach makes self-consistent HF- forces. Moreover, being intrinsically polarized and coupling RPA calculations possible. Calculations using either a to the axial vector as well as to the vector part of the had- Skyrme or a Landau-Migdal force must give indications ronic current, neutrinos are able to reveal other and more about possible differences and sensitivity in methods to the precise nuclear structure information than, e.g., electrons do. residual two-body interaction used. Finally, we discuss ap- The most important problem in extracting information from plications for neutral-current reactions on 16O and 12C, two neutrino-nucleus scattering experiments remains the very nuclei that are very important from an astrophysical point of small interaction cross sections. view. In Sec. VI, we discuss some aspects of neutrino nu- These restrictions become rather unimportant when con- cleosynthesis and in Sec. VII, the stability of the RPA and sidering astrophysical processes. The amount of neutrinos Tamm-Dancoff approximation ~TDA! methods, using differ- produced at the end of the lifetime of a massive star during ent two-body forces in calculating the neutrino scattering the neutronization of the collapsing core of a star and its cross section, is discussed. subsequent cooling, is as large as ;1058, representing ap- proximately 99% of the total released energy @1,2#. These II. QUASIELASTIC NEUTRINO SCATTERING supernova neutrinos will play an important role in explosive nucleosynthesis processes, causing a considerable transfor- In the neutral-current neutrino scattering reactions, a neu- W mation of the material synthesized during the hydrostatic trino with four-momentum (ei ,ki) is scattered inelastically burning phases in the life of the star. from a nucleus with initial energy and momentum Ei ,PW i . During the last few years, a large number of quasielastic The nucleus is supposed to be spherically symmetric and in neutrino-nucleus scattering studies have been carried out, in- its ground state, Jpi501. After the reaction, the nucleus is cluding shell model @3#, relativistic fermi gas @3,4#, and ran- i left in an excited state with final parity and angular momen- dom phase approximation ~RPA! calculations using various tum J ,p . The energy transferred from neutrino to nucleus forces @4–8#. Since both the LSND and the KARMEN Col- f f equals v5e 2e 5E 2E ,e and E being the final neu- laborations have been measuring neutrino-nucleus scattering i f f i f f trino and nuclear energy respectively. The transferred mo- cross sections on 12C @9,10#, special attention was paid to the 12 2 mentum is denoted by qW 5kW i2kW f , k5uqWu. calculation of cross sections for the reactions C(ne ,e )X 12 2 As the interaction between the neutrino and a nucleus is and C(nm ,m )X. Despite the theoretical and experimental efforts, no clear agreement between theory and experiment, mediated by the weak interaction, the cross section can be and between the different theoretical results for derived using Fermi’s golden rule. In Born approximation, 12 2 12 the outgoing neutrino is described by a plane wave. Using the C(nm ,m ) X reaction could be reached @8,9,11–13#. Next to these problems, we observe that relatively few natural units (\5c51), the differential cross section is then neutral-current calculations have been performed @3,5#. given by In the present work, we examine quasielastic neutral- d2s 1 current neutrino-nucleus reactions in an energy region rel- 5~2p!4k « u^ fuHˆ ui&u2. ~1! dVdv f f ( 2J 11 ( W evant to explosive nucleosynthesis processes, using a con- s f ,si i M f ,M i tinuum random phase approximation ~CRPA! formalism ˆ ~Sec. III!. The CRPA equations are solved using a Green’s The weak interaction Hamiltonian HW has the current- current structure G *Corresponding author. ˆ ˆ ˆ m,hadronic HW5 dxW jm,leptonic~xW !J ~xW !, ~2! †Present address: CERN CH-1211, Geneva 23, Switzerland. A2 E 0556-2813/99/59~6!/3246~10!/$15.00PRC 59 3246 ©1999 The American Physical Society PRC 59 CROSS SECTIONS FOR NEUTRAL-CURRENT . 3247 211 22 with G51.16639310 MeV the weak coupling con- ˆ and ˆ denote the Coulomb and longitudinal opera- stant. The neutral leptonic current reads MJM LJM ˆ el ˆ mag tor respectively, whereas JM and JM are the transverse ˆj0 ~x!5C¯ ~x!g ~12g !C ~x! J J m ne m 5 ne electric and magnetic operators: 1C¯ ~x!g ~12g !C ~x! nm m 5 nm ¯ ˆ ~k!5 dxW@j ~kr!YM~V !#Jˆ ~xW!, 1Cn ~x!gm~12g5!Cn ~x!. ~3! JM E J J x o t t M The weak neutral hadronic current is given by @15# ˆ 0 ˆ vector ˆ axial vector i M ˆ Jm5Jm 1Jm ˆ ~k!5 dxW$¹W @j ~kr!Y ~V !#%JW~xW!, LJM kE J J x 2 ˆ V3 2 ˆ S ˆ A3 5~122sin uW!Jm 22sin uWJm1Jm 1 ¯ V 2 V 2 n 1 ˆ 5CN GE~q !gm1 GM~q !smnq ˆ el W W W M W W 2M JM~k!5 dx$¹3@jJ~kr! J,J~Vx!#%J~x!, H J k E Y A 2 1G ~q !gmg5J . ~4! ˆ ˆ mag~k!5 dxW@j ~kr!W M ~V !# JW~xW!. ~9! 2 JM E J J,J x • Here sin uW50.2325, where uW is the Weinberg angle. For J Y the isospin operators, the convention t3up&511,t3un&5 ˆ V3 21 is adopted. Jm denotes the t3 component of the electro- S III. THE CONTINUUM RANDOM PHASE magnetic current and Jm is its scalar counterpart. The vector form factors can be obtained directly from those in electro- APPROXIMATION magnetic interactions applying the CVC theorem: The transition densities necessary to calculate the cross 1 V 2 2 section ~8! are determined within a continuum random phase GE5 ~122sin uW!t32sin uW , ~5! 2 approximation. The unperturbed single-particle wave- functions are generated by a Hartree-Fock calculation, using 1 V 2 2 GM5 ~122sin uW!~m p2mn!t32sin uW~m p1mn!. a Skyrme potential @16–19#. The CRPA formalism is based 2 on a Green’s function approach @14,16,20–22#. The RPA 6 ~ ! polarization propagator is obtained by the iteration to all or- ders of the first-order contribution to the particle-hole GA is given by Green’s function A G 52gat3521.262 t3 . ~7! (RPA) (0) For low momentum transfers (k,400 MeV/c), only P ~x1 ,x2 ;v!5P ~x1 ,x2 ;v! lowest-order contributions to the hadronic current have to be retained @15#. The differential cross section for neutral- 1 1 dx dx8P(0)~x ,x;v! current neutrino scattering finally becomes \E E 1 u 2 cos2 3˜V~x,x8!P(RPA)~x8,x ;v!, ~10! d2s G2«2 S 2D ` ` 2 i f f → J J 5 ( sCL1( sT , ~8! S dVdv D n p 2Ji11 F J50 J51 G ¯n where P(0) denotes the zeroth-order contribution to the po- where larization propagator. V˜ is the antisymmetrized form of the 2 residual interaction which in the following will be supposed v ˜ J ˆ ˆ to be rotationally invariant, allowing us to write V(x1 ,x2)as sCL5 Jf J~k!1 J~k! Ji , UK UUM uqWuL UU LU q2 u ˜ J JM† ˆ JM ˆ J m 2 ˆ mag 2 V~x1,x2!5 ( Uab~r1 ,r2!Xa ~x1!Xb ~x2!, ~11! sT5 2 1tan @u^J fuu J ~k!uuJi&u ab,JM S 2uqWu2 S 2D D J 2 u qm u 1 J ˆ el~k! J 2#7tan 2 1tan2 where the XJM(xˆ) represent spherical tensor operators of u^ fuu J uu i&u 2 J S 2DA uqWu S 2D rank J,M. A solution to the RPA Bethe-Salpeter equation ~10! is 3 @2Re~^J uu ˆ mag~k!uuJ &^J uu ˆ el~k!uuJ &*!#. f J J i f J J i given by the set of wave functions implicitly defined by 3248 JACHOWICZ, ROMBOUTS, HEYDE, AND RYCKEBUSCH PRC 59 c ~x !c† ~x ,e ! 21 ˜ h8 1 p8 1 p8 21 uCC~E!&5uph ~E!&1E dx1 E dx2 V~x1 ,x2!( E dep8 up8h8 ~ep8h8!& c P F E2e 8 p8h8 c† ~x !c ~x ,e ! h8 1 p8 1 p8 21 ˆ † ˆ 2 uh8p8 ~2ep h !& ^C0uc ~x2!c~x2!uCC~E!&, ~12! E1e 8 8 G p8h8 where denotes the Cauchy principal value, and the 21 P 21 dr dr R(0) r,r ;E uph (E)& and uhp (2E)& are the unperturbed particle- E E 8 hm;JM~ 8 ! hole and backward hole-particle solutions of the mean-field problem.
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]
  • 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]
  • 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]
  • How the First Neutral-Current Experiments Ended
    How the first neutral-current experiments ended Peter Galison Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138 At the beginning of the 1970s there seemed little reason to believe that strangeness-conserving neutral currents existed: theoreticians had no pressing need for them and several experiments suggested that they were suppressed if they were present at all. Indeed the two remarkable neutrino experiments that eventual- ly led to their discovery were designed and built for very different purposes, including the search for the vector boson and the investigation of the parton model. In retrospect we know that certain gauge theories (notably the Weinberg-Salam model) predicted that neutral currents exist. But until 't Hooft and Veltman proved that such theories were renormalizable, little effort was made to test the new theories. After the proof the two experimental groups began to reorient their goals to settle an increasingly central issue of physics. Do neutral currents exist? We ask here: What kind of evidence and arguments persuaded the par- ticipants that they had before them a real effect and not an artifact of the apparatus~ What eventually con- vinced them that their experiment was over? An answer to these questions requires an examination of the organization of the experiments, the nature of the apparatus, and the previous work of the experimentalists. Finally, some general observations are made about the recent evolution of experimental physics. CONTENTS weak interaction. Certainly the provisional advance af- I. Introduction 477 forded by such a move had many historical precedents. A II. The Experiment "Cxargamelle": from W Search to hundred years earlier Ampere unravelled many of the Neutral-Current Test 481 laws of electrodynamics by studying the interactions of III.
    [Show full text]
  • ELEMENTARY PARTICLES in PHYSICS 1 Elementary Particles in Physics S
    ELEMENTARY PARTICLES IN PHYSICS 1 Elementary Particles in Physics S. Gasiorowicz and P. Langacker Elementary-particle physics deals with the fundamental constituents of mat- ter and their interactions. In the past several decades an enormous amount of experimental information has been accumulated, and many patterns and sys- tematic features have been observed. Highly successful mathematical theories of the electromagnetic, weak, and strong interactions have been devised and tested. These theories, which are collectively known as the standard model, are almost certainly the correct description of Nature, to first approximation, down to a distance scale 1/1000th the size of the atomic nucleus. There are also spec- ulative but encouraging developments in the attempt to unify these interactions into a simple underlying framework, and even to incorporate quantum gravity in a parameter-free “theory of everything.” In this article we shall attempt to highlight the ways in which information has been organized, and to sketch the outlines of the standard model and its possible extensions. Classification of Particles The particles that have been identified in high-energy experiments fall into dis- tinct classes. There are the leptons (see Electron, Leptons, Neutrino, Muonium), 1 all of which have spin 2 . They may be charged or neutral. The charged lep- tons have electromagnetic as well as weak interactions; the neutral ones only interact weakly. There are three well-defined lepton pairs, the electron (e−) and − the electron neutrino (νe), the muon (µ ) and the muon neutrino (νµ), and the (much heavier) charged lepton, the tau (τ), and its tau neutrino (ντ ). These particles all have antiparticles, in accordance with the predictions of relativistic quantum mechanics (see CPT Theorem).
    [Show full text]
  • Field Theory and the Standard Model
    Field theory and the Standard Model W. Buchmüller and C. Lüdeling Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany Abstract We give a short introduction to the Standard Model and the underlying con- cepts of quantum field theory. 1 Introduction In these lectures we shall give a short introduction to the Standard Model of particle physics with empha- sis on the electroweak theory and the Higgs sector, and we shall also attempt to explain the underlying concepts of quantum field theory. The Standard Model of particle physics has the following key features: – As a theory of elementary particles, it incorporates relativity and quantum mechanics, and therefore it is based on quantum field theory. – Its predictive power rests on the regularization of divergent quantum corrections and the renormal- ization procedure which introduces scale-dependent `running couplings'. – Electromagnetic, weak, strong and also gravitational interactions are all related to local symmetries and described by Abelian and non-Abelian gauge theories. – The masses of all particles are generated by two mechanisms: confinement and spontaneous sym- metry breaking. In the following chapters we shall explain these points one by one. Finally, instead of a summary, we briefly recall the history of `The making of the Standard Model' [1]. From the theoretical perspective, the Standard Model has a simple and elegant structure: it is a chiral gauge theory. Spelling out the details reveals a rich phenomenology which can account for strong and electroweak interactions, confinement and spontaneous symmetry breaking, hadronic and leptonic flavour physics etc. [2, 3]. The study of all these aspects has kept theorists and experimenters busy for three decades.
    [Show full text]
  • 1973-DISCOVERY of NEUTRAL CURRENTS
    Gestion INIS LAPP-EXP-Q^ m Doc. enreg. Io : /.3.[f3.yfl.H JUIN ÎWJ N" TRN : ^LaJi Destinriicn . 1973-DISCOVERY of NEUTRAL CURRENTS B.AUBERT CNRS-IN2P3 LAPP-ANNECY ^ It is difficult to speak on "1973 -Discovery of Neutral Currents" without first mentioning earlier events, mainly 1953 in Paris the July 1st, signing of the convention setting the basis for the creation of this place "CERN in Geneva", and 1963 in a trattoria of the Siena's Palio the birth of the HLBC Gargamelle, on a napkin on a warm summer day. I must also apologize that I am not able to pay any special individual tribute here to each one who acted for the good of this enterprise : engineers and technicians from the machine and the beam, the bubble chamber physicists, theorists and experimentalists, administrative personnel and scanning girls. The only names I would like to honor are A.Lagarrigue who was the real leader of the Heavy Liquid Bubble Chamber (HLBC) active community and P.Musset who acted as the convener and the driving force behind the neutral current analysis. I will spend few minutes on the status of the weak interaction theory and the search for neutral currents in the late 1960's, and on the tooling available at this time. Then I will review the analysis of the Gargamelle experiment and finally I will give a brief look on what happened elsewhere. Status of the weak interaction theory. The current theory for weak interaction, able to represent p decay, \i decay and the decays of strange particles, called the Universal Fermi Interaction (UFI), was "local", which means a priori, it does not need a propagator.
    [Show full text]
  • 9. the Weak Force Particle and Nuclear Physics
    9. The Weak Force Particle and Nuclear Physics Dr. Tina Potter Dr. Tina Potter 9. The Weak Force 1 In this section... The charged current weak interaction Four-fermion interactions Massive propagators and the strength of the weak interaction C-symmetry and Parity violation Lepton universality Quark interactions and the CKM Dr. Tina Potter 9. The Weak Force 2 The Weak Interaction The weak interaction accounts for many decays in particle physics, e.g. − − − − µ ! e ν¯eνµ τ ! e ν¯eντ + − − π ! µ ν¯µ n ! pe ν¯e Characterised by long lifetimes and small interaction cross-sections Dr. Tina Potter 9. The Weak Force 3 The Weak Interaction Two types of weak interaction Charged current (CC): W ± bosons Neutral current (NC): Z bosons See Chapter 10 The weak force is mediated by massive vector bosons: mW = 80 GeV mZ = 91 GeV Examples: (The list below is not complete, will see more vertices later!) Weak interactions of electrons and neutrinos: − νe − e e νe Z W − W + Z + ν¯e e+ e ν¯e Dr. Tina Potter 9. The Weak Force 4 Boson Self-Interactions In QCD the gluons carrycolour charge. In the weak interaction the W ± and Z bosons carry the weak charge W ± also carry the electric charge ) boson self-interactions W − W − Z γ W + W + Z W + Z W + γ W + W + W + W − W − Z W − γ W − γ W − (The list above is complete as far as weak self-interactions are concerned, but we have still not seen all the weak vertices. Will see the rest later) Dr.
    [Show full text]
  • Neutrinos and Our Sun - Part 1
    GENERAL I ARTICLE Neutrinos and our Sun - Part 1 S N Ganguli The elusive .neutrinos have periodically yielded their secrets. to man and at each such juncture major advances }lave been achieved in our under­ standing of the sub-atomic phenomena. These particles also carry invaluable information about the centre of the Sun where energy is generated through nuclear fusion. In Part I of this article, S N Ganguli, an experi­ history of the discovery of neutrinos is traced, mental high energy their properties and types are described. Also, physicist, retired last year the Standard Model which forms the basis of the from the Tata Institute of structure of matter and of which massless neu­ Fundamental Research, Mumbai. He participated trinos are an integral part, is described. in the LHC experiment at The role of neutrinos in solar energy generation CERN, Geneva. He studied properties of Z and and the great 'solar neutrino puzzle' and its so­ W bosons produced in lution will be described later in the series. electron-positron collisions at the Large 1. Introduction Electron Positron Collider, also at CERN. He now The neutrino is one of the elusive t.iny part.icles creat.ed lives in Pondicherry. by nature. The hint of its exist.ence came from radioac­ tive beta-decay of nuclei. Although radioactivity was discovered at the very end of the nineteenth century (1896), it was only in 1931 that the neutrino was postu­ lated by Pauli to save t.he principle of energy conserva­ tion in radioactive beta-decay. It. took another twenty five years to det.ec', neutrino interactions in the labora­ tory (1956).
    [Show full text]
  • How to Discern a Physical Effect from Background Noise: the Discovery of Weak Neutral Currents
    How to Discern a Physical Effect from Background Noise: The Discovery of Weak Neutral Currents Samuel Schindler Department of Philosophy Division of History and Philosophy of Science University of Leeds Woodhouse Lane Leeds, LS2 9JT, UK [email protected] ****************************************************************************** Under Review! Please do not cite without permission! ****************************************************************************** Abstract In this paper I try to shed some light on how one discerns a physical effect or phenomenon from experimental background ‘noise’. To this end I revisit the discovery of Weak Neutral Currents (WNC), which has been right at the centre of discussion of some of the most influential available literature on this issue. Bogen and Woodward (1988) have claimed that the phenomenon of WNC was inferred from the data without higher level physical theory explaining this phenomenon (here: the Weinberg-Salam model of electroweak interactions) being involved in this process. Mayo (1994, 1996), in a similar vein, holds that the discovery of WNC was made on the basis of some piecemeal statistical techniques—again without the Salam-Weinberg model (predicting and explaining WNC) being involved in the process. Both Bogen & Woodward and Mayo have tried to back up their claims by referring to the historical work about the discovery of WNC by Galison (1983, 1987). Galison’s presentation of the historical facts, which can be described as realist, has however been challenged by Pickering (1984, 1988, 1989), who has drawn sociological-relativist conclusions from this historical case. Pickering’s conclusions, in turn, have recently come under attack by Miller and Bullock (1994), who delivered a defence of Galison’s realist account.
    [Show full text]