DOCSLIB.ORG

Testing Discrete Symmetries in K Decays

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Testing Discrete Symmetries in K Decays ,fe-a very successful theory for physics phe­ nomena, valid for many human applica­ Testing discrete symmetries tions. What about the symmetry proper­ ties ofthe other theories? There is an im­ portanttheorem,known as the CPT theo­ in Kdecays rem, which states that, under very general assumptions, any theory of microscopic P. DEBU - (EA Saclay - France interactions must respect the CPT sym­ February 7,2000 metry. This means that in the present day the­ oretical framework ofparticle physics, it is Discrete symmetries, P and C Weak interactions and violation of P and believed that the laws of physics are in­ hen physicists try to lay down the Csymmetries variant under CPT. Wlaws that govern the processes they There are four known fundamental As a consequence, CP symmetry im­ are studying, they use as a first guidance interactions between elementary plies T symmetry, andvice-versa, because the most general properties ofthe system. particles. Gravitation is felt by all any CP violation should be compensated There are fundamental and universal particles. Charged particles undergo by some T violation to follow the CPT the­ examples. The laws ofNature are believed electromagnetic interactions. The orem. to be independent of the position of the protons and the neutron are bound in The 1957 observation that CP symme­ observer, or of his orientation. One says nuclei by the strong interaction. Weak trystill holds could be seen as a necessary that they are invariant by translation and interactions transform quarks into one consequence that microscopic phenome­ rotation. another and cause the f3 decays of na obey the T symmetry. Consider now a simple experiment,like unstable nuclei. playing billiards. Imagine you are looking It was assumed for a long time that the CP violation at the image ofthe game in a large mirror fundamental interactions respect both P CP violation was discovered in 1964 in instead of looking directly at the billiard and C symmetries, but experimental ob­ an experiment dedicated to the study of table. Would you be able to tell from the servations led two theoreticians, T.D. Lee KO and KO mesons. It was performed by moves ofthe balls that you are looking at a and C.N. Yang, to suggest in 1956 that P J.H. Christenson, J.W. Cronin, Y.L. Fitch virtual image? The answer is no. Laws of and C symmetries might be violated by and R. Turlay. classical mechanics are obeyed bythe mir­ the weak interactions. One year later, an The KO is a particle made of an anti s ror experiment. They are invariant under experiment led by C.S. Wu, a detailed quark (8) and a d quark. Because weak in­ the transformation called Parity (P), study ofthe f3 decay ofC0 60 in a magnetic teractions can change a strange quark in­ which consists in changing the sign ofspa­ field, brought indeed the proofthat P sym­ to a non strange quark, both KO and KO tial coordinates. metry was violated by weak interactions. mesons can decay into the same final state We say that classical mechanics respect Additional theoretical work showed that of 2 pions, and moreover, by a succession the P symmetry. at the same time, the C symmetry was vi­ oftwo weak processes, the KOcan become Imagine that instead of looking at the olated. However, it was also realized that a KO and vice-versa! billiards game in a mirror, you replace the observed processes do respect the CP During the propagation of the K every piece ofmatterbyantimatter. Could transformation, the one obtained by ap­ mesons, a continuous KO H KO oscillation you tell the difference from the moves? plying both the C and the P transforma­ occurs. Were CP conserved, the propagat­ The answer is again no. Laws of classical tions. In other words, the virtual experi­ ing states would be the symmetric and an­ mechanics apply to antimatter. The oper­ ment obtained by looking at the original tisymmetric states superpositions ation which consists in replacing a particle process in a mirror AND by replacing all K 1 = (KO + [(0)1"'/2 and K 2 = (KO - KO)1"'I2. by its antiparticle is called Charge Conju­ particles by their antipartners would obey The 2 pion state issued ofa K decay being gation (C). the known properties of weak interac­ a CP even state, this decay would be al­ Classical mechanics respect the C sym­ tions. lowed for the K 1 which is also a CP even metry. This was a very important observation. state, andforbidden for the K 2,which is CP Every particle has its corresponding an­ odd. tiparticle, which has the same mass butthe Time reversal and CPT symmetry Indeed, physicists observed both a opposite charge. This is the origin of the There is a fundamental reason why CP short lived K meson, called Ks, decaying name Charge Conjugation. The antiparti­ symmetry plays a crucial role. It is indeed into 2 pions, and a 500 times longer lived cle ofthe electron e- is the positron e+. The linked to the Time Reversal transforma­ K L which could only undergo three body antiparticle ofthe proton p is the antipro­ tion (T). decays. The whole picture seemed consis­ ton p. The proton is made of3 quarks, 2 u This transformation consists in "look­ tent with the previous description. quarks and 1 d quark. The an!iproton is ing" at an experiment backwards in time, The 1964 experimental demonstration made of3 antiquarks,2 iiand 1d The neu­ like playing a movie backwards. Although, ofCP violation was the detection ofKL de­ tron is made of3 quarks, 2 d quarks and! at the macroscopic level, one can immedi­ cays into 2 charged pions. Although this u quark. The antineutron is made of 2 d ately distinguish which is the real experi­ happened only rarely, about twice every and 1 ii. One can imagine building an an­ ment and which is the reversed movie, this thousand decays, it was a clear sign of CP tiworld from these elementary pieces. If is not a priori the case at the microscopic violation in microscopic processes. the laws ofNature would be C symmetric, level. Indeed, the laws ofclassical mechan­ This came as a big surprise, but it was this antiworld could not be distinguished ics remain valid after Time Reversal. also soon realized, in 1967, byA. Sakharov, from the world we know. But they are not. Classical mechanics is an example of a that CP violation is one of the necessary europhysics news MAY/JUNE 2000 s Article available at http://www.europhysicsnews.org or http://dx.doi.org/10.1051/epn:2000301 FEATURES conditions to explain why our universe is Ithas been established that the K L state Although it is inprinciple possible to com­ almost exclusively made of matter, al­ is not the pure antisymmetric stateK 2, but pute the value of E'IE in the standard though it starts from a symmetricstate af­ rather an admixture ofK 1 and K 2: model, it is in practice avery difficult task. ter the Big-Bang model. Most theorists give estimates in the range 4 This made CP violation even more fas­ KL=K2 + E K 1 ofa few 10- for the ratio E'/E. cinating. In 1988, a first evidence for the exis­ At that time, it was necessary to intro­ This small impurity (E '" 2 10-3) allows the tence ofdirect CP violation was published duce new types of interactions to imple­ K L to decay into 2 pions. This is referred to bythe NA31 collaboration at CERN [1] : ment CP violation in the theoretical as CP violation in the mixing. While the framework. One very popular model was introduction of this E parameter allows a E'IE = (3.3 ± 1.1) 10-3 proposedby1.Wolfenstein in 1964. He in­ proper phenomenological description of troduced a so called superweak interac­ the observations, itbrings no understand­ Later, their american competitors, E731 at tion, the strength and properties ofwhich ing ofthe origin ofCP violation. FNAL, published [2]: were such that CP violationwas a small ef­ However, in the standard model of fect which could only be seen with the K weak interactions with 3 families, CP vio­ E'IE = (7.4 ± 5.9) 10-4 mesons, and came solely through the lation can also occur directly in the decay KO H KO oscillation. ofthe K 2 itself. This is called CP violation The NA31 completed their experiment In 1973, M. Kobayashi and T. Maskawa in the decay, or direct CP violation. Con­ and obtained in 1993 [3] : showed that CP violation could also occur trarily, the superweak model of1.Wolfen­ in weak interactions under the condition stein does not allow such a decay. E'IE = (2.3 ± .65) 10-3 that at least 3 families of2 quarks exist. To­ Many experiments have been launched day, the existence of6 quarks is established already in the late 60's to search for direct This experimental situation, two results (the heaviest one, the t quark, has been dis­ CP violation. It can be detected through a hardly compatible, did not allow to con­ covered in 1995),but at that time, only the tiny difference between decays in 2 clude. This led the two groups to launch existence of3 quarks was postulated. This charged pions and 2 neutral pions. This more precise experiments, E832 at FNAL is a noticeable theoretical insight. difference is parametrizedby a very small and NA48 at CERN. The presence ofthree families ofquarks quantity E', which can be measured byus­ allows the introduction of one single pa­ ing the very simple relation: rameter in the theorywhich causes CP vi­ olation.
Load more

Recommended publications
  • ANTIMATTER a Review of Its Role in the Universe and Its Applications
    A review of its role in the ANTIMATTER universe and its applications THE DISCOVERY OF NATURE’S SYMMETRIES ntimatter plays an intrinsic role in our Aunderstanding of the subatomic world THE UNIVERSE THROUGH THE LOOKING-GLASS C.D. Anderson, Anderson, Emilio VisualSegrè Archives C.D. The beginning of the 20th century or vice versa, it absorbed or emitted saw a cascade of brilliant insights into quanta of electromagnetic radiation the nature of matter and energy. The of definite energy, giving rise to a first was Max Planck’s realisation that characteristic spectrum of bright or energy (in the form of electromagnetic dark lines at specific wavelengths. radiation i.e. light) had discrete values The Austrian physicist, Erwin – it was quantised. The second was Schrödinger laid down a more precise that energy and mass were equivalent, mathematical formulation of this as described by Einstein’s special behaviour based on wave theory and theory of relativity and his iconic probability – quantum mechanics. The first image of a positron track found in cosmic rays equation, E = mc2, where c is the The Schrödinger wave equation could speed of light in a vacuum; the theory predict the spectrum of the simplest or positron; when an electron also predicted that objects behave atom, hydrogen, which consists of met a positron, they would annihilate somewhat differently when moving a single electron orbiting a positive according to Einstein’s equation, proton. However, the spectrum generating two gamma rays in the featured additional lines that were not process. The concept of antimatter explained. In 1928, the British physicist was born.
    [Show full text]
  • Andreas Meyer Hamburg University
    CP/ Part 1 Andreas Meyer Hamburg University DESY Summer Student Lectures, 1+4 August 2003 (this file including slides not shown in the lecture) CP-Violation Violation of Particle Anti-particle Symmetry Friday: Symmetries • Parity-Operation and Charge-Conjugation • The neutral K-Meson-System • Discovery of CP-violation (1964) • CP-Violation in the Standard model • Measurements at the CPLEAR Experiment (CP Violation in K 0-Mixing) • Slides only: Latest Results from NA48 (CP Violation in K 0-Decays) • Monday: Recap: Discovery of CP-Violation • The neutral B-Meson-System • CKM Matrix and Unitarity Triangle • Prediction for the B-System from K-Results • B-Factories BaBar and Belle (Test of Standard Model) • Future Experiments, CP-Violation in the Lepton-Sector? • Summary • The Universe Matter exceeds Antimatter, why? Big-Bang model: Creation of matter and antimatter in equal amounts • Baryogenesis: Where did the antimatter go? • Three necessary conditions for Baryogenesis: A. Sacharov, 1967 Baryon-number violation • no problem for gauge theories but not seen yet Thermodynamical non-equilibrium • C and CP-violation (!) • What is CP-Violation? CP: Symmetry between Particles and Antiparticles CP-Symmetry is known to be broken: The Universe • { Matter only, no significant amount of antimatter The neutral K-Meson (most of todays lecture) • { discovered 1964 (Fitch, Cronin, Nobel-Prize 1980) { almost 40 years of K-physics with increasing precision The neutral B-Meson (on Monday) • { measured 2001 (expected in Standard Model) Symmetry Image = Mirror-Image
    [Show full text]
  • CP Violation in K Decays: Experimental Aspects
    CP violation in K decays: experimental aspects M. Jeitler Institute for High Energy Physics, Vienna, Austria Abstract CP violation was originally discovered in neutral K mesons. Over the last few years, it has also been seen in B mesons, and most of the research in the field is currently concentrating on the B system. However, there are some parameters which could be best measured in kaons. In order to see to which extent our present understanding of CP violation within the framework of the CKM matrix is correct, one has to check for possible differences between the K system and the B system. After an historical overview, I discuss a few of the most important recent results, and give an outlook on experiments that are being prepared. 1 The discovery of CP violation Symmetries are a salient feature of our world, but so is the breaking of approximate symmetries. Still, for a long time physicists believed that at the level of elementary particles, a high level of symmetry should prevail. In particular, it was expected that all fundamental interactions should be symmetric under the discrete transformations of spatial inversion (parity transformation P), substitution of antiparticles for particles (charge conjugation C), and time inversion (T). However, in 1956 Lee and Yang concluded from experimental data that the weak interactions might not be invariant under spatial inversion, in other words that parity might be violated. This was then explicitly shown in an experiment by Wu in 1957 [1]. For a few years, physicists were inclined to believe that although parity was broken, this symme- try violation was exactly compensated by the charge symmetry violation, and that the symmetry under a combined charge and parity transformation (CP) was exactly conserved.
    [Show full text]
  • Measurements of Discrete Symmetries in the Neutral Kaon System with the CPLEAR (PS195) Experiment
    Measurements of Discrete Symmetries in the Neutral Kaon System with the CPLEAR (PS195) Experiment Thomas Ruf CERN, CH-1211, Geneva 23, Switzerland [email protected] The antiproton storage ring LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of T , CPT and CP symmetries in the neutral kaon system. It measured with high precision the time evolution of initially strangeness-tagged K0 and K0 states to determine the size of violations with respect to these symmetries in the context of a systematic study. In parallel, limits concerning quantum-mechanical predictions (EPR paradox, coherence of the wave function) or the equivalence principle of general relativity have been obtained. This article will first discuss briefly the unique low energy antiproton storage ring LEAR followed by a description of the CPLEAR experiment, including the basic formalism necessary to understand the time evolution of a neutral kaon state and the main results related to measurements of discrete symmetries in the neutral kaon system. An excellent and exhaustive review of the CPLEAR experiment and all its measurements is given in Ref. 1. 1. The Low Energy Antiproton Ring The Low Energy Antiproton Ring (LEAR)2, 3 decelerated and stored antiprotons for eventual extraction to the experiments located in the South Hall. It was built in 1982 and operated until 1996, when it was converted into the Low Energy Ion Ring (LEIR), which provides lead-ion injection for the Large Hadron Collider (LHC). Under the LEAR programme, four machines — the Proton Synchrotron (PS), 60 Years of CERN Experiments and Discoveries Downloaded from www.worldscientific.com the Antiproton Collector (AC), the Antiproton Accumulator (AA), and LEAR — worked together to collect, cool and decelerate antiprotons for use in experiments.
    [Show full text]
  • 389 the CPLEAR Experiment at CERN Studies the CP, T and CPT
    389 RESULTS FROM CP, T AND CPT MEASUREMENTS AT CPLEAR Christos Touramanis PPE Division, CERN, CH1211 Geneva 23, Switzerland for the CPLEAR collaboration R. Adler', T. Alhalel2 , A. Angelopoulos1 , A. Apostolakis1, E. Aslanides11, G. Backenstoss2 , C.P. Bee2 , Behnke 11, 0. A. Benelli 9, V. Bertin11, F. Blanc7•13, P. Bloch\ Ch. Bula13, P. Carlson", M. Carroll9 J. Carvalho', E. Cawley9, S. Charalarnbous16, M. Chardalas16, G. Chardin1\ M.B. Chertok3, A. Cody9, M. Danielsson15, S. Dedoussis16, M. Dejardin14, J. Derre14, Duclos14, A. Ealet11 , B. Eckart', C. Eleftheriadis16, I. Evangelou8 , L. Faravel 7, J. P. Fassnacht11, J .L. Faure14, C. Felder2, R. Ferreira-Marques5, W. Fetscher17, M. Fidecaro4, A. FilipCiC10 1 D. Francis3 , Fry9, E. Gabathuler9, R. Gamet9, D. Garreta14, H.-J. Gerber17, A. Go15, C. Guyot14, A. Haselden9, J. P.J. Hayrnan9, F. Henry-Couannier11 , R.W. Hollander6,E. Hubert11, K. Jon-And15, P.-R. Kettle13, C. Kochowski14, P. Kokkas5, R. Kreuger6, R. Le Gac11, F. Leirngruber',A. Liolios16, E. Machado5, I. Mandic10, N. Manthos8, G. Marei14, M. Mikuz10, J. Miller3 , F. Montanet11, T. Nakada13, A. Onofre', B. Pagels 17, I. Papadopoulos16, P. Pavlopoulos', J. Pinto da Cunha5, A. Policarpo', G. Polivka' , R. Rickenbach', B.L. Roberts", E. Rozaki', T. Ruf\ L. Sakeliou', P. Sanders9, C. Santoni', K. Sarigiannis1, M. Schii.fer17, L.A. Schaller7, A. Schopper\ P. Schune1\ A. Soares14, L. Tauscher2, C. Thibault12, F. To uchard1\ C. Touramanis\ F. Triantis8, E. Van Beveren5, C.W.E. Van Eijk6, G. Varner", S. Vlachos' , P. Weber17, Wigger13, M. Wolter'7, C. Yeche14, 0. D. Zavrtanik10 and D. Zimmerman3 ABSTRACT The CPLEAR experiment at CERN studies the CP, T and CPT symmetries in the neutral K0 K0• kaon system using initially tagged and Results from the 1990 to 1993 data on 71+-• Am and are reported, as well as the first direct measurement of T violation and 71+-o , x cs.
    [Show full text]
  • Heavy-Quark Physics and Cp Violation
    COURSE HEAVYQUARK PHYSICS AND CP VIOLATION Jerey D Richman University of California y Santa Barbara California USA y Email richmancharmphysicsucsbedu c Elsevier Science BV Al l rights reserved Photograph of Lecturer Contents Intro duction Roadmap and Overview of Bottom and Charm Physics Intro duction to the Cabibb oKobayashiMaskawa Matrix and a First Lo ok at CP Violation Exp erimental Challenges and Approaches in HeavyQuark Physics Historical Persp ective Bumps in the Road and Lessons in Data Analysis Avery short history of heavyquark physics Bumps in the road case studies Some rules for data analysis Leptonic Decays Intro duction to leptonic decays Measurements of leptonic decays Lattice calculations of leptonic decay constants Semileptonic Decays Intro duction to semileptonic decays Dynamics of semileptonic decay Heavy quark eective theory and semileptonic decays Inclusive semileptonic decay and jV j cb Leptonendp oint region in semileptonic B deca y and jV j ub Form factors and kinematic distributions for exclusive semileptonic decay HQET predictions and the IsgurWise function Exclusive semileptonic decay jV j and jV j cb ub Hadronic Decays Lifetimes and Rare Decays Hadronic Decays Lifetimes Rare decays CP Violation and Oscillations Intro duction to CP violation CP violation and cosmology CP violation in decay direct CP violation CP violation in mixing indirect CP violation Phenomenology of mixing CP violation due to interference b etween mixing and decay Acknowledgements
    [Show full text]
  • CPLEAR Results on the CP Parameters of Neutral Kaons Decaying to Π+Π−Π0 R
    CPLEAR results on the CP parameters of neutral kaons decaying to π+π−π0 R. Adler, A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, P. Bargassa, C P. Bee, O. Behnke, A. Benelli, V. Bertin, et al. To cite this version: R. Adler, A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, et al.. CPLEAR results on the CP parameters of neutral kaons decaying to π+π−π0. Physics Letters B, Elsevier, 1997, 407, pp.193-200. in2p3-00000063 HAL Id: in2p3-00000063 http://hal.in2p3.fr/in2p3-00000063 Submitted on 16 Nov 1998 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN–PPE/97–54 12 May 1997 + 0 CPLEAR results on the CP parameters of neutral kaons decaying to The CPLEAR Collaboration 1 1 11 2 R. Adler 2 , A. Angelopoulos , A. Apostolakis ,E.Aslanides , G. Backenstoss , 9 17 9 11 7;13 P. Bargassa13 ,C.P.Bee,O.Behnke ,A.Benelli ,V.Bertin ,F.Blanc , 15 9 5 9 16 P. Bloch 4 ,P.Carlson ,M.Carroll,J.Carvalho,E.Cawley, S. Charalambous , 3 9 15 14 14 G.
    [Show full text]
  • The CPLEAR Collaboration Athens, Basel, Boston, DAPNINSPP-Saclay
    371 THE STUDY THE CP, T AND CPT SYMMETRIES OFTHE CPLEAR EXPERIMENT IN The CPLEAR Collaboration Athens, Basel, Boston, DAPNINSPP-Saclay, Coimbra, Delft, Elli-IMP Zilrich, Fribourg, 1N2P3/CPPM-Marseille, IN2P3/CSNSM-Orsay,CERN, Ioannina, Liverpool, Ljubljana, PSI, MSI-Stockholm,Thessaloniki R. Adler, T. Alhalel, A. Angelopoulos, A. Apostolakis, E. Aslanides, G. Backenstoss, C.P.Bee, Behnke, J. Bennet, Bertin, Blanc, P. Bloch, Ch. Bula, P. Carlson, M. Carroll J. Carvalho, Cawley, E. 0. S. Charalambous, M. Chardalas,G. Chardin, M.B. Chertok, M. Danielsson, A. Cody, S. Dedoussis, V. F. M. De ardin, J. Derre,M. Dodgson, Duclos, A. et, B. C. Eleftheriadis, I. Evangelou, L. Faravel, P. Fassnacht, J.L. C. Felder, R. Ferreira-Marques, Fetscher, M. Fidecaro, F l i Francis, Faure, W. A. i i D. j J. Eal Eckart, . Fry, E. Gabathuler, R. Gamet, Garreta, T. Geralis, H.-J. Gerber, A. Go, P. Gumplinger, C. Guyot, D. ¢ � A. Haselden, Hayman, Henry-Couannier, R.W. Hollander,E. Hoben, K. Jansson, H.U. Johner, J. PJ. F. K. Jon-And, P. R. Kettle, C. Kochowski, Kokkas, R. Kreuger, T. Lawry, R. Gae, Leimgruber, Le F. A. Liolios, E. Machado, P. Maley, I. N. G. Marel, M. Miku�. J. Miller, Montane!, P. F. T. A. Onofre, B. Pagels, P. Pavlopoulos, Pelucchi, J. Pinto Cunha, A. Policarpo, G. Polivka, Mandie, Manthos,F. H. Postma, R. Rickenbach, B.L. Robens, E. Rozaki, Ruf, L. Sacks, L. Sakeliou, P. Sanders, C. Santoni, Nakada, T. da K. Sarigiannis, M. Schafer, L.A. Schaller, A. Schopper, P. Schone, A. Soares, L. Tauscher, C.
    [Show full text]
  • ANTIMATTER and GRAVITATION 1 Scientific Aim 1.1 the Equivalence
    ANTIMATTER AND GRAVITATION P. DEBU Direction de la recherche fondamentale, CEA Saclay, 91191 Gif-sur-Yvette cedex, France Three experiments et CERN are about to “weight” antihydrogen. We describe the objectives of the experiments trying to measure the gravitation effect on antimatter, we review some of the theoretical constraints on a possible different gravitational behavior between matter and antimatter, and give an overview of the existing experimental limits and proposals. 1 Scientific aim 1.1 The Equivalence Principle The main objective of the measurement of the action of gravity on antimatter is to perform a direct test with antimatter of the Einstein Equivalence Principle which states that the trajectory of a test particle is independant of its composition and internal structure when its is solely subject to gravitational forces. This principle has been verified with many materials. A very high precision of around 10−13 has been reached. A torsion pendulum experiment 1 with Beryllium and Titanium test bodies led to the following difference between their gravitational acceleration: −13 (∆a=a)Be=Ti = (0:3 ± 1:8) × 10 : (1) A precise follow up of the relative motion of the Earth and the Moon (“Lunar Laser Ranging” 2) gave: −13 (∆a=a)Earth=Moon = (−1:0 ± 1:4) × 10 : (2) 1.2 Antimatter In the Standard Model of particle physics, every particle comes with its own antiparticle which carries an opposite charge but, as stated by the CPT theorem, has exactly the same inertial mass and the same lifetime. The most stringent limit on the inertial mass equality is 3: −19 (MK0 − MK¯0 )=Maverage < 6 × 10 (90 % CL): (3) As we will see, there is nos such comparison for the particle and its antiparticle gravitational mass, a quantity which we define in the next section.
    [Show full text]
  • Glasgow Conference
    Glasgow conference Pierre Darriulat of CERN gives the summary talk at this year's International Conference on High Energy Physics, held in Glasgow. (Photos University of Glasgow) he biennial 'Rochester' Interna­ T tional Conferences on High Energy Physics which tick the rhythm of high energy physics progress reflect the dominance of the 'Standard Model' - the picture of electroweak and quark/gluon interactions in a simple framework of six weakly- interacting particles (leptons) and six quarks. Despite its limited intellectual appeal, after a decade of intense probing the Standard Model still refuses to budge. This year's Rochester event, held in Glasgow from 20-27 July, followed the trend. But conformity is not a synonym for a physics vacuum. The advent of high precision data from big colliding beam experiments provides a treasure trove of detailed information on particle characteristics and decays, so that Standard Model physics becomes charted in finer and which has already definitely ruled out for the top quark but does not firmly finer detail. (A preliminary Glasgow the top quark being lighter than 131 establish its existence,' declared report appeared last month, page 1.) GeV. Jensen. However the map is far from com­ After careful elimination of back­ Seven CDF events have enough plete, and as Glasgow summarizer ground effects in the initial data kinematical information to calculate Pierre Darriulat of CERN concluded, sample, CDF found two spectacular the top quark mass, giving a value of there is a lot to do while waiting for events producing an electron and a 174 GeV ± 10%. the next round, which will begin in muon, but none with an electron or a DO reports one example of a muon- about ten years when CERN's LHC muon pair.
    [Show full text]
  • Parity Violation
    Parity violation • Wu experiment: b decay of polarized nuclei of Cobalt: Co (spin 5) decays to Ni (spin 4), electron and anti-neutrino (spin ½) • Parity changes the helicity (H). Ø P-conservation assumes a symmetry between the left and right handed particles, e.g. counting rates for LH and RH electrons are the same �$ �" Co Ni �$ �" no left-handed �$ are produced Charge conjugation violation • Lederman et al (1957) C-violation in charged pion decays to muons and neutrinos • Charge conjugation replaces particles with anti-particles CP is conserved no left-handed neutrinos and right-handed anti-neutrinos are observed – C-violation https://journals.aps.org/pr/pdf/10.1103/PhysRev.105.1415 CP Violation in the Early Universe • Very early in the universe might expect equal numbers of baryons and anti-baryons, which would all annihilate to photons • The universe is matter dominated (no evidence for anti-galaxies, etc.) • From “Big Bang Nucleosynthesis” obtain the matter/anti-matter asymmetry i.e. for every baryon in the universe today there are photons • How did this happen? « Early in the universe need to create a very small asymmetry between baryons and anti-baryons, e.g. for every 109 anti-baryons there were 109+1 baryons baryons/anti-baryons annihilate 1 baryon + ~109 photons + no anti-baryons « To generate this initial asymmetry three conditions must be met (Sakharov, 1967): • CP Violation is an essential aspect of our understanding of the universe • A natural question is whether the SM of particle physics can provide the necessary CP violation? • There are two places in the SM where CP violation enters: the PMNS matrix and the CKM matrix • To date CP violation has been observed only in the quark sector • Because we are dealing with quarks, which are only observed as bound states, this is a fairly complicated subject.
    [Show full text]
  • The CKM Matrix and CP Violation
    Particle Physics Dr. Alexander Mitov Handout 12 : The CKM Matrix and CP Violation Dr. A. Mitov Particle Physics 410 CP Violation in the Early Universe • Very early in the universe might expect equal numbers oF baryons and anti-baryons • However, today the universe is matter dominated (no evidence for anti-galaxies, etc.) • From “Big Bang Nucleosynthesis” obtain the matter/anti-matter asymmetry i.e. for every baryon in the universe today there are photons • How did this happen? « Early in the universe need to create a very small asymmetry between baryons and anti-baryons e.g. for every 109 anti-baryons there were 109+1 baryons baryons/anti-baryons annihilate 1 baryon + ~109 photons + no anti-baryons « To generate this initial asymmetry three conditions must be met (Sakharov, 1967): “Baryon number violation”, i.e. is not constant “C and CP violation”, if CP is conserved for a reaction which generates a net number oF baryons over anti-baryons there would be a CP conjugate reaction generating a net number oF anti-baryons “Departure from thermal equilibrium”, in thermal equilibrium any baryon number violating process will be balanced by the inverse reaction Dr. A. Mitov Particle Physics 411 • CP Violation is an essential aspect of our understanding of the universe • A natural question is whether the SM oF particle physics can provide the necessary CP violation? • There are two places in the SM where CP violation enters: the PMNS matrix and the CKM matrix • To date CP violation has been observed only in the quark sector • Because we are dealing with quarks, which are only observed as bound states, this is a fairly complicated subject.
    [Show full text]