Showing papers on "Elementary particle published in 2000"

Review of particle physics. Particle Data Group

Abstract: This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 1600 new measurements from 550 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http: //pdg. lbl. gov.

Review of Particle Physics

Abstract: This biennial Review summarizes much of particle physics. Using data from previous editions., plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors., probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V-ud & V-us, V-cb & V-ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.

A Full next-to-leading order study of direct photon pair production in hadronic collisions

Abstract: We discuss the production of photon pairs in hadronic collisions, from fixed target to LHC energies. The study which follows is based on a QCD calculation at full next-to-leading order accuracy, including single and double fragmentation contributions, and implemented in the form of a general purpose computer program of “partonic event generator” type. To illustrate the possibilities of this code, we present a comparison with observables measured by the WA70 and D0 collaborations, and some predictions for the irreducible background to the search of Higgs bosons at LHC in the channel $h \rightarrow \gamma \gamma$ . We also discuss theoretical scale uncertainties for these predictions, and examine several infrared sensitive situations which deserve further study.

Supersymmetric electroweak baryogenesis

Abstract: We re-examine the generation of the baryon asymmetry in the minimal supersymmetric standard model (MSSM) during the electroweak phase transition. We find that the dominant source for baryogenesis arises from the chargino sector. The CP-violation comes from the complex phase in the μ parameter, which provides CP-odd contributions to the particle dispersion relations. This leads to different accelerations for particles and antiparticles in the wall region which, combined with diffusion, leads to the separation of higgsinos and their antiparticles in the front of the wall. These asymmetries get transported to produce perturbations in the left-handed chiral quarks, which then drive sphaleron interactions to create the baryon asymmetry. We present a complete derivation of the semiclassical WKB formalism, including the chargino dispersion relations and a self-consistent derivation of the diffusion equations starting from semiclassical Boltzmann equations for WKB-excitations. We stress the advantages of treating the transport equations in terms of the manifestly gauge invariant physical energy and kinetic momentum, rather than in the gauge variant canonical variables used in previous treatments. We show that a large enough baryon asymmetry can be created for the phase of the complex μ-parameter as small as ~ 10−3, which is consistent with bounds from the neutron electric dipole moment.

The Rigidity Dependence of Solar Particle Scattering Mean Free Paths

Abstract: The rigidity dependence of solar particle scattering mean free paths in the range from 0.1 to a few GV is a key parameter to distinguish between different models for the nature of wave-particle interactions and of interplanetary magnetic turbulence. Here we present an analysis of electron and ion data, covering a large portion of the above range, obtained from modeling intensity and anisotropy profiles of a series of solar particle events in 1982 August that show exceptionally large but finite mean free paths. Combined with particle measurements from previously analyzed events that exhibit mean free paths in the range of 0.02 to 0.5 AU, we find that a uniform shape of the functional form of the rigidity dependence, which varies only in absolute height for different events, can explain all observations. These results place severe constraints on any propagation theory and rule out a number of recently suggested models to improve the standard quasilinear theory of particle scattering. Our findings may indicate that the component of the turbulence the particles interact with does not vary much with respect to its decomposition into different modes and their respective spectral and angular wavenumber dependencies, and basically the total power of this component is responsible for the level of the mean free paths.

Landau-Pomeranchuk-Migdal effect in thermal field theory

Abstract: In recent studies, the production rate of photons or lepton pairs by a quark gluon plasma has been found to be enhanced due to collinear singularities. This enhancement pattern is very dependent on rather strict collinearity conditions between the photon and the quark momenta. It was estimated by neglecting the collisional width of quasiparticles. In this paper, we study the modifications of this collinear enhancement when we take into account the possibility for the quarks to have a finite mean free path. Assuming a mean free path of order $[{g}^{2}T\mathrm{ln}(1/g){]}^{\ensuremath{-}1},$ we find that only low invariant mass photons are affected. The region where collision effects are important can be interpreted as the region where the Landau-Pomeranchuk-Migdal effect plays a role in thermal photon production by bremsstrahlung. It is found that this effect modifies the spectrum of very energetic photons as well. Based on these results and on a previous work on infrared singularities, we end this paper with a reasonable physical picture for photon production by a quark gluon plasma that should be useful to set directions for future technical developments.

Extra dimensions and Strong Neutrino-Nucleon interactions above $10^{19}$ eV : Breaking the GZK Barrier

Abstract: Cosmic ray events above $10^{20}$ eV are on the verge of confronting fundamental particle physics. The neutrino is the only candidate primary among established particles capable of crossing 100 Mpc intergalactic distances unimpeded. The magnitude of $ u N$ cross sections indicated by events, plus consistency with the Standard Model at low-energy, point to new physics of massive spin-2 exchange. In models based on extra dimensions, we find that the $ u N$ cross section rises to typical hadronic values of between 1 and 100 mb at energies above $10^{20}$ eV. Our calculations take into account constraints of unitarity. We conclude that air-showers observed with energies above $10^{19}$ eV are consistent with neutrino primaries and extra-dimension models. An {\it upper bound} of 1-10 TeV on the mass scale at which graviton exchange becomes strong in current Kaluza-Klein models follows.

Beyond the Standard Model (In Search of Supersymmetry)

Abstract: The present lectures contain an introduction to low energy supersymmetry, a new symmetry that relates bosons and fermions, in particle physics. The Standard Model of fundamental interactions is briefly reviewed, and the motivation to introduce supersymmetry is discussed. The main notions of supersymmetry are introduced. The supersymmetric extension of the Standard Model - the Minimal Supersymmetric Standard Model - is considered in more detail. Phenomenological features of the MSSM as well as possible experimental signatures of SUSY are described. An intriguing situation with the supersymmetric Higgs boson is discussed.

Can lepton flavor violating interactions explain the atmospheric neutrino problem

Abstract: We investigate whether flavor changing neutrino interactions (FCNIs) can be sufficiently large to provide a viable solution to the atmospheric neutrino problem. Effective operators induced by heavy boson exchange that allow for flavor changing neutrino scattering off quarks or electrons are related by an SU(2){sub L} rotation to operators that induce anomalous tau decays. Since SU(2){sub L} violation is small for new physics at or above the weak scale, one can use the upper bounds on lepton flavor violating tau decays or on lepton universality violation to put severe, model-independent bounds on the relevant non-standard neutrino interactions. Also Z-induced flavor changing neutral currents, due to heavy singlet neutrinos, are too small to be relevant for the atmospheric neutrino anomaly. We conclude that the FCNI solution to the atmospheric neutrino problem is ruled out. (c) 2000 The American Physical Society.

A4 model for the quark mass matrices

Abstract: We propose a model for the quark masses and mixings based on an A4 family symmetry. Three scalar SU(2) doublets form a triplet of A4. The three left-handed-quark SU(2) doublets are also united in a triplet of A4. The right-handed quarks are singlets of A4. The A4-symmetric scalar potential leads to a vacuum in which two of the three scalar SU(2) doublets have expectation values with equal moduli. Our model makes an excellent fit of the observed |Vub/Vcb|. CP symmetry is respected in the charged gauge interactions of the quarks.

Construction of a minimal Higgs SO(10) supersymmetric grand unified model

Abstract: A full account is given of the procedure used by the authors to construct an SO(10) supersymmetric grand unified model of the fermion mass matrices. Various features of the model which gives remarkably accurate results for the quark and lepton masses and mixings were presented earlier in separate publications. The construction of the matrices is first discussed in the framework of effective operators, from which one naturally obtains the maximal {nu}{sub {mu}}-{nu}{sub {tau}} mixing, while the small angle or maximal mixing solutions for the solar neutrinos depend upon the nature of the Majorana matrix. A set of Higgs and fermion superfields is then introduced from which the Higgs and Yukawa superpotentials uniquely give the structure of the mass matrices previously obtained. The right-handed Majorana matrix arises from one Higgs field coupling to several pairs of superheavy conjugate neutrino singlets. For the simple version considered, 10 input parameters accurately yield the 20 masses and mixings of the quarks and leptons, and the 3 masses of the right-handed neutrinos.

The higgs sector of the mssm in the decoupling limit

Abstract: We study the heavy Higgs sector of the MSSM composed of the H ± , H 0 and A 0 particles in the so-called decoupling limit where mA0 ≫ mZ. By integrating out these heavy Higgs particles to one-loop, we compute the effective action for the electroweak gauge bosons and find out that, in the decoupling limit, all the heavy Higgs effects can be absorbed into redefinitions of the Standard Model electroweak parameters. This demonstrates explicitely that the decoupling theorem works for the heavy MSSM Higgs particles. This is also compared with the paradigmatic and different case of the Standard Model heavy Higgs particle. Finally, this work together with our two previous works, complete the demonstration that all the non-standard particles in the MSSM, namely, squarks, sleptons, charginos, neutralinos and the heavy Higgs particles, decouple to one-loop from the low energy electroweak gauge boson physics.

Anomalous quartic couplings in $W^+W^-\gamma$ , $Z^0Z^0\gamma$ and $Z^0\gamma\gamma$ production at present and future $e^+e^-$ colliders

Abstract: The production of three electroweak gauge bosons in high-energy $e^+e^-$ collisions offers a window on anomalous quartic gauge boson couplings. We investigate the effect of three possible anomalous couplings on the cross sections for $W^+W^-\gamma$ , $Z^0Z^0\gamma$ and $Z^0\gamma\gamma$ productions at LEP2 ( $\sqrt{s} = 200$ GeV) and at a future linear collider ( $\sqrt{s} = 500$ GeV). We find that the combination of energies and processes provides reasonable discrimination between the various anomalous contributions.

On the Fission of Elementary Particles and the Evidence for Fractional Electrons in Liquid Helium

Abstract: We consider the possibility that as a result of interactions between an elementary particle and a suitably designed classical system, the particle may be divided into two or more pieces that act as though they are fractions of the original particle. We work out in detail the mechanics of this process for an electron interacting with liquid helium. It is known that when an electron is injected into liquid helium, the lowest energy configuration is with the electron localized in a 1s state inside a spherical cavity from which helium atoms are excluded. These electron bubbles have been studied in many experiments. We show that if the electron is optically excited from the 1s to the 1p state, the bubble wall will be set into motion, and that the inertia of the liquid surrounding the bubble can be sufficient to lead to the break-up of the bubble into two pieces. We call the electron fragments “electrinos.” We then show that there is a substantial amount of experimental data in the published literature that gives support to these theoretical ideas. The electrino bubble theory provides a natural explanation for the photoconductivity experiments of Northby, Zipfel, Sanders, Grimes and Adams, and possibly also the ionic mobility measurements of Ihas, Sanders, Eden and McClintock. Previously, these experimental results have not had a satisfactory explanation. In a final section, we describe some further experiments that could test our theory and consider the broader implications of these results on fractional particles.

Discrete spectrum of the graviton in the AdS5 black hole background

Abstract: The model with the $SU(2)_{\mathrm{L}} \times SU(2)_{\mathrm {R}}\times U(1)_{B-L}$ gauge group, containing one bidoublet and two triplets in the Higgs sector, is considered. The link between the constants determining the physical Higgs boson interactions and the neutrino oscillation parameters is found. It is shown that the observation of the ultrahigh-energy neutrinos with the help of the processes $e^- u_e\rightarrow W^-Z, e^- u_e\rightarrow \mu^- u_{\mu}$ , gives us information on the singly charged Higgs bosons. The processes of the doubly charged Higgs bosons production, $e^-\mu^-\rightarrow \Delta^{(--)}_1\gamma, e^-\mu^-\rightarrow \Delta^{(--)}_1Z$ , are investigated. From the point of view of detecting the neutral Higgs bosons the process of the electron–muon recharge $ e^-\mu^+\rightarrow e^+\mu^- $ is studied.

Higgs bosons in the left–right model

Abstract: The model with the $SU(2)_{\mathrm{L}} \times SU(2)_{\mathrm {R}}\times U(1)_{B-L}$ gauge group, containing one bidoublet and two triplets in the Higgs sector, is considered. The link between the constants determining the physical Higgs boson interactions and the neutrino oscillation parameters is found. It is shown that the observation of the ultrahigh-energy neutrinos with the help of the processes $e^- u_e\rightarrow W^-Z, e^- u_e\rightarrow \mu^- u_{\mu}$ , gives us information on the singly charged Higgs bosons. The processes of the doubly charged Higgs bosons production, $e^-\mu^-\rightarrow \Delta^{(--)}_1\gamma, e^-\mu^-\rightarrow \Delta^{(--)}_1Z$ , are investigated. From the point of view of detecting the neutral Higgs bosons the process of the electron–muon recharge $ e^-\mu^+\rightarrow e^+\mu^- $ is studied.

Observables in the decays of B to two vector mesons

Abstract: In general there are nine observables in the decay of a B meson to two vector mesons defined in terms of polarization correlations of these mesons. Only six of these can be detected via the subsequent decay angular distributions because of parity conservation in those decays. The remaining three require the measurement of the spin polarization of one of the decay products. (c) 2000 The American Physical Society.

Enhancement of the loop-inducedH±W∓Z0vertex in the two-Higgs-doublet model

Abstract: The non-decoupling effects of heavy Higgs bosons as well as fermions on the loop-induced $H^\pm W^\mp Z^0$ vertex are discussed in the general two Higgs doublet model. The decay width of the process $H^+ \to W^+ Z^0$ is calculated at one-loop level and the possibility of its enhancement is explored both analytically and numerically. We find that the novel enhancement of the decay width can be realized by the Higgs non-decoupling effects with large mass-splitting between the charged Higgs boson and the CP-odd one. This is due to the large breakdown of the custodial $SU(2)_V$ invariance in the Higgs sector. The branching ratio can amount to $10^{-2} \sim 10^{-1}$ for $m_{H^\pm} = 300$ GeV within the constraint from the present experimental data. Hence this mode may be detectable at LHC or future $e^+e^-$ linear colliders.

Supersymmetric structure of spacetime and matter -superon-graviton model-

Abstract: A unified description of spacetime and matter is proposed by using a single irreducible representation of SO(10) Super-Poincare algebra(SO(10)SPA). All (observed) elementary particles except the graviton are the (massless) eigenstates of SO10)SPA composed of fundamental Nambu-Goldstone fermions with spin 1/2, superons, associating with the spontaneous breakdown of the supertranslation of the spacetime. The systematic investigations of the standard model(SM) and SU(5)GUT by using superon diagrams may reveal the generation structure, the stability of the proton, K-, B-, D- mixings, CP-violation, the atmospheric and solar neutrino deficits and the absence of the electroweak lepton-flavor-mixing. The fundamental action of the superon-graviton model(SGM) for spacetime and matter is proposed, which is invariant under a new supersymmetry.

Towards a geometrical theory for the unification of all fundamental forces

Abstract: Strongly localized ripples created initially by violent fluctuation in the geometry of space-time are interpreted within the Cantorian E (∞) theory as possible Boson elementary particles. These wave-particle “fluction” is predicted to have a Compton wavelength of the order of 10 −21 cm ⩽λ c , f ⩽10 −22 cm and a rest mass in the region of (10 7 ) Gev ⩽m f ⩽(10 8 ) Gev . Consequently this particle represents an intermediate particle at a length scale between λc,W∼10−16 cm of SU(2)×U(1) and λc,G∼10−28 of GUT. This tentative conclusion is found to be consistent with cosmological and entropy considerations of the universe at certain ages as well as the possible fractal nature of the inner structure of baryons and leptons.

Discovering a light Higgs boson with light

Abstract: We evaluate the prospects for detecting a non-standard light Higgs boson with a significant branching ratio to two photons, in run II of the Fermilab Tevatron. We derive the reach for several channels: $2\ensuremath{\gamma}$ inclusive, $2\ensuremath{\gamma}+1$ jet, and $2\ensuremath{\gamma}+2$ jets. We present the expected run II limits on the branching ratio of $\stackrel{\ensuremath{\rightarrow}}{h}\ensuremath{\gamma}\ensuremath{\gamma}$ as a function of the Higgs boson mass, for the case of ``bosonic,'' as well as ``top-color'' Higgs bosons.

Supersymmetry: what? why? when?

Abstract: This article is a colloquium-level review of the idea of supersymmetry and why so many physicists expect it to soon be a major 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.