Showing papers on "Elementary particle published in 2004"
TL;DR: The Particle Data Group's biennial review as discussed by the authors summarizes much of Particle Physics using data from previous editions plus new measurements from papers, and evaluate and average measured properties of gauge bosons leptons quarks mesons and baryons.
3,025 citations
TL;DR: In this article, the authors review the recent progress in atomic parity nonconservation and atomic electric dipole moments (time reversal symmetry violation), with a particular focus on the atomic theory required to interpret the measurements.
478 citations
TL;DR: In this article, the authors generalize a model-independent approach of Weinberg to the case of unstable particles and apply it to the a 0 (980) and f 0(980) resonances and address the question whether these particles are predominantly genuine, confined quark states or governed by mesonic components.
340 citations
CERN1
TL;DR: In this paper, the authors investigated Higgs boson pair production at hadron colliders for Higgs masses mH ≤ 140 GeV and rare decay of one of the two Higgs particles.
Abstract: We investigate Higgs boson pair production at hadron colliders for Higgs boson masses mH ≤ 140 GeV and rare decay of one of the two Higgs bosons. While in the Standard Model the number of events is quite low at the LHC, a first, albeit not very precise, measurement of the Higgs self-coupling is ˜
257 citations
TL;DR: In this paper, the effects of tree-level mixing effects on the trilinear coupling of weak gauge bosons with the lightest CP-even Higgs boson (h), hZZ, at the one-loop order were investigated.
Abstract: We study new physics effects on the couplings of weak gauge bosons with the lightest CP-even Higgs boson (h), hZZ, and the trilinear coupling of the lightest Higgs boson, hhh, at the one-loop order, as predicted by the two Higgs doublet model. Those renormalized coupling constants can deviate from the standard model (SM) predictions due to two distinct origins: the tree level mixing effect of Higgs bosons and the quantum effect of additional particles in loop diagrams. The latter can be enhanced in the renormalized hhh coupling constant when the additional particles show the nondecoupling property. Therefore, even in the case where the hZZ coupling is close to the SM value, deviation in the hhh coupling from the SM value can become as large as plus 100%, while that in the hZZ coupling is at most minus 1% level. Such large quantum effect on the Higgs trilinear coupling is distinguishable from the tree level mixing effect, and is expected to be detectable at a future linear collider.
228 citations
TL;DR: In this article, a simple model, originally intended for stable gluino hadrons, is developed to describe the nuclear interactions of hadrons containing any new colour triplet or octet stable parton.
Abstract: In this article, we study the interactions of stable, hadronising new states, arising in certain extensions of the standard model. A simple model, originally intended for stable gluino hadrons, is developed to describe the nuclear interactions of hadrons containing any new colour triplet or octet stable parton. Hadron mass spectra, nuclear scattering cross sections and interaction processes are discussed. Furthermore, an implementation of the interactions of heavy hadrons in GEANT 3 is presented, signatures are studied, and a few remarks about possible detection with the ATLAS experiment are given.
119 citations
TL;DR: In this paper, the authors use soft collinear effective field theory (SCET) to study nonperturbative strong interaction effects in Z decays to hadronic final states that are enhanced in corners of phase space.
Abstract: We use soft collinear effective field theory (SCET) to study nonperturbative strong interaction effects in Z decays to hadronic final states that are enhanced in corners of phase space. These occur, for example, in the jet energy distribution for two jet events near E_J=M_Z/2, the thrust distribution near unity and the jet invariant mass distribution near zero. The extent to which such nonperturbative effects for different observables are related is discussed.
109 citations
TL;DR: In this article, the authors present a general formalism for studying CP-violating phenomena in the production, mixing and decay of a coupled system of CPviolating neutral Higgs bosons at high-energy colliders.
Abstract: We present the general formalism for studying CP-violating phenomena in the production, mixing and decay of a coupled system of CP-violating neutral Higgs bosons at high-energy colliders. Considering the Minimal Supersymmetric Standard Model (MSSM) Higgs sector in which CP violation is radiatively induced by phases in the soft supersymmetry-breaking third-generation trilinear squark couplings and gaugino masses, we apply our formalism to neutral Higgs production via ¯, gg and W + W − collisions at the LHC. We discuss CP asymmetries in the longitudinal and transverse polarizations of τ + τ − pairs. The signatures of CP violation are more prominent in the production via gg and W + W − than via ¯, and are resonantly enhanced when two (or all three) neutral Higgs bosons are nearly degenerate with mass differences comparable to their decay widths. Such scenarios occur naturally in the MSSM for values of tan β > 5 (30) and large (small) charged Higgs-boson masses. We analyze representative examples with large mixing between the three neutral Higgs bosons weighing about 120 GeV, that may exhibit observable CP asymmetries even as large as 80%.
104 citations
TL;DR: In this article, the authors considered the emission of a photon by an electron in the field of a strong laser wave and derived the probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles.
Abstract: We consider the emission of a photon by an electron in the field of a strong laser wave. Polarization effects in this process are important for a number of physical problems. The probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles is calculated. We obtain the complete set of functions which describe such a probability in a compact invariant form. Besides this, we discuss in some detail the polarization effects in the kinematics relevant to the problem of $e\to \gamma$
conversion at $\gamma \gamma$
and $\gamma e$
colliders.
101 citations
TL;DR: In this paper, the possibility of α-cluster condensation in 12 C was examined using a fully microscopic 12-nucleon, 3 α -cluster model for the ground state and the 0 + state near the 3 α-particle threshold.
86 citations
TL;DR: In this article, the authors describe recent developments of so-called slow muon beams, where the energy is reduced down to the electronvolt to kiloelectronvolt range, thus making the probe depth sensitive on the nanometre scale.
Abstract: The muon is an elementary particle and, as such, forms a fundamental building block of the Standard Model of elementary particles. At the same time, the muon, especially the positively charged muon, when implanted in matter has established itself as a magnetic spin microprobe and hydrogen-like probe to study a variety of static and dynamic phenomena in superconductivity, magnetism, radical chemistry, semiconductor physics and many other fields. The limitation of this technique has been up until recently that it is restricted to investigation of bulk properties, because muons are generated from pion decay as high-energy particles with a broad stopping depth profile. This article describes recent developments of so-called ‘slow muon’ beams, where the energy is reduced down to the electronvolt to kiloelectronvolt range, thus making the probe depth sensitive on the nanometre scale. Some recent applications of this novel probe are described, such as the measurement of magnetic field profiles at the surface of ...
TL;DR: In this article, low-energy effective theories of Goldstone bosons, gauge fields and chiral fermions applied to low energy QCD and to Higgs-less electroweak symmetry breaking are introduced via constraints enforced by a set of nonpropagating covariantly constant spurion fields.
Abstract: Inspired by recent developments of moose models, we reconsider low-energy effective theories of Goldstone bosons, gauge fields and chiral fermions applied to low-energy QCD and to Higgs-less electroweak symmetry breaking. Couplings and the corresponding reduction of symmetry are introduced via constraints enforced by a set of non-propagating covariantly constant spurion fields. Relics of the latter are used as small expansion parameters conjointly with the usual low-energy expansion. Certain couplings can only appear at higher orders of the spurion expansion and, consequently, they become naturally suppressed independently of the idea of dimensional deconstruction. At leading order this leads to a set of generalized Weinberg sum rules and to the suppression of non-standard couplings to fermions in Higgs-less EWSB models with the minimal particle content. Within the latter, higher spurion terms allow for a fermion mass matrix with the standard CKM structure and CP violation. In addition, Majorana masses for neutrinos are possible. Examples of non-minimal models are briefly mentioned.
TL;DR: In this article, the production of Higgs bosons at the large hadron collider via cascade decays of scalar quarks and gluinos is studied. But the authors focus on the cascades involving heavier charginos and neutralinos, which decay into the neutral h, A, H and charged H± bosons and lighter charginos.
TL;DR: In this paper, it was shown that the next-lightest supersymmetric particle (NLSP) decays to the gravitino through gravitational interactions after about a year, and this lifetime can be measured by stopping NLSPs at colliders and observing their decays.
Abstract: The gravitational interactions of elementary particles are suppressed by the Planck scale M*~1018GeV and are typically expected to be far too weak to be probed by experiments. We show that, contrary to conventional wisdom, such interactions may be studied by particle physics experiments in the next few years. As an example, we consider conventional supergravity with a stable gravitino as the lightest supersymmetric particle. The next-lightest supersymmetric particle (NLSP) decays to the gravitino through gravitational interactions after about a year. This lifetime can be measured by stopping NLSPs at colliders and observing their decays. Such studies will yield a measurement of Newton's gravitational constant on unprecedentedly small scales, shed light on dark matter, and provide a window on the early universe.
TL;DR: In this article, the authors derive from general symmetry properties of the hadron electromagnetic interaction, such as C-invariance and crossing symmetry, the general characteristics of two-photon exchange in electron-proton elastic scattering.
Abstract: We derive from general symmetry properties of the hadron electromagnetic interaction, such as C-invariance and crossing symmetry, the general characteristics of two-photon exchange in electron-proton elastic scattering. We show that the presence of this mechanism destroys the linearity of the Rosenbluth separation.
TL;DR: In this paper, the authors discuss the predictions of the model for proton decay induced at the GUT scale and find upper bounds on the partial lifetime for the modes τ(n→π 0 ν ) = 2τ(p→π + ν)⩽(5.7−13)×10 32 yrs and τ (n→K 0 −2.97×10 33 yrs for the average squark mass of a TeV and wino mass of 200 GeV, when the parameters satisfy the present lower limits on τ(p
TL;DR: In this article, it was shown that C invariance is not exact even in the free massive theory and (iii) elementary particles cannot be neutral in the SO(1, 4) invariant theory.
Abstract: In standard Poincare and anti de Sitter SO(2, 3) invariant theories, antiparticles are related to negative energy solutions of covariant equations while independent positive energy unitary irreducible representations (UIRs) of the symmetry group are used for describing both a particle and its antiparticle. Such an approach cannot be applied in de Sitter SO(1, 4) invariant theory. We argue that it would be more natural to require that (*) one UIR should describe a particle and its antiparticle simultaneously. This would automatically explain the existence of antiparticles and show that a particle and its antiparticle are different states of the same object. If (*) is adopted then among the above groups only the SO(1, 4) one can be a candidate for constructing elementary particle theory. It is shown that UIRs of the SO(1, 4) group can be interpreted in the framework of (*) and cannot be interpreted in the standard way. By quantizing such UIRs and requiring that the energy should be positive in the Poincare approximation, we conclude that (i) elementary particles can be only fermions. It is also shown that (ii) C invariance is not exact even in the free massive theory and (iii) elementary particles cannot be neutral. This gives a natural explanation of the fact that all observed neutral states are bosons.
TL;DR: In this article, it was shown that the next-lightest supersymmetric particle (NLSP) decays to the gravitino through gravitational interactions after about a year, and this lifetime can be measured by stopping NLSPs at colliders and observing their decays.
Abstract: The gravitational interactions of elementary particles are suppressed by the Planck scale M_P ~ 10^18 GeV and are typically expected to be far too weak to be probed by experiments. We show that, contrary to conventional wisdom, such interactions may be studied by particle physics experiments in the next few years. As an example, we consider conventional supergravity with a stable gravitino as the lightest supersymmetric particle. The next-lightest supersymmetric particle (NLSP) decays to the gravitino through gravitational interactions after about a year. This lifetime can be measured by stopping NLSPs at colliders and observing their decays. Such studies will yield a measurement of Newton's gravitational constant on unprecedentedly small scales, shed light on dark matter, and provide a window on the early universe.
TL;DR: In this paper, the authors studied the central diffractive production of the (three neutral) Higgs bosons, with a rapidity gap on either side, in an MSSM scenario with CP-violation, and emphasise the advantage of reactions with the rapidity gaps to probe CP-parity and to determine the quantum numbers of the produced central object.
Abstract: We study the central diffractive production of the (three neutral) Higgs bosons, with a rapidity gap on either side, in an MSSM scenario with CP-violation. We consider the $b\bar{b}$
and $\tau\bar{\tau}$
decay for the light H
1 boson and the four b-jet final state for the heavy H
2 and H
3 bosons, and discuss the corresponding backgrounds. A direct indication of the existence of CP-violation can come from the observation of either an azimuthal asymmetry in the angular distribution of the tagged forward protons (for the exclusive $pp\to p + H + p$
process) or of a $\sin 2\varphi$
contribution in the azimuthal correlation between the transverse energy flows in the proton fragmentation regions for the process with the diffractive dissociation of both incoming protons (
$pp\to X + H + Y$
). We emphasise the advantage of reactions with the rapidity gaps (that is, production by pomeron-pomeron fusion) to probe CP-parity and to determine the quantum numbers of the produced central object.
TL;DR: In this paper, the ground-state masses of the light pseudo-scalar and vector mesons were obtained on the basis of the phenomenological relativistic harmonic model for quarks.
Abstract: On the basis of the phenomenological relativistic harmonic model for quarks, we have obtained the ground-state masses of the light pseudo-scalar and vector mesons. The full Hamiltonian used in the investigation has Lorentz scalar + vector confinement potential, along with one-gluon-exchange potential (OGEP) and the instanton-induced quark-antiquark interaction. A good agreement is obtained with the experimental masses. The respective role of instanton-induced interaction and OGEP for the determination of the meson masses is discussed.
[...]
TL;DR: The top quark is by far the heaviest elementary particle known and a measurement of its mass with higher precision has bearing on the understanding of the fundamental interactions of nature.
Abstract: The top quark is by far the heaviest elementary particle known. A measurement of its mass with higher precision has bearing on our understanding of the fundamental interactions of nature.
Posted Content•
TL;DR: In this article, the authors considered the lower orders of the perturbation theory using nonlocal Hamiltonian in the Foldy-Wouthuysen (FW) representation.
Abstract: The paper considers quantum electrodynamics (QED) and weak interaction of elementary particles in the lower orders of the perturbation theory using nonlocal Hamiltonian in the Foldy-Wouthuysen (FW) representation. Feynman rules in the FW representation are specified, specific QED processes are calculated. Cross sections of Coulomb scattering of electrons, Muller scattering, Compton effect, electron self-energy, vacuum polarization, anomalous magnetic moment of electron, Lamb shift of atomic energy levels are calculated. The possibility of the scattering matrix expansion in powers of the coupling constant, in which matrix elements contain no terms with fermion propagators, is demonstrated for external fermion lines corresponding to real particles (antiparticles).
It is shown that a method to include the interaction of real particles with antiparticles in the FW representation is to introduce negative mass particles and antiparticles to the theory. The theory is degenerate with respect to the particle (antiparticle) mass sign, however the masses of the particle and antiparticle interacting with each other should be of opposite sign.
QED in the FW representation is invariant under C, P, T inversions. The weak interaction breaks the C and P invariance, but preserves the combined CP parity. In the theory there is a possibility to relate the break of CP invariance to total or partial removal of the degeneracy in particle (antiparticle) mass sign.
TL;DR: In this article, the behavior of overlap fermions, which are chirally invariant, and of Wilson twisted mass fermion at full twist in the approach to the chiral limit were compared.
Abstract: We compare the behavior of overlap fermions, which are chirally invariant, and of Wilson twisted mass fermions at full twist in the approach to the chiral limit. Our quenched simulations reveal that with both formulations of lattice fermions pion masses of (250 MeV) can be reached in practical applications. Our comparison is done at a fixed value of the lattice spacing a 0.123 fm. A number of quantities are measured such as hadron masses, pseudoscalar decay constants and quark masses obtained from Ward identities. We also determine the axial vector renormalization constants in the case of overlap fermions.
TL;DR: In this article, an intensive cosmological production of vector W and Z bosons is considered within a cosmology model that involves a relative scale of measurement, and field-theory models are studied in which cosmic microwave background radiation and baryon matter may appear as products of the decay of such primordial bosons.
Abstract: An intensive cosmological production of vector W and Z bosons is considered within a cosmological model that involves a relative scale of measurement. Field-theory models are studied in which cosmic microwave background radiation and baryon matter may appear as products of the decay of such primordial bosons.
TL;DR: In the 20th century the mystery of the atom was unravelled, the atomic nucleus was smashed, and two new forces of nature were revealed as discussed by the authors, the weak force and the nuclear force binding the nucleus.
Abstract: The discovery of x-rays and radioactivity in the waning years of the 19th century led to one of the most awe-inspiring scientific eras in human history. The 20th century witnessed a level of scientific discovery never before seen or imagined. At the dawn of the 20th century only two forces of nature were known—gravity and electromagnetism. The atom was believed by chemists to be the elemental, indestructible unit of matter, coming in many unexplainably different forms. Yet J J Thomson, soon after the discovery of x-rays, had measured the charge to mass ratio of the electron, demonstrating that this carrier of electric current was ubiquitous and fundamental. All electrons could be identified by their unique charge to mass ratio.In the 20th century the mystery of the atom was unravelled, the atomic nucleus was smashed, and two new forces of nature were revealed—the weak force (responsible for radioactive β decay and the nuclear fusion reaction powering the stars) and the nuclear force binding the nucleus. Quantum mechanics enabled the understanding of the inner structure of the atom, its nucleus and further inward to quarks and gluons (the building blocks of the nucleus) and thence outward to an understanding of large biological molecules and the unity of chemistry and microbiology.Finally the myriad of new fundamental particles, including electrons, quarks, photons, neutrinos, etc and the three fundamental forces—electromagnetism and the weak and the strong nuclear forces—found a unity of description in terms of relativistic quantum field theory. These three forces of nature can be shown to be a consequence of symmetry rotations in internal spaces, and the particular interactions of each particle are solely determined by their symmetry charge. This unifying structure, describing all the present experimental observations, is known as the standard model (SM). Moreover, Einstein's theory of gravity can be shown to be a consequence of the symmetry of local translations and Lorentz transformations.As early as the 1970s, it became apparent that two new symmetries, a grand unified theory of the strong, weak and electromagnetic interactions in conjunction with supersymmetry (SUSY), might unify all the known forces and particles into one unique structure. Now 30 years later, at the dawn of a new century, experiments are on the verge of discovering (or ruling out) these possible new symmetries of nature. In this paper we try to clarify why SUSY and supersymmetric grand unified theories are the new SM of particle physics, i.e. the standard against which all other theories and experiments are measured.
TL;DR: The total and differential cross sections for the production of triply charmed Ωccc baryons in e+e− annihilation are calculated at the Z-boson pole as discussed by the authors.
Abstract: The total and differential cross sections for the production of triply charmed Ωccc baryons in e+e− annihilation are calculated at the Z-boson pole
TL;DR: A brief review of the present status of searches for isolatable fractional charge particles is given in this article, with the aim of increasing the range of known search methods and to urge the invention of new search methods.
Abstract: Since the initial measurements of the electron charge a century ago, experimenters have faced the persistent question as to whether elementary particles exist that have charges that are fractional multiples of the electron charge. In the standard model of particle physics the quarks are such particles, but it is assumed that quarks cannot be individually isolated, the quarks always being confined inside hadrons. This paper is a brief review of the present status of searches for isolatable fractional charge particles such as a lepton-like particle with fractional charge or an unconfined quark. There have been a very large number of searches but there is no confirmed evidence for existence of isolatable fractional charge particles. It may be that they do not exist, but it is also possible that they are very massive or that their production mechanisms are very small so that they have been missed by existing searches. Therefore the aim of this review is to urge (a) the invention of ways to substantially increase the range of known search methods and (b) to urge the invention of new search methods for isolatable fractional charge particles.
TL;DR: The relation between the Peccei-Quinn symmetry breaking and some experimental evidence for new elementary particles with an expectation mass of 26.18 and 42.36 MeV is discussed in this paper.
Abstract: The work connects instantons to the symplictic geometry of the VAK of vacuum fluctuation as envisaged by e (∞) theory. Subsequently the relation between the Peccei–Quinn symmetry breaking and some experimental evidence for new elementary particles with an expectation mass of 26.18 and 42.36 MeV are discussed in connection with the super symmetric unification of all fundamental interactions.
TL;DR: In this paper, the existence of massless elementary particles in a quantum theory based on a Galois field (GFQT) was shown to be compatible with all operators describing massless particles.
Abstract: We consider massless elementary particles in a quantum theory based on a Galois field (GFQT). We previously showed that the theory has a new symmetry between particles and antiparticles, which has no analogue in the standard approach. We now prove that the symmetry is compatible with all operators describing massless particles. Consequently, massless elementary particles can have only half-integer spin (in conventional units), and the existence of massless neutral elementary particles is incompatible with the spin–statistics theorem. In particular, this implies that the photon and the graviton in the GFQT can only be composite particles.
TL;DR: In this paper, a careful counting of all experimentally confirmed elementary particles plus the theoretically conjectured ones needed for a sound formulation of a mathematically consistent field theory is undertaken within a minimal N = 1 super symmetric extension of the standard model of high energy physics.
Abstract: Die Elementarteilchen k o nnen mit den regul a ren K o rpern in Platos “Timaios” verglichen werden. Sie sind die Urbilder, die Ideen der Materie . (Werner Heisenberg) A careful counting routine of all experimentally confirmed elementary particles plus the theoretically conjectured ones needed for a sound formulation of a mathematically consistent field theory is undertaken within a minimal N =1 super symmetric extension of the standard model of high energy physics. The number arrived at is subsequently linked to certain massless on shell representations connected to the quantized gravity interaction. Finally with the help of number theoretical arguments arising from a rigorous application of the formalism of transfinite Heterotic super string and E-infinity theory, we show that the proposed scheme would lack mathematical consistency and elegant simplicity unless we retain a postulated triplet which is logically identified as the H + , H − and H 0 Higgs particles. Connections to the 11 dimensional M theory and Harari's extended “sub-quarks” theory is also discussed.