Showing papers on "Elementary particle published in 2002"
Journal Article•
2,092 citations
TL;DR: This work demonstrates the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment and detects the neutral anti-atoms directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.
Abstract: A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem—experimental investigations involving comparisons of particles with antiparticles are numerous1. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN)2 and at Fermilab3, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.
635 citations
TL;DR: Higgs boson production via weak boson fusion at the CERN Large Hadron Collider has the capability to determine the dominant CP nature of a Higgs bosons, via the tensor structure of its coupling to weak bosons.
Abstract: Higgs boson production via weak boson fusion at the CERN Large Hadron Collider has the capability to determine the dominant CP nature of a Higgs boson, via the tensor structure of its coupling to weak bosons. This information is contained in the azimuthal angle distribution of the two outgoing forward tagging jets. The technique is independent of both the Higgs boson mass and the observed decay channel.
229 citations
TL;DR: In this paper, a renormalization flow of scalar bound states which are formed out of fundamental fermions is studied in the context of effective average action, where the notions of a bound state or fundamental particle become scale dependent, being classified by the fixed-point structure of the flow of effective couplings.
Abstract: A renormalization group flow equation with a scale-dependent transformation of field variables gives a unified description of fundamental and composite degrees of freedom. In the context of the effective average action, we study the renormalization flow of scalar bound states which are formed out of fundamental fermions. We use the gauged Nambu--Jona-Lasinio model at weak gauge coupling as an example. Thereby, the notions of a bound state or fundamental particle become scale dependent, being classified by the fixed-point structure of the flow of effective couplings.
182 citations
TL;DR: In this paper, it was shown that the nuclear matrix elements can be reduced by about 25% in the case of light neutrinos by modifying the axial current of the nucleon current.
175 citations
TL;DR: In this paper, it was shown that neutrinoless double beta decay is a very important process both from the particle and nuclear physics point of view and that it pops up in almost every model, giving rise, among others, to the following mechanisms: a) the traditional contributions like the light neutrino mass mechanism, b) the exotic R-parity violating supersymmetric (SUSY) contributions.
Abstract: Neutrinoless double beta decay is a very important process both from the particle and nuclear physics point of view. From the elementary particle point of view it pops up in almost every model. giving rise, among others, to the following mechanisms: a) The traditional contributions like the light neutrino mass mechanism . b) The exotic R-parity violating supersymmetric (SUSY) contributions. Similar considerations apply to its sister lepton and muon number violating muon to positron conversion. The observation of neutrinoless double beta decay will signal that the neutrinos are massive Majorana particles. For nuclear physics it is challenging, because: 1) The nuclei, which can undergo double beta decay, have complicated structure. 2) The energetically allowed transitions are suppressed. 3) One must cope with the short distance behavior of the transition operators. Thus novel effects (decay of pions in flight between nucleons etc) have to be considered. 4) One has to take into account possible momentum dependent terms of the nucleon current. For light neutrinos such modifications of the nucleon current reduce the nuclear matrix elements by about 25 per cent. In the case of heavy neutrino the effect is much larger and model dependent. With the above effects the nuclear matrix elements for all interesting nuclei A = 76, 82, 96, 100, 116, 128, 130, 136 and 150 are discussed. Some have been obtained in the shell model but most in QRPA. Thus we have extracted new limits on the various lepton violating parameters. We find an average neutrino mass of about 0.5eV and, for reasonable choices of the parameters of SUSY models, we get a stringent limit on the R-parity violating parameter less than 0.00068.
169 citations
TL;DR: In this article, the effect of SU(3)-flavor breaking on high-density quark matter was studied, in particular a nonzero electron chemical potential and a finite strange-quark mass.
169 citations
TL;DR: In this paper, it was shown that the electroweak Higgs particles can be identified with extra-dimensional components of the gauge fields, which after compactification on a certain topologically non-trivial background become tachyonic and condense.
Abstract: We suggest that the electroweak Higgs particles can be identified with extra-dimensional components of the gauge fields, which after compactification on a certain topologically non-trivial background become tachyonic and condense. If the tachyonic mass is a tree level effect, the natural scale of the gauge symmetry breaking is set by the inverse radius of the internal space, which, in case of the electroweak symmetry, must be around $\sim 1/$TeV. We discuss the possibility of a vanishing tree level mass for the Higgs. In such a scenario the tachyonic mass can be induced by quantum loops and can be naturally smaller than the compactification scale. We give an example in which this possibility can be realized. Starting from an Einstein--Yang--Mills theory coupled to fermions in 10-dimensions, we are able to reproduce the spectrum of the Standard Model like chiral fermions and Higgs type scalars in 4-dimensions upon compactifying on ${\mathbb{C}}P^1\times {\mathbb{C}}P^2$. The existence of a monopole solution on ${\mathbb{C}}P^1$ and a self dual U(1) instanton on ${\mathbb{C}}P^2$ are essential in obtaining chiral fermions as well as tachyonic or massless scalars in 4-dimensions. We give a simple rule which helps us to identify the presence of tachyons on the monopole background on $S^2$.
159 citations
01 Apr 2002
TL;DR: In this article, it was shown that neutrinoless double beta decay is a very important process both from the particle and nuclear physics point of view and that it pops up in almost every model, giving rise, among others, to the following mechanisms: a) the traditional contributions like the light neutrino mass mechanism, b) the exotic R-parity violating supersymmetric (SUSY) contributions.
Abstract: Neutrinoless double beta decay is a very important process both from the particle and nuclear physics point of view. From the elementary particle point of view it pops up in almost every model. giving rise, among others, to the following mechanisms: a) The traditional contributions like the light neutrino mass mechanism . b) The exotic R-parity violating supersymmetric (SUSY) contributions. Similar considerations apply to its sister lepton and muon number violating muon to positron conversion. The observation of neutrinoless double beta decay will signal that the neutrinos are massive Majorana particles. For nuclear physics it is challenging, because: 1) The nuclei, which can undergo double beta decay, have complicated structure. 2) The energetically allowed transitions are suppressed. 3) One must cope with the short distance behavior of the transition operators. Thus novel effects (decay of pions in flight between nucleons etc) have to be considered. 4) One has to take into account possible momentum dependent terms of the nucleon current. For light neutrinos such modifications of the nucleon current reduce the nuclear matrix elements by about 25 per cent. In the case of heavy neutrino the effect is much larger and model dependent. With the above effects the nuclear matrix elements for all interesting nuclei A = 76, 82, 96, 100, 116, 128, 130, 136 and 150 are discussed. Some have been obtained in the shell model but most in QRPA. Thus we have extracted new limits on the various lepton violating parameters. We find an average neutrino mass of about 0.5eV and, for reasonable choices of the parameters of SUSY models, we get a stringent limit on the R-parity violating parameter less than 0.00068.
143 citations
TL;DR: In this paper, the status of thermal model descriptions of particle ratios in central nucleus-nucleus collisions at ultra-relativistic energy is discussed, and an alternative to the Cleymans-Redlich interpretation of the freeze-out trajectory is given in terms of the total baryon density.
Abstract: We discuss the status of thermal model descriptions of particle ratios in central nucleus–nucleus collisions at ultra-relativistic energy. An alternative to the 'Cleymans–Redlich' interpretation of the freeze-out trajectory is given in terms of the total baryon density. Emphasis is placed on the relation between the chemical equilibration parameters and the QCD phase boundary. Furthermore, we trace the essential difference between thermal model analyses of data from collisions between elementary particles and from heavy ion collisions due to a transition from local strangeness conservation to percolation of strangeness over large volumes, as occurs naturally in a deconfined medium. We also discuss predictions of the thermal model for composite particle production.
99 citations
TL;DR: The origin of neutrinos may be the origin of the entire matter-antimatter asymmetry of the universe as mentioned in this paper, which is the theory explaining the cosmic neutrino asymmetry.
TL;DR: In this paper, the virtual electroweak Sudakov (double) logarithm at one-and two-loop level for arbitrary on-shell/on-on-resonance particles in the Standard Model was calculated in the temporal Coulomb gauge.
CERN1
TL;DR: In this paper, the CP-violating rate asymmetry of H? decays into tau and neutrino at one loop in the MSSM with complex parameters, depending mainly on the phases of the trilinear coupling A? and the gaugino mass M1.
Abstract: We calculate the CP-violating rate asymmetry of H? decays into tau and neutrino at one loop in the MSSM with complex parameters. We find that the asymmetry is typically of the order of 10?3, depending mainly on the phases of the trilinear coupling A? and the gaugino mass M1.
TL;DR: In this paper, the electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent quark model, and the calculated K+ form factor is consistent with almost all of the available experimental data at low-energy scale.
Abstract: The electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent quark model. The calculated K+ form factor is consistent with almost all of the available experimental data at low-energy scale, while other properties of the kaon could also be interrelated in this representation with reasonable parameters. Predictions of the form factors for the charged and neutral kaons at a higher-energy scale are also given, and we find the non-zero K0 form factor at Q2≠ 0 due to the mass difference between the strange and down quarks inside K0.
Posted Content•
TL;DR: In this article, the SM-like Higgs boson was observed in multiple channels at the LHC, allowing the extraction of Higgs couplings to gauge bosons and fermions.
Abstract: The observation of a SM-like Higgs boson in multiple channels at the LHC allows the extraction of Higgs couplings to gauge bosons and fermions. The precision achievable at the LHC, for an integrated luminosity of 200 fb^{-1}, is reviewed and updated.
TL;DR: In this article, one-loop induced couplings of two gaugino-like neutralinos to the Z and Higgs bosons in the Minimal Supersymmetric Standard Model were calculated.
Abstract: We calculate the one-loop induced couplings of two gaugino–like neutralinos to the Z and Higgs bosons in the Minimal Supersymmetric Standard Model. These couplings, which vanish at the tree level, can be generated through loops involving fermions and sfermions. We show that, while the neutralino contribution to the invisible Z boson decay width remains small, the loop induced couplings to the lightest Higgs boson might be sufficiently large to yield a rate of invisible decaysof this Higgs boson that should be detectable at future e + e − colliders. We also study the implications of these couplings for direct searches of Dark Matter and show that they can modify appreciably the neutralino–nucleon elastic cross section for some parameter range.
11 Nov 2002
TL;DR: The theoretical status of Higgs boson and supersymmetric particle production at hadron colliders is reviewed in this article with particular emphasis on recent results and open problems with respect to open problems.
Abstract: The theoretical status of Higgs boson and supersymmetric particle production at hadron colliders is reviewed with particular emphasis on recent results and open problems.
TL;DR: In this paper, the authors investigated the particle spectrum within the modified NMSSM, which leads to the self-consistent solution in the limit of strong Yukawa coupling, where all solutions to renormalization-group equations are concentrated near the quasifixed point.
Abstract: Nowadays, in the MSSM, the moderate values of tan β are almost excluded by the LEP II lower bound on the mass of the lightest Higgs boson. In the next-to-minimal supersymmetric standard model (NMSSM), the theoretical upper bound on it increases and reaches a maximal value in the limit of strong Yukawa coupling, where all solutions to renormalization-group equations are concentrated near the quasifixed point. For a calculation of the Higgs boson spectrum, the perturbation-theory method can be applied. We investigate the particle spectrum within the modified NMSSM, which leads to the self-consistent solution in the limit of strong Yukawa coupling. This model allows one to get mh∼125 GeV at tan β≥1.9. In the model under investigation, the mass of the lightest Higgs boson does not exceed 130.5±3.5 GeV. The upper bound on the mass of the lightest CP-even Higgs boson in more complicated supersymmetric models is also discussed.
TL;DR: In this paper, the authors compute the complete one-loop contributions to low-energy charged current weak interaction observables in the minimal supersymmetric standard model (MSSM) and obtain the constraints on the MSSM parameter space which arise when precision low energy charged current data are analyzed in tandem with measurements of the muon anomaly.
Abstract: We compute the complete one-loop contributions to low-energy charged current weak interaction observables in the minimal supersymmetric standard model (MSSM). We obtain the constraints on the MSSM parameter space which arise when precision low-energy charged current data are analyzed in tandem with measurements of the muon anomaly. While the data allow the presence of at least one light neutralino, they also imply a pattern of mass splittings among first and second generation sleptons and squarks which contradicts predictions of widely used models for supersymmetry-breaking mediation.
TL;DR: In this article, the authors estimate the number of events produced at the LHC collider, as a function of the Higgs boson mass and its decay channel, by optimizing an analysis between higher cross-sections of the inclusive mode (all Pomeron remnants) and cleaner signals of the exclusive mode.
TL;DR: In this article, the authors investigated the discovery of neutral Higgs bosons (φ0=H0,h0,A0) produced with bottom quarks via Higgs decays into muon pairs ( pp→b b φ 0 →b b μ μ +X ) at the CERN LHC.
TL;DR: In this paper, a simple extension of the standard model was proposed, in which the predominant decay of the Higgs boson occurs into a pair of light bottom squarks that, in turn, manifest themselves as hadronic jets.
Abstract: The remarkable agreement of electroweak data with standard model (SM) predictions motivates the study of extensions of the SM in which the Higgs boson is light and couples in a standard way to the weak gauge bosons. Postulated new light particles should have small couplings to the gauge bosons. Within this context it is natural to assume that the branching fractions of the light SM-like Higgs boson mimic those in the standard model. This assumption may be unwarranted, however, if there are nonstandard light particles coupled weakly to the gauge bosons but strongly to the Higgs field. In particular, the Higgs boson may effectively decay into hadronic jets, possibly without important bottom or charm flavor content. As an example, we present a simple extension of the SM, in which the predominant decay of the Higgs boson occurs into a pair of light bottom squarks that, in turn, manifest themselves as hadronic jets. Discovery of the Higgs boson remains possible at an electron-positron linear collider, but prospects at hadron colliders are diminished substantially.
TL;DR: In this article, the running electromagnetic coupling constant in the MS scheme is calculated at a low energy normalization scale equal to the τ-lepton mass Mτ. This low-energy boundary value is used for running the electromagnetic coupling to larger scales, where high-precision experimental measurements can be performed.
Abstract: A numerical value for the running electromagnetic-coupling constant in the
$$\overline {MS} $$
scheme is calculated at a low-energy normalization scale equal to the τ-lepton mass M
τ. This low-energy boundary value is used for running the electromagnetic coupling to larger scales, where high-precision experimental measurements can be performed. Particular scales of interest are the b-quark mass for studying ϒ-resonance physics and the Z-boson mass M
Z
for high-precision tests of the Standard Model and for the determination of the Higgs boson mass from radiative corrections. A numerical value of the running electromagnetic-coupling constant at M
Z
in the on-shell renormalization scheme is also given.
TL;DR: The first possible evidence for the Higgs particle was obtained by the four collaborations using the Large Electron-Positron colliding accelerator (LEP) at CERN, Geneva, Switzerland.
Abstract: At present, all the data obtained from the many experiments in particle physics are in agreement with the standard model. In the standard model there is one particle, the Higgs particle, that is responsible for giving masses to all particles with mass. In this sense, the Higgs particle occupies a unique position. Before the latter part of the year 2000, however, the Higgs particle was not observed experimentally. It is the purpose of this report to describe the first possible evidence for this particle, obtained by the four collaborations using the Large Electron-Positron colliding accelerator (LEP) at CERN, Geneva, Switzerland. The data were taken with the LEP centre-of-mass energy between 200 and 209 GeV. The result is dominated by the observation of an excess of four-jet events by ALEPH, one of the four experiments at LEP. Its mass, which is a free parameter in the standard model, is about 115 GeV/c2.
TL;DR: In this article, free elementary particles with rest mass $m$ and total energy $E < m c^2$ in the Rindler wedge, outside Reissner-Nordstrom black holes and in the spacetime of relativistic (and non-relativistic) stars, and use Unruh-DeWitt-like detectors to calculate the associated particle detection rate in each case.
Abstract: We analyze free elementary particles with rest mass $m$ and total energy $E < m c^2$ in the Rindler wedge, outside Reissner-Nordstrom black holes and in the spacetime of relativistic (and non-relativistic) stars, and use Unruh-DeWitt-like detectors to calculate the associated particle detection rate in each case. The (mean) particle position is identified with the spatial average of the excitation probability of the detectors, which are supposed to cover the whole space. Our results are shown to be in harmony with General Relativity classical predictions. Eventually we reconcile our conclusions with Earth-based experiments which are in good agreement with $E \geq m c^2$.
TL;DR: In this paper, the results from a recent experimental search for SIMPs in a collection of gold and iron samples with various exposures to cosmic rays and to a SIMP component of dark matter were analyzed.
Abstract: Strongly interacting neutral massive particles (SIMPs) have been proposed as candidates for dark matter, as the lightest supersymmetric particle, as a possible explanation for ultra-high-energy cosmic rays, and as a dark matter solution to galactic structure problems. If bound to nuclei, SIMPs could manifest themselves as anomalously heavy isotopes of known elements. We analyze the results from a recent experimental search for SIMPs in a collection of gold and iron samples with various exposures to cosmic rays and to a SIMP component of dark matter. The samples included gold flown on the NASA Long-Duration Exposure Facility, as well as geological samples and an iron meteorite. We show that the bounds on SIMPs from that experiment can be used to set nontrivial constraints on the SIMP contribution to the cosmological density parameter Ω.
TL;DR: In this article, the probability of having Δ(1232) resonance in frozen and hot neutron, nuclear and β-stable matter was calculated using the temperature dependence correlation functions generated through a lowest order constrained variational calculation with the Δ-Reid potential.
Abstract: In this article we calculate the probabilty of having Δ(1232) resonance in frozen and hot neutron, nuclear and β-stable matter. We use the temperature dependence correlation functions that are generated through a lowest order constrained variational calculation with the Δ-Reid potential. The NN → NΔ transition is built in through a two-pion exchange interaction. The electrons and muons are treated relativistically in the total Hamiltonian at given temperature and density, in order to make the fluid electrically neutral and stable with respect to β-decay. We ignore the weak interaction. It is seen that the Δ probability in neutron matter is much larger than in nuclear and β-stable matter at a given temperature and density. As we increase the temperature, the Δ probability decreases in nuclear and neutron matter. However, this decrease is not significant in case of β-stable nuclear matter. There is overall agreement between our Δ probability calculation and the recent experiments performed on 3 He up to 2 0 8 Pb nuclei. It is concluded that the isobar degrees of freedom could make the equation of state of neutron star matter harder at finite temperature and suppress the numbers of protons and leptons in the proto-neutron stars.
01 Jan 2002
TL;DR: In this article, a physical geometrical packing model for the structure of the atom is developed based on the physical toroidal ring model of elementary particles proposed by Bergman, and the model explains the physical origin of the valence electrons for chemical binding and the reason why the periodic table has only seven periods.
Abstract: A physical geometrical packing model for the structure of the atom is developed based on the physical toroidal ring model of elementary particles proposed by Bergman.(1) From the physical characteristics of real electrons from experiments by Compton (2,3,4) this work derives, using combinatorial geometry, the number of electrons that will pack into the various physical shells about the nucleus in agreement with the observed structure of the Periodic Table of the Elements. The constraints used in the combinatorial geometry derivation are based upon Joseph's simple but fundamental ring dipole magnet experiments and spherical symmetry. From a magnetic basis the model explains the physical origin of the valence electrons for chemical binding and the reason why the periodic table has only seven periods. The same geometrical packing model is extended to describe the physical geometrical packing of protons and neutrons in the physical shells of the nucleus. It accurately predicts the nuclear "magic numbers" indicative of nuclear shell structure as well as suggesting the physical origin of the nuclide spin and the liquid- drop features of nuclides.