Showing papers on "Elementary particle published in 2003"

The CP-conserving two-Higgs-doublet model: the approach to the decoupling limit

Abstract: A CP-even neutral Higgs boson with standard-model-like couplings may be the lightest scalar of a two-Higgs-doublet model. We study the decoupling limit of the most general CP-conserving two-Higgs-doublet model, where the mass of the lightest Higgs scalar is significantly smaller than the masses of the other Higgs bosons of the model. In this case, the properties of the lightest Higgs boson are nearly indistinguishable from those of the standard model Higgs boson. The first nontrivial corrections to Higgs boson couplings in the approach to the decoupling limit are also evaluated. The importance of detecting such deviations in precision Higgs boson measurements at future colliders is emphasized. We also clarify the case in which a neutral Higgs boson can possess standard-model-like couplings in a regime where the decoupling limit does not apply. The two-Higgs-doublet sector of the minimal supersymmetric model illustrates many of the above features.

Unification and Supersymmetry

Abstract: Derived from a course given at the University of Maryland for advanced graduate students, this book deals with some of the latest developments in our attempts to construct a unified theory of the fundamental interactions of nature. Among the topics covered are spontaneous symmetry breaking, grand unified theories, supersymmetry and supergravity. The books starts with a quick review of elementary particle theory and continues with a discussion of composite quarks, leptons, Higgs bosons and CP violation; it concludes with consideration of supersymmetric unification schemes, in which bosons and leptons are considered in some sense equivalent. The second edition is updated and corrected and contains new chapters on recent developments.

Particle production in heavy ion collisions

Abstract: The status of thermal model descriptions of particle production in heavy ion collisions is presented. We discuss the formulation of statistical models with different implementation of the conservation laws and indicate their applicability in heavy ion and elementary particle collisions. We analyze experimental data on hadronic abundances obtained in ultrarelativistic heavy ion collisions, in a very broad energy range starting from RHIC/BNL ($\sqrt s=200$ A GeV), SPS/CERN ($\sqrt s\simeq 20$ A GeV) up to AGS/BNL ($\sqrt s\simeq 5$ A GeV) and SIS/GSI ($\sqrt s\simeq 2$ A GeV) to test equilibration of the fireball created in the collision. We argue that the statistical approach provides a very satisfactory description of experimental data covering this wide energy range. Any deviations of the model predictions from the data are indicated. We discuss the unified description of particle chemical freeze--out and the excitation functions of different particle species. At SPS and RHIC energy the relation of freeze--out parameters with the QCD phase boundary is analyzed. Furthermore, the application of the extended statistical model to quantitative understanding of open and hidden charm hadron yields is considered.

Three-dimensional imaging of atomic four-body processes

Abstract: To understand the physical processes that occur in nature we need to obtain a solid concept about the ‘fundamental’ forces acting between pairs of elementary particles. It is also necessary to describe the temporal and spatial evolution of many mutually interacting particles under the influence of these forces. This latter step, known as the few-body problem, remains an important unsolved problem in physics. Experiments involving atomic collisions represent a useful testing ground for studying the few-body problem. For the single ionization of a helium atom by charged particle impact, kinematically complete experiments have been performed1,2,3,4,5,6 since 1969 (ref. 7). The theoretical analysis of such experiments was thought to yield a complete picture of the basic features of the collision process, at least for large collision energies8,9,10,11,12,13,14. These conclusions are, however, almost exclusively based on studies of restricted electron-emission geometries1,2,3. Here, we report three-dimensional images of the complete electron emission pattern for the single ionization of helium by the impact of C6+ ions of energy 100 MeV per a.m.u. (a four-body system) and observe features that have not been predicted by any published theoretical model. We propose a higher-order ionization mechanism, involving the interaction between the projectile and the target nucleus, to explain these features.

Observation of nuclear scaling in the A(e,e′) reaction at X B>1

Abstract: The ratios of inclusive electron scattering cross sections of ${}^{4}\mathrm{He},$ ${}^{12}\mathrm{C},$ and ${}^{56}\mathrm{Fe}$ to ${}^{3}\mathrm{He}$ have been measured for the first time. It is shown that these ratios are independent of ${x}_{B}$ at ${Q}^{2}g1.4{\mathrm{GeV}}^{2}$ for ${x}_{B}g1.5,$ where the inclusive cross section depends primarily on the high momentum components of the nuclear wave function. The observed scaling shows that the momentum distributions at high-momenta have the same shape for all nuclei and differ only by a scale factor. The observed onset of the scaling at ${Q}^{2}g1.4{\mathrm{GeV}}^{2}$ and ${x}_{B}g1.5$ is consistent with the kinematical expectation that two-nucleon short range correlations (SRC) dominate the nuclear wave function at ${p}_{m}\ensuremath{\gtrsim}300\mathrm{MeV}/c.$ The values of these ratios in the scaling region can be related to the relative probabilities of SRC in nuclei with $Ag~3.$ Our data, combined with calculations and other measurements of the ${}^{3}\mathrm{H}\mathrm{e}/\mathrm{d}\mathrm{e}\mathrm{u}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{u}\mathrm{m}$ ratio, demonstrate that for nuclei with $Ag~12$ these probabilities are 4.9--5.9 times larger than in deuterium, while for ${}^{4}\mathrm{He}$ it is larger by a factor of about 3.8.

Facts and mysteries in elementary particle physics

Abstract: Introduction Preliminaries The Standard Model Quantum Mechanics. Mixing Energy, Momentum and Mass-Shell Detection Accelerators and Storage Rings The CERN Neutrino Experiment The Particle Zoo Particle Theory Finding the Higgs Quantum Chromodynamics Epilogue.

Spin-orbit and tensor forces in heavy-quark light-quark mesons: Implications of the new D s state at 2.32 GeV

Abstract: We consider the spectroscopy of heavy-quark light-quark mesons with a simple model based on the non-relativistic reduction of vector and scalar exchange between fermions. Four forces are induced: the spin-orbit forces on the light and heavy quark spins, the tensor force, and a spin-spin force. If the vector force is Coulombic, the spin-spin force is a contact interaction, and the tensor force and spin-orbit force on the heavy quark to order $1/m_1m_2$ are directly proportional. As a result, just two independent parameters characterize these perturbations. The measurement of the masses of three p-wave states suffices to predict the mass of the fourth. This technique is applied to the $D_s$ system, where the newly discovered state at 2.32 GeV provides the third measured level, and to the $D$ system. The mixing of the two $J^P=1^+$ p-wave states is reflected in their widths and provides additional constraints. The resulting picture is at odds with previous expectations and raises new puzzles.

The mass of the graviton and the cosmological constant

Abstract: We show that the graviton has a mass in an anti-de Sitter (? < 0) background given by m2g = ?2/3?. This is precisely the fine-tuning value required for the perturbed gravitational field to maintain its two degrees of freedom.

Self-interacting dark matter and Higgs bosons in the SU(3)C?SU(3)L?U(1)N model with right-handed neutrinos

Abstract: We investigate the possibility that dark matter could be made from CP-even and CP-odd Higgs bosons in the SU(3)C⊗SU(3)L⊗U(1)N (3-3-1) model with right-handed neutrinos This self-interacting dark matters are stable without imposing new symmetry and should be weak interacting

Improved constraints on supersymmetric dark matter from muon g-2

Abstract: The new measurement of the anomalous magnetic moment of the muon by the Brookhaven AGS experiment 821 again shows a discrepancy with the standard model value. We investigate the consequences of these new data for neutralino dark matter, updating and extending our previous work [E. A. Baltz and P. Gondolo, Phys. Rev. Lett. 86, 5004 (2001)]. The measurement excludes the standard model value at $3.0\ensuremath{\sigma}$ confidence, assuming the evaluation using the hadronic ${e}^{+}{e}^{\ensuremath{-}}$ cross section (the $\ensuremath{\tau}$ decay evaluation yields only a $1.6\ensuremath{\sigma}$ discrepancy). We analyze a phenomenological set of supersymmetric models with gaugino mass unification imposed but without a priori constraints on the Higgs sector. Taking the discrepancy as a sign of supersymmetry, we find that the lightest superpartner must be relatively light and it must have a relatively high elastic scattering cross section with nucleons, which brings it almost within reach of proposed direct dark matter searches. The SUSY signal from neutrino telescopes correlates fairly well with the elastic scattering cross section. The rate of cosmic ray antideuterons tends to be large in the allowed models, but the constraint has little effect on the rate of gamma ray lines. We stress that being more conservative may eliminate the discrepancy, but it does not eliminate the possibility of high astrophysical detection rates.

Neutral Higgs boson masses of the MSSM at the one-loop level in an explicit CP violation scenario

Abstract: The neutral Higgs sector of the minimal supersymmetric standard model in an explicit $\mathrm{CP}$ violation scenario is investigated at the one-loop level. Within the context of the effective potential formalism, the masses of the neutral Higgs bosons are calculated at the one-loop level by taking into account the contributions of the following loops of ordinary particles and superpartners: the top quark, the scalar top quarks, the bottom quark, the scalar bottom quarks, the tau lepton, the scalar tau leptons, the W boson, the charged Higgs boson, the charginos, the Z boson, the scalar and pseudoscalar Higgs bosons, and the neutralinos. Our calculation is an improvement in the sense that both the terms which are quartic in the electroweak coupling constants are taken into account, and the pseudoscalar Higgs loop contribution is explicitly included.

Exact results of the ground state and excitation properties of a two-component interacting Bose system

Abstract: We study a one-dimensional Bose system with repulsive δ-function interaction in the presence of an SU(2) intrinsic degree of freedom on the basis of the coordinate Bethe ansatz. The ground state and the low-lying excitations are determined by both numerical and analytical methods. It is shown that the ground state is an isospin-ferromagnetic state, and the excitations are composed of three elementary particles: holons, antiholons, and isospinons. The isospinon is a triplet coupled to the ferromagnetic background anti-parallelly.

Measuring the Higgs boson parity at a Linear Collider using $\tau$ impact parameter and $\tau \to \rho \nu$ decay

Abstract: We demonstrate that a measurement of the impact parameter in one-prong $\tau$ decay can be useful for the determination of the Higgs boson parity in the $H/A\to\tau^{+}\tau^{-}$ ; $\tau^{\pm}\to\rho^{\pm}\bar{ u}_{\tau}( u_{\tau})$ decay chain. We have estimated that for a detection set-up such as TESLA, use of the information from the $\tau$ impact parameter can improve the significance of the measurement of the parity of the Standard Model 120 GeV Higgs boson to $\sim$ 4.5 $\sigma$ , and in general by a factor of about 1.5 with respect to the method where this information is not used. We also show that the variation in the assumption on the precision of the measurement of the impact parameter and/or $\pi$ 's momenta does not affect the sensitivity of the method. This is because the method remains limited by the type of twofold ambiguity in reconstructing the $\tau$ momentum.

New Velocity Distribution for Cold Dark Matter in the Context of the Eddington Theory

Abstract: Exotic dark matter, together with the vacuum energy (associated with the cosmological constant), seems to dominate the universe. Thus, its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). One essential ingredient in obtaining the direct detection rates is the density and velocity distribution of the LSP. The detection rate is proportional to this density in our vicinity. Furthermore, since this rate is expected to be very low, one should explore the two characteristic signatures of the process, namely, the modulation effect, i.e., the dependence of the event rate on the Earth's motion, and the correlation of the directional rate with the motion of the Sun. Both of these crucially depend on the LSP velocity distribution. In the present paper we study simultaneously density profiles and velocity distributions based on the Eddington theory.

An investigation of the parametric X-rays along the velocity of emitting particle

Abstract: Parametric X-rays (PXR) along the velocity of relativistic electrons crossing a crystalline target is studied in this work The detailed theory of PXR for Laue scattering geometry is developed with account of contributions of both PXR and transition radiation (TR) to the total emission yield An influence of photoabsorption and interference between PXR and TR on the forward PXR properties are studied Most appropriate conditions for the real experiment devoted to forward PXR observation are elucidated on the basis of the developed theory The advantage of the use of heavy crystals with this aim in mind is shown The expected experimental results are discussed

Trilepton + top signal from chargino neutralino decays of MSSM charged Higgs bosons at the LHC

Abstract: We perform for the Large Hadron Collider (LHC) a detailed study of charged Higgs boson production via the top-bottom quark associated mode followed by decays into a chargino and a neutralino, with masses and couplings as given by the general minimal supersymmetric standard model (MSSM). We focus our attention on the region of parameter space with \(m_{H^{\pm}} > m_t\) and intermediate values of \(\tan\beta\), where identification of \(H^{\pm}\) via decays into standard model (SM) particles has proven to be ineffective. Modelling the CMS detector, we find that a signature consisting of three hard leptons accompanied by a hadronically reconstructed top quark plus substantial missing transverse energy, which may result from \(H^{\pm} \rightarrow {{\widetilde\chi}}_{1,2}^{\pm} {{\widetilde\chi}}_{1,2,3,4}^0\) decays, can be made viable over a large variety of initially overwhelming SM and MSSM backgrounds, provided MSSM input parameters are favourable: notably, small \(\vert \mu \vert\) and light sleptons are important prerequisites. We quantify these statements by performing a fairly extensive scan of the parameter space, including realistic hadron-level simulations, and delineate some potential discovery regions.

T-odd asymmetries in the angular distributions of fragments originating from the ternary fission of nuclei

Abstract: A version of a theoretical explanation is proposed for the recently discovered effect of T-odd correlation in ternary nuclear fission induced by polarized neutrons. It is shown that the inclusion of the Coriolis interaction between a third particle and the fissile-nucleus spin within the quantum theory of fission makes it possible to explain the experimental features of the effect and provides a correct estimate of its magnitude.

Mass bounds in a model with a triplet Higgs

Abstract: We perform an analysis of the Renormalization Group evolution of the couplings in an extension to the Standard Model which contains a real triplet in the Higgs sector. Insisting that the model remain valid up to 1 TeV allow us to map out the region of allowed mass for the Higgs bosons. We conclude that it is possible for there to be no light Higgs bosons without any otherwise dramatic deviation from the physics of the Standard Model.

Baryon asymmetry of the universe from evaporation of primordial black holes

Abstract: The process of baryogenesis through evaporation of black holes formed at the end of the inflation phase is considered. The increase in black hole mass due to accretion from the surrounding radiation after reheating is taken into account. It is shown that the influence of the accretion on the baryogenesis is important only in the case where the initial values of black hole mass are larger than ∼104 g. The behavior of the calculated baryon asymmetry as a function of model parameters is studied.

Excited baryons from Bayesian priors and overlap fermions

Abstract: Using the constrained-fitting method based on Bayesian priors, we extract the masses of the two lowest states of octet and decuplet baryons with both parities. The calculation is done on quenched 163 × 28 lattices ofa = 0.2 fm using an improved gauge action and overlap fermions, with the pion mass as low as 180 MeV. The Roper stateN(1440)½+ is clearly observed for the first time as the 1st-excited state of the nucleon from the standard interpolating field. Together with other baryons, our preliminary results indicate that the level-ordering of the low-lying baryon states on the lattice is largely consistent with experiment. The realization is helped by cross-overs between the excited½+ and½− states in the region ofmπ ∼ 300 to 400MeV.