Standard Model Quarks Research Articles

Implications of BNL measurement of $\delta a_{\mu}$ on a class of scalar leptoquark interactions

Recently BNL have measured the muon magnetic moment anomaly with increased precision. The world average experimental value at present shows a discrepancy of $43(16)\times 10^{-10}$ from the standard model (SM) value. In this paper we investigate the implications of this difference on a class of scalar leptoquark interactions to SM quark–lepton pair. We find that for a leptoquark mass of a few hundred GeV the BNL muon anomaly can arise from couplings much smaller than even the electromagnetic coupling. We also find that the BNL value for the muon anomaly leads to an unambiguous prediction for the electric dipole moment of the muon and a bound on the flavor changing leptoquark coupling relevant for the rare decay $\mu\rightarrow e\gamma $ .

B-physics constraints on baryon number violating couplings: Grand unification, supersymmetry, or compositeness

We investigate the role that baryon number violating interactions may play in $B$ phenomenology. Present in various grand unified theories, supersymmetric theories with R-parity violation and composite models, a diquark state could be quite light. Using the data on B decays as well as $B - {\bar B}$ mixing, we find strong constraints on the couplings that such a light diquark state may have with the Standard Model quarks.

Meson-meson scattering in the quark model: Spin dependence and exotic channels

We apply a quark interchange model to spin-dependent and exotic meson-meson scattering. The model includes the complete set of standard quark model forces, including OGE spin-orbit and tensor and scalar confinement spin-orbit. Scattering amplitudes derived assuming SHO and Coulomb plus linear plus hyperfine meson wavefunctions are compared. In I=2 pi pi we find approximate agreement with the S-wave phase shift from threshold to 1.5 GeV, where we predict an extremum that is supported by the data. Near threshold we find rapid energy dependence that may reconcile theoretical estimates of small scattering lengths with experimental indications of larger ones based on extrapolation of measurements at moderate kpi^2. In PsV scattering we find that the quark-quark L*S and T forces map into L*S and T meson-meson interactions, and the P-wave L*S force is large. Finally we consider scattering in J^PC-exotic channels, and note that some of the Deck effect mechanisms suggested as possible nonresonant origins of the pi_1(1400) signal are not viable in this model.

Gaugino mediated supersymmetry breaking

We consider supersymmetric theories where the standard-model quark and lepton fields are localized on a "3-brane" in extra dimensions, while the gauge and Higgs fields propagate in the bulk. If supersymmetry is broken on another 3-brane, supersymmetry breaking is communicated to gauge and Higgs fields by direct higher-dimension interactions, and to quark and lepton fields via standard-model loops. We show that this gives rise to a realistic and predictive model for supersymmetry breaking. The size of the extra dimensions is required to be of order 10-100 times larger than fundamental scale (e.g. the string scale). The spectrum is similar to (but distinguishable from) the predictions of "no-scale" models. Flavor-changing neutral currents are naturally suppressed. The \mu term can be generated by the Giudice-Masiero mechanism. The supersymmetric CP problem is naturally solved if CP violation occurs only on the observable sector 3-brane. These are the simplest models in the literature that solve all supersymmetric naturalness problems.

Baryon magnetic moments in a QCD-based quark model with loop corrections

We study meson loop corrections to the baryon magnetic moments starting from a QCD-based quark model derived earlier in a quenched approximation to QCD. The model reproduces the standard quark model with extra corrections for the binding of the quarks. The loop corrections are necessary to remove the quenching. Our calculations use heavy baryon perturbation theory with chiral baryon-meson couplings and a form factor characterizing the structure of baryons as composite particles. The form factor reflects soft wave function effects with characteristic momenta $\approx 400$ MeV, well below the usual chiral cutoff of $\approx 1$ GeV. The resulting model involves only three parameters, the quark moments $\mu_u$ and $\mu_s$ and a parameter $\lambda$ that sets the momentum scale in the wavefunctions. We find that this approach substantially improves the agreement between the theoretical and experimental values of the octet baryon magnetic moments, with an average difference between the theoretical and experimental moments of 0.05$\mu_N$. An extension to the decuplet states using the same input predicts a moment of 1.97 $\mu_N$ for the $\Omega^-$ hyperon, in excellent agreement with the measured moment of $2.02\pm0.05 \mu_N$.

Gauged B−3Lτ and radiative neutrino masses

If the minimal standard model of quarks and leptons is extended to include just a righthanded partner to ν τ , then the quantum number B −3 L τ can be added as a gauge symmetry without the appearance of anomalies. A suitable extension of the scalar sector allows one neutrino to have a seesaw mass, and the other two to have radiative masses, with acceptable phenomenological values for neutrino oscillations. The B −3 L τ gauge boson may be light and be observable through its decay into τ + τ − .

Z→cc¯,bb¯decays and the aspon model

The aspon model predicts mixing of hypothetical new quarks with the standard model quarks. This mixing modifies the decay rates of the $Z$ boson into quarks. In this paper, it is examined whether the measured values of ${R}_{b}\ensuremath{\equiv}\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{Z}b\overline{b})/\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{Z}\mathrm{hadrons})$ and ${R}_{c}\ensuremath{\equiv}\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{Z}c\overline{c})/\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{Z}\mathrm{hadrons})$ provide any constraints on the aspon model parameters.

Sea Contributions to Spin 1/2 Baryon Structure, Magnetic Moments, and Spin Distribution

We treat the baryon as a composite system made out of a "core" of three quarks (as in the standard quark model) surrounded by a "sea" (of gluons and [Formula: see text]-pairs) which is specified by its total quantum numbers like flavor, spin and color. Specifically, we assume the sea to be a flavor octet with spin 0 or 1 but no color. The general wave function for spin 1/2 baryons with such a sea component is given. Application to the magnetic moments is considered. Numerical analysis shows that a scalar (spin 0) sea with an admixture of a vector (spin 1) sea can provide very good fits to the magnetic moment data using experimental errors. These fit also give reasonable values for the spin distributions of the proton and neutron.

PARTICLE PHYSICS SUMMARYA Digest of the1996 Review of Particle Physics

This report summarizes the highlights of the 1996 {ital Review} {ital of} {ital Particle} {ital Physics} (Phys. Rev. D {bold 54}, 1 (1996)). Using data from previous editions, plus 1900 new measurements from 700 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. We also give numerous reviews, tables, figures, and formulae. The present edition marks the apparent completion of the table of Standard Model quarks with the discovery of the top. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of the full {ital Review}. {copyright} {ital 1996 The American Physical Society.}

CP violation for electroweak baryogenesis from mixing of standard model and heavy vector quarks.

It is known that the CP violation in the minimal standard model is insufficient to explain the observed baryon asymmetry of the Universe in the context electroweak baryogenesis. In this paper we consider the possibility that the additional CP violation required could originate in the mixing of the standard model quarks and heavy vector quark pairs. We consider the baryon asymmetry in the context of the spontaneous baryogenesis scenario. It is shown that, in general, the CP-violating phase entering the mass matrix of the standard model and heavy vector quarks must be space dependent in order to produce a baryon asymmetry, suggesting that the additional CP violation must be spontaneous in nature. This is true for the case of the simplest models which mix the standard model and heavy vector quarks. We derive a charge potential term for the model by diagonalizing the quark mass matrix in the presence of the electroweak bubble wall, which turns out to be quite different from the fermionic hypercharge potentials usually considered in spontaneous baryogenesis models, and obtain the rate of baryon number generation within the wall. We find, for the particular example where the standard model quarks mix with weak-isodoublet heavy vector quarks via the expectation value of a gauge singlet scalar, that we can account for the observed baryon asymmetry with conservative estimates for the uncertain parameters of electroweak baryogenesis, provided that the heavy vector quarks are not heavier than a few hundred GeV and that the coupling of the standard model quarks to the heavy vector quarks and gauge singlet scalars is not much smaller than order of 1, corresponding to a mixing angle of the heavy vector quarks and standard model quarks not much smaller than order of ${10}^{\mathrm{\ensuremath{-}}1}$. \textcopyright{} 1996 The American Physical Society.

Neutrons, Nuclei and Matter: An Exploration of the Physics of Slow Neutrons

A selection of topics: The neutron as an elementary particle: The nuclear atom The constituents of nuclei Discovery of the neutron Neutron capture Mechanical properties of the neutron Neutron sources Neutron detection and measurement. Neutron scattering and two-particle interactions: Fundamental interactions of the neutron Two-particle collisions Scattering in a central potential Scattering parameters Scattering length and effective range Discrete states of the scattering potential The neutron-proton system. Neutrons and nuclei: Nuclear stability and binding energy Nuclear sizes Nuclear forces Nuclear isospin pions. Neutrons and nuclear structures: Models of the nucleus The nuclear shell model Simple shell-model tests The extended shell-model Collective motion collective motion and unitary symmetry Neutron reactions and nuclear structure. Neutrons and nuclear energy: Energetics of nuclear transformation and decay Nuclear fission Neutron transport and diffusion Neutron moderation The nuclear fission chain reactor Controlled nuclear fusion. Foundations of neutron optics: Wave-particle duality The eikonal approximation for neutrons Neutron propagation in condensed media Phase relations and superposition of states. Wave phenomena with neutrons: The Huygens-Fresnel principle for neutrons Neutron diffraction Neutron interference Neutron polarization Neutron spin resonances. The neutron and condensed states of matter: Applied neutron optics Neutron scattering in condensed systems The Van Hove theory of space-time correlations Neutron scattering in magnetic media Neutron scattering instrumentation. The neutron as a composite system: Strong interactions and flavour SU(3) symmetry Electromagnetic interactions Weak interactions. Fundamental processes and the role of the neutron: Parity violation in the nucleus The Standard Model of quarks and leptons Quark models of the nucleon Neutron physics beyond the Standard Model The neutron in astrophysics and cosmology.

Mesonic probes

Celebrating the forty years since the landmark paper of Bohr and Mottelson on nuclear collective motion with a perspective which looks both backward and forward, we consider here the role of mesons as nuclear probes. We have had two decades of experiments at the meson factories — LAMPF, PSI & TRIUMF — during which our thinking about the role of mesons in the nucleus has changed dramatically. Twenty years ago the π — N system was believed to be well understood and the pion was heralded as an ideal probe. Now with the advent of the standard model of quarks, leptons and unified forces (and, especially, QCD) the pion is a useful but very complex nuclear probe and we understand little of the π — N system. The evolution of the ideas during the past two decades is described as well as the current issues for mesons as nuclear probes. This perspective comes at a time when large new facilities are emerging to address the new issues of the field — for example, CEBAF, Bates, RHIC, DAΦNE, COSY, MAMI and GSI — and we can look forward to new hadronic probes from the KAON Factory.

Unified universal seesaw models.

A set of grand unified theories based upon the gauge groups SU(5)[sub [ital L]][times]SU(5)[sub [ital R]], SO(10)[sub [ital L]][times]SO(10)[sub [ital R]] and SU(4)[sub [ital C]][times]SU(4)[sub [ital L]][times]SU(4)[sub [ital R]] is explored. Several novel features distinguish these theories from the well-known SU(5), SO(10), and SU(4)[sub [ital C]][times]SU(2)[sub [ital L]][times]SU(2)[sub [ital R]] models which they generalize. Firstly, standard model quarks and leptons are accompanied by and mix with heavy SU(2)[sub [ital L]][times]SU(2)[sub [ital R]] singlet partners. The resulting fermion mass matrices are seesaw in form. Discrete parity symmetries render the determinants of these mass matrices real and eliminate [ital CP]-violating gauge terms. The unified seesaw models consequently provide a possible resolution to the strong [ital CP] problem. Secondly, sin[sup 2][theta][sub [ital W]] at the unification scale is numerically smaller than the experimentally measured [ital Z] scale value. The weak angle must therefore increase as it evolves down in energy. Finally, proton decay is suppressed by small seesaw mixing factors in all these theories.

The natural suppression of the π 0→2γ width in the quark model

Standard quark model calculation of the pion width disagree with the experimental measurement by three orders of magnitude. A recent calculation, within the Bethe-Salpeter formalism, using an ansatz proposed by Gromes, resolved this discrepancy. We now give the physical interpretation and mechanism responsible for this result.

The fermion mass hierarchy and gauged chiral flavour quantum numbers

We briefly argue that the fermion mass hierarchy points toward a class of extensions of the Standard Model gauge group which has received scant attention in the literature. The members of this class are characterised by having the same irreducible representations as exist in the Standard Model and by having the Standard Model embedded within them as a diagonal subgroup. The anomalies of the new mass protecting gauge quantum numbers cancel amongst the Standard Model quarks and leptons alone, and we analyse how well some specific groups can naturally produce the hierarchies of fermion masses and mixing angles, at least order of magnitude wise.

I=3/2 K pi scattering in the nonrelativistic quark potential model.

We study $I=3/2$ elastic $K\pi $ scattering to Born order using nonrelativistic quark wavefunctions in a constituent-exchange model. This channel is ideal for the study of nonresonant meson-meson scattering amplitudes since s-channel resonances do not contribute significantly. Standard quark model parameters yield good agreement with the measured S- and P-wave phase shifts and with PCAC calculations of the scattering length. The P-wave phase shift is especially interesting because it is nonzero solely due to $SU(3)_f$ symmetry breaking effects, and is found to be in good agreement with experiment given conventional values for the strange and nonstrange constituent quark masses.

Thermodynamics of quark matter with saturated confinement interactions

A consistent set of thermodynamical relations for a strongly coupled many-quark system at finite temperature and vanishing baryon number density is derived within the Hartree approximation. Confining interactions are assumed to be saturated within colour singlet quark-antiquark pairs. For a system of massless quarks, simple analytical expressions for the pressure and the energy density are obtained and compared with those of a standard thermodynamical bag model of non-interacting quarks and gluons. We observe that the two equations of state have similar thermodynamical behaviour. A qualitative comparison with results from lattice gauge simulations (LGS) shows that the saturation of energy density above the chiral transition can be interpreted as being due to dynamically confined quark matter.

A new standard-like model in the four dimensional free fermionic string formulation

I present a new three generation superstring standard-like model in the free fermionic formulation with the following properties. The complete massless spectrum is derived and shown to be anomaly free apart from a single anomalous U(1). The Dine-Seiberg-Witten mechanism is applied to cancel the anomaly, leaving a supersymmetric vacuum. I show that the resulting observable gauge symmetry is SU(3)×SU(2)×U(1) n where n = 1 or 2. All trilinear superpotential couplings have been calculated. I show that of the standard model quarks and leptons only +2 3 charged quarks obtain a non vanishing trilevel coupling, which suggest a possible explanation for the heaviness of the top quark relative to the lighter quarks and leptons. The additional, generation independent, U(1) symmetry may remain unbroken down to low energies and prevents fast proton decay.

Chapter VI. Chiral Quark Soliton Model and Skyrme Model

The chiral quark model as an effective theory of low energy QCD contains an abundance of physics despite its extremely simple appearance. The soliton model of baryons based on this effective lagrangian is reviewed, by paying special attention to the comparison with other models of baryons, especially the Skyrme model. A careful study of the baryon number and the flavor-singlet axial charge is shown to reveal the special role of valence quarks, which is the core of the standard quark models of baryons but is definitely missing in the skyrmion idea

Form factor analysis and unitarity effects in [formula omitted

The large polarization recently reported by Fermilab experiment E691 in D→K ∗ lν casts doubt on quark model from factors. We investigate whether unitarity corrections can make the standard quark model consistent with the E691 data. Despite significant corrections, we show that the quark model still cannot achieve the high polarization of the E691 data. Unitarity corrections, including CP-odd effects, will be visible in the next generation experiments.