Radial Excitation Research Articles

QCD vs. the Centrifugal Barrier: a New QCD Effect

We propose an extended schematic model for hadrons in which quarks and diquarks alike serve as building blocks. The outcome is a reclassification of the hadron spectrum in which there are no radially excited hadrons: all mesons and baryons pre- viously believed to be radial excitations are orbitally excited states involving diquarks. Also, there are no exotic hadrons: all hadrons previously believed to be exotic are states involving diquarks and are an integral part of the model. We discuss the implications of this result for a new understanding of confinement and its relation to asymptotic freedom, as well as its implications for a novel relation between the size and energy of hadrons, whereby an orbitally excited hadron shrinks.

Mass dependence of short-range correlations in nuclei and the EMC effect

We sketch an approximate method to quantify the number of correlated pairs in any nucleus $A$. It is based on counting independent-particle model (IPM) nucleon-nucleon pairs in a relative $S$-state with no radial excitation. We show that IPM pairs with those quantum numbers are most prone to short-range correlations and are at the origin of the high-momentum tail of the nuclear momentum distributions. Our method allows to compute the $a_2$ ratios extracted from inclusive electron scattering. Furthermore, our results reproduce the observed linear correlation between the number of correlated pairs and the magnitude of the EMC effect. We show that the width of the pair center-of-mass distribution in exclusive two-nucleon knockout yields information on the quantum numbers of the pairs.

Simulated and Experimental Study on the Effect of Wheel Web Shape on Its Vibration and Sound Radiation Characteristics under Radial Excitation

Simulated and Experimental Study on the Effect of Wheel Web Shape on Its Vibration and Sound Radiation Characteristics under Radial Excitation

Unbalance, misalignment, fluid-induced, frictional, anisotropic and torsional-lateral vibrations in turbomachines

Practical notes on unbalance, misalignment, excessive radial loads, fluid-induced vibrations, frictional excitations, and torsional-lateral coupled vibrations in turbomachines are discussed. Advanced vibrational condition monitoring methods are presented which can be used for identification of these malfunctions. The effects of the anisotropic supports, asymmetric rotor assemblies, bearings and couplings on rotordynamics of turbomachines are described. Case studies are also presented. The damped unbalance dynamic response test (known as the “synchronous test”) consists of inputting a controlled unbalance to the rotor and measuring its synchronous response. An active magnetic bearing can be employed as an exciter for turbomachine rotordynamics verifications (including a “non-synchronous testing”). Higher harmonics (particularly 2x) and an abnormal orbital motion are indicative of an excessive misalignment or a radial load. The fluid whirl vibrations because of bearing fluid interactions have frequencies slightly lower than 0.5x. The anisotropy can result in closely spaced, coupled “pairs” of natural frequencies (the “split resonances”). When using a high angular stiffness coupling, the driver and driven equipment will not behave as two independent turbomachines.

Spectroscopy and Regge trajectories of heavy quarkonia in the relativistic quark model

The mass spectra of charmonia and bottomonia are calculated in the framework of the relativistic quark model up to high orbital and radial excitations. The Regge trajectories of heavy quarkonia are constructed both in the (J,M2) and (nr,M2) planes, where J is the total angular momentum and nr is the radial quantum number. All daughter trajectories turn out to be almost linear and parallel, while parent trajectories exhibit some nonlinearity. Such nonlinearity occurs only in the vicinity of ground states and few lowest excitations and is more pronounced for bottomonia, while it is only marginal for charmonia. The obtained results are compared with available experimental data, and a possible interpretation of the new charmonium-like states above open charm production threshold is discussed.

Vector-meson dominance and photonuclear interactions at superhigh energies

It is shown that experimental data on the electromagnetic structure functions of a nucleon in the kinematic region of low x can be described in terms of a two-component approach in which the nonperturbative part of photon-nucleon interaction is described in terms of a updated variant of the generalized model of vector dominance that includes the radial excitations of mesons and off-diagonal elements of the matrix of meson-nucleon scattering. The perturbative component is described using the color-dipole model.

Lagrangian alternative to QCD string

The spectrum of radially excited hadrons provides much information about the confinement forces in QCD. The confinement is realized most naturally in terms of the QCD string whose quantization gives rise to the radially excited modes. We propose an alternative framework for the description of the excited spectrum. Namely we put forward some effective field models in which the hadrons acquire masses due to interaction with a scalar field modeling the non-perturbative gluon vacuum. The effective potential for this field is periodic with an infinite number of non-equivalent vacua. The radially excited hadrons emerge as elementary excitations over different vacua. We construct explicit examples for such effective theories in the meson sector. An interesting byproduct of the considered models is the existence of a classical field configuration in each vacuum. Depending on the model, it can represent a domain wall, Nielsen-Olesen vortex or 't Hooft-Polyakov monopole. In the pure scalar sector, it is shown that the first quantum correction leads to splitting of the radially excited modes into two nearly degenerate states. Such a phenomenon has some phenomenological support. The presented approach may be also viewed as an alternative framework to the bottom-up AdS/QCD models where the radial excitations appear on the classical level as well.

STRONG DECAYS OF FIRST RADIAL EXCITATIONS OF LIGHTEST VECTOR MESON STATES

In this work, we have employed Bethe–Salpeter equation (BSE) under Covariant Instantaneous Ansatz (CIA) to study strong decays of first radial excitations, ω(1420) and ρ(1450) of lightest vector mesons, ω(782) and ρ(770) respectively, through the processes: ω(1420)→ρ+π and ρ(1450)→ω+π. The main motivation for this work was our intention to resolve the problems involved in calculations of triangle quark-loop diagrams as pointed out earlier in Ref. 1 which appear in processes such as h→h'+h" and h→h'+γ (attempted recently) in BSE under CIA, which gives rise to complexities in amplitudes making calculations difficult. We explicitly show the mathematical procedure for handling the process, h→h'+h" involving three hadron–quark vertex functions, which is more involved than that for h→h'+γ and leads to decay widths which are in rough agreement with data.

Two- and three-body calculations within the dominantly orbital state method

The dominantly orbital state method allows a semiclassical description of quantum systems. At the origin, it was developed for two-body relativistic systems. Here, the method is extended to treat two-body Hamiltonians and systems with three identical particles, in $D\ge 2$ dimensions, with arbitrary kinetic energy and potential. This method is very easy to implement and can be used in a large variety of fields. Results are expected to be reliable for large values of the orbital angular momentum and small radial excitations, but information about the whole spectrum can also be obtained in some very specific cases.

Relativistic effects in the tidal interaction between a white dwarf and a massive black hole in Fermi normal coordinates

We consider tidal encounters between a white dwarf and an intermediate mass black hole. Both weak encounters and those at the threshold of disruption are modeled. The numerical code combines mesh-based hydrodynamics, a spectral method solution of the self-gravity, and a general relativistic Fermi normal coordinate system that follows the star and debris. Fermi normal coordinates provide an expansion of the black hole tidal field that includes quadrupole and higher multipole moments and relativistic corrections. We compute the mass loss from the white dwarf that occurs in weak tidal encounters. Secondly, we compute carefully the energy deposition onto the star, examining the effects of nonradial and radial mode excitation, surface layer heating, mass loss, and relativistic orbital motion. We find evidence of a slight relativistic suppression in tidal energy transfer. Tidal energy deposition is compared to orbital energy loss due to gravitational bremsstrahlung and the combined losses are used to estimate tidal capture orbits. Heating and partial mass stripping will lead to an expansion of the white dwarf, making it easier for the star to be tidally disrupted on the next passage. Finally, we examine angular momentum deposition. By including the octupole tide, we are able for the first time to calculate deflection of the center of mass of the star and debris. With this observed deflection, and taking into account orbital relativistic effects, we compute directly the change in orbital angular momentum and show its balance with computed spin angular momentum deposition.

No radial excitations in low energy QCD. II. The shrinking radius of hadrons

We discuss the implications of our prior results obtained in our companion paper [arXiv:0910.2229]. Inescapably, they lead to three laws governing the size of hadrons, including in particular protons and neutrons that make up the bulk of ordinary matter: a) there are no radial excitations in low-energy QCD; b) the size of a hadron is largest in its ground state; c) the hadron's size shrinks when its orbital excitation increases. The second and third laws follow from the first law. It follows that the path from confinement to asymptotic freedom is a Regge trajectory. It also follows that the top quark is a free, albeit short-lived, quark. [For Note Added regarding experimental support, including the experiments studying muonic hydrogen, and other experiments, see last page.]

No radial excitations in low energy QCD. I. Diquarks and classification of mesons

We propose a new schematic model for mesons in which the building blocks are quarks and flavor-antisymmetric diquarks. The outcome is a new classification of the entire meson spectrum into quark–antiquark and diquark–antidiquark states which does not give rise to a radial quantum number: all mesons which have so far been believed to be radially excited are orbitally excited diquark–antidiquark states; similarly, there are no radially excited baryons. Further, mesons that were previously viewed as “exotic” are no longer exotic as they are now naturally integrated into the classification as diquark–antidiquark states. The classification also leads to the introduction of isorons (iso-hadrons), which are analogs of atomic isotopes, and their magic quantum numbers, which are analogs of the magic numbers of the nuclear shell model. The magic quantum numbers of isorons match the quantum numbers expected for low-lying glueballs in lattice QCD. We observe that interquark forces in mesons behave substantially differently from those in baryons: qualitatively, they are color–magnetic in mesons but color–electrostatic in baryons. We comment on potential models and the hydrogen atom. The implications of our results for confinement, asymptotic freedom, and a new set of relations between two fundamental properties of hadrons—their size and their energy—are discussed in our companion paper (Eur. Phys. J. C (2013). doi:10.1140/epjc/110052-013-2299-8).

Photonuclear interactions at very high energies and vector meson dominance

We show that nucleon electromagnetic structure functions of deep inelastic scattering in Regge-Gribov limit (fixed Q-squared, asymptotically large 1/x and s) can be well described in the two-component (soft + hard) approach. In the concrete model elaborated by authors, the soft part of the virtual photon-nucleon scattering is given by the vector meson dominance, with taking into account the radial excitations of the rho-meson and nondiagonal transitions in meson-nucleon interactions. The hard part is calculated by using the dipole factorization, i.e., the process is considered as the dissociation of the photon into a -pair (the "color dipole") and the subsequent interaction of this dipole with the nucleon. The dipole cross section has a Regge-type s-dependence and vanishes in the limit of large transverse sizes of the dipole. We give the brief description of the model and present results of the detailed comparison of model predictions with experimental data for electromagnetic structure functions of the nucleon.

Generalized Soft Wall model

We develop an exactly solvable generalization of the Soft Wall holographic model for the vector mesons. The generalization preserves the ultraviolet and infrared asymptotics of the Soft Wall model and contains an additional free parameter. This new parameter provides an arbitrary intercept in the Regge like spectrum of radial excitations and leads to a substantial modification of asymptotic expansion of the vector correlator at large momentum. The matching to the Operator Product Expansion from QCD allows to estimate the value of the new parameter which is shown to be in a good agreement with the phenomenology. In addition, the mass splitting between the vector and axial mesons arises naturally via the opposite sign of the introduced contribution to the intercept.

1/3 Subharmonic resonance of a nonlinear composite laminated cylindrical shell in subsonic air flow

The 1/3 subharmonic resonance of a composite laminated circular cylindrical shell with clamped boundary conditions at both ends in subsonic air flow under radial harmonic excitation is investigated. The equation of motion of the composite cylindrical shell is derived from the Donnell’s nonlinear shell theory and the Galerkin’s method is adopted to transform the equation of motion of the shell into a nonlinear ordinary differential equation. The 1/3 subharmonic resonance of the shell is analyzed by using the method of multiple scales and the sufficient and necessary conditions for the stability of the steady-states of the 1/3 subharmonic resonance is obtained by solving the eigenvalue problem of the linearized equations. The influences of the subsonic air flow on the 1/3 subharmonic resonance of the shell are discussed for different modes and the effects of the ply angles are analyzed for the fundamental mode. The numerical results of the threshold curves and the amplitude–frequency relations of the 1/3 subharmonic resonance are illustrated. From the results it can be seen that the existence region for the 1/3 subharmonic resonance is reduced and the amplitude of the subharmonic resonance is dropped with the flow velocity increasing. The composite shell with 45° ply angle exhibits better dynamic characteristic than that with other ply angles. The interval of the frequency ratio for the instability of the steady-state of the subharmonic resonance is broader when the ply angle is chosen as 45° than that of other ply angles for given amplitude of the external excitation.

Experimental Study on Vibration and Sound Radiation Characteristics of New Type of Damped Wheel with Web-mounted Noise Shielded

The wheel/rail noise is the main component of the urban rail traffic noise. Low noise wheel is a key measure for reducing noise of train. A new type of web-mounted noise shielded and vibration damped device is designed and installed on a straight web metro wheel. Acoustic experiments of this new type damped wheels are carried out in a semi-anechoic chamber. Using a force-hammer and a 25 mm diameter steel ball to hit the wheel as the excitations, the frequency response and the acoustic radiation characteristics of the damped wheel can be obtained through the tests. The experimental results show that the damping ratio of the damped wheel increases significantly. The modal damping ratio increases by more than 10 times above 800 Hz, compared to the original wheel. The amplitude of the frequency response function reduces significantly in the frequency range of 0-6 400 Hz. Under the radial and axial excitations, the sound energy level of the damped wheel decreases by 12.4-13.5 dB and 12.4-14.7 dB, respectively. In some significant frequency bands, the sound energy level of the damped wheel decreases about 15dB.

Vibration Studies of Dynamically Loaded Deep Groove Ball Bearings in Presence of Local Defects on Races

Theoretical and experimental vibration studies of dynamically loaded deep groove ball bearings having local circular shape defects on either race are reported in this paper. The shaft, housing, raceways and ball masses are incorporated in the proposed mathematical model. Coupled solutions of governing equations of motion have been achieved using Runge-Kutta method. The model provides the vibrations response for the shaft, balls, and housing in time and frequency domains. The results achieved based on the proposed mathematical model have been validated with the experimental results. In experiments, the test bearings were radially loaded using an electro-mechanical shaker. The radial load excitation frequency ranged 10 - 1000Hz. The characteristic defect frequencies and related harmonics are broadly investigated and presented herein.

Formula omitted] and [formula omitted] heavy four-quark and molecule states in QCD

We estimate the masses of the 1−− heavy four-quark and molecule states by combining exponential Laplace (LSR) and finite energy (FESR) sum rules known perturbatively to lowest order (LO) in αs but including non-perturbative terms up to the complete dimension-six condensate contributions. We use double ratio of sum rules (DRSR) for determining the SU(3) breakings terms. The SU(3) mass-splittings of about (50–110) MeV and the ones of about (250–300) MeV between the lowest ground states and their 1st radial excitations are (almost) heavy-flavour independent. The mass predictions summarized in Table 2 are compared with the ones in the literature (when available) and with the three Yc(4260,4360,4660) and Yb(10890) 1−− experimental candidates. We conclude that the lowest observed state cannot be a pure 1−− four-quark nor a pure molecule but may result from their mixings. We extend the above analyzes to the 0++ four-quark and molecule states which are about (0.5–1) GeV heavier than the corresponding 1−− states, while the splittings between the 0++ lowest ground state and the 1st radial excitation is about (300–500) MeV. We complete the analysis by estimating the decay constants of the 1−− and 0++ four-quark states. Our predictions can be tested using some alternative non-perturbative approaches or/and at LHCb or some other hadron factories.

Bethe-Salpeter study of radially excited vector quarkonia

We solve the Bethe-Salpeter equation (BSE) for a system of a heavy quark-antiquark pair interacting with a Poincare invariant generalization of screened linear confining potential. In order to get reliable description the Lorentz scalar confining interaction is complemented by the effective one gluon exchange. Within presented model we reasonably reproduce all known radial excitations of the vector charmonia. We have found that $J/\Psi$ is the only charmonium left bellow naive quark-antiquark threshold $2m_c$, while the all excited states are situated above this threshold. We develop a method which is enable to provide solution of full four dimensional BSE for the all excited states. We discuss the consequences of the use of the free propagators for calculation of excited states above the threshold. The Bethe-Salpeter string breaking scale $\mu\simeq 350MeV$ appears to be relatively larger then the one defined in various potential models $\mu\simeq 150MeV$.

χb(3P)splitting predictions in potential models

Recently a new state of the $b\overline{b}$ system has been observed by the ATLAS Collaboration, with a mass of $10530\ifmmode\pm\else\textpm\fi{}5\ifmmode\pm\else\textpm\fi{}9\text{ }\text{ }\mathrm{MeV}$. This state has been identified with the $n=3$ $P$-wave radial excitations of the $b\overline{b}$ system with parallel quark spins, called ${\ensuremath{\chi}}_{b}(3P)$. The measured value of the mass corresponds to the average of the $J=0$, 1, and 2 states, while the splittings of these states are not yet resolved. In this work we present predictions from different potentials models for the values of these splittings.