Search Results (13)

Motivated by the recent CMS observation of a near-threshold enhancement in top quark pair production, we investigate a novel class of hadronic systems containing a single top quark: the topped mesons ($t\overline{q}$, with $\overline{q}=\overline{u},\overline{d},\overline{s}$). In contrast to the extensively studied toponium ($t\overline{t}$) system—analyzed primarily within perturbative QCD—topped mesons offer a complementary nonperturbative probe of QCD dynamics in the heavy quark limit. These states are expected to exhibit longer lifetimes and narrower decay widths than toponium, as only a single top quark undergoes weak decay. We employ QCD sum rules within the framework of heavy quark effective theory to study the structure and mass spectrum of ground-state topped mesons. Our analysis predicts masses near 173.1 GeV, approximately 0.5–0.6 GeV above the top quark pole mass. Compared with singly topped baryons ($tqq$, with $q=u,d,s$), topped mesons have a simpler quark composition and more favorable decay channels (a topped meson is anticipated to decay weakly into a $\mathrm{{\rm Y}}$ meson and a charmed meson), enhancing their potential for both theoretical analysis and experimental discovery. Full article

In this work, we present an overview of the recent results, obtained in the framework of the fractional analytic QCD in the space-like (Euclidean) and time-like regions. The Higgs boson decays into a bottom–antibottom pair, and the polarized Bjorken sum rule is considered as an application of the obtained results. Full article

It is widely known that the nucleon scalar charge is proportional to the pion–nucleon sigma term as one of the important low-energy observables of QCD. Especially interesting to us is the physics of the nucleon scalar charge densities. This comes from the fact that the corresponding operator has the same quantum number as the physical vacuum. It indicates unusual behavior of the nucleon scalar density as a function of the distance r from the nucleon center. Namely, it would not be reduced down to zero at the spatial infinity but rather approach some nonzero constant corresponding to the vacuum quark condensate. Naturally, this unique nature of the nucleon scalar density in the position space also affects the corresponding density in the momentum space, i.e., the corresponding parton distribution function (PDF) as a function of the Bjorken variable x. This PDF is known as the chiral-odd twist-3 PDF $e\left(x\right)$. We argue that $e\left(x\right)$ is likely to have a delta-function-type singularity at $x=0$ and that the appearance of this singularity can be interpreted as a signal of the nontrivial vacuum structure of QCD. Full article

Currently, flavour-cryptoexotic tetraquarks form the most common sort of all experimentally established exotic multiquark hadrons. This note points out a few promising concepts that should help improve theoretical (but, for several reasons, not quite straightforward) analyses of this kind of states; among others, their scope of application encompasses the strong interactions in the limit of (arbitrarily) large numbers of colours, and equally analytical and nonperturbative approaches to multiquark states. Full article

Motivated by recent experimental progress in establishing the likely existence of (variants of) exotic hadrons, predicted to be formed by the strong interactions, various proposed concepts and ideas are compiled in an attempt to draft a coherent picture of the achievable improvement in the theoretical interpretation of exotic hadrons in terms of the underlying quantum field theory of strong interactions. Full article

In the current paper, we argue that the ground state of a hadron contains a significant perturbative quantum chromodynamics (pQCD) core as the result of color gauge invariance and the values of chiral and gluon vacuum condensates. The evaluation within the method of dispersion sum rules (DSR) of the vacuum matrix elements of the correlator of local currents with the proper quantum numbers leads to the value of the radius of the pQCD core of a nucleon of about 0.4–0.5 fm. The selection of the initial and final states allows to select processes in which the pQCD core of the projectile gives the dominant contribution to the process. It is explained that the transparency of nuclear matter for the propagation of a spatially small and color-neutral wave packet of quarks and gluons—a color transparency (CT) phenomenon—for a group of hard processes off nuclear targets can be derived in the form of the QCD factorization theorem accounting for the color screening phenomenon. Based on the success of the method of DSR, we argue that a pQCD core in a hadron wave function is surrounded by the layer consisting of quarks interacting with quark and gluon condensates. As a result, in the quasi-elastic processes $e+A\to e^{\prime }+N+{(A-1)}^{\ast }$, the quasi-Feynman mechanism could be dominating in a wide range of the momentum transfer squared, $Q^2$. In this scenario, a virtual photon is absorbed by a single quark, which carries a large fraction of the momentum of the nucleon and dominates in a wide range of $Q^2$. CT should reveal itself in these processes at extremely large $Q^2$ as the consequence of the presence of the Sudakov form factors, which squeeze a nucleon. Full article

We briefly review some essential aspects of the QCD instanton vacuum in relation to the quantum breaking of conformal symmetry, the spontaneous breaking of chiral symmetry, and the axial U(1) anomaly. The anomaly causes the intrinsic nucleon spin to transmute to the vacuum topological charge by quantum tunneling. We use Ji${}^{\prime }s$ invariant spin decomposition to discuss the spin budget of the nucleon as a quark–diquark state in the QCD instanton vacuum. A measure of the intrinsic quark spin of the nucleon is a measure of the quenched topological susceptibility of the QCD instanton vacuum. Full article

Within the framework of the light-cone QCD sum rules method (LCSR’s), the radiative $\Delta \left(1600\right)\to \gamma N$ decay is studied. In particular, the magnetic dipole moment $G_M^1\left(0\right)$ and the electric quadrupole moment $G_E^1\left(0\right)$ are estimated. We also calculate the ratio $R_{EM}=-\frac{G_E^1\left(0\right)}{G_M^1\left(0\right)}$ and the decay rate. The predicted multipole moments and the decay rate strongly agree with the existing experimental results as well as with the other available phenomenological approaches. Full article

We study the ${\mathsf{\Lambda }}_b{\left(6146\right)}^0$ and ${\mathsf{\Lambda }}_b{\left(6152\right)}^0$ recently observed by LHCb using the method of Quantum Chromodynamics (QCD) sum rules within the framework of heavy quark effective theory. Our results suggest that they can be interpreted as D-wave bottom baryons of $J^P=3/2^{+}$ and $5/2^{+}$ respectively, both of which contain two $\lambda$ -mode excitations. We also investigate other possible assignments containing $\rho$ -mode excitations. We extract all the parameters that are necessary to study their decay properties when using the method of light-cone sum rules. We predict masses of their strangeness partners to be $m_{{\Xi }_b(3/2^{+})}={6.26}_{-0.14}^{+0.11}$ GeV and $m_{{\Xi }_b(5/2^{+})}={6.26}_{-0.14}^{+0.11}$ GeV with the mass splitting $\Delta M=m_{{\Xi }_b(5/2^{+})}-m_{{\Xi }_b(3/2^{+})}={4.5}_{-1.5}^{+1.9}$ MeV, and propose to search for them in future CMS, EIC, and LHCb experiments. Full article

This is a review of the production of heavy quark states via relativistic heavy ion collisions in RHIC. The heavy quarks here are c, charm quark, and b, bottom quark. The states are charmonium meson states $\Psi \left(nS\right)$ , with n = 1,2 and upsilon meson states ${\rm Y}\left(mS\right)$ , with m = 1,2,3. Quantum Chromodynamics (QCD) sum rules were used to derive the result that the $\Psi \left(2S\right)$ and ${\rm Y}\left(3S\right)$ are mixed hybrid states, which increase their production cross sections. We also review the $\Psi \left(nS\right)$ and ${\rm Y}\left(mS\right)$ production cross sections via Cu-Cu and Au-Au collisions, which are very important for this review of the production of heavy quark states in RHIC. The possible detection of the Quark Gluon Plasma (QGP) is also reviewed. Full article

Using the light-cone sum rules at leading order, we present an approach to perform the preliminary upper estimation for the nucleon gravitational form factor $\mathbb{D}\left(t\right)$ (D-term contribution). Comparison with the experimental data and with the results of different models is discussed. Full article

The QCD Lagrangian is based on quark and gluonic fields—not squarks nor gluinos. However, one can show that its hadronic eigensolutions conform to a representation of superconformal algebra, reflecting the underlying conformal symmetry of chiral QCD. The eigensolutions of superconformal algebra provide a unified Regge spectroscopy of meson, baryon, and tetraquarks of the same parity and twist as equal-mass members of the same 4-plet representation with a universal Regge slope. The predictions from light-front holography and superconformal algebra can also be extended to mesons, baryons, and tetraquarks with strange, charm and bottom quarks. The pion $q\overline{q}$ eigenstate has zero mass for $m_q=0.$ A key tool is the remarkable observation of de Alfaro, Fubini, and Furlan (dAFF) which shows how a mass scale can appear in the Hamiltonian and the equations of motion while retaining the conformal symmetry of the action. When one applies the dAFF procedure to chiral QCD, a mass scale $\kappa$ appears which determines universal Regge slopes, hadron masses in the absence of the Higgs coupling. One also predicts the form of the nonperturbative QCD running coupling: ${\alpha }_s\left(Q^2\right)\propto e^{-Q^2/4{\kappa }^2}$ , in agreement with the effective charge determined from measurements of the Bjorken sum rule. One also obtains viable predictions for spacelike and timelike hadronic form factors, structure functions, distribution amplitudes, and transverse momentum distributions. The combination of conformal symmetry, light-front dynamics, its holographic mapping to AdS ${}_5$ space, and the dAFF procedure thus provide new insights, not only into the physics underlying color confinement, but also the nonperturbative QCD coupling and the QCD mass scale. Full article

Atomic nuclei exhibit approximate pseudospin symmetry. We review the arguments that this symmetry is a relativistic symmetry. The condition for this symmetry is that the sum of the vector and scalar potentials in the Dirac Hamiltonian is a constant. We give the generators of pseudospin symmetry. We review some of the predictions that follow from the insight that pseudospin symmetry has relativistic origins . We show that approximate pseudospin symmetry in nuclei predicts approximate spin symmetry in anti-nucleon scattering from nuclei. Since QCD sum rules predict that the sum of the scalar and vector potentials is small, we discuss the quark origins of pseudospin symmetry in nuclei and spin symmetry in hadrons. Full article