Meson and Baryon Spectroscopy

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Lattice QCD calculations of these highly excited states and resonances remain very challenging. In this talk, I will review recent progress on studying these states on the lattice and describe the remaining problems. I will show how rotational invariance is systematically recovered from calculations on hyper-cubic lattices through the use of lattice operators that smoothly evolve into continuum operators with definite angular momentum as the lattice spacing is reduced, and that are smeared throughout a spatial volume with dimensions that are large compared to the lattice spacing, but small compared to the hadronic scale; as a result no power divergence of lower dimensional operators survives.

The results presented are accurate up to exponentially suppressed corrections in the volume. The formalism allows one to determine the phase shifts and mixing parameters of pipi-KK isosinglet coupled channels directly from Lattice Quantum Chromodynamics. We show that the extension to more than two channels is straightforward.

From the energy quantization condition, the volume dependence of electroweak matrix elements of two-hadron processes is extracted, for both relativistic and non-relativistic systems. In the non-relativistic case, we pay close attention to processes that mix the isosinglet-isotriplet two-nucleon states, e.

Attempt is made to understand the nature of Roper resonance from its radial Bethe-Salpeter wavefunction. The strategy to extract the potential in lattice QCD is explained in detail.


The method is applied to extract NN potentials, hyperon potentials and the meson-baryon potentials. A theoretical investigation is made to understand the origin of the repulsive core using the operator product expansion. Some recent extensions of the method are also discussed. The experiment features charged particle tracking as well as good coverage by electromagnetic calorimetry. One primary goal is the search for exotic hadronic states, in particular spin-exotic hybrid quark-gluon mesons and glueballs. Our data provide an excellent opportunity for simultaneous observation of such states in different decay modes by the same experiment.

We describe also the COMPASS potential and data for hybrid meson production in photon-pion interactions via Primakoff scattering of high energy pions from virtual photons in the Coulomb field of High-Z targets. A status report on various claimed hybrid meson resonances is given. For resonances it is important to extend the basis of interpolators to two-hadron states.

From the energy values one can determine the scattering phase shifts. The efficiency of the used tools is demonstrated for the case of meson decays. It is valid in the elastic regime for the two-pion state, and has been successfully applied to the two pion decay of the kaon. In many weak decays of interest e.

As a step on the way to a complete analysis of such decays, we consider the case with multiple two-particle channels, and show how the Lellouch-Luscher formula can be generalized. This also requires a generalization Luscher's finite-volume quantization results, which have been given previously for vanishing total momentum, and which we generalize to arbitrary total momentum. The masses and the widths of the open-charm resonances in these channels are extracted from the corresponding phase shifts.

Meson and baryon spectrum for QCD with two light dynamical quarks

K pi scattering in s-wave and p-wave will also be discussed. The total momentum of the system is zero in this simulation. In the second part of the talk I will focus on the scattering of two non-degenerate particles with non-zero total momenta. Sample interpolators and the Luscher-type relations will be presented. I will pay particular attention to the difficulties that such simulations will be facing.

In a dynamical lattice simulation we remove the lowest lying eigenmodes of the Dirac operator from the valence quark propagators and study evolution of the hadron masses obtained. All mesons and baryons in our study, except for a pion, survive unbreaking the chiral symmetry and their exponential decay signals become essentially better.

From the analysis of the observed spectroscopic patterns we conclude that confinement still persists while the chiral symmetry is restored. All hadrons fall into different chiral multiplets. We also observe signals of some higher symmetry that includes chiral symmetry as a subgroup.


Under the isospin model, they were considered to be a single particle in different charged states. The mathematics of isospin was modeled after that of spin. Isospin projections varied in increments of 1 just like those of spin, and to each projection was associated a " charged state ".

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Another example is the "nucleon particle". In the "isospin picture", the four Deltas and the two nucleons were thought to be the different states of two particles. Isospin, although conveying an inaccurate picture of things, is still used to classify baryons, leading to unnatural and often confusing nomenclature. The strangeness flavour quantum number S not to be confused with spin was noticed to go up and down along with particle mass. The higher the mass, the lower the strangeness the more s quarks.

Particles could be described with isospin projections related to charge and strangeness mass see the uds octet and decuplet figures on the right. As other quarks were discovered, new quantum numbers were made to have similar description of udc and udb octets and decuplets.


Since only the u and d mass are similar, this description of particle mass and charge in terms of isospin and flavour quantum numbers works well only for octet and decuplet made of one u, one d, and one other quark, and breaks down for the other octets and decuplets for example, ucb octet and decuplet. If the quarks all had the same mass, their behaviour would be called symmetric , as they would all behave in the same way to the strong interaction. Since quarks do not have the same mass, they do not interact in the same way exactly like an electron placed in an electric field will accelerate more than a proton placed in the same field because of its lighter mass , and the symmetry is said to be broken.

They are related to the number of strange, charm, bottom, and top quarks and antiquark according to the relations:. Spin quantum number S is a vector quantity that represents the "intrinsic" angular momentum of a particle. The total angular momentum total angular momentum quantum number J of a particle is therefore the combination of intrinsic angular momentum spin and orbital angular momentum.

This phenomenon of having multiple particles in the same total angular momentum configuration is called degeneracy. How to distinguish between these degenerate baryons is an active area of research in baryon spectroscopy. If the universe were reflected in a mirror, most of the laws of physics would be identical—things would behave the same way regardless of what we call "left" and what we call "right".

This concept of mirror reflection is called " intrinsic parity " or simply "parity" P. Gravity , the electromagnetic force , and the strong interaction all behave in the same way regardless of whether or not the universe is reflected in a mirror, and thus are said to conserve parity P-symmetry. However, the weak interaction does distinguish "left" from "right", a phenomenon called parity violation P-violation.

Based on this, if the wavefunction for each particle in more precise terms, the quantum field for each particle type were simultaneously mirror-reversed, then the new set of wavefunctions would perfectly satisfy the laws of physics apart from the weak interaction. For baryons, the parity is related to the orbital angular momentum by the relation: [16]. Baryons are classified into groups according to their isospin I values and quark q content.

Types of Elementary Particles - Photons, Leptons, Mesons and Baryons - Physics4students

The rules for classification are defined by the Particle Data Group. These rules consider the up u , down d and strange s quarks to be light and the charm c , bottom b , and top t quarks to be heavy. The rules cover all the particles that can be made from three of each of the six quarks, even though baryons made of top quarks are not expected to exist because of the top quark's short lifetime.

The rules do not cover pentaquarks. It is also a widespread but not universal practice to follow some additional rules when distinguishing between some states that would otherwise have the same symbol.

The Charm and Beauty of Strong Interactions

Quarks carry a charge, so knowing the charge of a particle indirectly gives the quark content. From Wikipedia, the free encyclopedia. Hadron that is composed of three quarks. For the dinosaur, see Baryonyx. Elementary particles of the Standard Model. Main article: Baryogenesis. Main article: Isospin. Main articles: Spin physics , Angular momentum operator , Quantum numbers , and Clebsch—Gordan coefficients. Main article: Parity physics. Physics Letters. Bibcode : PhL Progress of Theoretical Physics.

The 'baryon' is the collective name for the members of the nucleon family. This name is due to Pais. See ref. Yao et al. Amsler et al. Retrieved Aaij et al. LHCb collaboration Physical Review Letters. Bibcode : PhRvL. Garcilazo et al. Particle Data Group Physics Letters B.