Conveners
Light quarks: B1a
- Xiangdong Ji (Shanghai)
Light quarks: B1b
- Liping Gan (Univerisity of North Carolina Wilmington)
Light quarks: B2a
- Enrique Ruiz Arriola (Universidad de Granada)
Light quarks: B2b
- Wolfgang Lucha (Austrian Academy of Sciences)
Light quarks: B3a
- Hagop Sazdjian (University Paris-Sud)
Light quarks: B3b
- Jose Luis Goity (Hampton University/Jefferson Lab)
Light quarks: B5a
- Jozef Dudek
Light quarks: B5b
- Raul Briceno (Thomas Jefferson National Accelerator Facillity)
Light cone distribution amplitudes are needed in the theoretical description of exclusive processes. I will summarize results on their first Gegenbauer moments obtained by recent lattice simulations and comment on attempts to directly compute them in coordinate space.
The light-cone definition of Parton Distribution Functions (PDFs) does not allow for a direct ab initio determination employing methods of Lattice QCD simulations that naturally take place in Euclidean spacetime. In this presentation we focus on pseudo-PDFs where the starting point is the equal time hadronic matrix element with the quark and anti-quark fields separated by a finite distance.ย ...
I will present recent lattice QCD calculations for the pion form factors and quasi parton distributions using partially quenched calculations with HYP smeared Wilson quarks in the valance sector and highly improved staggered quarks in the sea. The calculations are performed at two lattice spacings a=0.06fm and a=0.04fm.
One of the most celebrated features of QCD is the asymptotic freedom that allows calculations of strong interaction with a perturbative method when the momentum transferred is sufficiently large. The non perturbative regime, however, remains veiled to {\it ab initio} calculations, and it is expected that the large amount of data made available by high energy experiments will give some insight...
In the recent years COMPASS at CERN has started to investigate the
proton structure using exclusive reactions like Deeply Virtual Compton
Scattering (DVCS), where high energy muons are scattered off a hydrogen
target. This reaction allows to access Generalised Parton Distributions
and thus the 3-dimensional structure of the proton. From a pilot
measurement in 2012 first results were...
Hadron spectroscopy is a well known powerful tool to study the properties of confinement and the nature of strong interactions. Electro- and photoproduction reactions were never extensively exploited in the past due to the lack of beams of sufficient intensity and momentum resolution. However, a new generation of experiments started recently their operations at Jefferson Lab, exploiting the...
Multiparticle production is studied experimentally and theoretically in QCD that describes interactions in the language of quarks and gluons. In the experiment the real hadrons are registered. For transfer from quarks and gluons to observed hadrons various phenomenological models are used.
In order to describe the high multiplicity region, we have developed a gluon dominance model (GDM). It...
We present recent experimental results for e+eโ annihilation into hadrons below 2 GeV obtained with the SND detector at the VEPP-2000 collider. The analyses are based on data collected in the detector runs from 2010 to 2017 years.
Chiral perturbation theory (ChPT) and the $1/N_c$ expansion provide systematic frameworks in investigating the strong interactions at low energy. A combined framework of both approaches has been developed and applied for baryons with three light-quark-flavors. The small scale expansion of the combined approach is identified as the $\xi$-expansion, in which the power counting of $1/N_c$ and...
We studied the transition form factor involved in pseudoscalar meson ($\pi$,$\eta$,$\eta$') decays into two virtual photons by means of a chiral-invariant Lagrangian, considering the lowest-lying multiplet of vector and pseudoscalar resonances. Accounting for $U(3)$ breaking effects, we give the most general corrections of order $m_P^2$ to the form factor. Most parameters are fixed requiring...
We briefly summarize current experimental and theoretical results on the two important processes of the low energy hadron physics involving neutral pions: the Dalitz decay of $\pi^0$ and the rare decay $\pi^0\to e^+e^-$. As novel results we present the complete set of radiative corrections to the Dalitz decays $\eta^{(\prime)}\to\ell^+\ell^-\gamma$ beyond the soft-photon approximation, i.e....
The properties of the form factors describing the rare CP conserving decay modes $K \to \pi l^+ l^-$, $(K,\pi) = (K^\pm,\pi^\pm)$ or $(K_S,\pi^0)$, $l=e,\mu$, are addressed. First, a full two-loop representation of the corresponding form factors in the low-energy expansion is constructed. Next, the contribution from pi-pi intermediate states is considered from a dispersive point of view....
Recent developments in the calculation of radiative QED corrections to hadronic weak decays are described and results of numerical simulations presented. A critical discussion of possible future developments will also be given.
Quark masses are fundamental parameters of the standard
model that are key for our understanding of the natural laws. Light quark masses give valuable information on the flavor structure of natural laws and on the nature of spontaneous chiral symmetry breaking. The masses of the heavy charm and bottom quark play a key role in the theoretical predictions of the Higgs boson decay rates. Due...
The light pseudoscalar meson decays provide a unique laboratory to test fundamental QCD symmetries at low energies. A comprehensive Primako๏ฌ experimental program at Je๏ฌerson Laboratory (JLab) is aimed at gathering high precision measurements of the two-photon decay widths and the transition form factors (at low four-momentum transfer squares) of ฯ0, ฮท and ฮทโฒ via the Primako๏ฌ e๏ฌect. The results...
COMPASS is a multi-purpose fixed-target experiment at CERN aimed at studying the structure and spectrum of hadrons. The two-stage spectrometer has a good acceptance over a wide kinematic range and is thus able to measure a wide range of reactions. Light mesons are studied with a negative hadron beam (mostly $\pi^-$) with a momentum of $190~\text{GeV}/c$.
The light-meson spectrum is...
I will report on recent progress using lattice QCD to study coupled-channel meson resonances with particular focus on the light scalars and tensors. Taking advantage of the relation between scattering amplitudes and the discrete spectrum of states in a box of finite-size, the presence and properties of resonances can be determined in a rigorous manner.
We quantify the importance of dynamical spin effects in the holographic light-front wavefunctions of the pion, kaon, ฮท and ฮทโฒ. Using a universal AdS/QCD scale and constituent quark masses, we find that such effects are maximal in the pion where they lead to an excellent simultaneous description of a wide range of data: the decay constant, charge radius, spacelike EM and transition form...
In this work, we examine the flavour-dependence of dynamical chiral symmetry
breaking (DCSB) due to the effect of different model kernels in the gap equation.
For that, we have computed the quarkโs sigma term and its ratio to the
Euclidean constituent mass, that computes the DCSB contribution.
The first measurements of the production of lambda, sigma, cascade, and omega hyperons at large timelike momentum transfers of 13.6, 14.2, and 17.4 GeV^2 have been made using e+e- annihilation data taken at the CESER electron-positron collider at Cornell using the CLEOc detector. The measurements reveal interesting features of hyperon production systematics and timelike form factors, and...
Recent years have seen significantly increased interest in hadron spectroscopy, triggered primarily by the experimental discovery of unconventional states. However, experimental data alone is not always sufficient to discern the nature and structure of a given state. In this talk, I discuss a class of observables that are experimentally inaccessible but can be accessed
via lattice QCD. I will...
Discussing four-point Green functions of bilinear quark currents in large-Nc QCD, we formulate rigorous criteria for selecting diagrams appropriate for the analysis of potential tetraquark poles. We find that both flavor-exotic and cryptoexotic (i.e., flavor-nonexotic) tetraquarks, if such poles exist, have a width of order O(1/Ncยฒ), so they are parametrically narrower compared to the ordinary...
We explore the validity of vector meson dominance in the radiative decay of the $b_1(1235)$ meson. In order to explain the violation of the vector meson dominance hypothesis in this decay process, we investigate a model where the $b_1$ meson strongly couples with the local current in tensor bilinear representation. The tensor representation is investigated in the framework of the operator...
In this talk I will review the recent analyses and other activities carried
out by the JPAC collaboration. In particular, the phenomenological analysis of
the COMPASS data on $\eta \pi$ and $\eta' \pi$ partial waves, with the goal of
determining in a robust way the pole position of the hybrid meson $\pi_1(1400)$,
as well as the ordinary mesons $a_2(1320)$ and the $a'_2(1700)$
Significant progress has been achieved recently in the determination
of properties of nucleons by lattice methods. This includes studies of
the response of the nucleon to electromagnetic, weak or beyond the
Standard Model probes and the internal dynamics in terms of the
contributions from quarks and gluons. In particular, the systematics
due to simulating in a finite box with a finite lattice...
In this talk I shall reexamine the possibility of extracting parton distribution functions from lattice simulations. I discuss the case of quasi-parton distribution functions, the more recent proposal of directly trying to compute the current-current $T$-product on the lattice and the possibility of making reference to the reduced Ioffe-time distribution. I show that the process of...
Direct lattice computation of the key measures of hadron structure such as the form factors, parton distribution functions, quark distribution amplitudes have always been challenging. With current enormous experimental efforts at JLab (with its 12 GeV upgrade), COMPASS in CERN, RHIC-spin and at a future EIC, it is now crucial to test and exploit the newly proposed lattice QCD ideas in hadron...
We consider a class of gauge-invariant nonlocal quark bilinear operators, including a finite-length Wilson-line (called Wilson-line operators). The matrix elements of these operators are involved in the recent "quasi-distribution" approach for computing parton distributions nonperturbatively.
In this work, we study the renormalization of two types of classes of Wilson-line operators:...
I will discuss some recent progress in studying excited and exotic mesons using first-principles lattice QCD calculations. In particular, I will present some new work on meson-meson scattering involving mesons with non-zero spin, an area which is important for understanding many of the various puzzling structures that have been observed in experiment but where so far lattice QCD calculations...
We study the nonperturbative structure of the quark-photon vertex in Landau gauge. To this end we utilize Green's functions from two-flavor lattice QCD simulations and extract all longitudinal and transversal form factors. Interestingly, our lattice results fit rather well with solutions of the inhomogenous Bethe-Salpether equation of the vertex in the rainbow-ladder approximation. Though,...
The goal of calculating the one loop hadronic contribution to the muon
anomalous magnetic moment using lattice QCD, with an error under 1%,
requires the calculation of the disconnected contributions. We discuss
some of the numerical challenges of computing disconnected vector
correlators, in lattice QCD calculations using the highly improved
staggered quark (HISQ) action. We report preliminary...
The JIMWLK equation, which describes the evolution of color fields, together with a choice of the initial conditions, for instance according to the Venugopalan-McLerran model, provide a framework in which correlation functions of Wilson lines and their derivatives can be estimated, hence providing necessary information to describe hadron Transverse Momentum Dependent structure functions. After...
One of the main physics goals of the NA61/SHINE programme on strong interactions is the study of the properties of the onset of deconfinement. This goal is pursued by performing an energy (beam momentum 13A - 158A GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La) scan. This talk will review results and plans of NA61/SHINE. In particular, recently obtained inclusive spectra in inelastic...
