scholarly journals Improved Parton Distributions from the Quark Model

1991 ◽  
Vol 44 (4) ◽  
pp. 363 ◽  
Author(s):  
SD Bass ◽  
A Schreiber ◽  
AW Thomas ◽  
JT Londergan
Keyword(s):  
Quark Model ◽  
Constant Density ◽  
Matrix Elements ◽  
Significant Progress ◽  
Parton Distributions ◽  
Quark Field ◽  
Hadronic States

There has recently been significant progress in the calculation of the twist-two piece of the quark/parton distributions corresponding to models like the MIT bag. However, in evaluating the required matrix elements of the quark field operators Signal and Thomas (1988, 1989) resorted to the Peierls-Yoccoz (1957) approximation-albeit with some cautionary remarks. We point out a problem with that approach which is solved by using the Peierls-Thouless (1962) approximation for the hadronic states. The very simple case of a nonrelativistic constant density quark wavefunction is solved in detail.

scholarly journals Double parton distributions in the pion from lattice QCD

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Gunnar S. Bali ◽  
Luca Castagnini ◽  
Markus Diehl ◽  
Jonathan R. Gaunt ◽  
Benjamin Gläßle ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Lattice Qcd ◽  
Quark Mass ◽  
Matrix Elements ◽  
Parton Distributions ◽  
Almost All ◽  
The Relationship

Abstract We perform a lattice study of double parton distributions in the pion, using the relationship between their Mellin moments and pion matrix elements of two local currents. A good statistical signal is obtained for almost all relevant Wick contractions. We investigate correlations in the spatial distribution of two partons in the pion, as well as correlations involving the parton polarisation. The patterns we observe depend significantly on the quark mass. We investigate the assumption that double parton distributions approximately factorise into a convolution of single parton distributions.

scholarly journals Studying ε′/ε in the chiral quark model: γ5-scheme independence and NLO hadronic matrix elements

1995 ◽  
Vol 449 (1-2) ◽  
pp. 197-225 ◽  
Author(s):  
Stefano Bertolini ◽  
Jan O. Eeg ◽  
Marco Fabbrichesi
Keyword(s):  
Quark Model ◽  
Chiral Quark Model ◽  
Matrix Elements

scholarly journals Computation of parton distributions from the quasi-PDF approach at the physical point

2018 ◽  
Vol 175 ◽  
pp. 14008 ◽  
Author(s):  
Constantia Alexandrou ◽  
Simone Bacchio ◽  
Krzysztof Cichy ◽  
Martha Constantinou ◽  
Kyriakos Hadjiyiannakou ◽  
...  
Keyword(s):  
Pion Mass ◽  
Distribution Functions ◽  
Matrix Elements ◽  
Parton Distribution Functions ◽  
Physical Point ◽  
Parton Distributions ◽  
The Matrix ◽  
First Results ◽  
Perturbative Renormalization ◽  
Vector Combination

We show the first results for parton distribution functions within the proton at the physical pion mass, employing the method of quasi-distributions. In particular, we present the matrix elements for the iso-vector combination of the unpolarized, helicity and transversity quasi-distributions, obtained with Nf = 2 twisted mass cloverimproved fermions and a proton boosted with momentum [see formula in PDF] = 0.83 GeV. The momentum smearing technique has been applied to improve the overlap with the proton boosted state. Moreover, we present the renormalized helicity matrix elements in the RI’ scheme, following the non-perturbative renormalization prescription recently developed by our group.

RADIATIVE DECAYS OF BARYONS IN A FIELD THEORETIC QUARK MODEL

1996 ◽  
Vol 11 (32) ◽  
pp. 5685-5700 ◽  
Author(s):  
A.R. PANDA ◽  
R.K. SAHOO
Keyword(s):  
Quark Model ◽  
Radiative Decay ◽  
Constituent Quark ◽  
Theoretical Calculations ◽  
Wave Functions ◽  
Radiative Decays ◽  
Quark Field ◽  
Decay Widths ◽  
Helicity Amplitudes ◽  
Decays Of Baryons

Radiative decays of baryons are considered in a field theoretic quark model of composite hadrons where the translationally invariant SU (6) hadron states are described by constituent quark field operators and harmonic oscillator wave functions. The constituent quark field operators of the model satisfying the equal time algebra are also Lorentz-boosted through a spin rotation to describe hadrons in motion. The model, like its earlier success in describing the different hadronic phenomena, in the present investigation without any free parameters, obtains the radiative decay widths and helicity amplitudes in reasonable agreement with other theoretical calculations as well as with the available experimental measurements.

scholarly journals DEEPLY VIRTUAL AND EXCLUSIVE PRODUCTION OF THE OMEGA MESON

2005 ◽  
Vol 20 (08n09) ◽  
pp. 1943-1946
Author(s):  
◽  
M. GARÇON ◽  
L. MORAND ◽  
D. DORÉ ◽  
J.-M. LAGET ◽  
...  
Keyword(s):  
Density Matrix ◽  
Momentum Transfer ◽  
Cross Sections ◽  
Spin Density Matrix ◽  
Matrix Elements ◽  
Photon Virtuality ◽  
Parton Distributions ◽  
Exclusive Production ◽  
Generalized Parton Distributions ◽  
Omega Meson

Exclusive ω electroproduction off the proton was measured at the highest possible four-momentum transfer with the (close to) 6 GeV beam now available at CEBAF. Cross sections are presented, together with an analysis of the ω spin density matrix elements. Indications are that π0 exchange in the t-channel (or rather the exchange of the corresponding saturating Regge trajectory) seems to dominate the process γ*p→ωp, even for photon virtuality Q2 as large as 5 GeV2. Contributions of the handbag type, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract from this particular process.

scholarly journals Two-current correlations in the pion in the Nambu and Jona-Lasinio model

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Aurore Courtoy ◽  
Santiago Noguera ◽  
Sergio Scopetta
Keyword(s):  
High Energy ◽  
Low Energy ◽  
Matrix Elements ◽  
Lattice Data ◽  
Energy Matrix ◽  
Parton Distributions ◽  
Factorization Approximation ◽  
Lattice Result ◽  
Villars Regularization ◽  
Current Correlations

AbstractWe present an analysis of two-current correlations for the pion in the Nambu–Jona-Lasinio model, with Pauli–Villars regularization. We provide explicit expressions in momentum space for two-current correlations corresponding to the zeroth component of the vector Dirac bilinear in the quark vertices, which has been evaluated on the lattice, thinking to applications in a high energy framework, as a step towards the calculation of pion double parton distributions. The numerical results show a remarkable qualitative agreement with recent lattice data. The factorization approximation into one-body currents is discussed based on previous evaluation of the relevant low energy matrix elements in the Nambu–Jona-Lasinio model, confirming the lattice result.

Deep inelastic parton distributions and the constituent quark model

1992 ◽  
Vol 544 (3-4) ◽  
pp. 731-746 ◽  
Author(s):  
Marco Traini ◽  
Laura Conci ◽  
Ugo Moschella
Keyword(s):  
Quark Model ◽  
Constituent Quark ◽  
Constituent Quark Model ◽  
Parton Distributions
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