P. A. Guichon - The Jefferson Lab Hall A Collaboration

P. A. Guichon
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P. A. Guichon
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The Jefferson Lab Hall A Collaboration
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Nuclear Theory (23)
 
High Energy Physics - Phenomenology (18)
 
High Energy Physics - Lattice (12)
 
Nuclear Experiment (8)
 
High Energy Physics - Experiment (5)
 
Astrophysics (1)
 
Solar and Stellar Astrophysics (1)

Publications Authored By P. A. Guichon

We report the first use of the effective QMC energy density functional (EDF), derived from a quark model of hadron structure, to study a broad range of ground state properties of even-even nuclei across the periodic table in the non-relativistic Hartree-Fock+BCS framework. The novelty of the QMC model is that the nuclear medium effects are treated through modification of the internal structure of the nucleon. The density dependence is microscopically derived and the spin-orbit term arises naturally. Read More

We present final results on the photon electroproduction ($\vec{e}p\rightarrow ep\gamma$) cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region from Jefferson Lab experiment E00-110. Results from an analysis of a subset of these data were published before, but the analysis has been improved which is described here at length, together with details on the experimental setup. Furthermore, additional data have been analyzed resulting in photon electroproduction cross sections at new kinematic settings, for a total of 588 experimental bins. Read More

We present a precise non-perturbative determination of the renormalization constants in the mass independent RI'-MOM scheme. The lattice implementation uses the Iwasaki gauge action and four degenerate dynamical twisted mass fermions. The gauge configurations are provided by the ETM Collaboration. Read More

We summarize recent non-perturbative results obtained for the renormalization constants computed in the RI'-MOM scheme for $N_{\rm f}=2+1+1$ twisted mass QCD. Our implementation employs the Iwasaki gauge action and four dynamical degenerate twisted mass fermions. Renormalization constants for scalar, pseudo-scalar, vector and axial operators, as well as the quark propagator renormalization, are computed at three different values of the lattice spacing, two different volumes and several values of the twisted mass. Read More

2012May
Authors: H. Fonvieille1, G. Laveissiere2, N. Degrande3, S. Jaminion4, C. Jutier5, L. Todor6, R. Di Salvo7, L. Van Hoorebeke8, L. C. Alexa9, B. D. Anderson10, K. A. Aniol11, K. Arundell12, G. Audit13, L. Auerbach14, F. T. Baker15, M. Baylac16, J. Berthot17, P. Y. Bertin18, W. Bertozzi19, L. Bimbot20, W. U. Boeglin21, E. J. Brash22, V. Breton23, H. Breuer24, E. Burtin25, J. R. Calarco26, L. S. Cardman27, C. Cavata28, C. -C. Chang29, J. -P. Chen30, E. Chudakov31, E. Cisbani32, D. S. Dale33, C. W. deJager34, R. De Leo35, A. Deur36, N. d'Hose37, G. E. Dodge38, J. J. Domingo39, L. Elouadrhiri40, M. B. Epstein41, L. A. Ewell42, J. M. Finn43, K. G. Fissum44, G. Fournier45, B. Frois46, S. Frullani47, C. Furget48, H. Gao49, J. Gao50, F. Garibaldi51, A. Gasparian52, S. Gilad53, R. Gilman54, A. Glamazdin55, C. Glashausser56, J. Gomez57, V. Gorbenko58, P. Grenier59, P. A. M. Guichon60, J. O. Hansen61, R. Holmes62, M. Holtrop63, C. Howell64, G. M. Huber65, C. E. Hyde66, S. Incerti67, M. Iodice68, J. Jardillier69, M. K. Jones70, W. Kahl71, S. Kato72, A. T. Katramatou73, J. J. Kelly74, S. Kerhoas75, A. Ketikyan76, M. Khayat77, K. Kino78, S. Kox79, L. H. Kramer80, K. S. Kumar81, G. Kumbartzki82, M. Kuss83, A. Leone84, J. J. LeRose85, M. Liang86, R. A. Lindgren87, N. Liyanage88, G. J. Lolos89, R. W. Lourie90, R. Madey91, K. Maeda92, S. Malov93, D. M. Manley94, C. Marchand95, D. Marchand96, D. J. Margaziotis97, P. Markowitz98, J. Marroncle99, J. Martino100, K. McCormick101, J. McIntyre102, S. Mehrabyan103, F. Merchez104, Z. E. Meziani105, R. Michaels106, G. W. Miller107, J. Y. Mougey108, S. K. Nanda109, D. Neyret110, E. A. J. M. Offermann111, Z. Papandreou112, B. Pasquini113, C. F. Perdrisat114, R. Perrino115, G. G. Petratos116, S. Platchkov117, R. Pomatsalyuk118, D. L. Prout119, V. A. Punjabi120, T. Pussieux121, G. Quemener122, R. D. Ransome123, O. Ravel124, J. S. Real125, F. Renard126, Y. Roblin127, D. Rowntree128, G. Rutledge129, P. M. Rutt130, A. Saha131, T. Saito132, A. J. Sarty133, A. Serdarevic134, T. Smith135, G. Smirnov136, K. Soldi137, P. Sorokin138, P. A. Souder139, R. Suleiman140, J. A. Templon141, T. Terasawa142, R. Tieulent143, E. Tomasi-Gustaffson144, H. Tsubota145, H. Ueno146, P. E. Ulmer147, G. M. Urciuoli148, M. Vanderhaeghen149, R. L. J. Van der Meer150, R. Van De Vyver151, P. Vernin152, B. Vlahovic153, H. Voskanyan154, E. Voutier155, J. W. Watson156, L. B. Weinstein157, K. Wijesooriya158, R. Wilson159, B. B. Wojtsekhowski160, D. G. Zainea161, W. -M. Zhang162, J. Zhao163, Z. -L. Zhou164
Affiliations: 1The Jefferson Lab Hall A Collaboration, 2The Jefferson Lab Hall A Collaboration, 3The Jefferson Lab Hall A Collaboration, 4The Jefferson Lab Hall A Collaboration, 5The Jefferson Lab Hall A Collaboration, 6The Jefferson Lab Hall A Collaboration, 7The Jefferson Lab Hall A Collaboration, 8The Jefferson Lab Hall A Collaboration, 9The Jefferson Lab Hall A Collaboration, 10The Jefferson Lab Hall A Collaboration, 11The Jefferson Lab Hall A Collaboration, 12The Jefferson Lab Hall A Collaboration, 13The Jefferson Lab Hall A Collaboration, 14The Jefferson Lab Hall A Collaboration, 15The Jefferson Lab Hall A Collaboration, 16The Jefferson Lab Hall A Collaboration, 17The Jefferson Lab Hall A Collaboration, 18The Jefferson Lab Hall A Collaboration, 19The Jefferson Lab Hall A Collaboration, 20The Jefferson Lab Hall A Collaboration, 21The Jefferson Lab Hall A Collaboration, 22The Jefferson Lab Hall A Collaboration, 23The Jefferson Lab Hall A Collaboration, 24The Jefferson Lab Hall A 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Virtual Compton Scattering (VCS) on the proton has been studied at Jefferson Lab using the exclusive photon electroproduction reaction (e p --> e p gamma). This paper gives a detailed account of the analysis which has led to the determination of the structure functions P_LL-P_TT/epsilon and P_LT, and the electric and magnetic generalized polarizabilities (GPs) alpha_E(Q^2) and beta_M(Q^2) at values of the four-momentum transfer squared Q^2= 0.92 and 1. Read More

We present results on the electroweak form factors and on the lower moments of parton distributions of the nucleon, within lattice QCD using two dynamical flavors of degenerate twisted mass fermions. Results are obtained on lattices with three different values of the lattice spacings, namely a=0.089 fm, a=0. Read More

2011Apr
Affiliations: 1Univ. of Cyprus & Cyprus Inst., 2Univ. of Grenoble, 3Univ. of Cyprus, 4Univ. of Grenoble, 5Saclay, 6DESY-Zeuthen, 7Univ. of Cyprus, 8Humboldt Univ. Berlin, 9Univ. of Grenoble

We present results on the lower moments of the nucleon generalized parton distri butions within lattice QCD using two dynamical flavors of degenerate twisted mass fermions. Our simulations are performed on lattices with three different values of the lattice spacings, namely $a=0.089$ fm, $a=0. Read More

2011Feb
Affiliations: 1Univ. of Cyprus & Cyprus Inst., 2Univ. of Grenoble, 3Univ. of Grenoble, 4Univ. of Cyprus, 5Univ. of Grenoble, 6Saclay, 7DESY-Zeuthen, 8Humboldt Univ., 9Univ. of Grenoble

We present results on the nucleon electromagnetic form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length L=2.1 fm and L=2. Read More

Prompted by the level of accuracy now being achieved in tests of the unitarity of the CKM matrix, we consider the possible modification of the Fermi matrix element for the $\beta$-decay of a neutron, including possible in-medium and isospin violating corrections. While the nuclear modifications lead to very small corrections once the Behrends-Sirlin-Ademollo-Gatto theorem is respected, the effect of the $u-d$ mass difference on the conclusion concerning $V_{ud}$ is no longer insignificant. Indeed, we suggest that the correction to the value of $|V_{ud}|^2 \, + \, |V_{us}|^2 \, + \, |V_{ub}|^2$ is at the level of $10^{-4}$. Read More

The latest observation of a Shapiro delay of the binary millisecond pulsar J1614-2230 by Demorest et al. Nature 467 1081 (2010) yielded the pulsar gravitational mass to be 1.97 +/- 0. Read More

2010Dec
Affiliations: 1Univ. of Cyprus and Cyprus Instit., 2Univ. of Cyprus, 3Humboldt Univ. Berlin, 4Univ. of Grenoble, 5Univ. of Grenoble, 6Univ.of Grenoble, 7Saclay, 8DESY-Zeuthen

We present results on the nucleon form factors and moments of generalized parton distributions obtained within the twisted mass formulation of lattice QCD. We include a discussion of lattice artifacts by examining results at different volumes and lattice spacings. We compare our results with those obtained using different discretization schemes and to experiment. Read More

2010Dec
Affiliations: 1Univ. of Cyprus and Cyprus Instit., 2Univ. of Grenoble, 3Univ. of Grenoble, 4Univ. of Cyprus, 5Univ. of Grenoble, 6Saclay, 7DESY-Zeuthen, 8Humboldt Univ., 9Univ. of Grenoble

We present results on the nucleon axial form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length $L=2.1$ fm and $L=2. Read More

We present results of hypernuclei calculated in the latest quark-meson coupling (QMC) model, where the effect of the mean scalar field in-medium on the one-gluon exchange hyperfine interaction, is also included self-consistently. The extra repulsion associated with this increased hyperfine interaction in-medium completely changes the predictions for {\Sigma} hypernuclei. Whereas in the earlier version of QMC they were bound by an amount similar to {\Lambda} hypernuclei, they are unbound in the latest version of QMC, in qualitative agreement with the experimental absence of such states. Read More

2009Oct
Affiliations: 1U. of Cyprus & Cyprus Institute, 2U. of Cyprus, 3U. of Cyprus & Wuppertal, 4Saclay, 5Saclay, 6U. of Grenoble, 7U. of Grenoble, 8U. of Grenaoble, 9DESY-Zeuthen

We present results on the electromagnetic and axial nucleon form factors using two degenerate flavors of twisted mass fermions on lattices of spatial size 2.1 fm and 2.7 fm and a lattice spacing of about 0. Read More

2009Oct
Affiliations: 1U. of Cyprus and Cyprus Institute, 2Saclay, 3U. of Grenoble, 4U. of Grenoble, 5Saclay, 6DESY-Zeuthen, 7U. of Cyprus, 8Orsay

The masses of the low lying baryons are evaluated using two degenerate flavors of twisted mass sea quarks corresponding to pseudo scalar masses in the range of about 270-500 MeV. The strange valence quark mass is tuned to reproduce the mass of the kaon in the physical limit. The tree-level Symanzik improved gauge action is employed. Read More

We present results on the mass of the baryon octet and decuplet using two flavors of light dynamical twisted mass fermions. The strange quark mass is fixed to its physical value from the kaon sector in a partially quenched set up. Calculations are performed for light quark masses corresponding to a pion mass in the range 270-500 MeV and lattice sizes of 2. Read More

We study the binding of hypernuclei based on the latest version of quark-meson coupling model, and estimate the phtoproduction cross sections for the $^{12}$C($\gamma,K^+$)$^{12}_\Lambda$B reaction using the bound $\Lambda$ spinors obtained in the model. Read More

We present results on the mass of the nucleon and the Delta using two dynamical degenerate twisted mass quarks and the tree-level Symanzik improved gauge action. The evaluation is performed at four quark masses corresponding to a pion mass in the range of about 300-600 MeV on lattices of 2.1-2. Read More

The most recent development of the quark-meson coupling (QMC) model, in which the effect of the mean scalar field in-medium on the hyperfine interaction is also included self-consistently, is used to compute the properties of finite hypernuclei. The calculations for $\Lambda$ and $\Xi$ hypernuclei are of comparable quality to earlier QMC results without the additional parameter needed there. Even more significantly, the additional repulsion associated with the increased hyperfine interaction in-medium completely changes the predictions for $\Sigma$ hypernuclei. Read More

2007Oct
Affiliations: 1Univ. of Cyprus, 2Univ. of Cyprus, 3Univ. of Cyprus, 4Saclay, 5Saclay, 6Grenoble, 7Grenoble, 8Grenoble, 9Orsay, 10Orsay, 11Univ. of Liverpool

We present results on the mass of the nucleon and the $\Delta$ using two dynamical degenerate twisted mass quarks. The evaluation is performed at four quark masses corresponding to a pion mass in the range of 690-300 MeV on lattices of size 2.1 fm and 2. Read More

At the present time there is a lively debate within the nuclear community concerning the relevance of quark degrees of freedom in understanding nuclear structure. We outline the key issues and review the impressive progress made recently within the framework of the quark-meson coupling model. In particular, we explain in quite general terms how the modification of the internal structure of hadrons in-medium leads naturally to three- and four-body forces, or equivalently, to density dependent effective interactions. Read More

2006Nov

A new density dependent effective baryon-baryon interaction has been recently derived from the quark-meson-coupling (QMC) model, offering impressive results in application to finite nuclei and dense baryon matter. This self-consistent, relativistic quark-level approach is used to construct the Equation of State (EoS) and to calculate key properties of high density matter and cold, slowly rotating neutron stars. The results include predictions for the maximum mass of neutron star models, together with the corresponding radius and central density, as well the properties of neutron stars with mass of order 1. Read More

A density dependent, effective nucleon-nucleon force of the Skyrme type is derived from the quark-meson coupling model -- a self-consistent, relativistic quark level description of nuclear matter. This new formulation requires no assumption that the mean scalar field is small and hence constitutes a significant advance over earlier work. The similarity of the effective interaction to the widely used SkM$^*$ force encourages us to apply it to a wide range of nuclear problems, beginning with the binding energies and charge distributions of doubly magic nuclei. Read More

As we search for an ever deeper understanding of the structure of hadronic matter one of the most fundamental questions is whether or not one can make a connection to the underlying theory of the strong interaction, QCD. We build on recent advances in the chiral extrapolation problem linking lattice QCD at relatively large ``light quark'' masses to the physical world to estimate the scalar polarizability of the nucleon. The latter plays a key role in modern relativistic mean-field descriptions of nuclei and nuclear matter (such as QMC) and, in particular, leads to a very natural saturation mechanism. Read More

We discuss the two-photon exchange contribution to observables which involve lepton helicity flip in elastic lepton-nucleon scattering. This contribution is accessed through the spin asymmetry for a lepton beam polarized normal to the scattering plane. We estimate this beam normal spin asymmetry at large momentum transfer using a parton model and we express the corresponding amplitude in terms of generalized parton distributions. Read More

We formulate the quark meson coupling model as a many-body effective Hamiltonian. This leads naturally to the appearance of many-body forces. We investigate the zero range limit of the model and compare its Hartree-Fock Hamiltonian to that corresponding to the Skyrme effective force. Read More

The apparent discrepancy between the Rosenbluth and the polarization transfer method for the ratio of the electric to magnetic proton form factors can be explained by a two-photon exchange correction which does not destroy the linearity of the Rosenbluth plot. Though intrinsically small, of the order of a few percent of the cross section, this correction is kinematically enhanced in the Rosenbluth method while it is small for the polarization transfer method, at least in the range of (Q^2) where it has been used until now. Read More

Using a soft pion theorem based on chiral symmetry and a $\Delta(1232)$ resonance model we propose an estimate for the production cross section of low energy pions in the deeply virtual Compton scattering (DVCS) process. In particular, we express the $e p \to e \gamma \pi N$ processes in terms of generalized parton distributions. We provide estimates of the contamination of the $e p \to e \gamma p$ DVCS observables due to this associated pion production processes when the experimental data are not fully exclusive, for a set of kinematical conditions representative of present or planned experiments at JLab, HERMES and COMPASS. Read More

We study the nuclear modification of the scalar QCD susceptibility, calculated as the derivative of the quark condensate with respect to the quark mass. We show that it has two origins. One is the low lying nuclear excitations. Read More

This paper presents the reactions which can be performed at COMPASS to study the Generalized Parton Distributions (GPDs). The high energy muon beam at CERN allows to measure Hard Exclusive Meson Production or Deeply Virtual Compton Scattering (DVCS) in the Bjorken regime in a large range of Q^2 and x_Bj (1.5Read More

Using the linear sigma model, we study the evolutions of the quark condensate and of the nucleon mass in the nuclear medium. Our formulation of the model allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It guarantees that the low energy theorems and the constrains of chiral perturbation theory are respected. Read More

We give predictions for the leading order amplitudes for deeply virtual Compton scattering and hard meson electroproduction reactions at large Q^2 in the valence region in terms of skewed quark distributions. We give first estimates for the power corrections to these leading order amplitudes. In particular, we outline examples of experimental opportunities to access the skewed parton distributions at the current high-energy lepton facilities : JLab, HERMES and COMPASS. Read More

We estimate the leading order amplitudes for exclusive photon and meson electroproduction reactions at large Q^2 in the valence region in terms of skewed quark distributions. As experimental investigations can currently only be envisaged at moderate values of Q^2, we estimate power corrections due to the intrinsic transverse momentum of the partons in the meson wavefunction and in the nucleon. To this aim the skewed parton distribution formalism is generalized so as to include the parton intrinsic transverse momentum dependence. Read More

Chiral symmetry restoration in a dense medium is to some extent a consequence of the nuclear pion cloud. These pions induce a mixing of the axial and vector current contributions in the axial and vector correlators. We discuss their influence on hadron masses and investigate the signal produced by the remaining contribution associated with chiral symmetry restoration. Read More

We review the recent developments of virtual Compton scattering. We focus on the kinematical regimes which look the most promising. The threshold regime gives access to the generalized polarizabilities of the proton. Read More

We calculate the $N^*$ contributions to the generalized polarizabilities of the proton in virtual Compton scattering. The following nucleon excitations are included: $N^*(1535)$, $N^*(1650)$, $N^*(1520)$, $N^*(1700)$, $\Delta(1232)$, $\Delta^*(1620)$ and $\Delta^*(1700)$. The relationship between nucleon structure parameters, $N^*$ properties and the generalized polarizabilities of the proton is illustrated. Read More

Threshold photon electroproduction off the proton allows one to measure new electromagnetic observables which generalise the usual polarisabilities. There are -- a priori -- ten "generalised polarisabilities", functions of the virtual photon mass. The purpose of this paper is to lay down the appropriate formalism to extract these quantities from the photon electroproduction cross sections. Read More

We describe the development of a theoretical description of the structure of finite nuclei based on a relativistic quark model of the structure of the bound nucleons which interact through the (self-consistent) exchange of scalar and vector mesons. Read More

The quark-meson coupling model, based on a mean field description of non-overlapping nucleon bags bound by the self-consistent exchange of $\sigma$, $\omega$ and $\rho$ mesons, is extended to investigate the properties of finite nuclei. Using the Born-Oppenheimer approximation to describe the interacting quark-meson system, we derive the effective equation of motion for the nucleon, as well as the self-consistent equations for the meson mean fields. The model is first applied to nuclear matter, after which we show some initial results for finite nuclei. Read More

The amplitudes for virtual Compton scattering off protons are calculated within the framework of the diquark model in which protons are viewed as being built up by quarks and diquarks. The latter objects are treated as quasi-elementary constituents of the proton. Virtual Compton scattering, electroproduction of photons and the Bethe-Heitler contamination are discussed for various kinematical situations. Read More