Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session JC: Mini-symposium: The Energy Momentum Tensor of Hadrons II |
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Chair: Yoshitaka Hatta, BNL Room: Studio 2 |
Wednesday, October 13, 2021 9:30AM - 9:42AM |
JC.00001: Holographic energy momentum tensor of the nucleon ismail zahed, Kiminad Mamo We derive the energy momentum tensor of the nucleon using holographic QCD, and use it to estimate the nucleon gravitational radius. The ensuing gravitational form factors are compared with the recently reported lattice results. We show that the treshold photo-production of heavy mesons reported by GlueX provides a direct measurement of the tensor part of the gravitational form factor in the holographic approach. |
Wednesday, October 13, 2021 9:42AM - 9:54AM |
JC.00002: Distribution of strong forces on quarks in the proton from DVCS experiments. Volker D Burkert, Latifa Elouadrhiri, Francois-Xavier Girod The structure of the proton, the nucleus of the hydrogen atom, has been studied in electron scattering for over 60 years, and resulted in a wealth of knowledge of its substructure expressed in electromagnetic form factors and in parton distribution functions (PDFs). Yet, there is a complete lack of knowledge of the protons mechanical or gravitational properties. These are expressed in terms of internal forces, angular momentum and mass distributions. This situation has only recently changed with experiments that study the protons internal structure in deeply virtual Compton scattering (DVCS), a process that is linked to the gravitational structure through sum rules of GPDs. The extraction of radial and shear forces makes use of the connection of the DVCS process to the unpolarized GPD H(x,x,t) and, through a sum rule to the gravitational form factor d1(t). This form factor is one of the 3 scalar form factors of the proton’s energy-momentum tensor, and it encodes the distribution of forces and pressure inside the proton. In this talk we present the first extraction of the shear forces in the proton from the DVCS data taken with CLAS at Jefferson Lab, and discuss prospects of employing new data at higher precision from CLAS12 covering a larger kinematic range. |
Wednesday, October 13, 2021 9:54AM - 10:06AM |
JC.00003: Partonic Pressure in the Nucleon: Results and Future Plans Latifa Elouadrhiri, Volker D Burkert, Francois - Xavier Girod Protons and neutrons, generally referred to as nucleons, are the fundamental building blocks of nuclei and make up nearly 100% of the mass of normal matter in the universe. They are composed of elementary objects, quarks and gluons. The latter are the carrier of the strong force that governs the dynamics binding quarks and gluons together. It is well established that quarks do not exist in isolation but only in the confines of nucleons and mesons (hadrons) of finite size. Mechanical properties of the proton such as pressure, forces between quarks and the angular momentum distributions are largely unknown. |
Wednesday, October 13, 2021 10:06AM - 10:18AM |
JC.00004: Gravitational Form Factors of Hadrons from Lattice QCD Dimitra A Pefkou, Daniel Hackett, Phiala E Shanahan The gravitational structure of hadrons is encoded in the gravitational form factors (GFFs), which are the form factors of the energy-momentum tensor of QCD. Just like the energy-momentum tensor, GFFs can be split into individual quark and gluon contributions, and are directly related to the frame dependent energy, angular momentum, pressure and shear force densities within hadrons. We use lattice QCD techniques to calculate the gluon GFFs of the pion, nucleon, rho meson and delta baryon in the spacelike kinematic region of 0 < -t < 2 GeV^2 at an unphysical pion mass of 450 MeV and 2+1 fermion flavors. From the renormalized GFFs, we extract the energy, pressure and shear force densities in different frames, as well as the mass and mechanical radii, and compare between the different hadrons and frames. |
Wednesday, October 13, 2021 10:18AM - 10:30AM |
JC.00005: Relativity demands two-dimensional densities Gerald A Miller, Adam Freese We explain why using a light front formulation is necessary to properly define true densities that involve absolute squares of wave functions. Light front coordinates allow separation between barycenter and relative coordinates, which is necessary to remove artifacts of state preparation from the densities. This applies to densities associated with every elastic proton form factor, including the electromagnetic, axial and EMT form factors. |
Wednesday, October 13, 2021 10:30AM - 10:42AM |
JC.00006: Two-dimensional relativistic densities of the EMT Adam J Freese, Gerald A Miller We explain how to obtain properly relativistic two-dimensional densities associated with the energy-momentum tensor (EMT), including momentum, angular momentum, and pressure densities. We present results for these densities in the proton using phenomenological form factors, and contrast the relativistic densities to their three-dimensional non-relativistic counterparts. |
Wednesday, October 13, 2021 10:42AM - 10:54AM |
JC.00007: Equation of State of Neutron Stars from the Quantum Chromodynamics Energy-Momentum Tensor Simonetta Liuti, Abha Rajan The recent detection of gravitational waves from merging neutron-star events, in particular the GW170817 neutron-star-merger, has opened a new window on the many unknown aspects of their internal dynamics. We established a connection between hadronic physics observables describing pressure, energy, as well as other mechanical properties of the nucleon through the matrix elements of the QCD Energy-Momentum Tensor, and the high-density regime inside neutron stars which is assumed to be dominated by quark and gluon degrees of freedom. |
Wednesday, October 13, 2021 10:54AM - 11:06AM |
JC.00008: The D-term form factor in the presence of electromagnetic long-range forces: a case study in a classical model of the proton Mira Varma, Peter J Schweitzer The prospects of accessing information on the hadronic form factors of the energy-momentum tensor (EMT) have attracted sizable attention in recent literature. This concerns especially the D-term form factor D(t) with its appealing interpretation in terms of internal forces. With the focus on hadron structure, so far theoretical and model studies concentrated on strongly interacting systems with short-range forces and neglected to consider long-range forces like electromagnetic interaction. But the long-range nature of electromagnetic forces introduces features that were not encountered before. We show how the presence of long-range forces alters some notions of the EMT which are taken for granted in short-range systems. We focus our attention on the D-term form factor. The important conclusion is that a more careful definition of the D-term may be required when long-range forces are present. |
Wednesday, October 13, 2021 11:06AM - 11:18AM |
JC.00009: Nucleon Gravitational Form Factor studies at the EIC Francois-Xavier Girod, Volker D Burkert, Latifa Elouadrhiri We demonstrate the potential of low center of mass and high luminosity data at the Electron Ion Collider to constrain Nucleon Gravitational Form Factors (GFFs), using Deeply Virtual Compton Scattering (DVCS). The Energy Momentum Tensor is parameterized by three GFFs corresponding to the distributions of mass, angular momentum, and spatial distributions forces. We will focus our discussion on expected constraints to the pressure and shear force distributions, which together translate into normal and tangential force distributions. We perform local fits to Compton Form Factors (CFFs) using pseudo data generated according to current detector designs, and explore the expected kinematical phase space coverage. We also discuss how the availability of a positron beam at the EIC can further help reduce systematic uncertainties in the extraction of the real part of the DVCS amplitudes. |
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