The pressure distribution inside the proton

Gravitational Form Factors of the Proton from Lattice QCD

The gravitational form factors (GFFs) of a hadron encode fundamental aspects of its structure, including its shape and size as defined from, e.g., its energy density. This Letter presents a determination of the flavor decomposition of the GFFs of the proton from lattice QCD, in the kinematic region 0≤-t≤2  GeV^{2}. The decomposition into up-, down-, strange-quark, and gluon contributions provides first-principles constraints on the role of each constituent in generating key proton structure observables, such as its mechanical radius, mass radius, and D term.

Extraction of the Parton Momentum-Fraction Dependence of Generalized Parton Distributions from Exclusive Photoproduction

The x dependence of hadrons' generalized parton distributions (GPDs) F(x,ξ,t) is the most difficult to extract from the existing known processes, while the ξ and t dependence are uniquely determined by the kinematics of the scattered hadron. We study the single diffractive hard exclusive processes for extracting GPDs in the photoproduction. We demonstrate quantitatively the enhanced sensitivity on extracting the x dependence of various GPDs from the photoproduction cross sections, as well as the asymmetries constructed from photon polarization and hadron spin that could be measured at JLab Hall D by GlueX Collaboration and future facilities.

First Measurement of Timelike Compton Scattering

We present the first measurement of the timelike Compton scattering process, γp→p^{'}γ^{*}(γ^{*}→e^{+}e^{-}), obtained with the CLAS12 detector at Jefferson Lab. The photon beam polarization and the decay lepton angular asymmetries are reported in the range of timelike photon virtualities 2.25<Q^{'2}<9  GeV^{2}, squared momentum transferred 0.1<-t<0.8  GeV^{2}, and average total center-of-mass energy squared s=14.5  GeV^{2}. The photon beam polarization asymmetry, similar to the beam-spin asymmetry in deep virtual Compton scattering, is sensitive to the imaginary part of the Compton form factors and provides a way to test the universality of the generalized parton distributions. The angular asymmetry of the decay leptons accesses the real part of the Compton form factors and thus the D-term in the parametrization of the generalized parton distributions.

Separation of Quark Flavors Using Deeply Virtual Compton Scattering Data

Using the available data on deeply virtual Compton scattering (DVCS) off protons and utilizing neural networks enhanced by the dispersion relation constraint, we determine six out of eight leading Compton form factors in the valence quark kinematic region. Furthermore, adding recent data on DVCS off neutrons, we separate contributions of up and down quarks to the dominant form factor, thus paving the way towards a three-dimensional picture of the nucleon.

N* Experiments and what they tell us about Strong QCD Physics

I give an overview on experimental studies of the spectrum and the structure of the excited states of the nucleon and what we can learn about their in ternal structure. One focus is on the efforts to obtain a more complete picture of the light-quark baryon exci tation spectrum employing electromagnetic beams that will allow us to draw some conclusions on the symme tries underlying the spectrum. For the higher mass ex citations, the full employment of coupled channel ap proaches is essential when searching for new excited states in the large amounts of data already accumulated in different channels involving a variety of polarization observables. The other focus is on the study of transition form factors and helicity amplitudes and their de pendences on Q2, especially on some of the more promi nent resonances, especially Δ(1232)3/2+, N(1440)1/2+, and negative parity states N(1535)1/2-, and N(1675)5/2-.These were obtained in pion and eta electroproduction experi ments off proton targets and have already led to further insights in the active degrees-of-freedom as a function of the distance scale involved.

Mass-Energy Equivalence Extension onto a Superfluid Quantum Vacuum

In contemporary physics, the model of space–time as the fundamental arena of the universe is replaced by some authors with the superfluid quantum vacuum. In a vacuum, time is not a fourth dimension of space, it is merely the duration of the physical changes, i.e. motion in a vacuum. Mass–energy equivalence has its origin in the variable density of the vacuum. Inertial mass and gravitational mass are equal and both originate in the vacuum fluctuations from intergalactic space towards stellar objects.

Pressure Distribution and Shear Forces inside the Proton

The distributions of pressure and shear forces inside the proton are investigated using lattice quantum chromodynamics (LQCD) calculations of the energy momentum tensor, allowing the first model-independent determination of these fundamental aspects of proton structure. This is achieved by combining recent LQCD results for the gluon contributions to the energy momentum tensor with earlier calculations of the quark contributions. The utility of LQCD calculations in exploring, and supplementing, the assumptions in a recent extraction of the pressure distribution in the proton from deeply virtual Compton scattering is also discussed. Based on this study, the target kinematics for experiments aiming to determine the pressure and shear distributions with greater precision at Thomas Jefferson National Accelerator Facility and a future electron ion collider are investigated.

Cul-De-Sac of the Spatial Image of Proton Interactions

The unitarity condition in the impact parameter space is used to obtain some information about the shape of the interaction region of colliding protons. It is shown that, strictly speaking, a reliable conclusion can be gained only if the behavior of the elastic scattering amplitude (especially, its imaginary part) at all transferred momenta is known. This information is currently impossible to obtain from experimentation. In practice, several assumptions and models are used. They lead to different results as shown below.