“…The twist-4 contribution is required in order to generate the proton's anomalous magnetic moment and its Pauli form factor. This predicts a larger value of Q 2 in order to produce color transparency for the proton, consistent with the recent JLab electroproduction measurement [9]. In fact, the proton is predicted to have a "two-stage" color transparency starting at Q 2 > 14 GeV 2 for the twist-3 valence Fock state with orbital angular momentum L = 0 and at Q 2 > 22 GeV 2 for the full onset of CT for its L = 0 and L = 1 twist-4 components.…”
Section: Discussion Of the Resultssupporting
confidence: 86%
“…[3,4,8]. However, a recent measurement of the electroproduction of protons by the Hall C Collaboration at JLab [9], does not observe CT in quasielastic 12 C(e, e p) for Q 2 up to 14.2 GeV 2 , thus setting strong constraints for the onset of color transparency for baryons.…”
The color transparency (CT) of a hadron, propagating with reduced absorption in a nucleus, is a fundamental property of QCD, reflecting its internal structure and effective size when it is produced at high transverse momentum Q. CT has been confirmed in many experiments, such as semi-exclusive hard electroproduction, eA → e πX for mesons produced at Q 2 > 3 GeV 2 . However, a recent JLab measurement for a proton electroproduced in carbon eC → e pX fails to observe CT at Q 2 up to 14.2 GeV 2 . In this article we determine the onset of CT by comparing the Q 2 dependence of the hadronic cross sections for the initial formation of a small color-singlet configuration using the generalized parton distributions from holographic light-front QCD. We find a critical dependence on the hadron's twist τ , the number of its constituents, for the onset of CT, with no significant effects from the nuclear medium. This effect can explain the absence of proton CT in the present kinematic range of the JLab experiment. The proton is predicted to have a "two-stage" color transparency with the onset of CT differing for the spin-conserving (twist-3) Dirac form factor with a later onset for the spin-flip Pauli (twist-4) form factor.
“…The twist-4 contribution is required in order to generate the proton's anomalous magnetic moment and its Pauli form factor. This predicts a larger value of Q 2 in order to produce color transparency for the proton, consistent with the recent JLab electroproduction measurement [9]. In fact, the proton is predicted to have a "two-stage" color transparency starting at Q 2 > 14 GeV 2 for the twist-3 valence Fock state with orbital angular momentum L = 0 and at Q 2 > 22 GeV 2 for the full onset of CT for its L = 0 and L = 1 twist-4 components.…”
Section: Discussion Of the Resultssupporting
confidence: 86%
“…[3,4,8]. However, a recent measurement of the electroproduction of protons by the Hall C Collaboration at JLab [9], does not observe CT in quasielastic 12 C(e, e p) for Q 2 up to 14.2 GeV 2 , thus setting strong constraints for the onset of color transparency for baryons.…”
The color transparency (CT) of a hadron, propagating with reduced absorption in a nucleus, is a fundamental property of QCD, reflecting its internal structure and effective size when it is produced at high transverse momentum Q. CT has been confirmed in many experiments, such as semi-exclusive hard electroproduction, eA → e πX for mesons produced at Q 2 > 3 GeV 2 . However, a recent JLab measurement for a proton electroproduced in carbon eC → e pX fails to observe CT at Q 2 up to 14.2 GeV 2 . In this article we determine the onset of CT by comparing the Q 2 dependence of the hadronic cross sections for the initial formation of a small color-singlet configuration using the generalized parton distributions from holographic light-front QCD. We find a critical dependence on the hadron's twist τ , the number of its constituents, for the onset of CT, with no significant effects from the nuclear medium. This effect can explain the absence of proton CT in the present kinematic range of the JLab experiment. The proton is predicted to have a "two-stage" color transparency with the onset of CT differing for the spin-conserving (twist-3) Dirac form factor with a later onset for the spin-flip Pauli (twist-4) form factor.
“…Another example is the semi-inclusive electron scattering at Jefferson Lab (JLAB), where reactions such as (e,e'p) on nuclear targets need a firm basis to describe the background. These experiments aim for solving fundamental questions, such as about color transparency [129], short-range correlations [130], and hadronization inside a nuclear medium [131]. Experiments in the fixed target mode at the planned Electron-Ion Collider (EIC) will also need a good description of final state interactions.…”
Transport models are the main method to obtain physics information on the nuclear equation of state and in-medium properties of particles from low to relativistic-energy heavy-ion collisions. The Transport Model Evaluation Project (TMEP) has been pursued to test the robustness of transport model predictions in reaching consistent conclusions from the same type of physical model. To this end, calculations under controlled conditions of physical input and set-up were performed with various participating codes. These included both calculations of nuclear matter in a box with periodic boundary conditions, which test separately selected ingredients of a transport code, and more realistic calculations of heavy-ion collisions. Over the years, five studies have been performed within this project. In this intermediate review, we summarize and discuss the present status of the project. We also provide condensed descriptions of the 26 participating codes, which contributed to some part of the project. These include the major codes in use today. After a compact description of the underlying transport approaches, we review the main results of the studies completed so far. They show, that in box calculations the differences between the codes can be well understood and a convergence of the results can be reached. These studies also highlight the systematic differences between the two families of transport codes, known under the names of Boltzmann-Uehling-Uhlenbeck (BUU) and Quantum Molecular Dynamics (QMD) type codes. However, when the codes were compared in full heavy-ion collisions using different physical models, as recently for pion production, they still yielded substantially different results. This calls for further comparisons of heavy-ion collisions with controlled models and of box comparisons of important ingredients, like momentum-dependent fields, which are currently underway. Our evaluation studies often indicate improved strategies in performing transport simulations and thus can provide guidance to code developers. Results of transport simulations of heavy-ion collisions from a given code will have more significance if the code can be validated against benchmark calculations such as the ones summarized in this review.
“…In a recent JLab Hall C experiment [16], the nuclear transparency for the 12 C(e, e p) process at Q 2 = 8-14 GeV 2 appeared to be close to constant value which excludes CT. In hindsight, this result may not be so unexpected since in the BNL data [17] for C(p, pp) at Θ c.m.…”
Exclusive channels of antiproton annihilation on the bound nucleon are sensitive to mesonic interactions with the target residue. If the hard scale is present, then such interactions should be reduced due to color transparency (CT). In this paper, the d(p¯,π−π0)p reaction is discussed at a large center-of-mass angle. Predictions for the future PANDA (antiProton ANnihilations at DArmstadt) experiment at FAIR (Facility for Antiproton and Ion Research, Germany) are given for nuclear transparency ratios calculated within the generalized eikonal approximation and the quantum diffusion model of CT.
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