Virtual Compton Scattering in the Resonance Region Up to the Deep Inelastic Region at Backward Angles and Momentum Transfer Squared of Q**2 PDF Download
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Languages : en
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Category :
Languages : en
Pages : 15201
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We have made the first measurements of the virtual Compton scattering (VCS) process via the H(e, e'p)? exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the W-dependence at fixed Q2=1 GeV2, and for the Q2-dependence at fixed W near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed Q2-dependence is smooth. The measured ratio of H(e, e'p)? to H(e, e'p)?0 cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to Real Compton Scattering (RCS) at high energy and large angles, our VCS data at the highest W (1.8-1.9 GeV) show a striking Q2-independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.
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Languages : en
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The authors calculate the cross section of the deeply virtual Compton scattering at large energies and intermediate momentum transfers. In recent years the study of the deeply virtual Compton scattering (DVCS) became one of the most popular topics in QCD due to the fact that it is determined by skewed parton distributions which generalize usual parton densities introduced by Feynman. These new probes of the nucleon structure are accessible in exclusive processes such as DVCS and potentially they can give more information than the traditional parton densities. In this paper the authors consider the small-x DVCS where the energy of the incoming virtual photon E is very large in comparison to its virtuality Q2. To be specific, they calculate the DVCS amplitude in the region s” Q2” -t” m2 where s = 2mE, m is the nucleon mass, and t is the momentum transfer. The DVCS in this region is a semihard process which can be described by the BFKL (Balitsky-Fadin-Kuraev-Lipatov) pomeron. It turns out that at large momentum transfer the coupling of the BFKL pomeron to the nucleon is essentially equal to the Dirac form factor of the nucleon F1(t), so the DVCS amplitude in the region can be calculated without any model assumptions. The results obtained in this region can be used for the estimates of the amplitude at experimentally accessible energies where one or more conditions in Eq. (1) are relaxed. To be specific, they have in mind the HERA kinematics where x H"10−2 ̦ 10−4, Q2 e"6 GeV2, and -t H"1 ̦ 5 GeV2. Since there are only model predictions for the small-x DVCS in current literature, even the approximate calculations of the cross section in QCD are very timely.
Author: Robin Devenish
Publisher: OUP Oxford
ISBN: 0191621951
Category : Science
Languages : en
Pages : 418
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This book provides an up-to-date, self-contained account of deep inelastic scattering in high-energy physics, intended for graduate students and physicists new to the subject. It covers the classic results which led to the quark-parton model of hadrons and the establishment of quantum chromodynamics as the theory of the strong nuclear force, in addition to new vistas in the subject opened up by the electron-proton collider HERA. The extraction of parton momentum distribution functions, a key input for physics at hadron colliders such as the Tevatron at Fermi Lab and the Large Hadron Collider at CERN, is described in detail. The challenges of the HERA data at 'low x' are described and possible explanations in terms of gluon dynamics and other models outlined. Other chapters cover: jet production at large momentum transfer and the determination of the strong coupling constant, electroweak interactions at very high momentum transfers, the extension of deep inelastic techniques to include hadronic probes, a summary of fully polarised inelastic scattering and the spin structure of the nucleon, and finally a brief account of methods in searching for signals 'beyond the standard model'.
Author: Christophe Jutier
Publisher:
ISBN:
Category : Electrons, Compton
Languages : en
Pages : 458
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Category : Nuclear energy
Languages : en
Pages : 1590
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Author: Luminita Anca Todor
Publisher:
ISBN:
Category : Electrons, Compton
Languages : en
Pages : 378
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Category :
Languages : en
Pages :
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The authors propose a measurement of the Deep Virtual Compton Scattering process (DVCS) ep → ep[gamma] in Hall A at Jefferson Lab with a 6 GeV beam. The authors are able to explore the onset of Q2 scaling, by measuring a beam helicity asymmetry for Q2 ranging from 1.5 to 2.5 GeV2 at x{sub B} ≈ 0.35. At this kinematics, the asymmetry is dominated by the DVCS Bethe-Heitler (BH) interference, which is proportional to the imaginary part of the DVCS amplitude amplified by the full magnitude of the BH amplitude. The imaginary part of the DVCS amplitude is expected to scale early. Indeed, the imaginary part of the forward Compton amplitude measured in deep inelastic scattering (via the optical theorem) scales at Q2 as low as 1 GeV2. If the scaling regime is reached, they make an 8% measurement of the skewed parton distributions (SPD) contributing to the DVCS amplitude. Also, this experiment allows them to separately estimate the size of the higher-twist effects, since they are only suppressed by an additional factor 1/Q compared to the leading-twist term, and have a different angular dependence. They use a polarized electron beam and detect the scattered electron in the HRSe, the real photon in an electromagnetic calorimeter (under construction) and the recoil proton in a shielded scintillator array (to be constructed). This allows them to determine the difference in cross-sections for electrons of opposite helicities. This observable is directly linked to the SPD's. The authors estimate that 25 days of beam (600 hours) are needed to achieve this goal.
Author:
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ISBN:
Category : Nuclear energy
Languages : en
Pages : 1100
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Author: Frédéric Georges
Publisher:
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Category :
Languages : en
Pages : 0
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Introduced in the mid 90's, Generalized Parton Distributions (GPDs) are now a key element in the study of the nucleon internal structure. GPDs are a generalization of Form Factors and Parton Distribution Functions. They encapsulate both spatial and momentum distributions of partons inside a nucleon, allowing to perform its three-dimensional tomography. Furthermore, they allow to derive the total orbital angular momentum of quarks through the Ji sum rule, which is a crucial point to unravel the nucleon spin structure. By providing a more complete description of hadrons in terms of quarks and gluons, a deeper understanding of Quantum Chromodynamics can be reached.GPDs are experimentally accessible through deeply exclusive electro-production processes, and one of the simplest channels available is Deeply Virtual Compton Scattering (DVCS). A worldwide experimental program was started in the early 2000's to extract these GPDs. The DVCS experiment E12-06-114 performed at Jefferson Laboratory Hall A (Virginia, USA) between 2014 and 2016, is encompassed in this program. The aim of this experiment is to extract with high precision the DVCS helicity-dependent cross sections as a function of the momentum transfer Q2, for fixed values of the Bjorken variable xBj, on a proton target. The recent upgrade of the accelerator facility to 12 GeV allows to cover a larger Q2 range than in previous measurements and probe yet unexplored kinematic regions, while the polarized electron beam allows the separation of the contributions from the real and imaginary parts of the DVCS amplitude to the total cross section. In this document, a brief summary of the worldwide experimental program for the study of GPDs will be provided, followed by a description of the E12-06-114 apparatus and data analysis. Finally, the results of the unpolarized and polarized cross-section measurements are presented and compared to a few selected models.
