Download or read book Virtual Compton Scattering in the Resonance Region Up to the Deep Inelastic Region at Backward Angles and Momentum Transfer Squared of Q 2 written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region Up to the Deep Inelastic Region at Backward Angles written by and published by . This book was released on 2009 with total page 15201 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Deeply Virtual Compton Scattering at Small X written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1970 with total page 1202 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Measurement of Virtual Compton Scattering Below Pion Threshold at Invariant Four momentum Transfer Squared Q2 written by Christophe Jutier and published by . This book was released on 2001 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Deeply Virtual Compton Scattering at 6 GeV written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Virtual Compton Scattering in the Nucleon Resonance Region written by Luminita Anca Todor and published by . This book was released on 2000 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Physics Briefs written by and published by . This book was released on 1982 with total page 1126 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scaling Limit of Deeply Virtual Compton Scattering written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Light Cone Wavefunction Representation of Deeply Virtual Compton Scattering written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors give a complete representation of virtual Compton scattering gamma*p --> gamma-p at large initial photon virtuality Q2 and small momentum transfer squared t in terms of the light-cone wavefunctions of the target proton. They verify the identities between the skewed parton distributions H(x, zeta, t) and E(x, zeta, t) which appear in deeply virtual Compton scattering and the corresponding integrands of the Dirac and Pauli form factors F1(t) and F2(t) and the gravitational form factors A{sub q}(t) and B{sub q}(t) for each quark and anti-quark constituent. The authors illustrate the general formalism for the case of deeply virtual Compton scattering on the quantum fluctuations of a fermion in quantum electrodynamics at one loop.
Download or read book Deep Inelastic Scattering written by Robin Devenish and published by OUP Oxford. This book was released on 2003-11-20 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book is 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'.
Download or read book Deeply Virtual Compton Scattering at Jefferson Lab written by Frédéric Georges and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Unitary Constraints on Deeply Virtual Compton Scattering written by and published by . This book was released on 2007 with total page 52201 pages. Available in PDF, EPUB and Kindle. Book excerpt: At moderately low momentum transfer ($-t$ up to 1 GeV$^2$) the coupling to the vector meson production channels gives the dominant contribution to real Compton and deeply virtual Compton scattering (DVCS). Starting from a Regge Pole approach that successfully describes vector meson production, the singular part of the corresponding box diagrams (where the intermediate vector meson-baryon pair propagates on-shell) is evaluated without any further assumptions (unitarity). Such a treatment explains not only the unexpectedly large DVCS unpolarized cross section that has been recently measured at Jefferson Laboratory (JLab), but also all the beam spin and charge asymmetries that has been measured at JLab and Hermes, without explicit need of Generalized Parton Distributions (GPD). The issue of the relationship between the two approaches is addressed.
Download or read book Virtual Compton Scattering written by L. Van Hoorebeke and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Virtual Compton Scattering o013 the proton has been studied at Q 2 -values of 1:0 and 1:9 (GeV=c) 2 in Hall A at the Thomas Je013erson National Accelerator Facility (JLab). Data were taken below and above the pion production threshold as well as in the resonance region. Results obtained below pion threshold at Q 2 = 1:0 (GeV=c) 2 are presented in this paper.
Download or read book Dispersion Approach to Real and Virtual Compton Scattering written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, new precision experiments have become possible withthe high luminosity accelerator facilities at MAMIand JLab, supplyingphysicists with precision data sets for different hadronic reactions inthe intermediate energy region, such as pion photo- andelectroproduction and real and virtual Compton scattering. By means of the low energy theorem (LET), the global properties of thenucleon (its mass, charge, and magnetic moment) can be separated fromthe effects of the internal structure of the nucleon, which areeffectively described by polarizabilities. Thepolarizabilities quantify the deformation of the charge andmagnetization densities inside the nucleon in an applied quasistaticelectromagnetic field. The present work is dedicated to develop atool for theextraction of the polarizabilities from these precise Compton data withminimum model dependence, making use of the detailed knowledge of pionphotoproduction by means of dispersion relations (DR). Due to thepresence of t-channel poles, the dispersion integrals for two ofthe six Compton amplitudes diverge. Therefore, we have suggested to subtract the s-channel dispersion integrals at zero photon energy($nu=0$). The subtraction functions at $nu=0$ are calculated through DRin the momentum transfer t at fixed $nu=0$, subtracted at t=0. For this calculation, we use the information about the t-channel process, $gammagammatopipito Nbar{N}$. In this way, four of thepolarizabilities can be predicted using the unsubtracted DR in the $s$-channel. The other two, $alpha-beta$ and $gamma_pi$, are free parameters in ourformalism and can be obtained from a fit to the Compton data. We present the results for unpolarized and polarized RCS observables, %in the kinematics of the most recent experiments, and indicate anenhanced sensitivity to the nucleon polarizabilities in theenergy range between pion production threshold and the $Delta(1232)$-resonance.newlineindentFurthermore, we extend the DR formalism to virtual Compton scatter.
Download or read book Deeply Virtual Compton Scattering at COMPASS written by Johannes Vincenzo Giarra and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Studying hard exclusive reactions in lepton-nulceon scattering like for e.g. hard exclusive photoproduction in Deeply Virtual Compton Scattering (DVCS), allows to study the 3-dimensional nucleon structure in the framework of Generalized Parton Distribution functions (GPDs). From the DVCS cross section, combinations of Compton Form Factors (CFFs) can be extracted, which are used to further constrain the related GPDs. In 2016 and 2017, COMPASS measured DVCS on a 2.5 m long liquid hydrogen target using high energy (160 GeV), positively and negatively charged polarized muon beams provided by the M2 beamline of the SPS at CERN. The scattered muons and the produced real photons were detected by the COMPASS spectrometer, which was supplemented by an additional electromagnetic calorimeter for the detection of large-angle photons. To perform an exclusive measurement of the full final state, the target was surrounded by a barrel-shaped time-of-flight system to detect the recoiling target protons. The exclusive photon event sample is extracted using a dedicated event selection to identify all participating particles. This event selection includes the use of exclusivity conditions like for e.g. restricting the missing mass and is further improved by a kinematic fit under the assumption of the topology of a exclusive photon event. Its quality is used as an additonal selecting criterium. The fit also improves the resolution of the event kinematics, in particular on the square of the four-momentum transfer to the proton |t|. The selected data sample does not only include DVCS events, but also contributions by radiative photons produced in the Bethe-Heitler (BH) process and a background contamination by photons originating from the decay of neutral pions. These contributions are determined using dedicated Monte-Carlo samples and are subtracted from the data sample to obtain the pure DVCS contribution. The DVCS cross section is extracted in bins of |t|, separately for each beam charge and polarization. These cross section values are averaged over both beam charges, which allows to extract the |t|-dependence of the charge spin cross section sum. Studying this dependence allows to extract the slope parameter B by a binned log-likelihood fit using an exponential ansatz of the from: e^-B|t|}. The slope parameter is dominated by the contribution of the imaginary part of CFF H. At the COMPASS kinematics, which covers the x_Bj}-domain of sea quarks, it is related to the transverse extension of the proton due to the quark distributions. In the present analysis about 2/3 of the available data in 2016 are used. The 2017 sample is expected to provide two to three times higher statistics, which will allow to extend the analysis and extract the dependence of the slope parameter on x_Bj}.
Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2352 pages. Available in PDF, EPUB and Kindle. Book excerpt:
