Deeply Virtual Compton Scattering

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Deeply virtual Compton scattering off the neutron

Deeply virtual Compton scattering off the neutron

Deeply virtual Compton scattering (DVCS) is the sim- plest reaction to access GPDs (Fig. 1). In the Bjorken limit, similar to DIS, where −t ≪ Q 2 and Q 2 is much larger than the quark confinement scale, the factoriza- tion theorem separates the reaction amplitude into the convolution of a known perturbative γ ∗ q → γq kernel with an unknown soft matrix element describing the nu- cleon structure (GPDs) [15, 16]. The Bethe-Heitler (BH) process, where the real photon is emitted by either the incoming or scattered electrons, serves as a reference am- plitude that interferes with the Compton amplitude. The difference between polarized cross sections for opposite
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Scaling tests of the cross section for deeply virtual compton scattering

Scaling tests of the cross section for deeply virtual compton scattering

ture functions, now called generalized parton distribu- tions (GPD), became of experimental interest when it was shown [1] that they are accessible through deeply virtual Compton scattering (DVCS) and its interference with the Bethe-Heitler (BH) process (Fig. 1). Figure 1 presents our kinematic nomenclature. DVCS is defined kinematically by the limit −t ≪ Q 2 and Q 2 much larger than the quark confinement scale.

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Measurements of the electron-helicity dependent cross sections of deeply virtual compton scattering with CEBAF at 12 GeV

Measurements of the electron-helicity dependent cross sections of deeply virtual compton scattering with CEBAF at 12 GeV

2 and low t , the nal photon is highly aligned with the virtual photon and therefore highly orrelated with the s attered ele tron. Thus, even with a modest alorimeter, our oin iden e a eptan e for DVCS is essentially limited only by the ele tron spe trometer. As a onsequen e, very high values of the produ t of luminosity times oin iden e a eptan e are possible. The radiation hard PbF 2 alorimeter gives a fast (Cerenkov) time response, and ea h hannel is re orded with a 1 GHz digitizer whi h allows o-line identi ation of the DVCS photon. The identi ation of the ex lusive hannel is illustrated in Fig. 3. In Hall A, our systemati errors are minimized by the ombination of the Compton polarimeter, the well-understood opti s and a eptan e of the High Resolution Spe trometer (HRS), and a ompa t, hermeti , alorimeter. All of those fa tors allowed the measurements of ross-se tions. The high-pre ision ele tron dete tion minimizes systemati errors on t and φ γγ . Therefore, we exploit the pre ision φ γγ -dependen e to extra t the ross se tion terms whi h have the form of a nite F ourier series modulated by the ele tron propagators of the BH amplitude.
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Beam spin asymmetries in deeply virtual Compton scattering (DVCS) with CLAS at 4.8 GeV

Beam spin asymmetries in deeply virtual Compton scattering (DVCS) with CLAS at 4.8 GeV

Contraction of the leptonic and hadronic tensors generates an azimuthal angular dependence of each of the three terms in Eq. ( 8 ) [ 10 ]. In a frame with the z axis along the virtual photon, the dependence of the amplitudes on φ yields a finite sum of Fourier harmonics. The amplitude of deeply virtual production of a photon has been derived up to twist-3 accuracy [ 8 ]. In the notation of Ref. [ 8 ], the helicity-dependent angular moments are presented in a series of sin(nφ), with n = 1, 2, 3. Only n = 1 is a twist-2 quark matrix element. The n = 2 terms are twist-3 and the n = 3 terms are twist-2 double-helicity-flip gluon transversity terms, which are kinematically suppressed. If these terms are omitted, then at the twist-2 level, the BH, DVCS, and interference contributions to the total cross section in Eq. ( 8 ) read
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Measurement of Deeply Virtual Compton Scattering Beam-Spin Asymmetries

Measurement of Deeply Virtual Compton Scattering Beam-Spin Asymmetries

π ℑmH = H(ξ, ξ, t) − H(−ξ, ξ, t) , (4) up to corrections of order of the strong coupling constant, with similar expressions for ˜ H, E and ˜ E. The GPD H yields the dominant contribution to the harmonic coef- ficients considered above. Neglecting the small contri- butions from the three other GPDs, one can express the beam-spin asymmetry A in terms of only ℜeH and ℑmH. Thus in this approximation, which is expected to hold for small values of |t|, the parameters a, c and d of Eq. (2) are uniquely related to the imaginary and real parts of the Compton form factor H, yielding respectively the GPD H at points x = ±ξ and the principal value integral of Eq. (3). Going beyond this approximation requires ad- ditional theoretical or experimental constraints on the other GPDs.
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Exclusive Neutral Pion Electroproduction in the Deeply Virtual Regime

Exclusive Neutral Pion Electroproduction in the Deeply Virtual Regime

PACS numbers: 13.60.Hb, 13.60.Le, 13.87.Fh, 14.20.Dh, 25.30.Rw I. INTRODUCTION The past decade has shown a strong evolution of the study of hadron structure through exclusive pro- cesses, allowing access to the three-dimensional structure of hadrons. Exclusive processes include deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP). This document focuses on the lat- ter, and more precisely on neutral pion production. We present measurements of the differential cross sec- tion for the forward exclusive electroproduction reaction
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The experimental challenge of virtual compton scattering above 8 GeV - (VCS above 8 GeV: the experimental challenge)

The experimental challenge of virtual compton scattering above 8 GeV - (VCS above 8 GeV: the experimental challenge)

In a contribution to the workshop CEBAF at 8 GeV [3] we stressed the ben- efits of the VCS approach. This paper will focus on the experimental challenges for VCS experiments above 8 GeV. Our interest in VCS is twofold: • Deeply Virtual Compton Scattering (DVCS) corresponding to the diffrac- tion of a virtual photon in the forward direction. DVCS[4] [5] [6] allows us to access the Off Forward Parton Distribution (OFPD) directly linked to the non perturbative part of the nucleon. The kinematic domain of DVCS is deep inelastic electron scattering (large s and Q 2 ) with the final
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Virtual coupling potential for elastic scattering of $^{10,11}$Be on proton and carbon targets

Virtual coupling potential for elastic scattering of $^{10,11}$Be on proton and carbon targets

Several theories were developed to have a deeper understanding of the continuum effects : for high- energy reaction studies (few 100A MeV) the role of the continuum coupling has been addressed in sev- eral few-body approaches, by implicitly including the coupling to all orders [23–25]. In the study of re- action mechanisms at lower energy (few 10A MeV), the coupling effects have been taken into account by explicitly coupling to a discretized continuum [3,26]. More generally, for the analysis of the one nucleon- transfer reactions and elastic scattering on light tar- gets like deuteron targets, a coupled-reaction frame- work [27] is needed. A complete study of the 10,11 Be
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Virtual compton scattering in the resonance region up to the deep inelastic region at backward angles and momentum transfer squared of $Q^2$ = 1.0 $GeV^2$

Virtual compton scattering in the resonance region up to the deep inelastic region at backward angles and momentum transfer squared of $Q^2$ = 1.0 $GeV^2$

the ep → epγ process in CM backward kinematics (~q ′ opposite to ~ q). In the one photon exchange approximation, the ep → epγ amplitude (Fig. 1a) includes the coherent superpo- sition of the VCS Born (Fig. 1b and 1c) and Non-Born (Fig. 1d) amplitudes, and the Bethe-Heitler (BH) am- plitude (Fig. 1e and 1f) [7]. Note that in the BH am- plitude, the mass of the virtual photon (elastically ab- sorbed by the proton) is t. In the VCS amplitude, the mass of the virtual photon (inelastically absorbed) is − Q 2 . The BH amplitude dominates over the VCS when the photon is emitted in either the direction of the inci- dent or scattered electron, and breaks the symmetry of the electroproduction amplitude around the virtual pho- ton direction. Thus, it is not possible to expand the φ γγ -dependence of the ep → epγ cross section in terms
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Deeply scaled CMOS for RF power applications

Deeply scaled CMOS for RF power applications

Gain, PAE and output power density at peak PAE as a function of Vdd for 250 nm devices with three different gate oxide thicknesses at 8 GHz. Impedances and input power drive were re[r]

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Measurement of the generalized polarizabilities of the proton in virtual compton scattering at $Q^2=0.92 and 1.76 GeV^2$: II. Dispersion relation analysis

Measurement of the generalized polarizabilities of the proton in virtual compton scattering at $Q^2=0.92 and 1.76 GeV^2$: II. Dispersion relation analysis

37 Institut fuer Kernphysik, University of Mainz, D-55099 Mainz, Germany 38 Harvard University, Cambridge, MA 02138 Virtual Compton Scattering is studied at the Thomas Jefferson National Accelerator Facility in the energy domain below pion threshold and in the ∆(1232) resonance region. The data analysis is based on the Dispersion Relation (DR) approach. The electric and magnetic Generalized Polarizabilities (GPs) of the proton and the structure functions P LL − P T T /ǫ and P LT are determined at four-

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Measurement of the generalized polarizabilities of the proton in virtual compton scattering at $Q^2=0.92 and 1.76 GeV^2$: I. Low energy expansion analysis

Measurement of the generalized polarizabilities of the proton in virtual compton scattering at $Q^2=0.92 and 1.76 GeV^2$: I. Low energy expansion analysis

The electric and magnetic polarizabilities of the nu- cleon reflect its response to a static electromagnetic field. These are fundamental observables of the ground state, closely related to the entire excitation spectrum of the nu- cleon. The polarizabilities of the proton have been mea- sured in Real Compton Scattering (RCS) experiments γp → γp; see e.g. [1]. Contrary to atomic polarizabilities, which are of the size of the atomic volume [2], the proton electric polarizability is much smaller than one cubic fm, the volume scale of a nucleon. In a simplified harmonic oscillator model, such a small electric polarizability is a natural indication of the intrinsic relativistic character of the nucleon. The smallness of the proton magnetic polar- izability β M relative to α E reflects a strong cancellation
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Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz

Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz

SLAC, 2575 Sand Hill Road, Menlo Park, California 94025, USA (Received 30 July 2014; published 1 December 2014) A design for a compact x-ray light source (CXLS) with flux and brilliance orders of magnitude beyond existing laboratory scale sources is presented. The source is based on inverse Compton scattering of a high brightness electron bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency standing- wave linac and rf photoinjector powered by a single ultrastable rf transmitter at X-band rf frequency. The high efficiency permits operation at repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire accelerator is approximately 1 meter long and produces hard x rays tunable over a wide range of photon energies. The colliding laser is a Yb ∶YAG solid-state amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as the accelerator. The laser pulse is frequency-doubled and stored for many passes in a ringdown cavity to match the linac pulse structure. At a photon energy of 12.4 keV, the predicted x-ray flux is 5 × 10 11 photons=second in a 5% bandwidth and the brilliance is 2 × 10 12 photons=ðsec mm 2 mrad 2 0.1%Þ in pulses with rms pulse length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic energy, 10 microamp average current, 0.5 microsecond macropulse length, resulting in average electron beam power of 180 W. Optimization of the x-ray output is presented along with design of the accelerator, laser, and x-ray optic components that are specific to the particular characteristics of the Compton scattered x-ray pulses.
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Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles

Virtual Compton Scattering and Neutral Pion Electroproduction in the Resonance Region up to the Deep Inelastic Region at Backward Angles

the cross section for the two reactions H(e, e ′ p)γ and H(e, e ′ p)π 0 . The γ-to-π 0 ratio shows strong variations with W across the resonance region. At our highest W (1.8-1.9 GeV) the comparison with wide-angle RCS may suggest that the VCS process undergoes a transition to a hard-scattering mechanism at the quark level. Therefore the data presented in this paper emphasize the interest of exploring a new kinematic domain of exclusive electroproduction reactions (high W , high Q 2 ,

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Initiation à une expérience de diffusion d'électrons : la diffusion Compton virtuelle

Initiation à une expérience de diffusion d'électrons : la diffusion Compton virtuelle

Intro du tion La stru ture du proton est en ore bien loin d'être onnue. Or, depuis quelques années, la mise en servi e d'a élérateurs d'éle trons de grand y le utile, 'est-à-dire dont les éle trons sont envoyés de façon pratiquement ontinue, a permis d'étudier expérimentalement la diusion Compton virtuelle qui permet de mesurer les propriétés de déformation éle tromagnétique du proton. L'a élérateur MAMI (Mainz Mi rotron) à Mayen e (en Allemagne) est idéal pour réaliser ette expérien e.

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L’ETUDE DE L’EFFET COMPTON DANS LE CADRE DE l’ELECTRODYNAMIQUE QUANTIQUE

L’ETUDE DE L’EFFET COMPTON DANS LE CADRE DE l’ELECTRODYNAMIQUE QUANTIQUE

FAIBLE Z°, W +, W- Table. I.2- caractéristique des bosons des trois interactions décrites par le modèle standard. I.3 Interaction photon dans la matière Le rayonnement électromagnétique γ ne possède pas de charge électrique peut être représente comme une onde électromagnétique. Il interagit dans la matière suivant trois processus principaux : l’effet photoélectrique, l’effet Compton, et la création de paires. L’importance relative de ces trois effets dépend de l’´energie du γ et du numéro atomique Z du milieu (fig. I.6).
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Experimental Evidence for a Liquid-Liquid Crossover in Deeply Cooled Confined Water

Experimental Evidence for a Liquid-Liquid Crossover in Deeply Cooled Confined Water

presence of calorimetric phase transitions. For ENS experiments we used the high hydrostatic pressure equipment developed at the Institut Laue Langevin (ILL) in Grenoble (France) [32] for neutron scattering studies of powder and solution samples. The cylindrical cell, built of the high-tensile aluminium alloy (7049-T6), is 4 mm thick and can withstand pressure loads up to 1.5 kbar. To transmit the pressure homogeneously, we used Fluorinert™ liquid [33] that has a pour point of 178 K and was tested to be completely inert. This avoids using gas for pressure transmission and therefore possible artifacts arising from gas diffusion inside the matrix pores; on the other hand, Fluorinert™ diffusion was excluded by weight- ing the sample before and after the measurements. The stick was put inside the closed cycle dry cryostat of the back- scattering spectrometer IN13 [34] at the ILL and cooled down to 210 or 250 K. When the temperature was reached, the compressor of the cryostat was stopped, so as to avoid the cold point and thus freezing of the liquid transmitting the pressure. The temperature was controlled to stay constant along the data collection time. We measured each pressure and temperature point for 5 –8 h, at 210 and 250 K, for pressure values between 20 and 1200 bar in steps of 300 bar. MSD values were obtained from elastic spectra with the usual procedure: MSD ¼ −6dln½IðQ; ω ¼ 0Þ=dQ 2 [where I ðQ; ω ¼ 0Þ is the scattering intensity at the elastic line, defined by the width of the resolution function Δω ¼ 8 μeV FWHM], in the limit of the Gaussian approximation when Q → 0 [35] . On the other hand, limiting the analysis to Q ≤ 1.1 Å −1 allows us to neglect contributions arising from rotational motions [13] , so that, in the diffusion limit, MSD is related to the translational diffusion coefficient D by the Einstein relation MSD ¼ 6Dτ res , where τ res ¼ 100 ps,
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en
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en fr Gamma-ray detection and Compton camera image reconstruction with application to hadron therapy. Détection des rayons gamma et reconstruction d'images pour la caméra Compton : Application à l'hadronthérapie. 

dépasse la capacité des systèmes d’imagerie médicale existants. Une technique avancée de détection des rayons gamma est proposée. Elle est basée sur la diffusion Compton avec possibilité de poursuite des électrons diffusés. Cette technique de détection Compton a été initialement appliquée pour observer les rayons gamma en astrophysique (télescope Compton). Un dispositif, inspiré de cette technique, a été modélisé avec une géométrie adaptée à l’Imagerie en HadronThérapie (IHT). Il se compose d’un diffuseur, où les électrons Compton sont mesurés et suivis (’tracker’), et d’un calorimètre, où les rayons gamma sont absorbés par effet photoélectrique. Un scénario d’hadronthérapie a été simulé par la méthode de Monte-Carlo, en suivant la chaîne complète de détection, de la reconstruction d’événements individuels jusqu’à la reconstruction d’images de la source de rayons gamma. L’algorithme ’Expectation Maximisation’ (EM) à été adopté dans le calcul de l’estimateur du maximum de vraisemblance (MLEM) en mode liste pour effectuer la reconstruction d’images. Il prend en compte la réponse du système d’imagerie qui décrit le comportement complexe du détecteur. La modélisation de cette réponse nécessite des calculs com- plexes, en fonction de l’angle d’incidence de tous les photons détectés, de l’angle Compton dans le diffuseur et de la direction des électrons diffusés. Dans sa forme la plus simple, la réponse du système à un événement est décrite par une conique, in- tersection du cône Compton et du plan dans lequel l’image est reconstruite. Une forte corrélation a été observée entre l’image de la source gamma reconstruite et la position du pic de Bragg. Les performances du système IHT dépendent du détecteur, en termes d’efficacité de détection, de résolution spatiale et énergétique, du temps d’acquisition et de l’algorithme utilisé pour reconstituer l’activité de la source de rayons gamma.
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Computation of acoustic scattering from elastic conical shells with endcaps using the hybrid finite element/ virtual source approach

Computation of acoustic scattering from elastic conical shells with endcaps using the hybrid finite element/ virtual source approach

The main objective of this research is to implement the FE method for elastic axi- symmetric conical shells with endcaps to derive the dynamic flexibility matrix [r]

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Analytical model for RF power performance of deeply scaled CMOS devices

Analytical model for RF power performance of deeply scaled CMOS devices

Massachusetts Institute of Technology, Cambridge, MA, 2 IBM T.J. Watson Research Center Abstract — This paper presents a first order model for RF power of deeply scaled CMOS. The model highlights the role of device on-resistance in determining the maximum RF power. We show excellent agreement between the model and the measured data on 45 nm CMOS devices across a wide range of device widths, under both maximum output power and maximum PAE conditions. The model allows circuit designers to quickly estimate the power and efficiency of a device layout without need for complicated compact models or simulations.
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