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Generation of Femtosecond X-Rays by 90 degrees Compton Scattering

Description: We propose Compton scattering of a short pulse visible laser beam by a low energy (but relativistic) electron beam at a right angle for generation of femtosecond x-rays. Simple analysis to determine the qualitative and quantitative characteristics of the x-ray pulse is presented.
Date: December 1, 1992
Creator: Kim, K.-J.; Chattopadhyay, S. & Shank, C.V.
Partner: UNT Libraries Government Documents Department

Deeply Virtual Compton Scattering and Meson Production at Jlab/CLAS

Description: This report reviews the recent experimental results from the CLAS collaboration (Hall B of Jefferson Lab, or JLab) on Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP) and discusses their interpretation in the framework of Generalized Parton Distributions (GPDs). The impact of the experimental data on the applicability of the GPD mechanism to these exclusive reactions is discussed. Initial results obtained from JLab 6 GeV data indicate that DVCS might already be interpretable in this framework while GPD models fail to describe the exclusive meson production (DVMP) data with the GPD parameterizations presently used. An exception is the {phi} meson production for which the GPD mechanism appears to apply. The recent global analyses aiming to extract GPDs from fitting DVCS CLAS and world data are discussed. The GPD experimental program at CLAS12, planned with the upcoming 12 GeV upgrade of JLab, is briefly presented.
Date: April 1, 2012
Creator: Jo, Hyon-Suk
Partner: UNT Libraries Government Documents Department

A Set of Monte Carlo Subroutines for Treating the Physics of Compton Scattering

Description: A set of portable Monte Carlo subroutines is presented to treat the physics of Compton scattering. Electron binding energies are included by the modification of the Klein-Nishina probability distribution by the incoherent scattering function. In addition the scattered photon's energy is calculated by taking into account the momentum distribution of the electron. These subroutines have been verified and validated by calculating the total cross section over incident photon energies of 10 keV to 100 MeV for elements of Z=l to Z=l 00 and are within 1.08% of published values.
Date: December 1, 1998
Creator: Lestone, John; Earnhart, Jonathan & Prettyman, Thomas
Partner: UNT Libraries Government Documents Department

FRONT-END ASIC FOR A SILICON COMPTON TELESCOPE.

Description: We describe a front-end application specific integrated circuit (ASIC) developed for a silicon Compton telescope. Composed of 32 channels, it reads out signals in both polarities from each side of a Silicon strip sensor, 2 mm thick 27 cm long, characterized by a strip capacitance of 30 pF. Each front-end channel provides low-noise charge amplification, shaping with a stabilized baseline, discrimination, and peak detection with an analog memory. The channels can process events simultaneously, and the read out is sparsified. The charge amplifier makes uses a dual-cascode configuration and dual-polarity adaptive reset, The low-hysteresis discriminator and the multi-phase peak detector process signals with a dynamic range in excess of four hundred. An equivalent noise charge (ENC) below 200 electrons was measured at 30 pF, with a slope of about 4.5 electrons/pF at a peaking time of 4 {micro}s. With a total dissipated power of 5 mW the channel covers an energy range up to 3.2 MeV.
Date: October 27, 2007
Creator: DE GERONIMO,G.; FRIED, J.; FROST, E.; PHLIPS, B.; VERNON, E. & WULF, E.A.
Partner: UNT Libraries Government Documents Department

HPGe compton suppression using pulse shape analysis

Description: We present a new technique for High Purity Germanium (HPGe) Compton suppression using pulse shape analysis (PSA). The novel aspect of our approach involves a complete unfolding of the charge pulse shape into a discrete sum of component y-ray interactions. Using the energy and position information obtained from such an unfolding, an algorithm is then applied which favorably rejects Compton escape events. The advantage of the current PSA approach, as compared with other recent approaches, is the potential to reject not only single-site escape events, but also multiple site escape events. Here we discuss the details of our algorithm, and present experimental results from a real-time implementation on a 5 cm X 5 cm HPGe. An experimental comparison with a standard BGO suppresser is shown. We also discuss the possible improvements to the current PSA approach that could be obtained if the HPGe could be highly segmented on the outer contact.
Date: April 15, 1998
Creator: Schmid, G.J.; Beckedahl, D.; Blair, J.J. & Kammeraad, J.E.
Partner: UNT Libraries Government Documents Department

High Power Picosecond Laser Pulse Recirculation

Description: We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering based light sources. We demonstrate up to 36x average power enhancement of frequency doubled sub-millijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.
Date: April 12, 2010
Creator: Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J et al.
Partner: UNT Libraries Government Documents Department

Low-Intensity Nonlinear Spectral Effects in Compton Scattering

Description: Nonlinear effects are known to occur in Compton scattering light sources, when the laser normalized 4-potential, A = e{radical}-A{sub {mu}}A{sup {mu}}/m{sub 0}c approaches unity. In this letter, it is shown that nonlinear spectral features can appear at arbitrarily low values of A, if the fractional bandwidth of the laser pulse, {Delta}{phi}{sup -1}, is sufficiently small to satisfy A{sup 2} {Delta}{phi} {approx_equal} 1. A three dimensional analysis, based on a local plane-wave, slow-varying envelope approximation, enables the study of these effects for realistic interactions between an electron beam and a laser pulse, and their influence on high-precision Compton scattering light sources.
Date: February 23, 2010
Creator: Hartemann, F V; Albert, F; Siders, C W & Barty, C P
Partner: UNT Libraries Government Documents Department

Final state effects and correlation in atomic and molecular systems

Description: This is the final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project`s goals were to experimentally examine phenomena caused by final state interactions of the photo-excited electron with the remaining ionic system. This includes multiple ionization by a single photon, which cannot be described solely within a one-electron framework, but requires explicit incorporation of correlation effects between the second electron and the primary electron. Having only two electrons, helium is one of the simplest systems which exhibits electron correlation and thus is an ideal choice for testing electron correlation models in atoms. The authors measured the double to single ionization ratio in helium and the multiple ionization ratio in several other rare gases to test the recent theories. They found an unexpected ionization channel caused by Compton scattering.
Date: April 1, 1996
Creator: Bartlett, R.J.; Morgan, D.V.; Samson, J.A. & Sagurton, M.
Partner: UNT Libraries Government Documents Department

Review of window and filter requirements for commissioning of the Advanced Photon Source insertion device beamlines

Description: The Advanced Photon Source (APS) is building 16 insertion device (ID) front ends for the first phase of the project. Eleven of these are to be equipped with the APS Undulator A and the other five with a Wiggler-A-type source. The Undulator A front ends are designed to operate in a ``windowless`` mode using an APS-designed differential pump. However, during beamline commissioning and early operations of the storage ring, it is prudent to install windows to ensure storage ring vacuum safety before easing into windowless operation. However, the window designed for this interim period may not meet all the needs of a user`s scientific program. In the early phases of the project through commissioning and start of operations, such a window will permit the user to prepare for his program, while allowing both the user and the facility operators to gain experience for safe phasing into eventual windowless operations. In this report, we will present analysis and design options for a variety of windows particularly suited to either the APS Undulator A front ends or as user windows located in the first optics enclosure (FOE).
Date: June 2, 1994
Creator: Kuzay, T.M. & Wang, Zhibi
Partner: UNT Libraries Government Documents Department

Virtual Compton Scattering on the proton at high s and low t

Description: Virtual Compton Scattering (VCS) at low transferred momenta to the proton (t) and sufficiently high c.m. energies (s) may be used to (a) study Q{sup 2}-dependence of leading t-channel exchanges and (b) look for onset of scaling behavior with increasing Q{sup 2}. The author discusses the implications for perturbative and nonperturbative QCD and suggests possible experiments.
Date: August 1, 1996
Creator: Afanasev, Andrei
Partner: UNT Libraries Government Documents Department

Test of QED at critical field strength

Description: In a new experiment at the Final Focus Test Beam at SLAC, a low-emittance 46.6 GeV electron beam is brought into collision with terawatt pulses of 1,054 nm or 527 nm wavelength from a Nd:glass laser. Peak laser intensities of 10{sup 18} W/cm{sup 2} have been achieved corresponding to a value of 0.6 for the parameter {eta} = e{var_epsilon}m{omega}{sub 0}c. In this case, an electron that crosses the center of the laser pulse has near-unit interaction probability. Results are presented for multiphoton Compton scattering in which an electron interacts with up to four laser photons, in agreement with theoretical calculations.
Date: October 1, 1996
Creator: Bula, C. & Collaboration, E-144
Partner: UNT Libraries Government Documents Department

First electron beam polarization measurements with a Compton polarimeter at Jefferson Laboratory

Description: A Compton polarimeter has been installed in Hall A at Jefferson Laboratory. This letter reports on the first electron beam polarization measurements performed during the HAPPEX experiment at an electron energy of 3.3 GeV and an average current of 40 muA. The heart of this device is a Fabry-Perot cavity which increased the luminosity for Compton scattering in the interaction region so much that a 1.4% statistical accuracy could be obtained within one hour, with a 3.3% total error.
Date: March 1, 2002
Creator: Baylac, Maud; Burtin, E.; Cavata, C.; Escoffier, S.; Frois, B.; Lhuillier, D. et al.
Partner: UNT Libraries Government Documents Department

Electroproduction of Photons and of Pawns on the Proton in Quadrimoment of Transfer Q2=1.0GeV2. Measure Cross Sections and Extraction of Polarizabilities Generalities; Electroproduction de Photons et de Pions sur le Proton au Quadrimoment de Transfert Q2=1.0GeV2. Mesure des Sections Efficaces et Extraction des Polarisabilites Generalisees

Description: In hadronic physics, the nucleon structure and the quarks confinement are still topical issues. The neutral pion electroproduction and virtual Compton scattering (VCS) reactions allow us to access new observables that describe this structure. This work is focused on the VCS experiment performed at Jefferson Lab in 1998.
Date: November 6, 2001
Creator: Laveissiere, Geraud
Partner: UNT Libraries Government Documents Department

Electroexcitation of Nucleon Resonances

Description: Recent electroproduction results in the domain of s-channel nucleon resonance excitation are presented, and preliminary data in the search for missing states will be discussed. I also address a new avenue to pursue N* physics using exclusive deeply virtual Compton scattering, recently measured for the first time at JLab and DESY.
Date: March 1, 2002
Creator: Burkert, Volker D.
Partner: UNT Libraries Government Documents Department

Laser cooling of TeV muons

Description: The authors show that Compton scattering can be used to cool TeV-scale muon beams, and derive analytical expressions for the equilibrium transverse angular spread, longitudinal energy spread, and power requirements. They find that a factor of a few thousand reduction in emittance is possible for a 3 TeV muon collider.
Date: August 8, 2000
Creator: DeJongh, Fritz
Partner: UNT Libraries Government Documents Department

Compton scattering in the ALS booster

Description: Femtosecond x-ray pulses may be generated by 90{degrees} Compton side scattering of a short visible laser beam by a well-focused relativistic electron beam. A proof-of-principle experiment is underway using the ALS linac. From this experiment an x-ray pulse of 10{sup 5} photons with a duration of 230 fs in a bandwidth of 10% at 10 Hz is expected. In this paper we explore using the ALS booster instead to increase the average x-ray flux. To generate the small beam size we plan to radiation damp electrons by accelerating them to 600 MeV and decelerate quickly to 50 MeV before intra-beam scattering can increase the beam size. We can achieve a vertical emittance of <5 {times} 10{sup {minus}9} m-rad. With a small modification of the booster lattice it is possible to focus the beam to a vertical beta function of {Beta}{sub y}* = 10 cm. By reflecting the incident laser pulse many times we expect to be able to obtain an increase of the average x-ray flux.
Date: April 1, 1995
Creator: Robin, D.; Kim, C. & Sessler, A.
Partner: UNT Libraries Government Documents Department

Gamma-gamma collider based on Compton back-scattering

Description: A {gamma}{gamma} collider would extend and complement the physics capability of a linear collider; e.g. it would be suitable for direct measurement of the partial decay width of a Higgs boson into two gamma quanta. This paper discusses choice of laser parameters, luminosity optimization, electron and laser parameters for a gamma- gamma collider as a second interaction region for the Next Linear Collider, laser path, and the lasers. It is concluded that a gamma- gamma collider is technically feasible; however it will require a significant investment in preparatory R&D.
Date: August 1, 1996
Creator: Kim, Kwang-Je & Group, Gamma-Gamma Working
Partner: UNT Libraries Government Documents Department

Measurement of Deeply Virtual Compton Scattering (DVCS) cross sections with CLAS

Description: Extraction of DVCS unpolarized and polarized cross sections in the largest kinematic domain ever explored in the valence region. Results are in good agreement with GPD model (VGG) predictions. Extraction of Compton Form Factors (M. Guidal) by fitting simultaneously these unpolarizedand polarized cross sections gives a large set of results in a very large kinematic domain for Re(H ) and Im(H ). Analysis of the data from the second part of the e1-DVCS experiment underway.
Date: April 1, 2012
Creator: Jo, Hyon-Suk
Partner: UNT Libraries Government Documents Department

Deeply virtual Compton scattering on longitudinally polarized protons and neutrons at CLAS

Description: This paper focuses on a measurement of deeply virtual Compton scattering (DVCS) performed at Jefferson Lab using a nearly-6-GeV polarized electron beam, two longitudinally polarized (via DNP) solid targets of protons (NH{sub 3}) and deuterons (ND{sub 3}) and the CEBAF Large Acceptance Spectrometer. Here, preliminary results for target-spin asymmetries and double (beam-target) asymmetries for proton DVCS, as well as a very preliminary extraction of beam-spin asymmetry for neutron DVCS, are presented and linked to Generalized Parton Distributions.
Date: April 1, 2012
Creator: Niccolai, Silvia
Partner: UNT Libraries Government Documents Department

Exclusive photon-photon processes

Description: Exclusive gamma gamma right arrow hadron pairs are among the most fundamental processes in QCD, providing a detailed examination of Compton scattering in the crossed channel. In the high momentum transfer domain (s, t, large, Theta cm for t/s fixed), these processes can be computed from first principles in QCD, yielding important information on the nature of the QCD coupling data and the form of hadron distribution amplitudes. Similarly, the transition form factors gamma star gamma, gamma star gamma right arrow pi(o), Eta (0), Eta`, Eta(c)... provide rigorous tests of QCD and definitive determinations of the meson distribution amplitudes Phi H(x,Q). We show that the assumption of a frozen coupling at low momentum transfers can explain the observed scaling of two-photon exclusive processes.
Date: July 1, 1997
Creator: Brodsky, S.J.
Partner: UNT Libraries Government Documents Department