790 Matching Results

Search Results

Advanced search parameters have been applied.

Triple Differential Cross sections and Nuclear Recoil in Two-Photon Double Ionization of Helium

Description: Triple differential cross sections (TDCS) for two-photon double ionization of helium are calculated using the method of exterior complex scaling both above and below the threshold for sequential ionization (54.4 eV). It is found that sequential ionization produces characteristic behavior in the TDCS that identifies that process when it is in competition with nonsequential ionization. Moreover we see the signature in the TDCS and nuclear recoil cross sections of"virtual sequential ionization" below the threshold for the sequential process.
Date: April 29, 2008
Creator: Horner, Daniel A.; McCurdy, C. William & Rescigno, Thomas N
Partner: UNT Libraries Government Documents Department

Supersymmetry tests at future linear colliders

Description: If new particles are discovered, it will be important to determine if they are the supersymmetric partners of standard model bosons and fermions. Supersymmetry predicts relations among the couplings and masses of these particles. We discuss the prospects for tests of these relations at a future e+e- linear collider.
Date: December 1, 1994
Creator: Feng, J.L.
Partner: UNT Libraries Government Documents Department

Properties of the Lambda(1405) Measured at CLAS

Description: The nature of the {Lambda}(1405), and its place in the baryon spectrum has remained uncertain for decades. Theoretical studies have shown that it may possess strong dynamical components which are not seen in other well-known baryons. Using the CLAS detector system in Hall B at Jefferson Lab, we have measured the photoproduction reaction {gamma} + p {yields} K{sup +} {Lambda}(1405) with high statistics and over different {Sigma}{pi} decay channels. The reconstructed invariant mass distribution (lineshape) has been measured, as well as the differential cross sections for the {Lambda}(1405), {Sigma}(1385), and {Lambda}(1520). Our analysis method is discussed and our near-final results for the {Lambda}(1405) lineshape and differential cross section are presented.
Date: April 1, 2012
Creator: Moriya, Kei & Schumacher, Reinhard
Partner: UNT Libraries Government Documents Department

Two-photon double ionization of H2 at 30 eV using Exterior Complex Scaling

Description: Calculations of fully differential cross sections for two-photon double ionization of the hydrogen molecule with photons of 30 eV are reported. The results have been obtained by using the method of exterior complex scaling, which allows one to construct essentially exact wave functions that describe thedouble continuum on a large, but finite, volume. The calculated cross sections are compared with those previously obtained by Colgan et al., and discrepancies are found for specific molecular orientations and electron ejection directions.
Date: January 20, 2009
Creator: Morales, Felipe; Martin, Fernando; Horner, Daniel; Rescigno, Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

Longitudinal double-spin asymmetry and cross section for inclusivejet production in polarized proton collisions at sqrt(s) = 200 GeV

Description: We report a measurement of the longitudinal double-spinasymmetry A_LL and the differential cross section for inclusivemidrapidity jet production in polarized proton collisions at sqrt(s)=200GeV. The cross section data cover transverse momenta 5<pT<50GeV/c and agree with next-to-leading order perturbative QCD evaluations.The A_LL data cover 5<pT<17 GeV/c and disfavor at 98 percentC.L. maximal positive gluon polarization in the polarizednucleon.
Date: August 10, 2006
Creator: Abelev, B.I.; Adams, J.; Aggarwal, M.M.; Ahammed, Z.; Amonett,J.; Anderson, B.D. et al.
Partner: UNT Libraries Government Documents Department

CHARGE-EXCHANGE SCATTERING OF NEGATIVE PIONS BY HYDROGEN AT 230,260, 290, 317 AND 371 MeV

Description: The differential cross section for charge-exchange scattering of negative pions by hydrogen has been observed at 230, 260, 290, 317, and 371 Mev. The reaction was observed by detecting one gamma ray from the {pi}{sup 0} decay with a scintillation-counter telescope.
Date: March 18, 1960
Creator: Caris, John C
Partner: UNT Libraries Government Documents Department

Interpretation of High Energy p-p Scattering.

Description: High energy p-p scattering has been interpreted by several authors in terms of highly singular noncentral interactions. The triplet state calculations were carried out in the Born approximation and, together with the singlet, yielded an almost isotropic (c.m. system) differential cross section. Agreement with experiment was good at large angles but the theoretical peak in the forward direction, due mostly to singlet d scattering, was too large. It is not clear however that the Born approximation should be valid for singular potentials.
Date: September 19, 1952
Creator: Swanson, Don R.
Partner: UNT Libraries Government Documents Department

Decoding sequential vs non-sequential two-photon double ionizationof helium using nuclear recoil

Description: Above 54.4 eV, two-photon double ionization of helium isdominated by a sequential absorption process, producing characteristicbehavior in the single and triple differential cross sections. We showthat the signature of this process is visible in the nuclear recoil crosssection, integrated over all energy sharings of the ejected electrons,even below the threshold for the sequential process. Since nuclear recoilmomentum imaging does not require coincident photoelectron measurement,the predicted images present a viable target for future experiments withnew short-pulse VUV and soft X-ray sources.
Date: January 7, 2008
Creator: Horner, Daniel A.; Rescigno, Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

First Principles Study of Double Photoionization of H2 UsingExterior Complex Scaling

Description: Exterior complex scaling provides a practical path forfirst-principles studies of atomic and molecular ionizationproblemssince it avoids explicit enforcement of asymptotic boundary conditionsfor 3-body Coulomb breakup. We have used the method of exterior complexscaling, implemented with both the discrete variable representation andB-splines, to obtain the first-order wave function for molecular hydrogencorresponding to a single photon having been absorbed by a correlatedinitial state. These wave functions are used to construct convergedtriple differential cross sections for double photoionization of alignedH2 molecules.
Date: July 21, 2006
Creator: Rescigno, Thomas N.; Vanroose, Wim; Horner, Daniel A.; Martin,Fernando & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

The Role of Nuclear Motion in the Photo-Double Ionization ofMolecular Hydrogen

Description: We examine the origin of recently observed variations with internuclear distance (R) of the fully differential cross sections for double ionization of aligned H2 by absorption of a single photon. Using the results of fully converged numerical solutions of the Schroedinger equation, we show that these variations arise primarily from pronounced differences in the R-dependence of the parallel and perpendicular components of the ionization amplitude. We also predict that R-dependences should be readily observable in the asymmetry parameter for photo-double ionization, even in experimental measurements that are not differential in the energy sharings between ejected photo-electrons.
Date: October 26, 2006
Creator: Horner, Daniel A.; Vanroose, Wim; Rescigno, Thomas N.; Martin,Fernando & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

Measurement of the N --> Delta^+ (1232) Transition at High-Momentum Transfer by pi^0 Electroproduction

Description: We report a new measurement of the exclusive electroproduction reaction gamma*_p --> pi0_p to explore the evolution from soft nonperturbative physics to hard processes via the Q2 dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the N --> Delta transition. 9000 differential cross section data points cover W from threshold to 1.4 GeV/c2, 4pi center-of-mass solid angle, and Q2 from 3 to 6 GeV2/c2, the highest yet achieved. It is found that the magnetic form factor G^*M decreases with Q2 more steeply than the proton magnetic form factor, the ratio E1+/M1+ is small and negative, indicating strong helicity nonconservation, and the ratio S1+/M1+ is negative, while its magnitude increases with Q2.
Date: September 1, 2006
Creator: Ungaro, M.; Stoler, P.; Aznauryan, I.; Burkert, V. D.; Joo, K.; Smith, L. C. et al.
Partner: UNT Libraries Government Documents Department

Measurement of the Diphoton Differential Cross Section in p anti-p Collisions at s**(1/2) = 1.96-TeV

Description: The diphoton differential cross-section as a function of mass up to 300 GeV/c{sup 2}, q{sub T} up to 100 GeV/c, and opening angle over a range of 0 to {pi} radians is measured. The measurement is performed using 1046.19 pb{sup -1} of data collected at Fermi National Accelerator Laboratory using the D0 detector. This analysis considers all direct diphoton states but attempts to suppress contributions due to fragmentation.
Date: January 1, 2007
Creator: Dyer, Joshua Marc & U., /Michigan State
Partner: UNT Libraries Government Documents Department

First Principles Calculations of the Double Photoionization ofAtoms and Molecules using B-splines and Exterior Complex Scaling

Description: We report a fully ab initio implementation of exterior complex scaling in B-splines to evaluate total, singly and triply differential cross sections in double photoionization problems. Results for He and H{sub 2} double photoionization are presented and compared with experiment.
Date: November 4, 2005
Creator: Martin, Fernando; Horner, Daniel A.; Vanroose, Wim; Rescigno,Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

Nuclear Recoil Cross Sections from Time-dependent Studies of Two-Photon Double Ionization of Helium

Description: We examine the sensitivity of nuclear recoil cross sections produced by two-photon double ionization of helium to the underlying triple differential cross sections (TDCS) used in their computation. We show that this sensitivity is greatest in the energy region just below the threshold for sequential double ionization. Accurate TDCS, extracted from non-perturbative solutions of the time-dependent Schroedinger equation, are used here in new computations of the nuclear recoil cross section.
Date: December 21, 2009
Creator: Horner, Daniel A.; Rescigno, Thomas N. & McCurdy, C. William
Partner: UNT Libraries Government Documents Department

Measurement of the Forward-Backward Charge Asymmetry($A_{FB}$) using $p\bar{p}\rightarrow Z/\gamma*\rightarrow e^+e^-$ events in $\sqrt{S} = 1.96$ TeV

Description: This dissertation describes a measurement of the forward-backward asymmetry(A<sub>FB</sub>) in p$\bar{p}$ → Z/γ* → ee events using 5.0 fb<sup>-1</sup> data collected by the D0 detector at the Fermilab Tevatron. The AFB is measured as a function of the invariant mass of the electron-positron pair. Along with obtaining normalized differential cross section 1/σ x dσ/dM and Z to light quark couplings, we measured the Standard Model(SM) fundamental parameter, the effective weak mixing angle sin<sup>2</sup> θ$lept\atop{eff}$, with an unprecedented precise in light quark sector, namely the single D0 measurement has surpassed the LEP combination of four experiment results of inclusive hadronic charge asymmetry.
Date: June 1, 2010
Creator: Yin, Hang
Partner: UNT Libraries Government Documents Department

Probing the nuclear medium with the K{sup +} meson

Description: Elastic differential cross sections for K{sup +} mesons scattered from targets of carbon and {sup 6}Li have been measured at an incident momentum of 715 MeV/c. The ratios of scattering cross sections from these targets are not predicted by theory, and are consistent with earlier suggestions that the K{sup +}-nucleon interaction is modified in the nuclear medium.
Date: December 31, 1995
Creator: Chrien, R.E.
Partner: UNT Libraries Government Documents Department

Nondipolar photoelectron angular distributions

Description: The deviations of photoelectron angular distributions from the simple, highly symmetric shapes predicted within the electric-dipole approximation are investigated. The admixture of an electric-quadrupole component in the photon-atom interaction causes an asymmetry in the angular distribution with respect to the direction of photon propagation. The reported measurement of the angular distributions of argon {ital 1s}, krypton {ital 2s}, and krypton {ital 2p} photoemission within 2-3 keV above their respective thresholds reveal pronounced asymmetries which are present even at low electron kinetic energies. The measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations.
Date: December 31, 1996
Creator: Kraessig, B.; Jung, M.; Gemmell, D.S.; Kanter, E.P.; LeBrun, T.; Southworth, S.H. et al.
Partner: UNT Libraries Government Documents Department

Two-component multistep direct reactions: A microscopic approach

Description: The authors present two principal advances in multistep direct theory: (1) A two-component formulation of multistep direct reactions, where neutron and proton excitations are explicitly accounted for in the evolution of the reaction, for all orders of scattering. While this may at first seem to be a formidable task, especially for multistep processes where the many possible reaction pathways becomes large in a two-component formalism, the authors show that this is not so -- a rather simple generalization of the FKK convolution expression 1 automatically generates these pathways. Such considerations are particularly relevant when simultaneously analyzing both neutron and proton emission spectra, which is always important since these processes represent competing decay channels. (2) A new, and fully microscopic, method for calculating MSD cross sections which does not make use of particle-hole state densities but instead directly calculates cross sections for all possible particle-hole excitations (again including an exact book-keeping of the neutron/proton type of the particle and hole at all stages of the reaction) determined from a simple non-interacting shell model. This is in contrast to all previous numerical approaches which sample only a small number of such states to estimate the DWBA strength, and utilize simple analytical formulae for the partial state density, based on the equidistant spacing model. The new approach has been applied, along with theories for multistep compound, compound, and collective reactions, to analyze experimental emission spectra for a range of targets and energies. The authors show that the theory correctly accounts for double-differential nucleon spectra.
Date: March 1, 1998
Creator: Koning, A.J. & Chadwick, M.B.
Partner: UNT Libraries Government Documents Department

Electron-helium scattering in the S-wave model using exterior complex scaling

Description: Electron-impact excitation and ionization of helium is studied in the S-wave model. The problem is treated in full dimensionality using a time-dependent formulation of the exterior complex scaling method that does not involve the solution of large linear systems of equations. We discuss the steps that must be taken to compute stable ionization amplitudes. We present total excitation, total ionization and single differential cross sections from the ground and n=2 excited states and compare our results with those obtained by others using a frozen-core model.
Date: June 16, 2004
Creator: Horner, Daniel A.; McCurdy, C. William & Rescigno, Thomas N.
Partner: UNT Libraries Government Documents Department

Neutron interaction with doubly-magic {sup 40}Ca

Description: Differential neutron elastic and inelastic-scattering cross sections of elemental calcium (96.94% doubly-magic {sup 40}Ca) are measured from {approx} 1.5 to 10 MeV with sufficient detail to determine their energy-averaged behavior in the highly fluctuating environment. These results, combined with values previously reported in the literature, are assessed in the contexts of optical-statistical, dispersive optical, and coupled-channels models, applicable to the energy domain 0 {yields} 30+ MeV, with particular emphasis on the lower energies where the interpretations are sensitive to the dispersion relationship and the effective mass. The interpretations define the energy dependencies of the potential parameters (resolving prior ambiguities), suggest that previous estimates of the prominent low-energy (n,p) and (n,a) reactions are too large, reasonably describe observables to at least 30 MeV, and provide a vehicle for extrapolation into the bound-state regime that gives a good description of hole- and particle-state binding energies. The resulting real-potential parameters (in contrast to many {sup 40}Ca parameters reported in the literature) are shown consistent with global trends.
Date: November 1, 1993
Creator: Smith, A.B.
Partner: UNT Libraries Government Documents Department

Ab initio study of low-energy electron collisions withtertafluoroethene, C2F4

Description: We report the results of variational calculations of elastic electron scattering by tetrafluoroethene, C{sub 2}F{sub 4}, with incident electron energies ranging from 0.5 to 20 eV, using the complex Kohn method and effective core potentials. These are the first fully calculations to reproduce experimental angular differential cross sections at energies below 10 eV. Low-energy electron scattering by C{sub 2}F{sub 4} is sensitive to the inclusion of electronic correlation and target-distortion effects. We therefore present results that describe the dynamic polarization of the target by the incident electron. The calculated cross sections are compared with recent experimental measurements.
Date: April 26, 2004
Creator: Trevisan, C.S.; Orel, A.E. & Rescigno, T.N.
Partner: UNT Libraries Government Documents Department

Electron-impact excitation-autoionization of helium in the S-wave limit

Description: Excitation of the autoionizing states of helium by electron impact is shown in calculations in the s-wave limit to leave a clear signature in the singly differential cross section for the (e,2e) process. It is suggested that such behavior should be seen generally in (e,2e) experiments on atoms that measure the single differential cross section.
Date: October 1, 2004
Creator: Horner, Daniel A.; McCurdy, C. William & Rescigno, Thomas N.
Partner: UNT Libraries Government Documents Department

High P{sub T} Jet Physics

Description: Recent precise measurements of various jet cross sections have allowed stringent tests of next-to-leading order (NLO) predictions hinting the need for higher order calculations and/or the rethinking of the theoretical predictions. We examine the inclusive jet cross sections at center of mass energies of 1800 and 630 GeV and the ra- tio of these two cross sections. We also explore the sensitivity to parton distribution functions (PDF's) by looking at the triple differential dijet cross sections.
Date: August 3, 1999
Creator: Nang, Freedy
Partner: UNT Libraries Government Documents Department

Dijet results from CDF

Description: Recent dijet results from CDF are presented. The preliminary dijet mass distribution measured by CDF is presented and compared to QCD calculations. Measurements of dijet angular distributions are used to place limits on quark compositness. A preliminary measurement of the inclusive dijet differential cross section is presented.
Date: July 21, 1999
Creator: Chlebana, Frank
Partner: UNT Libraries Government Documents Department