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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Measurement of the spin-structure function g {sub 2} and the semi-inclusive double-spin asymmetries at HERMES

A measurement of the virtual-photon asymmetry A {sub 2} and of the spin-structure function g {sub 2} of the proton are presented for the kinematic range of the HERMES experiment carried out at the HERA electron storage ring at DESY. Semi-inclusive longitudinal double-spin asymmetries provide new insight into the valence quark helicity distributions Δu {sub v} and Δd {sub v}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Inclusive Deep Inelastic Scattering at HERA

Recent inclusive charged and neutral current scattering data from HERA are presented. Emphasis is placed on the resulting constraints on the proton parton densities and on the influence of low x proton structure on diffraction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Jets and Heavy Flavors at HERA

Recent results on jet cross sections and heavy-flavor production in photoproduction and neutral current deep inelastic ep scattering from the H1 and ZEUS Collaborations are presented. The jet measurements are used to perform stringent tests of perturbative QCD, to extract precise values of the strong coupling and to constrain further the proton and photon parton distribution functions. The measurement of beauty and charm production at HERA is an important testing ground for perturbative QCD and can provide information on the structure of the proton.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Inclusive diffraction at HERA

Results are reported on recent measurements, performed by the H1 and ZEUS Collaborations, of the cross section of the diffractive deep-inelastic process ep{yields}eXp using different experimental methods. In particular, first results using the Very Forward Proton Spectrometer of H1 are discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Diffractive PDF fits and factorisation tests at HERA

A DGLAP next-to-leading-order QCD analysis to extract the diffractive parton distribution functions, using DIS inclusive and dijet diffractive HERA data, is presented. Predictions based on the extracted parton densities are compared to diffractive dijet photoproduction data to discuss factorisation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Diffraction from HERA to the LHC

Following a 15 year programme of intensive research into diffractive electron-proton scattering at HERA, it is important to transfer the knowledge and experience gained into the LHC programme. This contribution raises some current issues in diffraction at the LHC and suggests ways in which they might be addressed using HERA results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Vector meson production and DVCS at HERA

An overview of the latest results obtained by the H1 and ZEUS experiments at HERA on diffractive production of Vector Mesons and Deeply Virtual Compton Scattering (DVCS) is presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Hard Exclusive Vector Meson Leptoproduction At HERMES

The HERMES experiment at DESY, Hamburg collected a set of data on hard exclusive vector meson ({rho}{sup 0}{phi},{omega}) leptoproduction using the 27.6 GeV longitudinally polarized lepton beam of HERA accelerator and longitudinally or transversely polarized or unpolarized gas targets. Measurements of exclusive vector meson production provide access to the structure of the nucleon since the process can be described in terms of Generalized Parton Distributions (GPDs). An overview of the HERMES results on exclusive vector mesons production is presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

DVCS - HERMES

The study of Generalised Parton Distributions (GPDs) promises to provide new knowledge of the structure of the nucleon, including, most notably, access to the total angular momentum of quarks within the nucleon. It can be difficult to ascertain new information on the distributions, but amongst all the exclusive processes that can provide access, Deeply Virtual Compton Scattering (DVCS) is relatively simple and experimentally accessible. The HERMES collaboration has the most diverse results pertaining to DVCS of any experiment, extracting asymmetries in the azimuthal distribution of produced photons according to both beam helicity and charge and target spin state. In this talk, we provide an overview of the HERMES DVCS result catalogue and explain how the results are used to improve constraints on the underlying GPDs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Exclusive production of vector mesons in pp and pp-bar collisions

Protons and antiprotons at collider energies are a source of high energy Weizsaecker-Williams photons. This opens up a possibility to study at the LHC exclusive photoproduction of heavy vector mesons at energies much larger than possible at the HERA accelerator.We present selected results on the production of vector mesons {rho}, {omega}, {phi}, J/{Psi} and {Upsilon}. We show distributions in rapidity, transverse momentum of mesons and azimuthal angle between outgoing protons for RHIC, Tevatron and LHC energies. The absorption effects are discussed.The amplitude for {gamma}p{yields}Vp is calculated in a pQCD k{sub T}-factorization approach with an unintegrated gluon distribution constrained by inclusive deep-inelastic structure function. The total cross section for diffractive meson (virtual) photo-production as a function of energy and photon virtuality is calculated and compared to HERA data. We also discuss the ratio of the first radial excitation state (2S) to the ground state (1S) in diffractive J/{Psi} and {Upsilon} production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Soft color screening effects in diffractive DIS

We construct a QCD-based model where soft gluon rescattering between final state partons in deep inelastic scattering leads to events with large rapidity gaps and a leading proton. The model successfully describes the precise HERA data on the diffractive deep inelastic structure function in the whole available kinematical range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Prompt photon photoproduction at HERA with non-collinear parton dynamics

We investigate the prompt photon photoproduction at HERA within the framework of the k{sub T}-factorization approach to QCD. Our consideration is based on the off-shell matrix elements for the underlying partonic subprocesses and the Kimber-Martin-Ryskin (KMR) unintegrated parton densities in the proton. We also use the Ciafaloni-Catani-Fiorani-Marchesini (CCFM) unintegrated gluon as well as valence and sea quark distributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Higgs boson photoproduction at the LHC

We present the current development of the photoproduction approach for the Higgs boson with its application to pp and pA collisions at the LHC. We perform a different analysis for the Gap Survival Probability, where we consider a probability of 3% and also a more optimistic value of 10% based on the HERA data for dijet production. As a result, the cross section for the exclusive Higgs boson production is about 2 fb and 6 fb in pp collisions and 617 and 2056 fb for pPb collisions, considering the gap survival factor of 3% and 10%, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Parton Distributions from HERA

A QCD fit analysis to the combined HERA-I inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for e{sup {+-}p} scattering resulting into a competitive NLO PDF set, HERAPDF1.0 is presented. HERAPDF at NNLO fits are presented as well, resulting, however, in a worse description of the combined HERA data. In addition, the QCD fit analysis of the combined HERA-I inclusive deep inelastic cross sections has been extended to include combined HERA II measurements at high Q{sup 2}. The effect of including these data on the determination of parton distribution functions is analysed, resulting into HERAPDF1.5. The precision of the new PDFs at high-x is considerably improved, particularly in the valence sector. The predictions based on HERAPDF1.0 and HERAPDF1.5 are compared to pp-bar processes at Tevatron, and also used for predictions of the pp processes at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Studies of Partonic Transverse Momentum and Spin Structure of the Nucleon at HERMES

The investigation of the partonic degrees of freedom beyond collinear approximation (3D description) has been gained increasing interest in the last decade. At the HERMES experiment, azimuthal single-spin asymmetries of pions and charged kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons off a transversely (polarized) hydrogen and deuterium target have been measured. Such asymmetries provide new insights on crucial aspects of the parton dynamics. By measuring various hadron types in the initial and final states, flavor sensitivity is achieved. Evidence is reported of the poorly known transversity function and of naive-T-odd transverse-momentum-dependent parton distribution functions related to spin-orbit effects. Evidence of spin-orbit effects in quark fragmentation is also observed, which are opposite in sign for favored and disfavored processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Experimental investigation of the stimulated Brillouin scattering growth and saturation at 526 and 351 nm for direct drive and shock ignition

We have designed experiments to study the effect of the laser wavelength (0.527 versus 0.351 {mu}m) on the coupling efficiency in plasma conditions relevant to compression and shock ignition (SI) schemes in different intensity regimes. A difficult issue was to produce interaction conditions that are equivalent for the two wavelengths. This was obtained by using plasma preformed from a solid target with a plasma-preforming beam at the same wavelength as the interaction beam. This produced an almost exponential density profile from vacuum to the critical density of the interaction beam in which all interaction mechanisms are taken into account. The growth and saturation of stimulated Brillouin scattering (SBS) have been measured at the two wavelengths, in backward as well as in near-backward directions. We have found that the SBS intensity threshold is {approx}1.5 times higher at 3{omega} than at 2{omega} in agreement with the I{lambda} dependence of the SBS gain. The SBS behaviour is very well reproduced by the linear calculations of the postprocessor PIRANAH, giving us confidence that we have a good control of the relevance of the experimental conditions for the study of the laser wavelength effect on laser-plasma coupling. When SBS reaches the saturation regime, same levels of reflectivity are measured at 2 and 3{omega}. Numerical simulations were performed with the paraxial code HERA to study the contribution of the fluid mechanisms in the saturation of SBS, showing that pump depletion and interplay with filamentation are likely to be the most important processes in SBS saturation for these conditions. This scenario also applies to the SBS of shock ignition high-intensity beams.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

The combined measurements of NC and CC DIS cross-sections at HERA

A combination is presented of the inclusive cross sections measured by the H1 and ZEUS Collaborations in neutral and charged current deep-inelastic ep scattering at HERA. The combination uses data from unpolarized ep scattering taken during the HERA-I phase as well as measurements with longitudinally polarized electron or positron beams from the HERAII running period. The combination method takes the correlations of systematic uncertainties into account. The inclusion of the large HERA-II data set leads to an improved uncertainty especially at large four momentum transfer squared Q{sup 2}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗