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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Measurement of the photon electroproduction cross section at JLAB with the goal of performing a Rosenbluth separation of the DVCS contribution

The study of the inner structure of hadrons allows us to understand the nature of the interactions between partons, quarks and gluons, described by Quantum Chromodynamics. The elastic scattering reactions, which have been studied in order to measure the nucleon form factors, are included in this frame. The inelastic scattering reactions are also included in this frame, they allow us to obtain information about the nucleon structure thanks to the development of the parton distribution functions (PDFs). While through elastic scattering we can obtain information about the charge distribution of the nucleon, and hence, about the spatial distribution of the partons, through inelastic scattering we obtain information about the momentum distributions of partons, by employing the PDFs. However, we can study the exclusive inelastic scattering reactions, such as the Deeply Virtual Compton Scattering (DVCS), wich allow us to access to the spatial and momentum distributions simultaneously. This is possible thanks to the generalized parton distributions (GPDs), which allow us to correlate both types of distributions. The process known as DVCS is the easiest way to access the GPDs. This process can be expressed as the scattering of an electron by a proton by means of a virtual photon with the result of the scattered initial particles plus a real photon. We find a process competing with DVCS known as Bethe-Heitler (BH), in which the real photon is radiated by the lepton rather than the quark. Due to the small cross section of DVCS, of the order of nb, in order to conduct these kind of experiments it is necessary to make use of facilities capable of providing high beam intensities. One of these facilities is the Thomas Jefferson National Accelerator Facility , where the experiment JLab E07-007, "Complete Separation of Virtual Photon and π⁰ Electroproduction Observables of Unpolarized Protons", took place during the months of October to December of 2010. The main goal of this experiment is the isolation of the contribution from the term coming form the DVCS from the interference term, resulting from the BH contribution. This isolation is known as "Rosenbluth Separation". The work presented in this thesis focuses on the analysis of the data stored by the electromagnetic calorimeter, employed for the detection of real photons. There is also a a theoretical introduction to the study of the nucleon structure, reviewing the concepts of form factors and parton distributions through elastic and inelastic processes. The computation of the photon leptoproduction cross section is described in detail, as well as the goals of experiment E07-007. This thesis also describes the analysis of the data stored by the electromagnetic calorimeter, with the purpose of obtaining the kinematic variables of the real photons resulting from DVCS reactions. Finally, it describes the selection of events from stored data, the applied cuts to kinematical variables and the background subtraction. Also, the process of extraction of the necessary observables for computing the photon leptoproduction cross section is described, along with the main steps followed to perform the Monte Carlo simulation used in this computation. The resulting cross sections are shown at the end of this thesis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Navigating collinear superspace

We introduce a new set of effective field theory rules for constructing Lagrangians with \( \mathcal{N} \) = 1 supersymmetry in collinear superspace. In the standard superspace treatment, superfields are functions of the coordinates \( \left({x}^{\mu },{\theta}^{\alpha },{\theta}^{\dagger \overset{\cdot }{\alpha }}\right) \) , and supersymmetry preservation is manifest at the Lagrangian level in part due to the inclusion of auxiliary F - and D -term components. By contrast, collinear superspace depends on a smaller set of coordinates ( x μ , η , η † ), where η is a complex Grassmann number without a spinor index. This provides a formulation of supersymmetric theories that depends exclusively on propagating degrees of freedom, at the expense of obscuring Lorentz invariance and introducing inverse momentum scales. After establishing the general framework, we construct collinear superspace Lagrangians for free chiral matter and non-Abelian gauge fields. For the latter construction, an important ingredient is a superfield representation that is simultaneously chiral, anti-chiral, and real; this novel object encodes residual gauge transformations on the light cone. Additionally, we discuss a fundamental obstruction to constructing inter- acting theories with chiral matter; overcoming these issues is the subject of our companion paper, where we introduce a larger set of superfields to realize the full range of interactions compatible with \( \mathcal{N} \) = 1. Along the way, we provide a novel framing of reparametrization invariance using a spinor decomposition, which provides insight into this important light-cone symmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Deeply Virtual Compton Scattering on the Proton in Hall A at Jefferson Lab

The structure of nucleons as they are composed of quarks and gluons is not well understood. Non-perturbative methods (such as lattice-QCD) describing quark/gluon interactions are ongoing in development, but still cannot fully reproduce the structure of hadrons. Among the observables which describe longitudinal momentum and transverse position of partons, generalized parton distributions (GPDs) describe the correlations between the two, and are accessible through p(right-arrow e;e'y)p scattering experiments in the Bjorken limit when factorization holds. A complete understanding of these functions will help us to better understand the structure of nucleons. Experiment E12-06-114 was performed by JLab's DVCS Hall A Collaboration in 2014 and 2016. Using a polarized electron beam and a liquid hydrogen target, the collaboration measured cross sections for the exclusive reaction p(right-arrow e;e'y)p at xB=0.36, 0.48, and 0.60,3 .2 lte Q2 lte 9.00, and -1.28 lte t lte -0.69. This dissertation details the analysis and results of measuring the p(right-arrow e;e'y)p cross section at xB=0.48. The measured cross section results allow us to demonstrate the validity of factorization in our kinematic regime, and extract Compton Form Factor combinations important for understanding GPDs. Additionally, the cross section results are used to test existing GPD models, KM10a and KM15.

Johnson, Alexa N.↗
DOE OSTI2022

MINERvA results and prospects

MINERvA is a dedicated neutrino cross section experiment that ran in the NuMI beamline at Fermilab from 2009 through 2019. MINERvA has made a broad suite of measurements that are informing the neutrino interaction models in use by not only today's oscillation experiments but also by future generations of oscillation experiments. Of particular interest are MINERvA's measurements of the quasielastic-like and pion production processes, since those channels dominate the oscillation landscape. MINERvA has also ushered in the era of using neutrino electron scattering to make precise flux predictions, another important input for oscillation experiments. This paper briefly describes a few recently published results from MINERvA's neutrino and antineutrino scattering sample on the hydrocarbon target including its new flux constraints, and points to some upcoming quasielastic and pion production results that will showcase simultaneous measurements of exclusive final states across different nuclei, ranging from carbon and water to iron and lead.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Activation of Lattice and Adatom Oxygen by Highly Stable Ceria-Supported Cu Single Atoms

Requiring catalysts to be both active yet stable over long periods of time under variable reaction conditions including high and low temperatures is a daunting challenge due to the almost mutual exclusivity of these constraints. Using CO oxidation as a probe reaction, in this work we demonstrate that thermally stable single atom copper catalysts prepared by high temperature synthesis (atom trapping) on ceria can achieve this feat by allowing modulation of the Cu charge state through facile charge transfer between active site and support. This provides the catalysts with an ability to activate either lattice or adatom oxygen atoms, accessing additional reaction channels depending on the reaction conditions. Such adaptability allows dynamic response of catalysts enabling them to remain active under variable reaction conditions. The inherent stability of the catalyst arises from the enhanced strength of the Cu-O interactions from high temperature synthesis that exist even when Cu oxidation state varies, which retards sintering and deactivation. As we show here, one can circumvent the dilemma of designing catalysts that are simultaneously active and stable by matching the redox properties of the active site and support and establishing an environmental adaptability around the active sites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Action at a distance: The remarkable coupling of CO 2 uptake to electron transfer in specialized cyanobacterial NDH-1 complexes

Cyanobacteria achieve highly efficient photosynthesis using a CO 2 -concentrating mechanism relying on specialized Type I (NDH-1) complexes. Among these, NDH-1 3 and NDH-1 4 catalyze redox-coupled hydration of CO 2 to bicarbonate, supporting carbon fixation in carboxysomes. The mechanism of coupling electron transfer to CO 2 -hydration by these variant NDH-1 complexes remains unknown. We engineered a Synechococcus PCC7942 strain that expresses exclusively the high flux/low affinity NDH-14 complex, enabling the observation of the coupling of CO 2 hydration to cyclic electron flow in isolation from the other NDH-1 isoforms normally present in cells. We found that inhibition of the CupB protein by the carbonic anhydrase inhibitor ethoxzolamide (EZ) suppressed CO 2 uptake, slowed photosystem I rereduction, and abolished proton pumping as probed by acridine orange fluorescence. These effects were absent in strains lacking Cup proteins, confirming specificity. The results demonstrate that CO 2 hydration and electron transfer through NDH-14 are tightly coupled via proton translocation across the thylakoid membrane. These findings provide direct evidence for the bidirectional interaction in bioenergetic coupling between the plastoquinone reduction and the CO 2 uptake at the distal Zn-site over a span of ~150 Å and support a proton-removal hypothesis involving the proton transfer pathways from the Zn-site of CO2 hydration to an energetically coupled proton loading site evolutionarily repurposed from the ancestral proton pumping mechanism to enable energetic CO 2 uptake.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

DETECTION OF AN OUTBURST ONE YEAR PRIOR TO THE EXPLOSION OF SN 2011ht

Using imaging from the Pan-STARRS1 survey, we identify a precursor outburst at 287 and 170 days prior to the reported explosion of the purported Type IIn supernova (SN) 2011ht. In the Pan-STARRS data, a source coincident with SN 2011ht is detected exclusively in the z {sub P1} and y {sub P1}-bands. An absolute magnitude of M{sub z} ≅ –11.8 suggests that this was an outburst of the progenitor star. Unfiltered, archival Catalina Real Time Transient Survey images also reveal a coincident source from at least 258 to 138 days before the main event. We suggest that the outburst is likely to be an intrinsically red eruption, although we cannot conclusively exclude a series of erratic outbursts which were observed only in the redder bands by chance. This is only the fourth detection of an outburst prior to a claimed SN, and lends credence to the possibility that many more interacting transients have pre-explosion outbursts, which have been missed by current surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Measuring Thickness-Dependent Relative Light Yield and Detection Efficiency of Scintillator Screens

Digital camera-based neutron imaging systems consisting of a neutron scintillator screen optically coupled to a digital camera are the most common digital neutron imaging system used in the neutron imaging community and are available at any state-of-the-art imaging facility world-wide. Neutron scintillator screens are the integral component of these imaging system that directly interacts with the neutron beam and dictates the neutron capture efficiency and image quality limitations of the imaging system. This work describes a novel approach for testing neutron scintillators that provides a simple and efficient way to measure relative light yield and detection efficiency over a range of scintillator thicknesses using a single scintillator screen and only a few radiographs. Additionally, two methods for correlating the screen thickness to the measured data were implemented and compared. An example 6LiF:ZnS scintillator screen with nominal thicknesses ranging from 0–300 μm was used to demonstrate this approach. The multi-thickness screen and image and data processing methods are not exclusive to neutron scintillator screens but could be applied to X-ray imaging as well. This approach has the potential to benefit the entire radiographic imaging community by offering an efficient path forward for manufacturers to develop higher-performance scintillators and for imaging facilities and service providers to determine the optimal screen parameters for their particular beam and imaging system.

42 ENGINEERING↗
DOE OSTI2011

Proteomic identification of dysferlin-interacting protein complexes in human vascular endothelium

Highlights: Black-Right-Pointing-Pointer Bi-directional (inward and outward) movement of GFP-dysferlin in COS-7 cells. Black-Right-Pointing-Pointer Dysferlin interacts with key signaling proteins for transcytosis in EC. Black-Right-Pointing-Pointer Dysferlin mediates trafficking of vesicles carrying protein cargos in EC. -- Abstract: Dysferlin is a membrane-anchored protein known to facilitate membrane repair in skeletal muscles following mechanical injury. Mutations of dysferlin gene impair sarcolemma integrity, a hallmark of certain forms of muscular dystrophy in patients. Dysferlin contains seven calcium-dependent C2 binding domains, which are required to promote fusion of intracellular membrane vesicles. Emerging evidence reveal the unexpected expression of dysferlin in non-muscle, non-mechanically active tissues, such as endothelial cells, which cast doubts over the belief that ferlin proteins act exclusively as membrane repair proteins. We and others have shown that deficient trafficking of membrane bound proteins in dysferlin-deficient cells, suggesting that dysferlin might mediate trafficking of client proteins. Herein, we describe the intracellular trafficking and movement of GFP-dysferlin positive vesicles in unfixed reconstituted cells using live microscopy. By performing GST pull-down assays followed by mass spectrometry, we identified dysferlin binding protein complexes in human vascular endothelial cells. Together, our data further support the claims that dysferlin not only mediates membrane repair but also trafficking of client proteins, ultimately, help bridging dysferlinopathies to aberrant membrane signaling.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Assessing plant community composition fails to capture impacts of white-tailed deer on native and invasive plant species

Excessive herbivory can have transformative effects on forest understory vegetation, converting diverse communities into depauperate ones, often with increased abundance of non-native plants. White-tailed deer are a problematic herbivore throughout much of eastern North America and alter forest understory community structure. Reducing (by culling) or eliminating (by fencing) deer herbivory is expected to return understory vegetation to a previously diverse condition. We examined this assumption from 1992 to 2006 at Fermilab (Batavia, IL) where a cull reduced white-tailed deer ( Odocoileus virginianus ) abundance in 1998/1999 by 90 % from 24.6 to 2.5/km 2 , and at West Point, NY, where we assessed interactive effects of deer, earthworms, and invasive plants using 30 × 30 m paired fenced and open plots in 12 different forests from 2009 to 2012. We recorded not only plant community responses (species presence and cover) within 1 m 2 quadrats, but also responses of select individual species (growth, reproduction). At Fermilab, introduced Alliaria petiolata abundance initially increased as deer density increased, but then declined after deer reduction. The understory community responded to the deer cull by increased cover, species richness and height, and community composition changed but was dominated by early successional native forbs. At West Point plant community composition was affected by introduced earthworm density but not deer exclusion. Native plant cover increased and non-native plant cover decreased in fenced plots, thus keeping overall plant cover similar. At both sites native forb cover increased in response to deer reduction, but the anticipated response of understory vegetation failed to materialize at the community level. Deer-favoured forbs ( Eurybia divaricata, Maianthemum racemosum, Polygonatum pubescens and Trillium recurvatum ) grew taller and flowering probability increased in the absence of deer. Plant community monitoring fails to capture initial and subtle effects of reduced or even cessation of deer browse on browse sensitive species. As a result, measuring responses of individual plants (growth, flowering and reproductive success) provides a more sensitive and powerful assessment of forest understory responses to deer management.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Results from a search for dark matter in the complete LUX exposure

Here, we report constraints on spin-independent weakly interacting massive particle (WIMP)-nucleon scattering using a 3.35 ×10 4 kg day exposure of the Large Underground Xenon (LUX) experiment. A dual-phase xenon time projection chamber with 250 kg of active mass is operated at the Sanford Underground Research Facility under Lead, South Dakota (USA). With roughly fourfold improvement in sensitivity for high WIMP masses relative to our previous results, this search yields no evidence of WIMP nuclear recoils. At a WIMP mass of 50 GeV c –2 , WIMP-nucleon spin-independent cross sections above 2.2 ×10 –46 cm 2 are excluded at the 90% confidence level. When combined with the previously reported LUX exposure, this exclusion strengthens to 1.1 × 10 –46 cm 2 at 50 GeV c –2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

K*{sup +} Photoproduction at CLAS

The study of hyperon resonances has entered a new era of precision with advent of high-statistics photoproduction data from the CLAS detector at Jefferson Lab and elsewhere. These data have multi-particle final states, allowing clean identification of exclusive reactions associated with strange mesons and baryons. In this paper, cross sections for K* photoproduction are presented that will provide a future test of the existence of the purported K{sub 0}(800) meson via comparison with theoretical models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

New Concepts in Electrolytes

Over the past decades, Li-ion battery (LIB) has turned into one of the most important advances in the history of technology due to its extensive and in-depth impact on our life. Its omnipresence in all electric vehicles, consumer electronics and electric grids relies on the precisely tuned electrochemical dynamics and interactions among the electrolytes and the diversified anode and cathode chemistries therein. Furthermore, with consumers' demand for battery performance ever increasing, more and more stringent requirements are being imposed upon the established equilibria among these LIB components, and it became clear that the state-of-the-art electrolyte systems could no longer sustain the desired technological trajectory. Driven by such gap, researchers started to explore more unconventional electrolyte systems. From superconcentrated solvent-in-salt electrolytes to solid-state electrolytes, the current research realm of novel electrolyte systems has grown to unprecedented levels. In this review, we will avoid discussions on current state-of-the-art electrolytes but instead focus exclusively on unconventional electrolyte systems that represent new concepts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Study of charm hadronization with prompt $ {\Lambda}_{\textrm{c}}^{+} $ baryons in proton-proton and lead-lead collisions at $ \sqrt{s_{\textrm{NN}}} $ = 5.02 TeV

The production of prompt $ {\Lambda}_{\textrm{c}}^{+} $ baryons is measured via the exclusive decay channel $ {\Lambda}_{\textrm{c}}^{+}\to p{\textrm{K}}^{-}{\pi}^{+} $ at a center-of-mass energy per nucleon pair of 5.02 TeV, using proton-proton (pp) and lead-lead (PbPb) collision data collected by the CMS experiment at the CERN LHC. The pp and PbPb data were obtained in 2017 and 2018 with integrated luminosities of 252 and 0.607 nb$^{−1}$, respectively. The measurements are performed within the $ {\Lambda}_{\textrm{c}}^{+} $ rapidity interval |y| < 1 with transverse momentum (p$_{T}$) ranges of 3–30 and 6–40 GeV/c for pp and PbPb collisions, respectively. Compared to the yields in pp collisions scaled by the expected number of nucleon-nucleon interactions, the observed yields of $ {\Lambda}_{\textrm{c}}^{+} $ with p$_{T}$> 10 GeV/c are strongly suppressed in PbPb collisions. The level of suppression depends significantly on the collision centrality. The $ {\Lambda}_{\textrm{c}}^{+} $/D$^{0}$ production ratio is similar in PbPb and pp collisions at p$_{T}$> 10 GeV/c, suggesting that the coalescence process does not play a dominant role in prompt $ {\Lambda}_{\textrm{c}}^{+} $ baryon production at higher p$_{T}$.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Assessing the Reliability and Quality of Online Uterine Fibroid Embolization Resources

This study was designed to examine the best internet resources about uterine fibroid embolization (UFE) pertinent to medical trainees, radiologists, gynecologists, family physicians, and patients. The terms 'uterine fibroid embolization,' 'uterine fibroid embolization,' and 'uterine artery embolization' were entered into Google, Yahoo, and Bing search engines; the top 20 hits were assessed. The hits were categorized as organizational or nonorganizational. Additionally, 23 radiological and obstetrical organizations were assessed. The DISCERN instrument and Journal of the American Medical Association (JAMA) benchmarks (authorship, attribution, currency, disclosure) were used to assess the information critically. The scope, strength, weaknesses, and unique features were highlighted for the top five organizational and nonorganizational websites. A total of 203 websites were reviewed; 23 were removed in accordance with the exclusion criteria and 146 were duplicate websites, for a total of 34 unique sites. It was found that 35 % (12/34 websites) were organizational (family medicine, radiology, obstetrics/gynecology) and 65 % (22/34 websites) were nonorganizational (teaching or patient resources). The overall mean DISCERN score was 49.6 (10.7). Two-tailed, unpaired t test demonstrated no statistically significant difference between organizational and nonorganizational websites (p = 0.101). JAMA benchmarks revealed 44 % (15/34 websites) with authorship, 71 % (24/34 websites) with attribution, 68 % (23/34 websites) with disclosure, and 47 % (16/34 websites) with currency. The overall quality of websites for UFE is moderate, with important but not serious shortcomings. The best websites provided relevant information about the procedure, benefits/risks, and were interactive. DISCERN scores were compromised by sites failing to provide resources for shared decision-making, additional support, and discussing consequence of no treatment. JAMA benchmarks revealed lack of authorship and currency.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Probing Nitrogen-Doping Effects in the Core-Shell Structured Catalysts for Bifunctional Electrocatalysis.

The design of core-shell structured catalysts has attracted wide interests due to their remarkable catalytic performances in many fields. Although the nitrogen doping is often integrated in such kind of catalysts, the main contribution is exclusively attributed to the metal sites or the core-shell configuration. The role of nitrogen doping is often believed to be less important, which remains largely unexplored. Here, in an effort to probe the catalytic role of heterogeneous doping in such core-shell structure, the effect of nitrogen doping on the activation of cobalt and iron carbide-based materials for the electrocatalytic reduction of oxygen and the hydrogen evolution reaction is originally revealed. The nitrogen doping in the core-shell structured biphasic interfaces is found to be of critical importance for triggering the electrocatalytic activity and selectivity. Therefore, this study shows the neglected but critical role of nitrogen doping and biphasic interactions in a core-shell configuration, paving a new pathway towards the performance enhancement.

biphasic interfaces↗
DOE OSTI2019

Triplet Tuning: A Novel Family of Non-Empirical Exchange–Correlation Functionals

In the framework of density functional theory (DFT), the lowest triplet excited state (T1) can be evaluated using multiple formulations, the most straightforward of which are unrestricted density functional theory (UDFT) and time-dependent density functional theory (TDDFT). Assuming the exact exchange-correlation (XC) functional is applied, UDFT and TDDFT provide identical energies for T1 ( ET), which is also a constraint that we require our XC functionals to obey. However, this condition is not satisfied by most of the popular XC functionals, leading to inaccurate predictions of low-lying, spectroscopically and photochemically important excited states, such as T1 and the lowest singlet excited state (S1). Inspired by the optimal tuning strategy for frontier orbital energies [T. Stein, L. Kronik, and R. Baer, J. Am. Chem. Soc. 2009, 131, 2818], we proposed a novel and nonempirical prescription of constructing an XC functional in which the agreement between UDFT and TDDFT in ET is strictly enforced. Referred to as "triplet tuning", our procedure allows us to formulate the XC functional on a case-by-case basis, using the molecular structure as the exclusive input, without fitting to any experimental data. The first triplet tuned XC functional, TT-ωPBEh, is formulated as a long-range-corrected (LRC) hybrid of Perdew-Burke-Ernzerhof (PBE) and Hartree-Fock (HF) functionals [M. A. Rohrdanz, K. M. Martins, and J. M. Herbert, J. Chem. Phys. 2009, 130, 054112] and tested on four sets of large organic molecules. Compared to existing functionals, TT-ωPBEh manages to provide more accurate predictions for key spectroscopic and photochemical observables, including but not limited to ET, the optical band gap ( ES), the singlet-triplet gap (Δ EST), and the vertical ionization potential ( I⊥), as it adjusts the effective electron-hole interactions to arrive at the correct excitation energies. This promising triplet tuning scheme can be applied to a broad range of systems that were notorious in DFT for being extremely challenging.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Kinematical correlations of dielectrons from semileptonic decays of heavy mesons and Drell-Yan processes at BNL RHIC

We discuss kinematical correlations between charged leptons from semileptonic decays of open charm/bottom leptons produced in the Drell-Yan mechanism as well as some other mechanisms not included so far in the literature in proton-proton scattering at Brookhaven National Laboratory (BNL) Relativistic Heavy Ion Collider (RHIC). The distributions of charm and bottom quarks/antiquarks are calculated in the framework of the k{sub t}-factorization approach. For this calculation we use different unintegrated parton distributions from the literature. The hadronization of heavy quarks is done with the help of well-known fragmentation functions. Uncertainties of our predictions related to heavy quark masses, factorization, and renormalization scales as well as due to the choice of fragmentation model are also discussed. We use semileptonic decay functions found by fitting recent semileptonic data obtained by the CLEO and BABAR collaborations. The Drell-Yan processes were calculated including transverse momenta of quarks and antiquarks, using the Kwiecinski parton distributions. We have also taken into consideration reactions initiated by purely QED {gamma}{sup *{gamma}*} fusion in elastic and inelastic pp collisions as well as a recently proposed diffractive mechanism of exclusive charm-anticharm production. The contribution of the latter mechanism is rather small. We get a good description of the dilepton invariant mass spectrum measured recently by the PHENIX Collaboration and present predictions for the dilepton pair transverse momentum distribution as well as the distribution in the azimuthal angle between electron and positron.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗