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N*(1535) electroproduction at high Q2 (open access)

N*(1535) electroproduction at high Q2

A covariant spectator quark model is applied to study the {gamma}N {yields} N*(1535) reaction in the large Q{sup 2} region. Starting from the relation between the nucleon and N*(1535) systems, the N*(1535) valence quark wave function is determined without the addition of any parameters. The model is then used to calculate the {gamma}N {yields} N*(1535) transition form factors. A very interesting, useful relation between the A{sub 1/2} and S{sub 1/2} helicity amplitudes for Q{sup 2} > GeV{sup 2}, is also derived.
Date: April 1, 2012
Creator: G. Ramalho, M.T. Pena, K. Tsushima
System: The UNT Digital Library
Absorber Alignment Measurement Tool for Solar Parabolic Trough Collectors: Preprint (open access)

Absorber Alignment Measurement Tool for Solar Parabolic Trough Collectors: Preprint

As we pursue efforts to lower the capital and installation costs of parabolic trough solar collectors, it is essential to maintain high optical performance. While there are many optical tools available to measure the reflector slope errors of parabolic trough solar collectors, there are few tools to measure the absorber alignment. A new method is presented here to measure the absorber alignment in two dimensions to within 0.5 cm. The absorber alignment is measured using a digital camera and four photogrammetric targets. Physical contact with the receiver absorber or glass is not necessary. The alignment of the absorber is measured along its full length so that sagging of the absorber can be quantified with this technique. The resulting absorber alignment measurement provides critical information required to accurately determine the intercept factor of a collector.
Date: April 1, 2012
Creator: Stynes, J. K. & Ihas, B.
System: The UNT Digital Library
An Alternative View of the Dynamical Origin of the P11 Nucleon Resonances: Results from the Excited Baryon Analysis Center (open access)

An Alternative View of the Dynamical Origin of the P11 Nucleon Resonances: Results from the Excited Baryon Analysis Center

We present an alternative interpretation for the dynamical origin of the P{sub 11} nucleon resonances, which results from the dynamical coupled-channels analysis at Excited Baryon Analysis Center of Jefferson Lab. The results indicate the crucial role of the multichannel reaction dynamics in determining the N* spectrum. An understanding of the spectrum and structure of the excited nucleon (N*) states is a fundamental challenge in the hadron physics. The N* states, however, couple strongly to the meson-baryon continuum states and appear only as resonance states in the {gamma}N and {pi}N reactions. One can expect from such strong couplings that the (multichannel) reaction dynamics will affect significantly the N* states and cannot be neglected in extracting the N* parameters from the data and giving physical interpretations. It is thus well recognized nowadays that a comprehensive study of all relevant meson production reactions with {pi}N,{eta}N,{pi}{pi}N,KY, {hor_ellipsis} final states is necessary for a reliable extraction of the N* parameters. To address this challenging issue, the Excited Baryon Analysis Center (EBAC) of Jefferson Lab has been conducting the comprehensive analysis of the world data of {gamma}N,{pi}N {yields} {pi}N,{eta}N,{pi}{pi}N,KY, {hor_ellipsis} reactions systematically, covering the wide energy and kinematic regions. The analysis is pursued with a dynamical …
Date: April 1, 2012
Creator: Kamano, Hiroyuki
System: The UNT Digital Library
Analytical Approach Treating Three-Dimensional Geometrical Effects of Parabolic Trough Collectors: Preprint (open access)

Analytical Approach Treating Three-Dimensional Geometrical Effects of Parabolic Trough Collectors: Preprint

An analytical approach, as an extension of one newly developed method -- First-principle OPTical Intercept Calculation (FirstOPTIC) -- is proposed to treat the geometrical impact of three-dimensional (3-D) effects on parabolic trough optical performance. The mathematical steps of this analytical approach are presented and implemented numerically as part of the suite of FirstOPTIC code. In addition, the new code has been carefully validated against ray-tracing simulation results and available numerical solutions. This new analytical approach to treating 3-D effects will facilitate further understanding and analysis of the optical performance of trough collectors as a function of incidence angle.
Date: April 1, 2012
Creator: Binotti, M.; Zhu, G.; Gray, A. & Manzollini, G.
System: The UNT Digital Library
Approaching Conformality with Ten Flavors (open access)

Approaching Conformality with Ten Flavors

We present first results for lattice simulations, on a single volume, of the low-lying spectrum of an SU(3) Yang-Mills gauge theory with N{sub f} = 10 light fermions in the fundamental representation. Fits to the fermion mass dependence of various observables are found to be globally consistent with the hypothesis that this theory is within or just outside the strongly-coupled edge of the conformal window, with mass anomalous dimension {gamma}* {approx} 1 over the range of scales simulated. We stress that we cannot rule out the possibility of spontaneous chiral-symmetry breaking at scales well below our infrared cutoff. We discuss important systematic effects, including finite-volume corrections, and consider directions for future improvement.
Date: April 1, 2012
Creator: Appelquist, Thomas; Brower, Richard C.; Buchoff, Michael I.; Cheng, Michael; Cohen, Saul D.; Fleming, George T. et al.
System: The UNT Digital Library
Assessment of Possible Cycle Lengths for Fully-Ceramic Micro-Encapsulated Fuel-Based Light Water Reactor Concepts (open access)

Assessment of Possible Cycle Lengths for Fully-Ceramic Micro-Encapsulated Fuel-Based Light Water Reactor Concepts

The tri-isotropic (TRISO) fuel developed for High Temperature reactors is known for its extraordinary fission product retention capabilities [1]. Recently, the possibility of extending the use of TRISO particle fuel to Light Water Reactor (LWR) technology, and perhaps other reactor concepts, has received significant attention [2]. The Deep Burn project [3] currently focuses on once-through burning of transuranic fissile and fissionable isotopes (TRU) in LWRs. The fuel form for this purpose is called Fully-Ceramic Micro-encapsulated (FCM) fuel, a concept that borrows the TRISO fuel particle design from high temperature reactor technology, but uses SiC as a matrix material rather than graphite. In addition, FCM fuel may also use a cladding made of a variety of possible material, again including SiC as an admissible choice. The FCM fuel used in the Deep Burn (DB) project showed promising results in terms of fission product retention at high burnup values and during high-temperature transients. In the case of DB applications, the fuel loading within a TRISO particle is constituted entirely of fissile or fissionable isotopes. Consequently, the fuel was shown to be capable of achieving reasonable burnup levels and cycle lengths, especially in the case of mixed cores (with coexisting DB and regular …
Date: April 1, 2012
Creator: Sen, R. Sonat; Pope, Michael A.; Ougouag, Abderrafi M. & Pasamehmetoglu, Kemal O.
System: The UNT Digital Library
ASSESSMENT OF POSSIBLE CYCLE LENGTHS FOR FULLY-CERAMIC MICRO-ENCAPSULATED FUEL-BASED LIGHT WATER REACTOR CONCEPTS (open access)

ASSESSMENT OF POSSIBLE CYCLE LENGTHS FOR FULLY-CERAMIC MICRO-ENCAPSULATED FUEL-BASED LIGHT WATER REACTOR CONCEPTS

The use of TRISO-particle-based dispersion fuel within SiC matrix and cladding materials has the potential to allow the design of extremely safe LWRs with failure-proof fuel. This paper examines the feasibility of LWR-like cycle length for such a low enriched uranium fuel with the imposed constraint of strictly retaining the original geometry of the fuel pins and assemblies. The motivation for retaining the original geometry is to provide the ability to incorporate the fuel 'as-is' into existing LWRs while retaining their thermal-hydraulic characteristics. The feasibility of using this fuel is assessed by looking at cycle lengths and fuel failure rates. Other considerations (e.g., safety parameters, etc.) were not considered at this stage of the study. The study includes the examination of different TRISO kernel diameters without changing the coating layer thicknesses. The study shows that a naive use of UO{sub 2} results in cycle lengths too short to be practical for existing LWR designs and operational demands. Increasing fissile inventory within the fuel compacts shows that acceptable cycle lengths can be achieved. In this study, starting with the recognized highest packing fraction practically achievable (44%), higher enrichment, larger fuel kernel sizes, and the use of higher density fuels have been …
Date: April 1, 2012
Creator: Sen, R. Sonat; Pope, Michael A.; Ougouag, Abderrafi M.; Pasamehmetoglu, Kemal & Venneri, Francesco
System: The UNT Digital Library
Axial couplings and strong decay widths of heavy hadrons (open access)

Axial couplings and strong decay widths of heavy hadrons

We calculate the axial couplings of mesons and baryons containing a heavy quark in the static limit using lattice QCD. These couplings determine the leading interactions in heavy hadron chiral perturbation theory and are central quantities in heavy quark physics, as they control strong decay widths and the light-quark mass dependence of heavy hadron observables. Our analysis makes use of lattice data at six different pion masses, 227 MeV < m{sub {pi}} < 352 MeV, two lattice spacings, a = 0.085, 0.112 fm, and a volume of (2.7 fm){sup 3}. Our results for the axial couplings are g{sub 1} = 0.449(51), g{sub 2} = 0.84(20), and g{sub 3} = 0.71(13), where g{sub 1} governs the interaction between heavy-light mesons and pions and g{sub 2,3} are similar couplings between heavy-light baryons and pions. Using our lattice result for g{sub 3}, and constraining 1/m{sub Q} corrections in the strong decay widths with experimental data for {Sigma}{sub c}{sup (*)} decays, we obtain {Gamma}[{Sigma}{sub b}{sup (*)} {yields} {Lambda}{sub b} {pi}{sup {+-}}] = 4.2(1.0), 4.8(1.1), 7.3(1.6), 7.8(1.8) MeV for the {Sigma}{sub b}{sup +}, {Sigma}{sub b}{sup -}, {Sigma}{sub b}{sup *+}, {Sigma}{sub b}{sup *-} initial states, respectively. We also derive upper bounds on the widths of the …
Date: April 1, 2012
Creator: William Detmold, C.-J. David Lin, Stefan Meinel
System: The UNT Digital Library
Battery Electric Vehicle Driving and Charging Behavior Observed Early in The EV Project (open access)

Battery Electric Vehicle Driving and Charging Behavior Observed Early in The EV Project

As concern about society's dependence on petroleum-based transportation fuels increases, many see plug-in electric vehicles (PEV) as enablers to diversifying transportation energy sources. These vehicles, which include plug-in hybrid electric vehicles (PHEV), range-extended electric vehicles (EREV), and battery electric vehicles (BEV), draw some or all of their power from electricity stored in batteries, which are charged by the electric grid. In order for PEVs to be accepted by the mass market, electric charging infrastructure must also be deployed. Charging infrastructure must be safe, convenient, and financially sustainable. Additionally, electric utilities must be able to manage PEV charging demand on the electric grid. In the Fall of 2009, a large scale PEV infrastructure demonstration was launched to deploy an unprecedented number of PEVs and charging infrastructure. This demonstration, called The EV Project, is led by Electric Transportation Engineering Corporation (eTec) and funded by the U.S. Department of Energy. eTec is partnering with Nissan North America to deploy up to 4,700 Nissan Leaf BEVs and 11,210 charging units in five market areas in Arizona, California, Oregon, Tennessee, and Washington. With the assistance of the Idaho National Laboratory, eTec will collect and analyze data to characterize vehicle consumer driving and charging behavior, evaluate …
Date: April 1, 2012
Creator: Smart, John & Schey, Stephen
System: The UNT Digital Library
A COUPLED TH/NEUTRONICS/CRUD FRAMEWORK IN PREDICTION OF CIPS PHENOMENON (open access)

A COUPLED TH/NEUTRONICS/CRUD FRAMEWORK IN PREDICTION OF CIPS PHENOMENON

A coupled TH/Neutronics/CRUD framework, which is able to simulate the CRUD deposits impact on CIPS phenomenon, was described in this paper. This framework includes the coupling among three essential physics, thermal-hydraulics, CRUD and neutronics. The overall framework was implemented by using the CFD software STAR-CCM+, developing CRUD codes, and using the neutronics code DeCART. The coupling was implemented by exchanging data between softwares using intermediate exchange files. A typical 3 by 3 PWR fuel pin problem was solved under this framework. The problem was solved in a 12 months length period of time. Time-dependent solutions were provided, including CRUD deposits inventory and their distributions on fuels, boron hideout amount inside CRUD deposits, as well as power shape changing over time. The results clearly showed the power shape suppression in regions where CRUD deposits exist, which is a strong indication of CIPS phenomenon.
Date: April 1, 2012
Creator: Zou, Ling; Zhang, Hongbin; Gehin, Jess & Kochunas, Brendan
System: The UNT Digital Library
Deeply Virtual Compton Scattering and Meson Production at Jlab/CLAS (open access)

Deeply Virtual Compton Scattering and Meson Production at Jlab/CLAS

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
System: The UNT Digital Library
Deeply virtual Compton scattering on longitudinally polarized protons and neutrons at CLAS (open access)

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

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
System: The UNT Digital Library
Design and Performance of Solar Decathlon 2011 High-Penetration Microgrid: Preprint (open access)

Design and Performance of Solar Decathlon 2011 High-Penetration Microgrid: Preprint

The U.S. Department of Energy Solar Decathlon challenges collegiate teams to design, build, and operate solar-powered houses that are cost-effective, energy-efficient, and attractive. The Solar Decathlon 2011 was held in Washington, D.C., from September 23 to October 2, 2011 . A high-penetration microgrid was designed, installed, and operated for the Solar Decathlon 2011 to grid-connect 19 highly energy-efficient, solar-powered competition houses to a single utility connection point. The capacity penetration of this microgrid (defined as maximum PV generation divided by maximum system load over a two-week period) was 74% based on 1-minute averaged data. Temporary, ground-laid conductors and electrical distribution equipment were installed to grid-connect the Solar Decathlon village, which included the houses as well as other electrical loads used by the event organizers. While 16 of the houses were connected to the 60 Hz microgrid, three houses from Belgium, China, and New Zealand were supplied with 50 Hz power. The design of the microgrid, including the connection of the houses powered by 50 Hz and a standby diesel generator, is discussed in this paper. In addition to the utility-supplied net energy meters at each house, a microgrid monitoring system was installed to measure and record energy consumption and PV …
Date: April 1, 2012
Creator: Stafford, B.; Coddington, M.; Butt, R.; Solomon, S.; Wiegand, G.; Wagner, C. et al.
System: The UNT Digital Library
Determining Wind Turbine Gearbox Model Complexity Using Measurement Validation and Cost Comparison: Preprint (open access)

Determining Wind Turbine Gearbox Model Complexity Using Measurement Validation and Cost Comparison: Preprint

The Gearbox Reliability Collaborative (GRC) has conducted extensive field and dynamometer test campaigns on two heavily instrumented wind turbine gearboxes. In this paper, data from the planetary stage is used to evaluate the accuracy and computation time of numerical models of the gearbox. First, planet-bearing load and motion data is analyzed to characterize planetary stage behavior in different environments and to derive requirements for gearbox models and life calculations. Second, a set of models are constructed that represent different levels of fidelity. Simulations of the test conditions are compared to the test data and the computational cost of the models are compared. The test data suggests that the planet-bearing life calculations should be made separately for each bearing on a row due to unequal load distribution. It also shows that tilting of the gear axes is related to planet load share. The modeling study concluded that fully flexible models were needed to predict planet-bearing loading in some cases, although less complex models were able to achieve good correlation in the field-loading case. Significant differences in planet load share were found in simulation and were dependent on the scope of the model and the bearing stiffness model used.
Date: April 1, 2012
Creator: LaCava, W.; Xing, Y.; Guo, Y. & Moan, T.
System: The UNT Digital Library
Diffraction Results from CDF (open access)

Diffraction Results from CDF

We present final results by the CDF II collaboration on diffractive W and Z production, report on the status of ongoing analyses on diffractive dijet production and on rapidity gaps between jets, and briefly summarize results obtained on exclusive production pointing to their relevance to calibrating theoretical models used to predict exclusive Higgs-boson production at the LHC.
Date: April 1, 2012
Creator: Goulianos, Konstantin
System: The UNT Digital Library
EBAC-DCC Analysis of World Data of pi N, gamma N, and N(e,e') Reactions (open access)

EBAC-DCC Analysis of World Data of pi N, gamma N, and N(e,e') Reactions

The development, results, and prospect of the Dynamical Coupled-Channels analysis at Excited Baryon Analysis Center (EBAC-DCC) are reported. In this contribution, we report on the development, results, and prospect of EBAC. The EBAC project has three components, as illustrated in Fig. 1. The first task is to perform a dynamical coupled-channels analysis of the world data of {pi}N, {gamma}*N {yields} {pi}N, {eta}N, {pi}{pi}N, K{Lambda}, K{Sigma}, {omega}N, {hor_ellipsis} to determine the meson-baryon partial-wave amplitudes. The second step is to develop a procedure to extract the N* parameters from the determined partial-wave amplitudes. The third step is to investigate the interpretations of the extracted N* properties in terms of the available hadron models and Lattice QCD.
Date: April 1, 2012
Creator: Hiroyuki Kamano,Tsung-Shung Lee
System: The UNT Digital Library
Electromagnetic polarizabilities: Lattice QCD in background fields (open access)

Electromagnetic polarizabilities: Lattice QCD in background fields

Chiral perturbation theory makes definitive predictions for the extrinsic behavior of hadrons in external electric and magnetic fields. Near the chiral limit, the electric and magnetic polarizabilities of pions, kaons, and nucleons are determined in terms of a few well-known parameters. In this limit, hadrons become quantum mechanically diffuse as polarizabilities scale with the inverse square-root of the quark mass. In some cases, however, such predictions from chiral perturbation theory have not compared well with experimental data. Ultimately we must turn to first principles numerical simulations of QCD to determine properties of hadrons, and confront the predictions of chiral perturbation theory. To address the electromagnetic polarizabilities, we utilize the background field technique. Restricting our attention to calculations in background electric fields, we demonstrate new techniques to determine electric polarizabilities and baryon magnetic moments for both charged and neutral states. As we can study the quark mass dependence of observables with lattice QCD, the lattice will provide a crucial test of our understanding of low-energy QCD, which will be timely in light of ongoing experiments, such as at COMPASS and HI gamma S.
Date: April 1, 2012
Creator: W. Detmold, B.C. Tiburzi, A. Walker-Loud
System: The UNT Digital Library
Electroproduction of $Λ$(1405) (open access)

Electroproduction of $Λ$(1405)

The electroproduction of K{sup +} {Lambda}(1405) was studied by analyzing the E1F data set collected in Hall B at Jefferson Lab. The analysis utilized the decay channel {Sigma}{sup +} {pi}{sup -} of the {Lambda}(1405) and p{pi}{sup 0} of the {Sigma}{sup +}. Simulations of background, {Lambda}(1405) and {Lambda}(1520) production according to PDG values were performed by using standard CLAS analysis tools adapted for the E1F run. Fits of the acceptance-corrected simulations were made to the acceptance-corrected data to determine contributions from signal and background processes. The line shape of {Lambda}(1405) varies with the four momentum transfer, Q{sup 2}, and does not match the line shape based on PDG resonance parameters. It corresponds approximately to predictions of a recent two-pole meson-baryon picture of this state.
Date: April 1, 2012
Creator: Haiyun Lu, Reinhard Schumacher, Brian Raue, Marianna Gabrielyan
System: The UNT Digital Library
Establishing a Secure Data Center with Remote Access: Preprint (open access)

Establishing a Secure Data Center with Remote Access: Preprint

Access to existing travel data is critical for many analysis efforts that lack the time or resources to support detailed data collection. High-resolution data sets provide particular value, but also present a challenge for preserving the anonymity of the original survey participants. To address this dilemma of providing data access while preserving privacy, the National Renewable Energy Laboratory and the U.S. Department of Transportation have launched the Transportation Secure Data Center (TSDC). TSDC data sets include those from regional travel surveys and studies that increasingly use global positioning system devices. Data provided by different collecting agencies varies with respect to formatting, elements included and level of processing conducted in support of the original purpose. The TSDC relies on a number of geospatial and other analysis tools to ensure data quality and to generate useful information outputs. TSDC users can access the processed data in two different ways. The first is by downloading summary results and second-by-second vehicle speed profiles (with latitude/longitude information removed) from a publicly-accessible website. The second method involves applying for a remote connection account to a controlled-access environment where spatial analysis can be conducted, but raw data cannot be removed.
Date: April 1, 2012
Creator: Gonder, J.; Burton, E. & Murakami, E.
System: The UNT Digital Library
EVALUATION OF CORE PHYSICS ANALYSIS METHODS FOR CONVERSION OF THE INL ADVANCED TEST REACTOR TO LOW-ENRICHMENT FUEL (open access)

EVALUATION OF CORE PHYSICS ANALYSIS METHODS FOR CONVERSION OF THE INL ADVANCED TEST REACTOR TO LOW-ENRICHMENT FUEL

Computational neutronics studies to support the possible conversion of the ATR to LEU are underway. Simultaneously, INL is engaged in a physics methods upgrade project to put into place modern computational neutronics tools for future support of ATR fuel cycle and experiment analysis. A number of experimental measurements have been performed in the ATRC in support of the methods upgrade project, and are being used to validate the new core physics methods. The current computational neutronics work is focused on performance of scoping calculations for the ATR core loaded with a candidate LEU fuel design. This will serve as independent confirmation of analyses that have been performed previously, and will evaluate some of the new computational methods for analysis of a candidate LEU fuel for ATR.
Date: April 1, 2012
Creator: DeHart, Mark & Chang, Gray S.
System: The UNT Digital Library
Evidence for a bound H-dibaryon using lattice QCD (open access)

Evidence for a bound H-dibaryon using lattice QCD

The H-dibaryon, a J = 0 state with the valence quark content udsuds, has long been hypothesized to exist because of the attractive nature of color magnetic gluon exchange in the flavor- singlet channel. Using lattice QCD the NPLQCD collaboration have investigated this system and evidence is presented for the existence of a stable H-dibaryon, albeit at a quark mass somewhat larger than that in nature. This calculation is reviewed and combined with subsequent calculations by the HALQCD collaboration at the SU(3) flavor symmetric point to identify bounds on the H-dibaryon mass at the physical quark masses.
Date: April 1, 2012
Creator: Detmold, Will
System: The UNT Digital Library
Excited light meson spectroscopy from lattice QCD (open access)

Excited light meson spectroscopy from lattice QCD

I report on recent progress in calculating excited meson spectra using lattice QCD, emphasizing results and phenomenology. With novel techniques we can now extract extensive spectra of excited mesons with high statistical precision, including spin-four states and those with exotic quantum numbers. As well as isovector meson spectra, I will present new calculations of the spectrum of excited light isoscalar mesons, something that has up to now been a challenge for lattice QCD. I show determinations of the flavor content of these mesons, including the eta-eta' mixing angle, providing a window on annihilation dynamics in QCD. I will also discuss recent work on using lattice QCD to map out the energy-dependent phase shift in pi-pi scattering and future applications of the methodology to the study of resonances and decays.
Date: April 1, 2012
Creator: Christopher Thomas, Hadron Spectrum Collaboration
System: The UNT Digital Library
Exciting Baryons: now and in the future (open access)

Exciting Baryons: now and in the future

This is the final talk of NSTAR2011 conference. It is not a summary talk, but rather a looking forward to what still needs to be done in excited baryon physics. In particular, we need to hone our tools connecting experimental inputs with QCD. At present we rely on models that often have doubtful connections with the underlying theory, and this needs to be dramatically improved, if we are to reach definitive conclusions about the relevant degrees of freedom of excited baryons. Conclusions that we want to have by NSTAR2021.
Date: April 1, 2012
Creator: Pennington, Michael
System: The UNT Digital Library
Experimental challenges of the N* program (open access)

Experimental challenges of the N* program

The first challenge faced in investigating the strong interaction from partially explored, where meson-cloud degrees of freedom dominate, to still unexplored distance scales, where the dressed-quark contributions are the dominating degrees of freedom, is to find an experiment that allows to measure observables that are probing this evolving nonperturbative QCD regime over the full range. Baryon spectroscopy can establish more sensitively, and in an almost model-independent way, nucleon excitation and non-resonant reaction amplitudes by complete measurements of pseudo-scalar meson photoproduction off nucleons. Elastic and transition form factors can then trace this evolution by measurements of elastic electron scattering and exclusive single-meson and double-pion electroproduction cross sections off the nucleon that will be extended to higher momentum transfers with the energy-upgraded CEBAF beam at JLab to study the dressed quark degrees of freedom, where their strong interaction is responsible for the ground and excited nucleon state formations. After establishing unprecedented high-precision data, the immanent next challenge is a high-quality analysis to extract these relevant electrocoupling parameters for various resonances that then can be compared to state of the art models and QCD-based calculations. Recent results demonstrate the status of the analysis and pinpoint further challenges, including those to establish QCD-based results …
Date: April 1, 2012
Creator: Gothe, Ralf
System: The UNT Digital Library