Página 6 dos resultados de 19478 itens digitais encontrados em 0.073 segundos

## Development of an experiment to study the effects of transverse stress on the critical current of a niobium-tin superconducting cable

Chiesa, Luisa
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 199 leaves
ENG
Relevância na Pesquisa
45.91%
Superconducting magnets will play a central role for the success of the International Thermonuclear Experimental Reactor (ITER). ITER is a current driven plasma experiment that could set a milestone towards the demonstration of fusion as a source of energy in the future. Cable-in-Conduit is the typical geometry for the conductor employed in superconducting magnets for fusion application. The cable is composed of over 800 strands. Once energized, the magnets produce an enormous electromagnetic force defined by the product of the current and the magnetic field. The strands move under the effect of this force, and the force accumulates against one side of the conduit thereby pressing transversally against the strands. The experiment proposed here has the goal of assessing the functionality of the apparatus designed to study the effect of transverse load on a cable composed of 36 superconducting strands (with a 3x3x4 pattern) by mechanically simulating the ITER Lorentz stress condition. The apparatus was assembled at MIT and preliminary tests at 77 K and room temperature were made to improve the design prior to carrying out the actual experiments. These were done at the National High Magnetic Field Laboratory (NHMFL) located in Florida. Ideally...

## Nuclear shadowing in photoproduction of $\rho$ mesons in ultraperipheral nucleus collisions at RHIC and the LHC

Frankfurt, L.; Guzey, V.; Strikman, M.; Zhalov, M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We argue that with an increase of the collision energy, elastic photoproduction of $\rho$ mesons on nuclei becomes affected by the significant cross section of photon inelastic diffraction which results in the sizable inelastic nuclear shadowing correction to $\sigma_{\gamma A \to \rho A}$ and by an enhanced contribution of weakly-interacting hadronic configurations in the photon which reduces the effective $\rho$-nucleon cross section. We take these effects into account by combining the vector meson dominance model, upgraded to include the contribution of high-mass fluctuations according to QCD constraints, with the Gribov-Glauber approximation for nuclear shadowing, where the inelastic nuclear shadowing is included by means of cross section fluctuations. The resulting approach allows us to successfully describe the data on elastic $\rho$ photoproduction on nuclei in heavy ion UPCs in the $7 < W_{\gamma p} < 46$ GeV energy range and to predict the value of the cross section of coherent $\rho$ photoproduction in Pb-Pb UPCs at $\sqrt{s_{NN}}=5.02$ TeV in Run 2 at the LHC, $d\sigma_{Pb Pb \to \rho Pb Pb} (y=0)/dy= 560 \pm 25$ mb.; Comment: 13 pages, 6 figures

## High $p_T$ Parton Energy Loss from Jet Pair Correlation Observables in the PHENIX Experiment

Chen, Chin-Hao; collaboration, for the PHENIX
Tipo: Artigo de Revista Científica
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By tuning several experimental observables, such as momentum and reaction plane, the PHENIX experiment has performed a systematic study of high $p_T$ parton energy loss in hot nuclear matter, as well as jet induced medium modifications, such as the ridge and shoulder. Baseline d+Au measurements are also studied to provide the comparison as control of cold nuclear matter effect.; Comment: 4 pages, 6 figures. To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee, with minor correction

## $J/\Psi$ mass shift and $J/\Psi$-nuclear bound state

Tsushima, K.; Lu, D. H.; Krein, G.; Thomas, A. W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We calculate mass shift of the $J/\Psi$ meson in nuclear matter arising from the modification of $DD, DD^*$ and $D^*D^*$ meson loop contributions to the $J/\Psi$ self-energy. The estimate includes the in-medium $D$ and $D^*$ meson masses consistently. The $J/\Psi$ mass shift (scalar potential) calculated is negative (attractive), and complementary to the attractive potential obtained from the QCD color van der Waals forces. Some results for the $J/\Psi$-nuclear bound state energies are also presented.; Comment: 6 pages, talk given at "T(r)opical QCD II", September 26 - October 1, 2010, Cairns, Australia

## Properties of charmed and bottom hadrons in nuclear matter: A plausible study

Tsushima, K.; Khanna, F. C.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.91%
Changes in properties of heavy hadrons with a charm or a bottom quark are studied in nuclear matter. Effective masses (scalar potentials) for the hadrons are calculated using quark-meson coupling model. Our results also suggest that the heavy baryons containing a charm or a bottom quark will form charmed or bottom hypernuclei, which was first predicted in mid 70's. In addition a possibility of $B^-$-nuclear bound (atomic) states is briefly discussed.; Comment: Latex, 11 pages, 3 figures, text was expanded substantially, version to appear in Phys. Lett. B

## Bound Nucleon Form Factors, Quark-Hadron Duality, and Nuclear EMC Effect

Tsushima, K.; Lu, D. H.; Melnitchouk, W.; Saito, K.; Thomas, A. W.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We discuss the electromagnetic form factors, axial form factors, and structure functions of a bound nucleon in the quark-meson coupling (QMC) model. Free space nucleon form factors are calculated using the improved cloudy bag model (ICBM). After describing finite nuclei and nuclear matter in the quark-based QMC model, we compute the in-medium modification of the bound nucleon form factors in the same framework. Finally, limits on the medium modification of the bound nucleon $F_2$ structure function are obtained using the calculated in-medium electromagnetic form factors and local quark-hadron duality.; Comment: 18 pages, 13 embedded figures, uses revtex (necessary files included), talk presented by KT at the Joint Jlab-UGA Workshop on Modern Sub-Nuclear Physics and Jlab Experiments", to honor the occasion of Dr. Joe Hamilton (Vanderbilt University), September 13, 2002, University of Georgia, Athens, Georgia, USA, and to be published in the proceedings

## Transport-theoretical Description of Nuclear Reactions

Buss, O.; Gaitanos, T.; Gallmeister, K.; van Hees, H.; Kaskulov, M.; Lalakulich, O.; Larionov, A. B.; Leitner, T.; Weil, J.; Mosel, U.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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In this review we first outline the basics of transport theory and its recent generalization to off-shell transport. We then present in some detail the main ingredients of any transport method using in particular the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) implementation of this theory as an example. We discuss the potentials used, the ground state initialization and the collision term, including the in-medium modifications of the latter. The central part of this review covers applications of GiBUU to a wide class of reactions, starting from pion-induced reactions over proton and antiproton reactions on nuclei to heavy-ion collisions (up to about 30 AGeV). A major part concerns also the description of photon-, electron- and neutrino-induced reactions (in the energy range from a few 100 MeV to a few 100 GeV). For this wide class of reactions GiBUU gives an excellent description with the same physics input and the same code being used. We argue that GiBUU is an indispensable tool for any investigation of nuclear reactions in which final-state interactions play a role. Studies of pion-nucleus interactions, nuclear fragmentation, heavy ion reactions, hyper nucleus formation, hadronization, color transparency, electron-nucleus collisions and neutrino-nucleus interactions are all possible applications of GiBUU and are discussed in this article.; Comment: 173 pages...

## The Qweak Experiment -- A search for new physics at the TeV Scale

Qweak Collaboration; van Oers, Willem T. H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.92%
A new precision measurement of the parity violating analyzing power in longitudinally polarized electron scattering from the proton at very low Q^2 at an incident energy of 1.16 GeV is in the final stages of preparation for execution at Jefferson Laboratory (JLab). A 2200 hour measurement of the parity violating asymmetry in elastic electron-proton scattering at Q^2 = 0.03 (GeV/c)^2 employing 180 microamp of 85% polarized beam on a 0.35 m long liquid hydrogen target will determine the weak charge of the proton, Q_w = 1 - 4sin^2(theta_W), with 4% combined statistical and systematic errors. The Standard Model makes a firm prediction of Q_w, based on the `running' of the weak mixing angle sin^2(theta_W) from the Z-pole down to lower energies. Any significant deviation of sin^2(theta_W) from its Standard Model prediction at low Q^2 would constitute a signal of new physics. In the absence of new physics, the envisaged experiment will provide a 0.3% determination of sin^2(theta_W), making this a very competitive measurement of the weak mixing angle. Complementary to the present experiment is a measurement of the weak charge of the electron in parity violating Moller scattering at 11 GeV, currently under consideration, with the upgraded CEBAF at JLab. The objective of that experiment would be a measurement of sin2(theta_W) with a precision comparable to or better than any individual measurement at the Z-pole.; Comment: 9 pages...

## Nuclear modification of vector boson production in proton-lead collisions at the LHC

Kang, Zhong-Bo; Qiu, Jian-Wei
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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In anticipating the upcoming proton-lead run at the LHC in the near future, we present predictions for the nuclear modification factor of transverse momentum spectrum of $Z^0$ production and transverse momentum broadening of vector boson ($J/\psi$, $\Upsilon$, $W/Z^0$) production in proton-lead collisions at $\sqrt{s}=5$ TeV, respectively. We find that the measurement of nuclear modification factor of $Z^0$ production provides a clean and unambiguous test of the nuclear anti-shadowing proposed in the recent EPS09. In addition, the dramatic difference in transverse momentum broadening between the heavy quarkonium and $W/Z^0$ production could be a signature prediction of QCD parton multiple scattering, and it provides valuable informations on color neutralization of a produced heavy quark pair when it transmutes into a physical quarkonium.; Comment: 9 pages, 5 figures, minor modification, version to appear in PLB

## Current Status of Nuclear Physics Research

Bertulani, C. A.; Hussein, M. S.
Tipo: Artigo de Revista Científica
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In this review we discuss the current status of research in nuclear physics which is being carried out in different centers in the World. For this purpose we supply a short account of the development in the area which evolved over the last 9 decades, since the discovery of the neutron. The evolution of the physics of the atomic nucleus went through many stages as more data become available. We briefly discuss models introduced to discern the physics behind the experimental discoveries, such as the shell model, the collective model, the statistical model, the interacting boson model, etc., some of these models may be seemingly in conflict with each other, but this was shown to be only apparent. The richness of the ideas and abundance of theoretical models attests to the important fact that the nucleus is a really singular system in the sense that it evolves from two-body bound states such as the deuteron, to few-body bound states, such as $^4$He, $^7$Li, $^9$Be etc. and up the ladder to heavier bound nuclei containing up to more than 200 nucleons. Clearly statistical mechanics does not work for such finite system, neither does other theories applicable to condensed matter systems. The richness of nuclear physics stems from these restrictions. New theories and models are presently being developed. Theories of the structure and reactions of neutron-rich and proton-rich nuclei...

## Nuclear modification of transverse-longitudinal structure function ratio

Ericson, M.; Kumano, S.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We investigate the nuclear effects on the transverse and longitudinal responses in the deep inelastic region due to the nuclear binding and nucleon Fermi motion. We display the role of the transverse-longitudinal admixture due to the transverse nucleon momentum. The mixing effect is appreciable at small Q^2 values, and gradually disappears at large Q^2 values. The nuclear modification is then dominated by the binding and Fermi-motion effects which are contained in the spectral function.; Comment: 4 pages, REVTeX4.0, revtex4.cls, url.sty, natbib.sty, revsymb.sty, 10pt.rtx, aps.rtx, amssymb.sty, amsfonts.sty, 2 eps figures. Submitted for publication. Email: Magda.Ericson@cern.ch, kumanos@cc.saga-u.ac.jp See: http://hs.phys.saga-u.ac.jp

## Germanium Detector Response to Nuclear Recoils in Searching for Dark Matter

Barker, D.; Mei, D. -M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The discrepancies in claims of experimental evidence in the search for weakly interacting massive particle (WIMP) dark matter necessitate a model for ionization efficiency (the quenching factor) at energies below 10 keV. We have carefully studied the physics processes that contribute to the ionization efficiency through stopping power. The focus of this work is the construction of a model for the ionization efficiency in germanium by analyzing the components of stopping power, specifically that of the nuclear stopping power, at low energies. We find a fraction of the ZBL nuclear stopping power can contribute to ionization efficiency. We propose a model that corrects the missing contribution to ionization efficiency from the ZBL nuclear stopping power. The proposed model is compared to previous measurements of ionization efficiency in germanium as well as that of other theoretical models. Using this new model, the thresholds of both CDMS II and CoGeNT are analyzed and compared in terms of the nuclear recoil energy.; Comment: 17 pages and 8 figures

## Pion-induced production of the $Z_c(3900)$ off nuclear target

Huang, Yin; He, Jun; Liu, Xiang; Zhang, Hong Fei; Xie, Ju Jun; Chen, Xu Rong
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.92%
We investigate the possibility to study the charmonium-like state $Z_c(3900)$ through the pion-induced production off nuclear target. By using high-energy pion beam, the $Z_c(3900)$ can be produced off proton or nucleus though the Primakoff effect. The production amplitude is calculated in an effective Lagrangian approach combined with the vector dominance model. The total cross sections of the $p(\pi^-, Z^-_c(3900))$ and $p(\pi^-, Z^-_c(3900)\to J/\psi\pi^-)$ reactions are calculated, which order of magnitude is about 0.1 and 0.01nb, respectively, with an assumption of branch ratio 10\% for the $Z_c(3900)$ decay in $J/\psi\pi$ channel. If proton target is replaced by nuclear target, the production of the $Z_c(3900)$ enhances obviously. The predicted total cross sections for the $A(\pi^-, Z^-_c(3900))$ and $A(\pi^-, Z^-_c(3900)\to J/\psi\pi^-)$ reactions with $A=^{12}$C or $^{208}$Pb are on the order of magnitude of 100 and 10 nb, respectively, which is about one thousand times larger than the cross sections off proton target. Based on the results, we suggest the experimental study of the $Z_c(3900)$ by using high-energy pion beams with nuclear target at facilities, such as COMPASS and J-PARC.; Comment: 5 pages, 3 figures

## Impact of the Nuclear Modification of the Gluon Densities on J/Psi production in pPb collisions at sqrt(s_NN) = 5 TeV

Ferreiro, E. G.; Fleuret, F.; Lansberg, J. P.; Rakotozafindrabe, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.92%
We update our previous studies of nuclear-matter effects on J/Psi production in proton-nucleus for the recent LHC pPb runs at sqrt(s_NN)=5 TeV. We have analysed the effects of the modification of the gluon PDFs in nucleus, using an exact kinematics for a 2->2 process, namely g+g->J/Psi+g as expected from LO pQCD. This allows to constrain the transverse-momentum while computing the nuclear modification factor for different rapidities, unlike with the usual simplified kinematics. Owing to the absence of measurement in pp collisions at the same sqrt(s_NN) and owing to the expected significant uncertainties in yield interpolations which would hinder definite interpretations of nuclear modification factor --R_pPb--, we have derived forward-to-backward and central-to-peripheral yield ratios in which the unknown proton-proton yield cancel. These have been computed without and with a transverse-momentum cut, e.g. to comply with the ATLAS and CMS constraints in the central-rapidity region.; Comment: 5 pages, 16 figures, LaTeX. v2: predictions on R_CP and 3 references added; introduction slightly extended

## Enhancement of the CP-odd effect in the nuclear electric dipole moment of $^6$Li

Yamanaka, Nodoka; Hiyama, Emiko
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.92%
We calculate for the first time the electric dipole moment (EDM) of the $^6$Li nucleus within the alpha + p + n three-body cluster model using the Gaussian expansion method, assuming the one meson exchange P, CP-odd nuclear forces. It is found that the EDM of the $^6$Li is 2 times more sensitive on the isovector pion exchange P, CP-odd nuclear force than the deuteron EDM, due to the CP-odd interaction between the nucleons and the alpha cluster. The $^9$Be EDM is also calculated in the same framework as an alpha + alpha + n three-body system. We also test the ab initio calculation of the EDM of the deuteron, $^3$H and $^3$He nuclei using the realistic Argonne $v18$ nuclear force. In the ab initio calculations, good agreements with previous studies are obtained. We finally discuss the prospects for the new physics beyond the standard model.; Comment: 6 pages, 1 figure

## Proton Structure and PHENIX Experiment

Qiu, Jian-Wei
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We briefly summarize the important and critical roles that PHENIX Experiment has played in determining the proton's internal structure in terms of quarks and gluons, and their dynamics. Some pioneering measurements by PHENIX Experiment on the motion and polarization of quarks and gluons, as well as their correlations inside a fast moving proton are presented. Some future opportunities and potentials of PHENIX Experiment are also discussed.; Comment: 18 pages, 9 figures, invited mini-review to be published in a special section on "PHYSICS at PHENIX, 15 years of discoveries" by the journal of Progress of Theoretical and Experimental Physics

## Determination of nuclear parton distribution functions and their uncertainties at next-to-leading order

Hirai, M.; Kumano, S.; Nagai, T. -H.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.92%
Nuclear parton distribution functions (NPDFs) are determined by global analyses of experimental data on structure-function ratios F_2^A/F_2^{A'} and Drell-Yan cross-section ratios \sigma_{DY}^A/\sigma_{DY}^{A'}. The analyses are done in the leading order (LO) and next-to-leading order (NLO) of running coupling constant \alpha_s. Uncertainties of the NPDFs are estimated in both LO and NLO for finding possible NLO improvement. Valence-quark distributions are well determined, and antiquark distributions are also determined at x<0.1. However, the antiquark distributions have large uncertainties at x>0.2. Gluon modifications cannot be fixed at this stage. Although the advantage of the NLO analysis, in comparison with the LO one, is generally the sensitivity to the gluon distributions, gluon uncertainties are almost the same in the LO and NLO. It is because current scaling-violation data are not accurate enough to determine precise nuclear gluon distributions. Modifications of the PDFs in the deuteron are also discussed by including data on the proton-deuteron ratio F_2^D/F_2^p in the analysis. A code is provided for calculating the NPDFs and their uncertainties at given x and Q^2 in the LO and NLO.; Comment: 15 pages, LaTeX, 22 eps files...

## Probing particle and nuclear physics models of neutrinoless double beta decay with different nuclei

Fogli, G. L.; Lisi, E.; Rotunno, A. M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Half-life estimates for neutrinoless double beta decay depend on particle physics models for lepton flavor violation, as well as on nuclear physics models for the structure and transitions of candidate nuclei. Different models considered in the literature can be contrasted - via prospective data - with a "standard" scenario characterized by light Majorana neutrino exchange and by the quasiparticle random phase approximation, for which the theoretical covariance matrix has been recently estimated. We show that, assuming future half-life data in four promising nuclei (Ge-76, Se-82, Te-130, and Xe-136), the standard scenario can be distinguished from a few nonstandard physics models, while being compatible with alternative state-of-the-art nuclear calculations (at 95% C.L.). Future signals in different nuclei may thus help to discriminate at least some decay mechanisms, without being spoiled by current nuclear uncertainties. Prospects for possible improvements are also discussed.; Comment: Minor corrections in the text, references added. Matches published version in Phys. Rev. D 80, 015024 (2009)

## Constraints on the time-scale of nuclear breakup from thermal hard-photon emission

Ortega, R.; d'Enterria, D.; Martinez, G.; Baiborodin, D.; Delagrange, H.; Diaz, J.; Fernandez, F.; Loehner, H.; Matulewicz, T.; Ostendorf, R. W.; Schadmand, S.; Schutz, Y.; Tlusty, P.; Turrisi, R.; Wagner, V.; Wilschut, H. W.; Yahlali, N.
Tipo: Artigo de Revista Científica
Measured hard photon multiplicities from second-chance nucleon-nucleon collisions are used in combination with a kinetic thermal model, to estimate the break-up times of excited nuclear systems produced in nucleus-nucleus reactions at intermediate energies. The obtained nuclear break-up time for the $^{129}${Xe} + $^{nat}${Sn} reaction at 50{\it A} MeV is $\Delta$$\tau \approx 100 -- 300 fm/c for all reaction centralities. The lifetime of the radiating sources produced in seven other different heavy-ion reactions studied by the TAPS experiment are consistent with \Delta$$\tau$ $\approx$ 100 fm/$c$, such relatively long thermal photon emission times do not support the interpretation of nuclear breakup as due to a fast spinodal process for the heavy nuclear systems studied.; Comment: 11 pages, 9 figures, submitted to EPJA