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Nuclear Theory·nucl-th

Thursday·December 11, 2014

7 papers—2 primary·5 cross-listed

All7Primary2Cross-lists5
  1. 01

    Signatures of collective behavior in small systems

    Igor Kozlov🇨🇦 · Matthew Luzum🇨🇦 · Gabriel Denicol🇨🇦 · Sangyong Jeon🇨🇦 · Charles Gale🇨🇦

    We perform 3+1D viscous hydrodynamics calculations of proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our goal is to understand the apparent collective behavior recently observed in pA collisions and to verify whether the highest multiplicity collision systems can be accurately described as a relativistic fluid. We compare our calculations of flow variables to existing measurements, and demonstrate that hydrodynamics correctly captures the measured trends. We show that our predictions for the pair correlation observable are validated by recent experimental pA measurements, and that our results are sensitive to the granularity of the initial state. We also compare our results with measurements done for nucleus-nucleus collisions.

    nucl-thnucl-exNPA(2014)·15 citations
  2. 02

    Photoproduction of the resonance

    Ju-Jun Xie🇨🇳 · E. Oset🇨🇳

    We have performed a calculation of the reaction, where the two pions have been separated in -wave producing the resonance. We use elements of the local hidden gauge approach that provides the interaction of vector mesons in which the resonance appears as a - molecular state in and spin 2. The vector meson dominance, incorporated in the local hidden gauge approach converts a photon into a meson and the other meson connects the photon with the proton. The picture is simple and has no free parameters, since the parameters of the theory have been constrained in the previous study of the vector-vector states. In a second step we introduce new elements, not present in the local hidden gauge approach, adapting the propagator to Regge phenomenology and introducing the tensor coupling. We find that both the differential cross section as well as the dependence of the cross section are in good agreement with the experimental results and provide support for the molecular picture of the in the first baryonic reaction where it has been tested.

    nucl-thhep-exhep-phnucl-exEPJA(2015)·18 citations
  3. 03

    Double parton correlations in Light-Front constituent quark model

    Matteo Rinaldi🇮🇹 · Sergio Scopetta🇮🇹 · Marco Traini🇮🇹 · Vicente Vento🇪🇸

    Double parton distribution functions (dPDF) represent a tool to explore the 3D proton structure. They can be measured in high energy proton-proton and proton nucleus collisions and encode information on how partons inside a proton are correlated among each other. dPFDs are studied here in the valence quark region, by means of a constituent quark model, where two particle correlations are present without any additional prescription. This framework allows to understand the dynamical origin of the correlations and to clarify which, among the features of the results, are model independent. Use will be made of a relativistic light-front scheme, able to overcome some drawbacks of the previous calculation. Transverse momentum correlations, due to the exact treatment of the boosts, are predicted and analyzed. The role of spin correlations is also shown. Due to the covariance of the approach, some symmetries of the dPDFs are seen unambigously. For the valence sector, the study of the QCD evolution of the model results, which can be performed safely thanks to the property of good support, has been also completed.

    ↳ hep-phnucl-thEPJ Web Conf.(2015)·0 citations
  4. 04

    Question of Lorentz invariance in muon decay

    J. P. Noordmans🇳🇱 · C. J. G. Onderwater🇳🇱 · H. W. Wilschut🇳🇱 · R. G. E. Timmermans🇳🇱

    Possibilities to test the Lorentz invariance of the weak interaction in muon decay are considered. We derive the direction-dependent muon-decay rate with a general Lorentz-violating addition to the W-boson propagator. We discuss measurements of the directional and boost dependence of the Michel parameters and of the muon lifetime as a function of absolute velocity. The total muon-decay rate in the Lorentz-violating Standard Model Extension is addressed. Suggestions are made for dedicated (re)analyses of the pertinent data and for future experiments.

    ↳ hep-phnucl-thPRD(2016)·17 citations
  5. 05

    Accounting for the analytical properties of the quark propagator from Dyson-Schwinger equation

    S. M. Dorkin🇷🇺 · L. P. Kaptari🇷🇺 · B. Kampfer🇩🇪

    An approach based on combined solutions of the Bethe-Salpeter (BS) and Dyson-Schwinger (DS) equations within the ladder-rainbow approximation in the presence of singularities is proposed to describe the meson spectrum as quark antiquark bound states. We consistently implement into the BS equation the quark propagator functions from the DS equation, with and without pole-like singularities, and show that, by knowing the precise positions of the poles and their residues, one is able to develop reliable methods of obtaining finite interaction BS kernels and to solve the BS equation numerically. We show that, for bound states with masses GeV, there are no singularities in the propagator functions when employing the infrared part of the Maris-Tandy kernel in truncated BS-DS equations. For GeV, however, the propagator functions reveal pole-like structures. Consequently, for each type of mesons (unflavored, strange and charmed) we analyze the relevant intervals of where the pole-like singularities of the corresponding quark propagator influence the solution of the BS equation and develop a framework within which they can be consistently accounted for. The BS equation is solved for pseudo-scalar and vector mesons. Results are in a good agreement with experimental data. Our analysis is directly related to the future physics programme at FAIR with respect to open charm degrees of freedom.

    ↳ hep-phnucl-thPRC(2015)·36 citations
  6. 06

    On the Accuracy of the Non-Classical Transport Equation in 1-D Random Periodic Media

    Richard Vasques · Kai Krycki

    We present a first numerical investigation of the accuracy of the recently proposed {\em non-classical transport equation}. This equation contains an extra independent variable (the path-length ), and models particle transport taking place in random media in which a particle's distance-to-collision is {\em not} exponentially distributed. To solve the non-classical equation, one needs to know the -dependent ensemble-averaged total cross section , or its corresponding path-length distribution function . We consider a 1-D spatially periodic system consisting of alternating solid and void layers, randomly placed in the infinite line. In this preliminary work, we assume transport in rod geometry: particles can move only in the directions . We obtain an analytical expression for , and use this result to compute the corresponding . Then, we proceed to solve the non-classical equation for different test problems. To assess the accuracy of these solutions, we produce "benchmark" results obtained by (i) generating a large number of physical realizations of the system, (ii) numerically solving the transport equation in each realization, and (iii) ensemble-averaging the solutions over all physical realizations. We show that the results obtained with the non-classical equation accurately model the ensemble-averaged scalar flux in this 1-D random system, generally outperforming the widely-used atomic mix model. We conclude by discussing plans to extend the present work to slab geometry, as well as to more general random mixtures.

    ↳ cond-mat.dis-nnmath-phmath.MPnucl-th0 citations
  7. 07

    Quasi-parton distribution functions: a study in the diquark spectator model

    Leonard Gamberg🇺🇸 · Zhong-Bo Kang🇺🇸 · Ivan Vitev🇺🇸 · Hongxi Xing🇺🇸

    A set of quasi-parton distribution functions (quasi-PDFs) have been recently proposed by Ji. Defined as the matrix elements of equal-time spatial correlations, they can be computed on the lattice and should reduce to the standard PDFs when the proton momentum is very large. Since taking the limit is not feasible in lattice simulations, it is essential to provide guidance for what values of the quasi-PDFs are good approximations of standard PDFs. Within the framework of the spectator diquark model, we evaluate both the up and down quarks' quasi-PDFs and standard PDFs for all leading-twist distributions (unpolarized distribution , helicity distribution , and transversity distribution ). We find that, for intermediate parton momentum fractions , quasi-PDFs are good approximations to standard PDFs (within ) when GeV. On the other hand, for large much larger GeV is necessary to obtain a satisfactory agreement between the two sets. We further test the Soffer positivity bound, and find that it does not hold in general for quasi-PDFs.

    ↳ hep-phhep-latnucl-thPLB(2015)·48 citations

Affiliations

first authorsco-authorsvia INSPIRE