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Nuclear Theory·nucl-th

Monday·February 15, 2016

7 papers—4 primary·3 cross-listed

All7Primary4Cross-lists3
  1. 01

    Green's function Monte Carlo calculations of the electromagnetic and neutral-weak response functions in the quasi-elastic sector

    Alessandro Lovato🇺🇸

    A quantitative understanding of neutrino-nucleus interactions is demanded to achieve precise measurement of neutrino oscillations, and hence the determination of their masses. In addition, next generation detectors will be able to detect supernovae neutrinos, which are likely to shed some light on the open questions on the dynamics of core collapse. In this context, it is crucial to account for two-body meson-exchange currents along within realistic models of nuclear dynamics. We summarize our progresses towards the construction of a consistent framework, based on the Green's function Monte Carlo method, that can be exploited to accurately describe neutrino interactions with atomic nuclei in the quasi-elastic sector.

    nucl-thhep-exJPS Conf.Proc.(2016)·1 citation
  2. 02

    The pion: an enigma within the Standard Model

    Tanja Horn🇺🇸 · Craig D. Roberts🇺🇸

    Almost 50 years after the discovery of gluons & quarks, we are only just beginning to understand how QCD builds the basic bricks for nuclei: neutrons, protons, and the pions that bind them. QCD is characterised by two emergent phenomena: confinement & dynamical chiral symmetry breaking (DCSB). They are expressed with great force in the character of the pion. In turn, pion properties suggest that confinement & DCSB are closely connected. As both a Nambu-Goldstone boson and a quark-antiquark bound-state, the pion is unique in Nature. Developing an understanding of its properties is thus critical to revealing basic features of the Standard Model. We describe experimental progress in this direction, made using electromagnetic probes, highlighting both improvements in the precision of charged-pion form factor data, achieved in the past decade, and new results on the neutral-pion transition form factor. Both challenge existing notions of pion structure. We also provide a theoretical context for these empirical advances, first explaining how DCSB works to guarantee that the pion is unnaturally light; but also, nevertheless, ensures the pion is key to revealing the mechanisms that generate nearly all the mass of hadrons. Our discussion unifies the charged-pion elastic and neutral-pion transition form factors, and the pion's twist-2 parton distribution amplitude. It also indicates how studies of the charged-kaon form factor can provide significant contributions. Importantly, recent predictions for the large- behaviour of the pion form factor can be tested by experiments planned at JLab 12. Those experiments will extend precise charged-pion form factor data to momenta that can potentially serve in validating factorisation theorems in QCD, exposing the transition between the nonperturbative and perturbative domains, and thereby reaching a goal that has long driven hadro-particle physics.

    nucl-thhep-exhep-lathep-ph+1J.Phys.G(2016)·192 citations
  3. 03

    On the phase-shift parameterization and ANC extraction from elastic-scattering data

    Oscar Leonardo Ramírez Suárez · Jean-Marc Sparenberg

    We develop a method to parameterize elastic-scattering phase-shifts for charged nuclei, based on Padé expansions of a simplified effective-range function. The method is potential independent and the input is reduced to experimental phase shifts and bound-state energies. It allows a simple calculation of resonance properties and of asymptotic normalization constants (ANCs) of subthreshold bound states. We analyze the and phase shifts of the C system and extract the ANCs of the corresponding bound states. For the state, a factor-3 improvement with respect to the best value available today is obtained, with a factor-10 improvement in reach. For the state, no improvement is obtained due to relatively larger error bars on the experimental phase shifts.

    nucl-thPRC(2017)·32 citations
  4. 04

    Evolution of the jet opening angle distribution in holographic plasma

    Krishna Rajagopal🇺🇸 · Andrey V. Sadofyev🇺🇸 · Wilke van der Schee🇺🇸

    We use holography to analyze the evolution of an ensemble of jets, with an initial probability distribution for their energy and opening angle as in proton-proton (pp) collisions, as they propagate through an expanding cooling droplet of strongly coupled plasma as in heavy ion collisions. We identify two competing effects: (i) each individual jet widens as it propagates; (ii) the opening angle distribution for jets emerging from the plasma within any specified range of energies has been pushed toward smaller angles, comparing to pp jets with the same energies. The second effect arises because small-angle jets suffer less energy loss and because jets with a higher initial energy are less probable in the ensemble. We illustrate both effects in a simple two-parameter model, and find that their consequence in sum is that the opening angle distribution for jets in any range of energies contains fewer narrow and wide jets. Either effect can dominate in the mean opening angle, for not unreasonable values of the parameters. So, the mean opening angle for jets with a given energy can easily shift toward smaller angles, as experimental data may indicate, even while every jet in the ensemble broadens.

    nucl-thhep-phhep-thnucl-exPRL(2016)·70 citations
  5. 05

    Mass Effect on Axial Charge Dynamics

    Er-dong Guo🇨🇳 · Shu Lin🇨🇳

    We studied effect of finite quark mass on the dynamics of axial charge using the D3/D7 model in holography. The mass term in axial anomaly equation affects both the fluctuation (generation) and dissipation of axial charge. We studied the dependence of the effect on quark mass and external magnetic field. For axial charge generation, we calculated the mass diffusion rate, which characterizes the helicity flipping rate. The rate is a non-monotonous function of mass and can be significantly enhanced by the magnetic field. The diffusive behavior is also related to a divergent susceptibility of axial charge. For axial charge dissipation, we found that in the long time limit, the mass term dissipates all the charge effectively generated by parallel electric and magnetic fields. The result is consistent with a relaxation time approximation. The rate of dissipation through mass term is a monotonous increasing function of both quark mass and magnetic field.

    ↳ hep-thhep-phnucl-thPRD(2016)·19 citations
  6. 06

    Modeling of critical experiments and its impact on integral covariance matrices and correlation coefficients

    Elisabeth Peters · Fabian Sommer · Maik Stuke

    In this manuscript we study the modeling of experimental data and its impact on the resulting integral experimental covariance and correlation matrices. By investigating a set of three low enriched and water moderated UO2 fuel rod arrays we found that modeling the same set of data with different, yet reasonable assumptions concerning the fuel rod composition and its geometric properties leads to significantly different covariance matrices or correlation coefficients. Following a Monte Carlo sampling approach, we show for nine different modeling assumptions the corresponding correlation coefficients and sensitivity profiles for each pair of the effective neutron multiplication factor keff. Within the 95% confidence interval the correlation coefficients vary from 0 to 1, depending on the modeling assumptions. Our findings show that the choice of modeling can have a huge impact on integral experimental covariance matrices. When the latter are used in a validation procedure to derive a bias, this procedure can be affected by the choice of modeling assumptions, too. The correct consideration of correlated data seems to be inevitable if the experimental data in a validation procedure is limited or one cannot rely on a sufficient number of uncorrelated data sets, e.g. from different laboratories using different setups etc.

    ↳ physics.data-annucl-thAnnals Nucl.Energy(2016)·2 citations
  7. 07

    INFN What Next: Ultra-relativistic Heavy-Ion Collisions

    A. Dainese🇮🇹 · E. Scomparin🇮🇹 · G. Usai🇮🇹 · P. Antonioli🇮🇹 · R. Arnaldi🇮🇹 · A. Beraudo🇮🇹 · E. Bruna🇮🇹 · G.E. Bruno🇮🇹 · S. Bufalino🇮🇹 · P. Di Nezza🇮🇹 · M.P. Lombardo🇮🇹 · R. Nania🇮🇹 and 129 other authors

    This document was prepared by the community that is active in Italy, within INFN (Istituto Nazionale di Fisica Nucleare), in the field of ultra-relativistic heavy-ion collisions. The experimental study of the phase diagram of strongly-interacting matter and of the Quark-Gluon Plasma (QGP) deconfined state will proceed, in the next 10-15 years, along two directions: the high-energy regime at RHIC and at the LHC, and the low-energy regime at FAIR, NICA, SPS and RHIC. The Italian community is strongly involved in the present and future programme of the ALICE experiment, the upgrade of which will open, in the 2020s, a new phase of high-precision characterisation of the QGP properties at the LHC. As a complement of this main activity, there is a growing interest in a possible future experiment at the SPS, which would target the search for the onset of deconfinement using dimuon measurements. On a longer timescale, the community looks with interest at the ongoing studies and discussions on a possible fixed-target programme using the LHC ion beams and on the Future Circular Collider.

    ↳ nucl-exnucl-thFrascati Phys.Ser.(2016)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE