Nuclear Theory·nucl-th

Wednesday·February 11, 2015

12 papers—7 primary·5 cross-listed

01
[Submitted on 9 Feb 2015]
Microscopic description of collective properties of even-even Xe isotopes
L. Prochniak
Collective properties of the even-even 118-144Xe isotopes have been studied within a model employing the general Bohr Hamiltonian derived from the mean-field theory based on the UNEDF0 energy functional. The calculated low energy spectra and E2 transition probabilities are in good agreement with experimental data.
Comments:
14 pages, 13 figures, based on a talk at the 21th Nuclear Physics Workshop, Kazimierz Dolny, Poland, September 23-28, 2014
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1502.02707 [pdf]
Phys.Scripta(2015)·12 citations
02
[Submitted on 10 Feb 2015]
6 $^{+}$ isomers in neutron-rich Sn-isotopes beyond N $= 82$ and effective interaction
Bhoomika Maheshwari · Ashok Kumar Jain · P. C. Srivastava
Recent observation of the 6 $^{+}$ seniority isomers and measurements of the B $(E 2)$ values in the $^{134 - 138}$ Sn isotopes lying close to the neutron drip line have raised some questions about the validity of the currently used effective interactions in the neutron-rich region. Simpson $et$ $al.$ [Phys. Rev. Lett. $113$ , 132502 (2014)] had to modify the diagonal and non-diagonal $ν f_{7/2}^{2}$ two body matrix elements of the " $V l k$ " interaction by $\sim 150$ keV in their shell model calculations in order to explain the data of $^{136}$ Sn. In contrast, we are able to explain the observed energy levels and the B $(E 2)$ values after marginal reduction of the same set of matrix elements by $25$ keV in the "RCDB" (Renormalized CD-Bonn) interaction. The observed mismatch in reproducing the data of $^{136}$ Sn is due to the seniority mixing. Further, we do not find it necessary to consider the core excitations, and the "RCDB" interaction seems better suited to explain the data beyond N $= 82$ magic number.
Comments:
5 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1502.02859 [pdf]
PRC(2015)·21 citations
03
[Submitted on 10 Feb 2015]
Standard and non-standard neutrino-nucleus reactions cross sections and event rates to neutrino detection experiments
D.K. Papoulias🇬🇷 · T.S. Kosmas🇬🇷
Open neutrino physics issues require precision studies, both theoretical and experimental ones, and towards this aim coherent neutral current neutrino-nucleus scattering events are expected to be observed soon. In this work, we explore $ν$ -nucleus processes from a nuclear theory point of view and obtain results with high confidence level based on accurate nuclear structure cross sections calculations. Besides cross sections, the present study includes simulated signals expected to be recorded by nuclear detectors, differential event rates as well as total number of events predicted to be measured. Our original cross sections calculations are focused on measurable rates for the Standard Model process, but we also perform calculations for various channels of the non-standard neutrino-nucleus reactions and come out with promising results within the current upper limits of the corresponding exotic parameters. We concentrate on the possibility of detecting (i) supernova neutrinos by using massive detectors like those of the GERDA and SuperCDMS dark matter experiments and (ii) laboratory neutrinos produced near the spallation neutron source facilities (at Oak Ridge National Lab) by the COHERENT experiment. Our nuclear calculations take advantage of the relevant experimental sensitivity and employ the severe bounds extracted for the exotic parameters entering the Lagrangians of various particle physics models and specifically those resulting from the charged lepton flavour violating $μ^{-} \to e^{-}$ experiments (Mu2e and COMET experiments).
Comments:
includes 3 tables, 9 figures, Article Ref.:Advances in High Energy Physics, Article ID 763648, in press
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1502.02928 [pdf]
Adv.High Energy Phys.(2015)·59 citations
04
[Submitted on 10 Feb 2015]
Efficient calculation of chiral three-nucleon forces up to N3LO for ab initio studies
K. Hebeler · H. Krebs · E. Epelbaum · J. Golak · R. Skibinski
We present a novel framework to decompose three-nucleon forces in a momentum space partial-wave basis. The new approach is computationally much more efficient than previous methods and opens the way to ab initio studies of few-nucleon scattering processes, nuclei and nuclear matter based on higher-order chiral 3N forces. We use the new framework to calculate matrix elements of chiral three-nucleon forces at N2LO and N3LO in large basis spaces and carry out benchmark calculations for neutron matter and symmetric nuclear matter. We also study the size of the individual three-nucleon force contributions for $^{3}$ H. For nonlocal regulators, we find that the sub-leading terms, which have been neglected in most calculations so far, provide important contributions. All matrix elements are calculated and stored in a user-friendly way, such that values of low-energy constants as well as the form of regulator functions can be chosen freely.
Comments:
10 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1502.02977 [pdf]
PRC(2015)·104 citations
05
[Submitted on 10 Feb 2015]
Non-perturbative Calculation of the Positronium Mass Spectrum in Basis Light-Front Quantization
Paul Wiecki · Yang Li · Xingbo Zhao · Pieter Maris · James P. Vary
We report on recent improvements to our non-perturbative calculation of the positronium spectrum. Our Hamiltonian is a two-body effective interaction which incorporates one-photon exchange terms, but neglects fermion self-energy effects. This effective Hamiltonian is diagonalized numerically in a harmonic oscillator basis at strong coupling ( $α = 0.3$ ) to obtain the mass eigenvalues. We find that the mass spectrum compares favorably to the Bohr spectrum of non-relativistic quantum mechanics evaluated at this unphysical coupling.
Comments:
Presented at LightCone 2014, Raleigh, North Carolina, USA
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1502.02993 [pdf]
Few Body Syst.(2015)·9 citations
06
[Submitted on 10 Feb 2015]
Electron-scattering form factors for 6Li in the ab initio symmetry-guided framework
T. Dytrych · A. C. Hayes · K. D. Launey · J. P. Draayer · P. Maris · J. P. Vary · D. Langr · T. Oberhuber
We present an ab initio symmetry-adapted no-core shell-model description for $^{6}$ Li. We study the structure of the ground state of $^{6}$ Li and the impact of the symmetry-guided space selection on the charge density components for this state in momentum space, including the effect of higher shells. We accomplish this by investigating the electron scattering charge form factor for momentum transfers up to $q \sim 4$ fm $^{- 1}$ . We demonstrate that this symmetry-adapted framework can achieve significantly reduced dimensions for equivalent large shell-model spaces while retaining the accuracy of the form factor for any momentum transfer. These new results confirm the previous outcomes for selected spectroscopy observables in light nuclei, such as binding energies, excitation energies, electromagnetic moments, E2 and M1 reduced transition probabilities, as well as point-nucleon matter rms radii.
Comments:
10 pages, 7 figures; accepted to Physical Review C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1502.03066 [pdf]
PRC(2015)·21 citations
07
[Submitted on 10 Feb 2015]
NJL model approach to diquarks and baryons in quark matter
D. Blaschke🇵🇱 · A. Dubinin🇵🇱 · D. Zablocki🇵🇱
We describe baryons as quark-diquark bound states at finite temperature and density within the NJL model for chiral symmetry breaking and restoration in quark matter. Based on a generalized Beth-Uhlenbeck approach to mesons and diquarks we present in a first step the thermodynamics of quark-diquark matter which includes the Mott dissociation of diquarks at finite temperature. In a second step we solve the Bethe-Salpeter equation for the baryon as a quark-diquark bound state in quark-diquark matter. We obtain a stable, bound baryon even beyond the Mott temperature for diquark dissociation since the phase space occupation effect (Pauli blocking for quarks and Bose enhancement for diquarks) in the Bethe-Salpeter kernel for the nucleon approximately cancel so that the nucleon mass follows the in-medium behaviour of the quark and diquark masses towards chiral restoration. In this situation the baryon is obtained as a "borromean" three-quark state in medium because the two-particle state (diquark) is unbound while the three-particle state (baryon) is bound.
Comments:
12 pages, 4 figures, Proceedings of the XXII International Baldin Seminar on High Energy Physics Problems, 15-20 September 2014, JINR, Dubna, Russia
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1502.03084 [pdf]
PoS(2015)·4 citations
08
[Submitted on 9 Feb 2015] (cross-list from nucl-ex)
The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC
Yasuyuki Akiba (RIKEN)🇯🇵 · Aaron Angerami (Columbia University)🇺🇸 · Helen Caines (Yale University)🇺🇸 · Anthony Frawley (Florida State University)🇺🇸 · Ulrich Heinz (Ohio State University)🇺🇸 · Barbara Jacak (University of California, Berkeley)🇺🇸 · Jiangyong Jia (Stony Brook University)🇺🇸 · Tuomas Lappi (Jyväskylä University)🇫🇮 · Wei Li (Rice University)🇺🇸 · Abhijit Majumder (Wayne State University)🇺🇸 · David Morrison (Brookhaven National Laboratory)🇺🇸 · Mateusz Ploskon (Lawrence Berkeley National Laboratory)🇺🇸 and 8 other authors
The past decade has seen huge advances in experimental measurements made in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and more recently at the Large Hadron Collider (LHC). These new data, in combination with theoretical advances from calculations made in a variety of frameworks, have led to a broad and deep knowledge of the properties of thermal QCD matter. Increasingly quantitative descriptions of the quark-gluon plasma (QGP) created in these collisions have established that the QGP is a strongly coupled liquid with the lowest value of specific viscosity ever measured. However, much remains to be learned about the precise nature of the initial state from which this liquid forms, how its properties vary across its phase diagram and how, at a microscopic level, the collective properties of this liquid emerge from the interactions among the individual quarks and gluons that must be visible if the liquid is probed with sufficiently high resolution. This white paper, prepared by the Hot QCD Writing Group as part of the U.S. Long Range Plan for Nuclear Physics, reviews the recent progress in the field of hot QCD and outlines the scientific opportunities in the next decade for resolving the outstanding issues in the field.
Comments:
110 pages, 33 figures, 429 references. Prepared as part of the U.S. Long-Range Plan for Nuclear Physics
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1502.02730 [pdf]
162 citations
09
[Submitted on 10 Feb 2015] (cross-list from nucl-ex)
Flavor decomposition of the nucleon electromagnetic form factors at low $Q^{2}$
I. A. Qattan🇦🇪 · J. Arrington🇺🇸 · A. Alsaad🇯🇴
The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors. These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions. In this work, we extract the proton and neutron form factors from world's data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we separate the up- and down-quark contributions to the proton form factors. We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parameterization of the neutron form factor data and uncertainties to separate the up- and down-quark contributions to the proton's charge and magnetic form factors. The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavor-separated form factors are extracted and compared to models of the nucleon structure. With the inclusion of the precise new data, the extracted TPE contributions show a clear change ofsign at low $Q^{2}$ , necessary to explain the high- $Q^{2}$ form factor discrepancy while being consistent with the known $Q^{2} \to 0$ limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavor-separated contributions. We also observe that the RMS radius of both the up- and down-quark distributions are smaller than the RMS charge radius of the proton.
Comments:
11 pages, 8 figures, Submitted to Phys. Rev. C
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1502.02872 [pdf]
PRC(2015)·32 citations
10
[Submitted on 10 Feb 2015] (cross-list from astro-ph.HE)
Magnetar superconductivity versus magnetism: neutrino cooling processes
Monika Sinha (ITP, Frankfurt) · Armen Sedrakian (ITP, Frankfurt)
We describe the microphysics, phenomenology, and astrophysical implication of a $B$ -field induced unpairing effect that may occur in magnetars, if the local $B$ -field in the core of a magnetar exceeds a critical value $H_{c 2}$ . Using the Ginzburg-Landau theory of superconductivity, we derive the $H_{c 2}$ field for proton condensate taking into the correction ( $\leq 30%$ ) which arises from its coupling to the background neutron condensate. The density dependence of pairing of proton condensate implies that $H_{c 2}$ is maximal at the crust-core interface and decreases towards the center of the star. As a consequence, magnetar cores with homogenous constant fields will be partially superconducting for "medium-field" magnetars ( $1 0^{15} \leq B \leq 5 \times 1 0^{16}$ G) whereas "strong-field" magnetars ( $B > 5 \times 1 0^{16}$ G) will be void of superconductivity. The neutrino emissivity of a magnetar's core changes in a twofold manner: (i)~the $B$ -field assisted direct Urca process is enhanced by orders of magnitude, because of the unpairing effect in regions where $B \geq H_{c 2}$ ; (ii)~the Cooper-pair breaking processes on protons vanish in these regions and the overall emissivity by the pair-breaking processes is reduced by a factor of only a few.
Comments:
v2: minor changes, matches published version; v1: 10 RevTex two-column pages, 7 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1502.02979 [pdf]
PRC(2015)·51 citations
11
[Submitted on 10 Feb 2015] (cross-list from hep-ph)
Kinematic biases on centrality selection of jet events in pPb collisions at the LHC
Nestor Armesto🇪🇸 · Doga Can Gulhan🇺🇸 · Jose Guilherme Milhano🇵🇹
Centrality selection has been observed to have a large effect on jet observables in pPb collisions at the Large Hadron Collider, stronger than that predicted by the nuclear modification of parton densities. We study to which extent simple considerations of energy-momentum conservation between the hard process and the underlying event affect jets observables in such collisions. We develop a simplistic approach that considers first the production of jets in a pp collision as described by PYTHIA. From each pp collision, the value of the energy of the parton from the proton participating in the hard scattering is extracted. Then, the underlying event is generated simulating a pPb collision through HIJING, but with the energy of the proton decreased according to the value extracted in the previous step, and both collisions are superimposed. This model is able to capture the bulk of the centrality effect for central to semicentral collisions, for the two available sets of data: dijets from the CMS Collaboration and single jets from the ATLAS Collaboration. As expected, the model fails for peripheral collisions where very few nucleons from Pb participate.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1502.02986 [pdf]
PLB(2015)·41 citations
12
[Submitted on 10 Feb 2015] (cross-list from astro-ph.HE)
Cooling of neutron stars and hybrid stars with a stiff hadronic EoS
H. Grigorian · D. Blaschke · D. N. Voskresensky
Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the high masses of the pulsars PSR J1614-2230 and PSR J0348-0432 on the one hand, and of the low masses for PSR J0737-3039B and the companion of PSR J1756-2251 on the other, provide independent proof for the existence of neutron stars with masses in a broad range from $\sim 1.2$ to 2 $M_{⊙}$ . The values $M > 2 M_{⊙}$ call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about $2.4 M_{⊙}$ would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner core. Without readjustment of cooling inputs the mass range required to cover all cooling data for the stiff DD2 equation of state should include masses of $2.426 M_{⊙}$ for describing the fast cooling of CasA while the existence of a quark matter core accelerates the cooling so that CasA cooling data are described with a hybrid star of mass $1.674 M_{⊙}$ .
Comments:
12 pages, 3 figures, typos corrected
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1502.03080 [pdf]
Phys.Part.Nucl.(2015)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE