Nuclear Theory·nucl-th

Wednesday·January 24, 2018

12 papers—7 primary·5 cross-listed

01
[Submitted on 22 Jan 2018]
Valence-quark structure N* resonances from DSEs
Jorge Segovia🇪🇸
We present a unified Quantum Chromodynamics (QCD)-based description of elastic and transition electromagnetic form factors involving the nucleon and its resonances. We compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-like momentum dependence with results obtained using a confining, symmetry-preserving treatment of a vector $\otimes$ vector contact-interaction in a widely-used leading-order (rainbow-ladder) truncation of QCD's Dyson-Schwinger equations. This comparison explains that the contact-interaction framework produces hard form factors, curtails some quark orbital angular momentum correlations within a baryon, and suppresses two-loop diagrams in the elastic and transition electromagnetic currents. Such defects are rectified in our QCD-based approach and, by contrasting the results obtained for the same observables in both theoretical schemes, shows those objects which are most sensitive to the momentum dependence of elementary quantities in QCD.
Comments:
Contribution to the proceedings of the 11th International Workshop on the Physics of Excited Nucleons (NSTAR17). Aug. 20-23, 2017. University of South Carolina, Columbia (SC), USA. arXiv admin note: text overlap with arXiv:1602.02768, arXiv:1801.04718, arXiv:1601.00973, arXiv:1611.02844, arXiv:1509.08952
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1801.07251 [pdf]
Few Body Syst.(2018)·0 citations
02
[Submitted on 23 Jan 2018]
Photo- and electroproduction of $K^{+} Λ$ with unitarity-restored isobar model
D. Skoupil🇨🇿 · P. Bydžovský🇨🇿
Exploiting the isobar model, kaon photo- and electroproduction on the proton in the resonance region comes under scrutiny. An upgrade of our previous model, comprising higher-spin nucleon and hyperon exchanges in the consistent formalism, was accomplished by implementing energy-dependent widths of nucleon resonances, which leads to a different choice of hadron form factor with much softer values of cutoff parameter for the resonant part. For a reliable description of electroproduction, the necessity of including longitudinal couplings of nucleon resonances to virtual photons was revealed. We present a new model whose free parameters were adjusted to photo- and electroproduction data and which provides a reliable overall description of experimental data in all kinematic regions. The majority of nucleon resonances chosen in this analysis coincide with those selected in our previous analysis and also in the Bayesian analysis with the Regge-plus-resonance model as the states contributing to this process with the highest probability.
Comments:
14 pages, 15 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1801.07466 [pdf]
PRC(2018)·47 citations
03
[Submitted on 23 Jan 2018]
Transport Dynamics of Parton Interactions in pp Collisions at LHC Energies
Dinesh K. Srivastava🇮🇳 · Rupa Chatterjee🇮🇳 · Steffen A. Bass🇺🇸
We investigate the transport dynamics of partons in proton-proton collisions at the Large Hadron Collider using a Boltzmann transport approach, the parton cascade model. The calculations include semi-hard pQCD interaction of partons populating the nucleons and provide a space-time description of the collision in terms of cascading partons undergoing scatterings and fragmentations. Parton production and number of collisions rise rapidly with increase in center of mass energy of the collision. For a given center of mass energy, the number of parton interactions is seen to rise stronger than linear with decreasing impact parameter before saturating for very central collisions. The strangeness enhance factor $γ_{s}$ for the semi-hard processes is found to rise rapidly and saturate towards the highest collision energies. Overall, our study indicates a significant amount of partonic interactions in proton-proton collisions, which supports the observation of fluid-like behavior for high multiplicity proton-proton collisions observed in the experiments.
Comments:
11 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1801.07482 [pdf]
PRC(2018)·6 citations
04
[Submitted on 23 Jan 2018]
Uncertainties in radiative neutron-capture rates relevant to the $A \sim 80$ $r$ -process peak
I. K. B. Kullmann · E. W. Hafli · A.C. Larsen · E. Lima
The rapid neutron-capture process ( $r$ -process) has for the first time been confirmed to take place in a neutron-star merger event. A detailed understanding of the rapid neutron-capture process is one of the holy grails in nuclear astrophysics. In this work we investigate one aspect of the $r$ -process modelling: uncertainties in radiative neutron-capture cross sections and astrophysical reaction rates for isotopes of the elements Fe, Co, Ni, Cu, Zn, Ga, Ge, As, and Se. In particular, we study deviations from standard libraries used for astrophysics, and the influence of a very-low $γ$ -energy enhancement in the average, reduced $γ$ -decay probability on the ( $n, γ$ ) rates. We find that the intrinsic uncertainties are in some cases extremely large, and that the low-energy enhancement, if present in neutron-rich nuclei, may increase the neutron-capture reaction rate significantly.
Comments:
13 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Experiment (nucl-ex)
arXiv:
1801.07522 [pdf]
1 citation
05
[Submitted on 22 Jan 2018]
Vorticity and hyperon polarization at NICA energies
E.E. Kolomeitsev🇸🇰 · V.D. Toneev🇷🇺 · V. Voronyuk🇷🇺
We study the formation of fluid vorticity and the hyperon polarization in heavy-ion collisions at NICA energies in the framework of the Parton-Hadron-String Dynamic Model, taking into account both hadronic and quark-gluonic (partonic) degrees of freedom. The vorticity properties in peripheral Au+Au collisions at $s_{N N} =$ 7.7\,GeV are demonstrated and confronted with other models. The obtained result for the $Λ$ polarization is in agreement with the experimental data by the STAR collaboration, whereas the model is not able to explain the observed high values of the anti-hyperon $Λ ˉ$ polarization.
Comments:
9 pages, 6 figure. arXiv admin note: text overlap with arXiv:1704.01507 by other authors
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1801.07610 [pdf]
PRC(2018)·46 citations
06
[Submitted on 23 Jan 2018]
Violent Nuclear Reactions: Large-Amplitude Nuclear Dynamic Phenomena in Fermionic Systems
Paolo Napolitani🇫🇷
Violent nuclear collisions are open systems which require a non-equilibrium description when the process should be followed from the first instants. The heated system produced in the collision, can no more be treated within an independent-particle picture and additional correlations should be taken into account: they rely to in-medium dissipation and phase-space fluctuations. Their interplay with the one-body collective behaviour activates the transport dynamics: large-amplitude fluctuations and bifurcations in a variety of mechanisms appear, from fusion to neck formation till eventually freezing out the system into several intermediate-mass clusters. Starting from fundamental concepts tested on nuclear matter, a microscopic description is built up to address violent processes occurring in heavy-ion collisions at Fermi energies and in spallation reactions, and it is applied to experimental observables.
Comments:
HDR report. Review written in order to be conferred the French accreditation to supervise research (Habilitation à diriger des recherches)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1801.07613 [pdf]
Universit\'e Paris Sud, HDR report, Orsay…·0 citations
07
[Submitted on 23 Jan 2018]
Cluster formation in nuclear reactions from mean-field inhomogeneities
P. Napolitani🇫🇷 · M. Colonna🇮🇹 · C. Mancini-Terracciano🇮🇹
Perturbing fluids of neutrons and protons (nuclear matter) may lead, as the most catastrophic effect, to the rearrangement of the fluid into clusters of nucleons. A similar process may occur in a single atomic nucleus undergoing a violent perturbation, like in heavy-ion collisions tracked in particle accelerators at around 30 to 50 MeV per nucleon: in this conditions, after the initial collision shock, the nucleus expands and then clusterises into several smaller nuclear fragments. Microscopically, when violent perturbation are applied to nuclear matter, a process of clusterisation arises from the combination of several fluctuation modes of large-amplitude where neutrons and protons may oscillate in phase or out of phase. The imposed perturbation leads to conditions of instability, the wavelengths which are the most amplified have sizes comparable to small atomic nuclei. We found that these conditions, explored in heavy-ion collisions, correspond to the splitting of a nucleus into fragments ranging from Oxygen to Neon in a time interval shorter than one zeptosecond (10 $^{- 21}$ s). From the out-of-phase oscillations of neutrons and protons another property arises, the smaller fragments belonging to a more volatile phase get more neutron enriched: in the heavy-ion collision case this process, called distillation, reflects in the isotopic distributions of the fragments. The resulting dynamical description of heavy-ion collisions is an improvement with respect to more usual statistical approaches, based on the equilibrium assumption. It allows in fact to characterise also the very fast early stages of the collision process which are out of equilibrium. Such dynamical description is the core of the Boltzmann-Langevin One Body (BLOB) model, which unifies in a common description fluctuations in nuclear matter and the disintegration of nuclei into nuclear fragments.
Comments:
Contribution to the symposium "Nuclear Reactions on Nucleons and Nuclei", Messina (Italy), October 25-26, 2017
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1801.07623 [pdf]
J.Phys.Conf.Ser.(2018)·2 citations
08
[Submitted on 20 Jan 2018] (cross-list from nucl-ex)
Total and differential cross sections of $η$ -production in proton-deuteron fusion for excess energies between $Q_{η} = 13 MeV$ and $Q_{η} = 81 MeV$
P. Adlarson🇸🇪 · W. Augustyniak🇵🇱 · W. Bardan🇵🇱 · M. Bashkanov🇬🇧 · F. S. Bergmann🇩🇪 · M. Berłowski🇵🇱 · A. Bondar🇷🇺 · M. Büscher🇩🇪 · H. Calén🇸🇪 · I. Ciepał🇵🇱 · H. Clement🇩🇪 · E. Czerwiński🇵🇱 and 81 other authors
New data on both total and differential cross sections of the production of $η$ mesons in proton-deuteron fusion to $^{3} He η$ in the excess energy region $13.6 MeV \leq Q_{η} \leq 80.9 MeV$ are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Jülich, using a proton beam at 15 different beam momenta between $p_{p} = 1.60 GeV / c$ and $p_{p} = 1.74 GeV / c$ . While significant structure of the total cross section is observed in the energy region $20 MeV ≲ Q_{η} ≲ 60 MeV$ , a previously reported sharp variation around $Q_{η} \approx 50 MeV$ cannot be confirmed. Angular distributions show the typical forward-peaking that was reported elsewhere. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a large interval.
Comments:
8 pages, 7 figures, preprint submitted to Physics Letters B
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1801.06671 [pdf]
PLB(2018)·14 citations
09
[Submitted on 21 Jan 2018] (cross-list from hep-ph)
Charm production in interactions of antiproton with proton and nuclei at $P ˉ A N D A$ energies
R. Shyam🇮🇳 · K. Tsushima🇧🇷
We study the production of charmed baryons in the antiproton-proton and antiproton-nucleus interactions within a fully covariant model that is based on an effective Lagrangian approach. The baryon production proceeds via the $t$ -channel $D^{0}$ and $D^{* 0}$ meson-exchange diagrams. We have also explored the production of the charm-baryon hypernucleus $_{Λ_{c}^{+}}^{16}$ O in the antiproton - $^{16}$ O collisions. For antiproton beam momenta of interest to the $P ˉ A N D A$ experiment, the 0 $^{\circ}$ differential cross sections for the formation of $_{Λ_{c}^{+}}^{16}$ O hypernuclear states with simple particle-hole configurations, have magnitudes in the range of a few $μ$ b/sr.
Comments:
5 pages, 3 figures, Talk presented at the conference "Light-Cone 2017", held at Mumbai India, Sept 18 - 22, 2017. Version as printed in the Journal. arXiv admin note: text overlap with arXiv:1701.02225
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1801.06823 [pdf]
Few Body Syst.(2018)·4 citations
10
[Submitted on 22 Jan 2018] (cross-list from astro-ph.HE)
Pulsar glitch and nuclear EoS: Applicability of superfluid model
A. Li · R. Wang
In this contribution, we have made use of the contemporary equation of states (EOSs) for the complete neutron star structure, and confronted them with one particular glitch constrain for the crustal moment of inertia (MOI). We find that with these EOSs, the radii of three millisecond pulsars selected by NICER: PSR J0437-4715, PSR J1614-2230, PSR J0751+1807, are all around 12.5 km. Also, a star with $M ≲ 1.55 M_{⊙}$ would fulfill the MOI calculation for glitch constrain with the latest neutron superfluidity density, and the glitch crisis might not be present.
Comments:
proceeding prepared for IAU Symposium 337: 50 Years of Pulsars, Jodrell Bank Observatory, United Kingdom, 4-8 September 2017; In press
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1801.07350 [pdf]
IAU Symp.(2017)·3 citations
11
[Submitted on 23 Jan 2018] (cross-list from hep-ph)
Baryon-antibaryon dynamics in relativistic heavy-ion collisions
Eduard Seifert🇩🇪 · Wolfgang Cassing🇩🇪
The dynamics of baryon-antibaryon annihilation and reproduction ( $B B ˉ \leftrightarrow 3 M$ ) is studied within the Parton-Hadron-String Dynamics (PHSD) transport approach for Pb+Pb and Au+Au collisions as a function of centrality from lower Super Proton Synchrotron (SPS) up to Large Hadron Collider (LHC) energies on the basis of the quark rearrangement model (QRM). At Relativistic Heavy-Ion Collider (RHIC) energies we find a small net reduction of baryon-antibaryon ( $B B ˉ$ ) pairs while for the LHC energy of $s_{N N}$ = 2.76 GeV a small net enhancement is found relative to calculations without annihilation (and reproduction) channels. Accordingly, the sizeable difference between data and statistical calculations in Pb+Pb collisions at $s_{N N}$ = 2.76 TeV for proton and antiproton yields \cite{53}, where a deviation of 2.7 $σ$ was claimed by the ALICE Collaboration, should not be attributed to a net antiproton annihilation. This is in line with the observation that no substantial deviation between the data and statistical hadronization model (SHM) calculations is seen for antihyperons, since according to the PHSD analysis the antihyperons should be modified by the same amount as antiprotons. As the PHSD results for particle ratios are in line with the ALICE data (within error bars) this might point towards a deviation from statistical equilibrium in the hadronization (at least for protons/antiprotons). Furthermore, we find that the $B B ˉ \leftrightarrow 3 M$ reactions are more effective at lower SPS energies where a net suppression for antiprotons and antihyperons up to a factor of 2 -- 2.5 can be extracted from the PHSD calculations for central Au+Au collisions.
Comments:
12 pages, 12 figures; Subsection III B added; Phys. Rev. C, in print
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1801.07557 [pdf]
PRC(2018)·18 citations
12
[Submitted on 23 Jan 2018] (cross-list from hep-ph)
Spin-1 particles and perturbative QCD
J. P. B. C. de Melo (LFTC - Cruzeiro do Sul)🇧🇷 · T. Frederico (Instituto Tecnológico de Aeronáutica - ITA)🇧🇷 · Chueng -R. Ji (Departament of Physics, North Carolina State University, NCSU)🇺🇸
Due to the angular condition in the light-front dynamics (LFD), the extraction of the electromagnetic form factors for spin-1 particles can be uniquely determined taking into account implicitly non-valence and/or the zero-mode contributions to the matrix elements of the electromagnetic current. No matter which matrix elements of the electromagnetic current is used to extract the electromagnetic form factors, the same unique result is obtained. As physical observables, the electromagnetic form factors obtained from matrix elements of the current in LFD must be equal to those obtained in the instant form calculations. Recently, the Babar collaboration \cite{Aubert2008} has analyzed the reaction $e^{+} e^{-} \to ρ^{+} + ρ^{-}$ at $s = 10.58 G e V$ to measure the cross section as well as the ratios of the helicity amplitudes $F_{λ^{'} λ}$ . We present our recent analysis of the Babar data for the rho meson considering the angular condition in LFD to put a stringent test on the onset of asymptotic perturbative QCD and predict the energy regime where the subleading contributions are still considerable.
Comments:
7 pages, 4 figures, Few-Body latex style. Contribuition to the Light-Cone 2017, 18-22 September, 2017, Mumbai, India. Submitted to Few-Body Systems
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Theory (hep-th); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1801.07631 [pdf]
Few Body Syst.(2018)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE