Nuclear Theory·nucl-th

Monday·August 13, 2018

12 papers—2 primary·10 cross-listed

03
[Submitted on 9 Aug 2018] (cross-list from hep-ph)
Contribution of the $a_{1}$ meson to the axial nucleon-to- $Δ$ transition form factors
Y. Unal🇹🇷 · A. Kucukarslan🇹🇷 · S. Scherer🇩🇪
We analyze the low- $Q^{2}$ behavior of the axial form factor $G_{A} (Q^{2})$ , the induced pseudoscalar form factor $G_{P} (Q^{2})$ , and the axial nucleon-to- $Δ$ transition form factors $C_{5}^{A} (Q^{2})$ and $C_{6}^{A} (Q^{2})$ . Building on the results of chiral perturbation theory, we first discuss $G_{A} (Q^{2})$ in a chiral effective-Lagrangian model including the $a_{1}$ meson and determine the relevant coupling parameters from a fit to experimental data. With this information, the form factor $G_{P} (Q^{2})$ can be predicted. For the determination of the transition form factor $C_{5}^{A} (Q^{2})$ we make use of an SU(6) spin-flavor quark-model relation to fix two coupling constants such that only one free parameter is left. Finally, the transition form factor $C_{6}^{A} (Q^{2})$ can be predicted in terms of $G_{P} (Q^{2})$ , the mean-square axial radius $⟨ r_{A}^{2} ⟩$ , and the mean-square axial nucleon-to- $Δ$ transition radius $⟨ r_{A N Δ}^{2} ⟩$ .
Comments:
22 pages, 6 figures, typo in Eq. (55) fixed, matches published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1808.03046 [pdf]
PRD(2019)·6 citations
04
[Submitted on 9 Aug 2018] (cross-list from hep-ph)
Collective Effects: the viewpoint of HEP MC codes
Torbjörn Sjöstrand🇸🇪
Collective effects are observed in high-multiplicity pp events, similar to the signals traditionally attributed to the formation of a Quark Gluon Plasma in heavy ion collisions. In core--corona models it is assumed that a partial plasma formation is indeed possible also in pp, but here the focus is on several recent models that attempt to explain pp data without invoking plasma formation. These attempts are partly successful, but there is still not a unified framework.
Comments:
8 pages, presented at XXVIIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2018)
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1808.03117 [pdf]
NPA(2019)·18 citations
05
[Submitted on 9 Aug 2018] (cross-list from hep-ph)
Updating spin-dependent Regge intercepts
Steven D. Bass🇵🇱 · Magdalena Skurzok🇵🇱 · Pawel Moskal🇵🇱
We use new high statistics data from CLAS and COMPASS on the nucleon's spin structure function at low Bjorken x and low virtuality, Q^2 < 0.5 GeV^2, together with earlier measurements from the SLAC E-143, HERMES and GDH experiments to estimate the effective intercept(s) for spin dependent Regge theory. We find alpha_{a_1} = 0.31 \pm 0.04 for the intercept describing the high-energy behaviour of spin dependent photoabsorption together with a new estimate for the high-energy part of the Gerasimov-Drell-Hearn sum-rule, -15 \pm 2 mu b from photon-proton centre-of-mass energy greater than 2.5 GeV. Our value of alpha_[a_1} suggests QCD physics beyond a simple straight-line a_1 trajectory.
Comments:
4 pages, 1 figure, to appear in Physical Review C
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1808.03202 [pdf]
PRC(2018)·15 citations
06
[Submitted on 9 Aug 2018] (cross-list from nucl-ex)
A novel invariant mass method to isolate resonance backgrounds from the chiral magnetic effect
Hanlin Li🇨🇳 · Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸
The Chiral Magnetic Effect (CME) refers to charge separation along a strong magnetic field, due to topological charge fluctuations in QCD. Charge correlation ( $Δ γ$ ) signals consistent with CME have been first observed almost a decade ago. It has also been known since then that the $Δ γ$ is contaminated by a major background from resonance decays coupled with elliptic flow. In this contribution, we propose differential $Δ γ$ measurements as function of the pair invariant mass ( $m_{inv}$ ). The $Δ γ$ in the high $m_{inv}$ region is essentially free of resonance backgrounds. In the low $m_{inv}$ region, the $Δ γ$ backgrounds show resonance peaks. The CME signal, presumably smooth in $m_{inv}$ , may thus be extracted from a two-component model fit. We demonstrate the feasibility and effectiveness of this novel method by using the AMPT and toy-model Monte-Carlo simulations. We also discuss an application of the method in data analysis.
Comments:
4 pages 4 figures. Quark Matter 2018 proceedings
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1808.03210 [pdf]
NPA(2019)·8 citations
07
[Submitted on 9 Aug 2018] (cross-list from hep-ph)
Precision Dijet Acoplanarity Tomography of the Chromo Structure of Perfect QCD Fluids
M. Gyulassy🇺🇸 · P. Levai🇭🇺 · J. Liao🇺🇸 · S. Shi🇺🇸 · F. Yuan🇺🇸 · X.N. Wang🇺🇸
Dijet acoplanarity is dominated by vacuum (Sudakov) pQCD radiation even in Pb+Pb collisions, but future higher precision measurements of the tails of the acoplanarity distributions can help to resolve {\em separately} the medium opacity, $χ = L / λ$ , and the color screening scale $μ^{2}$ from the path averaged BDMS saturation scale $Q_{s}^{2} [χ, μ] = \int d L q^(E, T (L)) \propto μ^{2} L / λ$ , that is already well constrained by nuclear modification factor data on $R_{AA} (p_{T})$ . We compare Gaussian (BDMS) and non-Gaussian (GLV) models of medium broadening of vacuum (Sudakov) induced acoplanarity distributions in A+A. With few percent accuracy on the ratio of A+A to p+p distributions, experiments can easily identify non-Gaussian Landau and Rutherford tails due to multiple collisions. However, we find that sub-percent precision will be required to constrain $χ$ and $μ$ separately from $Q_{s}$ .
Comments:
Final version accepted by Nucl.Phys.A for Proc. Quark Matter 2018, Venice, 4 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1808.03238 [pdf]
NPA(2019)·16 citations
08
[Submitted on 9 Aug 2018] (cross-list from hep-ph)
Neutrino induced reactions in core-collapse supernovae: effects on the electron fraction
M. M. Saez🇦🇷 · O. Civitarese🇦🇷 · M. E. Mosquera🇦🇷
Neutrino induced reactions are a basic ingredient in astrophysical processes like star evolution. The existence of neutrino oscillations affects the rate of nuclear electroweak decays which participates in the chain of events that determines the fate of the star. Among the processes of interest, the production of heavy elements in core-collapse supernovae is strongly dependent upon neutrino properties, like the mixing between different species of neutrinos. In this work we study the effects of neutrino oscillations upon the electron fraction as a function of the neutrino mixing parameters, for two schemes: the $1 + 1$ scheme (one active neutrino and one sterile neutrino) and the $2 + 1$ scheme (two active neutrinos and one sterile neutrino). We have performed this analysis considering a core-collapse supernovae and determined the physical conditions needed to activate the nuclear reaction chains involved in the r-process. We found that the interactions of the neutrinos with matter and among themselves and the initial amount of sterile neutrinos in the neutrino-sphere might change the electron fraction, therefore affecting the onset of the r-process. We have set constrains on the active-sterile neutrino mixing parameters. They are the square-mass-difference $Δ m_{14}^{2}$ , the mixing angle $sin^{2} 2 θ_{14}$ , and the hindrance factor $ξ_{s}$ for the occupation of sterile neutrinos. The calculations have been performed for different values of $X_{α}$ , which is the fraction of $α$ -particles. For $X_{α} = 0$ the r-process is taking place if $Δ m_{14}^{2} \geq 2 eV^{2}$ , $sin^{2} 2 θ_{14} < 0.8$ and $ξ_{s} < 0.5$ . For larger values of $X_{α}$ the region of parameters is strongly reduced. The present results are compared to results available in the literature.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1808.03249 [pdf]
Int.J.Mod.Phys.D(2018)·5 citations
09
[Submitted on 9 Aug 2018] (cross-list from hep-ph)
Molière Scattering in Quark-Gluon Plasma: Finding Point-Like Scatterers in a Liquid
Francesco D'Eramo🇮🇹 · Krishna Rajagopal🇺🇸 · Yi Yin🇺🇸
By finding rare (but not exponentially rare) large-angle deflections of partons within a jet produced in a heavy ion collision, or of such a jet itself, experimentalists can find the weakly coupled short-distance quark and gluon particles (scatterers) within the strongly coupled liquid quark-gluon plasma (QGP) produced in heavy ion collisions. This is the closest one can come to probing QGP via a scattering experiment and ultimately learning how a strongly coupled liquid emerges from an asymptotically free gauge theory. The short-distance, particulate, structure of liquid QGP can be revealed in events in which a jet parton resolves, and scatters off, a parton from the droplet of QGP. The probability for picking up significant transverse momentum via a single scattering was calculated previously, but only in the limit of infinite parton energy which means zero angle scattering. Here, we provide a leading order perturbative QCD calculation of the Molière scattering probability for incident partons with finite energy, scattering at a large angle. We set up a thought experiment in which an incident parton with a finite energy scatters off a parton constituent within a "brick" of QGP, which we treat as if it were weakly coupled, as appropriate for scattering with large momentum transfer, and compute the probability for a parton to show up at a nonzero angle with some energy. We include all relevant channels, including those in which the parton that shows up at a large angle was kicked out of the medium as well as the Rutherford-like channel in which what is seen is the scattered incident parton. The results that we obtain will serve as inputs to future jet Monte Carlo calculations and can provide qualitative guidance for how to use future precise, high statistics, suitably differential measurements of jet modification in heavy ion collisions to find the scatterers within the QGP liquid.
Comments:
51 pages, 6 figures. Matched to the version accepted by JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1808.03250 [pdf]
JHEP(2019)·79 citations
10
[Submitted on 10 Aug 2018] (cross-list from hep-ph)
Generalized distribution amplitudes and gravitational form factors for pion
Qin-Tao Song🇯🇵
Generalized parton distributions (GPDs) have been investigated in the deeply virtual Compton scattering (DVCS) to solve the proton spin puzzle. On the other hand, the generalized distribution amplitudes (GDAs) can be studied in the two-photon process $γ^{*} γ \to h h ˉ$ which is accessible at KEKB. Namely, the GDAs are the $s$ - $t$ crossed quantities of the GPDs. In 2016, the differential cross section of the process $γ^{*} γ \to π^{0} π^{0}$ was measured by the Belle collaboration in the $e^{+} e^{-}$ collision , so that the pion GDAs can be obtained by analyzing the Belle data. Expressing the GDAs with a few parameters, we determined the GDAs by a $χ^{2}$ analysis . The form factors of the quark energy-momentum tensor are obtained from the determined GDAs. Then, we calculated the mass radius as 0.56-0.69 fm for the pion by using the form factor. This is the first study on gravitational form factors and radius of hadrons from actual experimental measurements . The Belle II will start taking data in 2018 by the upgraded SuperKEKB. Therefore, much accurate data are expected for the pion, and other hadron-pair productions will be measured in the near future. The GDA studies are valuable for understanding not only the 3D structure but also gravitational properties of hadrons.
Comments:
6 pages, 5 figures, Proceedings of the XXVI International Workshop on Deep-Inelastic Scattering and Related Subjects, April 16-20, 2018, Kobe University, Japan
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1808.03422 [pdf]
PoS(2018)·1 citation
11
[Submitted on 10 Aug 2018] (cross-list from astro-ph.HE)
Black Hole Accretion Disk Diffuse Neutrino Background
T. S. H. Schilbach🇨🇦 · O. L. Caballero🇨🇦 · G. C. McLaughlin🇺🇸
We study the cosmic MeV neutrino background from accretion disks formed during collapsars and the coalescence of compact-object mergers. We provide updated estimates, including detection rates, of relic neutrinos from collapsars, as well as estimates for neutrinos that are produced in mergers. Our results show that diffuse neutrinos detected at HyperK would likely include some that were emitted from binary neutron-star mergers. The collapsar rate is uncertain, but at its upper limit relic neutrinos from these sources would provide a significant contribution to the Cosmic Diffuse Neutrino Background.
Comments:
10 pages, 6 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Nuclear Theory (nucl-th)
arXiv:
1808.03627 [pdf]
PRD(2019)·19 citations
12
[Submitted on 10 Aug 2018] (cross-list from physics.atom-ph)
Enhanced nuclear Schiff moment and time reversal violation in 229Th-containing molecules
V.V. Flambaum🇦🇺
Octupole deformation results in a strongly enhanced collective Schiff moment in 229Th nucleus. An additional enhancement of time reversal (T) and parity (P) violating effects (such as T,P-violating electric dipole moments) appears in the ground 1Sigma state and in the metastable 3Delta_1 state of diatomic molecule 229ThO. Similar enhancements exist in molecular ions 229ThOH+, 229ThF+ and 225,223RaOH+. Corresponding experiments may be used to test CP-violation theories predicting T,P-violating nuclear forces and to search for axions.
Subjects:
Atomic Physics (physics.atom-ph); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1808.03629 [pdf]
PRC(2019)·52 citations

Affiliations

first authorsco-authorsvia INSPIRE