Nuclear Theory·nucl-th

Monday·November 16, 2015

14 papers—6 primary·8 cross-listed

01
Decorrelation of anisotropic flows along the longitudinal direction
Long-Gang Pang🇩🇪 · Hannah Petersen🇩🇪 · Guang-You Qin🇨🇳 · Victor Roy🇩🇪 · Xin-Nian Wang🇨🇳
The initial energy density distribution and fluctuation in the transverse direction lead to anisotropic flows of final hadrons through collective expansion in high-energy heavy-ion collisions. Fluctuations along the longitudinal direction, on the other hand, can result in decorrelation of anisotropic flows in different regions of pseudo rapidity ( $η$ ). Decorrelation of the $2$ nd and $3$ rd order anisotropic flows with different $η$ gaps for final charged hadrons in high-energy heavy-ion collisions is studied in an event-by-event (3+1)D ideal hydrodynamic model with fully fluctuating initial conditions from A Multi-Phase Transport (AMPT) model. The decorrelation of anisotropic flows of final hadrons with large $η$ gaps are found to originate from the spatial decorrelation along the longitudinal direction in the AMPT initial conditions through hydrodynamic evolution. The decorrelation is found to consist of both a linear twist and random fluctuation of the event-plane angles. The agreement between our results and recent CMS data in most centralities suggests that the string-like mechanism of initial parton production in AMPT model captures the initial longitudinal fluctuation that is responsible for the measured decorrelation of anisotropic flows in Pb+Pb collisions at LHC. Our predictions for Au+Au collisions at the highest RHIC energy show stronger longitudinal decorrelation, indicating larger longitudinal fluctuations at lower beam energies. Our study also calls into question some of the current experimental methods for measuring anisotropic flows and extraction of transport coefficients through comparisons to hydrodynamic simulations that do not include longitudinal fluctuations.
nucl-thhep-exEPJA(2016)·107 citations
02
Cassiopeia A and direct URCA cooling
G. Taranto · G. F. Burgio · H.-J. Schulze (INFN Catania)
We model neutron star cooling, in particular the current rapid cooldown of the neutron star Cas A, with a microscopic nuclear equation of state featuring strong direct Urca processes and using compatible nuclear pairing gaps as well as effective masses. Several scenarios are possible to explain the features of Cas A, but only large and extended proton $^{1} S_{0}$ gaps and small neutron $^{3} P F_{2}$ gaps are able to accommodate also the major part of the complete current cooling data. We conclude that the possibility of strong direct Urca processes cannot be excluded from the cooling analysis.
nucl-thMNRAS(2016)·33 citations
03
Analysis of recent CLAS data on $Σ^{*} (1385)$ photoproduction off a neutron target
Xiao-Yun Wang🇨🇳 · Jun He🇨🇳 · Helmut Haberzettl🇺🇸
Based on recent experimental data obtained by the CLAS Collaboration, the $Σ (1385)$ photoproduction off a neutron target at laboratory photon energies $E_{γ}$ up to 2.5\,GeV is investigated in an effective Lagrangian approach including $s$ -, $u$ -, and $t$ -channel Born-term contributions. The present calculation does not take into account any explicit $s$ -channel baryon-resonance contributions, however, in the spirit of duality, we include $t$ -channel exchanges of mesonic Regge trajectories. The onset of the Regge regime is controlled by smoothly interpolating between Feynman-type single-meson exchanges and full-fledged Regge-trajectory exchanges. Gauge invariance broken by the Regge treatment is fully restored by introducing contact-type interaction currents that result from the implementation of \textit{local} gauge invariance in terms of generalized Ward-Takahashi identities. The cross sections for the $γ n \to K^{+} Σ^{*} (1385)^{-}$ reaction are calculated and compared with experimental results from the CLAS and LEPS collaborations. Despite its simplicity, the present theoretical approach provides a good description of the main features of the data. However, the parameters fitted to the data show that the gauge-invariance-restoring contact term plays a large role which may point to large contributions from final-state interactions.
nucl-thhep-exhep-phnucl-exPRC(2016)·23 citations
04
The effective description of non-strange hadrons low-energy electro-weak transitions
Gevorg G. Bunatian🇷🇺
Starting with the general principles of global and local symmetries, the effective pion-nucleon lagrangian, essentially non-linear in pion field, to describe the non-strange hadrons low-energy electro-weak transitions is developed. We encounter no divergence summarizing properly all the infinite power series in pion field which occur in the course of treatment. Our consistent approach proves to be relevant in considering P-parity violation in pion-nucleon interactions.
nucl-thhep-phJ.Phys.G(2018)·1 citation
05
Proton structure in the hyperfine splitting of muonic hydrogen
Franziska Hagelstein🇩🇪 · Vladimir Pascalutsa (KPH, JGU Mainz)🇩🇪
We present the leading-order prediction of baryon chiral perturbation theory for the proton polarizability contribution to the 2S hyperfine splitting in muonic hydrogen, and compare with the results of dispersive calculations.
nucl-thhep-phphysics.atom-phPoS(2016)·26 citations
06
Coexistence of nuclear shapes: self-consistent mean-field and beyond
Zhipan Li · Tamara Niksic · Dario Vretenar
A quantitative analysis of the evolution of nuclear shapes and shape phase transitions, including regions of short-lived nuclei that are becoming accessible in experiments at radioactive-beam facilities, necessitate accurate modeling of the underlying nucleonic dynamics. Important theoretical advances have recently been made in studies of complex shapes and the corresponding excitation spectra and electromagnetic decay patterns, especially in the "beyond mean-field" framework based on nuclear density functionals. Interesting applications include studies of shape evolution and coexistence in N = 28 isotones, the structure of lowest $0^{+}$ excitations in deformed N $\approx$ 90 rare-earth nuclei, and quadrupole and octupole shape transitions in thorium isotopes.
nucl-thJ.Phys.G(2016)·68 citations
07
Prompt double $J / ψ$ production in proton-proton collisions at the LHC
S. P. Baranov🇷🇺 · Amir H. Rezaeian🇨🇱
We provide a detailed study of prompt double $J / ψ$ production within the non-relativistic QCD (NRQCD) framework in proton-proton collisions at the LHC. We confront the recent LHC data with the results obtained at leading-order (LO) in the NRQCD framework within two approaches of the collinear factorization and the $k_{T}$ -factorization. We show that the LHCb data are consistent with the $k_{T}$ -factorized LO NRQCD results. We show that the full LO NRQCD formalism cannot describe the recent CMS data, with about one order of magnitude discrepancy. If the CMS data are confirmed, this indicates rather large higher-order corrections for prompt double $J / ψ$ production. We provide various predictions which can further test the NRQCD-based approach at the LHC in a kinematic region that LO contributions dominate. We also investigate long-range in rapidity double $J / ψ$ correlations. We found no evidence of a ridge-like structure for double $J / ψ$ production in proton-proton collisions at the LHC up to subleading $α_{s}^{6}$ accuracy.
↳ hep-phhep-exnucl-thPRD(2016)·35 citations
08
Searching for Axion Dark Matter in Atoms: Oscillating Electric Dipole Moments and Spin-Precession Effects
Benjamin M. Roberts🇦🇺 · Yevgeny V. Stadnik🇦🇺 · Victor V. Flambaum🇦🇺 · Vladimir A. Dzuba🇦🇺
We propose to search for axion dark matter via the oscillating electric dipole moments that axions induce in atoms and molecules. These moments are produced through the intrinsic oscillating electric dipole moments of nucleons and through the $P, T$ -violating nucleon-nucleon interaction mediated by pion exchange, both of which arise due to the axion-gluon coupling, and also directly through the axion-electron interaction. Axion dark matter may also be sought for through the spin-precession effects that axions produce by directly coupling to fermion spins.
↳ physics.atom-phhep-phnucl-th2 citations
09
Searching for Scalar Dark Matter in Atoms and Astrophysical Phenomena: Variation of Fundamental Constants
Yevgeny V. Stadnik🇦🇺 · Benjamin M. Roberts🇦🇺 · Victor V. Flambaum🇦🇺 · Vladimir A. Dzuba🇦🇺
We propose to search for scalar dark matter via its effects on the electromagnetic fine-structure constant and particle masses. Scalar dark matter that forms an oscillating classical field produces `slow' linear-in-time drifts and oscillating variations of the fundamental constants, while scalar dark matter that forms topological defects produces transient-in-time variations of the constants of Nature. These variations can be sought for with atomic clock, laser interferometer and pulsar timing measurements. Atomic spectroscopy and Big Bang nucleosynthesis measurements already give improved bounds on the quadratic interaction parameters of scalar dark matter with the photon, electron, and light quarks by up to 15 orders of magnitude, while Big Bang nucleosynthesis measurements provide the first such constraints on the interaction parameters of scalar dark matter with the massive vector bosons.
↳ hep-phastro-ph.COnucl-thphysics.atom-ph2 citations
10
Predictions for 5.023 TeV Pb+Pb collisions at the LHC
H. Niemi🇩🇪 · K. J. Eskola🇫🇮 · R. Paatelainen🇪🇸 · K. Tuominen🇫🇮
We compute predictions for various low-transverse-momentum bulk observables in $s_{N N} = 5.023$ TeV Pb+Pb collisions at the LHC from the event-by-event next-to-leading-order perturbative-QCD + saturation + viscous hydrodynamics ("EKRT") model. In particular, we consider the centrality dependence of charged hadron multiplicity, flow coefficients of the azimuth-angle asymmetries and correlations of event-plane angles. The centrality dependencies of the studied observables are predicted to be very similar to those at 2.76 TeV, and the magnitudes of the flow coefficients and event-plane angle correlations are predicted to be close to those at 2.76 TeV. The flow coefficients may, however, offer slightly more discriminating power on the temperature dependence of QCD matter viscosity than the 2.76 TeV measurements. Our prediction for the multiplicity in the 0-5\% centrality class, obtained using the two temperature-dependent shear-viscosity-to-entropy ratios that give the best overall fit to RHIC and LHC data is $d N_{ch} / d η_{∣ η ∣ \leq 0.5} = 1876 \dots 2046$ . We also predict a power-law increase from 200 GeV Au+Au collisions at RHIC to 2.76 and 5.023 TeV Pb+Pb collisions at the LHC, $d N_{ch} / d η_{∣ η ∣ \leq 0.5} \propto s^{0.164 \dots 0.174}$ .
↳ hep-phnucl-thPRC(2016)·107 citations
11
Strong Multi-step Interference Effects in 12C(d,p) to the 9/2+ State in 13C
N. Keeley · K. W. Kemper · K. Rusek
The population of the 9.50 MeV 9/2+ resonance in 13C by single neutron transfer reactions is expected to be dominated by the two-step route through the 12C 2+ (4.44 MeV) state, with another possible contribution via the strongly excited 3- (9.64 MeV) resonance in 12C. However, we find that a good description of the angular distribution for population of this state via the 12C(d,p)13C reaction is only possible when both direct 0+ x g_9/2 and two-step (via the 4.44 MeV 12C 2+ state) 2+ x d_5/2 paths are included in a coupled reaction channel calculation. While the calculated angular distribution is almost insensitive to the presence of the two-step path via the 9.64 MeV 12C 3- resonance, despite a much greater contribution to the wave function from the 3- x f_7/2 configuration, its inclusion is required to fit the details of the experimental angular distribution. The very large interference between the various components of the calculations, even when these are small, arises through the ``kinematic'' effect associated with the different transfer routes.
↳ nucl-exnucl-thPRC(2015)·5 citations
12
Higher order effective interactions and effective bosonized model for 2-N particle states
Fabio L. Braghin🇧🇷
In this work, an effective fermion model with particular higher order interactions given by: $I_{I I} = \sum_{n}^{N} g_{2^{n}} (ψ ˉ_{a} ψ_{a})^{2^{n}}$ , for finite $N$ , is investigated by means of the auxiliary field method by taking into account 2 $n$ -particle states as proposed in Ref. [1]. The bosonized model was found to exhibit an approximate symmetry when expanded for weak field fluctuations around the mean field solutions. In the present work, the role of the mean field solutions for the corresponding auxiliary fields is investigated. With the integration of fermions, the resulting determinant is expanded in a polynomial boson model in the weak field approximation and the approximate symmetry found for this series does not appear if the boson mean fields are set to zero.
↳ hep-phhep-thnucl-thEPJ Web Conf.(2016)·0 citations
13
On $γ N \to γ ρ N^{'}$ at large $γ ρ$ invariant mass
R. Boussarie🇫🇷 · B. Pire🇫🇷 · L. Szymanowski🇫🇷 · S. Wallon🇫🇷
Photoproduction of a pair of particles with large invariant mass is a natural extension of collinear QCD factorization theorems which have been much studied for deeply virtual Compton scattering and deeply virtual meson production. We consider the case where the wide angle Compton scattering subprocess $γ (q q ˉ) \to γ ρ$ factorizes from generalized parton distribution. At dominant twist, separating the transverse (respectively longitudinal) polarization of the $ρ$ meson allows one to get access to chiral-odd (respectively chiral-even) GPDs. This opens a new way to the extraction of these elusive transversity GPDs.
↳ hep-phhep-exnucl-exnucl-th2 citations
14
Experiment summary
Andrea Rossi (Padua University & INFN)🇮🇹
The measurement of the production of particles coming from hard scattering processes covers a fundamental role in the characterization of the system formed in heavy-ion collisions, allowing to probe the microscopic processes underlying the interaction of high energy partons with the medium. An impressive amount of measurements related to jet, quarkonia, open heavy flavor, and electroweak signal production in nucleus-nucleus as well as p(d)-nucleus collisions was delivered by experiments at RHIC and LHC in past years. In these proceedings, the main experimental results presented during the Hard Probes conference are summarized.
↳ hep-exhep-phnucl-exnucl-thNucl.Part.Phys.Proc.(2016)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE