Application of deep learning methods to the study of magnetic phenomena

Nowadays, methods and techniques of Machine Learning and Deep Learning are being used in various scientific areas. They help to automatize calculations without losing in quality. In this paper the applying of convolutional neural network was considered in frame of problems from statistical physics and computer simulation of magnetic films. In a frame of the first task, CNN was used to determine critical Curie point for Ising model on 2D square lattice. Obtained results were compared with classical Monte-Carlo methods and exact solution. Systems of various lattice sizes and the influence of the size effect on the results' accuracy were considered. Also, authors considered the classical two-dimensional Heisenberg model, a spin system with direct short-range exchange, and studied of its competition with the Dzyaloshinskii-Moriya interaction. A neural network was applied to the recognition of Spiral (Sp), Spiral-skyrmion (SpSk) Skyrmion (Sk), Skyrmion-ferromagnetic (SkF) and Ferromagnetic (FM) phases of the Heisenberg spin system with magnetic skyrmions. The advantage of CNN's application over conventional methods for determination of skyrmion's phases was revealed.Comment: 6 pages, 3 figure

Neutral Kaon Interferometry in Au+Au collisions at sqrt(s_NN) = 200 GeV

We present the first statistically meaningful results from two-K0s interferometry in heavy-ion collisions. A model that takes the effect of the strong interaction into account has been used to fit the measured correlation function. The effects of single and coupled channel were explored. At the mean transverse mass m_T = 1.07 GeV, we obtain the values R = 4.09 +/- 0.46 (stat.) +/- 0.31 (sys) fm and lambda = 0.92 +/- 0.23 (stat) +/- 0.13 (sys), where R and lambda are the invariant radius and chaoticity parameters respectively. The results are qualitatively consistent with m_T systematics established with pions in a scenario characterized by a strong collective flow.Comment: 11 pages, 10 figure

Identified baryon and meson distributions at large transverse momenta from Au+Au collisions at sNN=200\sqrt{s_{_{NN}}} = 200 GeV

Transverse momentum spectra of $\pi^{\pm}$, $p$ and $\bar{p}$ up to 12 GeV/c at mid-rapidity in centrality selected Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV are presented. In central Au+Au collisions, both $\pi^{\pm}$ and $p(\bar{p})$ show significant suppression with respect to binary scaling at $p_T >$ 4 GeV/c. Protons and anti-protons are less suppressed than $\pi^{\pm}$, in the range 1.5 $< p_{T} <$6 GeV/c. The $\pi^-/\pi^+$ and $\bar{p}/p$ ratios show at most a weak $p_T$ dependence and no significant centrality dependence. The $p/\pi$ ratios in central Au+Au collisions approach the values in p+p and d+Au collisions at $p_T >$ 5 GeV/c. The results at high $p_T$ indicate that the partonic sources of $\pi^{\pm}$, $p$ and $\bar{p}$ have similar energy loss when traversing the nuclear medium.Comment: 6 pages, 4 figure

Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at sqrt(s) = 200 GeV

We report a measurement of the longitudinal double-spin asymmetry A_LL and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at sqrt(s)=200 GeV. The cross section data cover transverse momenta 5 < pT < 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A_LL data cover 5 < pT < 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.Comment: 6 pages, 3 figures. Minor changes from review process in Phys. Rev. Lett. Plain text tables of data in STAR publications may be found at http://www.star.bnl.gov/central/publications

Minijet deformation and charge-independent angular correlations on momentum subspace (η,ϕ)(\eta,\phi) in Au-Au collisions at sNN\sqrt{s_{NN}} = 130 GeV

First measurements of charge-independent correlations on angular difference variables $\eta_1 - \eta_2$ (pseudorapidity) and $\phi_1 - \phi_2$ (azimuth) are presented for primary charged hadrons with transverse momentum $0.15 \leq p_t \leq 2$ GeV/$c$ and $|\eta| \leq 1.3$ from Au-Au collisions at $\sqrt{s_{NN}} = 130$ GeV. Strong charge-independent angular correlations are observed associated with jet-like structures and elliptic flow. The width of the jet-like peak on $\eta_1 - \eta_2$ increases by a factor 2.3 from peripheral to central collisions, suggesting strong coupling of semi-hard scattered partons to a longitudinally-expanding medium. New methods of jet analysis introduced here provide evidence for nonperturbative QCD medium effects in heavy ion collisions.Comment: 8 pages, 4 figure

Strangelet Search in AuAu Collisions at 200 GeV

We have searched for strangelets in a triggered sample of 61 million central (top 4%) Au+Au collisions at \sNN = 200 GeV near beam rapidities at the STAR detector. We have sensitivity to metastable strangelets with lifetimes of order $\geq 0.1 ns$, in contrast to limits over ten times longer in AGS studies and longer still at the SPS. Upper limits of a few 10^{-6} to 10^{-7} per central Au+Au collision are set for strangelets with mass ${}^{>}_{\sim}30$ GeV/c^{2}.Comment: As publishe

Longitudinal double-spin asymmetry for inclusive jet production in p+p collisions at sqrt(s)=200 GeV

We report a new STAR measurement of the longitudinal double-spin asymmetry A_LL for inclusive jet production at mid-rapidity in polarized p+p collisions at a center-of-mass energy of sqrt(s) = 200 GeV. The data, which cover jet transverse momenta 5 < p_T < 30 GeV/c, are substantially more precise than previous measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit of polarized deep-inelastic scattering measurements.Comment: 7 pages, 4 figures + 1 tabl

Systematic Measurements of Identified Particle Spectra in pp, d+Au and Au+Au Collisions from STAR

Identified charged particle spectra of $\pi^{\pm}$, $K^{\pm}$, $p$ and \pbar at mid-rapidity ($|y|<0.1$) measured by the \dedx method in the STAR-TPC are reported for $pp$ and d+Au collisions at \snn = 200 GeV and for Au+Au collisions at 62.4 GeV, 130 GeV, and 200 GeV. ... [Shortened for arXiv list. Full abstract in manuscript.]Comment: 58 pages, 46 figures, 37 table

System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider

We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)