Advances in High Energy Physics
[SJR: 1.334] [H-I: 12] [13 followers] Follow
Open Access journal
ISSN (Print) 1687-7357 - ISSN (Online) 1687-7365
Published by Hindawi Publishing Corporation [403 journals]
- On Productions of Net-Baryons in Central Au-Au Collisions at RHIC Energies
Abstract: The transverse momentum and rapidity distributions of net-baryons (baryons minus antibaryons) produced in central gold-gold (Au-Au) collisions at 62.4 and 200 GeV are analyzed in the framework of a multisource thermal model. Each source in the model is described by the Tsallis statistics to extract the effective temperature and entropy index from the transverse momentum distribution. The two parameters are used as input to describe the rapidity distribution and to extract the rapidity shift and contribution ratio. Then, the four types of parameters are used to structure some scatter plots of the considered particles in some three-dimensional (3D) spaces at the stage of kinetic freeze-out, which are expected to show different characteristics for different particles and processes. The related methodology can be used in the analyses of particle production and event holography, which are useful for us to better understand the interacting mechanisms.
PubDate: Mon, 29 Jun 2015 12:34:13 +000
- Virial Theorem for Nonrelativistic Quantum Fields in Spatial Dimensions
Abstract: The virial theorem for nonrelativistic complex fields in spatial dimensions and with arbitrary many-body potential is derived, using path-integral methods and scaling arguments recently developed to analyze quantum anomalies in low-dimensional systems. The potential appearance of a Jacobian due to a change of variables in the path-integral expression for the partition function of the system is pointed out, although in order to make contact with the literature most of the analysis deals with the case. The virial theorem is recast into a form that displays the effect of microscopic scales on the thermodynamics of the system. From the point of view of this paper the case usually considered, , is not natural, and the generalization to the case is briefly presented.
PubDate: Mon, 22 Jun 2015 13:21:24 +000
- Comparing Particle Productions at RHIC and LHC Energies
PubDate: Thu, 18 Jun 2015 08:04:24 +000
- Noether Gauge Symmetry of Dirac Field in (2 + 1)-Dimensional Gravity
Abstract: We consider a gravitational theory including a Dirac field that is nonminimally coupled to gravity in 2 + 1 dimensions. Noether gauge symmetry approach can be used to fix the form of coupling function and the potential of the Dirac field and to obtain a constant of motion for the dynamical equations. In the context of (2 + 1)-dimensional gravity, we investigate cosmological solutions of the field equations using these forms obtained by the existence of Noether gauge symmetry. In this picture, it is shown that, for the nonminimal coupling case, the cosmological solutions indicate both an early-time inflation and late-time acceleration for the universe.
PubDate: Mon, 15 Jun 2015 14:08:25 +000
- Production of Kaon and in Nucleus-Nucleus Collisions at Ultrarelativistic
Energy from a Blast-Wave Model
Abstract: The particle production of Kaon and is studied in nucleus-nucleus collisions at relativistic energy based on a chemical equilibrium blast-wave model. The transverse momentum spectra of Kaon and at the kinetic freeze-out stage from our model are in good agreement with the experimental results. The kinetic freeze-out parameters of temperature and radial flow parameter are presented for the FOPI, RHIC, and LHC energies. And the resonance decay effect is also discussed. The systematic study for beam energy dependence of the strangeness particle production will help us to better understand the properties of the matter created in heavy-ion collisions at the kinetic freeze-out stage.
PubDate: Sun, 14 Jun 2015 08:53:21 +000
- Pion Transverse Momentum Spectrum, Elliptic Flow, and Interferometry in
the Granular Source Model for RHIC and LHC Heavy Ion Collisions
Abstract: We systematically investigate the pion transverse momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in the granular source model for the heavy ion collisions of Au-Au at GeV and Pb-Pb at TeV with different centralities. The granular source model can well reproduce the experimental results of the heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). We examine the parameters involved in the granular source model. The experimental data of the momentum spectrum, elliptic flow, and HBT radii for the two collision energies and different centralities impose very strict constraints on the model parameters. They exhibit certain regularities for collision centrality and energy. The space-time structure and expansion velocities of the granular sources for the heavy ion collisions at the RHIC and LHC energies with different centralities are investigated.
PubDate: Wed, 10 Jun 2015 13:29:39 +000
- Recognizing Critical Behavior amidst Minijets at the Large Hadron Collider
Abstract: The transition from quarks to hadrons in a heavy-ion collision at high energy is usually studied in two different contexts that involve very different transverse scales: local and nonlocal. Models that are concerned with the spectra and azimuthal anisotropy belong to the former, that is, hadronization at a local point in space, such as the recombination model. The nonlocal problem has to do with quark-hadron phase transition where collective behavior through near-neighbor interaction can generate patterns of varying sizes in the space. The two types of problems are put together in this paper both as brief reviews separately and to discuss how they are related to each other. In particular, we ask how minijets produced at LHC can affect the investigation of multiplicity fluctuations as signals of critical behavior. It is suggested that the existing data from LHC have sufficient multiplicities in small intervals to make the observation of distinctive features of clustering of soft particles, as well as voids, feasible that characterize the critical behavior at phase transition from quarks to hadrons, without any ambiguity posed by the clustering of jet particles.
PubDate: Wed, 10 Jun 2015 09:39:07 +000
- The Unified Hydrodynamics and the Pseudorapidity Distributions in Heavy
Ion Collisions at BNL-RHIC and CERN-LHC Energies
Abstract: The charged particles produced in nucleus-nucleus collisions are divided into two parts. One is from the hot and dense matter created in collisions. The other is from leading particles. The hot and dense matter is assumed to expand according to unified hydrodynamics and freezes out into charged particles from a space-like hypersurface with a fixed proper time of . The leading particles are conventionally taken as the particles which inherit the quantum numbers of colliding nucleons and carry off most of incident energy. The rapidity distributions of the charged particles from these two parts are formulated analytically, and a comparison is made between the theoretical results and the experimental measurements performed in Au-Au and Pb-Pb collisions at the respective BNL-RHIC and CERN-LHC energies. The theoretical results are well consistent with experimental data.
PubDate: Wed, 10 Jun 2015 07:03:54 +000
- Transverse Momentum Spectra of and at Midrapidity in + Au, Cu + Cu, and
Collisions at GeV
Abstract: We analyze transverse momentum spectra of and at midrapidity in + Au, Cu + Cu, and collisions at GeV in the formworks of Tsallis statistics and Boltzmann statistics, respectively. Both of them can describe the transverse momentum spectra and extract the thermodynamics parameters of matter evolution in the collisions. The parameters are helpful for us to understand the thermodynamics factors of the particle production.
PubDate: Tue, 09 Jun 2015 17:06:15 +000
- Properties of Full Jet in High-Energy Heavy-Ion Collisions from Parton
Abstract: The properties of fully reconstructed jet are investigated in p + p and Pb + Pb collisions at = 2.76 TeV within a multiphase transport (AMPT) model with both partonic scatterings and hadronic rescatterings. A large transverse momentum () asymmetry of dijet or photon-jet arises from the strong interactions between jet and partonic matter. The -dependent jet fragmentation function in Pb + Pb collisions is decomposed into two contributions from different jet hadronization mechanisms, that is, fragmentation versus coalescence. The medium modification of differential jet shape displays that the jet energy is redistributed towards a larger radius owing to jet-medium interactions in heavy-ion collisions. Jet triangular azimuthal anisotropy coefficient, , which shows a smaller magnitude than the elliptic coefficient , decreases more quickly with increasing jet , which can be attributed to a path-length effect of jet energy loss. All of these properties of full jet are consistent with the jet energy loss mechanism in a stronglyinteracting partonic matter in high-energy heavy-ion collisions.
PubDate: Tue, 09 Jun 2015 14:26:03 +000
- Azimuthally Integrated HBT Parameters for Charged Pions in Nucleus-Nucleus
Interactions versus Collision Energy
Abstract: The energy dependence of spatiotemporal characteristics of particle emission region is studied for charged pions produced in nuclear collisions. No dramatic change is observed for the HBT parameters with increasing of the center-of-mass (c.m.) energy per nucleon-nucleon pair, , for of a few GeV to a few TeV. The emission duration is obtained to be almost independent of the c.m. energy within the measurement uncertainties. The analytic function is suggested for a smooth approximation of the energy dependence of the main HBT parameters. The fits demonstrate reasonable agreement with the experimental data. Predictions are made for future LHC and FCC experiments.
PubDate: Tue, 09 Jun 2015 13:34:01 +000
- Freeze-Out Parameters in Heavy-Ion Collisions at AGS, SPS, RHIC, and LHC
Abstract: We review the chemical and kinetic freeze-out conditions in high energy heavy-ion collisions for AGS, SPS, RHIC, and LHC energies. Chemical freeze-out parameters are obtained using produced particle yields in central collisions while the corresponding kinetic freeze-out parameters are obtained using transverse momentum distributions of produced particles. For chemical freeze-out, different freeze-out scenarios are discussed such as single and double/flavor dependent freeze-out surfaces. Kinetic freeze-out parameters are obtained by doing hydrodynamic inspired blast wave fit to the transverse momentum distributions. The beam energy and centrality dependence of transverse energy per charged particle multiplicity are studied to address the constant energy per particle freeze-out criteria in heavy-ion collisions.
PubDate: Tue, 09 Jun 2015 13:33:17 +000
- A Review on ϕ Meson Production in Heavy-Ion Collision
Abstract: The main aim of the relativistic heavy-ion experiment is to create extremely hot and dense matter and study the QCD phase structure. With this motivation, experimental program started in the early 1990s at the Brookhaven Alternating Gradient Synchrotron (AGS) and the CERN Super Proton Synchrotron (SPS) followed by Relativistic Heavy Ion Collider (RHIC) at Brookhaven and recently at Large Hadron Collider (LHC) at CERN. These experiments allowed us to study the QCD matter from center-of-mass energies () 4.75 GeV to 2.76 TeV. The ϕ meson, due to its unique properties, is considered as a good probe to study the QCD matter created in relativistic collisions. In this paper we present a review on the measurements of ϕ meson production in heavy-ion experiments. Mainly, we discuss the energy dependence of ϕ meson invariant yield and the production mechanism, strangeness enhancement, parton energy loss, and partonic collectivity in nucleus-nucleus collisions. Effect of later stage hadronic rescattering on elliptic flow () of proton is also discussed relative to corresponding effect on ϕ meson .
PubDate: Tue, 09 Jun 2015 13:30:19 +000
- The Profile of Inelastic Collisions from Elastic Scattering Data
Abstract: Using the unitarity relation in combination with experimental data about the elastic scattering in the diffraction cone, it is shown how the shape and the darkness of the inelastic interaction region of colliding protons change with increase of their energies. In particular, the collisions become fully absorptive at small impact parameters at LHC energies that results in some special features of inelastic processes. Possible evolution of this shape with the dark core at the LHC to the fully transparent one at higher energies is discussed that implies that the terminology of the black disk would be replaced by the black toroid. The approach to asymptotics is disputed. The ratio of the real to imaginary parts of the nonforward elastic scattering amplitude is briefly discussed. All the conclusions are only obtained in the framework of the indubitable unitarity condition using experimental data about the elastic scattering of protons in the diffraction cone without any reference to quantum chromodynamics (QCD) or phenomenological approaches.
PubDate: Tue, 09 Jun 2015 12:24:57 +000
- Energy Dependence of Slope Parameter in Elastic Nucleon-Nucleon Scattering
Abstract: The diffraction slope parameter is investigated for elastic proton-proton and proton-antiproton scattering based on all the available experimental data at low and intermediate momentum transfer values. Energy dependence of the elastic diffraction slope is approximated by various analytic functions. The expanded “standard” logarithmic approximations with minimum number of free parameters allow description of the experimental slopes in all the available energy range reasonably. The estimations of asymptotic shrinkage parameter are obtained for various domains based on all the available experimental data. Various approximations differ from each other both in the low energy and very high energy domains. Predictions for diffraction slope parameter are obtained for elastic proton-proton scattering from NICA up to future collider (FCC/VLHC) energies, for proton-antiproton elastic reaction in FAIR energy domain for various approximation functions.
PubDate: Tue, 09 Jun 2015 11:20:29 +000
- Exact Solution of the Curved Dirac Equation in Polar Coordinates: Master
Abstract: We show that the () curved Dirac equation in polar coordinates can be transformed into Schrodinger-like differential equation for upper spinor component. We compare this equation with the Schrodinger equation derived from shape invariance property of second order differential equations of mathematical physics. This formalism enables us to determine the electrostatic potential and relativistic energy in terms of master function and corresponding weight function. We also obtain the spinor wave function in terms of orthogonal polynomials.
PubDate: Sun, 31 May 2015 16:42:45 +000
- Bianchi Type-V Bulk Viscous Cosmic String in Gravity with Time Varying
Abstract: We study the Bianchi type-V string cosmological model with bulk viscosity in theory of gravity by considering a special form and linearly varying deceleration parameter. This is an extension of the earlier work of Naidu et al., 2013, where they have constructed the model by considering a constant deceleration parameter. Here we find that the cosmic strings do not survive in both models. In addition we study some physical and kinematical properties of both models. We observe that in one of our models these properties are identical to the model obtained by Naidu et al., 2013, and in the other model the behavior of these parameters is different.
PubDate: Sun, 31 May 2015 09:16:17 +000
- Effects of the Variation of SUSY Breaking Scale on Yukawa and Gauge
Abstract: The present analysis addresses an interesting primary question on how do the gauge and Yukawa couplings unification scales vary with varying SUSY breaking scales , assuming a single scale for all supersymmetric particles. It is observed that the gauge coupling unification scale increases with whereas third-generation Yukawa couplings unification scale decreases with . The rising of the unification scale and also the mass of the color triplet multiplets is necessary to increase the proton decay lifetime; the analysis is carried out with two-loop RGEs for the gauge and Yukawa couplings within the minimal supersymmetric SU(5) model, while ignoring for simplicity the threshold effects of the heavy particles, which could be as large as a few percentages.
PubDate: Sun, 31 May 2015 08:07:33 +000
- Spherically Symmetric Geometries in and Gravitational Theories
Abstract: Using the well know relation between Ricci scalar, , and torsion scalar, , that is, , we show that, for any spherically symmetric spacetime whose (i) scalar torsion vanishing, that is, or (ii) total derivative term, that is, with is the contraction of the torsion, vanishing, or (iii) the combination of scalar torsion and total derivative term vanishing, could be solution for and gravitational theories.
PubDate: Thu, 28 May 2015 07:40:56 +000
- Form Factor Near the Mass Shell
Abstract: The generalized Ward-Takahashi identity (gWTI) in the pion sector for broken isotopic symmetry is derived and used for the model-independent calculation of the longitudinal form factor of the vector vertex. The on-shell is found to be proportional to the mass difference of the pions and the difference between the vector isospin and scalar isospin pion radii. A numerical estimate of the form factor yields a value two times higher than the previous estimate from the quark model. Off-shell form factors are known to be ambiguous because of the gauge dependence and the freedom in the parameterization of the fields. The near-mass-shell appears to be an exception, allowing for experimental verification of the consequences of the gWTI. We calculate the near-mass-shell using the gWTI and dispersion techniques. The results are discussed in the context of the conservation of vector current (CVC) hypothesis.
PubDate: Wed, 27 May 2015 11:22:40 +000
- Similarity Solution for Free Convection Flow of a Micropolar Fluid under
Convective Boundary Condition via Lie Scaling Group Transformations
Abstract: The free convective flow of an incompressible micropolar fluid along permeable vertical plate under the convective boundary condition is investigated. The Lie scaling group of transformations is applied to get the similarity representation for the system of partial differential equations and then the resulting systems of equations are solved using spectral quasi-linearisation method. A quantitative comparison of the numerical results is made with previously published results for special cases and the results are found to be in good agreement. The results of the physical parameters on the developments of flow, temperature, concentration, skinfriction, wall couple stress, heat transfer, and mass transfer characteristics along vertical plate are given and the salient features are discussed.
PubDate: Wed, 27 May 2015 06:11:29 +000
- Discovery Potential for the Neutral Charmonium-Like by Annihilation
Abstract: Inspired by the observation of charmonium-like , we explore the discovery potential of the neutral production by antiproton-proton annihilation with an effective Lagrangian approach. By investigating the process including the signal and background contributions, it is found that the center of mass energy ≃ 4.0–4.5 GeV is the best energy window for searching the neutral , where the signal can be clearly distinguished from background. The relevant calculations not only are helpful to search for the neutral in the future experiment but also will promote the understanding of the nature and production mechanism of neutral better.
PubDate: Mon, 25 May 2015 11:59:39 +000
- Quasi-Normal Modes: The “Electrons” of Black Holes as
“Gravitational Atoms”' Implications for the Black Hole
Abstract: Some recent important results on black hole (BH) quantum physics concerning the BH effective state and the natural correspondence between Hawking radiation and BH quasi-normal modes (QNMs) are reviewed, clarified, and refined. Such a correspondence permits one to naturally interpret QNMs as quantum levels in a semiclassical model. This is a model of BH somewhat similar to the historical semiclassical model of the structure of a hydrogen atom introduced by Bohr in 1913. In a certain sense, QNMs represent the “electron” which jumps from a level to another one and the absolute values of the QNMs frequencies, “triggered” by emissions (Hawking radiation) and absorption of particles, represent the energy “shells” of the “gravitational hydrogen atom.” Important consequences on the BH information puzzle are discussed. In fact, it is shown that the time evolution of this “Bohr-like BH model” obeys a time dependent Schrödinger equation which permits the final BH state to be a pure quantum state instead of a mixed one. Thus, information comes out in BH evaporation in agreement with the assumption by ’t Hooft that Schröedinger equations can be used universally for all dynamics in the universe. We also show that, in addition, our approach solves the entanglement problem connected with the information paradox.
PubDate: Tue, 19 May 2015 10:14:28 +000
- A Study of Transverse Momentum Distributions of Jets Produced in -, -,
-Au, Au-Au, and Pb-Pb Collisions at High Energies
Abstract: The transverse momentum distributions of jets produced in -, -, -Au, Au-Au, and Pb-Pb collisions at high energies with different selected conditions are analyzed by using a multisource thermal model. The multicomponent (mostly two-component) Erlang distribution used in our description is in good agreement with the experimental data measured by the STAR, D0, CDF II, ALICE, ATLAS, and CMS Collaborations. Related parameters are extracted from the transverse momentum distributions and some information on different interacting systems is obtained. In the two-component Erlang distribution, the first component has usually two or more sources which are contributed by strong scattering interactions between two quarks or more quarks and gluons, while the second component has mostly two sources which are contributed by harder head-on scattering between two quarks.
PubDate: Tue, 19 May 2015 09:01:49 +000
- Effect of Generalized Uncertainty Principle on Main-Sequence Stars and
Abstract: This paper addresses the effect of generalized uncertainty principle, emerged from different approaches of quantum gravity within Planck scale, on thermodynamic properties of photon, nonrelativistic ideal gases, and degenerate fermions. A modification in pressure, particle number, and energy density are calculated. Astrophysical objects such as main-sequence stars and white dwarfs are examined and discussed as an application. A modification in Lane-Emden equation due to a change in a polytropic relation caused by the presence of quantum gravity is investigated. The applicable range of quantum gravity parameters is estimated. The bounds in the perturbed parameters are relatively large but they may be considered reasonable values in the astrophysical regime.
PubDate: Mon, 18 May 2015 13:11:59 +000
- Neutrino Physics in the Frontiers of Intensities and Very High
PubDate: Sun, 17 May 2015 13:20:51 +000
- High Energy Neutrino Emission from Astrophysical Jets in the Galaxy
Abstract: We address simulated neutrino emission originated from astrophysical jets of compact objects within the Galaxy. These neutrinos are of high energies ( of the order up to a few TeV) and for their observation specialized instruments are in operation, both on Earth and in orbit. Furthermore, some next generation telescopes and detector facilities are in the process of design and construction. The jet flow simulations are performed using the modern PLUTO hydrocode in its relativistic magnetohydrodynamic version. One of the main ingredients of the present work is the presence of a toroidal magnetic field that confines the jet flow and furthermore greatly affects the distribution of the high energy neutrinos.
PubDate: Thu, 14 May 2015 14:15:26 +000
- Null Geodesics and Strong Field Gravitational Lensing in a String Cloud
Abstract: This paper is devoted to studying two interesting issues of a black hole with string cloud background. Firstly, we investigate null geodesics and find unstable orbital motion of particles. Secondly, we calculate deflection angle in strong field limit. We then find positions, magnifications, and observables of relativistic images for supermassive black hole at the galactic center. We conclude that string parameter highly affects the lensing process and results turn out to be quite different from the Schwarzschild black hole.
PubDate: Thu, 14 May 2015 11:41:20 +000
- HepSim: A Repository with Predictions for High-Energy Physics Experiments
Abstract: A file repository for calculations of cross sections and kinematic distributions using Monte Carlo generators for high-energy collisions is discussed. The repository is used to facilitate effective preservation and archiving of data from theoretical calculations and for comparisons with experimental data. The HepSim data library is publicly accessible and includes a number of Monte Carlo event samples with Standard Model predictions for current and future experiments. The HepSim project includes a software package to automate the process of downloading and viewing online Monte Carlo event samples. Data streaming over a network for end-user analysis is discussed.
PubDate: Thu, 14 May 2015 05:55:44 +000
- Electron Capture Cross Sections for Stellar Nucleosynthesis
Abstract: In the first stage of this work, we perform detailed calculations for the cross sections of the electron capture on nuclei under laboratory conditions. Towards this aim we exploit the advantages of a refined version of the proton-neutron quasiparticle random-phase approximation (pn-QRPA) and carry out state-by-state evaluations of the rates of exclusive processes that lead to any of the accessible transitions within the chosen model space. In the second stage of our present study, we translate the abovementioned -capture cross sections to the stellar environment ones by inserting the temperature dependence through a Maxwell-Boltzmann distribution describing the stellar electron gas. As a concrete nuclear target we use the 66Zn isotope, which belongs to the iron group nuclei and plays prominent role in stellar nucleosynthesis at core collapse supernovae environment.
PubDate: Wed, 13 May 2015 14:27:10 +000