Search

It is generally believed that the quark-hadron transition at small values of baryon chemical potentials μ B is a crossover but changes to a first-order phase transition with an associated critical endpoint (CEP) as μ B increases. Such a μ B -dependent quark-hadron transition is expected to result in a double-peak structure in the collision energy dependence of the baryon density fluctuation in heavy-ion collisions with one at lower energy due to the spinodal instability during the first-order phase transition and another at higher energy due to the critical fluctuations in the vicinity of the CEP. By analyzing the data on the p , d and 3 H yields in central heavy-ion collisions within the coalescence model for light nuclei production, we find that the relative neutron density fluctuation Δ ρ n = 〈 ( δ ρ n ) 2 〉 / 〈 ρ n 〉 2 at kinetic freeze-out indeed displays a clear peak at s N N = 8.8 GeV and a possible strong re-enhancement at s N N = 4.86 GeV . Our findings thus provide a strong support for the existence of a first-order phase transition at large μ B and its critical endpoint at a smaller μ B in the temperature versus baryon chemical potential plane of the QCD phase diagram. [ABSTRACT FROM AUTHOR]

We re-analyse the associated production of a prompt J / ψ and a W boson in pp collisions at the LHC following the results of the ATLAS Collaboration. We perform the first study of the Single-Parton-Scattering (SPS) contributions at the Next-to-Leading Order (NLO) in α s in the Colour-Evaporation Model (CEM), an approach based on the quark–hadron-duality. Our study provides clear indications for Double-Parton-Scattering (DPS) contributions, in particular at low transverse momenta, since our SPS CEM evaluation, which can be viewed as a conservative upper limit of the SPS yields, falls short compared to the ATLAS experimental data by 3.1 standard deviations. We also determine a finite allowed region for σ eff , inversely proportional to the size of the DPS yields, corresponding to the otherwise opposed hypotheses, namely our NLO CEM evaluation and the LO direct Colour-Singlet (CS) Model contribution. In both cases, the resulting DPS yields are significantly larger than that initially assumed by ATLAS based on jet-related analyses but is consistent with their observed raw-yield azimuthal distribution and with their prompt J / ψ + J / ψ and Z + prompt J / ψ data. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the presence of multifractality and the possibility of quark-hadron phase transition in the multiparticle production in O-AgBr, Si-AgBr and S-AgBr interactions at 4.5AGeV/ in the framework of Ginzburg-Landau theory of second-order phase transition following the Takagi moment methodology. The same analysis with the factorial moment method has also been performed. Experimental results have been compared with the prediction of UrQMD and AMPT models. A comparison of experimental results with the analysis of UrQMD simulated RHIC data by the method of Takagi moment has also been presented. Comparison of experimental results with previous results of emulsion experiments has been mentioned. [ABSTRACT FROM AUTHOR]

In this article we evaluate some of the properties of strongly interacting hadronic matter using non-linear Walecka model in relativistic mean-field approximation. We find that due to the coupling of baryons and bosons, baryonic matter develops instability that is characterised by the appearance of baryonic state with negative entropy density. In the region of instability of baryonic matter we find no evidence of negative in-medium mass of baryons or any signal of kaon condensation. Further we find that this instability of baryonic matter can halt the process of first order phase transition from strongly interacting hadronic matter consisting of coupled baryons and bosons to a weakly interacting quark–gluon plasma phase. [ABSTRACT FROM AUTHOR]

Meson mixing is considered to be an ideal testing ground for new physics searches. Experimental precision has greatly increased over the recent years, exceeding in several cases the theoretical precision. A possible limit in the theoretical accuracy could be a hypothetical breakdown of quark–hadron duality. We propose a simple model for duality violations and give stringent phenomenological bounds on its effects on mixing observables, indicating regions where future measurements of Δ Γ d , a s l d and a s l s would give clear signals of new physics. Finally, we turn our attention to the charm sector, and reveal that a modest duality violation of about 20% could explain the huge difference between HQE predictions for D mixing and experimental data. [ABSTRACT FROM AUTHOR]

Quark-hadron phase transition at the end of evolution of the dense matter created in heavy-ion collisions is studied with particular attention given to the fluctuation of spatial patterns that is expected in a second-order phase transition, as found in the Ising model. Since QCD thermodynamics cannot easily be applied at low temperature and density, an event generator is constructed to simulate the dynamical properties of contraction due to confinement forces, and randomization due to the thermal behavior of a large quark system on the edge of hadronization. Fluctuations of the positions of emitted pions in the (η, Φ) space are analyzed using normalized factorial moments in a wide range of bin sizes. The scaling index ν is found to be very close to the predicted value in the Ginzburg-Landau formalism. The erraticity indices μq are determined in a number of ways that lead to the same consistent values. They are compared to the values from the Ising model, showing significant difference in a transparent plot. Experimental determination of ν and μq at the LHC are now needed to check the reality of the theoretical study, and to provide guidance for improving the model description of quark-hadron phase transition. [ABSTRACT FROM AUTHOR]

The presence of quark-hadron phase transitions in neutron stars can be related to several interesting phenomena. In particular, previous calculations have shown that fast rotating neutron stars, when subjected to a quark-hadron phase transition in their interiors, could give rise to the backbending phenomenon characterized by a spin-up era. In this work, we use an equation of state composed of two phases, containing nucleons (and leptons) and quarks. The hadronic phase is described in a relativistic mean field formalism that takes many-body forces into account, and the quark phase is described by the MIT bag model with a vector interaction. Stationary and axisymmetric stellar models are obtained in a self-consistent way by solving numerically the Einstein–Maxwell equations by means of a pseudo-spectral method. As a result, we obtain the interesting backbending phenomenon for fast spinning neutron stars. More importantly, we show that a magnetic field, which is assumed to be axisymmetric and poloidal, can also be enhanced due to the phase transition from normal hadronic matter to quark matter on highly magnetized neutron stars. Therefore, in parallel to the spin-up era, classes of neutron stars endowed with strong magnetic fields may go through a ‘magnetic-up era’ in their lives. [ABSTRACT FROM AUTHOR]

We study the quark–hadron phase transition in the framework of massive gravity. We show that the modification of the FRW cosmological equations leads to the quark–hadron phase transition in the early massive Universe. Using numerical analysis, we consider that a phase transition based on the chiral symmetry breaking after the electroweak transition, occurred at approximately 10 μs after the Big Bang to convert a plasma of free quarks and gluons into hadrons. [ABSTRACT FROM AUTHOR]

Hadronic spectral functions measured by the ALEPH collaboration in the vector and axial-vector channels are used to study potential quark-hadron duality violations (DV). This is done entirely in the framework of pinched kernel finite energy sum rules (FESR), i.e. in a model independent fashion. The kinematical range of the ALEPH data is effectively extended up to s = 10 GeV2 by using an appropriate kernel, and assuming that in this region the spectral functions are given by perturbative QCD. Support for this assumption is obtained by using e e annihilation data in the vector channel. Results in both channels show a good saturation of the pinched FESR, without further need of explicit models of DV. [ABSTRACT FROM AUTHOR]

We examine the interference γZ box corrections to parity-violating elastic electron–proton scattering in the light of the recent observation of quark–hadron duality in parity-violating deep-inelastic scattering from the deuteron, and the approximate isospin independence of duality in the electromagnetic nucleon structure functions down to Q 2 ≈ 1 GeV 2 . Assuming that a similar behavior also holds for the γZ proton structure functions, we find that duality constrains the γZ box correction to the proton's weak charge to be ℜ e □ γ Z V = ( 5.4 ± 0.4 ) × 10 − 3 at the kinematics of the Q weak experiment. Within the same model we also provide estimates of the γZ corrections for future parity-violating experiments, such as MOLLER at Jefferson Lab and MESA at Mainz. [ABSTRACT FROM AUTHOR]

Event-by-event (ebe) fluctuations of hadronic patterns are investigated in terms of voids by analyzing the experimental data on 4.5, 14.5 and 60 A GeV/c 16O-AgBr collisions. The findings are compared with the predictions of a multi-phase transport AMPT model. Dependence of voids on phase space bin width is examined in terms of two lowest moments of ebe fluctuations of voids, 〈Gq〉 and Sq. The findings reveal that scaling exponent estimated from the observed power-law behavior of the voids may be used to characterize the various properties of hadronic phase transition. The results also rule out occurrence of second-order quark-hadron phase transition at the projectile energies considered. [ABSTRACT FROM AUTHOR]

Reaction-diffusion equations with suitable boundary conditions have special propagating solutions which very closely resemble the moving interfaces in a first-order transition. We show that the dynamics of the chiral order parameter for the chiral symmetry breaking transition in heavy-ion collisions, with dissipative dynamics, is governed by one such equation; specifically, the Newell-Whitehead equation. Furthermore, required boundary conditions are automatically satisfied due to the geometry of the collision. The chiral transition is, therefore, completed by a propagating interface, exactly as for a first-order transition, even though the transition actually is a crossover for relativistic heavy-ion collisions. The same thing also happens when we consider the initial confinement-deconfinement transition with the Polyakov loop order parameter. The resulting equation, again with dissipative dynamics, can then be identified with the reaction-diffusion equation known as the FitzHugh-Nagumo equation which is used in population genetics. Observational constraints imply that the entire phase conversion cannot be achieved by such slow moving fronts, and some alternate faster dynamics needs also to be invoked; for example, involving fluctuations. We discuss the implications of these results for heavy-ion collisions. We also discuss possible extensions for the case of the early universe. [ABSTRACT FROM AUTHOR]

We report on the status of a direct computation of the time-like splitting functions at next-to-next-to-leading order in QCD. Time-like splitting functions govern the collinear kinematics of inclusive hadron production and the evolution of the parton fragmentation distributions. Current knowledge about them at three loops has been inferred by means of crossing symmetry from their related space-like counterparts, which has left certain parts of the off-diagonal quark--gluon splitting function undetermined. This motivates an independent calculation from first principles. We review the tools and methods which are applied to attack the problem. [ABSTRACT FROM AUTHOR]

Aims. We present a new microscopic hadron-quark hybrid equation of state model for astrophysical applications, from which compact hybrid star configurations are constructed. These are composed of a quark core and a hadronic shell with a first-order phase transition at their interface. The resulting mass-radius relations are in accordance with the latest astrophysical constraints. Methods. The quark matter description is based on a quantum chromodynamics (QCD) motivated chiral approach with higher-order quark interactions in the Dirac scalar and vector coupling channels. For hadronic matter we select a relativistic mean-field equation of state with density-dependent couplings. Since the nucleons are treated in the quasi-particle framework, an excluded volume correction has been included for the nuclear equation of state at suprasaturation density which takes into account the finite size of the nucleons. Results. These novel aspects, excluded volume in the hadronic phase and the higher-order repulsive interactions in the quark phase, lead to a strong first-order phase transition with large latent heat, i.e. the energy-density jump at the phase transition, which fulfils a criterion for a disconnected third-family branch of compact stars in the mass-radius relationship. These twin stars appear at high masses (~2 M☉) that are relevant for current observations of high-mass pulsars. Conclusions. This analysis offers a unique possibility by radius observations of compact stars to probe the QCD phase diagram at zero temperature and large chemical potential and even to support the existence of a critical point in the QCD phase diagram. [ABSTRACT FROM AUTHOR]

Using the recently published data from the BONuS (Barely Off-shell Nucleon Structure) experiment at Jefferson Lab, which utilized a spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F2 structure function. The data are used to reconstruct the lowest few (N=2, 4, and 6) moments of F2 in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark-hadron duality holds locally for the neutron in the second and third resonance regions down to Q² ≈ 1 GeV², with violations possibly up to 20% observed in the first resonance region. [ABSTRACT FROM AUTHOR]

The parity-violating asymmetries between a longitudinally polarized electron beam and an unpolarized deuterium target have been measured recently. The measurement covered two kinematic points in the deep-inelastic scattering region and five in the nucleon resonance region. We provide here details of the experimental setup, data analysis, and results on all asymmetry measurements including parity-violating electron asymmetries and those of inclusive pion production and beam-normal asymmetries. The parity-violating deep-inelastic asymmetries were used to extract the electron-quark weak effective couplings, and the resonance asymmetries provided the first evidence for quark-hadron duality in electroweak observables. These electron asymmetries and their interpretation were published earlier, but are presented here in more detail. [ABSTRACT FROM AUTHOR]

The boiling of possible quark nuggets during the quark-hadron phase transition of the Universe at nonzero chemical potential is revisited within the microscopic Brueckner–Hartree–Fock approach employed for the hadron phase, using two kinds of baryon interactions as fundamental inputs. To describe the deconfined phase of quark matter, we use a recently developed quark mass density-dependent model with a fully self-consistent thermodynamic treatment of confinement. We study the baryon number limit A boil (above which boiling may be important) with three typical values for the confinement parameter D . It is firstly found that the baryon interaction with a softer equation of state for the hadron phase would only lead to a small increase of A boil . However, results depend sensitively on the confinement parameter in the quark model. Specifically, boiling might be important during the Universe cooling for a limited parameter range around D 1 / 2 = 170 MeV, a value satisfying recent lattice QCD calculations of the vacuum chiral condensate, while for other choices of this parameter, boiling might not happen and cosmological quark nuggets of 10 2 < A < 10 50 could survive. [ABSTRACT FROM AUTHOR]

I review the historical development of QCD predictions for exclusive hadronic processes, beginning with constituent counting rules and the quark interchange mechanism, phenomena which gave early validation for the quark structure of hadrons. The subsequent development of pQCD factorization theorems for hard exclusive amplitudes and the development of evolution equations for the hadron distribution amplitudes provided a rigorous framework for calculating hadronic form factors and hard scattering exclusive scattering processes at high momentum transfer. I also give a brief introduction to the field of "light-front holography" and the insights it brings to quark confinement, the behavior of the QCD coupling in the nonperturbative domain, as well as hadron spectroscopy and the dynamics of exclusive processes. [ABSTRACT FROM AUTHOR]

We consider how the five-dimensional Randall-Sundrum (one-brane) theory becomes modified when account is taken of the bulk viscosity of the cosmic fluid on the brane. We focus on the plasma era between 10 K (muon pair annihilation) to about 5×10 K (electron-positron annihilation), which includes the first order quark-hadron transition beginning at an energy density of about 5×10 MeV. Various possibilities are examined for modeling the bulk viscosity, preference being at the end given to the results calculated from relativistic kinetic theory. According to this, the viscosity is negligible at the highest temperatures, but may amount to a few per cent corrections in the later stages of the plasma era. We also briefly consider anisotropic universes where the shear viscosity comes into play, and show that in the case of the Kasner model the influences from bulk viscosity and shear viscosity become comparable when the anisotropy parameter of the universe is of order A∼10 in the beginning of the plasma era, and A∼10 in its later region. [ABSTRACT FROM AUTHOR]

The directed flow of identified hadrons is studied within the parton-hadron-string-dynamics (PHSD) approach for the asymmetric system Cu + Au in noncentral collisions at √SNN = 200 GeV. It is emphasized that due to the difference in the number of protons of the colliding nuclei an electric field emerges, which is directed from the heavy to the light nucleus. This strong electric field is only present for about 0.25 fm/c at √SNN = 200 GeV and leads to a splitting of the directed flow v1, for particles with the same mass but opposite electric charges in case of an early presence of charged quarks and antiquarks. The microscopic calculations of the directed flow for π±,K±,p, and p are carried out in the PHSD by taking into account the electromagnetic field induced by the spectators as well as its influence on the hadronic and partonic quasiparticle trajectories. It is shown that the splitting of the directed flow as a function of pseudorapidity η and in particular as a function of the transverse momentum p, provides a direct access to the electromagnetic response of the very early (nonequilibrium) phase of relativistic heavy-ion collisions and allows us to shed light on the presence (and number) of electric charges in this phase. [ABSTRACT FROM AUTHOR]

At low temperatures, we expect that all QCD observables are defined in terms of hadrons. This includes the partition function as well as the Polyakov loop in all representations. We analyze the physics underlying a microscopic derivation of the hadron resonance gas. [ABSTRACT FROM AUTHOR]