Quark Transition Research Articles

Quark Deconfinement of a Hadron in Ultrarelativistic Nucleus-Nucleus Collisions

The temperature dependent energy and corresponding internal pressure of the hadron are obtained by taking Fermi weighted sums over internal discrete energy levels. We find that beyond the critical temperature, the solution of the hadron radius determined from the balance relation between the internal and external pressures of the hadron disappears, which shows that the quark deconfinement transition has occured. In addition, it is shown that the heat bath plays role in delaying the deconfinement process.

SIGNATURES OF SINGLE QUARK LINE WEAK TRANSITIONS

We study the ΔI = 1/2 single quark line transition that occurs in p-wave baryon B → B′π, in radiative Ξ− → Σ−γ, in decuplet Ω− → Ξπ and in kaon K° → ππ weak decays. This leads to five empirical signatures of the single quark line scale. This scale is also predicted from a quark loop model.

Heavy quark potential and phase transitions in continuum theory at finite temperature

The heavy quark potential in the continuum theory at finite temperature is calculated in different phases by using the Polyakov loop as the order parameter. We find a linearly rising potential in the confinement phase, a Debye screened potential in the deconfinement phase and a perturbative r −2 dependence at very high temperatures. Within the approximation used in this paper we report evidence for a first order phase transition accompanied by SU(2) symmetry restoration at very high temperatures in the static three dimensional theory.

Composition, structure and evolution of neutron stars with kaon condensates

We investigate the possibility of kaon condensation in the dense interior of neutron stars through the s-wave interaction of kaons with nucleons. We include nucleon-nucleon interactions by using simple parametrizations of realistic forces, and include electrons and muons in β-equilibrium. The equation of state above the condensate threshold is derived in the mean field approximation. The conditions under which kaon condensed cores undergo a transition to quark matter containing strange quarks are also established. The critical density for kaon condensation lies in the range (2.3–5.0) ϱ 0 where ϱ 0 = 0.16 fm −3 is the equilibrium density of nuclear matter. The critical density depends largely on the value of the strangeness content of the proton, the size of which is controversial. For too large a value of the strangeness content, matter with a kaon condensate is not sufficiently stiff to support the lower limit of 1.44 M ⊙ for a neutron star. Kaon condensation dramatically increases the proton abundance of matter and even allows positrons to exist inside the core. We also consider the case when neutrinos are trapped in the matter, a situation that applies to newly-formed neutron star matter that is less than about 10 s old. Neutrino trapping shifts both kaon condensation and the quark matter transition to higher densities than in the case of cold, catalyzed matter. A newly-formed neutron star is expected to have a rather low central density, the density rising only after mass accretion onto the star ends after a few seconds. Thus, it is likely that if kaon condensation and/or the quark-hadron phase transition occur, they do so only during or after the mass accretion and neutrino trapping stages. We suggest that neutrino observations from a galactic supernova may provide direct evidence for or against a condensate and/or a quark-hadron transition.

NEUTRON MATTER – QUARK MATTER PHASE TRANSITION AND QUARK STAR

We consider the neutron matter and quark matter phase transition along with possible existence of hybrid quark stars. The equation of state for neutron matter is obtained using a nonperturbative method with pion dressing of the neutron matter and an analysis similar to that of symmetric nuclear matter. The quark matter sector is treated perturbatively in the small distance domain. For bag constant B1/4=148 MeV , a first order phase transition is seen. In the context of neutron quark hybrid stars, Tolman-Oppenheimer-Volkoff equations are solved using the equations of state for quark matter and for neutron matter with a phase transition as noted earlier. Stable solutions for such stars are obtained with the Chandrasekhar limit as 1.58 Mʘ and radius around 10 km. The bulk of the star is quark matter with a thin crust of neutron matter of less than a kilometer.

Vertex Decoupling and Quark Deconfinement in Soliton Bag Model at Finite Temperature

By means of the Matsubara Green's function method, we investigate the temperature dependence of coupling constant gqqσ in soliton bag model. We find gqqσ will decrease as temperature increases in high temperature region and will approach zero at critical temperature. Tc. The quark deconfinement phase transition in soliton bag model is discussed.

QCD phase transitions in an effective field theory

We analyze the transitions between hadronic and quark-gluon phases of QCD using an effective low-energy lagrangian for chiral and scale invariance, which embodies quark and gluon condensation. We argue that the quark condensation and deconfinement transitions take place at the same temperature, T q, and that gluon condensation and confinement occur at a common temperature T g. The requirement that scale invariance be spontaneously broken before quarks condense imposes T q ⩽ T q. The gluon transition is in general first order, whereas the quark transition may be second order if T q < T g, or first order if T q = T g, which is favoured for large N c. We argue on general grounds and demonstrate with several model calculations that massive hadrons play a key role in driving the gluon transition, and suggest that T g is below the Hagedorn temperature. We also estimate the surface tension for hadronic bubbles forming in a quark-gluon plasma, finding it to be somewhat too small for inhomogeneities to affect the standard calculations of cosmological nucleosynthesis.

CP-violating dilepton asymmetry in a statistical model of B0 decay.

We construct a statistical model of {ital B}{sup 0} decays, in which the final state contains a multiplicity of pions determined by a Poisson or phase-space distribution. The model enables a calculation of the average {ital CP} value of hadronic configurations associated with the quark transitions {ital b}{r arrow}{ital c{bar c}d}, {ital b}{r arrow}{ital c{bar u}d} ({ital {bar c}ud}), and {ital b}{r arrow}{ital u{bar u}d}. Following Altomari, Wolfenstein, and Bjorken, we calculate the dilepton asymmetry parameter {ital a} which is a measure of {ital CP} violation in the mass matrix of the {ital B}{sup 0}-{ital {bar B}}{sup 0} system.

Observation of associated bottom production and decay in a high-energy hadron interaction.

Production and decay of a pair of bottom mesons, one charged and one neutral, have been observed in a 200-TeV cosmic-ray helium interaction in an emulsion chamber. Analysis of the event indicates that the charged meson decays most probably via a {ital b}{r arrow}{ital u} quark transition, which would imply a nonzero {ital V}{sub {ital u}{ital b}} element in the Kobayashi-Maskawa matrix. The simplest decay scheme consistent with the data is {ital B}{sup {minus}}{r arrow}{ital D}{sub {ital s}}{sup {minus}}{eta}{eta}. The neutral decay is interpreted as {ital B}{sup 0}{r arrow}{ital D}{sup {minus}}{ital e}{sup +}{nu}.

Invariant criteria for bound states, degree of ionization, and plasma phase transition.

Basis invariant characterizations of bound states and bound fraction of a partially ionized hydrogen plasma are given in terms of properties of the spectrum of eigenvalues and eigenfunctions of the equilibrium quantum statistical one-proton--one-electron reduced density matrix. It is suggested that these can be used to place theories of a proposed plasma-ionization phase transition on a firm foundation. This general approach may be relevant to cosmological questions such as the quark deconfinement-confinement transition.

Kaon condensation on the hypersphere

We discuss kaon condensation in baryon-rich hadronic matter in terms of the density dependence of the energy of kaons interacting with an SU(2) vector-meson skyrmion background. Density of — and interaction with — the surrounding nuclear matter is modeled by formulating the dynamics on a three-dimensional hypersphere of finite radius. The lowest energy (bound) state of the K − (and K 0 ) is studied in detail in the density region where the background fields undergo a phase transition from a localized to a homogeneous phase. We discuss the possible instability of the normal ground state with respect to the formation of a coherent kaon component and argue that it may effectively correspond to the strange quark matter phase transition predicted in quark-gluon descriptions of QCD. The lowest K + (and K 0) mode energy on the other hand increases rapidly with density and hence cannot be associated with any soft mode in the S = + 1 channel.

Effective lagrangian approach to QCD phase transitions

We use an effective low-energy lagrangian for broken chiral and scale invariance to discuss the condensation and confinement of quarks and of gluons in QCD. The Skyrme model convinces us that quark condensation and confinement are identical, and we argue that well-defined glueball states exist only when gluons condense. Previous calculations with chiral lagrangians have indicated that the quark transition at the finite temperature T q is second order if gluonic degrees of freedom can be neglected, and we argue that the gluonic transition at the finite temperature T g is generically first order. The scaling properties of the effective lagrangian tell us that T q⩽ T g. We argue that T q can be below T g in SU (2) gauge theory, whereas T q= T g and both quark and gluon transitions are simultaneous and first order in QCD with its SU(3) gauge group. These results agree qualitatively with lattice results. We speculate that the divergent Hagedorn spectrum may drive the joint quark/gluon transition at some temperature below the Hagedorn temperature.

A quark model study of weak nonleptonic decays of baryons

We study weak radiative and pionic decays of strange baryons in the framework of constituent quark model. We find that W-exchange two quark transitions dominate the radiative decays and a small single quark transition is necessary for ≡ − and Ω − decays. For the pionic decays, we employ a semidynamical scheme by considering weak spurion — quark (diquark) scattering process and derive new decay amplitude relations.

Thermal expansion and critical temperature in a geometric representation of quark deconfinement.

The critical temperature of the quark deconfinement transition is calculated combining a geometrical model of thermal expansion with a phenomenological description of hadronization. The value thus obtained is perfectly compatible with lattice QCD and bag-model estimates.

Observation of charmless B meson decays

Using the ARGUS detector at the e +e − storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π ± and pp̄π +π −. The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10 −4 for the three-body and (6.0±2.0±2.2)×10 −4 for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element V ub is non-zero.

Hyperon Decays in the Chiral Bag Model

In terms of the chiral bag model and Skyrme wave-functions of baryons, we investigate and case) hyperon decays. We have found that for , the Skyrme contribution is more important whereas in , the quark content transition dominates.

Lepton pair emission as a probe for the spacetime scenario of quark-hadron phase transition

The correlation between thermal lepton pair emission and hadronic multiplicity is explored to clear up the spacetime picture of quark matter hadronization phase transition in ultrarelativistic nuclear collisions.

Early neutron stars and quark matter

There may exist quark matter inside early hot neutron stars. Using the general method of Baym and Chin, we evaluated the pressure and density at neutron matter — quark matter phase transition for different temperatures and compared the values for stable hot neutron stars. We found (1) that whenever the neutron star temperature exceeds (+10)K, there will be a core of quark matter; (2) that the bag constant B is the most important determining factor of the quark core size. For a given temperature, the core is the larger, the smaller B is; (3) that by the conservation of baryon number, the total energy released by a star during its cooling is about (+53) ergs.

Exclusive decays B-->K(i) gamma resulting from b-->s gamma.

Recently it has been suggested that the quark transition b\ensuremath{\rightarrow}s\ensuremath{\gamma} might have a large enhancement. We use the quark model to estimate the rates for exclusive decays B\ensuremath{\rightarrow}${K}^{(i)}$\ensuremath{\gamma} that result from b\ensuremath{\rightarrow}s\ensuremath{\gamma}. The ${K}^{(i)}$ are various K-meson excited states. While the ground state ${K}^{\mathrm{*}}$(0.892) accounts for only a small fraction of the inclusive b\ensuremath{\rightarrow}s\ensuremath{\gamma} rate, we estimate that a substantial fraction (\ensuremath{\sim}37%) of b\ensuremath{\rightarrow}s\ensuremath{\gamma} decays will result in ${K}^{(i)}$ with . .AE

Quark deconfinement at finite temperature in the bag model.

A thermodynamical description of a single hadron at finite internal temperature is given within the framework of the MIT bag model. The quark deconfinement transition is characterized by the divergence of the bag radius R(T). The radius behaves like (${T}_{c}$${\mathrm{}}^{4}$-${T}^{4}$${)}^{\mathrm{\ensuremath{-}}1/4}$ as the temperature T increases toward the critical temperature ${T}_{c}$. A possible consequence from this result combined with a percolation picture is that the normalized critical baryon-number density may behave as ${\mathrm{\ensuremath{\rho}}}_{\mathit{c}}$(T)/${\mathrm{\ensuremath{\rho}}}_{\mathit{c}}$(0)\ensuremath{\simeq}(1-${\mathrm{T}}^{4}$/${\mathrm{T}}_{\mathit{c}}$${\mathrm{}}^{4}$${)}^{3/4}$ when T approaches ${T}_{c}$ from below.