Quark Matter Formation Research Articles

Heavy Baryon Clusters and Search for Signals of Quark Matter Formation

New experimental data are discussed on the distribution of protons over transverse momentum of p⊥ in the Fe + Em process at energies 2–200 GeV/n and of α-particles in the Au + Em process at incident energy 10.7 GeV/n. A possible interpretation of the experiment within the framework of the gluon dominance and the thermodynamic approximation can be achieved with a minor additional assumption only. This assumption is that at an early stage of evolution of the heavy baryon cluster matter the quark matter transforms into baryons at a temperature T ≈ 0.22 GeV and its global decay into nucleons is completed at T ≈ 0.14 GeV. The results are also of interest in connection with the problem of abundance of helium and hydrogen in the universe which has been considered in cosmology and astrophysics for a long time.

Photons fromPb+PbandS+Aucollisions at ultrarelativistic energies

The effects of the variation of vector meson masses and decay widths on photon production from hot strongly interacting matter formed after Pb + Pb and S + Au collisions at CERN SPS energies are considered. It has been shown that the present photon spectra measured by WA80 and WA98 Collaborations can not distinguish between the formation of quark matter and hadronic matter in the initial state.

Critical review of quark gluon plasma signatures

Nonequilibrium models (three-fluid hydrodynamics and UrQMD) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions. It is demonstrated that these two models — although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles) — both yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Ψ meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data.

Charm Correlation as a Diagnostic Probe of Quark Matter.

The use of correlation between two open-charm mesons is suggested to give information about the nature of the medium created in heavy-ion collisions. Insensitivity to the charm production rate is achieved by measuring normalized cumulant. The acollinearity of the $D$ momenta in the transverse plane is a measure of the medium effect. Its dependence on nuclear size or ${E}_{T}$ provides a signature for the formation of quark matter.

Dilepton Production in the Central Rapidity Region

Generalized Boltzmann approximation of the phase-space distribution function of quarks in the quark phase and of pions in the hadron phase, adopted by previous authors, to a complete expression, the dilepton production in Bjorken's (1+1) dimensional scaling expansion system is studied. We find that the dilepton production is heightened, and the shape of the characteristic dilepton distribution for the quark matter formation in ultrarelativistic nucleus-nucleus collisions is significantly changed.

Quark-gluon-plasma formation at CERN-SPS energies 200 GeV?

By colliding ultrarelativistic ions, one achieves presently energy densities close to the critical value, concerning the formation of a quark-gluon-plasma. This indicates the importance of fluctuations and the necessity to go beyond the investigation of average events. Therefore, we introduce a percolation approach to model the final stage ($\tau > 1$ fm/c) of ion-ion collisions, the initial stage being treated by well-established methods, based on strings and Pomerons. The percolation approach amounts to finding high density domains, and treating them as quark-matter droplets. In this way, we have a {\bf realistic, microscopic, and Monte--Carlo based model which allows for the formation of quark matter.} We find that even at SPS energies large quark-matter droplets are formed -- at a low rate though. In other words: large quark-matter droplets are formed due to geometrical fluctuation, but not in the average event.

A phenomenological QCD approach to the formation of primordial strange quark matter

A microscopic calculation using the chromoelectric flux tube model provides a low baryon penetrability at the surface of the quark-gluon plasma. Applying the low penetrability to the time evolution of universal baryon number density during the cosmic QCD phase transition, we find that the strange quark matter can be formed if the QCD phase transition is weakly first order and satisfies σ ≤ 5×10 5 MeV and 80 MeV ≤ T C ≤ 130 MeV.

Dilepton spectra from expanding hot quark matter

The previous dilepton spectrum expression and relativistic hydrodynamic equations derived from the energy-momentum conservation, are generalized to include the effect of the space-time distribution of particles. The influences of the particle distribution and the latent heat released by the phase transition on the dilepton spectrum are studied on the basis of the generalized formalism. We find that these two influences significantly change the characteristic dilepton spectrum for the formation of quark matter given by previous authors, they especially cause the non-monotony of the total dilepton yield with respect to the initial temperature. It is shown that these two influences must be included in order to get a more reasonable characteristic dilepton spectrum for the formation of the quark matter.

Λ0 POLARIZATION IN HADRON-NUCLEON, HADRON-NUCLEUS AND NUCLEUS-NUCLEUS INTERACTIONS

We discuss the experimental systematic characteristics of the Λ0 polarization observed in hadron-nucleon, hadron-nucleus, and nucleus-nucleus interactions. The current theoretical framework is reviewed and compared with the experimental data. We also discuss the effects of QCD deconfinement on the transverse and longitudinal polarization in nucleus-nucleus interactions and the possibility of using these effects as signals of quark matter formation.

Strangeness production by antiprotons

Specific features of strange-particle production in\(\bar p\)-nuclei annihilation are reviewed. The inclusive Λ/Ks0 production rate, sensitive to the relative weight of multinucleon annihilations, shows an enhancement in heavier nuclei with respect to the\(\bar p\)p and\(\bar p\)d annihilations. Rapidity distributions, obtained in the PS179 experiment at LEAR and in an experiment at KEK, seem to support the hypothesis of different effective targets for Λ’s and Ks0’s. The behaviour of the associated-to-strangeness pion rapidity distribution suggests the presence of a leading effect, bringing away a fraction of momentum not absorbed by any target system. The experimental signatures are analysed in the framework of theoretical models: the rescattering approach in the context of a conventional hadronic picture and a model of supercooled quark matter formation. Finally, the observed leading mesons can be included in a quark picture describing beam fragmentation.

K+/-, p-bar, and Omega - production in relativistic heavy ion collisions.

We discuss the production of antiprotons, kaons, and the ${\ensuremath{\Omega}}^{\mathrm{\ensuremath{-}}}$ in nuclear collisions at relativistic energies in the framework of a simplified hadrochemical model. We point out the importance of \ensuremath{\Delta} resonances for p\ifmmode\bar\else\textasciimacron\fi{} as well as ${K}^{\mathrm{\ensuremath{-}}}$ production at 1--2 GeV/nucleon, particularly in the region below the threshold for their production in individual NN collisions. Quark matter formation may enhance ${\ensuremath{\Omega}}^{\mathrm{\ensuremath{-}}}$ production to a measurable level at 15 GeV/nucleon.

Observation of hot and cold events in the12C-emulsion interaction at 4.5 GeV/c per nucleon-a signal for quark matter formation?

The authors present a study of the transverse momentum distribution of relativistic alpha particles emerging from the interaction of 12C and emulsion at 4.5 GeV/c per nucleon. A large statistics study of 1200 events when compared with the Maxwell-Boltzmann distribution reveals the existence of two temperatures, a hot and a cold, since a single Maxwell-Boltzmann distribution cannot fit the peak and the tail simultaneously. This yield of two distinctly different temperatures in the fragmentation region may be interpreted as a possible signal for the formation of a quark-gluon plasma.

Quark matter or new particles?

It has been argued that compression of nuclear matter to somewhat higher densities may lead to the formation of stable quark matter. A plausible alternative, which leads to radically new astrophysical scenarios, is that the stability of quark matter simply represents the stability of new particles compounded of quarks. A specific example is the SU(3)-symmetric version of the alpha particle, composed of spin-zero pairs of each of the baryon octet (an 'octet' particle).

Separation of strangeness from antistrangeness in the phase transition from quark to hadron matter: Possible formation of strange quark matter in heavy-ion collisions

We present a mechanism for the separation of strangeness from antistrangeness in the deconfinement transition. For a net strangeness of zero in the total system, the population of s quarks is greatly enriched in the quark-gluon plasma, while the s\ifmmode\bar\else\textasciimacron\fi{} quarks drift into the hadronic phase. This separation could result in ``strangelet'' formation, i.e., metastable blobs of strange-quark matter, which could serve as a unique signature for quark-gluon plasma formation in heavy-ion collisions.

Evidence for stabilized strange-quark matter in cosmic rays?

Centauros, mini-Centauros, Geminion events, halo events, . . . are interpreted as manifestations of the formation of strange-quark matter in collisions of heavy primaries with the atmosphere. The experimental information is compatible with ''conventional'' ideas on formation and properties of quark matter as well as its stabilization in the form of strange matter.

Relativistic nucleus-nucleus collisions

Recent investigations of relativistic heavy ion collisions are reviewed. In particular, use of 4π detector systems. Streamer Chamber and Plastic Ball, has yielded insight into the mechanisms of thermal and chemical equilibrium establishment at Bevalac and Dubna energies, as required for the formation of compressed fireball matter. Hydrodynamical flow of high density matter, and the total pion yield are established as primordial probes of the high density stage. First information is discussed about the nuclear matter equation of state. Towards higher energies, the conditions for quark matter formation are examined. First observations, in cosmic ray reactions, of extremely high mean transverse momenta, agree with predictions concerning possible signatures of a phase transition.

Spectator Temperature as a Signal for Quark-Matter Formation

A new signature for quark-matter formation in relativistic heavy-ion collisions, in terms of the emission spectra in the fragmentation regions, is proposed.

Quark-matter formation in the fragmentation rapidity region of ultrarelativistic heavy-ion collisions

A simple model of ultrarelativistic heavy-ion collisions is presented for energies above roughly-equal20 GeV/nucleon. The maximum excitation energy and baryon-charge density produced in the fragmentation region of such reactions are estimated analytically. The possibility of forming a quark-gluon plasma of high temperature and low pressure without large compression is pointed out.

Towards a new phase in physics?

Quark Matter Formation and Heavy Ion Collisions. Edited by M. Jacob and H. Satz World Scientific (distributed by Wiley): 1983. Pp.586. 49, 70.

Nuclear matter under extreme conditions

Nuclear matter is discussed under extreme conditions: Under high pressure and high temperature. The present status of pion condensation and Lee-Wick condensation is reviewed. Although one finds condensation at relatively low densities, if the pion or the σ propagator is calculated in nuclear matter in the random phase approximation the inclusion of the bubbles in bubbles shields against π and σ-condensation by the same mechanism which induces the condensation. Thus π and σ-condensation shields against π- and σ-condensation. Furthermore the critical temperature and critical density for the formation of quark matter is discussed. A high temperature and a high enough density can be reached by high energy collisions betweem two heavy nuclei. If one increases the temperature in the interaction region of the collision between two heavy ions one expects first to reach a “limiting temperature” with increasing bombarding energy of the heavy ions. In the interaction region (“fire ball”) more and heavier hadrons are produced and the bombarding energy is not any more going into an increase of the temperature. But if one increases farther the energy imput, hadronic matter starts to evaporate into a quark-gluon plasma. This should happen at a temperature of about 180 MeV (2.10 12 degrees Kelvin). Possible fingerprints of such a quark-gluon plasma are discussed.