841 research outputs found
Detectors For High Energy Nuclear Collisions: Problems, Progress and Promise
Some perspective of the main issues in high energy nuclear collision physics is offered. How to identify and measure a quark-gluon plasma is considered to still be an open question. The types of detector configurations to be used in high-energy nucleus-nucleus experiments are discussed. Particular issues covered are measurements of lepton pair spectra, tracking systems and multitrack resolution, event-rate capabilities, backgrounds and other problems close to the beam, and calorimetry. 2 refs. (LEW
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FUTURE SCIENCE AT THE RELATIVISTIC HEAVY ION COLLIDER.
QCD was developed in the 1970's as a theory of the strong interaction describing the confinement of quarks in hadrons. An early consequence of this picture was the realization that at sufficiently high temperature, or energy density, the confining forces are overcome by color screening effects, resulting in a transition from hadronic matter to a new state--later named the Quark Gluon Plasma--whose bulk dynamical properties are determined by the quark and gluon degrees of freedom, rather than those of confined hadrons. The suggestion that this phase transition in a fundamental theory of nature might occur in the hot, dense nuclear matter created in heavy ion collisions triggered a series of experimental searches during the past two decades at CERN and at BNL, with successively higher-energy nuclear collisions. This has culminated in the present RHIC program. In their first five years of operation, the RHIC experiments have identified a new form of thermalized matter formed in Au+Au collisions at energy densities more than 100 times that of a cold atomic nucleus. Measurements and comparison with relativistic hydrodynamic models indicate that the matter thermalizes in an unexpectedly short time ( < 1 fm/c) , has an energy density at least 15 times larger than needed for color deconfinement, has a temperature about 2 times the critical temperature of {approx}170 MeV predicted by lattice QCD, and appears to exhibit collective motion with ideal hydrodynamic properties--a ''perfect liquid'' that appears to flow with a near-zero viscosity to entropy ratio - lower than any previously observed fluid and perhaps close to a universal lower bound. There are also indications that the new form of matter directly involves quarks. Comparison of measured relative hadron abundances with very successful statistical models indicates that hadrons chemically decouple at a temperature of 160-170 MeV. There is evidence suggesting that this happens very close to the quark-hadron phase transition, ie. that hadrons are born in the phase transition from quark matter, and abundance-changing interactions then quickly cease. Valence quark number scaling of the measured anisotropy parameter for all hadrons suggests that the collectively flowing matter involves quarks, not hadrons. And the striking observation of a universal, strong enhancement of baryons relative to mesons at intermediate transverse momentum has been interpreted as evidence of competition between quark coalescence of the bulk medium and jet fragmentation. It is generally agreed that the new matter is not describable in terms of ordinary color neutral hadrons, and that many observations are consistent with models that incorporate quark and gluon degrees of freedom. The evidence is consistent with the matter being a strongly coupled quark gluon plasma (sQGP), and thus it behaves quite differently from the perturbative QCD parton gas that was expected by most people prior to RHIC data. The extraordinary properties of this new state of matter demand further measurements to better understand its behavior, properties, origin and description
RHIC And Quark Matter: A Proposed Heavy Ion Collider At Brookhaven National Laboratory
For some time there had been strong interest at Brookhaven in exploiting the existence of the Colliding Beam Accelerator, CBA (nee ISABELLE), for the generation of heavy ion collisions at very high energies. Now the opportunity arose to consider the design of a dedicated heavy ion collider which could take advantage of the work already invested in the CBA project. In its report the Working Group recommended a top energy of at least 50 + 50 GeV/amu, emphasizing the need to cover a continuous range of energies extending as low 5 + 5 GeV/amu, with ion masses ranging from protons up to A > 200, and luminosity L > 10/sup 25/cm/sup -2/sec/sup -1/ initially, ultimately reaching much higher values. These parameters were the subject of extensive scrutiny at the Quark Matter '83 Conference one month later at which several of the world's laboratories presented possibilities for very high energy nuclear beam facilities. After several days of such discussions a round table panel at the Conference strongly endorsed the recommendations of the August Working Group, with an emphasis on making the top energy as high as possible without sacrificing the capability for exploring the low energy range as well
Transport Coefficients of Gluon Plasma
Transport coefficients of gluon plasma are calculated for a SU(3) pure gauge
model by lattice QCD simulations on and
lattices. Simulations are carried out at a slightly above the deconfinement
transition temperature , where a new state of matter is currently being
pursued in RHIC experiments. Our results show that the ratio of the shear
viscosity to the entropy is less than one and the bulk viscosity is consistent
with zero in the region, .Comment: 10 pages, Late
Coupling Nonlinear Sigma-Matter to Yang-Mills Fields: Symmetry Breaking Patterns
We extend the traditional formulation of Gauge Field Theory by incorporating
the (non-Abelian) gauge group parameters (traditionally simple spectators) as
new dynamical (nonlinear-sigma-model-type) fields. These new fields interact
with the usual Yang-Mills fields through a generalized minimal coupling
prescription, which resembles the so-called Stueckelberg transformation, but
for the non-Abelian case. Here we study the case of internal gauge symmetry
groups, in particular, unitary groups U(N). We show how to couple standard
Yang-Mills Theory to Nonlinear-Sigma Models on cosets of U(N): complex
projective, Grassman and flag manifolds. These different couplings lead to
distinct (chiral) symmetry breaking patterns and \emph{Higgs-less}
mass-generating mechanisms for Yang-Mills fields.Comment: 11 pages. To appear in Journal of Nonlinear Mathematical Physic
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Summary Of The Physics Review Panel On Heavy Ion Collider Specifications
Color Skyrmions in the Quark-Gluon Plasma
We consider the general formulation of nonabelian fluid dynamics based on
symmetry considerations. We point out that, quite generally, this admits
solitonic excitations which are the color analog of skyrmions. Some general
properties of the solitons are discussed.Comment: LaTeX, 13 pages, references adde
Tips for research recruitment: The views of sexual minority youth
Researchers often experience difficulties recruiting hard-to-reach populations. This is especially so for studies involving those who have been historically stigmatized, such as individuals who challenge heteronormative expectations or people who experience mental ill health. The authors aimed to obtain the views of sexual minority adolescents (n=25) about what encouraged their participation in a research project. The authors used a general inductive approach to analyze interview data. Feedback consisted of 2 main overarching themes: tips and suggestions for future research and appreciate participants’ motivation to get involved in research. Strategies for how recruitment can be optimized for studies involving sexual minority young people are discussed
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