Almost exponential transverse spectra from power law spectra

We point out that exponential shape of transverse spectra can be obtained as the Fourier transform of the limiting distribution of randomly positioned partons with power law spectra given by pQCD, which actually realize Tsallis distributions. Such spectra were used to obtain hadron yields by recombination in relativistic heavy-ion collisions at RHIC energies.Comment: 5 pages, 3 figures, Phys.rev. styl

Formation of antideuterons in heavy ion collisions

The antideuteron production rate at high-energy heavy ions collisions is calculated basing on the concept of anti-d formation by antinucleons which move in the mean field of the fireball constituents (mainly pions). The explicit formula is presented for the coalescence parameter B_2 in terms of deuteron binding energy and fireball volume.Comment: 7 pages, 1 figure, latex. v3: argumentation improved, references adde

Mapping the QCD Phase Diagram

I review recent theoretical developments which show how a key qualitative feature of the QCD phase diagram, namely a critical point which in a sense defines the landscape which heavy ion collision experiments are seeking to map, can be discovered. The map of the phase diagram which I sketch is based on reasonable inference from universality, lattice gauge theory and models; the discovery of the critical point would provide an experimental foundation for the central qualitative feature of the landscape. I also review recent progress in our understanding of cold, dense quark matter, as may occur in the cores of neutron stars. In this regime, quarks form Cooper pairs. The formation of such superconducting phases requires only weak attractive interactions, as provided by one-gluon exchange at asymptotically high density; these phases may nevertheless break chiral symmetry (by locking flavor symmetries to color symmetry) and may have excitations which are indistinguishable from those in a confined phase. Mapping this part of the phase diagram will require a better understanding of how the presence of color superconductivity and color-flavor locking affects neutron star phenomenology.Comment: Contribution to proceedings of Quark Matter '99, Torino, Italy. 12 pages. 4 figure

Quark-Gluon Plasma: Status of Heavy Ion Physics

Lattice quantum chromodynamics (QCD), defined on a discrete space time lattice, leads to a spectacular non-perturbative prediction of a new state of matter, called quark-gluon plasma (QGP), at sufficiently high temperatures or equivalently large energy densities. The experimental programs of CERN, Geneva and BNL, New York of relativistic heavy ion collisions are expected to produce such energy densities, thereby providing us a chance to test the above prediction. After a brief introduction of the necessary theoretical concepts, I will present a critical review of the experimental results already obtained by the various experiments in order to examine whether QGP has already been observed by them.Comment: 11 Pages, LaTeX, Plenary talk given at 6th Workshop in High Energy Physics Phenomenology (WHEPP 6), Chennai (Madras), India, 3-15 Jan 2000 To appear in Pramana, Journal of Physic

Slowing Out of Equilibrium Near the QCD Critical Point

The QCD phase diagram may feature a critical end point at a temperature T and baryon chemical potential $\mu$ which is accessible in heavy ion collisions. The universal long wavelength fluctuations which develop near this Ising critical point result in experimental signatures which can be used to find the critical point. The magnitude of the observed effects depends on how large the correlation length $\xi$ becomes. Because the matter created in a heavy ion collision cools through the critical region of the phase diagram in a finite time, critical slowing down limits the growth of $\xi$, preventing it from staying in equilibrium. This is the fundamental nonequilibrium effect which must be calculated in order to make quantitative predictions for experiment. We use universal nonequilibrium dynamics and phenomenologically motivated values for the necessary nonuniversal quantities to estimate how much the growth of $\xi$ is slowed.Comment: 21 pages, 5 figures, reference added, typo corrected, to appear in Phys. Rev.

Signatures of the Tricritical Point in QCD

Several approaches to QCD with two massless quarks at finite temperature T and baryon chemical potential mu suggest the existence of a tricritical point on the boundary of the phase with spontaneously broken chiral symmetry. In QCD with massive quarks there is then a critical point at the end of a first order transition line. We discuss possible experimental signatures of this point, which provide information about its location and properties. We propose a combination of event-by-event observables, including suppressed fluctuations in T and mu and, simultaneously, enhanced fluctuations in the multiplicity of soft pions.Comment: 5 pages (published version

Upper Limit of D0 Production in Central Pb-Pb Collisions at 158A GeV

Results are presented from a search for the decays D0 -> Kmin piplus and D0bar -> Kplus pimin in a sample of 3.8x10^6 central Pb-Pb events collected with a beam energy of 158A GeV by NA49 at the CERN SPS. No signal is observed. An upper limit on D0 production is derived and compared to predictions from several models.Comment: REVTEX 5 pages, 4 figure

Heavy Ions at LHC: A Quest for Quark-Gluon Plasma

Quantum Chromo Dynamics (QCD), the theory of strong interactions, predicts a transition of the usual matter to a new phase of matter, called Quark-Gluon Plasma (QGP), at sufficiently high temperatures. The non-perturbative technique of defining a theory on a space-time lattice has been used to obtain this and other predictions about the nature of QGP. Heavy ion collisions at the Large Hadron Collider in CERN can potentially test these predictions and thereby test our theoretical understanding of confinement. This brief review aims at providing a glimpse of both these aspects of QGP.Comment: 26 pages, 31 Figures, Invited article for the volume on LHC physics to celebrate the Platinum Jubilee of the Indian National Science Academy, edited by Amitava Datta, Biswarup Mukhopadhyaya and Amitava Raychaudhuri. Needs style file insa.sty (included