Unitarity constraints on resonance mixing and the Okubo-Zweig-Iizuka rule

We discuss unitarity constraints on the (complex) mixing angle (δ) between resonances. In particular, when the mixing is small, as when it is forbidden by the Okubo-Zweig-Iizuka (OZI) rule, or some other mechanism, one can derive useful bounds on δ or determine Arg (δ) from the data of allowed decays of the resonances. In the case of f′−f mixing the unitarity bound |δ|≳0.05±0.015 is barely compatible with the experimental f′←ππ rate (if one assumes that it is dominated by f′←f←ππ transition). Furthermore, experimentally Im δ≈0 which together with unitarity gives Re δ=−0.08±0.03, in clear discrepancy with the observed f′←ππ rate. This suggests that the mixing of f′ with higher f-like recurre…

Equation of state and transverse expansion effects in heavy ion collisions

The effects of the equation of state on the expansion of hadronic matter and on the dilepton production rates in heavy ion collisions are studied. We have used two widely different descriptions of the hadron phase and considered scenarios with and without phase transition. The hadron phase is treated either as a gas of ideal massless pions or, more realistically, as a gas of different kinds of massive hadrons with finite size.

How To Find Charm in Nuclear Collisions at RHIC and LHC

Measurements of dilepton production from charm decay and Drell-Yan processes respectively probe the gluon and sea quark distributions in hadronic collisions. In nucleus-nucleus collisions, these hard scattering processes constitute a `background' to thermal contributions from the hot matter produced by the collision. To determine the magnitude and behavior of this background, we calculate the hard scattering contribution to dilepton production in nuclear collisions at RHIC and LHC at next to leading order in perturbative QCD. Invariant mass, rapidity and transverse momentum distributions are presented. We compare these results to optimistic hydrodynamic estimates of the thermal dilepton pro…

Central region in relativistic heavy ion collisions; results from hydrodynamic calculations and cascade simulation

Results of three dimensional hydrodynamic calculations with boost invariant longitudinal expansion are presented with special emphasis on the transverse momentum spectra of hadrons and production rates of dileptons. The effect and signatures of transverse collective motion are discussed in detail. The hydrodynamic results which are based on the assumption of the existence of a first order phase transition and formation of an equilibrium mixed phase are compared with cascade simulation where the mixed phase is modelled in terms of plasma droplets embedded in a pion gas. The comparison shows a great deal of similarity between the two approaches lending further support for the hydrodynamic app…

Production of thermal dileptons in high energy nucleus-nucleus collisions

A method for including realistic nuclear geometry and impact parameter effects in computations of production rates of thermal dileptons of mass in the 1.5 to 3 GeV range andy≈0 in nucleus nucleus collisions at $$\sqrt s = 20 - 200$$ GeV is given. A comparison with the Drell-Yan rate indicates that for large nuclei and energies thermal production gives a sizable contribution even atM=M Jψ and thus may contribute significantly toJ/ψ suppression as background enchancement.

Thermodynamic consistency of the equation of state of strongly interacting matter

Addressing strongly interacting matter in the region of energy density where the hadronic gas phase coexists with the quark-gluon plasma phase, we discuss how thermodynamic consistency can be used to constrain the equation of state for uniform matter and we illustrate the method by constructing a T{sub c}-dependent family of thermodynamically consistent equations of state based on simple spline interpolations between the gas and plasma phases.

Shock phenomena in baryonless strongly interacting matter.

Shock phenomena associated with the quark-to-hadron matter phase transition are studied using the concept of adiabats. To allow for an analysis of a medium with vanishing baryon density, the shock and Poisson adiabats are formulated in terms of hydrodynamic fluxes, rather than only thermodynamic variables. The bag-model equation of state is used to describe the phase transition. It is shown that deflagrations from the quark phase above the critical temperature and strong detonations from the supercooled quark phase to the superheated hadron phase are unlikely. Instead the possibility of weak condensation detonations from the supercooled quark phase to a mixed phase is indicated. Strong deto…

Photons and Lepton Pairs — The Deep Probes of Quark-Gluon Plasma

Photons and lepton pairs are close to the ideal probes to study the dynamics of the dense system of strongly interacting quanta expected to be produced in ultrarelativistic nucleus-nucleus collisions1,2. Electromagnetic interactions are strong enough to lead to a detectable signal from the secondary collisions of final state particles, yet, they are weak enough to let the emitted photons and leptons to escape from the finite nuclear system without further interactions. Thus, the spectra of photons and dileptons from the dense phase of the collision can provide information on the properties of the constituents and on their momentum distributions.

Hydrodynamic Description of Very High Energy Heavy Ion Collisions

In ultrarelativistic heavy-ion collisions, \(\sqrt {^\delta NN}\) ≳ 20 GeV, a large number of particles is produced. At the early stage the system is very dense and the mean free path of particles is much less than the size of produced matter. The system must expand before the particles can propagate freely out from the interaction zone.

Rapidity distributions of dileptons from a hadronizing quark-gluon plasma

It has been predicted that dilepton production may be used as a quark-gluon plasma probe. We calculate the rapidity distributions of thermal dileptons produced by an evolving quark-gluon plasma assuming a longitudinal scaling expansion with initial conditions locally determined from the hadronic rapidity density. These distributions are compared with Drell-Yan production and semileptonic charm decays at invariant mass $M = 2$, 4, and 6 GeV.

Studies of the hydrodynamic evolution of matter produced in fluctuations inp¯pcollisions and in ultrarelativistic nuclear collisions. II. Transverse-momentum distributions

From quark-gluon plasma to hadron spectra

Results on initial transverse energy production based on NLO perturbative QCD calculation with final state saturation of produced minijets are used to fix the initial energy density of produced matter. Assuming rapid thermalization, this provides the initial conditions for a hydrodynamic description of the expansion of final matter. Given a prescription of the the decoupling of particles from the thermal system to free particles, final transverse spectra of hadrons and integrated quantities like multiplicity and transverse energy can be calculated in the central rapidity region. Results are reported and compared with measurements.

Studies of the hydrodynamic evolution of matter produced in fluctuations inp¯pcollisions and in ultrarelativistic nuclear collisions

In this first paper of a series of two, we present a comprehensive study of the hydrodynamic evolution of matter produced in the central region of ultrarelativistic heavy-ion collisions and in high-multiplicity fluctuations of p-barp-italic collisions. We shall begin with a discussion of the limits of the applicability of a perfect-fluid hydrodynamic description of high-energy collisions. A simple bag-model equation of state is argued to have qualitative and semiquantitative features expected from lattice gauge theory and present theoretical understanding. We also discuss the boundary conditions for the perfect-fluid hydrodynamic equations, and what classes of simple events would correspond…

Long-range correlations in the pionization component

Recen t ly I S R measuremen t s (1,2) of corre la t ions be tween a p ion in t he p la teau (lY=I 0 . 2 ) have been carr ied out . A typ ica l resul t is a corre la t ion func t ion which (if one holds y= fixed and the t ransverse m o m e n t u m of t he p ro ton < 1 GeV/c) has a pos i t ive va lue a t smal ler x, a zero at about x = 0.5, a rough ly cons tan t nega t ive va lue for 0.5 < x < 0.8 and approaches a large nega t ive va lue for x close to 1 (see below). In the fol lowing we shall quan t i t a t i ve ly expla in this s t ruc tu re in t e rms of a mode l which essent ial ly amoun t s to pu t t i ng f ini te-energy correct ions to a mul t ipe r iphe ra l c luster model . I n t he t…