S. H. Kahana

Strange cluster formation in relativistic heavy ion collisions

Using the cascade code ARC to simulate relativistic heavy ion collisions at Brookhaven AGS energies (11.7--14.6 GeV/c), the authors have estimated the production rate of strange clusters ranging from a hypothetical doubly strange (S={minus}2) bound ({Lambda}{Lambda}){sub b} dibaryon to the hypernuclei {sub {Lambda}{Lambda}}{sup 6}He and {sub {Xi}{sup 0}{Lambda}{Lambda}}{sup 7}He. For the formation of multi-strange bound systems, high energy heavy ion collisions offer the only feasible method, since one can take advantage of the hyperons which are copiously produced in such collisions (typically 20 {Lambda}`s in a Au + Au central collision at the AGS) to form the composite object by coalescence.

ARC — A relativistic cascade

Abstract A general purpose relativistic cascade code ARC has been developed to study ion-ion collisions. As a first application of ARC we study Si+Au collisions at 14.6 GeV/ c using two hadronic models which use the same two-body data as input, but with different assumptions about the way particles are produced. Comparison with data from experiment E802 suggests the importance of baryonic resonances in nucleus-nucleus collisions at BNL-AGS energies.

H dibaryon and the hard core

The H dibaryon, a single, maximally symmetric bag containing two up, two down, and two strange quarks, has long been sought after in a variety of experiments. Its creation has been attempted with K{sup -}s or protons as projectiles and most recently in relativistic heavy ion induced reactions. We concentrate on the latter, but our conclusions are more generally applicable. The two baryons coalescing to form the single dibaryon, likely {lambda}{lambda} in the case of heavy ions, must penetrate the short range repulsive barrier which is expected to exist between them. We find that this barrier can profoundly affect the probability of producing the H state, should it actually exist. (c) 1999 The American Physical Society.

Resonant State in Helium-4 Lambda

In a recent experiment E906 at the BNL-AGS, a search for light S=-2 hypernuclei, strong evidence was found for the nuclide Hydrogen-4 double Lambda. One of the most striking components of this data was the appearance of a narrow low-momentum pi- line at k(pi-) = 104-105 MeV/c. This was ascribed to the decay of Hydrogen-4 double Lambda into a resonant state in Helium-4 Lambda. The existence of such a state is shown to be plausible and its characteristics are delineated.

Inclusive particle spectra at (56 and 130)A GeV

A simulation is performed of the recently reported data from PHOBOS at energies of 56 and 130 A GeV using the relativistic heavy ion cascade LUCIFER which had previously given a good description of the NA49 inclusive spectra at E=17.2 A GeV. The results compare well with these early measurements at RHIC.

A relativistic cascade for heavy ion collisions

Au on Au collisions at the BNL/AGS (11.6 GeV‐A/c) are expected to produce a short lived state of matter at high baryon density. If the baryons reach sufficiently high density, they may produce a quark‐gluon plasma (QGP). The signals from a QGP phase may be difficult to distinguish from those of ordinary hadronic matter. We have constructed a relativistic cascade (ARC) for hadrons in an attempt to model the dynamics of ordinary hadronic matter in a heavy ion collision, in the hopes that deviations from the cascade results may indicate new physics. In this contribution I will discuss the formation of high baryon density matter, and its effect on antiproton production.

Cronin effect and high-p{sub perpendicular} suppression in d+Au collisions

Great interest has attached to recent d+Au, {radical}(s)=200A GeV data at RHIC, obtained with the BRAHMS detector. Between pseudorapidities {eta}=0 and {eta}=3.2 the appropriately defined ratio R[dAu/pp], comparing transverse-momentum spectra of d+Au to pp, exhibits a steady decrease with {eta}. This diminution is examined within a two-stage simulation. In the first stage, initial nucleon-nucleon interactions are treated in parallel, as if occurring simultaneously, whereas the second stage is a considerably reduced energy hadronic cascade. This approach is by no means a standard hadronic cascade, never entailing an overly high density of cascading particles. Indeed a condition is imposed on the total multiplicity at the outset of the second stage permitting no overlap of intermediate interacting prehadrons. The result is an adequate description of the data, including the so-called Cronin effect. Additionally there is, in the second stage, clear evidence for suppression of relatively high trans-verse momentum {eta}=0 leading mesons (i.e., the Cronin effect is appreciably muted by final state interactions)

Ultrarelativistic cascades and strangeness production

A two phase cascade, LUCIFER II[1], developed for the treatment of ultra high energy ion-ion collisions is applied to the production of strangeness at SPS energies √ s = 17−20. This simulation is able to simultaneously describe both hard processes such as DrellYan and slower, soft processes such as the production of light mesons, including strange mesons, by separating the dynamics into two steps, a fast cascade involving only nucleons in the original colliding relativistic ions followed, after an appropriate delay, by multiscattering of the resulting excited baryons and mesons produced virtually in the first step. No energy loss can take place in the short time interval over which the first cascade takes place. The chief result is a reconciliation of the important Drell-Yan measurements with the apparent success of standard cascades to describe the nucleon stopping and meson production in heavy ion experiments at the CERN SPS. A byproduct, obtained here in preliminary calculations, is a description of strangeness production in the collision of massive ions.A two phase cascade, LUCIFER II, developed for the treatment of ultra high energy Ion-Ion collisions is applied to the production of strangeness at SPS energies. This simulation is able to simultaneously describe both hard processes such as Drell-Yan and slower, soft processes such as the production of light mesons by separating the dynamics into two steps, a fast cascade involving only the nucleons in the original colliding relativistic ions followed, after an appropriate delay, by a normal multiscattering of the resulting excited baryons and mesons produced virtually in the first step. No energy loss can take place in the short time interval over which the first cascade takes place. The chief result is a reconciliation of the important Drell-Yan measurements with the apparent success of standard cascades to describe the nucleon stopping and meson production in heavy ion experiments at the CERN SPS.

Strangeness from hadronic processes

Large amounts of experimental data on strangeness production in nucleon‐nucleon and in pion‐nucleon collisions, and data on hadronic scattering of strange particles, make it possible to calculate, with accuracy, the hadronic contribution to the strangeness production in nucleus‐nucleus reactions. The relativistic cascade model ARC, relying on the experimental measurements of elementary hadron‐hadron interactions, successfully predicted many single particle spectra in Au+Au collisions at BNL‐AGS, including those of strange mesons K±.