RHIC project overview

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Abstract

An overview of the RHIC Project, the construction and commissioning of the Relativistic Heavy Ion Collider and a set of four detectors at Brookhaven National Laboratory, will be presented as the introduction to this Special Issue of Nucl. Instr. and Meth.

Introduction

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory is the US Department of Energy's forefront research facility for the nuclear physics program. The construction of the collider and a complementary set of four detectors, BRAHMS, PHENIX, PHOBOS, and STAR, were completed, as scheduled, during 1999. Following the initial engineering test of the Collider within the same year, collisions of Au ions were achieved during the subsequent commissioning run in the year 2000, first at the beam energy of 28 GeV/nucleon on June 12, 2000 and later at 65 GeV/nucleon. Collisions of Au ions at the design beam energy of 100 GeV/nucleon were achieved on July 18, 2001. All the four detectors were also commissioned and collected significant amounts of data during the 4-week first physics run in 2000. This article covers an overview of the RHIC Project and its facility, and the commissioning activities that have opened a new frontier of nuclear matter research.

Fig. 1 shows the phase diagram of nuclear matter as the function of baryon density and temperature, with a contour showing the predicted transition of nuclear matter from the hadronic phase to the quark-gluon plasma (QGP) phase. Toward the far right on the horizontal axis for the matter density, one finds an extremely high baryon density state, such as in the neutron star where one may find the quark-gluon plasma phase. Going up along the temperature axis, the figure indicates the phase transitions into the QGP domain at a sufficiently high temperature of about 1012 K. It is expected that the collisions of Au ions at the beam energy of 100 GeV/nucleon at RHIC will result in the state of matter at a sufficiently high temperature that exceeds the transition temperature. The primary objective of RHIC, therefore, is to investigate this phase transition and to study the formation and property of QGP. With an addition of Siberian Snakes, which was made possible by the Spin Physics Collaboration with the RIKEN Laboratory of Japan, the scientific objective of RHIC was expanded to include the study of spin structure of nucleons and other spin physics studies in a range of collision energies never before possible. With RHIC, nuclear physics is entering into the “high-energy” domain in which the QCD structure of matter should be directly manifested in terms of the dynamics of quarks and gluons.

Section snippets

The RHIC facility

The idea to build RHIC dates back to 1983, when it was conceived as part of the long-range plan for nuclear science. The Nuclear Science Advisory Committee (NSAC), an advisory body to the US Department of Energy (DOE) and the National Science Foundation (NSF) made a declaration that “the United States should proceed with the planning for the construction of this relativistic heavy ion collider facility expeditiously; and we see it as the highest priority new scientific opportunity within the

RHIC collider

The basic design parameters of the collider are given in Table 1. The top energy for heavy ion beams (e.g., for gold ions) is 100 GeV/u and that for protons is 250 GeV. Counter-rotating beams collide head-on at six intersection points. The particle species that can be accelerated, stored, and collided at RHIC range from A=1 (protons) to A∼200 (gold), at present. Subject to the development of a suitable ion source [such as an Electron Beam Ion Source (EBIS)], collisions of heavier ions can be

Detectors

The arrangement of detectors around the RHIC ring is shown in Fig. 4. There are two major detectors (STAR and PHENIX) and two minor ones (PHOBOS and BRAHMS). Here, the qualifier major and minor refer to their scale or size, complexity, cost of construction, and size of the collaboration, and not to the depth of physics reach. These four detectors form a complementary set for the first round of experiments at RHIC.

The STAR detector utilizes a solenoidal geometry with a large cylindrical

Commissioning and first physics runs

After meeting successive milestones such as the first sextant test in February 1997, the completion of magnet production in September 1998 and the assembly of the RHIC rings in January 1999, almost on schedule, the engineering run to verify functionality of the collider system took place from June to September 1999. During this time, low energy/intensity beams were circulated independently in both rings together with the first acceleration. The actual commissioning with colliding beams, the

Near and long-term future

As is the case with any collider, a luminosity upgrade is one of the principal objectives for the future with RHIC. There are several paths for the luminosity upgrade. The possibility of increasing the number of bunches per ring is already built into the collider as well as detectors. Another immediate upgrade path is to invoke the collision optics with β*=1 m at selected interaction points. This very tight focusing of beams is possible because of the very high field quality of the final focus

Conclusions

After 17 years of gestation period, RHIC began to operate, opening a new frontier for nuclear research. The first glimpse of the landscape at this new frontier, as observed with collisions of Au ions at 2/3 of the design collision energy, i.e., 130A GeV, has already caught some tantalizing indications of unusual global behavior. These observations bode well for the exciting physics to come.

Acknowledgements

We would like to take this opportunity to commend the members of the RHIC team, both BNL staff and collaborators, who have been involved in the design, construction, and commissioning of the RHIC collider and detector for their outstanding job. On behalf of the RHIC team, we express our gratitude to our funding agency, the US DOE, in particular the Nuclear Physics Division and the local Project Office. The authors also wish to acknowledge with thanks the support the Project received from

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