Relativistic Nuclear Collisions (RNC) GroupRelativistic Nuclear Collisions (RNC) GroupNuclear Science Division (NSD), Lawrence Berkeley National Lab

The Relativistic Nuclear Collisions (RNC) group is the experimental high energy nuclear physics group in Nuclear Science Division at LBNL. The focus of the

RNC experimental physics program is the exploration of QCD matter under extreme conditions, and of the fundamental structure of nucleons and nuclei

through high energy collisions of (polarized) protons and nuclei. RNC plays leading roles in the STAR experiment at the Relativistic Heavy Ion Collider (RHIC)

at Brookhaven National Laboratory and the ALICE experiment at the Large Hadron Collider (LHC) at CERN. RNC is a physics leader in both experiments and

has contributed major equipment and upgrades. RNC is an international group of more than 25 scientists, about half of them students and postdocs. A small

group is stationed at the location of both of our experiments, at CERN and at BNL.

Inner Micro-Vertex Detector Project

Contact information:

MS70R0319, Lawrence Berkeley National Lab

One Cyclotron Road, Berkeley, 94720

Tel: 510-486-4974

Fax: 510-486-4818

Web: http://rnc.lbl.gov

Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab

The Relativistic Heavy Ion Collider (RHIC) locates at Brookhaven National Lab (BNL) at Long Island, NY. RHIC is the first machine in the world capable of colliding heavy ions and polarized protons (see the Spin section). The beams travel at nearly speed of light in opposite directions around RHIC's 2.4-mile, two-lane "racetrack." At six intersections, the lanes cross, leading to an intersection.

RHIC collisions occur thousands of times per second. Each one acts as a microscopic pressure cooker, producing temperatures and pressures more extreme than exist now even in the cores of the hottest stars. Temperature inside a RHIC collision can be many thousand times the temperature of the sun.

Relativistic heavy ion collisions provide us an effective tool to study the creation and characteristics of such a matter in laboratory. During the collision, tremendous amount of energy are dumped into a small volume to achieve sufficient energy density. Just after the collision, thousands more particles form as the area cools off. Each of these particles provides a clue as to what occurred inside the collision zone.

The Solenoidal Tracker At RHIC (STAR) detector is a specially designed detector to track thousands of particles simultaneously created in heavy ion collisions.

Protons and neutrons are made up of three quarks, along with the gluons that bind them together. Theory predicts at sufficient high temperature and density, quarks and gluons can be liberated and form a new state of matter - Quark Gluon Plasma (QGP). Theory also holds that for a brief time at the beginning of the universe there were no protons and neutrons, only free quarks and gluons.

A state of the art, high resolution vertex detector is being built for installation in the STAR experiment at RHIC. The purpose of this device is to identify D and B mesons created in the collisions of 200 GeV Au on Au collisions at RHIC, and thus provide a measure of heavy quark yields in these reactions. The D and B mesons are short lived and travel a short distance ( a few 10s of microns) from the collision point before decaying into secondary particles. The vertex detector with two layers of silicon pixel chips a few centimeters from the interaction point has position resolution sufficient to distinguish these relatively rare secondary tracks from the thousands of other tracks emanating from the collisions point thus allowing identification and measurement of D and B meson yields. Accomplishing the required track pointing resolution is an engineering challenge. The silicon detector with its support structures must be very thin, the silicon is 50 microns thick, to reduce multiple coulomb scattering. At the same time the detector must be mechanically quite stable to maintain good position resolution. The detectors, key to this device, are monolithic silicon mega pixel chips with 20 micron square pixels.

Large Hadron Collider (LHC)The LHC (Large Hadron Collider) is a 27km circumference synchrotron accelerator on the border of Switzerland and France.

ALICE (A Large Ion Collider Experiment ) is a collaboration of about 1000 physicists from 33 countries and 115 institutions.

ALICE is the dedicated heavy ion experiment at the LHC, optimized for comprehensive measurements of the very complex final state generated in high energy nuclear collisions. ALICE can track precisely many thousands of particles in each event, measuring jets, photons, heavy flavor mesons and baryons, and quarkonia.

The emphasis of the ALICE LBNL group is the study of jet quenching, which we pioneered in STAR at RHIC and which will be central to the LHC heavy ion program. There is broad theoretical interest in such measurements, aspects of which may even be calculable in string theory.

The RNC effort in STAR dates back to the inception of the experiment in 1990 and concerns research with collisions of heavy ion beams over a wide range in center-of-mass energies, ranging from √sNN = 7.7 GeV to 200 GeV, which enables us to study properties of new partonic matter at top energy as well as search for phase transition signatures.

Spin physics at RHIC

The spin physics program at RHIC studies the origin of the spin of the proton and the role of spin in QCD. Measurements are made of spin-dependent effects in the production of jet, W, and other probes in collisions of longitudinally and transversely polarized proton beams at collision energies of up to √s = 500 GeV.

Proton spin

Quark spins, gluon spins, and orbital momenta contribute to the proton spin:

Quark polarization ΔΣ

The sum of quark and anti-quark spin contributions to the proton spin is well-measured, and is found to account for only about 30% of the proton spin. The distribution among quark and anti-quarks of different flavors is not well known. STAR is delineating the contributions from the u and d quarks and anti-quarks with measurements of the spin-dependent production of W bosons in √s = 500 GeV proton collisions, and is studying the contributions from s quarks and anti-quarks via measurements of Λ hyperons.

Gluon polarization ΔG

The STAR LBNL group is measuring the dependence of the production rate of jets, jet pairs, and pions on the spin configuration of the colliding beams to determine the gluon spin contribution to the proton spin. The data are starting to provide strong constraints for this thus far elusive property of the proton.

Transverse spin phenomena

Large spin-dependent effects have been observed in particle production in the forward direction along the polarized beam in collisions of transversely polarized protons. STAR has observed such effects in production of neutrons and π0 and η mesons, and aims to extend these measurements to jets and photons.