Spin Physics with Star at Rhic

STAR collected data in proton-proton collisions at √ s = 200 GeV with transverse and longitudinal beam polarizations during the initial running periods in 2002–2004 at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Results on the single transverse spin asymmetries in the production of high energy forward neutral pions and of forward charged hadrons will be presented. Data have been obtained for double longitudinal asymmetries in inclusive jet production in 2003 and 2004. These data provide sensitivity to the polarization of gluons in the proton. In the future, we aim to determine the gluon polarization over a wide kinematic range using coincidences of direct photons and jets. Furthermore, we aim to determine the polarizations of the u, ¯ u, d and ¯ d quarks in the proton by measuring single longitudinal spin asymmetries in the production of weak bosons at √ s = 500 GeV. STAR is one of two large experimental facilities at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. One of the goals of the STAR physics program is to study the internal spin structure of the proton in polarized proton-proton collisions. In particular we aim to determine the gluon polarization in the proton and the flavor decomposition of the quark helicity densities in the nucleon sea. STAR is capable of tracking charged particles and measuring their momenta in a high multiplicity environment. The experimental setup [1] provides tracking, particle identification and electromagnetic calorimetry covering a large acceptance. The identification and measurement of jets, electrons, photons, and neutral pions are of particular importance to the spin program. During the first three polarized proton running periods at RHIC crucial machine components , including spin rotators and polarimeters [1], were successfully commissioned. Progress has been made towards the projected design luminosities and polarizations, L max = 0.8(2.0) × 10 32 cm −2 s −1 and P=0.7 at √ s = 200(500) GeV. Specifically, polarization development has resulted in an increase in beam polarization from about P = 0.15 in the first running period in 2002 to P = 0.40 in 2004, and peak luminosities have reached 0.5 × 10 31 cm −2 s −1. STAR has measured the single transverse spin cross-section asymmetry A N = (σ ↓ − σ ↑)/(σ ↓ + σ ↑) at √ s = 200 GeV in neutral pion and charged particle production in the forward region during the initial …