Spin Physics Highlights from STAR

As the world’s only polarized proton collider, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven plays an important role in understanding the spin structure of the proton. The STAR detector, with its large acceptance for calorimetry and tracking, has been used to study polarized proton collisions for more than a decade with a range of jet, meson, and boson probes. We will discuss jets, neutral pions, and W bosons as probes of the proton’s helicity structure. Here STAR measurements have significant impact on global fits of sea quark polarizations and have provided the first firm evidence of non-zero gluon polarization within the proton. We will discuss W/Z bosons, jets, pions, and pion-jet correlations as probes of the transverse spin structure of the proton, and we will use the example of a proposed dijet measurement with an upgraded STAR detector to peer into the future.

• Full azimuthal coverage • Charged particle tracking from TPC for |η| < 1.3 • E/BEMC provide electromagnetic energy reconstruction for -1 < η < 2.0 STAR well suited for jet measurements p. 9 August 2, 2014 A. Gibson [47]. The "new fit" includes 2009 jet A LL , unlike the original DSSV fits which include the less precise 2006 data. A factor three improvement in ∆g over the measured range in x is seen. drapidity (|η| < 0.5, upper panel) and forward rapidity (0.5 < |η| < 1, lower panel) inclusive jet jet p T , compared to predictions from several NLO global analyses. The error bars are ray boxes show the size of the systematic uncertainties.
PosiDve)A N )-)more)π 0 )to)le'(of) (up))polarized)beam) ween the TMD and the collinear, twist-3 frameworks was out by Ji et al. (2006). urprises continue to emerge from these kinds of measurents, with large asymmetries for negative kaons as well as iprotons from BRAHMS (Arsene et al., 2008) suggesting t the pion asymmetries are not a valence quark effect as viously believed, and a recent hint from STAR (Adamczyk l., 2012c) that the asymmetry for mesons may be larger n that of neutral pions. the property of the muon beam in which polarization chang sign when going from positive to negative muons. The fi result of the correlation of transverse size and longitudin momentum fraction might already be expected from a 20 pilot run. In parallel semi-inclusive DIS data will be taken the pure hydrogen target.

Two!op0ons!to!m SingleNar
There are proposals to create a polarized fixed-target Dre Yan program at Fermilab following the SeaQuest experime scheduled to complete data taking in 2014. Research a =6.6 GeV s

R)=)relaDve)luminosity) P)=)beam)polarizaDon)normal)to)π 0)
For a 2π detector, A N manifests as an azimuthal (  the hard processes. Two theoretical formalisms have been pr framework: transverse momentum dependent parton distribut provide the full transverse momentum information and the co provides the average transverse information.

Two!op0ons!to! SingleNa
At RHIC the p T -scale is sufficiently large to make the colline appropriate approach to calculate the spin asymmetries. At th model has been applied to the SSAs in these hadronic mechanisms can contribute and need to be disentangled t detail, in particular the p T -dependence. These mechanisms nucleon (Sivers/Qiu-Sterman effects) and outgoing hadrons (

Sivers and Collins Analyses for Jets at 200 GeV
( ) Probe gluons to x ~ 10 -3 An attractive probe at rather low x before the EIC era

Polarized-proton Collider
• Mitigate effects of depolarization resonances with "Siberian Snakes" • Polarization measured with CNI polarimeter • Spin rotators provide choice of spin orientation independent of experiment

RHIC Beam Characteristics
• Clockwise beam: "blue"; counter-clockwise beam: " " • Spin direction varies bucket-to-bucket (9.4 MHz) • Spin pattern varies fill-to-fill The COMPASS data sets will primarily affect the quark and antiquark helicity distributions as reported in [13].

Relativistic Heavy Ion Collider as a Spin Collider
The method for our global analysis has been described in detail in [3] and will not be presented here again. It is based on an efficient Mellin-moment technique that allows one to tabulate and store the computationally most demanding parts of a NLO calculation prior to the actual analysis. In this way, the evaluation of the relevant spin-dependent pp cross sections [14] becomes so fast that it can be easily performed inside a standard χ 2 minimization analysis. As a small technical point, we note that STAR has moved to the "anti-k t " jet algorithm [15] for their analysis of the data from the 2009 run. In order to match this feature, we use the NLO expressions derived in [16] for the polarized case. As in our previous DSSV analysis [3], standard Lagrange multiplier (LM) and Hessian techniques are employed in order to assess the uncertainties of the polarized parton distributions determined in the fit.
We adopt the same flexible functional form as in [3] to parametrize the NLO helicity parton densities at the initial scale Q 0 ¼ 1 GeV, for instance, tolerance and for the adopted functional form (2). The dotted-dashed curve represents the result of a fithenceforth labelled as "DSSV*"-for which we only include the updates to the various RHIC data sets already used for the original DSSV analysis [3] (dashed line); i.e., we exclude all the new 2009 data [6,7]. The new COMPASS inclusive [11] and semi-inclusive [12] DIS data sets have little impact on Δg and are included in the DSSV* fit.
The striking feature of our new polarized gluon distribution is its much larger size as compared to that of the DSSV analysis [3]. For Q 2 ¼ 10 GeV 2 , it is positive throughout and clearly away from zero in the regime