Speaker
Description
A quantitative understanding of how gluonic spin contributes to the spin of the proton has been a central goal of the RHIC spin program. In polarized pp collisions, the large kinematic coverage of the Solenoidal Tracker At RHIC (STAR) provides sensitivity to gluons over a broad range in their momentum fraction x through the qg and gg scattering processes that dominate jet production at RHIC energies. The gluon helicity function, Δg( x), can be probed via measurements of the longitudinal double-spin asymmetry A_LL in inclusive jet and dijet production, which are vital input to global analyses. Inclusive jet results from STAR at mid-rapidity (|η| < 1) using 2009 pp data at √s = 200 GeV, when added to such analyses, indicated substantial positive polarization (i.e., aligned with the proton spin direction) for gluons with x > 0.05. Since then, higher statistics data sets were collected in 2015 at the same energy, while significantly larger data samples have been recorded at √s = 510 GeV in 2012 and 2013. In addition, new analyses have pushed the kinematic reach to higher pseudorapidities (up to η ∼ 1.8) and have been extended to study dijet production as well, all of which provide new and much needed constraints in the largely unexplored region x < 0.05. The status of these analyses and their potential impact on Δg( x) will be discussed.
| Submitted on behalf of a Collaboration? | Yes |
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