# PANIC2017 Abstract

LaTeX pasted below, pdf attached.

v1.2

Constraining the Gluon Polarization Distribution with Jet, Dijet, and Neutral Pion Probes at STAR
Adam Gibson for the STAR Collaboration
Department of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383, USA

A major goal of the proton spin physics program at the Relativistic Heavy Ion Collider (RHIC) is to constrain the gluon polarization distribution $\Delta g (x)$ and thus determine the contribution of gluons to the spin of the proton. Measurements of spin asymmetries with jets and neutral pions at central pseudorapidities at STAR and PHENIX have been critical to this effort. Recent global analyses have demonstrated a positive contribution to the spin of the proton from mid-to-high $x$ gluons (e.g. $x > 0.05$). But, the gluon polarization remains poorly constrained at low $x$. A variety of measurements at STAR have been recently completed, or are now underway, to better constrain the gluon polarization distribution. The STAR detector is well suited for a campaign of spin asymmetry measurements featuring full azimuthal coverage and a range of detector capabilities. Specifically, we will present measurements of the doubly-longitudinal spin asymmetry, $A_{LL}$. STAR has excellent tracking in the mid-rapidity ($|\eta| < 1.3$) region, useful for jet measurements, while mid-rapidity ($|\eta| < 1.0$) and intermediate-rapidity calorimetry ($1.09 < \eta < 2.00$) contribute to jet measurements and both of these calorimeters and a forward system ($2.65 < \eta < 4.0$) allow measurements with neutral pions. Inclusive jet measurements at mid-rapidity remain a core part of the STAR program while measurements with correlated observables like dijets provide more precise information about the initial-state parton kinematics. Moving to forward pseudorapidities allows us to probe lower partonic momenta, as does moving to higher center-of-mass energy. We will present the status of a variety of asymmetry measurements and the results of others using jet, dijet and neutral pion probes with longitudinally polarized $p+p$ datasets at $\sqrt{s} = 200$ GeV (25 pb$^{-1}$) and $\sqrt{s} = 510$ GeV (382 pb$^{-1}$).

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v1.1

A major goal of the proton spin physics program at the Relativistic Heavy Ion Collider (RHIC) is to constrain the gluon polarization distribution $\Delta g (x)$ and thus determine the contribution of gluons to the spin of the proton. Measurements of spin asymmetries with jets and neutral pions at central pseudorapidities at STAR and PHENIX have been critical to this effort. Recent global analyses have demonstrated a positive contribution to the spin of the proton from mid-to-high $x$ gluons (e.g. $x > 0.05$). But, the gluon polarization remains poorly constrained at low $x$. A variety of measurements at STAR have been recently completed, or are now underway, to better constrain the gluon polarization distribution. The STAR detector is well suited for a campaign of spin asymmetry measurements featuring full azimuthal coverage and a range of detector capabilities. Specifically, we will present measurements of the doubly-longitudinal spin asymmetry, $A_{LL}$. The Time Projection Chamber (TPC) gives STAR excellent tracking in the mid-rapidity ($|\eta| < 1.3$) region, useful for jet measurements, while the Barrel Electromagnetic Calorimeter (BEMC, $|\eta| < 1.0$) and Endcap Electromagnetic Calorimeter (EEMC,  $1.09 < \eta < 2.00$) contribute to jet measurements and both of these calorimeters and the Forward Meson Spectrometer (FMS, $2.65 < \eta < 4.0$) allow measurements with neutral pions. These detectors are used individually and in combination. Inclusive jet measurements at mid-rapidity remain a core part of the STAR program while measurements with correlated observables like dijets provide more precise information about the initial-state parton kinematics. Moving to forward pseudorapdities (as in the EEMC and FMS) allows the opportunity to probe lower-energy initial-state partons, as does moving to higher center-of-mass energy collisions. We will present the status of a variety of asymmetry measurements and the results of others using jet, dijet and neutral pion probes with longitudinally polarized $p+p$ datasets at $\sqrt{s} = 200$ GeV (25 pb$^{-1}$) and very large datasets (82 pb$^{-1}$ and 300 pb$^{-1}$) at $\sqrt{s} = 510$ GeV.

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v1.0

One of the major goals of the proton spin physics program at the Relativistic Heavy Ion Collider (RHIC) is to constrain the gluon polarization distribution $g (x)$ and thus determine the contribution of gluons to the spin of the proton. Measurements of spin asymmetries with jets and neutral pions at central pseudorapidities at STAR and PHENIX have been critical to this effort. Recent global analyses have demonstrated a positive contribution to the spin of the proton from mid-to-high $x$ gluons (e.g. $x > 0.05$). But, the gluon polarization remains under-constrained at low $x$. A variety of measurements at STAR have been recently completed, or are now underway, to better constrain the gluon polarization distribution. The STAR detector is well suited for a campaign of spin asymmetry measurements featuring full azimuthal coverage and a range of detector capabilities. The Time Projection Chamber (TPC) gives STAR excellent tracking in the mid-rapidity ($|\eta| < 1.3$) range, useful for jet measurements, while the Barrel Electromagnetic Calorimeter (BEMC, $|\eta| < 1.0$) and Endcap Electromagnetic Calorimeter (EEMC,  $1.09 < \eta < 2.00$) contribute to jet measurements and both of these calorimeters and the Forward Meson Spectrometer (FMS, $2.65 < \eta < 4.0$) allow measurements with neutral pions. These detectors are used individually and in combination. We will present the status of a variety of asymmetry measurements and the results of others using jet, dijet and neutral pion probes with longitudinally polarized $p+p$ datasets at $\sqrt{s} = 200$ GeV and very large datasets at $\sqrt{s} = 510$ GeV.