Longitudinal Double Spin Asymmetries with π0-Jet Correla=ons in Polarized Proton Collisions at √s = 510 GeV at STAR

One of the primary goals of the spin physics program at STAR is to constrain the polarized gluon distribution function, Δg(x), by measuring the longitudinal double-spin asymmetry (ALL) of various f...

• DIS data measure the integral of quark polarization well to be around ~ 30% • Both DSSV and NNPDF, with 2009 RHIC results integrated in the fits, find evidence for positive gluon polarization: -DSSV: 0.19 +0.06 -0.05 at 90% c.l. for x > 0.05 • Uncertainties on integral over low x region are still sizeable. The Relativistic Heavy Ion Collider (RHIC), the world's first polarized hadron collider, is designed to collide many particle species energies.

Coherent Electron Cooling Electron Lenses
-World's only polarized hadron-hadron collider -Spin direc7on changes from bunch to bunch -Spin rotators provide choice of spin orienta7on 5 STAR Experiment at RHIC -STAR Detector

PANIC2017@Beijing, Yaping Wang
Channel: Using a jet in the mid-rapidity region correlated with an opposite-side neutral pion in the forward rapidity region 1.08 < η < 2.0 in the STAR EEMC provides a new tool to access the ΔG(x) distribution at Bjorken-x down to 0.01. ), Ø Compared to inclusive jet measurements, this π 0 -jet channel also allows to constrain the initial parton kinematics, such as x 1 , x 2 and √ŝ. Ø Theoretical description of hadron-jet A LL by next-to-leading order (NLO) model calculation: Daniel de Florian, PRD 79 (2009) 114014.

Parton vs. Reconstructed kinematics:
Ø Find that most of the generated events in the Monte Carlo implementation of the NLO corrections give the same value for the 'real' and 'measured' momentum fractions. Forward π 0 -barrel jet correlation using Daniel's NLO model calculation for this work x real x meas 10 π 0 -Jet A LL measurements at STAR

Analysis cuts for Run12 pp 510 GeV data:
Jet reconstruction: • Anti k T alogorithm, R=0.6 • Leading jet with p T > 8.0 GeV/c • Jet physics eta: (-0.9, 0.9) • Jet points to a jet patch (JP) trigger • Contribution from the calorimeters to the total jet energy (R t ) was required to be less than 0.95 • Sum track p T > 0.5 GeV/c π 0 reconstruction: Reconstructed kinematics from data: ), 13 π 0 -Jet A LL measurements at STAR

Pythia simulation VS. data:
• Ratio of leading jet p T from Run12 data to the leading jet p T from generator MC was taken as jet reconstruction efficiency.
• Weighted by the jet reconstruction efficiency, the π 0 /jet p T spectrum and Δϕ distribution from MC are consistent with data.

Background subtraction:
The invariant mass spectrum (weighted by relative luminosities and beam polarizations), are fitted to estimate signal yield for each kinematic variable bin, respectively.
• The raw yield of π 0 -jet are well fitted by extended likelihood formalism in RooFit, in which the signal shape was described by skewed Gaussian function  • STAR has been making significant contributions to the gluon polarization program via inclusive jets, inclusive neutral pions and dijets measurements.
• A LL measurements via correlations between forward neutral pion and barrel jet allow to constrain the initial partonic kinematics. Analysis results using this channel is underway.
• More data have been taken by STAR and more precision measurements are expected.