I. YOON*¹,*² for the PHENIX Collaboration The final goal of this research is to contrain polarized gluon distribution via measurement of the longitudi- nal double helicity asymmetry of π ⁰ production ( A T L) with √s = 510 GeV RHIC PHENIX data.  Based on the results of EMC experiment and other following ex- periments, the quark-spin component of a proton is only 0.330±0.011( Theo .)±0.025( Exp .)±0.028( Evol .). 1)2) The remaining spin might be carried by gluons or orbital momentum.  However, the gluon-spin compo- nent is poorly measured because polarized gluon dis- tribution has not been measured precisely. 2) However, measurement with √s = 510 GeV RHIC PHENIX data can contribute significantly toward constraining nent can be measured via A Z o lisions, which is defined as
t + and σ ī ै  denote the π 0 cross section from a where σ π collision between same helicity protons and that from a collision between opposite helicity protons, respec- tively. Compared to the previous measurement with √s = 200 GeV RHIC data (Run09), the ongoing measure- ment with √s = 510 GeV RHIC data (Run13) will cover a lower momentum-fraction (Bjorken x) kine- matic region, where the uncertainty large.  The inte- grated luminosity of Run13 is much higher compared to that of Run09. The figure of merit ( f L×P s × P s dt) considering beam polarization ( P B and P Y ) is also higher. Table 1 presents a comparison between Run09 Thus, this research can contribute to- and  Run13. ward constraining polarized gluon distribution.  The progress of the analysis is presented herein. Table 1. Measurement with RHIC Run09 and Run13 data
In this experiment, π 0 is measured via π 0 γγ decays using a highly segmented electromagnetic calorimeter (EMCal) covering | η | < 0.35 and Δφ = π. Thus far, event selection and related low-level study, EMCal warnmap generation, and EMCal TOF tower- by-tower correction have been done. An EMCal warnmap is a map of abnormal EMCal towers.  To reject events from the abnormal towers, a warnmap has been generated wherein noisy, dead and uncalibrated towers are marked.  EMCal tower- by-tower TOF correction has been performed. Before the correction, there was tower-by-tower TOF devia- tion, and the deviation depended on time.  After the correction, the TOFs of all towers are well aligned. For event selection, the shower-shape cut, charge- veto cut and TOF cut are applied to reject hadronic, charged and ghost events, respectively. Clusters in an EMCal can survive up to three bunch-crossings.  Clus- ters from previous crossings are called ghost clusters. For the charge-veto cut and TOF cut, cut parameters are optimized by the signal-to-noise ratio. In addition to the three cuts mentioned above, the conventional minimum energy cut and vertex cut are also applied. After event selection, the statistics for remaining π 0 is 6.97 × 107. The results of the event selection are summarized in Fig. 1. Fig. 1. Diphoton invariant mass distribution with various cuts for all P r bins. After event selection, 70% of the noise is suppressed, whereas 30% of the signal is lost. After the completion of event selection, A TLL calcu- lation has been started.  A T L  calculation is currently in preliminary stage. Estimation of statistical and sys- tematic uncertainties is also being carried on. To val- idate the analysis, single-spin asymmetry is being cal- culated.