Gluon polarization G measurements from PHENIX Swadhin Taneja

Gluon polarization ( G) measurements from PHENIX Swadhin Taneja (SUNY Stony Brook) For the PHENIX collaboration 10/25/2021 Swadhin Taneja DIS 09 1

Outline • Introduction • RHIC performance and PHENIX experiment • PHENIX cross section & double longitudinal asymmetry (ALL ) measurements • Extracting G from ALL - resulting constraint on G • Experimental and theory uncertainties on G • Summary and Outlook 10/25/2021 Swadhin Taneja DIS 09 2

Introduction q Polarized p+p collisions for ΔG measurement - π0, jet , direct photons etc. - double helicity asymmetry (ALL) q Inclusive π0 at mid-rapidity (|η| < 0. 35) is PHENIX main channel for the determination of ΔG at this time. 10/25/2021 Swadhin Taneja DIS 09 3

Extracting G from ALL measurements q Theory interpretation of ALL , - pol. (Δf) and unpol. pdf’s (f ) from DIS - pol. (Δσ) and unpol. (σ) hard scattering cross section from NLO PQCD - fragmentation functions (Dπ/c ), from e+ e- , Semi Inclusive DIS and pp q Three processes contribute to ALL, - Need to make sure p. QCD, factorization, universality in pdf and fragmentation WORK 10/25/2021 Swadhin Taneja DIS 09 4

Relativistic Heavy Ion Collider (RHIC) q Data accumulation in longitudinally polarized p+p Runs q 2005+2006 ~ 200 times increase in FOM than 2003+2004 q 2009 run at s = 500 Ge. V , L *~ 10 pb-1 q low s run for better sensitivity to large x Longitudinal 10/25/2021 Year s [Ge. V] L [pb-1] (recorded) 2003 200 0. 35 27 0. 0019 2004 200 0. 12 40 0. 0031 2005 200 3. 4 49 0. 20 2006 200 7. 5 57 0. 79 2006 62. 4 0. 08 48 0. 0042 Swadhin Taneja DIS 09 Pol. [%] FOM (P 4 L) 5

PHENIX Detector π0, η, γ detection • Electromagnetic Calorimeter (Pb. Sc/Pb. Gl): • High p. T photon trigger to collect π0's, η’s, γ’s • Acceptance: |η|<0. 35, φ= 2 x π/2 • High granularity (~10*10 mrad 2) π+ / π • Drift Chamber (DC) for Charged Tracks • Ring Imaging Cherenkov Detector (RICH) • High p. T charged pions (p. T>4. 7 Ge. V). Luminosity (Global) Detectors • Beam Counter (BBC) • Acceptance: 3. 0< η<3. 9 • Zero Degree Calorimeter (ZDC) • Acceptance: ± 2 mrad about beam axis 10/25/2021 Swadhin Taneja DIS 09 6

Cross section results from PHENIX q π0 , direct γ cross section 0 @ 200 Ge. V (PRD 76, 051106) Direct g @ 200 Ge. V - NLO p. QCD shows good agreement with the cross section data - Ready for the extraction of ΔG using NLO ALL predictions 10/25/2021 Swadhin Taneja DIS 09 7

Measurement of π0 ALL Well developed method q - 2003 (PRL 91, 241803) q π0 yield measurement - π0 → γγ BR ~ 98. 8 % - Combinatorial BG fraction w. BG = NBG / (NBG + Nπ ) q ALL measurement - signal ALL is corrected for background ALL, - PB , PY (~55%) beam polarization , less than 10 % relative error in PB. PY - R : relative luminosity, δALL = 2 x 10 -4 in 2005, 7 x 10 -4 in 2006 - N++ (N+- ) π0 yield with same (opposite) helicity of colliding beams 10/25/2021 Swadhin Taneja DIS 09 8

π0 and η asymmetry results from PHENIX q π0 ALL at 200 Ge. V - high statistics measurement - 2005: PRD 76, 051106 - 2006: Submitted to PRL (ar. Xiv: 0810. 0694) q η at 200 Ge. V - Analysis similar to 0 -Fractional sub process differ somewhat - Independent confirmation of G 10/25/2021 Swadhin Taneja DIS 09 9

π+, π- and γ asymmetry results from PHENIX q Charged pion at 200 Ge. V - Favored/Disfavored FF different qg contributions for +, 0, access sign of G q Direct photon ALL at 200 Ge. V - quark gluon scattering dominates - clean channel, isolation cut, linear in G - higher statistics needed 10/25/2021 Swadhin Taneja DIS 09 10

Constraining G q Vary G in GRSV fit, generate ALL , calculate 2 for each expectation curve, plot profile. ar. Xiv: 0810. 0694 - χ2 profile is asymmetric so Δχ2 =1 and 9 (1σ and 3σ) are significant From just the statistical uncertainty : 10/25/2021 Swadhin Taneja DIS 09 11

Experimental Uncertainty ar. Xiv: 0810. 0694 q Systematic uncertainty - The two primary systematic uncertainties are from polarization (ΔP) and relative luminosity (ΔR). - The polarization uncertainty is insignificant when extracting ΔG. - Uncertainty in relative luminosity while small is significant when extracting ΔG. Systematic uncertainty gives an additional +/- 0. 1 10/25/2021 Swadhin Taneja DIS 09 12

Theoretical uncertainty q q PDF functional form dependence as a function of x. Uncertainty in fragmentation functions (DSS, KKP). Theory energy scales, μ (factorization scale, fragmentation scale and renormalization) dependence. Strong coupling constant uncertainty dependence. 10/25/2021 Swadhin Taneja DIS 09 13

Uncertainty from paramaterizations The gluon polarization distribution as a function of x from five fits to polarized DIS data. q ar. Xiv: 0810. 0694 10/25/2021 Swadhin Taneja DIS 09 14

Theoretical uncertainty (Energy scale dependence) ar. Xiv: 0810. 0694 Uncertainty from scale is small (0. 1) for the positive values of ΔG but is sizable for negative values. 10/25/2021 Swadhin Taneja DIS 09 15

Extending x range q To measure ΔG, need as wide an x range as possible. - We can extend our x coverage towards lower x at s = 500 Ge. V. Run 9 - We can extend our x coverage towards higher x at s = 62. 4 Ge. V. Run 6 Extend to lower x at s = 500 Ge. V Extend to higher x at s = 62. 4 Ge. V present ( 0) x-range s = 200 Ge. V 10/25/2021 Swadhin Taneja DIS 09 16

Extending x range to large x q PRD 79, 012003 π0 ALL at 62. 4 Ge. V - clear statistical improvement at large x. T - increased sensitivity to large x (0. 06<x< 0. 4) - overlap with 200 Ge. V ALL providing measurements at same xg but different p. T - a preliminary version of this data set already a part of a global analysis 10/25/2021 Swadhin Taneja DIS 09 17

Summary & Outlook q From 0 ALL results, we find (0. 02<x<0. 3): Constraint at 3 of -0. 7 < G[0. 02, 0. 3] < 0. 5 is nearly shape independent. q PHENIX 0 data offers strong constraint of G as found by DSSV. q Other probes also can constrain G, and will be used in future global fits. q G at lower x range (x<0. 02) is presently being explored with s = 500 Ge. V at RHIC (2009 polarized pp run). q It is much too early to claim the G=0, as uncertainty in range 0<x<1 is large 10/25/2021 Swadhin Taneja DIS 09 18 q

Back up 10/25/2021 Swadhin Taneja DIS 09 19

Relative Luminosity • R = L++/L+- ; L = luminosity. • Luminosity is given by the number of BBC triggered events (NBBC). • For estimate of uncertainty, measure ALL in the ratio of our two luminosity detectors Year [Ge. V] d. ALL 2005 * 200 2 e-4 2006 * 200 7 e-4 * Longitudinal 10/25/2021 Swadhin Taneja DIS 09 20

• NLO p. QCD calculation of x distribution for 3 0 p. T bins. 10/25/2021 Swadhin Taneja DIS 09 21

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refit vs no refit 10/25/2021 Swadhin Taneja DIS 09 24

62. 4 ge. V 10/25/2021 Swadhin Taneja DIS 09 ar. Xiv: 0810. 0701 25

polarimeters 10/25/2021 Swadhin Taneja DIS 09 26