Determination of ΔG from pp ->π0 production at PHENIX

Swadhin Taneja SUNY Stony Brook University

Pre-Spin2008 RHIC Spin Meeting

Swadhin Taneja Pre- Spin2008 RHIC Spin Meeting

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Outline

• PHENIX Double helicity asymmetry (ALL) in π0 measurement.• Theory interpretation of ALL .

• Sensitivity of π0 ALL to the gluon spin, ΔG.

• Theoretical uncertainties in the extraction of ΔG.

• Results and Conclusions.

Swadhin Taneja Pre- Spin2008 RHIC Spin Meeting

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PHENIX π0 ALL from Run-5 and Run-6

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• New Run 6 PHENIX data. •13% CL with Run 5

• Systematic Uncertainty: - Relative luminosity (ΔR) - Beam polarization (ΔP) • NLO pQCD expectation (GRSV) - ΔG =0.24 , std. - ΔG = 0 , zero - ΔG = -1.05, negative

The measurements are more consistent with ΔG = 0 .

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Theory interpretation of ALL

•fa and fb are both quarks (qq).

•fa is quark and fb is gluon(qg).

•fa and fb are both gluons(gg).

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Sensitivity of π0 ALL to ΔG• Vary ΔG and refit to pDIS data (Fit by GRSV Group)• Calculate χ2 with PHENIX data ,

• χ2 profile is : - non- parabolic so both Δχ2 =1 and 9 (1σ and 3σ) are important - wider on the negative side

From just the statistical uncertainty :

Swadhin Taneja Pre- Spin2008 RHIC Spin Meeting

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Sensitivity of π0 ALL to ΔG

• The two primary systematic uncertainties are from polarization and relative luminosity.

• The polarization uncertainty is insignificant when extracting ΔG.

• Relative luminosity while small is significant.

Systematic uncertainty gives an additional +/- 0.1

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Theoretical uncertainties

• PDF model dependence as a function of x.

• Fragmentation functions model dependence.

• Theory energy scales, μ (factorization scale, fragmentation scale and renormalization) dependence.

• Strong coupling constant uncertainty dependence.

• Unmeasured x range dependence.

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PDF models from pDIS•The gluon polarization distribution as a function of x for five fits to polarized DIS data.

• Notice the 1σ experimental uncertainty (hatched band) from pDIS (Calculated by BB).

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ALL for different models

• Small ΔG in our measured x region 0.02 to 0.3 gives small ALL (DSSV and GS-C). Large ΔG gives comparatively larger ALL .

• Note small ALL (GS-C) does not necessarily mean small ΔG in the full x range.

• Obtain different ΔG’s by varying the size of a gluon distribution.

•Do not re-fit to the pDIS data.

• Plot the χ2 profile. The constraint at 3σ is nearly shape independent

Swadhin Taneja Pre- Spin2008 RHIC Spin Meeting

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Shape uncertainty

•Variation in ΔG due to shape in our x region is minimal.

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Re-fit vs no refit

• The two curves are consistent on the positive ΔG side.

• On the negative side thetwo are consistent.

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Theory scale (μ) uncertainty

• Uncertainty from scale is small for the positive values of ΔG but is sizable for negative values.

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Results & Conclusions• We presented the results for the double helicity asymmetry (ALL ) in p0 from PHENIX for Run 6.

• We studied the effects of theoretical uncertainties on the extraction of gluon spin, ΔG .• Based on our analysis we conclude that PHENIX Run5 and Run6 combined data for π0 ALL gives for DG in the x range (0.02- 0.3) , at μ2 = 4 GeV2 :

•For a variety of DG shapes we find at 3σ

• Caution: This is not the entire gluon spin, x range below 0.02 and above 0.3 is yet to be explored.

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Backup

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