Double Longitudinal Spin Asymmetry in Neutral Pion Production

Double Longitudinal Spin Asymmetry in Neutral Pion Production in Polarized p+p Collisions at =200 Ge. V at PHENIX Kieran Boyle (Stony Brook University) for the PHENIX Collaboration Outline: • Quick Physics overview • RHIC and PHENIX, and ALL requirements • Results and Dg constraints Kieran Boyle SPIN 2006—Oct. 3, 2006 1

Motivation with How to measure Dg: DS ~25% Dg not well constrained DL ? p 0 Hard Scattering Process Dg 2 Dg. Dq Dq 2 ~ agg * Dg 2 + bgq * Dg + cqq Kieran Boyle SPIN 2006—Oct. 3, 2006 2

ALL Requirements ++ = +- = + + Helicity Dependent Particle Yields (Local) Polarimetry Relative Luminosity (R=L++/L+-) Year [Ge. V] d. R d. ALL 2005 200 1. 0 e-4 2. 3 e-4 2006 200 1. 1 e-4 1. 5 e-4 ALL Kieran Boyle SPIN 2006—Oct. 3, 2006 3

RHIC Absolute Polarimeter (H jet) RHIC CNI (p. C) Polarimeters BRAHMS & PP 2 PP (p) PHENIX (p) STAR (p) Spin Rotators Siberian Snakes Partial Siberian Snake LINAC BOOSTER Pol. Proton Source AGS 200 Me. V Polarimeter Year AGS Internal Polarimeter Rf Dipoles [Ge. V] Luminosity [pb-1] (recorded) Polarization [%] Figure of Merit (P 4 L) 2005 * 200 3. 4 46 0. 15 2006 * 200 7. 5 62 1. 11 Run 6 Figure of Merit 7. 5 times that of Run 5 Kieran Boyle SPIN 2006—Oct. 3, 2006 * Longitudinal 4

PHENIX Detector p° detection • Electromagnetic Calorimeter: • High p. T photon trigger to collect p 0's • Acceptance: |h|<0. 35, f = 2 x p/2 • High granularity (~10*10 mrad 2) Relative Luminosity • Beam Counter (BBC) • Zero Degree Calorimeter (ZDC) • Acceptance: 3. 0< h<3. 9 • Minimum Bias event trigger • Acceptance: ± 2 mrad Local Polarimetry • ZDC BBC ZDC Level 2 Filtering • Run 6 p 0 results • Filter events with high p. T photons (>2. 5 Ge. V). • Statistics limited for p. T<5 Ge. V/c Kieran Boyle SPIN 2006—Oct. 3, 2006 5

• Use Zero Degree Calorimeter (ZDC) to measure a L-R and U-D asymmetry in forward neutrons (Acceptance: ± 2 mrad). • When transversely polarized, we see clear asymmetry. • When longitudinally polarized, there should be no asymmetry. BLUE Raw asymmetry Local Polarimetry at PHENIX YELLOW Idea: Use neutron asymmetry to study transversely polarized component. f Kieran Boyle f SPIN 2006—Oct. 3, 2006 6

Measured Asymmetry During Longitudinal Running (2005) LR c 2/NDF = 88. 1/97 p 0 = -0. 00323± 0. 00059 UD XF>0 LR c 2/NDF = 119. 3/97 p 0 = 0. 00056± 0. 00063 c 2/NDF = 82. 5/97 p 0 = 0. 00423± 0. 00057 UD c 2/NDF = 81. 7/97 p 0 = -0. 00026± 0. 00056 <PT/P>= 10. 25± 2. 05(%) <PL/P> = 99. 48± 0. 12± 0. 02(%) <PT/P>= 14. 47± 2. 20(%) <PL/P> = 98. 94± 0. 21± 0. 04(%) XF<0 Fill Number Kieran Boyle Fill Number SPIN 2006—Oct. 3, 2006 7

Remaining Transverse Component ATT • Here • ATT – azimuthally independent double transverse spin asymmetry. – ALL background (e<0. 01). – expected to be small, but previously unmeasured. • • • In Run 5, PHENIX took a short transverse run specifically to measure ATT. Consistent with zero. Possible systematic contribution to ALL <0. 05 d. ALL. Kieran Boyle SPIN 2006—Oct. 3, 2006 8

p 0 Cross Section • Consistent with previous PHENIX results. • Extends previous results to p. T of 20 Ge. V/c. • NLO p. QCD Theory is consistent with data over nine orders of magnitude. • As theory agrees well with our data, we can use it to interpret our results in terms of Dg Kieran Boyle SPIN 2006—Oct. 3, 2006 9

Calculating p 0 ALL 1. 2. 3. Calculate ALL(p 0+BG) and ALL(BG) separately. Get background ratio (w. BG) from fit of all data. Subtract ALL(BG) from ALL(p 0+BG): ALL(p 0+BG) = wp 0 · ALL(p 0) + w. BG · ALL(BG) p 0+BG region : ± 25 Me. V around p 0 peak BG region : two 50 Me. V regions around peak Kieran Boyle SPIN 2006—Oct. 3, 2006 10

Run 6 p 0 ALL • • GRSV: M. Gluck, E. Reya, M. Stratmann, and W. Vogelsang, Phys. Rev. D 63 (2001) 094005. Kieran Boyle SPIN 2006—Oct. 3, 2006 Run 6 Data set from 2. 0 -2. 7 times improvement on statistical uncertainties from Run 5. Variation due to Lv. L 2 “turn on. ” Due to unreleased absolute polarizations, which act a scale factor in ALL and which contain correlated and uncorrelated part, we have not combined the two data sets. For the confidence levels on the following slide, we assume complete correlation. 11

What about Dg? • Confidence levels from a simple c 2 test between our data and the four curves plotted. • Theoretical uncertainties are not taken into account (for now). C. L. (%) Theory model Run 5 Run 6 Run 5&Run 6 GRSV-std 18 -22 0. 5 -7. 0 0. 5 -7 1 -9 *GRSV-max (Dg=g) 0 -0 0 -0 *GRSV Dg=0 17 -19 14 -17 11 -12 *GRSV Dg=−g 0 -1 0 -0 Range is from varying ALL by polarization scale uncertainty * At input scale: Q 2 =. 4 Ge. V 2 • Run 6 rules out maximal gluon scenarios. • Expect clearer statement when lower p. T data from Run 6 is available; possibly will allow differentiation between STD and Dg=0. Kieran Boyle SPIN 2006—Oct. 3, 2006 12

Conclusions • Possible contaminating ATT shown to be consistent with zero for p 0. • PHENIX Run 5 data set excluded the positive maximal gluon scenario. With the addition of Run 6 data at high p. T (due to data filter), negative maximal gluon scenario also excluded. • For Run 6, an increase of 7. 5 in figure of merit will help reduce present uncertainty in Dg by factor of ~2 -2. 7, possibly allowing differentiation between STD and Dg=0. • More data expected at lower p. T points, as seen below: Kieran Boyle SPIN 2006—Oct. 3, 2006 13

Backups: 200 Ge. V Kieran Boyle SPIN 2006—Oct. 3, 2006 14

Relative Luminosity • Number of BBC triggered events used to calculate Relative Luminosity. • For estimate of Uncertainty, fit where Year [Ge. V] d. R d. ALL 2005 * 200 1. 0 e-4 2. 3 e-4 2006 * 200 1. 1 e-4 1. 5 e-4 * Longitudinal • Limited by ZDC statistics. Kieran Boyle SPIN 2006—Oct. 3, 2006 15

Soft Physics Bias? • To remove possibility that soft physics is influencing the result through the p. T<2 data, we calculated confidence levels excluding this point. • Theoretical uncertainties are not taken into account (for now). C. L. (%) Theory model Run 5 Run 6 Run 5&Run 6 (p. T>2 Ge. V) GRSV-std 18 -22 0. 5 -7 1 -9 1 -6 *GRSV-max (Dg=g) 0 -0 0 -0 *GRSV Dg=0 17 -19 14 -17 11 -12 8 -9 *GRSV Dg=−g 0 -1 0 -0 * At input scale: Q 2 =. 4 Ge. V 2 • No significant difference seen. • Expect clearer statement when lower p. T data from Run 6 is available; possibly will allow differentiation between STD and Dg=0. • More detailed analysis of Dg constraint underway. Kieran Boyle SPIN 2006—Oct. 3, 2006 16

Minimum Bias: Bunch Shuffle • Bunch Shuffling shows systematic difference from expected distribution at low p. T • We add a systematic error band to account for this. Kieran Boyle SPIN 2006—Oct. 3, 2006 17

Minbias: Mass Spectrum • Mass distributions for 6 p. T points. Kieran Boyle SPIN 2006—Oct. 3, 2006 18