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First 0 A LL results from PHENIX

First 0 A LL results from PHENIX. X-th Worshop on High Energy Spin Physics Dubna, Russia, September 16-20, 2003 A.Bazilevsky, Brookhaven National Laboratory For PHENIX Collaboration. A LL. ++ same helicity + opposite helicity. (P) Polarization (L) Relative Luminosity

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First 0 A LL results from PHENIX

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  1. First 0 ALLresults from PHENIX X-th Worshop on High Energy Spin Physics Dubna, Russia, September 16-20, 2003 A.Bazilevsky, Brookhaven National Laboratory For PHENIX Collaboration

  2. ALL ++ same helicity + opposite helicity (P) Polarization (L) Relative Luminosity (N) Number of pi0s

  3. RHIC pC Polarimeters BRAHMS & PP2PP PHOBOS Absolute Polarimeter (H jet) PHENIX STAR Siberian Snakes Spin Rotators 2  1011 Pol. Protons / Bunch e = 20 p mm mrad Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles RHIC as polarized proton collider “Blue” and “yellow” rings Run-2 configuration partially installed for Run-3

  4. PHENIX Detector • Philosophy: • High rate capability & granularity • Good mass resolution and particle ID • Sacrifice acceptance • 0 reconstruction and • high pT photon trigger: • EMCal: ||<0.38, = • Granularity  = 0.010.01 • Minimum Bias trigger and Relative Luminosity: • Beam-Beam Counter (BBC): • 3.0<||<3.9, =2

  5. Beam Polarization (in PHENIX) • Spin direction confirmation • With Spin Rotators and PHENIX Local Polarimeter • Confirmed • Long. component of the spin direction • PHENIX Local Polarimeter • Absolute polarization scale (see O.Jinnouchi talk) • With RHIC CNI polarimeter • Estimated to be ~30% • This error does not change the significance of non-zero ALL, because it scales both value and error in the same way (but it does change the comparison to theory)

  6. PHENIX Local Polarimeter • Forward neutron transverse asymmetry (AN) measurements • SMD (position) + ZDC (energy) f distribution SMD Vertical  f ~ ±p/2 Radial  f ~ 0 Longitudinal  no asymmetry ZDC

  7. Blue Yellow Blue Yellow Blue Yellow PHENIX Local Polarimeter:Spin direction confirmation Spin Rotators OFF Vertical polarization Spin Rotators ON Current Reversed Radial polarization Spin Rotators ON Correct Current ! Longitudinal polarization!

  8. Spin Long. Component ST is measured with PHENIX Local Polarimeter Left-Right asymmetry Up-Down asymmetry

  9. Relative Luminosity • Special scalers used • Counts live trigger in each bunch crossing • 4 inputs – for syst. error study: Beam Beam Counter and Zero Degree Calorimeter used – different kinematical region, different physics signals • Systematic error study through comparison of counts from different detectors • look at ratio of 2 detector scalers crossing-by-crossing: • a(i) = NA(i)/NB(i) • Ratio should be the same for all crossings (constant) if: • NA(i) = L * εA and NB(i) = L * εB • B is always the counts from the Beam-Beam Counter (BBCLL1), A is one of the other scalers. • Fit this by the expected pattern: • a(i) = C[1+ALLP1(i)P2(i)] • C, ALL are the fitting parameters. • c2 is a very important check of systematic errors ALL vs fill 30 2/NDF vs (ALL) 20 10 Not so good, but …

  10. Relative Luminosity Vertex width affects Rel. Lum. measurements After vertex correction ALL vs fill ZDC/BBC vs z-vertex width  2/NDF vs (ALL) 3 2 1 Now 2/NDF1

  11. Relative Luminosity: Results • Achieved relative luminosity precision R=2.510-4 • Pessimistic estimation limited by ZDC statistics (30 times less than BBC statistics used in Rel. Lum. measurements) • Rel. Lum. contribution for pi0 ALL less than 0.2% • For average beam polarizations of 26% • ALL of BBC relative to ZDC consistent with 0 (<0.2%) • Strong indication that both ALLs are zero (very different kinematical regions, different physics signals)

  12. Data set • Data collected with high pT photon trigger • Based on EMCal; Threshold ~1.4 GeV/c • Rejection factor ~110 • Analyzed data sample:42.7M events (~0.215 pb-1) • sqrt(<PbPy>)~26% • Minimum Bias data • To obtain “unbiased” 0 cross section at low pT • For high pT photon trigger efficiency study

  13. Photon trigger efficiency for 0 • Pi0 efficiency plateaus for pT>4 GeV/c • Limited efficiency at pT<4 GeV/c: 1-2 GeV/c: 6% 2-3 GeV/c: 60% 3-4 GeV/c: 90% 4-5 GeV/c: 95% • Monte Carlo reproduces Data well Data MC 0 pT (GeV/c)

  14. 0: Pi0 reconstruction

  15. Run-2 results 0 Cross section submitted to PRL, hep-ex/0304038 • Results consistent with pQCD calculation • Favours a larger gluon-to-pion FF (KKP) • Important confirmation of of theoretical foundations for spin program • Run3 results reproduce Run2 results • Confirm the Run-3 data reliability and consistency • Run3 data reaches even higher pTs; results will be finalized soon 9.6% normalization error not shown

  16. Pi0 reconstruction for ALL 1-2 GeV/c Bckgr=45% 2-3 GeV/c Bckgr=17% Results obtained for four pt bins from 1 to 5 GeV/c Pi0 peak width varies from 12 to 9.5 MeV/c2 from lowest to highest pt bins Background contribution under pi0 peak for 25 MeV/c2 mass cut varies from 45% to 5% from lowest to highest pt bins 3-4 GeV/c Bckgr=7% 4-5 GeV/c Bckgr=5%

  17. Pi0 counting for ALL • N0: • 25 MeV/c2 around 0 peak (and also 15 and 35 MeV/c2 for cross checks) • Nbck1: • Two 50 MeV/c2 wide areas adjacent to 0 peak • Nbck2: • 250 MeV/c2 wide area between 0 and peaks N0 and Nbck accumulated statistics

  18. ALL measurements ++ same helicity + opposite helicity • Procedure • Collect N and L for ++ and + configurations (sum over all crossings) and calculate ALL for each fill • Average ALL over fills; use 2/NDF to control fit quality; use “bunch shuffling” to check syst. errors

  19. ALL Calculations ALL averaged over fills 1-2 GeV/c 2-3 GeV/c • 1-2 GeV/c • ALL= -2.8%±1.2% • 2/ndf = 64/48 • 2-3 GeV/c • ALL= -2.2%±1.5% • 2/ndf = 34/48 • 3-4 GeV/c • ALL= -0.2%±3.3% • 2/ndf = 49/48 • 4-5 GeV/c • ALL= -2.3%±7.4% • 2/ndf = 39/48 4-5 GeV/c 3-4 GeV/c

  20. Bunch shufflingto check for syst. errors Bunch shuffling = Randomly assigns helicity for each crossing 2/NDF ALL 1-2 GeV/c 1-2 GeV/c 2-3 GeV/c 2-3 GeV/c 4-5 GeV/c 3-4 GeV/c 3-4 GeV/c 4-5 GeV/c Widths are consistent with obtained errors (ALL) All <2/NDF> are ~1

  21. ALL Calculations: background ALL averaged over fills • 1-2 GeV/c • ALL= 0.4%±1.0% • 2/ndf = 47/48 • <2/ndf> = 48/48 • 2-3 GeV/c • ALL= -2.2%±1.7% • 2/ndf = 35/48 • <2/ndf> = 50/48 • 3-4 GeV/c • ALL= 1.9%±5.5% • 2/ndf = 33/47 • <2/ndf> = 45/47 • 4-5 GeV/c • ALL= 10%±14% • 2/ndf = 47/44 • <2/ndf> = 41/44 1-2 GeV/c 2-3 GeV/c 3-4 GeV/c 4-5 GeV/c

  22. ALL results

  23. ALL results: plots 0+bck 15 MeV/c2 0+bck 25 MeV/c2 0+bck 35 MeV/c2 Bck1 Bck2

  24. Checks PID check ++ vs  and + vs + PID = Shower profile cut (0>96%) Consistent with 0 within 1.5 The same results

  25. AL check for “yellow” beam All are zeros within 1.5

  26. AL check for “blue” beam All are zeros within 1.5, except

  27. 0 ALL from pp at 200 GeV Polarization scaling error P ~30%: is not included • Enters the ALL quadratically • Analyzing power AN(100 GeV) ~ AN(22GeV) is assumed • P~30%: combined stat. and syst. error for AN(22GeV) (AGS E950) pT smearing correction is not included

  28. Summary • First Pi0 ALL results from long. polarized pp collisions with average beam polarizations of 26% presented • Results presented in four pT bins in the range 1-5 GeV/c • ALL sensitivity in the lowest pT bin (1-2 GeV/c) is 2.5% (1.2% without background subtracted) • 1.8 effect seen at 1-2 GeV/c bin (2.5  without background subtracted)

  29. ALL: PHENIX vs theory B.Jger e al., PRD67, 054005 (2003)

  30. Bunch fitting approach Collect N and L for each crossing i and fit ALLfrom N(i)/L(i)=C{1+ALLPB(i)PY(i)} for each fill;use 2/NDF to control fit quality 2/NDF 2-3 GeV/c 1-2 GeV/c 2/NDF from bunch fitting for each fill All 2/NDF ~ 1 => no problem seen within fills 4-5 GeV/c 3-4 GeV/c

  31. ALL from bunch fitting ALL averaged over fills • 1-2 GeV/c • ALL= -2.8%±1.2% • 2/ndf = 62/48 • <2/ndf> = 51/48 • 2-3 GeV/c • ALL= -2.2%±1.5% • 2/ndf = 35/48 • <2/ndf> = 48/48 • 3-4 GeV/c • ALL= -0.7%±3.3% • 2/ndf = 56/48 • <2/ndf> = 56/48 • 4-5 GeV/c • ALL= -7.2%±7.6% • 2/ndf = 46/48 • <2/ndf> = 56/48 1-2 GeV/c 2-3 GeV/c 3-4 GeV/c 4-5 GeV/c

  32. Luminosity vs bunch fitting • Results are identical at lower pt bins • Results start to deviate at higher pt bins • Pure statistical effect: too low statistics in each crossings to be used in bunch fitting • Confirmed from simple MC: deviations may be comparable to stat. error We use luminosity approach for final ALL for all pt bins

  33. N0statistical error estimation dk/dNev dk/dNev N0 Nbck2 • In multi-0 events: • Comparison to naïve approach: Fluctuation enhancement (squared) due to multi-particle events

  34. Backup slide: alpha Data MC vs Data

  35. Backup slide: alpha

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