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Accessing Transversity via Collins and Interference Fragmentation at RHIC
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  1. Accessing Transversity via Collins and Interference Fragmentation at RHIC UMass Amherst Christine Aidala QCDN-06, Rome June 15, 2006

  2. Increasing Interest in Transverse Spin Physics at RHIC Progress in e+e- and DIS measurements as well as theory allows us to learn more and more from p+p results • 2006 run (ends June 26): Both PHENIX and STAR dedicated a significant fraction of beam time to transversely polarized collisions • Transverse spin physics competes with longitudinal spin program (Dg) • PHENIX: 2.7 pb-1 sampled at ~55% polarization • STAR: 6.8 pb-1 sampled at ~60% polarization (Compare to < 1 pb-1 total for all previous runs combined) • Transverse running allows for qualitatively different physics results from RHIC spin program C. Aidala, QCD-N06, June 15, 2006

  3. Transverse spin only (No rotators) Transverse Spin at RHIC • Results from STAR, PHENIX, and BRAHMS from 2002-2005 data sets presented by S. Heppelmann • Additional transverse data taken this year by all three experiments • Future running only with STAR and PHENIX detectors Longitudinal or transverse spin Longitudinal or transverse spin C. Aidala, QCD-N06, June 15, 2006

  4. Avenue to Transversity at RHIC • Present and near-term: High-precision inclusive AN and jets (S. Heppelmann’s talk) • Mid-term: Collins and IFF (this talk) • Long-term: Drell-Yan (M. Grosse Perdekamp’s talk) • Parallel effort on spin-dependent FF’s at BELLE (R. Seidl’s talk) C. Aidala, QCD-N06, June 15, 2006

  5. Transversity from Collins Effect Collins Fragmentation J. Collins, Nucl.Phys. B396 (1993)161 Jet axis Jet Proton Structure Hard Scattering Process Jet PDFs Collins FF pQCD transversity distributions C. Aidala, QCD-N06, June 15, 2006

  6. Transversity from Interference Fragmentation Interference Fragmentation J. Collins, S. Heppelmann, G. Ladinsky, Nucl.Phys. B420 (1994)565 X. Ji, Phys. Rev. D49 (1994)114 Jet Jian Tang , Thesis MIT, June 1999 R. Jaffe, X.Jin, J. Tang Phys. Rev. D57 (1999)5920 A. Bianconi, S. Boffi, R. Jakob, M. Radici, Phys. Rev. D62 (2000) 034009 Proton Structure Hard Scattering Process Jet IFF PDFs pQCD transversity distributions C. Aidala, QCD-N06, June 15, 2006

  7. PHENIX Detector Overview Central arms Photons, electrons, identified charged hadrons |h| < 0.35 Df = 180 degrees Forward muon arms Track and identify muons 1.2 < |h| < 2.4 Df = 2p Fine segmentation and high rate but limited acceptance C. Aidala, QCD-N06, June 15, 2006

  8. PHENIX: EMCal-RICH Trigger Mid-rapidity trigger on electromagnetic energy Rare probes experiment—trigger capabilities essential! • 4x4 tower overlapping energy sum, 3 threshold settings • 1.4 GeV used for most p0 studies since 2003 • 2x2 tower non-overlapping energy sum, threshold ~ 0.6 GeV • Used in conjunction with RICH to form an electron trigger C. Aidala, QCD-N06, June 15, 2006

  9. PHENIX: IFF Using p0+p+- Simple error estimates using PYTHIA + PHENIX acceptance + 1.4 GeV photon trigger threshold. 0.5 < minv < 1.0 GeV/c2 R. Seidl Tang: hep-ph/9807560 p±p0 • Theory curve a particular model prediction for RHIC at 200 GeV: • dq(x) = | q(x) + Dq(x) | (Soffer bound) • IFF from phase-shift analysis Studies also underway for development of a high-pT charged pion trigger for 2008, which would greatly improve p++p- IFF measurements. pT pair (GeV/c) RUN 6 achieved: 2.7 pb-1, 55% Polarization RUN 7 projected: 5.0 pb-1, 65% Polarization (Note Run 7 Beam Use Proposal still under discussion) C. Aidala, QCD-N06, June 15, 2006

  10. STAR Detector Overview -1 < h < 1 Collins and IFF measurements possible 0 < h < 1 1 < h < 2 2.2 < |h| < 5 |h| ~3.3/3.7/4.0 C. Aidala, QCD-N06, June 15, 2006

  11. 2007 STAR: Collins 2006 • With upgraded Forward Pion Detector installed in 2006 run, sensitivity to p0 position in forward jets • Separate Collins vs. Sivers in observed p0 asymmetry • Simulation and data analysis underway to understand how precisely jet axis can be determined with FPD++ • Forward Meson Spectrometer to be installed for 2007 run will provide p0 pair measurements as well as fully contained jets • Continuous EMCal coverage h < 4.0 C. Aidala, QCD-N06, June 15, 2006

  12. EMCal Geometry in L2 trigger Barrel EMC -units 1 -1 0 2 L2 jet y y Endcap EMC   x x TPC -units 1 -1 STAR: IFF • Interference fragmentation measurement for h+h- possible with 2006 data • Like PHENIX measurement, sensitive to transversity with IFF available as input, e.g. from BELLE • Proposal by Bacchetta and Radici (PRD 90, 094032 (2004)) to measure IFF directly in unpolarized p+p collisions using dijets • Level-2 dijet trigger available • Based on energy deposit in EMCal  trigger-side jet (most often) has leading p0 • p0-charged hadron pair measurement possible • Several million dijet events collected in 2006 • Can look at this analysis this year C. Aidala, QCD-N06, June 15, 2006

  13. 1% IFF Example: 2% IFF from Belle AT from STAR+PHENIX 125 Longer-Term Future • End of 200 GeV running mid-Run-09 (2009): Plan for ~31 pb-1 transverse data at PHENIX • Sub-percent statistical errors up to pT ~ 8 GeV/c for p0p+ IFF • RHIC-II (M. Grosse Perdekamp’s talk) C. Aidala, QCD-N06, June 15, 2006

  14. Summary and Prospects • Increased interest in transverse spin physics at RHIC  better prospects for more beam time with transverse polarization • Possible to access transversity distribution via Collins effect at STAR and IFF at PHENIX and STAR • May get first results this year or next • Belle measurements of Collins FF and IFF will provide important input for p+p studies • Also possible to measure IFF directly in (unpolarized) p+p through dijets at STAR RHIC results, alongside e+e- and DIS measurements, will constitute an important part of a global analysis to understand transversity. C. Aidala, QCD-N06, June 15, 2006

  15. Extra Slides C. Aidala, QCD-N06, June 15, 2006

  16. PHENIX: pTpp-pTJetCorrelation • Jet transverse momentum determined by outgoing partons in Pythia • (entries 7 or 8, depending on proximity to pair momentum) • Nearly linear behaviour between jet transverse momentum and that of pion pair pT jet (GeV/c) p±p0 pT pair (GeV/c) C. Aidala, QCD-N06, June 15, 2006

  17. STAR Jet Cross Section C. Aidala, QCD-N06, June 15, 2006

  18. RHIC Specifications • 3.83 km circumference • Two independent rings • Up to 120 bunches/ring • 106 ns crossing time • Energy: • Up to 500 GeV for p-p • Up to 200 GeV for Au-Au(per N-N collision) • Luminosity • Au-Au: 2 x 1026 cm-2 s-1 • p-p : 2 x 1032 cm-2 s-1(polarized) C. Aidala, QCD-N06, June 15, 2006

  19. EMC Barrel  = -1 EMC Endcap y TPC   =+2 x BBC East BBC West Jet 1 ET> 3.6 GeV yellow blue -60 deg EMCal Geometry in L2 trigger +60 deg Barrel EMC -1 -units =+ 0 1 2 Endcap EMC Jet 2 ET> 3.3 GeV STAR Excellent Coverage for (Di-)Jets L2 jet C. Aidala, QCD-N06, June 15, 2006

  20. STAR Triggered on Di-Jet Found On-line • L0 di-jet logic: • BBC East.West • Etot >14 GeV • hardwired jet patches • jet size : 1x1 (x) • one jet Et>4.0 GeV • event rate ~120 Hz Comparison with off-line  similar Z=Et/GeV =360o 2005 data event Jet  is weighted with EM ET • L2 di-jet logic: • 5500 EMC towers • sliding jet patches • jet size : 0.6x0.6 (x) • jet1 Et>3.6, jet 2 Et>3.3 GeV • decision : 60 muSec/event • event rate ~8 Hz =180o ~180 o back-to-back di-jet L2 algo result • L0-L2 logic benefits: • large acceptance combined with trigger rejection power • full statistics on-line trigger monitoring of EMC • compact trig info saved for each event =0o  -1 0 +2 C. Aidala, QCD-N06, June 15, 2006

  21. Forward Pion Detector at STAR • 24 layer Pb-Scintillator Sampling Calorimeter • 12 towers • Shower-Maximum Detector - 2 orthogonal layers of 100 x 60 strips • 2 Preshower Layers • Top-Bottom-South Detectors • 4x4 array of Lead-Glass • No Shower Max • Used for systematic error studies • TRIGGEREDEP > 15 GeV C. Aidala, QCD-N06, June 15, 2006

  22. 2006 − Forward Pion Detector++ Large enough • to integrate over a jet cone • for direct photon isolation cuts C. Aidala, QCD-N06, June 15, 2006

  23. 2007 and Beyond – Forward Meson Spectrometer • FMS will provide full azimuthal • coverage for range 2.5  η 4.0 • • Broad acceptance in plane • for inclusive production • Broad acceptance for and • from forward jet pairs to probe • low-x gluon density Addition of FMS to STAR provides nearly continuous EMC from -1<η<+4 C. Aidala, QCD-N06, June 15, 2006

  24. y Barrel EMC Endcap EMC 2< 60o x -1 0 1 2 -units Back-to-back di-jets Opening angle kTx>0 kTx<0 2006 STAR Di-Jet Events  vs. 2 Reconstructed di-jets from EM calorimeter only trigger data: Transverse EM energy Jet 1 3,000,000 di-jets Stuck high bit in one tower Jet 2 C. Aidala, QCD-N06, June 15, 2006

  25. 2006 – Physics Goals • ♦ Forward jet shape ♦ Asymmetry for jet-like events • ♦ mapping ♦ ? • ♦ Inclusive/direct photon measurements FPD++ hardware-level calibration The data taken should allow most of the goals to be met; analysis is in progress 5/15 GeV summed energy threshold for large/small cells C. Aidala, QCD-N06, June 15, 2006

  26. IFF Asymmetries vs pT: p± p0 • Theory curve by [Tang:hep-ph9807560]: • dq(x) = | q + Dq(x) | (Soffer bound) • IFF from Phase-shift analysis [Tang:hep-ph9807560] • p0 – Trigger 1.4 GeV Photons • 0.5 < minv < 1 GeV • Calculated jet pT from pion pair (PYTHIA) 200 GeV RUN 6: 2.7 pb-1, 55% Polarization RUN 7: 5.0 pb-1, 65% Polarization 500 GeV May be possible to draw some early conclusions from 2007 data C. Aidala, QCD-N06, June 15, 2006