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

2. C. Aidala, QCD-N06, 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 (  g) 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

3. C. Aidala, QCD-N06, June 15, 2006 3 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 Transverse spin only (No rotators) Longitudinal or transverse spin

4. C. Aidala, QCD-N06, June 15, 2006 4 Avenue to Transversity at RHIC Present and near-term: High-precision inclusive A N 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)

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

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

7. C. Aidala, QCD-N06, June 15, 2006 7 PHENIX Detector Overview Central arms Photons, electrons, identified charged hadrons |  | < 0.35  = 180 degrees Forward muon arms Track and identify muons 1.2 < |  | < 2.4  Fine segmentation and high rate but limited acceptance

8. C. Aidala, QCD-N06, June 15, 2006 8 PHENIX: EMCal-RICH Trigger Rare probes experiment— trigger capabilities essential! 4x4 tower overlapping energy sum, 3 threshold settings –1.4 GeV used for most  0 studies since 2003 2x2 tower non-overlapping energy sum, threshold ~ 0.6 GeV –Used in conjunction with RICH to form an electron trigger Mid-rapidity trigger on electromagnetic energy

9. C. Aidala, QCD-N06, June 15, 2006 9 PHENIX: IFF Using  0 +  +- RUN 6 achieved: 2.7 pb -1, 55% Polarization RUN 7 projected: 5.0 pb -1, 65% Polarization  Simple error estimates using PYTHIA + PHENIX acceptance + 1.4 GeV photon trigger threshold. 0.5 < m inv < 1.0 GeV/c 2 (Note Run 7 Beam Use Proposal still under discussion) R. Seidl p T pair (GeV/c) Tang: hep-ph/9807560 Theory curve a particular model prediction for RHIC at 200 GeV:  q(x) = | q(x) +  q(x) | (Soffer bound) IFF from phase-shift analysis Studies also underway for development of a high-p T charged pion trigger for 2008, which would greatly improve     IFF measurements.

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

11. C. Aidala, QCD-N06, June 15, 2006 11 STAR: Collins With upgraded Forward Pion Detector installed in 2006 run, sensitivity to  0 position in forward jets –Separate Collins vs. Sivers in observed  0 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  0 pair measurements as well as fully contained jets –Continuous EMCal coverage  < 4.0 2006 2007

12. C. Aidala, QCD-N06, June 15, 2006 12 1  x y TPC  -units 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  0 –  0 -charged hadron pair measurement possible Several million dijet events collected in 2006 –Can look at this analysis this year EMCal Geometry in L2 trigger 0 1 2 Endcap EMC  x y Barrel EMC  -units L2 jet

13. C. Aidala, QCD-N06, June 15, 2006 13 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 p T ~ 8 GeV/c for  0  + IFF RHIC-II (M. Grosse Perdekamp’s talk) 1% 2% IFF from Belle A T from STAR+PHENIX IFF Example: 125

14. 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.

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

16. C. Aidala, QCD-N06, June 15, 2006 16 PHENIX: p T  -p T Jet Correlation 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 p±p0p±p0 p T pair (GeV/c) p T jet (GeV/c)

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

18. 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: è Up to 500 GeV for p-p è Up to 200 GeV for Au-Au (per N-N collision) Luminosity –Au-Au: 2 x 10 26 cm -2 s -1 – p-p : 2 x 10 32 cm -2 s -1 (polarized)

19. C. Aidala, QCD-N06, June 15, 2006 19 STAR Excellent Coverage for (Di-)Jets +60 deg Jet 1 E T > 3.6 GeV Jet 2 E T > 3.3 GeV -60 deg  =  +   =+2  = -1 TPC EMC Barrel EMC Endcap BBC East BBC West yellow blue EMCal Geometry in L2 trigger 01 2 Endcap EMC  x y Barrel EMC  -units L2 jet

20. C. Aidala, QCD-N06, June 15, 2006 20   =0 o L2 algo result STAR Triggered on Di-Jet Found On-line Comparison with off-line  similar 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 2005 data event 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 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 0 +2  =180 o  =360 o ~180 o back-to-back di-jet Z=Et/GeV Jet  is weighted with EM E T

21. 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 TRIGGER E DEP > 15 GeV

22. 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

23. C. Aidala, QCD-N06, June 15, 2006 23 Addition of FMS to STAR provides nearly continuous EMC from -1< η <+4 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 2007 and Beyond – Forward Meson Spectrometer

24. C. Aidala, QCD-N06, June 15, 2006 24 01 2  -units Barrel EMC Endcap EMC x y 2006 STAR Di-Jet Events Reconstructed di-jets from EM calorimeter only trigger data: Stuck high bit in one tower Jet 1 Jet 2 Back-to-back di-jets  2< 60 o  vs.  2 kTx<0 kTx>0 Opening angle Transverse EM energy

25. 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++ 5/15 GeV summed energy threshold for large/small cells hardware-level calibration The data taken should allow most of the goals to be met; analysis is in progress

26. C. Aidala, QCD-N06, June 15, 2006 26 IFF Asymmetries vs p T :  ±   [Tang:hep-ph9807560] p 0 – Trigger 1.4 GeV Photons 0.5 < m inv < 1 GeV Calculated jet p T from pion pair (PYTHIA) RUN 6: 2.7 pb -1, 55% Polarization RUN 7: 5.0 pb -1, 65% Polarization 200 GeV 500 GeV May be possible to draw some early conclusions from 2007 data Theory curve by [Tang:hep-ph9807560]: d q(x) = | q + D q(x) | (Soffer bound) IFF from Phase-shift analysis