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

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

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 Longitudinal or transverse spin C. Aidala, QCD-N06, June 15, 2006

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

Transversity from Collins Effect 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

Transversity from Interference Fragmentation J. Collins, S. Heppelmann, G. Ladinsky, Nucl.Phys. B420 (1994)565 Jet X. Ji, Phys. Rev. D49 (1994)114 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

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

PHENIX: EMCal-RICH Trigger 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 Mid-rapidity trigger on electromagnetic energy C. Aidala, QCD-N06, June 15, 2006

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

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

STAR: Collins 2006 2007 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

EMCal Geometry in L2 trigger STAR: IFF EMCal Geometry in L2 trigger -1 1 2 Endcap EMC  x y Barrel EMC -units L2 jet -1 1  x y TPC -units 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

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) 1% 2% IFF from Belle AT from STAR+PHENIX IFF Example: 125 C. Aidala, QCD-N06, June 15, 2006

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

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

PHENIX: pTpp -pTJet 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 pT jet (GeV/c) p±p0 pT pair (GeV/c) C. Aidala, QCD-N06, June 15, 2006

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

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

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

STAR Triggered on Di-Jet Found On-line Comparison with off-line  similar 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 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 back-to-back di-jet ~180 o L2 algo result Presented data only from d-jet L2 trigger, one of several contributiong to STAr di-jets 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 +2 C. Aidala, QCD-N06, June 15, 2006

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 In QCD AN for single-inclusive reaction is power suppressed as 1/ Pion pT in the hard scale. Makes calculations complicated. Talk about how difficult to disentangle Sivers from Qu and Sterman twist 3 effects. Also Collins effect plays a role here. “Boer,Mulders and Pijlman, Nucl.Phys. B 667(2003) Top-Bottom-South Detectors 4x4 array of Lead-Glass No Shower Max Used for systematic error studies TRIGGER EDEP > 15 GeV C. Aidala, QCD-N06, June 15, 2006

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

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

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

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

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