1. Accessing Transversity via Collins and Interference Fragmentation at RHIC
Christine Aidala
UMass Amherst
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 at RHIC
Results from STAR, PHENIX, and BRAHMS from 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

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
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
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)
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
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

9. PHENIX: IFF Using p0+p+-
Simple error estimates using PYTHIA + PHENIX acceptance GeV
photon trigger threshold < minv < 1.0 GeV/c2
R. Seidl
Tang: hep-ph/
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. 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

12. 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, (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. 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

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 -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

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. 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

20. 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

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
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

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. 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

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-ph ]:
dq(x) = | q + Dq(x) | (Soffer bound)
IFF from Phase-shift analysis
[Tang:hep-ph ]
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