1. Measurement of the Longitudinal Double Spin Asymmetry in Inclusive Jet Production at STAR
Katarzyna Kowalik (LBNL)
For the STAR Collaboration
Moriond 2007, March 17 – 24, La Thuile
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

2. Longitudinal Double Spin Asymmetry in Jet Production at STAR
Nucleon Spin
Spin of the nucleon is made of :
Orbital momentum
Quarks carry only small fraction of the nucleon spin ~ 25%
Gluons contribution – not well constrain by inclusive DIS,
sensitivity only indirectly via Q2
evolution of g1(x,Q2) in NLO QCD
Alternative Methods :
Semi-Inclusive DIS
Polarized proton-proton collisions
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

3. Inclusive Jet Production in Proton-Proton Collisions
Main objective : constrains gluon polarization in the proton
Several processes contribute to inclusive jet production
qg and gg scattering dominate polarized partonic cross section
B.Jager,M.Stratmann,W.Vogelsang,Phys.Rev.D70,034010,2004
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

4. Jet Asymmetry
Large partonic asymmetries for qg and gg at mid-rapidity (=90)
Experimentally measured :
with partonic asymmetry :
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

5. How to Measure ALL in pp collider ?
Collide polarized proton beams at √s =200GeV at RHIC:
Yellow (Y) and Blue (B)
The experimentally measured quantity is double-spin asymmetry :
Requires different measurements :
Beam Polarization (P) determined by RHIC Polarimeter
Spin dependent yields (N) – the number of reconstructed jets
Relative Luminosities (R) between different spin configurations
STAR detector
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

6. STAR Detector at RHIC
Large acceptance unique for jet reconstruction at RHIC
Main subsystems in jet analysis:
Time Projection Chamber (-1<η< 1)
Charged particle tracking
EM Barrel calorimeter ( 0 < η < 1)
Detect high energy , e and 0
Jet Triggering
BBC Counters (3.4<<5 ) used for:
Beam Collision Trigger ( Minimum Bias )
Relative Luminosities measurements
Local polarimetry
BBC West
BBC East X IR
Bottom
Left
Right
Top
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

7. Jet Triggers High Tower: HT1 (HT2)
Trigger Efficiency from MC Simulations
High Tower: HT1 (HT2)
Signal in at least one tower of size (ΔηxΔφ) = (0.05 x 0.05)
Jet Patch: JP1 (JP2) – new in 2005
Signal in one trigger patch of size (ΔηxΔφ) = (1.0 x 1.0)
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

8. Longitudinal Double Spin Asymmetry in Jet Production at STAR
Jet Reconstruction
Midpoint cone algorithm*
Use TPC tracks pT and BEMC energy deposits
Cone radius R=0.4 in η and Ф
Data
detector
Dijet Event
particle
parton
*(hep-ex/ )
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

9. Longitudinal Double Spin Asymmetry in Jet Production at STAR
First Results: Data
Published Phys.Rev.Lett.97, 2006
Curves are theory predictions based on DIS parameterizations of ΔG:
B.Jager et al,Phys.Rev.D70,034010,2004
NLO QCD: hep-ph/ (Jager et al.)
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

10. Longitudinal Double Spin Asymmetry in Jet Production at STAR
2005 STAR Jet ALL vs 2003/2004
2005 sampled luminosity ~3.0pb-1 - factor ~10 bigger than data
After run selection 1.6pb-1
P Beam ~50% compared to 30-45% in
Results agree within statistical uncertainties
Extend reach in pT with Jet Patch Trigger in 2005
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

11. 2005 Result Inclusive Jet ALL
STAR PRELIMINARY
2 fit to curves: (stat+syst error in quadrature)
GRSV-STD: 1.1
G = G: 12
G = 0: 0.7
G = -G: 1.4
Rules out maximum positive gluon polarization scenario
ΔG=GRSV Std
ΔG=0 vanishing
ΔG=G large positive
ΔG=-G large negative
25% beam polarization uncertainty not included
Total systematic error ~ (STAR) + beam polarization (RHIC)
Sources: trigger+reconstruction biases, false asymmetry, residual non-longitudinal effects, relative luminosities, bunch to bunch systematic variations
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR

12. Longitudinal Double Spin Asymmetry in Jet Production at STAR
Summary and Outlook
2005 preliminary results for inclusive jet ALL
Factor ~10 bigger sample than with higher beam polarization
Rules out the maximally positive gluon polarization
New data for the global QCD analysis to determine pdfs
2006 data:
Further improvement in precision
Full barrel calorimeter coverage
Emphasis on Di-jets and high-pT measurements
Analysis has started
Future ΔG Measurements:
Heavy quark production and prompt photon-jet
Katarzyna Kowalik
Longitudinal Double Spin Asymmetry in Jet Production at STAR