2012 Pions in Jets A_UT Paper

Paper Title:
Azimuthal transverse single-spin asymmetries of inclusive jets and charged pions within jets from polarized-proton collisions at √s = 200 GeV

Paper Abstract:
We present the first transverse single-spin asymmetry results measured in jet + π± events from midrapidity (|η|<1) polarized proton-proton collisions at √s=200 GeV. Included are measurements of the Collins asymmetry, sensitive to the transverse momentum dependent quark transversity distribution and Collins fragmentation function, and the ``Collins-like'' asymmetry, sensitive to linearly polarized gluons in a transversely polarized proton. Also, we include an update of the inclusive jet asymmetry, sensitive to the initial state twist-3 quark-gluon correlators. Data for these measurements were collected in 2012 with the STAR detector for an integrated luminosity of 14 pb-1 at an average polarization of 57%. With our precision, we find a significant Collins signal having greater than 6σ significance. The inclusive jet and ``Collins-like'' asymmetries are consistent with zero within our error budget. Using jets in the jet pT range 6 < pT < 31.6 GeV/c, these results probe a higher Q2 region than what is currently accessible by semi-inclusive deep inelastic scattering (SIDIS) experiments. These measurements, when compared to recent SIDIS and e+e- results, place limits on the size of factorization breaking effects. Comparisons to STAR asymmetry results at √s=500 GeV provides the first opportunity to study the evolution of transverse momentum dependent distributions in proton-proton collisions.

Target Journal:
Phys. Rev. D

Corrections and Systematic Errors:

  1. Apply kinematic shifts and their x-axis uncertainty
  2. Finite bin width dilution correction (0.989 dilution factor for all bins)
  3. Pion sample contamination correction and associated systematic error. Four relevant updates: one, two, three, and four.
  4. Trigger bias
  5. φC resolution correction and associated systematic error. Three relevant updates: one, two, and three.
  6. Leak through systematic error
  7. Error due to detector-to-parton jet matching fraction

Collins Analysis Money Plots:
(Note: Right click and select "Open Image in New Tab" to see full size image)

Figure 1:
 Collins vs. Jet-pT                                                                           Figure 2: Collins vs. z

Figure 3:
 Collins vs j                                                                                    Figure 4: Collins vs. jT

Collins-like Analysis Money Plots:

Figure 5:
 Collins-like vs jet pT                                                                      Figure 6: Collins-like vs. z
Inclusive Jet Analysis Money Plots:

Figure 7: Inclusive Jet vs. jet pT

Proposals for Additional Paper Plots:

1.) Kinematic coverage (x vs. Q2) similar to what Jim released in his recent publication (Phys.Rev. D 97 (2018) 032004). I will add points to this to show off kinematics for both COM energies.

Figure 8: Kinematic coverage for 500 GeV (to be updated to 200+500 GeV) - from Phys.Rev. D97 (2018) 032004

2.) Data/MC comparison plots like those below. These will be combined into one single three panel plot (potentially combining charge states?)

Figure 9: Data/MC comparison plots to be used in the paper 

3.) Comparison plots to 500 GeV: Show Collins as a function of jT for fixed xT, and ask Alexei and Zhongbo for curves to also add.

4.) Collins-like plotted over the maximal calculations.