Much work has been devoted to improving and building upon the 2006 EEMC π⁰ longitudinal analysis. However, there is also a transversely polarized dataset which to my knowledge no one has analyzed. It would be interesting to examine, among other things, A_N, in this region of 1 < η < 2. STAR has analyzed transverse-spin jets at mid-rapdity (-1 < η < 1) and transverse-spin pions at forward rapidity (2.5 < η < 4). Examining pions in the EEMC would provide information in a region of phase space between regions where we observe no asymmetry (mid-rapidity) and rather large asymmetries (forward rapidity).

My expectation is that no sizable effects will arise. The asymmetries are known to grow quite steeply as x_F increases. The vast majority of Run-6 EEMC data lie below the x_F range of the published FPD data, which did not see sizable effects below x_F ≈ 0.3. Thus, my expectation is that any effects in the EEMC will also be quite small. However, in my opinion, it is nonetheless worth the check. Here, I also post a link to a recent update to the VU-ANL group.

First Look

For this first look, I analyze 22 runs of 2006 ppTransverse data, prepared by Hal and Steve Gliske. I perform the same technique as used in my dissertation for FMS pions, 2-particle Sivers asymmetries, and recent analysis of 2011 jet Sivers. I bin yields in terms of spin-state, upper/lower-hemisphere, and as a function of the φ-angle. A cross-ratio is calculated in the standard way by combining yields from opposite sides of the detector with flipped spin-states. The asymmetry is extracted by fitting the cross-ratio vs. phi with a function of the form p₀+p₁×sin(φ_S). One expects the p₀ to be consistent with zero within statistics. The asymmetry is, then, extracted via the p₁ term. I calculate the asymmetry as a function of both p_T and x_F. The p_T binning is the same as that of the A_LL results. For this small sample, I have almost no data from 0 < x_F < 0.05 and 0.5 < x_F < 1. Thus, I show the x_F-asymmetries for three bins; and I hope to increase this as I integrate more statistics. These asymmetries have not been corrected for polarization. That will manifest as a scale of the vertical axis and error bars. These asymmetries are also not corrected for backgrounds. There may be azimuthal dependence to the background subtraction, so this will likely involve a restructuring of the code to accommodate the background subtraction prior to calculation of the cross-ratios.

Figure 1: Assorted Pion Distributions

Figure 2: x_F > 0

pT	xF

The top row shows the extracted asymmetry while the bottom row shows the constant of the fit. I would expect the constant to fluctuate around zero, however, it does seem to be systematically above the horizontal. I'm not entirely sure why this is, but I wouldn't draw too many conclusions until we integrate more statistics. As expected, the asymmetries are consistent with zero. As seen in Fig. 2, asymmetries for x_F < 0 are also consistent with zero.

Figure 3: x_F < 0

pT	xF

Below, I show the fits for individual bins (x_F < 0). I show not only the physics asymmetry but also the instrumental asymmetries and luminosity asymmetries. Sizable non-physical asymmetries show up as an expansion of the statistical errors in the physics asymmetry.

Figure 4: Fit Results for p_T Bins

0 < pT < 4 GeV/c
4 < pT < 5 GeV/c
5 < pT < 6 GeV/c
6 < pT < 7 GeV/c
7 < pT < 8 GeV/c
8 < pT < 9 GeV/c
9 < pT < 10 GeV/c
10 < pT < 12 GeV/c
12 < pT < 16 GeV/c

Within statistical uncertainties I see no sizable instrumental or luminosity asymmetries in the p_T bins. There may well be a non-zero luminosity asymmetry, though, I anticipate it will be quite small.

Figure 5: Fit Results for x_F Bins

0.05 < xF < 0.1
0.1 < xF < 0.2
0.2 < xF < 0.5

As with the p_T bins, I see no sizable instrumental or luminosity asymmetry in the x_F bins.