This page summarizes my study on how jet quantities change as they move from the barrel into the endcap.

For this analysis, I have looked at jets passing the dijet condition of the L2JetHigh trigger. I have looked at jets from the 12 point branch and the emc only branch of the jet finder. For each branch, I have separated jets into two classes, those associated with a fired jet patch and those not. For the jets not associated with a jet patch, I still require that at least one jet be associated with a jet patch in the event. The pdf files containing the various plots are below:

12 point branch, jets associated with jet patch

12 point branch, jets not associated with jet patch

Emc only branch, jets associated with jet patch

Emc only branch, jets not associated with jet patch

The analysis is done over the RFF runs included in the run list Pibero used for the inclusive jet analysis for the Spin2010 meeting. The list of runs can be seen here.

The profile plots each have three curves  which represent jets in a certain pt range. Black is 0.0 < pt < 8.0, red is 8.0 <= pt < 15.0, and blue is pt >= 15.0.

Figure 1: These plots show how the number of tracks and towers in a jet as a function of the jet's eta position in the detector. Plots from the 12 point, jets associated with jet patch set.

Figure 2: These plots show total jet pt, total track, and total tower pt, as well as jet phi. Plots from the 12 point, jets associated with jet patch set. For total jet pt, there is a slight decrease as jets move into the endcap region. The total track pt curves start decreasing sharply at a detector eta of 1. It is a bit odd that the decrease is so sharp considering that in figure 1 we see the decrease in number of tracks in a jet is smoother and sets in around an eta of 0.5. The total tower pt curves start increasing at detector eta of 1. It was thought this may be a result of the 100% subtraction scheme where the pt of a track is subtracted from the pt of the tower it points to. This seems to be confirmed by the emc only branch plots, see figure 3.

Figure 3: These are the same plots as in figure 2 for the emc only, jets associated with jet patch set. The total tower pt does not show the rise at detector eta of 1 like it does in the 12 point plot in figure 2. The values of the curves are also higher, having about the same value seen at the highest detector etas in figure 2 throughout the detector eta range here. Since there are no tracks in the emc only branch, no pt will be subtracted from the towers and there will be no change as tracking drops out in the endcap region.

Figure 4: These plots show the z-vertex for jets as a function of the detector eta of the jet. The top plot is for the 12 point, jets associated with jet patch set and the bottom plot is for the 12 point, jets not associated with jet patch set.

Figure 5: These plots show how the track and tower etas compare with the reconstructed jet eta as a function of the jet's detector eta. Again, the top plot is 12 point, jets associated with jet patch and the bottom plot is 12 point, jets not associated with jet patch.

 Plots Without Pt Cuts

The plots in figures 2 and 3 above seem to indicate that the potential loss in jet pt which arises as a consequence of falling number of tracks may be partially offset by the rise in tower pt which comes about due to the 100% subtraction scheme. If a charged track points at a tower, the pt of the tower is reduced by the amount of pt in the track. When there are fewer tracks, fewer towers have subtracted pt and the tower contribution to the jet pt should rise. This effect can be seen by looking at the bottom right pannels of figures 2 and 3 and observing how tower pt increases for eta > 1 (the region where tracking dies out) in figure 2 yet remains relatively flat in figure 3 where no tracks are present at any eta.

As I was investigating the systematic differences between matched 12 point and emc only branch jets, I noticed that the pt difference between the two branches was larger than I would have anticipated given figures 2 and 3 above. As part of my investigation into this, I added a fourth curve to the profile plots which shows the average value of the quantity for all jet pt.

The black, red, blue curves represent the same jet pt ranges as listed above, the green curve represents the average for all jets, regardless of pt.

Figure 6: This is the same plot as seen in figure 2 with the addition of the 'all jets' curve.

Figure 7: This is the same plot as seen in figure 3 with the addition of the 'all jets' curve.