Average and Peak ET
of probe jet vs iEta

1. Intro

It was found in the Hcal Dijet Logbook page 1 ( Sec.4.2.1 ) from the ET_peak / Pthat_threshold for tag jets in 2009 sample (PThat > 30) that the the uncorrected tag jet energy is underestimated by factor ~2. And the "unbiased" HF correction was found to be 0.50 (Sec.5.5). => It looks like the jet energy scale in HF is roughly correct.

Puprose of this study: try to see the jet scale recovery for probe jets as going from barrel region to HF, by looking at the evolution of the ET(probe jet) distribution.

Input sample: 2009 PThat>30, 10 TeV Version 1 , one root file QCD_Pt30_10TeV.hi_100.root with 70946 evs

Plots were made interactively with the script .

2. Probe jet only

The < ET > vs iEta plot:

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• ET growth in HF as |iEta| increases, stops at |iEta| ~34, and changes to a fall off. This must be a reflection of boudary condition E(true probe jet) < E(beam), thus only the lowest values of ET(probe) get allowed in this region. For the same reason, a third jet contribution may become more important near this boundary.

The ET distributions are shown below for 7 bins in |iEta|. The peak positions as found by the standard root peak finder (function ShowPeaks ) are marked with red triangles.

Original size: gif , eps

The ET peak values from the above plots are tabulated below:

• we do not get .50 , rather .60 only
• are numerous cutoffs applied in the calibrtion, important? May well be...

3. Selecting η(tag) < 1 . Zooming HF region. Use tag jet directly for a probe in HF.

Now we add cutoff η(tag jet) < 1, used in calibration normally.

Probe jet ET :

Original size: gif , eps

• In HF region, the average ET is only few percent bigger than on the plot w/o η cutoff . This seems to be insignificant.

Tag jet ET but still vs probe jet iEta:

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• The average ET( tag jet) in HF region (~20 GeV) is ~10% lower than ET( probe ) on the very first plot ( ~22 GeV at |iEta| <=12 ) .
• What about the shape of the ET(tag) distribution relative to the ET(probe) one:
  • does it shrink?
  • does the peak value move?

Let us see:

Original size: gif , eps

Peak values are collected in the table:

• Nothing good! We still get ~0.6 but not 0.5
• Peak method seems to be quite imprecise.
• Other cuts may be much more important than η < 1 ( e.g. ET(third jet) < 5 is a very stong one!)