Motivation:

Run11 Au+Au 200 GeV has a period of runs with maximum 10% lower refmult than the rest of run. How would it affect our Dijet Aj? (drupal.star.bnl.gov/STAR/blog/yili/qa-1-run11-auau-200-gev-2015-07-26)

More general question, how does the Aj change over refmult?

Dataset:

Au+Au 200 GeV run11

trigger:

NPE_18 (350503, 350513)

Centrality 0-20% from StRefMultCorrr

Method:

fastjet 
anti-kt algorithm
jetmedian for background subtruction
Constitutients cuts pT>2 GeV/c to find dijet pair with leading jet pT>20 GeV/c and subleading jet pT>10 GeV/c. Rerun the jet finding with particles pT>0.2 GeV/c for Aj calculation.

The code provided by Kolja Kauder github.com/kkauder/BasicAj branch master (~ Apr 20, 2015).

Result:

1.bad run period (low refmult)
refmult run dependence:

 
The dip runid is 12138081~ 12145020 (May 18th - 25th)

Dijet pair runid:

We still find *all* the dijet pair in the bad run. It was 1/5 data sample and we find 1/5 dijet pairs there.

bad run (low refmult period) vs good run (the rest)

No dramastical difference

2. Aj refmult dependence (for good run period)

default 0-20%: 

Cut on refmutl >400

Aj comparison

 No clear difference either.

However, If we plot Aj vs refmut:

The linear fit range is 270<refmult<500 to maximumize the statistics usage.
If we rebin:

Clearly Aj depends on refmult.