Run 6 Data / Monte Carlo Comparison

Partonic Cross Sections

xsec = {
'3_4' : 1.302,
'4_5' : 3.158E-01,
'5_7' : 1.372E-01,
'7_9' : 2.290E-02,
'9_11' : 5.495E-03,
'11_15' : 2.220E-03,
'15_25' : 3.907E-04,
'25_35' : 1.074E-05,
'35_45' : 5.000E-07,
'45_55' : 2.857E-08,
'55_65' : 1.451E-09

Normalization Procedure

I calculated the integrated luminosity for my dataset (5.43 pb^-1) and scaled all event- and jet-level histograms by that amount (in mb^-1 to match the partonic xsec numbers above). For the track histograms I added a multiplicative factor of 0.82 to account for imperfect PID efficiency in the data. I neglected PID contamination.

Event / Jet Comparisons

(General note — the ratio underneath each histogram is (data-simu)/data, and the range is -1..1. Apologies for the tiny axis labeling).

The first thing you’ll notice here is that my calculated normalization factor seems low by about ~30% for these comparisons. It does much better when comparing track quantities.

Inclusive Track Kinematics

The agreement over pT/η/ϕ is good here. There’s a suppression of high pT π- that you’ll see repeated throughout this page.

The differences in the nHitsFit and global DCA histograms might indicate that track reconstruction is cleaner/more efficient in the simulations than in the data.

Just a reminder that dE/dx information is not to be trusted in the simulations …

and finally, here’s a comparison of z-vertex distributions incremented per-pion instead of per-event. Remember, the data distribution uses a BBC timebin 6-9 cut, but the simulations apply no explicit vertex cut:

Comparison of Near and Away-side

These first four plots show the number of reconstructed charged pions of a given charge sign per event, where “near” means within deltaR of 0.4 of the trigger jet axis, and “away” means deltaR > 1.5. In both cases the simulations overestimate the charged pion multiplicity, but the effect is more pronounced on the near side.

Next comes inclusive track pT for each side. The near-side simulations show some additional suppression (~20%) of high pT pions relative to the data. The away-side has better agreement, although the general suppression of high pT π- is still there.

Finally I restricted my analysis to the highest pT charged pion on the near side and the highest pT charged pion on the away-side in each event … the agreement stays basically the same.

Kinematics Using Leading Pion on Away-side

The next three sets of histograms show the data / Monte Carlo agreement for different definitions of z. The definitions are

2: ratio pT(π)/pT(trigger jet), only use highest pT pion per event with Δϕ > 2.0 relative to trigger jet 3: fraction of non-trigger jet momentum carried by pion, same cuts on pion as 2 4: ratio pT(π)/pT(trigger jet), use multiple pions per event, but only if they fall into different histogram bins. Errors are still calculated using √N.

The high pT π- suppression we’ve been observing manifests itself here in the form of high z suppression, but the z>0.25 agreement for π+ using methods 2 and 4 is really excellent. There’s a drop-off at low z in the simulations that I can’t readily explain.

Now, using the cuts specified for z_away2, here are distributions for η, global DCA, and # of fit points. The MC statistics are getting thin, but we can see a clear difference between these η distributions and the inclusive ones: