Jet substructure analysis is an important tool for extractions of the significant signal in jets and the reconstruction of characteristic jet mass and shape variables, and the e.g. internal flow inside jets, for e.g. searches. This project tries to evaluate various substructure techniques and configurations with respect to their effectiveness in the suppression of pile-up for given observables, and the enhancement of signal-to-background ratios.

While the exact conditions at LHC are not yet know, we expect at least 30 but likely more (more than 200 is possible) pile-up interactions in each recorded event. The center-of-mass energy is set to $ \sqrt{s} = 13 {\rm\ TeV} $. }

Minimum bias samples have been produced with Pythia8 using the tune 4C. The samples include single, double and non-diffractive interactions at the default mix. Particles are generated without any phase space restriction. The generating code fills a ROOT tuple, the structure of which is documented in the BOOST2012 TWiki.

The generating code can be found in the file pythiasoftqcdall.cc.txt. The example Makefile is in the file makefile.txt. This is highly taylored for the setup on my machine, but should give you an idea.

The following signal samples are discussed:

1. Final states with boosted objects:
   1. boosted top in $t\bar{t}$ ($\hat{p}_{T} > 200(450) {\rm\ GeV}$); full hadronic ok;
   2. inclusive jets in similar phase space as $t\bar{t}$;
   3. $HZ\to b\bar{b} \nu\nu$ with $H(125)$; boosted $b\bar{b}$ system and large $E_{\rm T}^{\rm miss}$;
2. VBS/VBF with (not boosted) tag jets
   1. WW/ZZ/WZ continuum, high $M_{WW/ZZ/WZ} > 1 {\rm\ TeV}$ (may be not possible in Pythia8 - maybe have to go for a high mass Higgs-like particle?)
   2. VBF Higgs $H(125)$, $H\to\gamma\gamma$

The following configurations for the (average) number of pile-up interactions $\langle\mu\rangle$ are suggested $$ \langle\mu\rangle = \{ 30, 60, 120, 240 \} $$ The actual number of pile-up interactions added to the signal event is taken from a Poisson distribution around $\langle\mu\rangle$.

Pile-up can be added dynamically using this software. The main concept here is that the ROOT based raw data is converted into an Event obejct containing lists of PseudoJets (from Fastjet) representing

• the total particle (hadron) level event (signal + pile-up)
• the particle (hadron) level signal event
• the particle (hadron) level pile-up event

The code is not very convenient to use in this version. After unpacking with

tar zxvf <archive>.tar.gz

on most systems I expect a

make all

should work to compile the library and the example in anal02.C. For implementing your own analysis, please check the anal02.C and Zprime_Py8::analyze(Event& rEvt) (your playground) in Zprime_Py8.C as examples. The program supports a few command line arguments

anal02.exe --help --mu=<mu> --nevts=<number of (signal) events>
           --sigflist=<text file with list of signal files>
           --puflist=<text file with list of pile-up files>

Some hints:

• –help prints a brief usage instruction (which I think is not up-to-date, so please ignore!)
• –mu=<mu> expects the number of interactions per event. if <mu> < 0, exactly |<mu>| interactions are collected into one event. <mu> > 0 means a Poisson-distributed number of pile-up interactions will be collected from the pile-up (minimum bias) event samples.
  • if you specify both signal and pile-up input, <mu> should be the number of pile-up events to be added to one signal event