Setup Madgraph to use the CLICdet Delphes card

The CLICdet card is a part of the central git repository, but the card and some new implementations in the Delphes code itself are not yet included in the Delphes version shipped by Madgraph (install Delphes) (status April 2018). The following instructions show how to use Madgraph with the Delphes code which includes the new CLICdet card and all necessary implementations.

  • Set up the software environment as you would for Madgraph (ROOT etc)
e.g. on lxplus:
source /cvmfs/clicdp.cern.ch/iLCSoft/builds/current/CI_gcc/init_ilcsoft.sh
The card has been tested with ROOT 6.08.00.

  • Work in some directory, whose absolute path is meant by
    <BASEDIR>
    in the following instructions

  • Clone the Delphes repo from github:

cd <BASEDIR>
git clone https://github.com/delphes/delphes.git
cd delphes/
make

tar -xvzf MG5_aMC_v2.6.1.tar.gz
cd MG5_aMC_v2_6_1/

  • Modify the configuration file input/mg5_configuration.txt : The line
 # delphes_path = ./Delphes 
needs to be changed to
delphes_path = <BASEDIR>/delphes
(note that the # in the beginning must be removed)

  • Start Madgraph with
cd MG5_aMC_v2_6_1/
./bin/mg5_aMC
to check that it is taking the right delphes:
>display options delphes_path

  • Copy the respective delphes cards to the Template directory. There are 3 cards for the 3 energy stages of CLIC. Please choose the one appropriate for your scenario:
Stage Energy
Stage1 380 (350) GeV
Stage2 1.5 (1.4) TeV
Stage3 3 TeV

cp <BASEDIR>/delphes/cards/delphes_card_CLICdet_StageN.tcl Template/Common/Cards/delphes_card.dat
and
cp -r <BASEDIR>/delphes/cards/CLIC/ Template/Common/Cards/
where StageN can be Stage1, Stage2, or Stage3 depending on the center-of-mass energy as indicated in the table.

  • If you use the LHCO file format in your analysis chain: Decide which jet clustering parameters to use. For advice, check #AWordAboutJets below. Once you know which N and R values you like, change the corresponding line in the TreeWriter module at the end of the card Template/Common/Cards/delphes_card.dat, e.g. if you decide your analysis needs N=4 and R=1.0 jets:
add Branch FastJetFinderVLC_R10_N4/VLCjetsR10N4 VLCjetR10N4 Jet
should be modified to:
add Branch FastJetFinderVLC_R10_N4/VLCjetsR10N4 Jet Jet

  • Install Pythia (if you have not already)
>install pythia8
  • Generate your favorite process and its output
>generate e+ e- > h z > b b~ j j
>output PROCESS

  • Exit the MG5 prompt and proceed as usual
cd PROCESS
./bin/generate_events EVENTDIR

when prompted for it, apply:

>detector=ON

  • A root file tag_1_delphes_events.root can be found in the Events/EVENTDIR folder.

  • When the Delphes code has changed, change to the < BASEDIR >/delphes/ directory and do
git pull 
make

A word about jets

At linear colliders, rather large cone size parameters (R) can be used for jet algorithms, regardless if using kt or VLC etc. This is due to the lower levels of soft interaction background (pile-up).

However, it implies that more often than for lower R jets, the jets have a substructure of lower R jets, i.e. two jets are merged. At analysis level, this is usually crucial information, e.g. for suppression of backgrounds with a slightly different jet multiplicity or in order to use the correct objects for invariant masses.

Therefore, jet clustering is often run in "exclusive mode" (see FastJet manual), usually with a fixed number of jets. This forces the algorithm to stop when a certain number of jets has been clustered, thus revealing the substructure information directly.

In order to accomodate for a range of jet multiplicities that might be useful for the analyses conducted here, the Delphes card for CLICdet contains N=2,3,4,5,6 jets algorithms with 5 different R parameter values. (Of course more can be added). The user should pick the one most suitable for their analysis. As a rule of thumb, N should of course correspond to the number of partons expected in the tree level final state. R can be large for low center-of-mass and slightly reduced for higher center-of-mass due to higher levels of background.

Warning, important Upshot: Use large R radii, e.g. 1.2 or 1.5 for Stage 1, 1.0 or 1.2 for Stage 2, and 0.7 or 1.0 for Stage 3. To avoid loosing the jet substructure through the large radius, use exclusive Njets clustering

Flavor tagging

B-tagging is implemented in the card with 3 working points (WP), which tag 50%, 70%, and 90% of all b-quark-initiated jets, respectively. The corresponding mis-tagging rates are implemented in the CLICdet card. Delphes uses different bits to store the b-tagging information in the following way, where bit 0 is the tight WP with 50% tagging efficiency, bit 1 is the medium WP with 70% efficiency, and bit 2 is the loose WP with 90% b-tagging efficiency. This leads to the following combinations:

BTag value 7 6 5 4 3 2 1 0
BTag binary 111 110 101 100 011 010 001 000
(bit 0) & BTag T F T F T F T F
(bit 1) & BTag T T F F T T F F
(bit 2) & BTag T T T T F F F F

In summary, to require loosely b-tagged jets, please choose BTag>=4; for medium b-tagged jets, require the BTag to be one among 2, 3, 6, and 7, and for the tight WP the BTag should be 1, 3, 5 or 7.

Warning, important this does not correspond to the PGS4-based LHCO format defaults.

Taking into account the effect of gamma gamma -> hadrons background

The effect from gamma gamma -> hadrons background is more severe at the high energy stages, Stage2 and Stage3. To account for its effects, a jet energy smearing and scaling is applied in those two cards. The branches with these effects applied are then named
JES_VLCjetR<r>N<njets>
in the resulting root file.

Contact

Ulrike Schnoor ulrike.schnoor@cern.ch

-- UlrikeSchnoorSecondary - 2018-02-15

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Topic revision: r14 - 2018-04-18 - UlrikeSchnoor
 
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