Overview

This is a tutorial on the simulation and reconstruction software for the Muon Collider, which is based on CLIC's ILCSoft. It has been setup to run on the Snowmass machine login.snowmass21.io.

See also Tutorial Agenda: https://indico.fnal.gov/event/45187/

Monte Carlo samples

The Monte Carlo samples used in this tutorial are stored in the directory:

/collab/project/snowmass21/data/muonc/

Signal samples

The available μ⁻μ⁺ hard-scattering processes are:

1. μ⁻μ⁺ → Hνν̄ → bb̄νν̄ at √s = 1.5 TeV, generated with PYTHIA8;
2. μ⁻μ⁺ → HHνν̄ → bb̄bb̄νν̄ at √s = 3 TeV, generated with WIZARD;
3. μ⁻μ⁺ → bb̄bb̄νν̄ at √s = 3 TeV, generated with WIZARD.

Beam-induced background sample

The Beam-Induced Background (BIB) at 1.5 TeV for one bunch-crossing has been generated by N. Mokhov with MARS15.

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All the BIB has been split in 16 files which contain a total of 2993 pseudo-events; this is an artificial subdivision used to speed up the simulation.

Simulation and reconstruction code

The Muon Collider simulation and reconstruction code is available in a singularity container on CERN's cvmfs:

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N.B.: A docker container is also available at this link.

Steering files and ROOT macros

All the configuration files and ROOT macros used in this tutorial are available in the github repository:

https://github.com/MuonColliderSoft/MuC-Tutorial.git

Tutorial setup

1 - Log into the login.snowmass.io machine:

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cd  MuC-Tutorial && git checkout v2.0

1 - Running the simulation and reconstruction

Simulation step

The simulation program is part of the DD4Hep package, which uses as main components the ROOT geometry package, which is used for construction and visualization of geometry, and the Geant4 simulation toolkit, which can be interfaced via DD4hep to perform detector simulation in complex detector designs.

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Use the output of the command ddsim -h to see all the other parameters that you can set.

Digitization/reconstruction step

This second step is done using the command: Marlin: Modular Analysis and Reconstruction for the LINear Collider. As described in the main github page of the program: the idea is that every computing task is implemented as a processor (module) that analyses data in an LCEvent and creates additional output collections that are added to the event. The framework allows to define the processors (and their order) that are executed at runtime in a simple steering file. Via the steering file you can also define named parameters (string, float, int - single and arrays) for every processor as well as for the global scope. By using the framework users don't have to write any code that deals with the IO they simply write processors with defined callbacks, i.e. init(), processRunHeader(), processEvent(), end().

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the plot of the invariant mass of jet pair associated to Higgs with highest pT is shown

Some useful tools

The default output format of the reconstruction package is an LCIO (Linear Collider I/O)  file. You can inspect these files using these commands:

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This command produces the ROOT file: lctuple_example.root

Event display

To display events use the package CEDViewer:

ced2go -d /opt/ilcsoft/muonc/detector-simulation/geometries/MuColl_v1/MuColl_v1.xml Output_REC.slcio

2 - A look at the beam-induced background (BIB)

To get acquainted with the beam-induced background (BIB) two ROOT files have been prepared and are available in /data/ntuples/BIB (within the singularity container):

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https://github.com/MuonColliderSoft/MuC-Tutorial/blob/master/tutorial/2-BIB/readme.txt

3 - Overlaying the BIB to signals

To overlay background events from an additional set of LCIO files you can use the Overlay processor. You can list all files of the BIB and then decide which quota (i.e. the number of artificial pseudo events) to use. You can also decide a priori a set of time cuts to apply to each detector. Remember that  signal and BIB are overlaid in the digitization step so the signal and BIB samples must be generated and simulated prior to overlaying.

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In this way you can compare the track pt resolution with and without the BIB.

Advanced topics

Modifying an existing processor

If you want to modify an existing processor you can follow these simple steps:

1. clone the repository of the processor in your working directory. Look into the following repositories:
   1. Official ILCSoft repository
   2. Official Muon Collider repository
2. modify it
3. compile it following these steps:
   1. create a BUILD directory separated from the sources
      1. mkdir BUILD; cd BUILD
   2. create the make files:
      1. cmake -C $ILCSOFT/ILCSoft.cmake -DBOOST_INCLUDEDIR=/usr/include/boost173 -DBOOST_LIBRARYDIR=/usr/lib64/boost173 ../
   3. compile it as usual (this create a library under the lib directory)
      1. make
4. modify the MARLIN_DLL variable: you have to remove the old library path and add the new ones (this variable can not store duplicate libraries)

Creating a new processor

A script has been prepared to easily create a new processor, for details see here. 

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