Introduction

Chapter 1. Requirement

1. Softwares

CEPCsoft : contains some examples

WHIZARD ：Monte Carlo

ROOT : Analysis

ILCSoft : Contains all softs or frame we need. (etc. Mokka, Marlin, Gear ......)

2. Websites

CEPC WEB : website of CEPC

Indico-CEPC ：you can find some documents here

2020 BESIII Winter School in Changchun ：resources of BES3, whose general analytical frameworks are similar to CEPC.

THCondor : Job submission

Chapter 2. Event Generation

1. Theoretical Analysis

1) channals

Decay channel analysis is the most important step in the whole process. You need to get all the possible decay channels and draw feynman diagram. Provide a source for the background analysis below.

2)...

2. Generator

1) WHIZARD

Detailed information is in whizard_manual (Download in our github page)

NOTES : Version 2.X is recommended.

Here's how to run whizard 2.6 in an IHEP server:

Download and set environment :

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> cd /workfs/bes/$USER/
> cp /afs/ihep.ac.cn/users/l/liaoyp/besfs/load_* ./    # copy env files
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> source load_cepcsoft.sh
> source load_whizard.sh

Then you can execute "whizard".

For example:

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> mkdir HelloWorld
> cd HelloWorld
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> touch hello.sin      # whizard can run .sin(SINDARIN) file
> vim hello.sin
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printf "hello world!"
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> whizard -r hello.sin 
# Then you can see a banner and "hello world!"
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# Also, you can write a simple file named ee.sin
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process ee = e1,E1 => b,B
sqrts = 240 GeV
n_events = 10
sample_format = lhef
simulate (ee)
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# Execute whizard and it will take you several minetes.
# The final result is the desired event file, ee.lhe.
​

Job submission (HTCondor) :

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# All commands related to HepJob are in the following directory, which is recommended to    be added to the user's environment variable PATH:
> export PATH=/afs/ihep.ac.cn/soft/common/sysgroup/hep_job/bin:$PATH
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# Or you can add it in your environment variable file. "./bashrc"
> source ./bashrc
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# But I have to note here:if you only do this, you need source the file each time you enter Linux.
# To avoid, do this: add the following codes in "./bash_profile"
if test -f .bashrc ; then
source .bashrc 
fi
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> hep_sub $yourfile  #submit your jobs
> hep_q -u $USER  # Job status query
> hep_rm $jobID  #remove jobs
# For more details, you can find info in HTCondor.

An job example:

You need submit your job in /besfs/ , otherwise you won't have the permisson to execute the command.

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> touch jobs_bb.sh
> chmod -R 755 jobs_bb.sh
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# Then modify the shell script. 
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#environment
source /besfs/users/liaoyp/load_cepcsoft.sh
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cd /besfs/users/$USERS/TestExample/
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# Simulation
cd sim
exec /cvmfs/cepc.ihep.ac.cn/software/cepcsoft/x86_64-sl6-gcc49/cepcsoft/0.1.0-rc9/Simulation/MokkaC/0.1.1/bin/Mokka simu.macro
cd ..
​
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cd /besfs/users/$USERS/TestExample/
​
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# Reconstruction
cd rec
exec /cvmfs/cepc.ihep.ac.cn/software/cepcsoft/x86_64-sl6-gcc49/cepcsoft/0.1.0-rc9/Framework/Marlin/01-05/bin/Marlin reco.xml
cd ..
​

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#Bb.sin
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#Claim of model
model = SM 
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#Define the mass of particles
me = 0
...
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#Define the alias
alias l = e1:e2:e3
alias L = E1:E2:E3
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#Define the process
process bb = e1, E1 => B,b
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#Compile the process into library
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compile
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?rebuild_library = true
?rebuild_grids = true
​
​
​
#Define the beam
sqrts = 90 GeV
n_events = 1000
beams = e1,E1 => isr,isr
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#Default CEPC setting
$circe2_file = "cepc91.circe"
$circe2_design = "CEPC"
$circe2_polarized = false
isr_alpha = 0.0072993
isr_mass = 0.000511
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#Hadronization and fragmentation
$shower_method = "PYTHIA6"
?ps_isr_active = true
?ps_fsr_active = true
?hadronization_active = true
​
​
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# Integrate the process
integrate(bb)
simulate(bb) {sample_format = stdhep $extension_stdhep = "stdhep"}
# "stdhep" is the most common type of generator file.
​

Or, you can find some existing samples in /cefs/data/stdhep/CEPC91/2fermions

2) Simulation

Generate information of momentum from the generator and pass it on to the detector.

More details of Mokka could be found in MokkaFiles (Download in our github page) and MokkaPage.

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# Download test example.
git clone http://USERNAME@cepcgit.ihep.ac.cn/cepcsoft/TestExample.git
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cd TestExample/sim/   # You need modify the "event.macro" and "simu.macro".
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# simu.macro:
/Mokka/init/lcioFilename ../output/bb_sim.slcio   # rename the output file
# simu.macro can change stdhep into slcio.
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# event.macro:
/generator/generator ../stdhep/xxxxx.stdhep #move you stdhep file to diretory and choose your stdhep.
/run/beamOn 100   #set the number of event simulation
​
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#run simulation
Mokka simu.macro
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#For more details of Mokka, you can:
which Mokka
#Then search for some info there. Have fun! 

Chapter 3. Reconstruction

After simulation, what you get are electronic signals. Then the next step is to change electronic signals to physical information.

In this step, we can choose to the official files directly and set your own value. However, if you are doing research on detector, you need not do that.

More details of Marlin could be found in MarlinPage and his subpage MarlinManual .

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cd TestExample/rec/
#the rec directory includes the script reco.xml for reconstruction. This is a Marlin steer file.
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# You need modify the reco.xml and replace all default file names with your file name.
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Marlin reco.xml
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# The you can find all output files in /output/

After you finish all steps as shows, the data files just contain all simulation data.

So, you need select the cases you want. And this is Analysis Step.

Chapter 4. Analysis

In this step, you need write your own special package to analyze the data you get. And in our research, we recommend you to use C++ for analyze data.

You can find some examples in Analysis Example of CEPCsoft .

Also, some details of applying your package to analysis are in MarlinReco_Manual, which you can read in our github page.

1. Pre-filtering

General steps of pre-screening (Libo Liao, Hangzhou normal university, 2017) :

1. Firstly, some considerable measurement distributions of signal and background are obtained through the real information of monte carlo, and find differences between signal and background distribution. The measurement of observable information must be able to reflect the overall information of the case.
2. Filter the signals by significant difference in the observable measurement distribution.
3. After filter of the data of monte carlo, it is necessary to check the result after reconstruction.

In pre-filtering, the inv mass of e,e- is reduced to a specific interval (in the NU, c=hbar=1 to simplify the calculation, so that the dimensions of energy, momentum and mass are the same) to increase the proportion of the signal case and cut background case.

2. Background Analysis

Several common background deduction methods:

• mass selection

  The number of remaining particles is used for selection. In this process, 3-n (whose specific values have not been analyzed) remaining final state particles are selected.

• observe Jet

  By observing the constant mass peak of jet, speculate that an example of jet may be formed. Taking b quark jet as an example, the data of existing b quark jet was compared with the data, and the similar value b-tag was used for selection.

• secondary vertex

  For long-lived particles, because they don't decay quickly. So it's going to keep moving and it's going to create a subpeak, a secondary vertex. By looking at the secondary vertices, you can subtract some of the background.

• momentum filtering

  It can be deducted by using the small or large transverse momentum of some particles.

3. Signal Selection

After the background deduction, the number of signal cases is reduced step by step, and finally we get the signal cases of the decay channel we need.

Chapter 5. Calculation of Branch ratio

1. The equation of Branch ratio：

Chapter 6. Error Analysis