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Merge pull request #64 from eic/documentation-for-understanding-background-mixed-files
Create some guidelines for understanding background samples
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‎_resources/background_mixed_samples.md

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---
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title: Mixed Signal and Background Samples
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description: background_mixed_samples
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name: background_mixed_samples
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layout: default
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---
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{% include layouts/title.md %}
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---
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# Case 1: At least 1 Signal in Every Event of a Run
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A run is a collection of events and each event represents a 2000 nano second long integration frame.
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## Representation of a "Run" with 5 "Events"
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If we assume a signal frequency of 500 kHz, each event contains at least 1 signal contribution. The background contributions get allocated per event based on their sampling frequency. Processes with less than 500 kHz sampling frequency are not guaranteed a contribution in every event.
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| **Event** | **signal** | **synrad** | **ebrems** | **etouschek** | **ecoloumb** | **p.b.gas**|
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| ----------- | ----------- | -----------| --------- | ------------ | ----------- | ----------- |
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| **Event 1** | 🔴 | ⚪⚪⚪⚪ | 🔵 | | | |
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| **Event 2** | 🔴 | ⚪⚪⚪⚪ | | | 🟡 | 🟣 |
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| **Event 3** | 🔴 | ⚪⚪⚪ | | 🟢 | | |
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| **Event 4** | 🔴 | ⚪⚪⚪ | 🔵 | | | 🟣 |
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| **Event 5** | 🔴 | ⚪⚪⚪ ⚪ | 🔵 | | | |
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## Legend
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| Symbol | Process | Description | Sampling Frequency (kHz) | Status Code Shift |
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|--------|---------|-------------| ------------------| --------------------- |
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| 🔴 | **signal** | DIS NC 18x275 Q²>1 (Deep inelastic scattering neutral current) | 500 | 0
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| ⚪ | **synrad** | Synchrotron Radiation | 14000 | 2000
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| 🔵 | **ebrems** | Electron bremsstrahlung radiation | 316.94 | 3000
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| 🟢 | **etouschek** | Electron Touschek scattering (intrabeam scattering) | 1.3 | 4000
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| 🟡 | **ecoulomb** | Electron Coulomb scattering processes | 0.72 | 5000
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| 🟣 | **p.b.gas** | Proton beam gas interactions | 22.5 | 6000
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N.B.: The sampling frequencies in this example are taken from the [ePIC Background Wiki Page](https://wiki.bnl.gov/EPIC/index.php?title=Background)
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## Location of files
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**Simulation Output**
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```
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root://dtn-eic.jlab.org//volatile/eic/EPIC/FULL/25.06.1/epic_craterlake/Bkg_1SignalPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/DIS/NC/18x275/minQ2=1/
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```
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**Reconstructed Output**
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```
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root://dtn-eic.jlab.org//volatile/eic/EPIC/RECO/25.06.1/epic_craterlake/Bkg_1SignalPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/DIS/NC/18x275/minQ2=1/
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```
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N.B.: Increment the campaign tag (25.06.1) to get the latest campaigns. Reconstructed output is available for every campaign but simulation output is not always preserved to save storage resources.
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---
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---
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# Case 2: Realistic Signal Contribution Per Event of a Run
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A run is a collection of events and each event represents a 2000 nano second long integration frame. For the SIDIS pythia6 18x275 Q²<1, the signal frequency is 83 kHz which would result in 1 signal contribution every ~5 events.
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## Representation of a "Run" with 5 "Events"
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| **Event** | **signal** | **synrad** | **ebrems** | **etouschek** | **ecoloumb** | **p.b.gas**|
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| ----------- | ----------- | -----------| --------- | ------------ | ----------- | ----------- |
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| **Event 1** | | ⚪⚪⚪⚪ | 🔵 | | | |
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| **Event 2** | | ⚪⚪⚪⚪ | | | 🟡 | 🟣 |
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| **Event 3** | 🔴 | ⚪⚪⚪ | | 🟢 | | |
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| **Event 4** | | ⚪⚪⚪ | 🔵 | | | 🟣 |
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| **Event 5** | | ⚪⚪⚪ ⚪ | 🔵 | | | |
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## Legend
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| Symbol | Process | Description | Sampling Frequency (kHz) | Status Code Shift |
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|--------|---------|-------------| ------------------| --------------------- |
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| 🔴 | **signal** | SIDIS pythia6 18x275 Q²<1 (Deep inelastic scattering neutral current) | 500 | 0
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| ⚪ | **synrad** | Synchrotron Radiation | 14000 | 2000
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| 🔵 | **ebrems** | Electron bremsstrahlung radiation | 316.94 | 3000
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| 🟢 | **etouschek** | Electron Touschek scattering (intrabeam scattering) | 1.3 | 4000
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| 🟡 | **ecoulomb** | Electron Coulomb scattering processes | 0.72 | 5000
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| 🟣 | **p.b.gas** | Proton beam gas interactions | 22.5 | 6000
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## Location of files
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**Simulation Output**
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```
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root://dtn-eic.jlab.org//volatile/eic/EPIC/FULL/25.06.1/epic_craterlake/Bkg_RealisticSignalPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/SIDIS/pythia6-eic/1.0.0/18x275/q2_0to1
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```
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**Reconstructed Output**
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```
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root://dtn-eic.jlab.org//volatile/eic/EPIC/RECO/25.06.1/epic_craterlake/Bkg_RealisticSignalPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/SIDIS/pythia6-eic/1.0.0/18x275/q2_0to1
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```
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N.B.: Increment the campaign tag (25.06.1) to get the latest campaigns. Reconstructed output is available for every campaign but simulation output is not always preserved to save storage resources.
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---
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---
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# Case 3: Only Background Contributions Per Event of a Run
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A run is a collection of events and each event represents a 2000 nano second long integration frame. There are no signal contributions in any of the events.
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## Representation of a "Run" with 5 "Events"
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| **Event** | **signal** | **synrad** | **ebrems** | **etouschek** | **ecoloumb** | **p.b.gas**|
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| ----------- | ----------- | -----------| --------- | ------------ | ----------- | ----------- |
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| **Event 1** | | ⚪⚪⚪⚪ | 🔵 | | | |
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| **Event 2** | | ⚪⚪⚪⚪ | | | 🟡 | 🟣 |
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| **Event 3** | | ⚪⚪⚪ | | 🟢 | | |
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| **Event 4** | | ⚪⚪⚪ | 🔵 | | | 🟣 |
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| **Event 5** | | ⚪⚪⚪ ⚪ | 🔵 | | | |
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## Legend
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| Symbol | Process | Description | Sampling Frequency (kHz) | Status Code Shift |
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|--------|---------|-------------| ------------------| --------------------- |
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| ⚪ | **synrad** | Synchrotron Radiation | 14000 | 2000
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| 🔵 | **ebrems** | Electron bremsstrahlung radiation | 316.94 | 3000
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| 🟢 | **etouschek** | Electron Touschek scattering (intrabeam scattering) | 1.3 | 4000
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| 🟡 | **ecoulomb** | Electron Coulomb scattering processes | 0.72 | 5000
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| 🟣 | **p.b.gas** | Proton beam gas interactions | 22.5 | 6000
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## Location of files
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**Simulation Output**
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```
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root://dtn-eic.jlab.org//volatile/eic/EPIC/FULL/25.06.1/epic_craterlake/Bkg_OnlyPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/BACKGROUNDS/BEAMGAS/proton/pythia8.306-1.0/275GeV
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```
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**Reconstructed Output**
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```
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root://dtn-eic.jlab.org//volatile/eic/EPIC/RECO/25.06.1/epic_craterlake/Bkg_OnlyPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/BACKGROUNDS/BEAMGAS/proton/pythia8.306-1.0/275GeV
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```
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N.B.: Increment the campaign tag (25.06.1) to get the latest campaigns. Reconstructed output is available for every campaign but simulation output is not always preserved to save storage resources.
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---
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# Analyzing the output
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It's possible to separate the contribution from signal and background sources that are simulated by using cuts on the [status codes](https://arxiv.org/pdf/1912.08005.pdf) which are represented by the MCParticles.generatorStatus in the edm4hep output file.
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| Status code | Meaning | Usage |
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|-------------|-----------------------------|----------------------------------|
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| 0 | Not defined (null entry) | Not a meaningful status |
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| 1 | Undecayed physical particle | Recommended for all cases |
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| 2 | Decayed physical particle | Recommended for all cases |
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| 3 | Documentation line | Often used to indicate in/out particles in hard process |
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| 4 | Incoming beam particle | Recommended for all cases |
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| 5–10 | Reserved for future standards | Should not be used |
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| 11–200 | Generator-dependent | For generator usage |
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| 201– | Simulation-dependent | For simulation software usage |
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N.B.: By default, DD4hep takes primary particles (status code 1, 2)
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and also custom status code provided with
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```
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--physics.alternativeStableStatuses="1001 2001 …" --physics.alternativeDecayStatuses="xxxx yyy "
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```
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**Example: Minimal ROOT script to view counts of processes by status codes**
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```
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TChain *T=new TChain("events");
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T->Add("root://dtn-eic.jlab.org//volatile/eic/EPIC/RECO/25.06.1/epic_craterlake/Bkg_1SignalPer2usFrame/Synrad_18GeV_Vac_10000Ahr_Runtime_10ms_Egas_All_18GeV_Hgas_275GeV/DIS/NC/18x275/minQ2=1/*010*");
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T->Draw("MCParticles.generatorStatus", "MCParticles.generatorStatus>0");
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gPad->SetLogy();
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```
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<img width="488" height="402" alt="image" src="https://github.com/user-attachments/assets/040ccb77-e18c-4311-9a71-9a9a8ee2646a" />
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**Example: Charged Primary Particle Distribution in Eta**
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<img width="488" height="402" alt="image" src="https://github.com/user-attachments/assets/cd439c91-38b4-4df8-adfe-aa1f2ae66a61" />
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