Motivation:
Embedding technique is one of the method to study the detector efficiency. In case of PMD, embedding technique is used to estimate the number of photons detected, to reject the charge particles detected on the preshower plane. We also try to study the spatial distribution of photons in the forward rapidity using this technique.
1. Obtain the embedding efficiency and embedding purity as a function of pseudo-rapidity.
2. Study the energy and multiplicity dependence of photons detection efficiency using this method.
Go to Top of the pageThe Embedding Procedures:
Basically embedding is like merging a big event (hijing or pythia) with a small event (a single tagged photon or hadron) and then running the whole reconstruction chain. At the end of the chain one has to find out if the tagged particle remain or got lost in embedding.
We have embedded one photon or hadron at a time, p_t is selected by making the p-t distribution of the parent events (pythia, hijing etc.) and then generating random numbers according to that distribution, no cutoff is applied, so it simulates the actual cases closely. The eta and phi are varied randomly within our PMD acceptance.
We embeds one photon to a pythia/hijing event, the efficiency is estimated as the ratio of successes to detect the embedded photon cluster to the total number of embedded attempts.
We embeds one hadron (Pi- or Pi+) to a pythia/hijing event, the hadron impurity is estimated as the ratio of the hadron clusters formed (above Photon-Hadron threshold) to the total number of embedded attempts.
Threshold values in ADC used for photon hadron discrimination in pre-shower detector is: 35 ADC = 1 MPV.
Go to Top of the pagePythia: pp @ 7 TeV
Parameters used:
| Generator Type | Energy or Multiplicity | Detectors | No. of Events | Eta Range | Phi Range | Other parameters |
| Pythia | pp @ 7TeV | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 5000 | -8.0 to 8.0 | 0.0 to 360. (full) | Minimum Bias pythia, Pi0 decay ON |
| Single particle Photon | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 100,000 | 2.3 to 4.1 | 0.0 to 360. (full) | - |
| Single particle Pi- | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 100,000 | 2.3 to 4.1 | 0.0 to 360. (full) | - |
| Two particle - Photon & Pi- | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 5,000 | 2.3 to 4.1 | 0.0 to 360. (full) | - |
We have embedded a single particle (photon/hadron) in a pythia event. We embed first 5K single particle in 5K pythia events and use the same 5K pythia events to embed the next 5K single particle and so on. So, total we have 100K different embedded events. Embedding is done in the hits level. Then, we do digitisation --> run full reconstructions chain. After association we look for clusters formed by the embedded particle (photon/hadron).
The figure below shows the charge particle dN/deta distribution using 5K pythia events for pp @ 7TeV.
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1. Single Particle Photon Generator:
Single Particle Box Generator is used to generate single photon in the PMD eta region (2.3 to 4.1). The figures below show the Pt, Eta and Phi distribution of generated photons. Eta distribution is decreasing as the function of eta, we have specially generated single photons in the 3.0 to 4.1 eta range. Because of this reason there is peak at 3.0 eta. In total we have generated 100K events.
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Results after embedding a photon in a pythia event:
Efficiency using embedding technique:
Efficiency is defined as the ratio of detecting embedded photons to the total number of incident embedded photon in the eta ring of size 0.2. To calculate efficiency we have taken only the primary cluster.
Efficiency = Eff_{gamma det} = N_{gamma det} / N_{gamm inc}
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We compare efficiency as a function of eta after applying various cuts:
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Split Cluster Impurity:
Following plots show the fraction of split clusters formed by the embedded photon. Split Impurity fraction (Number of split clusters to the incident photons) is plotted as the function of eta. 1MPV is equal to 35 ADC value.
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2. Single Particle Pi- Generator:
Single Particle Box Generator is used to throw a charge particle in the PMD eta region (2.3 to 4.1). We have generated Pi- particle. The figures below show the Pt, Eta and Phi distribution of generated pi-. Eta distribution is decreasing as the function of eta, we have specially generated pi- in 3.0 to 4.1 eta range. Because of this reason there is peak at 3.0 eta. In total we have generated 100K events.
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Results after embedding a hadron (pi-) in a pythia event:
Charge Impurity fraction:
In the plots below charge impurity fraction is defined as the ratio of clusters formed by the embedded pi- to the total number of incident embedded pi- in the eta ring of size 0.2. 1MPV is equal to 35 ADC value.
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Purity using Embedding technique:
Purity is defined as the ratio of total number of detected embedded photons to the total number of clusters formed by the embedded photon and charge particle. To calculate purity we have used the following method:
We have taken equal number of trials (100K events each) to embed single photon and single charge particle in an event.
Purity = N_{gamma det} / N_{gamma like}
N_{gamma like} = N_{gamma det} + N_{split} + N_{charge}
N_{gamma like}/No. of trials = Eff_{gamma det} + Impurity_{split} + Impurity_{charge}
Purity = (N_{gamma det}/No. of trials) / (N_{gamma like}/No. of trials)
Purity = Eff_{gamma det} / (Eff_{gamma det} + Impurity_{split} + Impurity_{charge})
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We compare purity as a function of eta after applying various cuts:
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3. Two Particles (Photon + Pi-) Generator:
Box Generator is used to throw one photon and one pi- particle in an event on the PMD. The figures below show the Pt, Eta and Phi distribution of generated photon and pi-. In total we have generated 5K events.
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Results after embedding a photon AND pi- in a pythia event:
Efficiency:
Efficiency is defined as the ratio of detecting embedded photons to the total number of incident embedded photon in the eta ring of size 0.2. To calculate efficiency we have taken only the primary cluster.
Efficiency = N_{gamma det} / N_{gamma inc}
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- Go to Top of the page
Purity:
Purity is defined as the ratio of detected embedded photons to the total number of clusters formed by the embedded photon and embedded pi- in the eta ring of size 0.2.
Purity = N_{gamma det} / N_{gamma like}
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Parametrised Hijing : Nprimary = 2000
Parameters used:
| Generator Type | Energy or Multiplicity | Detectors | No. of Events | Eta Range | Phi Range | Other parameters |
| Parametrised Hijing | dN/deta = 2000 at mid-rapidity | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 1000 | 0.0 to 8.0 | 0.0 to 360. (full) | Pi0 decay ON |
| Single particle Photon | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 50,000 | 2.3 to 4.1 | 0.0 to 360. (full) | - |
| Single particle Pi- | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 50,000 | 2.3 to 3.7 | 0.0 to 360. (full) | - |
We have embedded a single particle (photon/hadron) in a parametrised Hijing event. We embed first 1000 single particle in 1000 paraHijing events, then next 1000 single particle in the same 1000 paraHijing events and so on. Total we have 50K different embedded events each for photon and charge particle. Embedding is done in the hits level. Then, we do digitisation --> run full reconstructions chain. After association we look for clusters formed by the embedded particle (photon/hadron).
The figure below shows the eta distribution of produced charge particles in 1000 parametrised hijing events. |
The below plots shows the eta distribution of produced charge particles and produced photons in PMD eta region.
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1. Single Particle Photon Generator:
The figure below shows the Pt and Eta distribution of generated single photon in the PMD region for 50K events.
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Results after embedding a photon in a parametrised Hijing event (p = 2000):
Efficiency:
Efficiency is defined as the ratio of detecting embedded photons to the total number of incident embedded photon in the eta ring of size 0.2. 1MPV is equal to 35 ADC value.
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We compare efficiency as a function of eta after applying various cuts:
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Split Cluster Impurity:
Following plots show the fraction of split clusters formed by the embedded photon. Split Impurity fraction (Number of split clusters to the incident photons) is plotted as the function of eta. 1MPV is equal to 35 ADC value.
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2. Single Particle Pi- Generator:
The figure below shows the Pt and Eta distribution of generated single pi- in the PMD region for 20K events.
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Results after embedding a hadron (pi-) in a parametrised hijing event (p = 2000):
Charge Impurity fraction:
Charge impurity fraction is defined as the ratio of clusters formed by the embedded pi- to the total number of incident (embedded) pi-. 1MPV is equal to 35 ADC value.
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Purity using Embedding technique (p = 2000):
Purity is defined as the ratio of total number of detected embedded photons to the total number of clusters formed by the embedded photon and charge particle. To calculate purity we have used the following method:
We have taken equal number of trials (20K events each) to embed single photon and single charge particle in an event.
Purity = Eff_{gamma det} / (Eff_{gamma det} + Impurity_{split} + Impurity_{charge})
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We compare purity as a function of eta after applying various cuts:
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Parametrised Hijing : Nprimary = 8000
Parameters used:
| Generator Type | Energy or Multiplicity | Detectors | No. of Events | Eta Range | Phi Range | Other parameters |
| Parametrised Hijing | dN/deta = 8000 at mid-rapidity | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 100 | 1.5 to 8.0 | 0.0 to 360. (full) | Pi0 decay ON |
| Single particle Photon | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 5,000 | 2.3 to 4.1 | 0.0 to 360. (full) | - |
| Single particle Pi- | pt from random number | PMD, TPC, ITS, V0, T0, Pipe, FMD, Hall, Dipole | 5,000 | 2.3 to 3.7 | 0.0 to 360. (full) | - |
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Results after embedding a photon in a parametrised Hijing event (p = 8000):
Efficiency:
Efficiency is defined as the ratio of detecting embedded photons to the total number of incident embedded photon in the eta ring of size 0.2. 1MPV is equal to 35 ADC value.
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Split Cluster Impurity:
Following plots show the fraction of split clusters formed by the embedded photon. Split Impurity fraction (Number of split clusters to the incident photons) is plotted as the function of eta. 1MPV is equal to 35 ADC value.
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Results after embedding a hadron (pi-) in a parametrised hijing event (p = 8000):
Charge Impurity fraction:
Charge impurity fraction is defined as the ratio of clusters formed by the embedded pi- to the total number of incident (embedded) pi-. 1MPV is equal to 35 ADC value.
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Results:
Efficiency and Purity of pythia and paraHijing events(p = 2000) using embedding technique
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Efficiency as function of eta for different multiplicity
In figures below we the X-Y display of the hits on preshower plane at digits level. The left panel shows the X-Y display for pythia, parametrised hijing with no. of primary particles as 2000 and parametrised hijing with no. of primary particles as 8000. The right panel shows the efficiency using different generators for NO MPV cuts. It can be seen clearly from the figures that Embedding Technique works good for the low multiplicty events or for pp collisions only. As we go to the heavy ion collision, the efficiency to detect photons using Embedding Technique decreases and goes to zero.
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