At Large Hadron Collider (LHC) in CERN, particles ranging from protons to heavy ions are accelerated through magnetic and electric field to reach high speeds. These energetic particles are collided at four locations corresponding to the positions of four particle detectors (ATLAS, CMS, ALICE and LHCb) and the result of such collisions is different types of exotic particles! Particle Detectors
After producing these exotic particles at LHC, the next step is to detect them using different detectors. Each of four detectors mentioned above has its own unique design which is based on specific detector physics. ATLAS experiment, one of the largest detectors ever made, is one the detectors at LHC designed to detect different particles from the Higgs boson to extra dimensions and particles that could make up dark matter.
The detector consists of six detecting subsystems wrapped around the collision point and it can record the trajectory, momentum and energy of the produced particles. In the inner part of the ATLAS, lies a silicon strip detector system (SCT). These strip sensors are AC-coupled with n-type implants in a p-type silicon bulk (n-in-p).
Educational Alibava System for Particle Detectors
The Educational Alibava System (EASy) is a complete instrumentation system dedicated to Silicon micro-strip Radiation Detectors. It is based on the Alibava System (ALIBAVA Collaboration) largely used within the CERN community to test micro-strip detectors for their experiments. It can be used to simulate a high energy physics experiment just with a compact set-up.
EASy at its core, uses a silicon microstrip detector, similar to the ATLAS SCT, and it can operate with radioactive source and laser as its source of radiation. Using EASy, students can learn a lot about particle detectors. We will go over some examples in this post.
- Detector Structure: A silicon microstrip detector is composed of a bulk of n or p type silicon with the opposite composition of silicon and Aluminum strips. Depending on where the focused laser is injected, it can either produce a signal on the detector or be reflected by the Aluminum strips. This behavior can help the students to understand the structure of these type of detectors.
- Noise: In such delicate experiments, noise plays an important role, affecting our measurements. Electronics and the detector itself introduce noise in the measurements. Students can use the data acquired from EASy to understand the sources of these noises and learn how to deal with them in the analysis of their experiments, calculate and use the signal to noise ratio.
- Efficiency: When a charged particle crosses the detector, the free charge carriers formed by ionization in the silicon will move in in the depleted part of the detector where a field is present. While in the not depleted part, there is not electric field and charge will be reconvened. Therefore, only the charge generated in the depletion part will contribute to the signal. The Charge Collection Efficiency (CCE) is defined as the ratio of the collected charge over the collected charge when the detector is fully depleted.
- Energy spectrum: EASy can help students to produce the spectrum of the deposited energy in the silicon detector. This spectrum is a non-symmetric distribution described by Landau and therefore it takes his name. The Landau theory assumes a free charge electron cross section neglecting the atomic bonds. So, a Gaussian distribution convoluted with a Landau curve is used to reproduce the experimental energy distribution.
This device has been used in past editions of the CERN’s Summer Student Programme, in this article you can read the article dedicated to our participation in last year’s CERN’s Summer Student Programme 2023.
