ShowerMax

ShowerMax's Role in the MOLLER Experiment

Unlike the main detectors in the MOLLER experiment, ShowerMax is specifically designed to measure the energy of scattered electrons in an energy-dependent manner. This allows us to accurately account for the energy dependence in the signal and helps cancel out background events that could otherwise introduce errors into the measurement of Apy.

ShowerMax will also provide an independent measurement of Apy. This is essential for ensuring the robustness of the MOLLER experiment's results. By offering an alternative way to measure this property, ShowerMax serves as a valuable cross-check, allowing us to confirm our findings and be more confident in our conclusions.

So, it provides an independent measurement of Apy, and it helps us account for background events as a electromagnetic calorimeter. The next section will go into more detail on what an electromagnetic calorimeter is and how it works.

What is an Electromagnetic Calorimeter?

An electromagnetic calorimeter is a device used in particle physics experiments to measure the energy of particles like electrons, photons, and positrons. These particles interact with the detector material, producing a cascade of secondary particles in a process called an electromagnetic shower. The energy fo the original particle is directly related to the electromagnetic shower that it produces. The shower produces light that we measure with a photomultiplier tube (PMT), which converts the light into an electrical signal.

How Does an Electromagnetic Shower Work?

When a high-energy particle like an electron or photon enters the calorimeter, it interacts with the atoms in the detector material. These interactions can produce additional electrons and photons, which then interact with more atoms, producing even more particles. This process continues, creating a cascade of secondary particles that will generate light in the process.

The main interactions that take place are bremsstrahlung for electrons and pair production for photons.

Bremsstrahlung: Means "braking radiation" in German, is a phenomenon that occurs when a charged particle, typically an electron, passes through the vicinity of an atomic nucleus or another charged particle. The electric field of the nucleus or the charged particle exerts a force on the moving charged particle, causing it to decelerate or change direction. This acceleration leads to the emission of electromagnetic radiation in the form of photons, known as bremsstrahlung radiation. The emitted radiation carries away energy and momentum from the charged particle, effectively slowing it down.

Pair production: Is the process by which a high-energy photon transforms into an electron-positron pair when it interacts with the strong electric field near an atomic nucleus or an electron. In this process, the photon effectively disappears, and its energy is converted into the mass and kinetic energy of the newly created electron and positron.

Both of these processes produce secondary particles that interact with the detector material, producing light that we can measure with a PMT.

ShowerMax Design Principles

ShowerMax has a unique design to maximize its efficiency and accuracy in detecting and measuring the energy of particles. Its key features include:

1. Tungsten and Quartz Layers: ShowerMax consists of four layers of tungsten interleaved with four layers of optically polished quartz. Tungsten is an excellent material for initiating electromagnetic showers, while the quartz layers produce Cherenkov radiation which we can measure.

2. Specially Designed Light Guide: A custom-designed light guide is used to efficiently collect and transmit the light produced in the quartz layers to a photomultiplier tube (PMT), a device that converts light into an electrical signal.

3. Ring Geometry: In the MOLLER experiment, 28 ShowerMax detectors are arranged in a ring with approximately a 1-meter radius around the beamline. This arrangement ensures that the detectors can accurately measure the scattered electrons in the experiment.

This is a brief video how the ShowerMax detector works.

ShowerMax Summary

In this section, we discussed the ShowerMax detector, which is a key component of the MOLLER experiment. Its main purpose is to make an independent measurment of the Apy, and to help us account for background events as an electromagnetic calorimeter. It does this by measuring Cherenkov radiation made from the electromagnetic showers of the scatterd electrons from the beam intereacting with the tungsten atoms.