Minimal Supersymmetric Standard Model

Scientists think of new tiny parts.

These parts could be partners to the parts we know. Every known part might have a hidden partner. These partners could be dark matter. This is the stuff in space we cannot see.

Big machines try to find them. They use a lot of energy to look. We have not found them yet. Maybe one day we will.

Scientists use a theory called the MSSM. It is an extension of the Standard Model. This model uses a rule called supersymmetry. This rule says every known particle has a partner. We call these partners superparticles.

There are five main types of superparticles. They are squarks, gluinos, charginos, neutralinos, and sleptons. Squarks are partners to quarks. Gluinos are partners to gluons. These parts are very heavy. They are 100 to 1000 times heavier than a proton. Because they are so heavy, we need huge power to make them. Scientists use big machines called particle accelerators. The Large Hadron Collider is one such machine.

Finding these particles would help us solve big mysteries. One mystery is dark matter. Dark matter is stuff in space we cannot see. The lightest superparticle could be dark matter. Another mystery is the mass of the Higgs boson. The MSSM helps explain why that mass is stable. We have not found these particles yet. Scientists are still looking for them at the LHC.

Scientists use a special theory called the Minimal Supersymmetric Standard Model, or MSSM. It is an extension of the Standard Model, which is our current map of how particles work. The MSSM uses a rule called supersymmetry to add new pieces to that map. This rule suggests that every known particle has a hidden partner. We call these partners superparticles.

These new particles could help us understand the deep secrets of our universe. They might explain what dark matter is or how all forces join together.

How does this system work? In the MSSM, particles are paired up in a specific way. Every boson, which is a type of force particle, has a partner called a fermion. Every fermion has a partner called a boson. This creates five main classes of superparticles. These include squarks, gluinos, charginos, neutralinos, and sleptons.

Because these particles are so heavy, we cannot find them easily. They are 100 to 1000 times heavier than a single proton.

People first proposed the MSSM in 1981. They wanted to solve a hard job called the hierarchy problem. This problem involves the mass of the Higgs boson. In the Standard Model, the Higgs mass is unstable. The MSSM uses superpartners to keep this mass stable. For example, the Higgs boson has a partner called the Higgsino. This partner helps the Higgs mass stay at the right level.

There are many specific facts about these particles. The Higgs boson was found in 2012 with a mass of 125 to 126 GeV. Scientists look for superparticles using huge machines called particle accelerators. The Tevatron was one such machine before it shut down on 30 September 2011. Now, most physicists look to the Large Hadron Collider, or LHC, for answers. They look for a sign called "missing energy." This happens when the lightest superparticle escapes the detector without being seen.

Understanding the MSSM connects to things we already know about space. One big idea is dark matter, which is invisible stuff in space. If a rule called R-parity is kept, the lightest superparticle is stable. This particle could be the dark matter that holds galaxies together. The MSSM also suggests that different forces might become one at very high energies. This idea is called gauge coupling unification. Finding these particles would turn these big ideas into real facts.

The Minimal Supersymmetric Standard Model, or MSSM, is a theoretical extension of the Standard Model of particle physics. It is designed to realize a concept called supersymmetry. This principle suggests a fundamental symmetry between two different types of particles: bosons and fermions. In the Standard Model, these two groups are distinct. In the MSSM, every known particle is paired with a yet-undiscovered superpartner. This model is considered "minimal" because it only includes the smallest number of new particle states and interactions required to remain consistent with reality.

One of the primary reasons scientists study the MSSM is to solve the hierarchy problem. This problem involves the stability of the Higgs boson mass. In the Standard Model, the Higgs mass is unstable due to quantum corrections. These corrections could theoretically make the Higgs mass much larger than what we actually observe. The MSSM provides a solution through a process of cancellation. The Higgs boson has a fermionic superpartner called a Higgsino. Because fermion masses are radiatively stable, the Higgs boson inherits this stability from its partner.

To make this system work, the MSSM requires more than one Higgs field. A single Higgsino would cause a gauge anomaly, which would make the theory inconsistent. Therefore, the MSSM introduces two Higgsinos and two scalar Higgs doublets. This setup also allows for Yukawa couplings. These are the specific interactions that allow the Higgs field to give mass to both up-type and down-type quarks. This complexity is necessary to maintain the mathematical integrity of the model.

Superparticles are categorized into five distinct classes based on their properties. First are squarks, which are the scalar partners of quarks. There is a version of a squark for every quark in the Standard Model. Second are gluinos, the fermionic partners of gluons. Third are charginos, which are electrically charged fermions. Fourth are neutralinos, which are electrically neutral fermions. Finally, there are sleptons, the scalar partners of leptons.

These particles have very specific ways of interacting and decaying. For example, gluinos are Majorana fermions, meaning they are their own antiparticles. They interact through the strong force and can be produced significantly at particle accelerators. Squarks also interact strongly and can be produced in pairs. When these heavy particles decay, they often produce a signature called "missing energy." This happens because the lightest supersymmetric particle, or LSP, is stable and escapes the detector without being seen. This LSP is a candidate for dark matter, specifically a Weakly Interacting Massive Particle, or WIMP.

Scientists have searched for these particles for decades using massive particle accelerators. The Tevatron was a major tool for this research until it shut down on 30 September 2011. Today, the Large Hadron Collider, or LHC, is the primary machine used to hunt for supersymmetry. Because superparticles are expected to be 100 to 1000 times heavier than a proton, they require immense energy to create. While the LHC has not yet found evidence for the MSSM, the search continues because the model offers powerful theoretical motivations.

Beyond solving the hierarchy problem, the MSSM supports the idea of gauge coupling unification. This is the theory that the three fundamental forces of the Standard Model join together at extremely high energies. If superpartners exist near the TeV scale, the measured gauge couplings unify with remarkable accuracy. Some calculations show this unification occurs to an accuracy of about 1%. This provides indirect evidence for both the MSSM and Grand Unified Theories. Finding these particles would link the physics of the very small to the grand structure of the entire universe.