# Numerical simulation are necessary

Each collision in the **Large Hadron Collider** will produce **thousands of particles,** many of which we cannot observe since they decay long before they reach the detector.

However we can infer the existence of **invisible particles** and their properties by looking at the recorded decay products which are **visible**, and their distribution in the detector over many thousands of collisions.

The main way to understand and interpret these observations is to **simulate on a computer** what we expect to see for different theoretical models, and then **compare** the simulated result with real data. This mens that the *mathematical model* must be translated into a *numerical one* and implemented into a software. Some of the techniques used to perform the simulations are referred to as **Monte Carlo methods**. These computational alghoritms rely on repeated random sampling to obtain numerical results.

Numerical simulations provide a reliable bridge between our best theories and our most powerful experiments.

# Simulations at the edge of knowledge

The IPPP in Durham is **world leading** in developing computer programs, such as ** Sherpa** and **Herwig**, which are used to simulate the high-energy collisions occurring at the LHC. *Herwig* and *Sherpa* have been instrumental in the discovery of the Higgs Boson at the LHC in 2012.

These softwares use Monte Carlo methods and numerical algorithms to **predict** the enormous amount of events generated in the LHC. The plot below shows the comparison between *experimental data *collected at the LHC (black dots) and the **results of simulations** (coloured areas). To match the experimental data, a **signal contribution** (pale-blue area) needed to be added to the background: this provided the evidence of the existence of a particle of **mass 125 GeV**, identified with the Higgs Boson.

If you want an idea on how simulations work, have a look at our Galton board!