# Strong interactions

### Proton–proton collisions become stranger

Recreating the intense fireball of quarks and gluons that existed immediately after the Big Bang, the quark–gluon plasma (QGP), traditionally requires high-energy collisions between heavy ions such ...

### LHCb brings cosmic collisions down to Earth

In an effort to improve our understanding of cosmic rays, the LHCb collaboration has generated high-energy collisions between protons and helium nuclei similar to those that take place when cosmic ray...

### ALICE reveals dominance of collective flow

The study of the anisotropic flow in heavy-ion collisions at the LHC, which measures the momentum anisotropy of the final-state particles, has been effective in characterising the extreme states of ma...

### ATLAS reveals more strangeness in the proton

The excellent theoretical understanding of the production of electroweak W and Z gauge bosons in proton–proton collisions at the LHC makes these “standard-candle” processes ideal for studying th...

### ALICE measures shape of the QGP fireball at freeze-out

Heavy-ion collisions at LHC energies create a hot and dense medium of deconfined quarks and gluons, known as the quark–gluon plasma (QGP). The QGP fireball first expands, cools and then freezes out ...

### The two-loop explosion

Studying matter at the highest energies possible has transformed our understanding of the microscopic world. CERN’s Large Hadron Collider (LHC), which generates proton collisions at the highest ener...

### A 30-year adventure with heavy ions

Heavy-ion and proton–proton collisions at ultrarelativistic energies provide a unique system with which to investigate the dynamics of matter in the early universe. By generating an incredibly hot a...

### ALICE studies beauty in the quark–gluon plasma

In high-energy nucleus–nucleus collisions, heavy-flavour quarks (charm and beauty) are produced on a very short time scale in initial hard-scattering processes and thus they experience the entire ev...

### Quark–gluon plasma insights

Powerful supercomputer simulations of colliding atomic nuclei have provided new insights about quark–gluon plasma (QGP), a superhot fluid of de-confined partons produced in heavy-ion collisions at t...

### ALICE zeroes in on cold-matter effects

Measuring the production cross-section of charm hadrons in proton–proton collisions provides an important test of perturbative quantum chromodynamics (QCD). In proton–nucleus collisions, “cold-m...