Missing transverse energy (MET) is a vital concept in particle physics experiments, especially at high-energy colliders like the Large Hadron Collider (LHC). It refers to an imbalance in the measured energy of particles moving perpendicular to the beam direction (transverse plane), suggesting the presence of undetected or invisible particles.
Here’s how it works:
- In a collider, the total transverse momentum before a collision is essentially zero, since the particles move head-on along the beamline.
- After the collision, if all particles are detected, the total transverse momentum should still sum to zero.
- If there’s a discrepancy, it implies that some particle(s) carried away momentum without being detected.
Common reasons for MET include:
- Neutrinos, which interact very weakly and usually escape the detectors.
- Hypothetical particles like dark matter candidates or gravitons, if they exist, would also escape detection, leading to missing energy.
- MET is thus a powerful indirect tool for discovering new physics beyond the Standard Model.
Physicists carefully analyze MET to:
- Confirm known processes involving neutrinos (like W boson decays).
- Search for signatures of supersymmetry (SUSY) or extra dimensions.
- Investigate possible dark matter production events.
In short, missing transverse energy acts like a footprint in the snow—you don’t see the particle directly, but you know it was there from the imbalance it leaves behind.