LHCb has taken its first snapshots of the W boson in action. This particle conveys the weak force, which makes certain forms of radioactivity possible. It is shown here having decayed to a muon μ (shown as a straight white line, pointing to the filled green muon detector hit circles in the 2D picture, and as a red line pointing to blue muon hits in the 3D picture), which we see, and a neutrino ν, which we don’t, with very little else around it.
click in images to get them in higher resolution
Eolas (gaelic for ‘knowledge’) is a 2D view of a collision inside LHCb. It is a transmogrified view, chosen to illustrate where particles deposit energy as they fly outwards from the collision point. The radius represents flight through the detector along the beam direction – through the tracking detectors, then the first muon chamber, then the electromagnetic and hadronic calorimeters, and finally the last four muon chambers. The φ angle represents the angle in the x,y direction perpendicular to the beam. Information is colour coded. Particle tracks are shown by the dashed lines. The transverse momentum of the particle is shown by the solid white long along this path – the higher this is, the longer the solid white bar is. Yellow bars show energy deposited in the electromagnetic calorimeter, cyan energy deposited in the hadronic calorimeter. Deposits in muon chambers are illustrated by green circles. If these are filled, they are associated with a particle track passing through them.
We will use samples of W bosons to test our theory of particle physics, the Standard Model, to high precision. This is exciting because we don’t know yet if our theory holds at LHC energies – if it doesn’t, if there are new particles to find in nature, we’ll see W bosons behaving in a way we don’t expect. With these first snapshots taken, we’re on our way to finding out.
The W boson was discovered in 1983 at CERN by the UA1 and UA2 experiments giving the Nobel Prize to Carlo Rubbia and Simon van der Meer.