First collisions at 13 TeV as the Large Hadron Colllider restarts


On May 21, 2015 proton beams were collided together in the Large Hadron Collider at the record energy of 13 TeV, as the LHC restarts after extensive upgrades over the past two years.  This is the total energy in the center-of-mass frame, so each beam contains protons of energy 6.5 TeV.  That’s about 6,500 times the rest energy of a proton (roughly 1 GeV), hence the relativistic gamma factor for these protons is about 6,500.

Read the CERN article on this important milestone here.

Higgs boson paper has 5,154 authors

CMS and Atlas, the two big experimental collaborations at the Large Hadron Collider, have joined forces to produce the most accurate determination of the Higgs boson mass to date.  By combining their data sets they obtained

$$ M_H=125.09\pm0.24~GeV$$

for a relative error of about 0.2%.  The paper in Physical Review Letters describing these results has the longest author list ever: 5,154 names.  In the published version, there are 9 pages describing the research and 24 pages of authors and their affiliations.

Read the associated APS Physics Viewpoint article here.