LHC accelerates protons, not electrons. The protons have a Energy of 7 TeV, or a momentum of 7 TeV/c. Since protons at rest have a rest mass of about 0.001 TeV/c^2, then the calculation is easy \(\gamma = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}} = \frac{7 \textrm{TeV}}{0.001 \textrm{TeV}} = 7000\) And time slows down by this same factor of 7000. Using the real value of the proton mass ( 0.000938272 TeV) gives a number closer to 7460, but until the LHC actually runs, I don't know what confidence to put into the goal of 7 TeV. In the same tunnel as the LHC, there used to be the biggest electron-positron collider, the LEP, with a maximum electron energy of 104000 MeV. So the gamma factor was: 104000 MeV/0.5109989 MeV = 203500.