First 13 Tev proton-proton collisions at the Large Hadron Collider

My heartfelt congratulations to the physicists, engineers and technicians of the Large Hadron Collider (LHC) at CERN. They accelerated protons to 6.5 Tev energy while keeping them in 27 km circumference circular orbits. They also made these counter circulating protons collide at 4 locations around the 27 km ring. This is an incredible technological and scientific accomplishment. Accelerating protons to 6.5 Tev is the result of more than 30 years of research and development. Making the counter-circulating 6.5 Tev protons collide is equally impressive.

We don’t have the technology to aim the individual protons against each other precisely. We aim the proton beams against each other. Only 1 in 50 million protons of the first beam end up in a collision with a proton of the opposite beam.

Beam is a collection of protons. Each beam contains bunches (pulses) of protons. When LHC reaches its full potential there will be 2808 bunches in each beam but the first collisions (6.5 Tev protons colliding head-on with 6.5 Tev protons) were accomplished with just one or two bunches per beam.

Each bunch is few cm long and a mm wide when they are far from a collision point. As they approach the collision points, they are squeezed to about 16 microns (a human hair is about 50 micron thick).

6.5 Tev is the energy record for human-accelerated protons. Nature can accelerate protons to much higher energies. Among the cosmic rays that hit Earth there are protons with much higher energies.

The 6.5 Tev refers to the energy of a single proton. Total energy of the beam will be 6.5 Tev times the number of protons in the beam. Assuming there are 2808 bunches in each beam and each bunch contains 1.1 x 10^11 protons, the total energy of the beam comes to 2.01 x 10^15 Tev which is equal to 322 MJ which is enough energy to melt approximately 500 kg of copper.  Since there are 2 counter-circulating beams in the beam pipes the total beam energy of the 2 beams can melt 1000 kg of copper. Therefore, the total beam energy is very significant. LHC beams have to be controlled by super-strong magnets. In the case of any failure beams have to be diverted to special areas. Among the many upgrades that was implemented during the 2-year shut-down was the all important upgrade related to the controlled beam dump.

Few parameters of the LHC

• Circumference = 26 659 meters
• Dipole operating temperature = -271.3 degrees Celcius (colder than outer space)
• Number of magnets = 9593
• Number of main dipole magnets (bending the protons into orbit) = 1232
• Number of main quadrupole magnets (focusing the proton beams) = 392
• Number of RF cavities (maintaining beam energy) = 8 per beam
• Peak magnetic dipole field strength = 8.33 Tesla
• Minimum distance between proton bunches = 7 meters (25 ns in units of time)
• Number of bunches per proton beam = 2808
• Number of protons per bunch (at start) = 1.1 x 10^11
• Number of turns per second = 11 245
• Number of proton-proton collisions per second at the crossing points = 600 million

Discovery potential at 13 Tev

When a 6.5 Tev proton collides with a another 6.5 Tev proton head-on the center-of-mass energy of the collision will be 13 Tev.  A proton is composed of quarks and gluons.  Most of the 13 Tev energy will go into tearing the protons apart and  only about 1-2 Tev energy will go into quark-antiquark, quark-gluon or gluon-gluon collisions which may result in the creation of yet unknown particles.

In the second run of the LHC – scheduled to start next month – the collision energy available for particle creation is approximately twice the energy that was available during the first run. Is this enough to discover new physics? We don’t know. We hope for surprises but 1-2 Tev is probably  not enough to answer questions related to supersymmetry. One thing is clear, however, with 2808 bunches in each beam the accuracy of measurements (Higg’s particle mass, for example) will improve dramatically. This is very important. Once we know the mass of the Higgs particle with precision we will be able to discriminate and make judgments about the BSM (beyond Standard Model) theories.