The Large Hadron Collider (LHC) has been restarted after a two-year hiatus, which allowed the CERN team to significantly upgrade it. Most notably, the LHC is responsible for confirming the existence of the Higgs Boson, which gives other particle mass. The second run of operation, which commenced in June, aims to prove or disprove the existence of particles predicted by supersymmetric theories as well as investigating more exotic physics. The findings are to be published in Physics Letters B.
Over the summer, the Compact Muon Solenoid (CMS) collaboration at CERN studied in detail what the average collision between protons would look like at 13 teraelectron volts (TeV), the energy at which the LHC is currently operating. Normally 13 TeV would be a minuscule amount of energy; it is about the same energy as a strand of hair falling for roughly a foot, but when packed into a single tiny proton the particle's energy density is enormous. Smash two energy-packed particles like this together and it can lead to the formation of particles that are hardly ever observed otherwise.
The LHC sends two high energy particle beams traveling almost at the speed of light in opposite directions around the accelerator. The beams collide inside one of the four experiments, in this case CMS, which record the new particles. Each beam contains 476 bunches of 100 billion protons and when they meet, collisions occur every 50 nanoseconds. In this study, the team has identified 150,000 events due to proton collisions, and has detected 30% more particles per collision than during the collider's first operational run, between 2010 and 2013.
CMS can track hundreds of millions of particles each second, but the vast majority of these are from background events. The team has analyzed, in detail, the amount and direction of particles produced in the proton collisions. In each event, about 22 charged particles, known as hadrons, were emitted, and they moved mainly in a plane perpendicular to the direction of the beam.
The detailed analysis was obtained by switching off the powerful magnet situated inside the detector. The magnet is used by the scientists to measure the particles’ momentum with high precision, but it is so strong (100,000 times stronger than the Earth's magnetic field) that the lighter particles with low momentum tend to move towards the magnet and never reach the detector. By turning off the magnets, the researchers were able to precisely count how many particles were produced by colliding protons and at which angle they reached the detector.
The authors of this study claim to have significantly reduced the uncertainty associated with measuring. Theoretical models have a sizeable uncertainty (30-40%) when it comes to predicting the observation of new particles. The study shrunk that uncertainty to just a small percentage.
[H/T: MIT News]
Image credit: CMS Detector under construction by Mike Procario via Flickr. CC BY-ND 2.0
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