Higgs Searches at the LHC

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It has long been the goal of particle physicists to discover and understand the building blocks of the universe. Over the years a theoretical description of these building blocks has been developed which describes the fundamental particles and how they interact with one another. The theory is called the 'Standard Model'. Although this theory has been extremely successful - with many measurements confirming its predictions to great precision - there are missing pieces in the puzzle. One particularly compelling open question is that of the origin of mass. In its simplest form the Standard Model does not allow for the fundamental particles such as quarks, electrons, muons, photons, gluons etc to possess mass. This is a real problem since experimental evidence overwhelmingly supports the proposition that some of these particles are massive. A modification to this theory based on the work of many but most prominently, Higgs, Weinberg and Salaam, proposes a mechanism known as 'Spontaneous Electroweak Symmetry Breaking'. Also known as the Higgs mechanism, one of the predictions of this theory is the existence of a neutral particle called the Higgs Boson. This is not the only possibility, another popular class of theories which further extend the Standard Model - called 'Super-Symmetry', or SUSY for short, predict the existence of many new particles - amongst them several Higgs bosons. By searching for Higgs boson(s) one can thus find evidence to support or refute these theories. Current experimental results rule out the existence of a Higgs boson with a mass less than around 115 times that of the proton. It is hoped that existing experiments will be able to extend this boundary out to about 130 times the mass of the proton. Since we know from Einstein that E = mc*c, where E is energy, m is mass and c is the speed of light, it follows that if one wishes to produce heavier particles one needs to use higher energies. The Large Hadron Collider (LHC) will smash protons together at an energy equivalent to 14,000 times the mass of the proton. Theoretical calculations show that this will be sufficient to produce enough Higgs bosons such that we can discover and measure them so long as they have a mass anywhere between 100 and 1000 times the mass of the proton. There are other calculations which suggest that if there is a Higgs boson it must have a mass less than around 1000 times the mass of the proton. When the protons collide at the LHC they produce a huge spray of particles. The collisions will take place inside three detectors: CMS, ATLAS and LHC-B which will detect some of the particles in this spray. Unfortunately not every proton collision produces interesting results and even when they do they do not always produce those we were looking for. Since we cannot detect a Higgs directly in the detector - it exists only for fleeting moments before decaying into other lighter particles - we must try and find the particles it has decayed into and from measurements of their properties derive the properties of the particle from which they came. So in order to pick these interesting 'signal' events out from the not-so-interesting 'background' events it is necessary to have good methods for analysing the signals which come from the detector in order to reconstruct what actually happened in a particular collision and see if there was something that looked like it might be a Higgs particle. It is the primary purpose of the proposed research to analyse the data collected from collisions at the CMS detector to search for evidence of the existence of the Higgs Boson.