CERN SUMMER STUDENT PROJECT 2017

Large Hadron Collider (LHC) in CERN is one of the main particle accelerator in the world that produces two proton beam and accelerating then before merging them at several collision point. Compact Muon Solenoid (CMS) is second biggest detector located at one of the collision point purposed as a big camera to record all the events emerges during the high impact collision of the protons that is accelerated nearly speed of light. There are a lot of Standard Model (SM) particle produced during the collision and the trajectories of nearly all the particles are captured by the huge precision detector. This is also how Higgs Boson was discovered 5 years ago. Particles of matter for example like fermions and force particles such as gauge bosons are indeed SM particles. Neverthless, Higgs is quite different from all gauge bosons (W, Z and gluon)[1]. Protons are made up of quarks, anti-quarks and gluons. During the high energy collisions in LHC we produce Higgs from many interaction of matter and anti-matter particles. The main production channel is from gluon fusion. Then, the Higgs will immediately decays into lighter SM particles. All of the particles that are produced from the collision will form jets that contains hadrons which are the final states of SM particles which include bottom quark, charm quark, strange quark, up and down quark, leptons and many others as well as their antimatter. But top quark will not be in the final states as jets because of its short lifetime. Higgs decay branching ratio From theory it is known that Higgs prefer to decay into bottom quark which is about 58% because it is the heaviest quark that could be found in the final state followed by the rest of the SM particles. There is another quark that have a small branching ratio of 3% which is the charm quark. The small branching ration of charm quark make it difficult to be detected[2][3]. B-tagging and C-tagging Experimentalists developed an algorithm to recognize which jets likely belongs to b- hadron jets or other hadron jets. The technique is called b-tagging where to tag b-hadron jets and c-tagging for jets that likely contain charm quark. B-jets are distinguishable because they have a secondary vertex. For other jets is hard to distinguish because all of the final state product come from original collision point while one can distinguish that the final state product is from b-hadron when reconstruction of the jets shows that it is not decayed from original collision point. The Jets likely contain a b-hadron when there is a lepton (D+meson) found near the jets because it is one of the 5 final state particles of bbbar[4].