GGLogbook

=**Compact Muon Solenoid (CMS) Detector**=

**Purposes**
One of two detectors in the proton-proton Large Hadron Collider (LHC), the CMS detector studies the energy and momentum of protons, electrons, and muons in order to answer some large-scale questions. These goals include finding evidence to expand the Standard Model of particle physics (i.e. supersymmetry, extra dimensions) and studying collisions at the TeV scale. Additionally, the detector serves to explore dark matter. Dark matter--which neither emits nor absorbs electromagnetic radiation--accounts for a huge portion of mass and matter in the universe (an estimated 84% of the universe's matter and 23% of its mass energy). While evidence has supported the idea of its presence, the subatomic particle of which it is composed has yet to be discovered. As of July 4, 2012, CERN reported finding a particle consistent with the Higgs boson, an elementary particle of the Standard Model. One of the main goals of the CMS and LHC, finding the Higgs boson confirms the existence of the Higgs field, which explains the origin of mass in elementary particles. The new particle is the heaviest boson ever found. While this is exciting news, the CERN press release reports that "more time is needed to prepare these results for publication" with further experimentation. The next steps to be taken are understanding the precise nature of the particle and its significance.

Structure
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The LHC is composed of two counter-rotating beams, between which the particle collisions occur. This is the interaction point. The next layer, the tracking chamber, is composed of 13 or 14 silicon strips. They are able to identify the trajectory of each particle and the spot of its origin. The Electromagnetic Calorimeter measures the energy of the photons. e-/e+ pairs are produced, which subsequently are deflected by the electric fields of atoms, causing more photons, and so on. The resulting number of e-/e+ pairs is proportional to the energy of the initiating particle. In the magnetic field, the tracks of charged particles have curvature; this makes their charge and momentum able to be measured. This is the world's largest silicon detector: more than 200 square meters of silicon and more than 70 million channels.The next layer is the Hadronic Calorimeter or HCAL. Brass and steel compose its layers, interwoven with scintillators: a = = combination that, within the coil of the magnet, allows the most material to be absorbed and recorded. It measures each individual hadron's energy (produced in each event) and identifies events without energy. Only muons and neutrinos make as far as the muon chambers. Muons' presence is noted, but that of neutrinos is not; their presence is accounted for by judging the "missing" energy. The next layer, the 13-by-6 meter solenoid magnet, determines the charge/mass ratio by observing the path a particle takes in the magnetic field. The last layer is composed of three types of detectors. The drift tubes are used to measure trajectory in the central barrel region. Cathode strip chambers do the same in the end caps. Resistive plate chambers occur in both locations, and are responsible for noting the presence of muons in the muon detectors. = =



Protons and Proton Collisions
Positively-charged protons, a subatomic particle, are located in the nuclei of atoms. It is a hadron composted of quarks: two up quarks and one down quarks bound in the gluon field. The majority of a proton's mass is kinetic energy. There are six types of quarks: up, down, top, bottom, strange, and charm, with up and down being the most common. The other four types only occur in high-energy collisions involving particle accelerators and cosmic rays. For every type of quark, there is an antiparticle (antiquark) that has an equal magnitude but an opposite charge. At high energies, a greater fraction of protons' quarks are virtual and can be any type or "flavor" of quark. In the LHC, two adjacent beam pipes emit proton beams that intersect at 4 points. They are kept in line around the circle by dipole magnets; quadrupole magnets keep the beams focused. Protons' energy is increased prior to collision in the LHC by radio frequency cavities for about 25 minutes until they reach their maximum 7-TeV energy. = = Beams divide into bunches and continue to accelerate before collision. When two protons collide (an "event"), they emit radiation and particles that the detector picks up. Quarks interact with quarks, gluons with gluons, and quarks with gluons.

Cosmic Rays
Cosmic rays are highly energetic particles that come from space (exact origin is undetermined), composed of familiar subatomic particles like protons, electrons, or atomic nuclei. They carry significantly more energy than even the most energetic particles in manmade accelerators. They appear in the collected data of these particle accelerators; they enter from space into the detector in a generally straight line, which--along with their highly energetic and more massive nature--differentiates them from other particles in the accelerator. Our first group project, as documented in the first several weeks' logbooks, deals with identifying these particles in a data set using two different websites.