Muon System

A basically similar low-energy muon system is installed at ISIS. The pulsed beam circumvents the start counter problems, but beam intensity is even lower. 

The CMS experiment—one of the four large LHC experiments— is a general-purpose detector designed to optimally exploit the physics potential of the LHC. Located inside the superconducting solenoid, which provides a 3.8 Tesla held, are the hadronic and electromagnetic calorimeters as well as the tracking system. The latter is based on silicon pixels and silicon strip detectors, with a total sUicon area of 210 m. A multi-layer muon system embedded in the return yoke outside the solenoid completes the CMS detector. 

Even though the CMS detector is primarily designed for high transverse momentum physics, it is very well suited for heavy flavor physics thanks to the muon system with the potential to identify low transverse momentum muons and the excellent tracking detectors. In particular, CMS features a novel three-layer silicon pixel detector which allows for a precise and efficient reconstruction of secondary vertices from heavy flavor decays. 

Fig. 2.11 Muon transverse momentum resolution as a function of the transverse momentum for muons detected in the barrel (left) and the endcap (right) regions [4], The resolution is given for the measurement using the muon system or the tracking system only and for a combined method...

The muon system is the outermost part of the CMS detector. The magnet return yoke is equipped with gaseous detector chambers for muon identification and momentum measurement. In the barrel, the muon stations are arranged in five separate iron wheels... 

Fig. 2.10 View of one quarter of the CMS detector illustrating the layout of the muon system in...

Muon reconstruction, after local-pattern recognition is performed in two stages stand-alone reconstruction based on information from the muon system only and global reconstmction including the hit information of the silicon tracker. Standalone reconstruction starts from track segments in the muon chambers and muon trajectories are built from the inside to the outside using the Kalman filter technique. After the trajectory is built, a second Kalman filter, working from outside in, is applied to determine the track parameters. In the end, the track is extrapolated to the nominal interaction point and a vertex-constrained fit of the track parameters is performed. 

In the global muon reconstmction the muon trajectories are extended to add hits measured by the tracker. The track parameters of a stand-alone reconstmcted muon are compared to the track parameters of the tracker tracks by extrapolating the trajectories to a common plane on the inner surface of the muon detector. If a tracker track is found that is compatible in momentum, position and direction, the hit information of the tracker and the muon system is combined and refitted to form a global muon track. The resulting global tracks are then checked for ambiguity and quality to choose at most one global track per stand-alone muon. 

Second Quantized Description of a System of Noninteracting Spin Particles.—All the spin particles discovered thus far in nature have the property that particles and antiparticles are distinct from one another. In fact there operates in nature conservation laws (besides charge conservation) which prevent such a particle from turning into its antiparticle. These laws operate independently for light particles (leptons) and heavy particles (baryons). For the light fermions, i.e., the leptons neutrinos, muons, and electrons, the conservation law is that of leptons, requiring that the number of leptons minus the number of antileptons is conserved in any process. For the baryons (nucleons, A, E, and S hyperons) the conservation law is the... 

Consider for example the simplest possible system consisting of the muon, an electron, and a single spin nucleus labelled i = n. Take the muon and nuclear hyperfine interactions to be istoropic. The level crossing of interest occurs near the field... 

The actual eigenstates are equal admixtures of the two unperturbed pure spin states when the field is exactly at the value at which the crossing would have occurred (v,m = 0). Since initially (when the muon stops) the system is in a well defined muon spin state, i.e., one of the two unperturbed pure spin states, the system oscillates at the frequency vT between the muon spin being along and opposite to the field, as implied by Eqs. 10 and 11. Thus, upon time averaging the positron counts the forward-backward asymmetry is reduced. 

One of our main interests is to describe quark matter at the interior of a compact star since this is one of the possibilities to find color superconducting matter in nature. It is therefore important to consider electrically and color neutral2 matter in /3-equilibrium. In addition to the quarks we also allow for the presence of leptons, especially electrons muons. As we consider stars older than a few minutes, when neutrinos can freely leave the system, lepton number is not conserved. The conditions for charge neutrality read... 

Muons can easily penetrate many meters of iron and can sometimes cause problems in particle physics research. For example, the upsilon experiment at Fermilab in 1977, conducted by L M. Uederman and olhers, required building a simple magnetic system that would remeasure each muon s energy after it emerged from the main detector. See also Upsilon Particle and Particles (Subatomic). 

The HSCC equations have been solved for various Coulomb three-body processes, such as photoionization and photodetachment of two-electron systems and positronium negative ions [51, 105-111], electron or positron collisions [52, 112-115], ion-atom collisions [116-119], and muon-involving collision systems [103, 114, 120-125]. Figures 4.6, 4.7, 4.8, 4.9, and 4.10 are all due to HSCC calculations. Figure 4.12 illustrates the good agreement between the results of HSCC calculations [51] and the high-resolution photoionization experiment on helium [126]. See Ref. [127] for further detailed account of the comparison between the theory and experiment on QBSs of helium up to the threshold of He+(n = 9). 

Snider is best known for his paper reporting what is now referred to as the Waldmann-Snider equation.34 (L. Waldmann independently derived the same result via an alternative method.) The novelty of this equation is that it takes into account the consequences of the superposition of quantum wavefunctions. For example, while the usual Boltzmann equation describes the collisionally induced decay of the rotational state probability distribution of a spin system to equilibrium, the modifications allow the effects of magnetic field precession to be simultaneously taken into account. Snider has used this equation to explain a variety of effects including the Senftleben-Beenakker effect (i.e., is, the magnetic and electric field dependence of gas transport coefficients), gas phase NMR relaxation, and gas phase muon spin relaxation.35... 

---