Hello,
Although a little bit old, the attached CMS physics analysis summary of 2012 may be useful. Which kind of problems do you have from experiments of CMS?
Sadataka Furui
In terms of the angle θ between particle 3 momentum and the positive direction of beam axis we have the following expression for pseudorapidity range η = -ln tan (θ/2)
Since the CMS (Compact Muon Solenoid), one of the four main detectors for the LHC, was first placed into operation, the preliminary selection of data was partly handled by a muon trigger which Polish physicists had a made a sizeable contribution to building. This system has recently undergone a thorough modernization and is now starting work in the new cycle of accelerator exposures. It is now significantly more accurate at detecting muons, particles that are products of the breakup of other particles appearing in collisions.
Devising new collision-selection algorithms and creating the software for carefully chosen electronics boards, which were then carefully tested. The use of modern laser design etching electronics helped significantly reduce the size of the device.
In successive cycles of operation the LHC will be increasing its particle energies, and the higher the energy the more secondary particles will be created in the collisions. The things are even more challenging, since the accelerator is continually increasing its luminosity, which is a measure of the intensity of the collisions and depends on the number of particles circulating in the accelerator and how they are packed. As a result, a significantly higher number of collisions are now occurring per unit of time. All of this is making greater and greater demands of the muon selection system...
Within the CMS detector, beams of protons accelerated nearly to the speed of light intersect every 25 nanoseconds. Each such beam intersection results in a few dozen interactions, each of which may give rise to many secondary particles. The muon trigger’s job is to very quickly and preliminarily identify, within this flurry of particles, muons that have very high transverse momentum, in other words those which few out of the collision point with high energy and inclined at a significant angle with respect to the direction of the beam.
The location where the beams intersect in the CMS detector is surrounded by several cylindrical layers of detector chambers, situated in the field of a gigantic superconducting magnet 7 m in diameter and 13 meters long, generating a tremendous magnetic field (nearly 4 tesla) inside a coil. The central portion of the detector, known informally as the barrel, is enclosed on either side by flat, circular endcaps containing further detector chambers. The overall length of the main portion of the detector is around 21 m, with an external diameter of around 15 m.
To identify a muon, one has to detect signals from many detector chambers. They have to come at the right time following a collision and in the right sequence. One also has to bear in mind that, being a charged particle, a muon will follow a curved path through a magnetic field. Within the CMS detector, that field changes: it is oriented one way along the axis of the beam, and the other way far from the beam. A muon moves through such a field along a path that looks like an asymmetrically stretched letter S. The chambers that it activates do not lie along a straight line, making describing the collision difficult. That is why the identification of muons in the trigger involves comparing the tracks they leave behind against model patterns. This is further complicated by random energy losses, multiple scattering, noise, making analysis truly challenging
...and that’s not the end of the complexities. In 2014, physicists drew the attention of the CMS experiment community to the overlaps between the barrel and the endcaps. The geometry of the detector system is uniform and relatively simple within the endcaps (flat circles) and barrel (the lateral surface of a cylinder), but not where they overlap. Moreover, different types of detectors were mounted in the barrel and endcaps, and along the overlaps all of them had to be taken into consideration – and there are as many as 18 layers of detector chambers here! Moreover, it is precisely in the overlap region that the magnetic field changes orientation. For these reasons, the CMS experiment made the decision to recognise the overlap region a separate, third region for the purpose of analysis, separate from the barrel and endcaps themselves. It was dubbed the Overlap Muon Track Finder (OMTF).
The current modernisation of the trigger required better and more precise algorithms to be devised for comparing the activation signals from the detection chambers against a set of respective patterns. The patterns themselves needed to be worked out from scratch, in a more universal way, ensuring that analysis could be completed within the allotted rigorous time frame.
The OMTF system, constructed by a group from Poland, consists of just two cases of electronics, each of which containing six trigger boards. The design and programming of the whole were made to facilitate its easy expansion in the future, to keep pace with the requirements imposed by the constantly growing luminosity of the LHC accelerator.
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