High-Energy Physics - Signal Processing Systems - page 138

of extra dimensions is also an essential facet of String Theory. A joint experiment
between the LHC's CMS and TOTEM systems could potentially detect the effects
of gravity from a 5th dimension [ 39 ] .

Quark Compositeness

On several occasions throughout the history of particle physics, physicists have
believed they had found the most basic building blocks of the Universe, only
to discover that those blocks were in fact made up of even smaller and more
basic pieces. Scientists found that atoms were made up of protons, neutrons, and
electrons; later they discovered protons were made up of quarks, which are currently
considered to be elementary particles. Some physicists have hypothesized that
quarks may themselves be composite structures made up of even smaller particles
called “preons” [ 26 ] . Part of the CMS experiment includes measurements that could
be used to find evidence of preons.

2.2 Sensors and Triggering Systems

To enable the search for new phenomena, the cylindrical CMS particle detector
consists of several layers of highly complex sensors. In total, the layers are nearly
seven meters thick, and each layer takes unique measurements designed to identify
different classes of particles. The innermost section of the cylinder is a silicon-based
particle tracker that is capable of measuring the deflection of particles subjected
to a strong magnetic field. It is used to calculate the charge-to-mass ratio of the
particles produced in collisions and reconstruct their trajectories. Beyond the tracker
are the Electromagnetic and Hadron Calorimeter layers. These sensors absorb
electromagnetic particles and hadrons—two types of fundamental particles—and
measure their energy. The calorimeters are surrounded by many layers of muon
absorption chambers, designed to capture muons—a class of weakly interacting
particles—that pass through the calorimeters [ 18 ] . An image of the CMS detector
as it was being assembled is shown in Fig. 2 .
Handling the data produced by these sensors presents significant challenges.
A particle tracking system monitors particle trajectories in order to estimate their
charge-to-mass ratio—a common process shared by most HEP experiments. The
CMS tracker achieves this goal by detecting particles passing over micrometer-scale
semiconductor strips. If the tracker's silicon detectors are viewed as analogous to
a camera sensor, the CMS tracker has a resolution of 66 megapixels, with each
pixel representing a detector with its own data channel. And unlike a typical digital
camera, which might be limited to a continuous shooting rate on the order of 10
frames per second by its data processing systems, the CMS sensors take a new
snapshot of particle collision data at a rate of up to 40 million times per second. The
tracker, however, only provides part of the sensor data that must be processed; the
two calorimeters each provide an additional 4096 data channels, with each channel