الفهرس 
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Abstract
The topic of this thesis is the search for new physics at the LHC, namely the search for a
soft signal studying the structure of so called ” exotic underlying events”. It is organized as
follow:
Chapter one deals with a brief review of a new type of particle that theorists have
suggested which can be produced in pp collisions at the LHC, namely so called heavy quirks.
These particles are charged under a new unbroken nonabelian
gauge group, characterized by
a new colour force with a very small string tension. As such, particles are expected with masses
of several hundreds of GeV, and when pairwise
created in high energy protonproton
collisions these will be connected by a colour string from this new force, and move away from
each other staying connected by the string. Unlike in QCD the energy in the string will not
build up to high enough values, due to the low string tension, so that these strings won’t break
up into quirk antiquirk
pairs and possibly would form ‘quirk mesons’. On the contrary the
particles that emerge from the interaction region will stay connected to each other which will
lead to very unusual signatures in the detector depending on the exact parameters of the
model. Two experimentally accessible signatures are the double track production, ie first a
track in the detector which actually corresponds to a pair of particles that are strongly
connected, and secondly a fast oscillation (yoyo effect) of two electromagnetically charged
particles in the tracker of the experiment, which form a dipole and will emit a lot of soft
photons. In this study we concentrate on the latter process.
In the second chapter, a full description of the CMS (Compact Muon Solenoid) particle
detector experiment, which is centered along the Large Hadron Collider (LHC), is given. The
Compact Muon Solenoid (CMS) detector is one of the two general purpose detectors installed
at the LHC. CMS is distinguished for this study by its large, high field solenoidal magnet, high
precision silicon tracker, and by its homogeneous scintillating crystal electromagnetic
calorimeter. The design of CMS was motivated by the main physics program of the LHC,
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namely the search for the mechanism of electroweak symmetry breaking and the search for
new physics beyond the Standard Model.
In the third chapter, we studied the signal and the possible backgrounds to signal of
new physics objects at colliders characterized by an “exotic underlying events”. Also we
measured and characterizing the soft events and underlying event which defined as ”every
thing in the event not associated with hard jets or leptons” by using Monte Carlo event
generator PYTHIA 8.186.
Chapter four focuses on comparison between the candidate signal of exotic particles
”Quirks” from beyond Standard Model and the background events of soft QCD which
simulated by Pythia8 event generator in two ways. First, study the signal and background in
case photons are unclustered. Secondly, we apply a clustering algorithm on the photons and
search for features of signal different from background. Then we studied the sensitivity for
finding signal of new physics by set simple cuts on the LHC production sample using the
transverse energy per events of clustered photons radiated by “Quirks”.
In the final chapter, we produced the simulation of soft photons in the detector which
are supposed to be emit in a particular angular distribution “antenna pattern” radiated by
“Quirks” then we compared this ”antenna” to simulation of soft photons emitted by the
background. Finally we discuss real data events from an early datataking
run, that were
collected in 2010 and we give our conclusion.