Model Independent Search for Deviations from the Standard Model ...

Chapter 7
Search Algorithm
In Chapter 6, the general agreement between data and Monte Carlo simulation (MC) was
examined. The Search Algorithm presented in this chapter represents a more detailed
data-MC comparison and is the actual core of this analysis. Its principles are based on the
proceduresofaModelIndependentSearchperformedattheH1experiment(see[19]). This
algorithmcanbedividedintotwoseparatesteps: First,thedistributionsaresystematically
scanned for the greatest deviation, then, in the next step, the statistical signicance of this
deviation is evaluated in order to separate discoveries from uctuations typical for the
specic event class.
7.1 Region of Interest
As stated above, this part of the algorithm has the task of identifying for every event class
the region of greatest deviation between data and MC in the variable ∑ p T or the MET
distribution.
The word region must be put in context here. Every distribution is characterized by
its binning. A region is no more than a connected combination of bins. The data-MC
comparison is executed for all possible regions of the distribution, so, for example, bin
3 is examined, bin 3 − 4, bin 3 − 5, ..., bin 3−last bin. The algorithm is thus sensitive
to deviations present in a single bin as well as to a continuous excess of data or MC in
a wide combination of bins. A narrow resonance would result in a deviation present in
only a few bins; a signal spread over a large energy region could be identied by analyzing
a combination of numerous bins. This reects the model independence as super massive
X-particles with extremely short lifetimes are given the same attention as more stable non-
Standard Model particles. Thus, the Search Algorithm can detect decit regions, excess
regions and single outstanding events. The task is to identify any possible deviation from
the SM.
Astheamountofpossiblebincombinationsdecreaseswithabroaderbinning, [5 GeV]bins
where chosen for all distributions in order to speed up the algorithm. Compared to the
momentum resolution of the central tracker for muons of ∆(p T )/p 2 T
and
of the calorimeter for electrons of ≈ 0.002 GeV−1 ∆(p T )/p T ≈ 0.04 (see Section 2.2), this binning should