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

Chapter 10
Conclusion
In this diploma thesis, the rst Model Independent Search for New Physics during DØ
Run II has been performed successfully.
In this apporach, all events detected with at least one electron/muon and a certain amount
of Missing Transverse Energy are selected. Following the specic topology of an event, exclusive
and inclusive event classes are constructed, e.g. 1ν 1µ 3jets(+X). This results
in a muon sample of 16 dierent particle combination and an electron sample of 17
combinations. In a rst step, the total number of events per class is compared to the
Standard Model prediction using Monte Carlo simulations. In a second step, these event
classes are systematically scanned for deviations from the Standard Model by examining
the variable ∑ p T and the MET distribution. Therefore, a special Search Algorithm has
been developed, based on the work of former Model Independent analyses ([18], [19] and
[20]). This algorithm identies the region with the greatest discrepancy between data and
Standard Model prediction, calculates the probablity of this deviation and tests its general
signicance. Statistical,aswellassystematicuncertaintiesareimplementedinthisroutine.
In the analysis presented here, a data set corresponding to an integrated luminosity
L ≈ 220 pb of p¯p-collisions is considered. These data were recorded by the DØ experiment
between −1 July 2002 and April 2004 with a center of mass energy of 1.96 TeV.
In the comparison of the total number of events per class, the general agreement between
data and Standard Model prediction is good. This leads to the conclusion that the DØexperimentisunderstoodwellandthedetectorsimulationreproducesmostoftheStandard
Model-processes corretly. All observed deviations could be explained with detector eects
not simulated properly in the Monte Carlo simulations. Nevertheless, the deviations already
observed at this level should be taken seriously in order to improve the description
of the data.
What concerns the dierential cross section, in the muon sample, 5 event classes with signicant
deviations have been found by the Search Algorithm {1ν 1µ(+X), 1ν 1µ 1j(+X),
1ν 2µ(+X), 1ν 1µ 2j(+X) and 1ν 1µ 1e 2j(+X)}. In the electron sample, 4 event classes
with signicant deviations have been found {1ν1e(+X), 1ν2e(+X), 1ν1µ1e(+X) and
1ν1µ1e2j(+X)}. Hence, three classes show discrepancies in both data samples, which
intensies the disagreement further.