2011 QCD and High Energy Interactions - Rencontres de Moriond ...

RECENT RESULTS ON JETS FROM CMS
F. PANDOLFI for the CMS Collaboration
Università di Roma ‘Sapienza’ and INFN Sezione di Roma,
Piazzale Aldo Moro 5, 00185 Rome Italy
We present an overview of the results on jets from proton-proton collisions at a center-of-mass
energy of √ s = 7 TeV using data collected by the CMS experiment in 2010. It includes the in
situ jet calibration and resolution measurements, the inclusive jet cross section measurement
and a search for quark contact interactions with a dijet angular analysis.
1 Introduction
The Large Hadron Collider offers the possibility of confronting QCD at the energy frontier. The
data it delivers gives us new insight on the precision of perturbative QCD (pQCD) predictions
and the modeling of non-perturbative effects in the current Monte Carlo (MC) generators. Jets
can also be employed, as will be shown, in the search for physics beyond the Standard Model.
At a hadron collider most final states have jets. Hence jets as a physics objects must be
understood, whether they are part of the signal being analysed, or of the background. In order
to do so both their energy scale and resolution have to be measured to a good degree of precision.
In this brief article an overview of the results on jets at the CMS 1 detector based on the
2010 data taking is given. Section 2 shows the results of the jet in situ calibration and resolution
measurements. Section 3 describes physics results obtained with jets.
2 Jet Calibration and Resolution Measurement
Three main methods are employed in CMS to reconstruct jets 2 : calorimeter jets are constructed
by the clustering of projective calorimeter towers; jet-plus-track jets improve the measurement of
calorimeter jets by exploiting the associated tracks; Particle-Flow jets cluster particle candidates
created by the Particle-Flow full-event reconstruction technique, which attempts to measure
every stable particle produced in a collision through the combination of all CMS subdetectors.
Jets are clustered using the anti-kT 3 algorithm, with a radius parameter of R = 0.5.
Jets have to undergo a series of energy corrections before they can be used in an analysis.
CMS has developed a factorized approach, in which the corrections are defined in order to be
be independent of each other, and can be applied sequentially. The corrections are:
• an offset correction, which takes into account multiple proton-proton interactions in the
given bunch crossing (pile-up);
• a relative correction, which uniforms the detector response as a function of pseudorapidity;