Event shapes and azimuthal correlations in Z + jets events in pp collisions at sqrt(s) =7 TeV

The CMS collaboration
Chatrchyan, Serguei , Khachatryan, Vardan , Sirunyan, Albert M , Tumasyan, Armen , Adam, Wolfgang , Aguilo, Ernest , Bergauer, Thomas , Dragicevic, Marko , Erö, Janos , Fabjan, Christian
Phys.Lett.B 722 (2013) 238-261, 2013.

Abstract (data abstract)
CERN-LHC. Measurements of event shapes and azimuthal correlations are presented for events where a Z boson is produced in association with jets in proton-proton collisions. The data collected with the CMS detector at the CERN LHC at sqrt(s) = 7 TeV correspond to an integrated luminosity of 5.0 inverse femtobarns. The analysis provides a test of predictions from perturbative QCD for a process that represents a substantial background to many physics channels. Results are presented as a function of jet multiplicity, for inclusive Z boson production and for Z bosons with transverse momenta greater than 150 GeV, and compared to predictions from Monte Carlo event generators that include leading-order multiparton matrix-element (with up to four hard partons in the final state) and next-to-leading-order simulations of Z + 1-jet events. The experimental results are corrected for detector effects, and can be compared directly with other QCD models For $Z/\gamma^{*}$ plus jets events we select: - two same flavour opposite sign leptons with $p_{T} > 20$ GeV and $|\eta| < 2.4$ and $71 < M_{\ell\ell} < 111 $ GeV - leptons are "dressed" with all photons in a cone of radius $\Delta R = 0.1$ - at least one jet, jet selection $p_{T} > 30$ GeV and $|\eta| < 2.4$, we remove jets within a radius of $\Delta R < 0.4$ with respect to the axes of each lepton - for the ratio plots a cut on Z rapidity |y|<1.4 is also applied The event shape variable is defined as $\tau_{\perp}\equiv 1-\max_{\vec{n}_{T}}\frac{\sum_{i}\left|\vec{p}_{\perp,i}\cdot \vec{n}_{T} \right|}{\sum_{i}p_{\perp,i}}$.

Loading Data...