Koulutusluokitus : Koulutuskoodimuutokset vuonna 1989, Liite 3

A measurement of inclusive ZZ production cross section and constraints on anomalous triple gauge couplings in proton-proton collisions at $\sqrt{s}$ = 8 TeV are presented. A data sample, corresponding to an integrated luminosity of 19.6 inverse-femtobarns was collected with the CMS experiment at the LHC. The measurements are performed in the leptonic decay modes $ZZ \to lll'l'$, where $l = e, \mu$ and $l' = e, \mu, \tau$. The measured total cross section, $\sigma (pp \to ZZ) = 7.7 \pm 0.5 (stat.)^{+0.5}_{-0.4} (syst.) \pm 0.4 (theo.) \pm 0.2 (lum.) pb$ for both Z bosons produced in the mass range $m_Z$ within 60 and 120 GeV, is consistent with standard model predictions. Differential cross sections are measured and well described by the theoretical predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ$\gamma$ couplings at the 95% confidence level: $f_4^Z$ in (-0.004,+0.004), $f_5^Z$ in (-0.005,+0.005), $f_4^\gamma$ in (-0.004,+0.004), and $f_5^\gamma$ in (-0.005,+0.005)

Search for excited quarks in the gamma plus jet final state in proton-proton collisions at root s=8 TeV

A search for excited quarks decaying into the gamma + jet final state is presented. The analysis is based on data corresponding to an integrated luminosity of 19.7 fb(-1) collected by the CMS experiment in proton-proton collisions at root s = 8 TeV at the LHC. Events with photons and jets with high transverse momenta are selected and the gamma + jet invariant mass distribution is studied to search for a resonance peak. The 95% confidence level upper limits on the product of cross section and branching fraction are evaluated as a function of the excited quark mass. Limits on excited quarks are presented as a function of their mass and coupling strength; masses below 3.5 TeV are excluded at 95% confidence level for unit couplings to their standard model partners

Performance of the ALICE experiment at the CERN LHC

ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables

Performance of the ALICE experiment at the CERN LHC

ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables

Medium modification of the shape of small-radius jets in central Pb-Pb collisions at root s(NN)=2:76 TeV

Abstract: We present the measurement of a new set of jet shape observables for track- based jets in central Pb-Pb collisions at √sNN = 2.76 TeV. The set of jet shapes includes the first radial moment or angularity, g; the momentum dispersion, pTD; and the differ- ence between the leading and sub-leading constituent track transverse momentum, LeSub. These observables provide complementary information on the jet fragmentation and can constrain different aspects of the theoretical description of jet-medium interactions. The jet shapes were measured for a small resolution parameter R = 0.2 and were fully corrected to particle level. The observed jet shape modifications indicate that in-medium fragmentation is harder and more collimated than vacuum fragmentation as obtained by PYTHIA cal- culations, which were validated with the measurements of the jet shapes in proton-proton collisions at √s = 7 TeV. The comparison of the measured distributions to templates for quark and gluon-initiated jets indicates that in-medium fragmentation resembles that of quark jets in vacuum. We further argue that the observed modifications are not consistent with a totally coherent energy loss picture where the jet loses energy as a single colour charge, suggesting that the medium resolves the jet structure at the angular scales probed by our measurements (R = 0.2). Furthermore, we observe that small-R jets can help to isolate purely energy loss effects from other effects that contribute to the modifications of the jet shower in medium such as the correlated background or medium response