Professor Daniela Bortoletto

Abstract:

The inclusive cross section for top-quark pair production measured by the CMS experiment in proton-proton collisions at a center-of-mass energy of 7 TeV is compared to the QCD prediction at next-to-next-to-leading order with various parton distribution functions to determine the top-quark pole mass, m t pole , or the strong coupling constant, α S . With the parton distribution function set NNPDF2.3, a pole mass of 176. 7 +3.8 -3.4 GeV is obtained when constraining α S at the scale of the Z boson mass, m Z , to the current world average. Alternatively, by constraining m t pole to the latest average from direct mass measurements, a value of α S (m Z ) = 0. 1151 +0.0033 -0.0032 is extracted. This is the first determination of α S using events from top-quark production. © 2013 The Authors. Published by Elsevier B.V.

Abstract:

A search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 fb-1 and 19.4 fb-1 collected with the CMS detector in pp collisions at √ s = 7 and 8 TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for m H = 125.6 GeV. The observed signal cross section times the branching fraction to WW for m H = 125.6 GeV is 0.72-0.18+0.20 times the standard model expectation. The spin-parity J P = 0+ hypothesis is favored against a narrow resonance with J P = 2+ or J P = 0- that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair. [Figure not available: see fulltext.] © 2014 Cern for the benefit of the CMS collaboration.