Combination of inclusive top-quark pair production cross-section measurements using ATLAS and CMS data at sqrt(s) = 7 and 8 TeV

A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron–muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb−1 at s√ = 7 TeV and about 20 fb−1 at s√ = 8 TeV for each experiment. The combined cross-sections are determined to be 178.5 ± 4.7 pb at s√ = 7 TeV and 243.3+6.0−5.9 pb at s√ = 8 TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be R8/7 = 1.363 ± 0.032. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are mpolet=173.4+1.8−2.0 GeV and αs(mZ)=0.1170+0.0021−0.0018

Low-mass fermiophobic charged Higgs phenomenology in two-Higgs-doublet models

After the recent discovery of a Higgs-like boson, the possibility of an enlarged scalar sector arises as a natural question. Experimental searches for charged scalars have been already performed with negative results. We analyze the phenomenology associated with a fermiophobic charged Higgs (it does not couple to fermions at tree level), in two-Higgs-doublet models. All present experimental bounds are evaded trivially in this case, and one needs to consider other decay and production channels. We study the associated production of a charged Higgs with either a W or a neutral scalar boson, and the relevant decays for a light fermiophobic charged Higgs. The interesting features of this scenario should result encouraging for the LHC collaborations to perform searches for such a particle

Measurement of the t(t)over-bar production cross section in the all-jet final state in pp collisions at √s=7 TeV

This article is the pre-print version of the final published paper that is available from the link below.A measurement is presented of the tt production cross section (σtt) in protonproton collisions at a centre-of-mass energy of 7TeV, in the all-jet final state that contains at least six jets, two of which are tagged as originating from b quarks. The data correspond to an integrated luminosity of 3.54 fb-1, collected with the CMS detector at the LHC. The cross section is determined through an unbinned maximum likelihood fit of background and tt signal to the reconstructed mass spectrum of tt candidates in the data, in which events are subjected to a kinematic fit assuming a tt → W+bW-b → 6 jets hypothesis. The measurement yields σtt = 139±10 (stat.) ±26 (syst.) ±3 (lum.) pb, a result consistent with those obtained in other tt decay channels, as well as with predictions of the standard model

Jet energy scale uncertainty correlations between ATLAS and CMS at 8 TeV

An evaluation of the correlations between ATLAS and CMS jet energy scale uncertainties is presented for $\sqrt{s}=8$ TeV $pp$ collisions recorded in 2012. Uncertainties within each experiment are grouped based on the general type of systematic effect they are intended to cover and the means by which they are derived. Inter-experimental correlation value ranges are established for each corresponding group of uncertainty components. This correlation range is intended to cover the possible correlation values when performing combinations between the two experiments, where the most conservative value obtained from scanning over the correlation range should be used for the final combined measurement. The procedure described here is primarily aimed at single-observable analyses, and has limitations when applied to multi-observable measurements

Candidate Higgs boson events from collisions between protons in the LHC

Candidate Higgs boson events from collisions between protons in the LHC. The top event in the CMS experiment shows a decay into two photons (dashed yellow lines and green towers). The lower event in the ATLAS experiment shows a decay into four muons (red tracks

Combination of results from the ATLAS and CMS experiments on anomalous triple gauge couplings in ZZ production from pp collisions at a centre-of-mass energy of 7 TeV at the LHC

A procedure is presented to combine data from the ATLAS and CMS experiments on ZZ production to obtain constraints on anomalous neutral triple gauge boson couplings. Statistical and systematic uncertainties and their correlations are taken into account. Data from pp collisions at a center-of-mass energy of 7 TeV delivered by the LHC are used. The datasets correspond to integrated luminosities of $4.6$ and $5.0~\mathrm{fb}^{-1}$ for ATLAS and CMS, respectively. The combination is performed in the fully leptonic decay channels $\mathrm{ZZ} \to \ell^+ \ell^- \nu \bar{\nu}$ (ATLAS) and $\mathrm{ZZ} \to \ell^+ \ell^- \ell'^+ \ell'^-$ (ATLAS, CMS). Combined limits on the coupling parameters are $-0.010 < f_4^\gamma < 0.011$, $-0.0087 <f_4^Z < 0.0091$, $-0.011 <f_5^\gamma < 0.010$, and $-0.0091 <f_5^Z < 0.0089$ at $95\%$ C.L., where all other parameters are fixed to the standard model values. These results represent the first combined limits of the ATLAS and CMS collaborations for anomalous gauge boson couplings