16 Search Results

Azimuthal correlations between the two jets with the largest transverse momenta $$p_{\mathrm {T}}$$ in inclusive 2-, 3-, and 4-jet events are presented for several regions of the leading jet $$p_{\mathrm {T}}$$ up to 4 $$\,\text {Te}\text {V}$$ . For 3- and 4-jet scenarios, measurements of the minimum azimuthal angles between any two of the three or four leading $$p_{\mathrm {T}}$$ jets are also presented. The analysis is based on data from proton–proton collisions collected by the CMS Collaboration at a centre-of-mass energy of 13 $$\,\text {Te}\text {V}$$ , corresponding to an integrated luminosity of 35.9 $$\,\text {fb}^{-1}$$ . Calculations basedmore » on leading-order matrix elements supplemented with parton showering and hadronization do not fully describe the data, so next-to-leading-order calculations matched with parton shower and hadronization models are needed to better describe the measured distributions. Furthermore, we show that azimuthal jet correlations are sensitive to details of the parton showering, hadronization, and multiparton interactions. A next-to-leading-order calculation matched with parton showers in the MC@NLO method, as implemented in herwig  7, gives a better overall description of the measurements than the powheg method.« less

This paper presents a measurement of the underlying event activity in proton-proton collisions at a center-of-mass energy of 13 TeV, performed using inclusive Z boson production events collected with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 2.1 fb$$^{−1}$$. The underlying event activity is quantified in terms of the charged particle multiplicity, as well as of the scalar sum of the charged particles’ transverse momenta in different topological regions defined with respect to the Z boson direction. The distributions are unfolded to the stable particle level and compared with predictions from various Montemore » Carlo event generators, as well as with similar CDF and CMS measurements at center-of-mass energies of 1.96 and 7 TeV respectively.« less

A search for resonancelike structures in the Bs0π± invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at s=8  TeV, corresponding to an integrated luminosity of 19.7  fb-1. The Bs0 mesons are reconstructed in the decay chain Bs0→J/ψϕ, with J/ψ→μ+μ- and ϕ→K+K-. The Bs0π± invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed Bs0 and π± candidates. Upper limits are set on the relative production rates of the X(5568) and Bs0 states times the branching fraction of the decay X(5568)±→Bs0π±. In addition, upper limits are obtained as amore » function of the mass and the natural width of possible exotic states decaying into Bs0π±.« less

Many measurements and searches for physics beyond the standard model at the LHC rely on the efficient identification of heavy-flavour jets, i.e. jets originating from bottom or charm quarks. In this paper, the discriminating variables and the algorithms used for heavy-flavour jet identification during the first years of operation of the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, are presented. Heavy-flavour jet identification algorithms have been improved compared to those used previously at centre-of-mass energies of 7 and 8 TeV. For jets with transverse momenta in the range expected in simulated events, these new developmentsmore » result in an efficiency of 68% for the correct identification of a b jet for a probability of 1% of misidentifying a light-flavour jet. The improvement in relative efficiency at this misidentification probability is about 15%, compared to previous CMS algorithms. In addition, for the first time algorithms have been developed to identify jets containing two b hadrons in Lorentz-boosted event topologies, as well as to tag c jets. The large data sample recorded in 2016 at a centre-of-mass energy of 13 TeV has also allowed the development of new methods to measure the efficiency and misidentification probability of heavy-flavour jet identification algorithms. The b jet identification efficiency is measured with a precision of a few per cent at moderate jet transverse momenta (between 30 and 300 GeV) and about 5% at the highest jet transverse momenta (between 500 and 1000 GeV).« less

An analysis of the bottom baryon decay Λb→J/ψ(→μ+μ-)Λ(→pπ-) is performed to measure the Λb polarization and three angular parameters in data from pp collisions at s=7 and 8 TeV, collected by the CMS experiment at the Large Hadron Collider. The Λb polarization is measured to be 0.00±0.06(stat)±0.06(syst) and the parity-violating asymmetry parameter is determined to be 0.14±0.14(stat)±0.10(syst). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.

The top quark pair production cross section $$ \left({\sigma}_{\mathrm{t}\overline{\mathrm{t}}}\right) $$ is measured for the first time in pp collisions at a center-of-mass energy of 5.02 TeV. The data were collected by the CMS experiment at the LHC and correspond to an integrated luminosity of 27.4 pb$$^{−1}$$. The measurement is performed by analyzing events with at least one charged lepton. The measured cross section is $$ {\sigma}_{\mathrm{t}\overline{\mathrm{t}}} $$ = 69.5 ± 6.1 (stat) ± 5.6 (syst) ± 1.6 (lumi) pb, with a total relative uncertainty of 12%. The result is in agreement with the expectation from the standard model. The impactmore » of the presented measurement on the determination of the gluon distribution function is investigated.« less