94 Search Results

Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and Pb-Pb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Fragmentation functions are obtained for jets with pTjet>30  GeV/c in events containing an isolated photon with pTγ>60  GeV/c, using charged tracks with transverse momentum pTtrk>1  GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial pT and azimuthal angle of the parton whose shower produced the jet. For central Pb-Pb collisions, modifications of themore » jet fragmentation functions are observed when compared to those measured in pp collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central Pb-Pb events show an excess (depletion) of low (high) pT particles, with a transition around 3  GeV/c. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well-defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the quark-gluon plasma.« less

Measurements of Higgs boson properties in the H → γγ decay channel are reported. The analysis is based on data collected by the CMS experiment in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV during the 2016 LHC running period, corresponding to an integrated luminosity of 35.9 fb$$^{−1}$$. Allowing the Higgs mass to float, the measurement yields a signal strength relative to the standard model prediction of 1.18$$_{− 0.14}^{+ 0.17}$$  = 1.18$$_{− 0.11}^{+ 0.12}$$ (stat)$$_{− 0.07}^{+ 0.09}$$ (syst)$$_{− 0.06}^{+ 0.07}$$ (theo), which is largely insensitive to the exact Higgs mass around 125 GeV. Signal strengths associated with the different Higgs boson production mechanisms, couplings to bosons and fermions, and effectivemore » couplings to photons and gluons are also measured.« less

A search for heavy resonances, decaying into the standard model vector bosons and the standard model Higgs boson, is presented. The final states considered contain a b quark-antiquark pair from the decay of the Higgs boson, along with electrons and muons and missing transverse momentum, due to undetected neutrinos, from the decay of the vector bosons. The mass spectra are used to search for a localized excess consistent with a resonant particle. The data sample corresponds to an integrated luminosity of 35.9 fb$$^{−1}$$ collected in 2016 by the CMS experiment at the CERN LHC from proton-proton collisions at a center-of-massmore » energy of 13 TeV. The data are found to be consistent with background expectations. Exclusion limits are set in the context of spin-0 two Higgs doublet models, some of which include the presence of dark matter. In the spin-1 heavy vector triplet framework, mass-degenerate W′ and Z′ resonances with dominant couplings to the standard model gauge bosons are excluded below a mass of 2.9 TeV at 95% confidence level.« less

The production of a $${\text {Z}}$$ boson, decaying to two charged leptons, in association with jets in proton-proton collisions at a centre-of-mass energy of 13 $$\,\text {TeV}$$ is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19 $$\,\text {fb}^\text {-1}$$ . The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the $${\text {Z}}$$ boson, the jet kinematic variables (transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance inmore » transverse momentum between the reconstructed jet recoil and the $${\text {Z}}$$ boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes one-loop corrections. The third is a fixed-order calculation with next-to-next-to-leading order accuracy for the process with a $${\text {Z}}$$ boson and one parton in the final state. The fourth combines the fully differential next-to-next-to-leading order calculation of the process with no parton in the final state with next-to-next-to-leading logarithm resummation and parton showering.« less

A search is presented for resonances decaying to a Z boson and a photon. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$$^{−1}$$, and collected with the CMS detector at the LHC in 2016. Two decay modes of the Z boson are investigated. In the leptonic channels, the Z boson candidates are reconstructed using electron or muon pairs. In the hadronic channels, they are identified using a large-radius jet, containing either light-quark or b quark decay products of the Z boson, via jet substructure andmore » advanced b quark tagging techniques. The results from these channels are combined and interpreted in terms of upper limits on the product of the production cross section and the branching fraction to Zγ for narrow and broad spin-0 resonances with masses between 0.35 and 4.0 TeV, providing thereby the most stringent limits on such resonances.« less

The process pp → pℓ$$^{+}$$ℓ$$^{−}$$p$$^{(*)}$$, with ℓ$$^{+}$$ℓ$$^{−}$$ a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the first time at the LHC in pp collisions at $$ \sqrt{s}=13 $$ TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the first time in 2016. The second proton either remains intact or is excited and then dissociates into a low-mass state p$$^{*}$$, which is undetected. The measurement is based on an integrated luminosity of 9.4 fb$$^{−1}$$ collected during standard, high-luminosity LHC operation.more » A total of 12 μ$$^{+}$$μ$$^{−}$$ and 8 e$$^{+}$$e$$^{−}$$ pairs with m(ℓ$$^{+}$$ℓ$$^{−}$$) > 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1.49 ± 0.07 (stat) ± 0.53 (syst) and 2.36 ± 0.09 (stat) ± 0.47 (syst), respectively. This corresponds to an excess of more than five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged γγ collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.« less

A measurement of the electroweak (EW) production of two jets in association with a $$\mathrm {Z} $$ boson in proton-proton collisions at $$\sqrt{s}=13\,\text {TeV} $$ is presented, based on data recorded in 2016 by the CMS experiment at the LHC corresponding to an integrated luminosity of 35.9 $$\,\text {fb}^{\text {--}1}$$ . The measurement is performed in the $$\ell \ell \mathrm {jj}$$ final state with $$\ell $$ including electrons and muons, and the jets j corresponding to the quarks produced in the hard interaction. The measured cross section in a kinematic region defined by invariant masses $$m_{\ell \ell } >50\,\text {GeV}more » $$ , $$m_{\mathrm {jj}} >120\,\text {GeV} $$ , and transverse momenta $$p_{\mathrm {T j}} > 25\,\text {GeV}$$ is $$\sigma _\mathrm {EW}(\ell \ell \mathrm {jj})= 534 \pm 20\,\text {(stat)} \pm 57\,\text {(syst) fb} $$ , in agreement with leading-order standard model predictions. The final state is also used to perform a search for anomalous trilinear gauge couplings. No evidence is found and limits on anomalous trilinear gauge couplings associated with dimension-six operators are given in the framework of an effective field theory. The corresponding 95% confidence level intervals are $$-2.6< c_{WWW}/\varLambda ^2 < 2.6\,\text {TeV}^{-2}$$ and $$-8.4< c_{W}/\varLambda ^2 < 10.1\,\text {TeV}^{-2}$$ . The additional jet activity of events in a signal-enriched region is also studied, and the measurements are in agreement with predictions.« less

A search is presented for a heavy resonance decaying into either a pair of Z bosons or a Z boson and a W boson (ZZ or WZ), with a Z boson decaying into a pair of neutrinos and the other boson decaying hadronically into two collimated quarks that are reconstructed as a highly energetic large-cone jet. The search is performed using the data collected with the CMS detector at the CERN LHC during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 35.9 fb$$^{−1}$$. No excess is observed in data withmore » regard to background expectations. Results are interpreted in scenarios of physics beyond the standard model. Limits at 95% confidence level on production cross sections are set at 0.9 fb (63 fb) for spin-1 W′ bosons, included in the heavy vector triplet model, with mass 4.0 TeV (1.0 TeV), and at 0.5 fb (40 fb) for spin-2 bulk gravitons with mass 4.0 TeV (1.0 TeV). Lower limits are set on the masses of W′ bosons in the context of two versions of the heavy vector triplet model of 3.1TeV and 3.4 TeV, respectively.« less

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