35 Search Results

Methods are presented for calibrating the hadron calorimeter system of the CMS detector at the LHC. The hadron calorimeters of the CMS experiment are sampling calorimeters of brass and scintillator, and are in the form of one central detector and two endcaps. These calorimeters cover pseudorapidities |η| < 3 and are positioned inside the solenoidal magnet. An outer calorimeter, outside the magnet coil, covers |η| < 1.26, and a steel and quartz-fiber Cherenkov forward calorimeter extends the coverage to |η| < 5.19. The initial calibration of the calorimeters was based on results from test beams, augmented with the use ofmore » radioactive sources and lasers. The calibration was improved substantially using proton-proton collision data collected at √s = 7, 8, and 13 TeV, as well as cosmic ray muon data collected during the periods when the LHC beams were not present. The present calibration is performed using the 13 TeV data collected during 2016 corresponding to an integrated luminosity of 35.9 fb^-1. The intercalibration of channels exploits the approximate uniformity of energy collection over the azimuthal angle. The absolute energy scale of the central and endcap calorimeters is set using isolated charged hadrons. The energy scale for the electromagnetic portion of the forward calorimeters is set using Z→ ee data. The energy scale of the outer calorimeters has been determined with test beam data and is confirmed through data with high transverse momentum jets. In this paper, we present the details of the calibration methods and accuracy.« less

A measurement is presented of differential cross sections for t-channel single top quark and antiquark production in proton–proton collisions at a centre-of-mass energy of 13$$\,\text {Te}\text {V}$$ by the CMS experiment at the LHC. From a data set corresponding to an integrated luminosity of 35.9$$\,\text {fb}^{-1}$$, events containing one muon or electron and two or three jets are analysed. The cross section is measured as a function of the top quark transverse momentum ($$p_{\mathrm{T}} $$), rapidity, and polarisation angle, the charged lepton $$p_{\mathrm{T}} $$ and rapidity, and the $$p_{\mathrm{T}} $$ of the $$\text {W}{}{}$$  boson from the top quark decay.more » In addition, the charge ratio is measured differentially as a function of the top quark, charged lepton, and $$\text {W}{}{}$$  boson kinematic observables. The results are found to be in agreement with standard model predictions using various next-to-leading-order event generators and sets of parton distribution functions. Additionally, the spin asymmetry, sensitive to the top quark polarisation, is determined from the differential distribution of the polarisation angle at parton level to be $$0.440 \pm 0.070$$, in agreement with the standard model prediction.« less

A search in an all-jet final state for new massive resonances decaying to $$\text{ W }{}{}\text{ W }{}{}$$, $$\text{ W }{}{}\text{ Z }{}{}$$, or $$\text{ Z }{}{}\text{ Z }{}{}$$ boson pairs using a novel analysis method is presented. The analysis is performed on data corresponding to an integrated luminosity of 77.3 $$\,\text {fb}^{-1}$$ recorded with the CMS experiment at the LHC at a centre-of-mass energy of 13 $$\text {Te}\text {V}$$. The search is focussed on potential narrow-width resonances with masses above 1.2 $$\text {Te}\text {V}$$, where the decay products of each $$\text{ W }{}{}$$ or $$\text{ Z }{}{}$$ boson are expected tomore » be collimated into a single, large-radius jet. The signal is extracted using a three-dimensional maximum likelihood fit of the two jet masses and the dijet invariant mass, yielding an improvement in sensitivity of up to 30% relative to previous search methods. No excess is observed above the estimated standard model background. In a heavy vector triplet model, spin-1 $${\text {Z}}^{\prime }$$ and $${\text {W}}^{\prime }$$ resonances with masses below 3.5 and 3.8  $$\text {Te}\text {V}$$, respectively, are excluded at 95% confidence level. In a bulk graviton model, upper limits on cross sections are set between 27 and 0.2 $$\,\text {fb}$$ for resonance masses between 1.2 and 5.2  $$\text {Te}\text {V}$$, respectively. The limits presented in this paper are the best to date in the dijet final state.« less

A search is presented for $$\tau$$ slepton pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The search is carried out in events containing two $$\tau$$ leptons in the final state, on the assumption that each $$\tau$$ slepton decays primarily to a $$\tau$$ lepton and a neutralino. Events are considered in which each $$\tau$$ lepton decays to one or more hadrons and a neutrino, or in which one of the $$\tau$$ leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to anmore » integrated luminosity of 77.2 fb$$^{-1}$$. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for $$\tau$$ slepton pair production in various models for $$\tau$$ slepton masses between 90 and 200 GeV and neutralino masses of 1, 10, and 20 GeV. In the case of purely left-handed $$\tau$$ slepton production and decay to a $$\tau$$ lepton and a neutralino with a mass of 1 GeV, the strongest limit is obtained for a $$\tau$$ slepton mass of 125 GeV at a factor of 1.14 larger than the theoretical cross section.« less

New sets of CMS underlying-event parameters ("tunes") are presented for the PYTHIA8 event generator. These tunes use the NNPDF3.1 parton distribution functions (PDFs) at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) orders in perturbative quantum chromodynamics, and the strong coupling evolution at LO or NLO. Measurements of charged-particle multiplicity and transverse momentum densities at various hadron collision energies are fit simultaneously to determine the parameters of the tunes. Comparisons of the predictions of the new tunes are provided for observables sensitive to the event shapes at LEP, global underlying event, soft multiparton interactions, and double-parton scattering contributions. In addition, comparisonsmore » are made for observables measured in various specific processes, such as multijet, Drell-Yan, and top quark-antiquark pair production including jet substructure observables. The simulation of the underlying event provided by the new tunes is interfaced to a higher-order matrix-element calculation. For the first time, predictions from PYTHIA8 obtained with tunes based on NLO or NNLO PDFs are shown to reliably describe minimum-bias and underlying-event data with a similar level of agreement to predictions from tunes using LO PDF sets.« less

Measurements are presented of the triple-differential cross section for inclusive isolated-photon+jet events in pp collisions at $$\sqrt{s} =$$ 8 TeV as a function of photon transverse momentum ($$p_\mathrm{T}^\gamma$$), photon pseudorapidity ($$\eta^\gamma$$), and jet pseudorapidity ($$\eta^\text{jet}$$). The data correspond to an integrated luminosity of 19.7 fb$$^{-1}$$ that probe a broad range of the available phase space, for $$|\eta^\gamma|<1.44$$ and 1.57$$<|\eta^\gamma|<$$2.50, $$|\eta^\text{jet}|<$$2.5, 40$$< p_\mathrm{T}^\gamma<$$ 1000 GeV, and jet transverse momentum, $$p_\mathrm{T}^\text{jet}$$, $$>$$25 GeV. The measurements are compared to next-to-leading order perturbative quantum chromodynamics calculations, which reproduce the data within uncertainties.

The average total energy as well as its hadronic and electromagnetic components are measured with the CMS detector at pseudorapidities $$-6.6<\eta <-5.2$$ in proton-proton collisions at a centre-of-mass energy $$\sqrt{s}=13\,\text {TeV} $$ . The results are presented as a function of the charged particle multiplicity in the region $$|\eta |<2$$ . This measurement is sensitive to correlations induced by the underlying event structure over a very wide pseudorapidity region. The predictions of Monte Carlo event generators commonly used in collider experiments and ultra-high energy cosmic ray physics are compared to the data. All generators considered overestimate the fraction of energymore » going into hadrons.« less

A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, $$\Delta\phi_{12}$$ , is presented. The measurement considers events where the two leading jets are nearly collinear ("back-to-back") in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb$$^{-1}$$ are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log partonmore » showers and hadronization are generally in agreement with the measurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177$$^\circ < \Delta\phi_{12} <$$ 180$$^\circ$$. The 2- and 3-jet measurements are not simultaneously described by any of models.« less

Exclusive $$\rho^0$$(770) photoproduction is measured for the first time in ultraperipheral pPb collisions at $$\sqrt{s_\mathrm{NN}} =$$ 5.02 TeV with the CMS detector. The cross section $$\sigma (\gamma$$p $$\to$$ $$\rho^0$$(770)p) is 11.2 $$\pm$$ 1.4 (stat) $$\pm$$ 1.0 (syst) $$\mu$$b at $$\langle W_{\gamma\mathrm{p}}\rangle =$$ 92.6 GeV for photon-proton centre-of-mass energies $$W_{\gamma\mathrm{p}}$$ between 29 and 213 GeV. The differential cross section d$$\sigma/$$d$$|t|$ is measured in the interval 0.025$ < |t| < 1$ GeV$$^{2}$$ as a function of $$W_{\gamma\mathrm{p}}$$, where $$t$$ is the squared four-momentum transfer at the proton vertex. The results are compared with previous measurements and theoretical predictions. The measured cross sectionmore » $$\sigma (\gamma$$ p$$ \to \rho^0$$(770)p) has a power-law dependence on the photon-proton centre-of-mass, consistent with electron-proton collision measurements performed at HERA. The $$W_{\gamma\mathrm{p}}$$ dependence of the exponential slope of the differential cross section d$$\sigma/$$d$$|t|$ is also measured and is consistent with the previous measurements.« less

The performance of missing transverse momentum (p^→_T^miss) reconstruction algorithms for the CMS experiment is presented, using proton-proton collisions at a center-of-mass energy of 13 TeV, collected at the CERN LHC in 2016. The data sample corresponds to an integrated luminosity of 35.9 fb^-1. The results include measurements of the scale and resolution of p^→_T^miss, and detailed studies of events identified with anomalous p^→_T^miss. The performance is presented of a p^→_T^miss reconstruction algorithm that mitigates the effects of multiple proton-proton interactions, using the "pileup per particle identification" method. The performance is shown of an algorithm used to estimate the compatibility ofmore » the reconstructed p^→_T^miss with the hypothesis that it originates from resolution effects.« less