A search is presented for an excess of events with heavy-flavor quark pairs (
t
t ¯
and
b
b ¯
) and a large imbalance in transverse momentum in data from proton-proton collisions at a center-of-mass energy of 13
TeV
. The data correspond to an integrated luminosity of 2.2
fb
- 1
collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in
t
t ¯
and
b
b ¯
final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states.
Events with no charged particles produced between the two leading jets are studied in proton-proton collisions at s = 7 TeV . The jets were required to have transverse momentum p T jet > 40 GeV and pseudorapidity 1.5 < | η jet | < 4.7 , and to have values of η jet with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8 pb - 1 . Events with no charged particles with p T > 0.2 GeV in the interval - 1 < η < 1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5-1% of the selected dijet sample, is measured as a function of the p T of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky-Fadin-Kuraev-Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
A measurement is presented of the triple-differential dijet cross section at a centre-of-mass energy of 8 TeV using 19.7 fb -1 of data collected with the CMS detector in proton-proton collisions at the LHC. The cross section is measured as a function of the average transverse momentum, half the rapidity separation, and the boost of the two leading jets in the event. The cross section is corrected for detector effects and compared to calculations in perturbative quantum chromodynamics at next-to-leading order accuracy, complemented with electroweak and nonperturbative corrections. New constraints on parton distribution functions are obtained and the inferred value of the strong coupling constant is α S ( M Z ) = 0.1199 ± 0.0015 ( exp ) - 0.0020 + 0.0031 ( theo ) , where M Z is the mass of the Z boson.
The cross section of top quark-antiquark pair production in proton-proton collisions at [Formula: see text] is measured by the CMS experiment at the LHC, using data corresponding to an integrated luminosity of 2.2[Formula: see text]. The measurement is performed by analyzing events in which the final state includes one electron, one muon, and two or more jets, at least one of which is identified as originating from hadronization of a b quark. The measured cross section is [Formula: see text], in agreement with the expectation from the standard model.
The differential cross section and charge asymmetry for inclusive [Formula: see text] production at [Formula: see text] are measured as a function of muon pseudorapidity. The data sample corresponds to an integrated luminosity of 18.8[Formula: see text] recorded with the CMS detector at the LHC. These results provide important constraints on the parton distribution functions of the proton in the range of the Bjorken scaling variable x from [Formula: see text] to [Formula: see text].
The production cross section of a W boson in association with two b jets is measured using a sample of proton-proton collisions at [Formula: see text] collected by the CMS experiment at the CERN LHC. The data sample corresponds to an integrated luminosity of 19.8[Formula: see text]. The W bosons are reconstructed via their leptonic decays, [Formula: see text], where [Formula: see text] or [Formula: see text]. The fiducial region studied contains exactly one lepton with transverse momentum [Formula: see text] and pseudorapidity [Formula: see text], with exactly two b jets with [Formula: see text] and [Formula: see text] and no other jets with [Formula: see text] and [Formula: see text]. The cross section is measured to be [Formula: see text]+[Formula: see text], in agreement with standard model predictions.
A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2[Formula: see text]. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8[Formula: see text] corresponding to an integrated luminosity of 19.7[Formula: see text]. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.
The WZ production cross section is measured by the CMS experiment at the CERN LHC in proton-proton collision data samples corresponding to integrated luminosities of 4.9[Formula: see text] collected at [Formula: see text], and 19.6[Formula: see text] at [Formula: see text]. The measurements are performed using the fully-leptonic WZ decay modes with electrons and muons in the final state. The measured cross sections for [Formula: see text] are [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text]. Differential cross sections with respect to the [Formula: see text] boson [Formula: see text], the leading jet [Formula: see text], and the number of jets are obtained using the [Formula: see text] data. The results are consistent with standard model predictions and constraints on anomalous triple gauge couplings are obtained.
Searches are presented for direct production of top or bottom squark pairs in proton-proton collisions at the CERN LHC. Two searches, based on complementary techniques, are performed in all-jet final states that are characterized by a significant imbalance in transverse momentum. An additional search requires the presence of a charged lepton isolated from other activity in the event. The data were collected in 2015 at a centre-of-mass energy of 13[Formula: see text] with the CMS detector and correspond to an integrated luminosity of 2.3[Formula: see text]. No statistically significant excess of events is found beyond the expected contribution from standard model processes. Exclusion limits are set in the context of simplified models of top or bottom squark pair production. Models with top and bottom squark masses up to 830 and 890[Formula: see text], respectively, are probed for light neutralinos. For models with top squark masses of 675[Formula: see text], neutralino masses up to 260[Formula: see text] are excluded at 95% confidence level.