43 Search Results

Two related searches for phenomena beyond the standard model (BSM) are performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2016-2018 and corresponding to an integrated luminosity of 137 fb$$^{-1}$$. The first search is inclusive, based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of jets identified as originating from bottom quarks, and the value of the kinematic variable $$M_\mathrm{T2}$$ for events with atmore » least two jets. For events with exactly one jet, the transverse momentum of the jet is used instead. The second search looks in addition for disappearing tracks produced by BSM long-lived charged particles that decay within the volume of the tracking detector. No excess event yield is observed above the predicted standard model background. This is used to constrain a range of BSM models that predict the following: the pair production of gluinos and squarks in the context of supersymmetry models conserving $$R$$-parity, with or without intermediate long-lived charginos produced in the decay chain; the resonant production of a colored scalar state decaying to a massive Dirac fermion and a quark; or the pair production of scalar and vector leptoquarks each decaying to a neutrino and a top, bottom, or light-flavor quark. In most of the cases, the results obtained are the most stringent constraints to date.« 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.

In 2017 a new pixel detector was installed in the CMS detector. This so-called Phase-1 pixel detector features four barrel layers in the central region and three disks per end in the forward regions. The upgraded pixel detector requires an upgraded data acquisition (DAQ) system to accept a new data format and larger event sizes. A new DAQ and control system has been developed based on a combination of custom and commercial microTCA parts. Custom mezzanine cards on standard carrier cards provide a front-end driver for readout, and two types of front-end controller for configuration and the distribution of clockmore » and trigger signals. Before the installation of the detector the DAQ system underwent a series of integration tests, including readout of the pilot pixel detector, which was constructed with prototype Phase-1 electronics and operated in CMS from 2015 to 2016, quality assurance of the CMS Phase-1 detector during its assembly, and testing with the CMS Central DAQ. This paper describes the Phase-1 pixel DAQ and control system, along with the integration tests and results. A description of the operational experience and performance in data taking is included.« less

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 search is presented for a Higgs boson that is produced in association with a Z boson and that decays to an undetected particle together with an isolated photon. The search is performed by the CMS Collaboration at the Large Hadron Collider using a data set corresponding to an integrated luminosity of 137 fb$$^{-1}$$ recorded at a center-of-mass energy of 13 TeV. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An uppermore » limit is set on the product of the cross section for associated Higgs and Z boson production and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a mass of 125 GeV, assuming the standard model production cross section, this corresponds to an observed (expected) upper limit on this branching fraction of 4.6 (3.6)% at 95% confidence level. These are the first limits on Higgs boson decays to final states that include an undetected massless dark photon.« 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

A search is presented for a heavy pseudoscalar boson $$\text {A}$$ decaying to a Z  boson and a Higgs boson with mass of 125 $$\,\text {GeV}$$ . In the final state considered, the Higgs boson decays to a bottom quark and antiquark, and the Z  boson decays either into a pair of electrons, muons, or neutrinos. The analysis is performed using a data sample corresponding to an integrated luminosity of 35.9 $$\,\text {fb}^{-1}$$ collected in 2016 by the CMS experiment at the LHC from proton–proton collisions at a center-of-mass energy of 13 $$\,\text {Te}\text {V}$$ . The data are foundmore » to be consistent with the background expectations. Exclusion limits are set in the context of two-Higgs-doublet models in the $$\text {A}$$ boson mass range between 225 and 1000 $$\,\text {GeV}$$ .« less

An embedding technique is presented to estimate standard model $$\tau\tau$$ backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed $$\mu\mu$$ events and replaced with simulated tau leptons with the same kinematic properties. In this way a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed.more » The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at $$\sqrt{s}=$$ 13 TeV corresponding to an integrated luminosity of 41.5 fb$$^{-1}$$.« less