62 Search Results

For the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both proton and lead dissociation processes are presented. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy per nucleon pair of $$\sqrt{s_{NN}}$$ = 8.16 TeV , almost 300 times higher than in previous measurements of diffractive production in proton-nucleus collisions. For lead dissociation processes, which correspond to the pomeron-lead event topology, the EPOS-LHC generator predictions are a factor of 2 below the data, but the model gives a reasonable description of the rapidity gap spectrum shape. For the pomeron-proton topology,more » the EPOS-LHC, QGSJET II, and HIJING predictions are all at least a factor of 5 lower than the data. The latter effect might be explained by a significant contribution of ultraperipheral photoproduction events mimicking the signature of diffractive processes. These data may be of significant help in understanding the high energy limit of quantum chromodynamics and for modeling cosmic ray air showers.« less

We present an observation of photon-photon production of $$\tau$$ lepton pairs in ultraperipheral lead-lead collisions. The measurement is based on a data sample with an integrated luminosity of 404 $$\mu$$b$$^{-1}$$ collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The $$\gamma\gamma$$$$\to$$$$\tau^+\tau^-$$ process is observed for $$\tau\tau$$ events with a muon and three charged hadrons in the final state. The measured fiducial cross section is $$\sigma(\gamma\gamma$$$$\to$$$$\tau^+\tau^-)$$ = 4.8 $$\pm$$ 0.6 (stat) $$\pm$$ 0.5 (syst) $$\mu$$b, in agreement with leading-order QED predictions. Using $$\sigma(\gamma\gamma$$$$\to$$$$\tau^+\tau^-)$$, we estimate a model-dependent value of the anomalous magnetic moment of the $$\tau$$ leptonmore » of $$a_\tau$$ = 0.001 $$^{+0.055}_{-0.089}$$.« less

A generic search is presented for the associated production of a Z boson or a photon with an additional unspecified massive particle X, pp → pp + Z/γ + X, in proton-tagged events from proton–proton collisions at $$\sqrt{s}$$ = 13 TeV, recorded in 2017 with the CMS detector and the CMS-TOTEM precision proton spectrometer. The missing mass spectrum is analysed in the 600–1600 GeV range and a fit is performed to search for possible deviations from the background expectation. No significant excess in data with respect to the background predictions has been observed. Model-independent upper limits on the visible promore » duction cross section of pp → pp + Z/γ + X are set« less

A search is presented for the Higgs boson decay to a pair of electrons (Image 1) in proton-proton collisions at $\sqrt{s}=13\text{TeV}$. The data set was collected with the CMS experiment at the LHC between 2016 and 2018, corresponding to an integrated luminosity of $138{\text{fb}}^{-1}$. The analysis uses event categories targeting Higgs boson production via gluon fusion and vector boson fusion. The observed upper limit on the Higgs boson branching fraction to an electron pair is $3.0\times {10}^{-4}more »$ ( $3.0\times {10}^{-4}$ expected) at the 95% confidence level, which is the most stringent limit on this branching fraction to date.« less

The first search is presented for vector-like leptons (VLLs) in the context of the “4321 model”, an ultraviolet-complete model with the potential to explain existing B physics measurements that are in tension with standard model predictions. The analyzed data, corresponding to an integrated luminosity of 96.5 ${\text{fb}}^{-1}$ , were recorded in 2017 and 2018 with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=13\text{TeV}$ . Final states with ≥3 b -tagged jets and two third-generation leptons (ττ, $\mathrm{\tau }{more »}_{}$ ν τ , or ${\mathrm{\nu }}_{\mathrm{\tau }}{\mathrm{\nu }}_{\mathrm{\tau }}$ ) are considered. Upper limits are derived on the VLL production cross section in the VLL mass range 500–1050 GeV. The maximum likelihood fit prefers the presence of signal at the level of 2.8 standard deviations, for a representative VLL mass point of 600 GeV. As a consequence, the observed upper limits are approximately double the expected limits.« less

A measurement is presented of the production of Z bosons that decay into two electrons or muons in association with jets, in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data were recorded by the CMS Collaboration at the LHC with an integrated luminosity of 35.9 fb$$^{-1}$$. The differential cross sections are measured as a function of the transverse momentum ($$p_\mathrm{T}$$) of the Z boson and the transverse momentum and rapidities of the five jets with largest $$p_\mathrm{T}$$. The jet multiplicity distribution is measured for up to eight jets. The hadronic activity in the events is estimated usingmore » the scalar sum of the $$p_\mathrm{T}$$ of all the jets. All measurements are unfolded to the stable particle-level and compared with predictions from various Monte Carlo event generators, as well as with expectations at leading and next-to-leading orders in perturbative quantum chromodynamics.« less

The Precision Proton Spectrometer (PPS) of the CMS and TOTEM experiments collected 107.7 fb$$^{-1}$$ in proton-proton (pp) collisions at the LHC at 13 TeV (Run 2). This paper describes the key features of the PPS alignment and optics calibrations, the proton reconstruction procedure, as well as the detector efficiency and the performance of the PPS simulation. The reconstruction and simulation are validated using a sample of (semi)exclusive dilepton events. The performance of PPS has proven the feasibility of continuously operating a near-beam proton spectrometer at a high luminosity hadron collider.

A novel technique based on machine learning is introduced to reconstruct the decays of highly Lorentz-boosted particles. Using an end-to-end deep learning strategy, the technique bypasses existing rule-based particle reconstruction methods typically used in high energy physics analyses. It uses minimally processed detector data as input and directly outputs particle properties of interest. The new technique is demonstrated for the reconstruction of the invariant mass of particles decaying in the CMS detector. The decay of a hypothetical scalar particle $\mathcal{A}$ into two photons, $\mathcal{A}\to \gamma \gamma$, is chosen as a benchmark decay. Lorentz boosts ${more »}_{}$ γ L =60–600 are considered, ranging from regimes where both photons are resolved to those where the photons are closely merged as one object. A training method using domain continuation is introduced, enabling the invariant mass reconstruction of unresolved photon pairs in a novel way. The new technique is validated using ${\pi }^0\to \gamma \gamma$ decays in LHC collision data.« less

The first observation of the production of W$$^\pm$$W$$^\pm$$ bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of 138 fb$$^{-1}$$ recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign W bosons decaying leptonically is 80.7 $$\pm$$ 11.2 (stat) $$^{+9.5}_{-8.6}$$ (syst) $$\pm$$ 12.1 (model)more » fb, whereas the measured fiducial cross section is 6.28 $$\pm$$ 0.81 (stat) $$\pm$$ 0.69 (syst) $$\pm$$ 0.37 (model) fb. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis.« less