Observation of Two Excited B\u3csup\u3e+\u3c/sup\u3e\u3csub\u3ec\u3c/sub\u3e States and Measurement of the B\u3csup\u3e+\u3c/sup\u3e\u3csub\u3ec\u3c/sub\u3e (2S) Mass in \u3ci\u3epp\u3c/i\u3e Collisions at √s = 13 TeV

Signals consistent with the B+c (2S) and B*c+(2S) states are observed in proton-proton collisions at √s = 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb−1, collected by the CMS experiment during the 2015–2018 LHC running periods. These excited []c states are observed in the B+c π+π− invariant mass spectrum, with the ground state B+c reconstructed through its decay to J/ψπ+. The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 ± 1.5(stat) ± 0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B+c (2S) meson is measured to be 6871.0 ± 1.2(stat) ± 0.8(syst) ± 0.8(B+c) MeV, where the last term corresponds to the uncertainty in the world-average B+c mass

Observation of Medium-Induced Modifications of Jet Fragmentation in Pb-Pb Collisions at √\u3csup\u3eS\u3c/sup\u3eNN =5.02 TeV Using Isolated Photon-Tagged Jets

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 pjetT \u3e 30 GeV/c in events containing an isolated photon with pγT \u3e 60 GeV/c, using charged tracks with transverse momentum ptrkT \u3e 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 the 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

Search for the Higgs Boson Decaying to Two Muons in Proton-Proton Collisions at √s =13 TeV

A search for the Higgs boson decaying to two oppositely charged muons is presented using data recorded by the CMS experiment at the CERN LHC in 2016 at a center-of-mass energy √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. Data are found to be compatible with the predicted background. For a Higgs boson with a mass of 125.09 GeV, the 95% confidence level observed (background-only expected) upper limit on the production cross section times the branching fraction to a pair of muons is found to be 3.0 (2.5) times the standard model expectation. In combination with data recorded at center-of-mass energies √s = 7 and 8 TeV, the background-only expected upper limit improves to 2.2 times the standard model value with a standard model expected significance of 1.0 standard deviation. The corresponding observed upper limit is 2.9 with an observed significance of 0.9 standard deviation. This corresponds to an observed upper limit on the standard model Higgs boson branching fraction to muons of 6.4 × 10−4 and to an observed signal strength of 1.0 ± 1.0(stat) ± 0.1(syst)

Jet Shapes of Isolated Photon-Tagged Jets in Pb-Pb and \u3ci\u3epp\u3c/i\u3e Collisions at √\u3csup\u3eS\u3c/sup\u3eNN=5.02 TeV

The modification of jet shapes in Pb-Pb collisions, relative to those in pp collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta (pT ) above 1 GeV/c in annuli around the axes of jets with pjetT \u3e 30 GeV/c associated with an isolated photon with pγT \u3e 60 GeV/c. The jet shape distributions are consistent between peripheral Pb-Pb and pp collisions, but are modified for more central Pb-Pb collisions. In these central Pb- Pb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to pp, reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons

Observation of Single Top Quark Production in Association with a \u3ci\u3eZ\u3c/i\u3e Boson in Proton-Proton Collisions at √s = 13 TeV

The observation of single top quark production in association with a Z boson and a quark (tZq) is reported. Events from proton-proton collisions at a center-of-mass energy of 13 TeV containing three charged leptons (either electrons or muons) and at least two jets are analyzed. The data were collected with the CMS detector in 2016 and 2017 and correspond to an integrated luminosity of 77.4fb−1. The increased integrated luminosity, a multivariate lepton identification, and a redesigned analysis strategy improve significantly the sensitivity of the analysis compared to previous searches for tZq production. The tZq signal is observed with a significance well over 5 standard deviations. The measured tZq production cross section is σ(pp → tZq → tℓ+þℓ−q) = 111 ± 13(stat)+-119 (syst) fb, for dilepton invariant masses above 30 GeV, in agreement with the standard model expectation

Search for Low-Mass Quark-Antiquark Resonances Produced in Association with a Photon at √s =13 TeV

A search for narrow low-mass resonances decaying to quark-antiquark pairs is presented. The search is based on proton-proton collision events collected at 13 TeV by the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of 35.9 fb−1, recorded in 2016. The search considers the case where the resonance has high transverse momentum due to initial-state radiation of a hard photon. To study this process, the decay products of the resonance are reconstructed as a single large-radius jet with two-pronged substructure. The signal would be identified as a localized excess in the jet invariant mass spectrum. No evidence for such a resonance is observed in the mass range 10 to 125 GeV. Upper limits at the 95% confidence level are set on the coupling strength of resonances decaying to quark pairs. The results obtained with this photon trigger strategy provide the first direct constraints on quark-antiquark resonance masses below 50 GeV obtained at a hadron collider

Combination of Searches for Higgs Boson Pair Production in Proton-Proton Collisions at √s = 13 TeV

This Letter describes a search for Higgs boson pair production using the combined results from four final states: bbγγ, bbττ, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250–3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section

Search for Dark Matter Particles Produced in Association with a Top Quark Pair at √s =13 TeV

A search is performed for dark matter particles produced in association with a top quark pair in proton-proton collisions at √s = 13 TeV. The data correspond to an integrated luminosity of 35.9 fb−1 recorded by the CMS detector at the LHC. No significant excess over the standard model expectation is observed. The results are interpreted using simplified models of dark matter production via spin-0 mediators that couple to dark matter particles and to standard model quarks, providing constraints on the coupling strength between the mediator and the quarks. These are the most stringent collider limits to date for scalar mediators, and the most stringent for pseudoscalar mediators at low masses

Search for Physics beyond the Standard Model in Events with Overlapping Photons and Jets

Results are reported from a search for new particles that decay into a photon and two gluons, in events with jets. Novel jet substructure techniques are developed that allow photons to be identified in an environment densely populated with hadrons. The analyzed proton-proton collision data were collected by the CMS experiment at the LHC, in 2016 at √s = 13 TeV, and correspond to an integrated luminosity of 35.9 fb−1. The spectra of total transverse hadronic energy of candidate events are examined for deviations from the standard model predictions. No statistically significant excess is observed over the expected background. The first cross section limits on new physics processes resulting in such events are set. The results are interpreted as upper limits on the rate of gluino pair production, utilizing a simplified stealth supersymmetry model. The excluded gluino masses extend up to 1.7 TeV, for a neutralino mass of 200 GeV and exceed previous mass constraints set by analyses targeting events with isolated photons

Studies of Beauty Suppression via Nonprompt \u3ci\u3eD\u3c/i\u3e\u3csup\u3e0\u3c/sup\u3e Mesons in Pb-Pb Collisions at √\u3csup\u3eS\u3c/sup\u3eNN =5.02 TeV

The transverse momentum spectra of D0 mesons from b hadron decays are measured at midrapidity (|y| \u3c 1) in pp and Pb-Pb collisions at a nucleon-nucleon center of mass energy of 5.02 TeV with the CMS detector at the LHC. The D0 mesons from b hadron decays are distinguished from prompt D0 mesons by their decay topologies. In Pb-Pb collisions, the B → D0 yield is found to be suppressed in the measured pT range from 2 to 100 GeV=c as compared to pp collisions. The suppression is weaker than that of prompt D0 mesons and charged hadrons for pT around 10 GeV=c. While theoretical calculations incorporating partonic energy loss in the quark-gluon plasma can successfully describe the measured B → D0 suppression at higher pT, the data show an indication of larger suppression than the model predictions in the range of 2 \u3c pT \u3c 5 GeV/c