Simple, Robust and Powerful Tests of the Breaking Trend Hypothesis*

In this paper we develop a simple procedure which delivers tests for the presence of a broken trend in a univariate time series which do not require knowledge of the form of serial correlation in the data and are robust as to whether the shocks are generated by an I(0) or an I(1) process. Two trend break models are considered: the first holds the level fixed while allowing the trend to break, while the latter allows for a simultaneous break in level and trend. For the known break date case our proposed tests are formed as a weighted average of the optimal tests appropriate for I(0) and I(1) shocks. The weighted statistics are shown to have standard normal limiting null distributions and to attain the Gaussian asymptotic local power envelope, in each case regardless of whether the shocks are I(0) or I(1). In the unknown break date case we adopt the method of Andrews (1993) and take a weighted average of the statistics formed as the supremum over all possible break dates, subject to a trimming parameter, in both the I(0) and I(1) environments. Monte Carlo evidence suggests that our tests are in most cases more powerful, often substantially so, than the robust broken trend tests of Sayginsoy and Vogelsang (2004). An empirical application highlights the practical usefulness of our proposed tests.Broken trend, power envelope, unit root, stationarity tests

Measurement of B0 s meson production in pp and PbPb collisions at √sNN = 5.02 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.The production cross sections of B0 s mesons and charge conjugates are measured in proton-proton (pp) and PbPb collisions via the exclusive decay channel B0 s → J/ψφ → μ+μ−K+K− at a center-of-mass energy of 5.02 TeV per nucleon pair and within the rapidity range |y| < 2.4 using the CMS detector at the LHC. The pp measurement is performed as a function of transverse momentum (pT) of the B0 s mesons in the range of 7 to 50 GeV/c and is compared to the predictions of perturbative QCD calculations. The B0 s production yield in PbPb collisions is measured in two pT intervals, 7 to 15 and 15 to 50 GeV/c, and compared to the yield in pp collisions in the same kinematic region. The nuclear modification factor (RAA) is found to be 1.5 ± 0.6(stat) ± 0.5(syst) for 7–15 GeV/c, and 0.87 ± 0.30(stat) ± 0.17(syst) for 15–50 GeV/c, respectively. Within current uncertainties, the B0 s results are consistent with models of strangeness enhancement, and suppression by parton energy loss, as observed for the B+ mesons

Measurement of prompt ψ(2S) production cross sections in proton–lead and proton–proton collisions at √sNN = 5.02 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.Measurements of prompt ψ(2S) meson production cross sections in proton–lead (pPb) and proton–proton (pp) collisions at a nucleon–nucleon center-of-mass energy of √sNN = 5.02 TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb−1 and 28.0 pb−1, respectively. The nuclear modification factor RpPb is measured for prompt ψ(2S) in the transverse momentum range 4 < pT < 30 GeV/c and the center-of-mass rapidity range −2.4 < yCM < 1.93. The results on ψ(2S) RpPb are compared to the corresponding modification factor for prompt J/ψ mesons. The results point to different nuclear effects at play in the production of the excited charmonium state compared to the ground state, in the region of backward rapidity and for pT < 10 GeV/c

Search for dark matter in events with a leptoquark and missing transverse momentum in proton-proton collisions at 13 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.A search is presented for dark matter in proton-proton collisions at a center-of-mass energy of √s = 13 TeV using events with at least one high transverse momentum (pT) muon, at least one high-pT jet, and large missing transverse momentum. The data were collected with the CMS detector at the CERN LHC in 2016 and 2017, and correspond to an integrated luminosity of 77.4 fb−1. In the examined scenario, a pair of scalar leptoquarks is assumed to be produced. One leptoquark decays to a muon and a jet while the other decays to dark matter and low-pT standard model particles. The signature for signal events would be significant missing transverse momentum from the dark matter in conjunction with a peak at the leptoquark mass in the invariant mass distribution of the highest pT muon and jet. The data are observed to be consistent with the background predicted by the standard model. For the first benchmark scenario considered, dark matter masses up to 500 GeV are excluded for leptoquark masses mLQ ≈ 1400 GeV, and up to 300 GeV for mLQ ≈ 1500 GeV. For the second benchmark scenario, dark matter masses up to 600 GeV are excluded for mLQ ≈ 1400 GeV

Search for a W boson decaying to a τ lepton and a neutrino in proton-proton collisions at √s = 13 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.A search for a new high-mass resonance decaying to a τ lepton and a neutrino is reported. The analysis uses proton-proton collision data collected by the CMS experiment at the LHC at √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The search utilizes hadronically decaying τ leptons. No excess in the event yield is observed at high transverse masses of the τ and missing transverse momentum. An interpretation of results within the sequential standard model excludes W boson masses below 4.0 TeV at 95% confidence level. Existing limits are also improved on models in which the W boson decays preferentially to fermions of the third generation. Heavy W bosons with masses less than 1.7–3.9 TeV, depending on the coupling in the non-universal G(221) model, are excluded at 95% confidence level. These are the most stringent limits on this model to date

Search for an Lμ − Lτ gauge boson using Z → 4μ events in proton-proton collisions at √s = 13 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.A search for a narrow Z gauge boson with a mass between 5 and 70 GeV resulting from an Lμ − Lτ U(1) local gauge symmetry is reported. Theories that predict such a particle have been proposed as an explanation of various experimental discrepancies, including the lack of a dark matter signal in directdetection experiments, tension in the measurement of the anomalous magnetic moment of the muon, and reports of possible lepton flavor universality violation in B meson decays. A data sample of protonproton collisions at a center-of-mass energy of 13 TeV is used, corresponding to an integrated luminosity of 77.3 fb−1 recorded in 2016 and 2017 by the CMS detector at the LHC. Events containing four muons with an invariant mass near the standard model Z boson mass are analyzed, and the selection is further optimized to be sensitive to the events that may contain Z → Z μμ → 4μ decays. The event yields are consistent with the standard model predictions. Upper limits of 10−8–10−7 at 95% confidence level are set on the product of branching fractions B(Z → Z μμ)B(Z → μμ), depending on the Z mass, which excludes a Z boson coupling strength to muons above 0.004–0.3. These are the first dedicated limits on Lμ − Lτ models at the LHC and result in a significant increase in the excluded model parameter space. The results of this search may also be used to constrain the coupling strength of any light Z gauge boson to muons

Search for invisible decays of a Higgs boson produced through vector boson fusion in proton-proton collisions at √s = 13 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.A search for invisible decays of a Higgs boson is performed using proton-proton collision data collected with the CMS detector at the LHC in 2016 at a center-of-mass energy √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The search targets the production of a Higgs boson via vector boson fusion. The data are found to be in agreement with the background contributions from standard model processes. An observed (expected) upper limit of 0.33 (0.25), at 95% confidence level, is placed on the branching fraction of the Higgs boson decay to invisible particles, assuming standard model production rates and a Higgs boson mass of 125.09 GeV. Results from a combination of this analysis and other direct searches for invisible decays of the Higgs boson, performed using data collected at √s = 7, 8, and 13 TeV, are presented. An observed (expected) upper limit of 0.19 (0.15), at 95% confidence level, is set on the branching fraction of invisible decays of the Higgs boson. The combined limit represents the most stringent bound on the invisible branching fraction of the Higgs boson reported to date. This result is also interpreted in the context of Higgs-portal dark matter models, in which upper bounds are placed on the spin-independent dark-matter-nucleon scattering cross section

Measurement and interpretation of differential cross sections for Higgs boson production at √s = 13 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.Differential Higgs boson (H) production cross sections are sensitive probes for physics beyond the standard model. New physics may contribute in the gluon-gluon fusion loop, the dominant Higgs boson production mechanism at the LHC, and manifest itself through deviations from the distributions predicted by the standard model. Combined spectra for the H → γγ , H → ZZ, and H → bb decay channels and the inclusive Higgs boson production cross section are presented, based on proton-proton collision data recorded with the CMS detector at √s = 13 TeV corresponding to an integrated luminosity of 35.9 fb−1. The transverse momentum spectrum is used to place limits on the Higgs boson couplings to the top, bottom, and charm quarks, as well as its direct coupling to the gluon field. No significant deviations from the standard model are observed in any differential distribution. The measured total cross section is 61.1 ± 6.0 (stat) ± 3.7 (syst) pb, and the precision of the measurement of the differential cross section of the Higgs boson transverse momentum is improved by about 15% with respect to the H → γγ channel alone

Search for anomalous electroweak production of vector boson pairs in association with two jets in proton-proton collisions at 13 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.A search for anomalous electroweak production of WW, WZ, and ZZ boson pairs in association with two jets in proton-proton collisions at √s = 13 TeV at the LHC is reported. The data sample corresponds to an integrated luminosity of 35.9 fb−1 collected with the CMS detector. Events are selected by requiring two jets with large rapidity separation and invariant mass, one or two leptons (electrons or muons), and a W or Z boson decaying hadronically. No excess of events with respect to the standard model background predictions is observed and constraints on the structure of quartic vector boson interactions in the framework of dimension-8 effective field theory operators are reported. Stringent limits on parameters of the effective field theory operators are obtained. The observed 95% confidence level limits for the S0, M0, and T0 operators are −2.7 < fS0/4 < 2.7, −1.0 < fM0/4 < 1.0, and −0.17 < fT0/4 < 0.16, in units of TeV−4. Constraints are also reported on the product of the cross section and branching fraction for vector boson fusion production of charged Higgs bosons as a function of mass from 600 to 2000 GeV. The results are interpreted in the context of the Georgi–Machacek model

Measurement of nuclear modification factors of ϒ(1S), ϒ(2S), and ϒ(3S) mesons in PbPb collisions at √sNN = 5.02 TeV

This work is licensed under a Creative Commons Attribution 4.0 International License.The cross sections for ϒ(1S), ϒ(2S), and ϒ(3S) production in lead–lead (PbPb) and proton–proton (pp) collisions at √sNN = 5.02 TeV have been measured using the CMS detector at the LHC. The nuclear modification factors, RAA, derived from the PbPb-to-pp ratio of yields for each state, are studied as functions of meson rapidity and transverse momentum, as well as PbPb collision centrality. The yields of all three states are found to be significantly suppressed, and compatible with a sequential ordering of the suppression, RAA(ϒ(1S)) > RAA(ϒ(2S)) > RAA(ϒ(3S)). The suppression of ϒ(1S) is larger than that seen at √sNN = 2.76 TeV, although the two are compatible within uncertainties. The upper limit on the RAA of ϒ(3S) integrated over pT, rapidity and centrality is 0.096 at 95% confidence level, which is the strongest suppression observed for a quarkonium state in heavy ion collisions to date