Constraints on models of scalar and vector leptoquarks decaying to a quark and a neutrino at √ s = 13 TeVThe CMS Collaboration * AbstractThe results of a previous search by the CMS Collaboration for squarks and gluinos are reinterpreted to constrain models of leptoquark (LQ) production. The search considers jets in association with a transverse momentum imbalance, using the M T2 variable. The analysis uses proton-proton collision data at √ s = 13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb −1 . Leptoquark pair production is considered with LQ decays to a neutrino and a top, bottom, or light quark. This reinterpretation considers higher mass values than the original CMS search to constrain both scalar and vector LQs. Limits on the cross section for LQ pair production are derived at the 95% confidence level depending on the LQ decay mode. A vector LQ decaying with a 50% branching fraction to tν, and 50% to bτ, has been proposed as part of an explanation of anomalous flavor physics results. In such a model, using only the decays to tν, LQ masses below 1530 GeV are excluded assuming the Yang-Mills case with coupling κ = 1, or 1115 GeV in the minimal coupling case κ = 0, placing the most stringent constraint to date from pair production of vector LQs.Published in Physical Review D as

A search for low mass narrow vector resonances decaying into quark-antiquark pairs is presented. The analysis is based on data collected in 2017 with the CMS detector at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 41.1 fb −1. The results of this analysis are combined with those of an earlier analysis based on data collected at the same collision energy in 2016, corresponding to 35.9 fb −1. Signal candidates will be recoiling against initial state radiation and are identified as energetic, large-radius jets with two pronged substructure. The invariant jet mass spectrum is probed for a potential narrow peaking signal over a smoothly falling background. No evidence for such resonances is observed within the mass range of 50-450 GeV. Upper limits at the 95% confidence level are set on the coupling of narrow resonances to quarks, as a function of the resonance mass. For masses between 50 and 300 GeV these are the most sensitive limits to date. This analysis extends the earlier search to a mass range of 300-450 GeV, which is probed for the first time with jet substructure techniques.

Single top quark events produced in the t channel are used to set limits on anomalous Wtb couplings and to search for top quark flavour-changing neutral current (FCNC) interactions. The data taken with the CMS detector at the LHC in proton-proton collisions at √ s = 7 and 8 TeV correspond to integrated luminosities of 5.0 and 19.7 fb −1 , respectively. The analysis is performed using events with one muon and two or three jets. A Bayesian neural network technique is used to discriminate between the signal and backgrounds, which are observed to be consistent with the standard model prediction. The 95% confidence level (CL) exclusion limits on anomalous right-handed vector, and left-and righthanded tensor Wtb couplings are measured to be |f R V | < 0.16, |f L T | < 0.057, and −0.049 < f R T < 0.048, respectively. For the FCNC couplings κ tug and κ tcg , the 95% CL upper limits on coupling strengths are |κ tug |/Λ < 4.1 × 10 −3 TeV −1 and |κ tcg |/Λ < 1.where Λ is the scale for new physics, and correspond to upper limits on the branching fractions of 2.0 × 10 −5 and 4.1 × 10 −4 for the decays t → ug and t → cg, respectively. The CMS collaboration 26 IntroductionSingle top quark (t) production provides ways to investigate aspects of top quark physics that cannot be studied with tt events [1]. The theory of electroweak interactions predicts three mechanisms for producing single top quarks in hadron-hadron collisions. At leading order (LO), these are classified according to the virtuality of the W boson propagation in t-channel, s-channel, or associated tW production [2]. Single top quark production in all channels is directly related to the squared modulus of the Cabibbo-Kobayashi-Maskawa matrix element V tb . As a consequence, it provides a direct measurement of this quantity and thereby a check of the standard model (SM Collaborations. There are two complementary strategies to search for FCNC in single top quark production. A search can be performed in the s channel for resonance production through the fusion of a gluon (g) with an up (u) or charm (c) quark, as was the case in analyses by the CDF and ATLAS Collaborations. However, as pointed out by the D0 Collaboration, the s-channel production rate is proportional to the square of the FCNC coupling parameter and is therefore expected to be small [22]. On the other hand, the t-channel cross section and its corresponding kinematic properties have been measured accurately at the LHC [24][25][26], with an important feature being that the t-channel signature contains a light-quark jet produced in association with the single top quark. This light-quark jet can be used to search for deviations from the SM prediction caused by FCNC in the top quark sector. This strategy was applied by the D0 Collaboration [22], as well as in our analysis. Models that have contributions from FCNC in the production of single top quarks can have sizable deviations relative to SM predictions. Processes with FCNC vertices in the decay of the top quark are negligible. In contrast, the ...

The thermal behavior of chemically delithiated Li0.35[Ni1/3Co1/3Mn1/3]O2 and the AlF3-coated material was studied in the temperature range from room temperature to 600 °C. Thermogravimetric analysis results showed that the uncoated and the AlF3-coated Li0.35[Ni1/3Co1/3Mn1/3]O2 powders experienced distinct weight loss with increasing temperature, of which the weight loss was ascribed to oxygen release from the active materials. The released oxygen amount was less for the AlF3-coated Li0.35[Ni1/3Co1/3Mn1/3]O2 than the uncoated material, probably due to the blocking of the oxygen evolution by the AlF3 coating. The weight loss was associated with the irreversible phase transformation from a rhombohedral layer (R3m̅) structure to a cubic spinel (Fd3m) structure, as confirmed by in situ high-temperature X-ray diffraction. The reduced oxygen release brought about by the AlF3 coating delayed the phase transformation to the cubic spinel structure. This entailed shifts of the main exothermic reactions to higher temperatures for the active material in the presence of an electrolyte. The AlF3 coating remained on the surface of the active material to 300 °C. Thereafter, the layer changed to Li−Al−O with increasing temperature, as observed by the time-of-flight secondary ion mass spectroscopy. The improved thermal properties of the chemically delithiated AlF3-coated Li0.35[Ni1/3Co1/3Mn1/3]O2 were ascribed to the suppression of oxygen release from the active material, and this, in turn, retarded the formation of the cubic spinel phase.

Results are reported for the B 0 s → µ + µ − branching fraction and effective lifetime and from a search for the decay B 0 → µ + µ −. The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7 TeV (5 fb −1), 8 TeV (20 fb −1), and 13 TeV (36 fb −1). The branching fractions are determined by measuring event yields relative to B + → J/ψK + decays (with J/ψ → µ + µ −), which results in the reduction of many of the systematic uncertainties. The decay B 0 s → µ + µ − is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be B(B 0 s → µ + µ −) = [2.9 ± 0.7(exp) ± 0.2(frag)] × 10 −9 , where the first uncertainty combines the experimental statistical and systematic contributions, and the second is due to the uncertainty in the ratio of the B 0 s and the B + fragmentation functions. No significant excess is observed for the decay B 0 → µ + µ − , and an upper limit of B(B 0 → µ + µ −) < 3.6 × 10 −10 is obtained at 95% confidence level. The B 0 s → µ + µ − effective lifetime is measured to be τ µ + µ − = 1.70 +0.61 −0.44 ps. These results are consistent with standard model predictions.