Measurement of the top quark mass using events with a single reconstructed top quark in pp collisions at root s=13 TeV

Abstract:A measurement of the top quark mass is performed using a data sample en-riched with single top quark events produced in thetchannel. The study is based on proton-proton collision data, corresponding to an integrated luminosity of 35.9 fb−1, recorded at√s= 13TeV by the CMS experiment at the LHC in 2016. Candidate events are selectedby requiring an isolated high-momentum lepton (muon or electron) and exactly two jets,of which one is identified as originating from a bottom quark. Multivariate discriminantsare designed to separate the signal from the background. Optimized thresholds are placedon the discriminant outputs to obtain an event sample with high signal purity. The topquark mass is found to be172.13+0.76−0.77GeV, where the uncertainty includes both the sta-tistical and systematic components, reaching sub-GeV precision for the first time in thisevent topology. The masses of the top quark and antiquark are also determined separatelyusing the lepton charge in the final state, from which the mass ratio and difference aredetermined to be0.9952+0.0079−0.0104and0.83+1.79−1.35GeV, respectively. The results are consistentwithCPTinvariance

Complex Formation and Rearrangement Reactions of the Phosphine Hydride Anions [OsH3(PPh3)3]- and [IrH2(PPh3)3]-

[OsH4(PPh3)3] (1) reacts with KH in THF in the presence of 18-crown-6 to form [K(THF)(18-crown-6)][OsH3(PPh3)3] (2), characterized by NMR spectroscopy and X-ray crystallography; cation−anion contact is achieved through three Os−H···K moieties. In contrast, [IrH3(PPh3)3] (6) reacts with KH and 18-crown-6 in THF with redistribution of ligands to produce the known bis-phosphine complex [K(18-crown-6)][IrH4(PPh3)2] (7). This reaction has been followed by NMR spectroscopy, and [IrH2(PPh3)3]- has been identified as a likely intermediate. K[OsH3(PPh3)3] (3) reacts with Bun3SnCl to form the tin-osmium complex [OsH3(SnBun3)(PPh3)3] (8), characterized by NMR spectroscopy and X-ray crystallography. The molecule contains a seven-coordinate osmium center, which can be described approximately as a distorted fac-[OsH3(PPh3)] arrangement, with the SnBun3 moiety capping the OsH3 face

Expanding metallaborane chemistry: an octahedral BH6 moiety supported through M-H-B bridges

The X-ray crystal structure of the complex [(triphos)Fe(mu,eta(4):eta(4)-BH6)Fe(triphos)](+) in conjunction with spectroscopic data reveals a central unit formally described as BH63-; DFT calculations show why this ligand is stable for iron but not for the ruthenium analogue

A high-resolution neutron powder diffraction study of ammonia dihydrate (ND3 center dot 2D(2)O) phase I

We have measured the thermal expansivity of ammonia dihydrate (ND3.O2D(2)O) phase I from 4.2 to 174 K at ambient pressure, and the incompressibility at 174 K from 0 to 0.45 GPa, using time-of-flight neutron powder diffraction. The unit cell volume as a function of temperature, V(T), was fitted with a Gruneisen approximation to the zero-pressure equation of state (with the lattice vibrational energy calculated from a double-Debye model fitted to heat capacity data) having the following parameters at zero pressure and temperature: V-0,V-0=356.464+/-0.005 Angstrom(3), (K-0,K-0/gamma)=7.163+/-0.024 GPa, and K'(0,0)=5.41+/-0.33 (where V-P,V-T is the unit cell volume at pressure P and temperature T, K-P,K-T is the isothermal bulk modulus, K'(P,T) is its first pressure derivative, and gamma is the Gruneisen ratio). The two Debye temperatures are theta(A)(D)=165+/-3 K and theta(D)(B)=729+/-4 K. The unit cell volume at 174 K as a function of pressure, V(P), was fitted with a third-order Birch-Murnaghan equation of state having the following parameters: V-0,V-174=365.69+/-0.16 Angstrom(3), K-0,K-174=7.02+/-0.25 GPa, and K'(0,174)=9.56+/-1.28. The volume thermal expansion coefficient, alpha(V), at 174 K and atmospheric pressure is 281.3x10(-6) K-1. The proton disorder manifested at high homologous temperatures is seen to be frozen in, on the time scale of these experiments, down to 4.2 K. A high-pressure polymorph of ammonia dihydrate was observed following melting of the sample at 179 K and 0.46 GPa. (C) 2003 American Institute of Physics

Measurement of the tt¯ charge asymmetry in events with highly Lorentz-boosted top quarks in pp collisions at s=13 TeV

The measurement of the charge asymmetry in top quark pair events with highly Lorentz-boosted top quarks decaying to a single lepton and jets is presented. The analysis is performed using proton-proton collisions at s=13TeV with the CMS detector at the LHC and corresponding to an integrated luminosity of 138 fb−1. The selection is optimized for top quarks produced with large Lorentz boosts, resulting in nonisolated leptons and overlapping jets. The top quark charge asymmetry is measured for events with a tt¯ invariant mass larger than 750 GeV and corrected for detector and acceptance effects using a binned maximum likelihood fit. The measured top quark charge asymmetry of (0.42−0.69+0.64)% is in good agreement with the standard model prediction at next-to-next-to-leading order in quantum chromodynamic perturbation theory with next-to-leading-order electroweak corrections. The result is also presented for two invariant mass ranges, 750–900 and >900GeV

Portable Acceleration of CMS Computing Workflows with Coprocessors as a Service

Computing demands for large scientific experiments, such as the CMS experiment at the CERN LHC, will increase dramatically in the next decades. To complement the future performance increases of software running on central processing units (CPUs), explorations of coprocessor usage in data processing hold great potential and interest. Coprocessors are a class of computer processors that supplement CPUs, often improving the execution of certain functions due to architectural design choices. We explore the approach of Services for Optimized Network Inference on Coprocessors (SONIC) and study the deployment of this as-a-service approach in large-scale data processing. In the studies, we take a data processing workflow of the CMS experiment and run the main workflow on CPUs, while offloading several machine learning (ML) inference tasks onto either remote or local coprocessors, specifically graphics processing units (GPUs). With experiments performed at Google Cloud, the Purdue Tier-2 computing center, and combinations of the two, we demonstrate the acceleration of these ML algorithms individually on coprocessors and the corresponding throughput improvement for the entire workflow. This approach can be easily generalized to different types of coprocessors and deployed on local CPUs without decreasing the throughput performance. We emphasize that the SONIC approach enables high coprocessor usage and enables the portability to run workflows on different types of coprocessors

Search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state in proton-proton collisions at s=13TeV

A search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state is presented. The analysis is based on proton-proton collision data recorded by the CMS detector in 2016–2018 at a centre-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 138fb−1. The search is sensitive to resonances with masses between 1.3 and 6TeV, decaying to bosons that are highly Lorentz-boosted such that each of the bosons forms a single large-radius jet. Machine learning techniques are employed to identify such jets. No significant excess over the estimated standard model background is observed. A maximum local significance of 3.6 standard deviations, corresponding to a global significance of 2.3 standard deviations, is observed at masses of 2.1 and 2.9 TeV. In a heavy vector triplet model, spin-1 Z′ and W′ resonances with masses below 4.8TeV are excluded at the 95% confidence level (CL). These limits are the most stringent to date. In a bulk graviton model, spin-2 gravitons and spin-0 radions with masses below 1.4 and 2.7TeV, respectively, are excluded at 95% CL. Production of heavy resonances through vector boson fusion is constrained with upper cross section limits at 95% CL as low as 0.1fb

Study of azimuthal anisotropy of ϒ(1S) mesons in pPb collisions at sNN = 8.16 TeV

The azimuthal anisotropy of Image 1 mesons in high-multiplicity proton-lead collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 8.16TeV. The Image 1 mesons are reconstructed using their dimuon decay channel. The anisotropy is characterized by the second Fourier harmonic coefficients, found using a two-particle correlation technique, in which the Image 1 mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. Nonflow contamination from the dijet background is removed using a low-multiplicity subtraction method, and the results are presented as a function of Image 1 transverse momentum. The azimuthal anisotropies are smaller than those found for charmonia in proton-lead collisions at the same collision energy, but are consistent with values found for Image 1 mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV