U. Acharya

The first evidence of electroweak (EW) production of pairs of Z bosons in association with two jets (jj) in the final state Z Z jj → ℓ ℓ ν ν jj , where ℓ = e , μ , is reported by the CMS experiment. The analysis is based on a data sample of proton-proton ( p p ) collisions at s = 13 TeV , corresponding to an integrated luminosity of 138 fb − 1 . Events are selected by requiring exactly two leptons of same flavor and opposite charge, large missing transverse momentum, and two jets with a large rapidity separation and large invariant mass. The EW production cross section in a fiducial volume is σ EW ( p p → Z Z jj → ℓ ℓ ν ν jj ) = 0.3 7 − 0.12 + 0.14 ( stat ) − 0.06 + 0.06 ( syst ) fb , in agreement with the standard model prediction of 0.39 ± 0.06 fb . The observed (expected) significance of the signal is 3.1 (2.8) standard deviations. Limits on anomalous quartic gauge couplings are derived in terms of dimension-8 effective field theory operators. A combination with the previously reported result from the Z Z decay channel with four charged leptons yields an observed (expected) significance of 5.0 (4.5) standard deviations for the EW production of Z boson pairs.

A search is presented for the production of a single narrow-width vectorlike B ′ quark that decays to a t quark and a W boson. This search targets a single-lepton final state, where a muon or electron originates either from the semileptonic decay of the t quark or from the leptonic decay of the W boson, with the other particle decaying hadronically. The (semi)leptonic portion of the event is reconstructed from an electron or muon, missing transverse momentum, and a small-radius jet identified as a b quark jet if the muon or electron originates from the t quark. The hadronic portion of the event is reconstructed as a single large-radius jet. The originating particle of the large-radius jet is identified using a neural-network-based tagger, and the dominant background contributions are modeled from data using a neural autoregressive flow network. The data were collected from 2016 to 2018 by the CMS experiment at the LHC in proton-proton collisions at s = 13 TeV , corresponding to an integrated luminosity of 138 fb − 1 . This search is the most sensitive to date to the production of single narrow-width B ′ quarks. It excludes electroweak-singlet B ′ quarks with Γ / m B ′ = 5 % for masses between 0.8 and 1.23 TeV. Limits are also placed on the production cross section of single B ′ quarks produced in association with t quarks, and on the coupling factor of the B ′ quark to electroweak bosons.

We present the first measurements of the forward and midrapidity η -meson cross sections from p + p collisions at s = 500 and 510 GeV, respectively. We also report the midrapidity η / π 0 ratio at 510 GeV. The forward cross section is measured differentially in η -meson transverse momentum ( p T ) from 1.0 to 6.5 GeV / c for pseudorapidity 3.0 < | η | < 3.8 . The midrapidity cross section is measured from 3.5 to 44 GeV / c for pseudorapidity | η | < 0.35 . Both cross sections serve as critical inputs to an updated global analysis of the η -meson fragmentation functions.

Utilizing the 2012 transversely polarized proton data from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, the forward η -meson transverse single-spin asymmetry ( A N ) was measured for p ↑ + p collisions at s = 200 GeV as a function of Feynman-x ( x F ) for 0.2 < | x F | < 0.8 and transverse momentum ( p T ) for 1.0 < p T < 5.0 GeV / c . Large asymmetries at positive x F are observed ( ⟨ A N ⟩ = 0.086 ± 0.019 ), agreeing well with previous measurements of π 0 and η A N , but with reach to higher x F and p T . The contribution of initial-state spin-momentum correlations to the asymmetry, as calculated in the collinear twist-3 framework, appears insufficient to describe the data.

Recent measurements of J / ψ production as a function of event charged-particle multiplicity at the collision energies of both the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC) show enhanced J / ψ production yields with increasing multiplicity. One potential explanation for this type of dependence is multiparton interactions (MPI). We present the first study of potential autocorrelations at RHIC energies and forward and backward rapidity of self-normalized J / ψ yields and ψ ( 2 S ) to J / ψ ratio, as a function of self-normalized multiplicity in p + p collisions. In addition, detailed studies tuned to RHIC energies were performed to investigate the MPI impacts. We find that the PHENIX data at RHIC are consistent with recent LHC measurements and can only be described by calculations that include MPI effects. The forward and backward ψ ( 2 S ) to J / ψ ratio is found to be less dependent on the charged-particle multiplicity.