• Energy Research

AbstractThe second-order (v2) and third-order (v3) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/ψ, as well as prompt ψ(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of$$ \sqrt{s_{\textrm{NN}}} $$sNN= 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb−1recorded with the CMS detector. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay channel. Thev2andv3coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measuredv2values for prompt J/ψ mesons are found to be larger than those for nonprompt J/ψ mesons. The prompt J/ψv2values at highpTare found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ψ mesonv3and prompt ψ(2S)v2andv3values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.

A search is presented for fractionally charged particles with charges below 1$e$, using their small energy loss in the tracking detector as a key variable to observe a signal. The analyzed dataset corresponds to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions collected at $\sqrt{s}$ = 13 TeV in 2016–2018 at the CERN LHC. This is the first search at the LHC for new particles with a charge between $e$/3 and 0.9$e$, including an extension of previous results at a charge of 2$e$/3. Masses up to 640 GeV and charges as low as $e$/3 are excluded at 95% confidence level. These are the most stringent limits to date for the considered Drell-Yan-like production mode. Physical review letters 134(13), 131802 (2025). doi:10.1103/PhysRevLett.134.131802 Published by APS, College Park, Md.

Abstract A search has been made for events containing an energetic jet and an imbalance in transverse momentum using a data sample of pp collisions at a center-of-mass energy of 7 TeV. This signature is common to both dark matter and extra dimensions models. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 5.0 fb−1. The number of observed events is consistent with the standard model expectation. Constraints on the dark matter-nucleon scattering cross sections are determined for both spin-independent and spin-dependent interaction models. For the spin-independent model, these are the most constraining limits for a dark matter particle with mass below 3.5 GeV/c 2, a region unexplored by direct detection experiments. For the spin-dependent model, these are the most stringent constraints over the 0.1–200 GeV/c 2 mass range. The constraints on the Arkani-Hamed, Dimopoulos, and Dvali model parameter M D determined as a function of the number of extra dimensions are also an improvement over the previous results.