Georgios Bakas

A search is presented for the production of two additional Higgs bosons from an off-shell boson, where both additional particles decay to τ lepton pairs. The search is performed with a data sample collected with the CMS detector from proton-proton collisions at the LHC at s = 13 TeV , corresponding to an integrated luminosity of 138 fb − 1 . No deviation from the standard model background is observed. Exclusion limits are set on the type-X two-Higgs-doublet model alignment scenario. These results exclude previously unexplored regions of parameter space and provide constraints complementary to those from earlier searches.

A bstract: The results of a search for the production of two scalar bosons in final states with two photons and two tau leptons are presented. The search considers both nonresonant production of a Higgs boson pair, HH, and resonant production via a new boson X which decays either to HH or to H and a new scalar Y. The analysis uses up to 138 fb ^{− 1} of proton-proton collision data, recorded between 2016 and 2018 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV. No evidence for signal is found in the data. For the nonresonant production, the observed (expected) upper limit at 95% confidence level (CL) on the HH production cross section is set at 930 (740) fb, corresponding to 33 (26) times the standard model prediction. At 95% CL, HH production is observed (expected) to be excluded for values of κ _λ outside the range between −12 (−9.4) and 17 (15). Observed (expected) upper limits at 95% CL for the X → HH cross section are found to be within 160 to 2200 (200 to 1800) fb, depending on the mass of X. In the X → Y(ττ)H(γγ) search, the observed (expected) upper limits on the product of the production cross section and decay branching fractions vary between 0.059–1.2 fb (0.087–0.68 fb). For the X → Y(γγ)H(ττ) search the observed (expected) upper limits on the product of the production cross section and Y → γγ branching fraction vary between 0.69–15 fb (0.73–8.3 fb) in the low Y mass search, tightening constraints on the next-to-minimal supersymmetric standard model, and between 0.64–10 fb (0.70–7.6 fb) in the high Y mass search.

A novel machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27 500 tagged B s 0 → J / ψ ϕ ( 1020 ) decays from p p collisions at s = 13 TeV , collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb − 1 . A time- and flavor-dependent angular analysis of the μ + μ − K + K − final state, consistent with a ϕ ( 1020 ) → K + K − decay, is used to measure parameters of the B s 0 − B ¯ s 0 system. The weak phase is measured to be ϕ s = − 73 ± 22 ( stat ) ± 10 ( syst ) mrad , which, combined with the s = 8 TeV CMS result, gives ϕ s = − 75 ± 23 mrad . This value differs from zero by 3.2 standard deviations, providing the first evidence for mixing-induced C P violation in B s 0 → J / ψ ϕ ( 1020 ) decays. All measured physics parameters are found to agree with standard model predictions where available.

A bstract: A search for a pair of light pseudoscalar bosons (a ₁ ) produced in the decay of the 125 GeV Higgs boson is presented. The analysis examines decay modes where one a ₁ decays into a pair of tau leptons and the other decays into either another pair of tau leptons or a pair of muons. The a ₁ boson mass probed in this study ranges from 4 to 15 GeV. The data sample was recorded by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV and corresponds to an integrated luminosity of 138 fb ^{− 1} . No excess above standard model (SM) expectations is observed. The study combines the 4τ and 2μ2τ channels to set upper limits at 95% confidence level (CL) on the product of the Higgs boson production cross section and the branching fraction to the 4τ final state, relative to the Higgs boson production cross section predicted by the SM. In this interpretation, the a ₁ boson is assumed to have Yukawa-like couplings to fermions, with coupling strengths proportional to the respective fermion masses. The observed (expected) upper limits range between 0.007 (0.011) and 0.079 (0.066) across the mass range considered. The results are also interpreted in the context of models with two Higgs doublets and an additional complex singlet field (2HD+S). The tightest constraints are obtained for the Type III 2HD+S model. In this case, assuming the Higgs boson production cross section equals the SM prediction, values of the branching ratio for the Higgs boson decay into a pair of a ₁ bosons exceeding 16% are excluded at 95% CL for a ₁ boson masses between 5 and 15 GeV and tan β > 2, with the exception of scenarios in which the a ₁ boson mixes with charm or bottom quark-antiquark bound states.