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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Probing bottom-associated production of a TeV scale scalar decaying to a top quark and dark matter at the LHC

Abstract A minimal non-thermal dark matter model that can explain both the existence of dark matter and the baryon asymmetry in the universe is studied. It requires two color-triplet, iso-singlet scalars with$$ \mathcal{O}\left(\textrm{TeV}\right) $$ O TeV masses and a singlet Majorana fermion with a mass of$$ \mathcal{O}\left(\textrm{GeV}\right) $$ O GeV . The fermion becomes stable and can play the role of the dark matter candidate. We consider the fermion to interact with a top quark via the exchange of QCD-charged scalar fields coupled dominantly to third generation fermions. The signature of a single top quark production associated with a bottom quark and large missing transverse momentum opens up the possibility to search for this type of model at the LHC in a way complementary to existing monotop searches.

Physics↗
DOE OSTI2025

Combination of searches for singly produced vectorlike top quarks in 𝑝⁢𝑝 collisions at $\sqrt{𝑠}$ =13 TeV with the ATLAS detector

A combination of searches for the single production of vectorlike top quarks (𝑇) is presented. These analyses are based on proton-proton collisions at $\sqrt{𝑠}$ = 13 TeV recorded in 2015–2018 with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb −1 . The 𝑇 decay modes considered in this combination are into a top quark and either a Standard Model Higgs boson or a 𝑍 boson (𝑇 → 𝐻⁡𝑡 and 𝑇 → 𝑍⁢𝑡). The individual searches used in the combination are differentiated by the number of leptons (𝑒, 𝜇) in the final state. The observed data are found to be in good agreement with the Standard Model background prediction. Interpretations are provided for a range of masses and couplings of the vectorlike top quark for benchmark models and generalized representations in terms of 95% confidence level limits. For a benchmark signal prediction of a vectorlike top quark SU(2) singlet with electroweak coupling, 𝜅, of 0.5, masses below 2.1 TeV are excluded, resulting in the most restrictive limits to date.

Composite models↗
DOE OSTI2025

Measurement of the $\textrm{t}\overline{\textrm{t}}\textrm{H}$ and tH production rates in the H → $\textrm{b}\overline{\textrm{b}}$ decay channel using proton-proton collision data at $\sqrt{s}$ = 13 TeV

An analysis of the production of a Higgs boson (H) in association with a top quark-antiquark pair ($\textrm{t}\overline{\textrm{t}}\textrm{H}$) or a single top quark (tH) is presented. The Higgs boson decay into a bottom quark-antiquark pair (H → $\textrm{b}\overline{\textrm{b}}$) is targeted, and three different final states of the top quark decays are considered, defined by the number of leptons (electrons or muons) in the event. The analysis utilises proton-proton collision data collected at the CERN LHC with the CMS experiment at $\sqrt{s}$ = 13 TeV in 2016–2018, which correspond to an integrated luminosity of 138 fb −1 . The observed $\sqrt{s}$ production rate relative to the standard model expectation is 0.33 ± 0.26 = 0.33 ± 0.17(stat) ± 0.21(syst). Additionally, the $\textrm{t}\overline{\textrm{t}}\textrm{H}$ production rate is determined in intervals of Higgs boson transverse momentum. An upper limit at 95% confidence level is set on the tH production rate of 14.6 times the standard model prediction, with an expectation of ${19.3}_{-6.0}^{+9.2}$. Finally, constraints are derived on the strength and structure of the coupling between the Higgs boson and the top quark from simultaneous extraction of the $\textrm{t}\overline{\textrm{t}}\textrm{H}$ and tH production rates, and the results are combined with those obtained in other Higgs boson decay channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

A precise electron EDM constraint on CP-odd heavy-quark Yukawas

CP-odd Higgs couplings to bottom and charm quarks arise in many extensions of the standard model and are of potential interest for electroweak baryogenesis. These couplings induce a contribution to the electron EDM. The experimental limit on the latter then leads to a strong bound on the CP-odd Higgs couplings. We point out that this bound receives large QCD corrections, even though it arises from a leptonic observable. We calculate the contribution of CP-odd Higgs couplings to the bottom and charm quarks in renormalisation-group improved perturbation theory at next-to-leading order in the strong interaction, thereby reducing the uncertainty to a few percent.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Hidden-flavor four-quark states in the charm and bottom region

We discuss the spectrum and the internal composition of ground and excited four-quark states in the charm and bottom energy region. To this end we extend previous calculations within the framework of the relativistic four-body Faddeev-Yakubovsky equation to include quantum numbers with J P C = 0 + + , 0 − + , 1 − − , 1 + − and 1 + + and study their internal composition in terms of heavy-light meson pairs, hadroquarkonia and diquark-antidiquark clusters. We observe similar patterns in the charm and bottom energy region with different compositions of the four-quark states depending on J P C quantum numbers. Most notably, we find that all states with C · P = + 1 are dominated by heavy-light meson contributions, whereas for axial-vector states with J P C = 1 + − including the Z c ( 3900 ) we find a much more complicated picture depending on the flavor content. We systematically compare our results for the spectrum with existing experimental results and provide predictions for future analyses. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2026

Search for single production of a vector-like T quark decaying to a top quark and a neutral scalar boson in the lepton+jets final state in proton-proton collisions at $\sqrt{s}=13$ TeV

A search for single production of a vector-like T quark with charge 2e/3, decaying to a top quark and a neutral scalar boson is presented. The boson can be a standard model Higgs boson (H) or a new scalar boson (ϕ). In the first case, a branching fraction of 25% is assumed for the decay T → tH, while in the second case the T quark is assumed to decay exclusively to tϕ. The top quark is identified via its lepton+jets decay, and the neutral boson via its decay into a bottom quark-antiquark pair. Final states with Lorentz-boosted topologies are considered and machine-learning techniques are exploited for optimal event classification. The analysis uses data collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb −1 recorded at the CERN LHC in 2016–2018. Upper limits at 95% confidence level are set on the product of cross section and branching fraction for a T quark in a narrow-width approximation. They vary between 14.7 and 0.1 fb, for T quark masses in the range 1.3–3.0 TeV and ϕ boson masses in the range 25–250 GeV. These are the first exclusion limits set on the production of a single T quark decaying into a top quark and a new neutral scalar boson. For the decay channel into a top quark and a standard model Higgs boson, the results provide the best limits on production cross sections to date, for T quark masses above 2 TeV.

hadron-hadron scattering↗
DOE OSTI2026

Search for a new heavy resonance decaying to a top quark and a neutral scalar boson in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A first search at the LHC for a new heavy resonance decaying to a top quark and a neutral scalar boson ϕ in the fully hadronic final state is presented, where the ϕ boson is identified by its decay into a bottom quark-antiquark pair. The search is focused on final states in which the decay products of the highly Lorentz boosted top quark and ϕ boson are each reconstructed as a single, large-radius jet with distinct substructure. The analysis is performed using proton-proton collision data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb −1 , recorded with the CMS detector at the LHC in 2016–2018. The single production of a vector-like top quark, T′, is used as a benchmark model for the signal process. The results of this search are combined with those of a previous CMS search in which semileptonic decays of the top quark were used. No significant excess of data is observed with respect to the background prediction. For the case where the neutral scalar is a standard model Higgs boson and the T′ quark width is 5% of its mass, T′ quark masses between 0.85 and 1.3 TeV are excluded at 95% confidence level and the most stringent limits to date are set for masses above 2 TeV . For other ϕ boson masses, upper limits as low as 0.1 fb are set on the product of the T′ quark production cross section and branching fraction for its decay to a top quark and a ϕ boson.

Boosted↗
DOE OSTI2026

Binding energy of the 𝑇 𝑏⁢𝑏 tetraquark from lattice QCD with relativistic and nonrelativistic heavy-quark actions

We present a new determination of the $b\bar{b}$𝑢⁢𝑑 (𝐽 𝑃 = 1 + , 𝐼 = 0) tetraquark binding energy using lattice quantum chromodynamics (QCD) with domain-wall light quarks and a nonperturbatively tuned three-parameter anisotropic-clover “relativistic” action for the 𝑏 quarks. We also perform a direct comparison with a reanalysis of data generated in prior work using a lattice-nonrelativistic QCD (NRQCD) action for the 𝑏 quarks and otherwise identical parameters. Using the new data with relativistic 𝑏 quarks from seven different ensembles with multiple lattice spacings and pion masses, we perform combined chiral and continuum extrapolations and obtain (𝑚 𝑇 𝑏⁢𝑏 −𝑚 𝐵 −𝑚 𝐵* ) RHQ =(−76 ±23) MeV. For the NRQCD data from five ensembles, we perform chiral-only extrapolations and obtain (𝑚 𝑇 𝑏⁢𝑏 −𝑚 𝐵 −𝑚 𝐵* ) NRQCD = (−74 ±17 ±10) MeV. The lower magnitude of the results obtained here, compared to the original analysis in [Phys. Rev. D 100, 014503 (2019)], is due to the use of the symmetric parts of the correlation matrices with local four-quark operators only.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Structure of open-flavor four-quark states in the charm and bottom region

We present quantitative results for masses and the internal structure of four-quark states with two heavy quarks, i.e., Q Q ′ q ¯ q ¯ ′ with Q , Q ′ ∈ { c , b } and q , q ′ ∈ { u , d , s } , and J P ∈ 1 + . The composition of these states in terms of meson-meson and diquark-antidiquark pairs, extracted from a relativistic four-body Faddeev-Yakubowski equation, is dynamically determined from underlying QCD forces. We find states at energy levels in very good agreement with lattice QCD and, where available, with experimental states. Their internal structure, most notably between the T c c + , T b c and T b b − , show significant and sizeable variations. Published by the American Physical Society 2025

Hoffer, Joshua (ORCID:0009000871793956)↗
DOE OSTI2025

Charm and bottom hadrons in hot hadronic matter

Heavy quarks, and the hadrons containing them, are excellent probes of the QCD medium formed in high-energy heavy-ion collisions, as they provide essential information on the transport properties of the medium and how quarks color-neutralize into hadrons. Large theoretical and phenomenological efforts have been dedicated thus far to assess the diffusion of charm and bottom quarks in the quark–gluon plasma and their subsequent hadronization into heavy-flavor (HF) hadrons. However, the fireball formed in heavy-ion collisions also features an extended hadronic phase, and therefore any quantitative analysis of experimental observables needs to account for the rescattering of charm and bottom hadrons. This is further reinforced by the presence of a QCD cross-over transition and the notion that the interaction strength is maximal in the vicinity of the pseudo-critical temperature. We review existing approaches for evaluating the interactions of open HF hadrons in a hadronic heat bath and the pertinent results for scattering amplitudes, spectral functions and transport coefficients. While most of the work to date has focused on D -mesons, we also discuss excited states as well as HF baryons and the bottom sector. Both the HF hadro-chemistry and bottom observables will play a key role in future experimental measurements. We also conduct a survey of transport calculations in heavy-ion collisions that have included effects of hadronic HF diffusion and assess its impact on various observables.

effective field theories↗
DOE OSTI2023

Search for a high-mass dimuon resonance produced in association with b quark jets at $ \sqrt{s} $ = 13 TeV

A search for high-mass dimuon resonance production in association with one or more b quark jets is presented. The study uses proton-proton collision data collected with the CMS detector at the LHC corresponding to an integrated luminosity of 138 fb$^{−1}$ at a center-of-mass energy of 13 TeV. Model-independent limits are derived on the number of signal events with exactly one or more than one b quark jet. Results are also interpreted in a lepton-flavor-universal model with Z′ boson couplings to a bb quark pair (g$_{b}$), an sb quark pair (g$_{b}$δ$_{bs}$), and any same-flavor charged lepton (g$_{ℓ}$) or neutrino pair (g$_{ν}$), with |g$_{ν}$| = |g$_{ℓ}$|. For a Z′ boson with a mass $ {m}_{{\textrm{Z}}^{\prime }} $ = 350 GeV (2 TeV) and |δ$_{bs}$| < 0.25, the majority of the parameter space with 0.0057 < |g$_{ℓ}$| < 0.35 (0.25 < |g$_{ℓ}$| < 0.43) and 0.0079 < |g$_{b}$| < 0.46 (0.34 < |g$_{b}$| < 0.57) is excluded at 95% confidence level. Finally, constraints are set on a Z′ model with parameters consistent with low-energy b → sℓℓ measurements. In this scenario, most of the allowed parameter space is excluded for a Z′ boson with 350 < $ {m}_{{\textrm{Z}}^{\prime }} $ < 500 GeV, while the constraints are less stringent for higher $ {m}_{{\textrm{Z}}^{\prime }} $ hypotheses. This is the first dedicated search at the LHC for a high-mass dimuon resonance produced in association with multiple b quark jets, and the constraints obtained on models with this signature are the most stringent to date.[graphic not available: see fulltext]

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Evidence for Modification of $b$ Quark Hadronization in High-Multiplicity $pp$ Collisions at $\sqrt{s}$ = 13 TeV

The production rate of $B^{0}_{s}$ mesons relative to $B^0$ mesons is measured by the LHCb experiment in $pp$ collisions at a center-of-mass energy $\sqrt{s}$ = 13 TeV over the forward rapidity interval 2 < $y$ < 4.5 as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4$σ$ level is found for an increase of the ratio of $B^{0}_{s}$ to $B^0$ cross sections with multiplicity at transverse momenta below 6 GeV /$c$, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from $e^+$ $e^–$ collisions implies that the density of the hadronic medium may affect the production rates of $B$ mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Search for Higgs bosons produced in association with a high-energy photon via vector-boson fusion and decaying to a pair of b -quarks in the ATLAS detector

A search for Standard Model Higgs bosons produced in association with a high-energy photon and decaying to $b\bar{b}$ is performed using 133 fb −1 of $\sqrt{s}$ = 13 TeV pp collision data collected with the ATLAS detector at the Large Hadron Collider at CERN. The photon requirement reduces the multijet background, and the H → $b\bar{b}$ decay is the dominant decay mode. Event selection requirements target events produced by vector-boson fusion, the dominant production mode in this channel. Several improvements enhance the search sensitivity compared to previous measurements. These improvements include better background modelling and characterization, the use of a neural-network classifier, and an updated signal extraction strategy adopting a direct binned-likelihood fit to the classifier output. With these improvements, the Higgs boson signal strength is measured to be 0.2 ± 0.7 relative to the Standard Model prediction. This corresponds to an observed significance of 0.3 standard deviations, compared to an expectation of 1.5 standard deviations assuming the Standard Model.

ATLAS experiment↗
DOE OSTI2026

Lessons from LHCb and Belle II measurements of B → J/ψπ and B → J/ψK decays

The LHCb collaboration has recently measured the CP asymmetry in B + → J/ψπ + decay, while the Belle II collaboration has recently measured the CP asymmetries in B 0 →J/ψπ 0 decay. Within the Standard Model, and using flavor-SU(3) relations including first-order breaking corrections, these measurements lead to new predictions with regard to CP violation in B + → J/ψK + and B s → J/ψ$\bar{K}$ 0 decays, the difference between S ψK S and sin 2β, and the rate and CP asymmetries in B s → J/ψπ 0 decay.

Bottom Quarks↗
DOE OSTI2023

Dark photon and dark Z mediated B meson decays

We study flavor changing neutral current decays of B and K mesons in the dark U(1) D model, with the dark photon/dark Z mass between 10 MeV and 2 GeV. Although the model provides an improved fit (compared to the standard model) to the differential decay distributions of B → K ($\ast$) ℓ + ℓ – , with ℓ = μ, e, and B s → $\phi$μ + μ – , the allowed parameter space is ruled out by measurements of atomic parity violation, K + → μ + + invisible decay, and ${B}_s-{\overline{B}}_s$ mixing, among others. To evade constraints from low energy data, we extend the model to allow for (1) additional invisible Z D decay, (2) a direct vector coupling of Z D to muons, and (3) a direct coupling of Z D to both muons and electrons, with the electron coupling fine-tuned to cancel the Z D coupling to electrons via mixing. We find that only the latter case survives all constraints.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Search for light pseudoscalar boson pairs produced from Higgs boson decays using the 4τ and 2μ2τ final states in proton-proton collisions at $\sqrt{s}=13$ TeV

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 a1 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 a1 bosons exceeding 16% are excluded at 95% CL for a1 boson masses between 5 and 15 GeV and tan β > 2, with the exception of scenarios in which the a1 boson mixes with charm or bottom quark-antiquark bound states.

Higgs physics↗