Semileptonic Decay Channel Research Articles

Search for nearly degenerate higgsinos via photon fusion with the semileptonic channel at the LHC

Electroweak scale higgsinos with a nearly degenerate spectrum in supersymmetric models are well-motivated, but generally less constrained at collider experiments as the decay products are often too soft to detect. Initial photon fusions alongside the collision of protons at the Large Hadron Collider (LHC) have drawn attention recently as a way to search for new physics with such kind of spectra. In this paper, we demonstrate a search strategy for chargino pair production from photon fusion pp→p(γγ→χ˜1+χ˜1−)p at the 13TeV LHC via the semileptonic decay channel, as a probe for the compressed spectra of higgsinos. Forward detectors make it possible to detect the outgoing protons after emitting the initial photons in these processes. We here provide simple event selections on missing energy and transverse momentum of leptons, which are effective enough to reach significant sensitivity. The chargino mass can be excluded at 95% C.L. up to about 295GeV with the mass difference Δm(χ˜1±,χ˜10) being only a few GeV with the integrated luminosity of 3ab−1. With a relatively small luminosity of 100fb−1, the 2σ exclusion bounds can as well exceed current experimental limits in the range of Δm=1∼2GeV, reaching over 190GeV for chargino mass.

Quantum entanglement and Bell inequality violation in semi-leptonic top decays

Quantum entanglement is a fundamental property of quantum mechanics. Recently, studies have explored entanglement in the tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} system at the Large Hadron Collider (LHC) when both the top quark and anti-top quark decay leptonically. Entanglement is detected via correlations between the polarizations of the top and anti-top and these polarizations are measured through the angles of the decay products of the top and anti-top. In this work, we propose searching for evidence of quantum entanglement in the semi-leptonic decay channel where the final state includes one lepton, one neutrino, two b-flavor tagged jets, and two light jets from the W decay. We find that this channel is both easier to reconstruct and has a larger effective quantity of data than the fully leptonic channel. As a result, the semi-leptonic channel is 60% more sensitive to quantum entanglement and a factor of 3 more sensitive to Bell inequality violation, compared to the leptonic channel. In 139 fb−1 (3 ab−1) of data at the LHC (HL-LHC), it should be feasible to measure entanglement at a precision of ≲ 3% (0.7%). Detecting Bell inequality violation, on the other hand, is more challenging. With 300 fb−1 (3 ab−1) of integrated luminosity at the LHC Run-3 (HL-LHC), we expect a sensitivity of 1.3σ (4.1σ). In our study, we utilize a realistic parametric fitting procedure to optimally recover the true angular distributions from detector effects. Compared to unfolding this procedure yields more stable results.

Rotation-equivariant graph neural network for learning hadronic SMEFT effects

We introduce a graph neural network architecture designed to extract novel phenomena in the standard model effective field theory (SMEFT) context from LHC collision data. The proposed infrared- and collinear-safe architecture is sensitive to the angular orientation of radiation patterns in jets from hadronic decays of highly energetic massive particles. Equivariance with respect to rotations around the jet axis allows for extracting the information on the angular orientation decoupled from the jet substructure. We demonstrate the robustness of the approach and its potential for future probes of the SMEFT at the LHC through toy studies and with realistic event simulations of the associated production of a W and a Z boson in the semileptonic decay channel. Published by the American Physical Society 2024

NLO QCD corrections to off-shell top–antitop production with semi-leptonic decays at lepton colliders

The study of top-quark properties will be a central aspect of the physics programme of any future lepton collider. In this article, we investigate the production of top-quark pairs in the semi-leptonic decay channel in {textrm{e}}^{+}textrm{e}^{-} collisions, whose experimental signature is one charged lepton, jets, and missing energy. We present for the first time fiducial cross sections and differential distributions at next-to-leading-order accuracy in QCD for the full off-shell process. We find that the QCD corrections for the considered process are strongly dependent on the beam energies and range from few per cent up to more than 100% (near threshold and above 1,text {TeV} ). We focus, in particular, on two scenarios: one close to threshold (365,text {GeV} ), dominated by top-pair production, and one at the TeV scale (1.5,text {TeV} ), for which irreducible-background contributions become relevant. An assessment of polarised-beam effects is also provided.

NLO QCD corrections to polarized diboson production in semileptonic final states

Understanding the polarization structure and providing precise predictions for multiboson processes at the LHC is becoming urgent in the light of the upcoming run-3 and high-luminosity data. The CMS and ATLAS collaborations have already started using polarized predictions to perform template fits of the data, getting access to the polarization of W and Z bosons. So far, only fully leptonic decay channels have been considered in this perspective. The natural step forward is the investigation of hadronic decays of electroweak bosons. In this work, we compute NLO QCD corrections to the production and decay of WZ pairs at the LHC in final states with two charged leptons and jets. The calculation relies on the double-pole approximation and the separation of polarized states at the level of Standard Model amplitudes. The presented NLO-accurate results are necessary building blocks for a broad understanding and precise modeling of polarized diboson production in semileptonic decay channels.

Analysis of the anomalous quartic WWWW couplings at the LHeC and the FCC-he

The quartic gauge boson couplings that identify the strengths of the gauge boson self-interactions are exactly determined by the non-Abelian gauge nature of the Standard Model. The examination of these couplings at $ep$ collisions with high center-of-mass energy and high integrated luminosity provides an important opportunity to test the validity of the Standard Model and the existence of new physics beyond the Standard Model. The quartic gauge boson couplings can contribute directly to multi-boson production at colliders. Therefore, we examine the potential of the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ at the Large Hadron Electron Collider and the Future Circular Collider-hadron electron to study non-standard $WWWW$ couplings in a model independent way by means of the effective Lagrangian approach. We present an investigation on measuring $W^{+}W^{-}$ production in pure leptonic and semileptonic decay channels. In addition, we calculate the sensitivity limits at $95\%$ Confidence Level on the anomalous $\frac{f_{M0}}{\Lambda^{4}}$, $\frac{f_{M1}}{\Lambda^{4}}$, $\frac{f_{M7}}{\Lambda^{4}}$, $\frac{f_{S0}}{\Lambda^{4}}$, $\frac{f_{S1}}{\Lambda^{4}}$, $\frac{f_{T0}}{\Lambda^{4}}$, $\frac{f_{T1}}{\Lambda^{4}}$ and $\frac{f_{T2}}{\Lambda^{4}}$ couplings obtained by dimension-8 operators through the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ for the Large Hadron Electron Collider and the Future Circular Hadron Electron Collider's different center-of-mass energies and integrated luminosities. Our results show that with the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ at the Large Hadron Electron Collider and the Future Circular Collider-hadron electron the sensitivity estimated on the anomalous $WWWW$ couplings can be importantly strengthened.

Light-cone sum rules for proton decay

We estimate the form factors that parametrise the hadronic matrix elements of proton-to-pion transitions with the help of light-cone sum rules. These form factors are relevant for semi-leptonic proton decay channels induced by baryon-number violating dimension-six operators, as typically studied in the context of grand unified theories. We calculate the form factors in a kinematical regime where the momentum transfer from the proton to the pion is space-like and extrapolate our final results to the regime that is relevant for proton decay. In this way, we obtain estimates for the form factors that show agreement with the state-of-the-art calculations in lattice QCD, if systematic uncertainties are taken into account. Our work is a first step towards calculating more involved proton decay channels where lattice QCD results are not available at present.

Prospects for precision measurement of diboson processes in the semileptonic decay channel in future LHC runs

Precision measurements at the LHC can provide probes of new physics, and they are complementary to direct searches. The high energy distribution of di-boson processes ($WW,WZ,Vh$) is a promising place, with the possibility of significant improvement in sensitivity as the data accumulates. We focus on the semi-leptonic final states, and make projections of the reach for future runs of the LHC with integrated luminosities of 300 fb$^{-1}$ and 3 ab$^{-1}$. We emphasize the importance of tagging the polarization of the vector bosons, in particular for the $WW$ and $WZ$ channels. We employ a combination of kinematical distributions of both the $W$ and $Z$, and their decay products to select the longitudinally polarized $W$ and $Z$. We have also included our projections for the reach using the associated production of vector boson and the Higgs. We demonstrate that di-boson measurement in the semi-leptonic channel can surpass the sensitivity of the precision measurement at LEP, and they can be significantly more sensitive than the HL-LHC $h \to Z \gamma$ measurements. Compared with fully leptonic decaying $WZ$ channel, the reach from semi-leptonic channel can be better with effective suppression of the reducible background and systematic error. We have also considered the reaches on the new physics mass scale in different new physics scenarios, including the Strongly Interacting-Light Higgs (SILH), the Strongly Coupled Multi-pole Interaction (Remedios), and the class of models with partially composite fermions. We find that in the SILH and non-compact Remedios scenario with large coupling $g_* > 7$, measurements in the di-boson channel is more sensitive than the Drell-Yan di-lepton channel at the HL-LHC.

Weak decays of the axial-vector tetraquark Tbb;u¯d¯−

The weak decays of the axial-vector tetraquark $T_{bb;\bar{u} \bar{d}}^{-}$ to the scalar state $Z_{bc;\bar{u} \bar{d}}^{0}$ are investigated using the QCD three-point sum rule approach. In order to explore the process $T_{bb; \bar{u} \bar{d}}^{-} \to Z_{bc;\bar{u} \bar{d}}^{0}l \bar{\nu_l}$, we recalculate the spectroscopic parameters of the tetraquark $T_{bb;\bar{u} \bar{d}}^{-}$ and find the mass and coupling of the scalar four-quark system $Z_{bc;\bar{u} \bar{d}}^{0}$, which are important ingredients of calculations. The spectroscopic parameters of these tetraquarks are computed in the framework of the QCD two-point sum rule method by taking into account various condensates up to dimension ten. The mass of the $T_{bb;\bar{u} \bar{ d}}^{-}$ state is found to be $m=(10035~\pm 260)~\mathrm{MeV}$, which demonstrates that it is stable against the strong and electromagnetic decays. The full width $\Gamma$ and mean lifetime $\tau$ of $T_{bb;\bar{u} \bar{d} }^{-}$ are evaluated using its semileptonic decay channels $T_{bb; \bar{u} \bar{d}}^{-} \to Z_{bc;\bar{u} \bar{d}}^{0}l \bar{\nu_l}$, $l=e,\mu$ and $\tau$. The obtained results, $\Gamma=(7.17\pm 1.23)\times 10^{-8\ \ } \mathrm{MeV}$ and $\tau =9.18_{-1.34}^{+1.90}~\mathrm{fs}$, can be useful for experimental investigations of the doubly-heavy tetraquarks.

Single lepton charge asymmetries in t {bar{t}} and t {bar{t}} gamma production at the LHC

We discuss lepton charge asymmetries in t {bar{t}} and t {bar{t}} gamma production at the LHC, which can be measured in the semileptonic decay channel t {bar{t}} rightarrow W^+ b , W^- {bar{b}} rightarrow ell ^+ nu b , q {bar{q}}' {bar{b}} (or the charge conjugate). Considering several variants of a new physics scenario with a light colour octet, it is seen that for t {bar{t}} these asymmetries may have a sensitivity competitive with the dilepton asymmetry already measured. For t {bar{t}} gamma the new leptonic asymmetries, as well as the t {bar{t}} charge asymmetry, will reach their full potential with the high luminosity LHC upgrade. These asymmetries can pinpoint deviations at the 3sigma -4sigma level for new physics scenarios where the charge asymmetries already measured in t {bar{t}} production agree within 1sigma .

Search for thj production with h → γγ at the LHC in the littlest Higgs model with T-parity

In the littlest Higgs model with T-parity, we study associated production of a Higgs and a single top quark at the 14 TeV LHC. We focus on the Higgs to two photons decay and the semileptonic top decay channel. By performing a fast detector simulation, we find that the thj search in the selected channel can excluded the top partner mass mT+ up to 805 (857) GeV for case A (case B) at 2σ confidence level at 14 TeV LHC with the integrated luminosity L=3ab−1.

Searching for Exotic States with b and c Quarks in D0 Experiment

The latest results of searching for exotic multiquark states with heavy quarks obtained in the D0 experiment (Fermi National Accelerator Laboratory, USA) are presented. In particular, the evidence of existence of a possible four-quark state X(5568) → B s 0 π±in the cases with hadronic and semileptonic decay channels of B s 0 meson is considered, as well as the results of searching for the five-quark states in the J/ψΛ system.

Measurement of open heavy-flavour production as a function of charged-particle multiplicity with ALICE at the LHC

Heavy quarks are produced in the early stages of ultra-relativistic hadron collisions via hard scatterings and are an important tool for studying different aspects of Quantum Chromodynamics (QCD) in hadronic collisions. Charged-particle multiplicity gives information on the global characteristics of the event and could be used to characterize particle production mechanisms. In hadronic collisions at Large Hadron Collider (LHC) energies, there is a significant contribution of multi-parton interactions. The measurement of heavy-flavour yields as a function of charged-particle multiplicity gives insight into the mechanisms influencing their production in hadronic collisions at these energies and it is a tool to test the possible influence of multi-parton interactions. Furthermore, the charged-particle multiplicity dependence of open heavy flavours is used to test the ability of QCD theoretical models to describe the data. In ALICE, heavy-flavour production is measured via the hadronic and semi-leptonic decay channels (electrons at central rapidity and muons at forward rapidity). Charged-particle multiplicity is measured at central and forward rapidity. We will present the results on open heavy-flavour production as a function of the charged-particle multiplicity in pp and p–Pb collisions. Results will be compared to quarkonia measurements as well as theoretical model calculations.

Probe of the Anomalous Quartic Couplings with Beam Polarization at the CLIC

We have investigated the anomalous quartic couplings defined by the dimension-8 operators in semileptonic decay channel of thee+e-→νeW-W+ν-eprocess for unpolarized and polarized electron (positron) beam at the Compact Linear Collider. We give the 95% confidence level bounds on the anomalousfS0/Λ4,fS1/Λ4, andfT0/Λ4couplings for various values of the integrated luminosities and center-of-mass energies. The best sensitivities obtained on anomalousfS0/Λ4,fS1/Λ4, andfT0/Λ4couplings through the processe+e-→νeW-W+ν-ewith beam polarization ats=3 TeV and an integrated luminosity ofLint=2000 fb-1are[-4.05;3.67]×10-12 GeV-4,[-3.08;2.12]×10-12 GeV-4, and[-1.98;0.64]×10-13 GeV-4, which show improvement over the current bounds.

Semihadronic and hadronic decays ofρ0andωmesons coherently photoproduced in isoscalar nuclei

The interference of the $\rho^0$ and $\omega$ mesons has been studied in the hadronic and leptonic decay channels, i.e., dipion and dilepton decay channels respectively, but this interference is not studied yet in the semihadronic or semileptonic decay channel, e.g., $V \to \pi^0\gamma$. $V$ denotes either $\rho^0$ or $\omega$ meson. To look for the quoted interference in the $\pi^0\gamma$ decay channel as well as the contribution of $\rho$ meson to the cross section, the correlated $\pi^0\gamma$ invariant mass distribution spectra are calculated in the photonuclear reaction in the multi-GeV region. It is assumed that these bosons arise in the final state due to the decay of $\rho^0$ and $\omega$ mesons which are photoproduced coherently in the isoscalar nucleus. The elementary reaction in the nucleus is considered to proceed as $\gamma N \to VN$; $V \to \pi^0\gamma$. The forward propagation of the $\rho$ and $\omega$ mesons and the near forward emission of pion are considered, so that they can be described by the eikonal form. The meson nucleus interactions are evaluated using $t\varrho$ approximation. Replacing the decay vertex $V \to \pi^0\gamma$ by $V \to \pi^+\pi^-$ in the above formalism, it is also used to study the $\rho-\omega$ interference in the $\pi^+\pi^-$ decay channel.

Stop search in the compressed region via semileptonic decays

In supersymmetric extensions of the Standard Model, the superpartners of the top quark (stops) play the crucial role in addressing the naturalness problem. For direct pair-production of stops with each stop decaying into a top quark plus the lightest neutralino, the standard stop searches have difficulty finding the stop for a compressed spectrum where the mass difference between the stop and the lightest neutralino is close to the top quark mass, because the events look too similar to the large $t\bar{t}$ background. With an additional hard ISR jet, the two neutralinos from the stop decays are boosted in the opposite direction and they can give rise to some missing transverse energy. This may be used to distinguish the stop decays from the backgrounds. In this paper we study the semileptonic decay of such signal events for the compressed mass spectrum. Although the neutrino from the $W$ decay also produces some missing transverse energy, its momentum can be reconstructed from the kinematic assumptions and mass-shell conditions. It can then be subtracted from the total missing transverse momentum to obtain the neutralino contribution. Because it suffers from less backgrounds, we show that the semileptonic decay channel has a better discovery reach than the fully hadronic decay channel along the compressed line $m_{\tilde{t}} - m_{\tilde{\chi}}\approx m_t$. With 300 $\text{fb}^{-1}$, the 13 TeV LHC can discover the stop up to 500 GeV, covering the most natural parameter space region.

Novel T-violation observable open to any decay channel at meson factories

Two genuine Quantum phenomena: Entanglement and Filtering Measurement are at the origin of the first direct observation of Time-Reversal-Violation in the time evolution of the B neutral meson system by BaBar. The used meson transitions are directly connected to semileptonic and CP-eigenstate decay channels. We analyse the possibility of extending the observable asymmetries to more decay channels. We propose an alternative T-Violation Asymmetry in the meson factories which allows its opening to any pair of decay channels. The new asymmetry needs also the measurement of the time dependent total survival probability of the initial tagged states. By combining several asymmetries these total survival probabilities can be avoided. We analyse carefully the channels that can be used and the sufficient condition in order the proposed asymmetry be a genuine T violation measurement.

Probing triple-W production and anomalous WWWW coupling at the CERN LHC and future O 100 $$ \mathcal{O}(100) $$ TeV proton-proton collider

Triple gauge boson production at the LHC can be used to test the robustness of the Standard Model and provide useful information for VBF di-boson scattering measurement. Especially, any derivations from SM prediction will indicate possible new physics. In this paper we present a detailed Monte Carlo study on measuring WWW production in pure leptonic and semileptonic decays, and probing anomalous quartic gauge WWWW couplings at the CERN LHC and future hadron collider, with parton shower and detector simulation effects taken into account. Apart from cut-based method, multivariate boosted decision tree method has been exploited for possible improvement. For the leptonic decay channel, our results show that at the sqrt{s}=8(14)[100] TeV pp collider with integrated luminosity of 20(100)[3000] fb-1, one can reach a significance of 0.4(1.2)[10]sigma to observe the SM WWW production. For the semileptonic decay channel, one can have 0.5(2)[14]sigma to observe the SM WWW production. We also give constraints on relevant Dim-8 anomalous WWWW coupling parameters.

Probing pseudoscalar and scalar mesons in semileptonic decays of $D_s^+$, D+ and D0

With the primary motivation of probing the quark substructure of scalar mesons, a generalized linear sigma model for the lowest and the next-to-lowest scalar and pseudoscalar mesons is employed to investigate several semileptonic decays of D mesons. The free parameters of the model (in its leading approximation) have been previously determined from fits to mass spectra and various low-energy parameters. With these fixed parameters, the model has already given encouraging predictions for different low-energy decays and scattering, as well as for semileptonic decay channels of [Formula: see text] that include a scalar meson in the final state. In the present work, we apply the same model (in its leading order with the same fixed parameters) to different semileptonic decay channels of [Formula: see text], D+ and D0. Although these decay channels produce only pseudoscalar mesons in the final states, since various properties of scalar mesons have been used in fixing the model parameters, this study further tests the model and its predictions for the quark substructure of both pseudoscalar as well as scalar mesons. We find that these predictions are in qualitative agreement with experiment.

Novel T-Violation observable open to any pair of decay channels at meson factories

Quantum entanglement between the two neutral mesons produced in meson factories has allowed the first indisputable direct observation of Time Reversal Violation in the time evolution of the neutral meson between the two decays. The exceptional meson transitions are directly connected to semileptonic and CP eigenstate decay channels. The possibility of extending the observable asymmetries to more decay channels confronts the problem of the “orthogonality condition”, which can be stated with this tongue-twister: Given a decay channel f, which is the decay channel f′ such that the meson state not decaying to f′ is orthogonal to the meson state not decaying to f? In this Letter we propose an alternative T-Violation asymmetry at meson factories which allows its opening to any pair of decay channels. Instead of searching which is the pair of decay channels associated to the T-reverse meson transition, we build an asymmetry which tags the initial states of both the Reference and the T-reverse meson transitions. This observable filters the appropriate final states by means of two measurable survival probabilities. We discuss the methodology to be followed in the analysis of the new observable and the results expected in specific examples.