Hadronic Decay Channels Research Articles

Measurement of the $$\boldsymbol{t}\bar{\boldsymbol{t}}\boldsymbol{H,H}{\rightarrow}\boldsymbol{b}\bar{\boldsymbol{b}}$$ Decay with Run II Data and Prospects for Run III

The search for the associated production of a Higgs boson with a top quark–antiquark pair with the CMS detector will be presented. Candidate $$t\bar{t}H$$ events are selected with criteria enhancing respectively the dileptonic, semileptonic and fully hadronic decay channels of the $$t\bar{t}$$ system and the decay of the Higgs boson into a bottom quark–antiquark pair ( $$H\rightarrow b\bar{b}$$ ). In order to increase the sensitivity of the search, selected events are split into several categories with different expected signal and background rates. A combined fit of multivariate discriminant templates across all categories and decay channels is performed to extract the result. Results for Run II data will be shown. Prospects for improvements towards Run III will also be discussed.

Production and reconstruction of short-lived resonances in heavy-ion collisions at NICA energies using the MPD detector

The short-lived resonances have been used to study properties of the heavy-ion collisions at SPS, RHIC and the LHC. The resonance yields measured in the hadronic decay channels are affected by the rescattering and regeneration effects in the late hadronic phase. The mesonic and baryonic resonances with different strangeness content are used to study the strangeness enhancement phenomenon predicted as one of the signatures for the QCD phase transition. Having different masses and baryonic numbers, the resonances contribute to the study of hadronization mechanisms at low and intermediate transverse momenta. The extensive resonance measurements are not experimentally available in heavy-ion collisions at NICA energies. In this contribution, we study the resonance properties and their sensitivity to different stages of Au+Au collisions at = 4–11 GeV. Results of feasibility studies for reconstruction of ρ(770)0, K*(892), ϕ(1020), Λ(1520), Σ(1385)± and Ξ(1530)0 resonances in the MPD detector at NICA are presented and discussed.

Study on the anomalous quartic W^+W^-gamma gamma couplings of electroweak bosons in e^-p collisions at the LHeC and the FCC-he

In this paper, a study is carried out on the e^-p rightarrow e^-gamma ^* p rightarrow p W^-gamma nu _e production to probe quartic W^+W^-gamma gamma couplings at the Large Hadron electron Collider (LHeC) with sqrt{s}= 1.30, 1.98,hbox {TeV} and at the Future Circular Collider-hadron electron (FCC-he) with sqrt{s}= 3.46, 5.29,hbox {TeV}. Production cross-sections are determined for both at leptonic and hadronic decay channels of the W-boson. With the data from future e^-p colliders, it is possible to obtain sensitivity measures at 95% C.L. on the anomalous f_ {M,i}/Lambda ^4 and f_ {T,j}/Lambda ^4 couplings which are competitive with the limits obtained by the LHC, as well as with others limits reported in the literature. The production mode e^-p rightarrow e^-gamma ^* p rightarrow p W^-gamma nu _e in e^-p collisions offers a window for study the quartic W^+W^-gamma gamma electroweak bosons couplings at the LHeC and the FCC-he, which provides a much cleaner collision environment than the LHC.

Prospects of measuring $$R_b$$ in hadronic $$\mathrm{Z}$$ decays at the CEPC

With an integrated luminosity of 45 $$\mathrm{ab}^{-1}$$ at $$\sqrt{s} = 91.2$$ GeV, more than $$10^{12}$$ $$\mathrm{Z}$$ bosons will be produced at the Circular Electron Positron Collider (CEPC). As a real $$\mathrm{Z}$$ boson factory, the precise study of $$\mathrm{Z}$$ boson physics can be achieved. In this paper, the relative partial width, $$R_{b}$$ , of $$\mathrm{Z}$$ boson into b quarks, is measured on the CEPC Monte Carlo level. Based on the latest CEPC detector concept, the $$\mathrm{Z}$$ hadronic decay channel is simulated and reconstructed by the CEPC software framework. By using the double-tagging method, $$R_b$$ can be solved from several equations referring to the ratios of b-tagged jet hemispheres in $$\mathrm{Z}$$ hadronic events. With the high performance of the b-tagging algorithm for CEPC, the b-tagging correlation between the two jet hemispheres can be reduced. By carrying out a closure test, the double-tagging method is verified to work well as we expected. We further estimated the dependence of systematic errors on the b-tagging efficiencies of the charm and light jet, as well as the b-tagging correlation between two jet hemispheres. The sources of systematic errors, such as physics modeling and hemisphere correlation, are investigated and studied preliminarily. Several kinds of error sources related to the hemisphere correlation are studied with the characterized variables.

Production and reconstruction of short-lived ρ(770)0, K*(892)0, ϕ(1020) and Λ(1520) resonances as a function of centrality and energy in Au+Au collisions at NICA

The short-lived resonances have proved to be very useful in the study of heavy-ion collisions at SPS, RHIC, and the LHC. Properties of these particles measured in dominant hadronic decay channels carry a wealth of information about the hadron chemistry and reaction dynamics. Resonances containing one or two strange quarks contribute to the study of the strangeness enhancement phenomenon predicted as a signature of the phase transition to quark-gluon plasma in heavy-ion collisions. Resonance integrated and differential yields are sensitive to the hadron re-scattering and regeneration in the hadronic phase. The resonance production has only scarcely been studied in heavy-ion collisions at NICA energies. These proceedings are devoted to the review of the expected properties of the resonances and their sensitivity to different stages of Au+Au collisions at = 11 GeV. Results of feasibility studies for reconstruction of ρ(770)0, K*(892)0, ϕ(1020) and Λ(1520) resonances in the MPD experimental setup as a function of collision energy and centrality are presented.

Tau neutrinos at DUNE: New strategies, new opportunities

We propose a novel analysis strategy, that leverages the unique capabilities of the DUNE experiment, to study tau neutrinos. We integrate collider physics ideas, such as jet clustering algorithms in combination with machine learning techniques, into neutrino measurements. Through the construction of a set of observables and kinematic cuts, we obtain a superior discrimination of the signal ($S$) over the background ($B$). In a single year, using the nominal neutrino beam mode, DUNE may achieve $S/\sqrt{B}$ of $3.3$ and $2.3$ for the hadronic and leptonic decay channels of the tau respectively. Operating in the tau-optimized beam mode would increase $S/\sqrt{B}$ to $8.8$ and $11$ for each of these channels. We premier the use of the analysis software Rivet, a tool ubiquitously used by the LHC experiments, in neutrino physics. For wider accessibility, we provide our analysis code.

Reconstruction of D0 meson in d+Au collisions at = 200 GeV by the STAR experiment

Owing to their large masses, charm quarks are predominantly produced through initial hard scatterings in heavy-ion collisions. Therefore, they can serve as penetrating probes to study the intrinsic properties of the hot medium created in heavy-ion collisions. However, Cold Nuclear Matter effects can also affect the charm quark production in nuclear collisions with respect to p + p collisions. These effects can be measured in small collision systems such as d/p+Au. In these proceedings, D0 meson reconstruction in d+Au collisions at at the STAR experiment is described. Thanks to the excellent impact parameter resolution provided by the Heavy Flavor Tracker detector, D0() mesons are topologically reconstructed from their hadronic decay channel D0 () (). The Boosted Decision Trees machine learning algorithm from the TMVA package is applied in order to improve signal/background separation.

Probing model-independent limits on W+W−γ triple gauge boson vertex at the LHeC and the FCC-he

We study the cross-section of production of a single W− boson in association with a neutrino through the process . Additionally, we obtain limits on the anomalous couplings Δκγ and λγ of the W+W−γ vertex at the Large Hadron electron Collider (LHeC) and the future circular collider hadron-electron (FCC-he). The impact of the polarized beam due to the electron is also analyzed. Our best limits for Δκγ and λγ at the 95% C.L. are: Δκγ = ±0.0017, (unpolarized electron beam) and , (polarized electron beam) identifying the W− boson through the hadronic decay channel. In addition, the collision is one of the clean, pure and simple processes to probe the W+W−γ coupling without the complications of QCD backgrounds.

Double parton scattering in pA collisions at the LHC revisited

We consider the production of W-boson plus dijet, W-boson plus b-jets and same sign WW via double parton scattering (DPS) in pA collisions at the LHC and evaluate the corresponding cross sections. The impact of a novel DPS contribution pertinent to pA collisions is quantified. Exploiting the experimental capability of performing measurements differential in the impact parameter in pA collisions, we discuss a method to single out this novel DPS contribution. The method allows the subtraction of the leading twist (LT) single parton scattering background and it gives access in a very clean way to double parton distribution functions in the proton. We calculate leading twist and DPS cross sections and study the dependence of the observables on the cuts in the jets phase space. In the Wjj channel the observation of DPS is possible with data already accumulated in pA runs and the situation will greatly improve for the next high luminosity runs. For the Wb{bar{b}} final state, the statistics within the current data is too low, but there is possibility to observe DPS in this channel in future runs, albeit with much reduced sensitivity than in Wjj final state. Finally the DPS observation in the same sign WW channel will require either significant increase of integrated luminosity beyond that foreseen in next pA runs or improved methods for W reconstruction, along with its charge, in hadronic decay channels.

Study of the proton deformation using the Out-Of-Plane Spectrometers

Nucleon deformation can be studied through electro-excitation to the first nucleon resonance, the Δ+(1232), and quantified through the quadrupole amplitudes in the γ*Ν --> Δ transition. A search for these small amplitudes has been the fo­ cus of a series of measurements undertaken at Bates-MIT. A first set of in-plane data show evidence for strong resonant and non-resonant ("background") ampli­ tudes in the longitudinal-transverse interference, which is sensitive to leading order to quadrupole contributions. Using beams of polarized electrons and the technique of out-of-plane detection, a second data set was collected on the two hadronic decay channels. It contains the first measurement of the fifth structure function on the nucléon, which provides an important theoretical constraint on the "background" amplitudes. Planned future measurements will focus on refining the resonance- background decomposition which is absolutely necessary before conclusions on the issue of nucléon deformation can be drawn.

Measurement of Lambda (1520) production in pp collisions at sqrt{s} = 7 hbox {TeV} and p\u2013Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 hbox {TeV}

The production of the Lambda (1520) baryonic resonance has been measured at midrapidity in inelastic pp collisions at sqrt{s} = 7 hbox {TeV} and in p–Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 hbox {TeV} for non-single diffractive events and in multiplicity classes. The resonance is reconstructed through its hadronic decay channel Lambda (1520) rightarrow hbox {pK}^{-} and the charge conjugate with the ALICE detector. The integrated yields and mean transverse momenta are calculated from the measured transverse momentum distributions in pp and p–Pb collisions. The mean transverse momenta follow mass ordering as previously observed for other hyperons in the same collision systems. A Blast-Wave function constrained by other light hadrons (pi , K, hbox {K}_{mathrm{S}}^0, p, Lambda ) describes the shape of the Lambda (1520) transverse momentum distribution up to 3.5 hbox {GeV}/c in p–Pb collisions. In the framework of this model, this observation suggests that the Lambda (1520) resonance participates in the same collective radial flow as other light hadrons. The ratio of the yield of Lambda (1520) to the yield of the ground state particle Lambda remains constant as a function of charged-particle multiplicity, suggesting that there is no net effect of the hadronic phase in p–Pb collisions on the Lambda (1520) yield.

Evidence of rescattering effect in Pb–Pb collisions at the LHC through production of K[formula omitted] and ϕ(1020) mesons

Measurements of K(892)0⁎ and ϕ(1020) resonance production in Pb–Pb and pp collisions at sNN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (|y| < 0.5) via their hadronic decay channels and the transverse momentum (pT) distributions are obtained for various collision centrality classes up to pT = 20 GeV/c. The pT-integrated yield ratio K(892)0⁎/K in Pb–Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the ϕ(1020)/K ratio does not show any suppression. Furthermore, the measured K(892)0⁎/K ratio in central Pb–Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the ϕ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K(892)0⁎ decay products in the hadronic phase of the collisions. The K(892)0⁎/K yield ratios in Pb–Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4–7 fm/c for central collisions. The pT-differential ratios of K(892)0⁎/K, ϕ(1020)/K, K(892)0⁎/π, ϕ(1020)/π, p/K(892)0⁎ and p/ϕ(1020) are also presented for Pb–Pb and pp collisions at sNN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-pT phenomenon.

Dynamical vector resonances from the EChL in VBS at the LHC: the WW case

In this work we study the phenomenology of the process pp → W+W−jj at the LHC, in the scenario of the resonant vector boson scattering subprocess W+W−→ W+W− which we describe within the effective field theory framework of the Electroweak Chiral Lagrangian. We assume a strongly interacting electroweak symmetry breaking sector in which dynamically generated resonances with masses in the TeV scale appear as poles in the Electroweak Chiral Lagrangian amplitudes unitarized with the Inverse Amplitude Method. The relevant resonance here, V0, is the neutral component of the triplet of vector resonances which are known to emerge dynamically at the TeV scale for specific values of the Electroweak Chiral Lagrangian parameters. With the aim of studying the production and possible observation of V0 at the LHC, via the resonant W+W−→ W+W− scatter- ing, a MadGraph 5 UFO model has been developed employing a phenomenological Proca Lagrangian as a practical tool to mimic the correct V0 properties that are predicted with the Inverse Amplitude Method. We choose to study the fully hadronic decay channel of the final gauge bosons W W → J (jj)J (jj) since it leads to larger event rates and because in the alternative leptonic decay channels the presence of neutrinos complicates the re- construction of the resonance properties. In this context, the 2 boosted jets from the W hadronic decays, jj, are detected as a single fat jet, J , due to their extreme collinearity. We perform a dedicated analysis of the sensitivity to these vector resonances V0 with masses between 1.5 and 2.5 TeV at the LHC with sqrt{s} = 13 TeV and the planned high luminosity of 3000 fb−1, paying special attention to the study of efficient cuts to extract the resonant vector boson fusion signal from the QCD background, which clearly represents the main challenge of this search.

INVESTIGATING DOUBLY CHARGED LEPTONS AT FUTURE ENERGY FRONTIER MUON-PROTON COLLIDERS

We study the doubly charged leptons considered in extended isospin models at muon-proton colliders. We respect the lepton flavor conservation and take into consideration the single production of the doubly charged leptons related to second generation. We give the effective lagrangian describing the doubly charged lepton gauge interactions. We calculate the signal and corresponding background cross sections and analyze the kinematical distributions to obtain the suitable cuts for the discovery. We choose the W-boson hadronic decay channel to get the accessible mass limits and couplings of doubly charged leptons for various muon-proton colliders.

Formula omitted] production in Pb–Pb collisions at [formula omitted] TeV

A measurement of the production of prompt Λc+ baryons in Pb–Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC is reported. The Λc+ and Λ‾c− were reconstructed at midrapidity (|y|<0.5) via the hadronic decay channel Λc+→pKS0 (and charge conjugate) in the transverse momentum and centrality intervals 6<pT<12 GeV/c and 0–80%. The Λc+/D0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at s=7 TeV and in p–Pb collisions at sNN=5.02 TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common pT interval covered by the measurements in the two collision systems. The Λc+/D0 ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The Λc+ nuclear modification factor, RAA, is also presented. The measured values of the RAA of Λc+, Ds+ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (RAAD0<RAADs+<RAAΛc+), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium.

Suppression of Λ(1520) resonance production in central Pb-Pb collisions at sNN=2.76 TeV

The production yield of the $\Lambda(1520)$ baryon resonance is measured at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV with the ALICE detector at the LHC. The measurement is performed in the $\Lambda(1520)\rightarrow {\rm pK}^{-}$ (and charge conjugate) hadronic decay channel as a function of the transverse momentum ($p_{\rm T}$) and collision centrality. The $p_{\rm T}$-integrated production rate of $\Lambda(1520)$ relative to $\Lambda$ in central collisions is suppressed by about a factor of 2 with respect to peripheral collisions. This is the first observation of the suppression of a baryonic resonance at the LHC and the first 3$\sigma$ evidence of $\Lambda(1520)$ suppression within a single collision system. The measured $\Lambda(1520)/\Lambda$ ratio in central collisions is smaller than the value predicted by the statistical hadronisation model calculations. The shape of the measured $p_{\rm T}$ distribution and the centrality dependence of the suppression are reproduced by the EPOS3 Monte Carlo event generator. The measurement adds further support to the formation of a dense hadronic phase in the final stages of the evolution of the fireball created in heavy-ion collisions, lasting long enough to cause a significant reduction in the observable yield of short-lived resonances.

Production and Hadronic Decays of Higgs Bosons in Heavy-Ion Collisions.

We examine Higgs boson production and decay in heavy-ion collisions at the LHC and future colliders. Owing to the long lifetime of the Higgs boson, its hadronic decays may experience little or no screening from the hot and dense quark-gluon plasma, whereas jets from hard scattering processes and from decays of the electroweak gauge bosons and the top quark suffer significant energy loss. This distinction can lead to enhanced signal to background ratios in hadronic decay channels and thus, for example, provide alternative ways to probe the Yukawa coupling of the Higgs boson to the bottom quark and its lifetime.

Probing anomalous tqgamma and tqg couplings via single top production in association with photon at FCC-hh

We study the anomalous FCNC tqgamma and tqg couplings via pprightarrow Wbgamma +X signal process including realistic detector effects for both leptonic and hadronic decay channels of the W boson at 100 TeV FCC-hh. The relevant backgrounds are considered in the cut based analysis to obtain not only limits on the anomalous lambda and zeta couplings but also branching ratios of trightarrow qgamma and trightarrow qg decay channels. We find that the sensitivity to the branching ratio of t rightarrow q gamma channel is three order better than the available LHC experimental limits, and it is comparable for the branching ratio of the trightarrow qg decay channel with an integrated luminosity of 10 text {ab}^{-1} at 2sigma significance level.

Search for lepton-flavour-violating decays of Higgs-like bosons

A search is presented for a Higgs-like boson with mass in the range 45 to 195,{{mathrm {GeV/}}c^2} decaying into a muon and a tau lepton. The dataset consists of proton-proton interactions at a centre-of-mass energy of 8~{mathrm {TeV}}, collected by the LHCb experiment, corresponding to an integrated luminosity of 2,text{ fb }^{-1}. The tau leptons are reconstructed in both leptonic and hadronic decay channels. An upper limit on the production cross-section multiplied by the branching fraction at 95% confidence level is set and ranges from 22,{mathrm {pb}} for a boson mass of 45,{{mathrm {GeV/}}c^2} to 4,{mathrm {pb}} for a mass of 195,{{mathrm {GeV/}}c^2}.

Search for single production of vector-like quarks decaying to a b quark and a Higgs boson

A search is presented for single production of heavy vector-like quarks (B) that decay to a Higgs boson and a b quark, with the Higgs boson decaying to a highly boosted mathrm{b}overline{mathrm{b}} pair reconstructed as a single collimated jet. The analysis is based on data collected by the CMS experiment in proton-proton collisions at sqrt{s}=13 TeV, corresponding to an integrated luminosity of 35.9 fb−1. The data are consistent with background expectations, and upper limits at 95% confidence level on the product of the B quark cross section and the branching fraction are obtained in the range 1.28–0.07 pb, for a narrow B quark with a mass between 700 and 1800 GeV. The production of B quarks with widths of 10, 20 and 30% of the resonance mass is also considered, and the sensitivities obtained are similar to those achieved in the narrow width case. This is the first search at the CERN LHC for the single production of a B quark through its fully hadronic decay channel, and the first study considering finite resonance widths of the B quark.