Meson Decay Research Articles

Pure annihilation decay of strange beauty meson into two charm heavy mesons

In this study, the heavy to heavy decay of is evaluated through the factorization approach by using the final state interaction as an effective correction. Under the factorization approach, this decay mode occurs only through the annihilation process, so a small amount is produced. Feynman's rules state that six meson pairs can be assumed for the intermediate states before the final meson pairs are produced. By taking into account the effects of twelve final state interaction diagrams in the calculations, a significant correction is obtained. These effects correct the value of the branching ratio obtained by the pure factorization approach from to . The value obtained for the branching ratio of the decay is consistent with the experimental results.

Higgs production in association with a dark-Z at future electron positron colliders

In recent years there have been many proposals for new electron–positron colliders, such as the circular electron–positron collider, the international linear collider, and the future circular collider in electron–positron mode. Much of the motivation for these colliders is precision measurements of the Higgs boson and searches for new electroweak states. Hence, many of these studies are focused on energies above the hZ threshold. However, there are proposals to run these colliders at the lower W W threshold and Z-pole energies. In this paper, we study a new search for Higgs physics accessible at lower energies: e + e − → hZ d, where Z d is a new light gauge boson such as a dark photon or dark-Z. Such searches can be conducted at the W W threshold, i.e. energies below the hZ threshold where exotic Higgs decays can be searched for in earnest. Additionally, due to very good angular and energy resolution at future electron–positron colliders, these searches will be sensitive to Z d masses below 1 GeV, which is lower than the current direct LHC searches. We will show that at GeV with 10 ab−1, a search for e + e − → hZ d is sensitive to h − Z − Z d couplings of δ ∼ 9 × 10−3 and cross sections of ab for Z d masses below 1 GeV. The results are similar at GeV with 5 ab−1. These limits are better than those expected from limits on the HL-LHC limits on Higgs branching ratio into generic non-standard model final states and comparable to meson decay limits.

Purely leptonic decays of the ground charged vector mesons

The study of the purely leptonic decays of the ground charged vector mesons is very interesting and significant in determining the CKM matrix elements, obtaining the decay constant of vector mesons, examining the lepton flavor universality, and searching for new physics beyond the standard model. These purely leptonic decays of the ground charged vector mesons are induced by the weak interactions within the standard model, and usually have very small branching ratios, mathcal{B}({rho }^{-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-13}), {{{mathcal {B}}}}(K^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }{{{mathcal {O}}}}(10^{-13}), mathcal{B}(D_{d}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-10}), mathcal{B}(B_{u}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-10}), mathcal{B}(D_{s}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-6}) and mathcal{B}(B_{c}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-6}). Inspired by the potential prospects of LHCb, Belle-II, STCF, CEPC and FCC-ee experiments, we discussed the probabilities of experimental investigation on these purely leptonic decays. It is found that the measurements of these decays might be possible and feasible with the improvement of data statistics, analytical technique, and measurement precision in the future. (1) With the hadron-hadron collisions, the purely leptonic decays of {rho }^{-}, K^{{*}-}, D_{d,s}^{{*}-} and B_{u,c}^{{*}-} mesons might be accessible at LHC experiments. (2) With the e^{+}e^{-} collisions, the purely leptonic decays of D_{d,s}^{{*}-} and B_{u,c}^{{*}-} mesons might be measurable with over 10^{12}Z^{0} bosons available at CEPC and FCC-ee experiments. In addition, the D_{d,s}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell } decays could also be studied at Belle-II and SCTF experiments.

Updated search for {B}_c^{+} decays to two charm mesons

A data set corresponding to an integrated luminosity of 9 fb−1 of proton-proton collisions collected by the LHCb experiment has been analysed to search for {B}_c^{+}to {D}_{(s)}^{left(ast right)+}{genfrac{}{}{0pt}{}{left(hbox{---} right)}{D}}^{left(ast right)0} decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the decay of an excited charm meson are allowed. Upper limits for the branching fractions, normalised to B+ decays to final states with similar topologies, are obtained for sixteen {B}_c^{+} decay modes. For the decay {B}_c^{+}to {D}_s^{+}{overline{D}}^0 , an excess with a significance of 3.4 standard deviations is found.

Four-lepton decays of neutral vector mesons

We investigate the rare electromagnetic decays of neutral vector mesons (exemplified by $J/\psi$, $\Upsilon$, $\rho^0$, $\omega,\phi$, \ldots) into four charged leptons ($2(e^+e^-)$, $2(\mu^+\mu^-)$, $2(\tau^+\tau^-)$, $e^+e^-\mu^+\mu^-$, $e^+e^-\tau^+\tau^-$, \ldots) at lowest order in QED. In contrast to the case of vector meson decay into a single pair of leptons, the lepton mass must be retained in these four-lepton decay channels to cutoff the mass singularity. Owing to more pronounced collinear enhancement, the branching fractions of vector mesons decays into $ 2(e^+e^-)$ are considerably greater than those for decays into $2(\mu^+\mu^-)$. The decay channels $J/\psi(\Upsilon)\to 2(e^+e^-), e^+e^-\mu^+\mu^-$ are predicted to have branching fractions of order $10^{-5}$, which appear to have bright observation prospect at {\tt BESIII}, {\tt Belle 2} and {\tt LHC} experiments.

Interference effect in lepton number violating and conserving meson decays for a left-right symmetric model

We study the effect of interference on the lepton number violating~(LNV) and lepton number conserving~(LNC) three-body meson decays $M_1^{+}\to l_i^{+} l_j^{\pm}\pi^{\mp}$, that arise in a TeV scale Left Right Symmetric model~(LRSM) with degenerate or nearly degenerate right handed~(RH) neutrinos. LRSM contains three RH neutrinos and a RH gauge boson. The RH neutrinos with masses in the range of $M_N \sim$ (MeV - few GeV) can give resonant enhancement in the semi-leptonic LNV and LNC meson decays. In the case, where only one RH neutrino contributes to these decays, the predicted new physics branching ratio of semi-leptonic LNV and LNC meson decays $M_1^{+}\to l_i^{+} l_j^{+}\pi^{-}$ and $M_1^{+}\to l_i^{+} l_j^{-}\pi^{+}$ are equal. We find that with at least two RH neutrinos contributing to the process, the LNV and LNC decay rates can differ. Depending on the neutrino mixing angles and $CP$ violating phases, the branching ratios of LNV and LNC decay channels mediated by the heavy neutrinos can be either enhanced or suppressed, and the ratio of these two rates can differ from unity.

Imprint of SUSY in radiative B -meson decays

We study supersymmetric (SUSY) effects on $C_7(\mu_b)$ and $C'_7(\mu_b)$ which are the Wilson coefficients (WCs) for $b \to s \gamma$ at b-quark mass scale $\mu_b$ and are closely related to radiative $B$-meson decays. The SUSY-loop contributions to $C_7(\mu_b)$ and $C'_7(\mu_b)$ are calculated at leading order (LO) in the Minimal Supersymmetric Standard Model (MSSM) with general quark-flavour violation (QFV). For the first time we perform a systematic MSSM parameter scan for the WCs $C_7(\mu_b)$ and $C'_7(\mu_b)$ respecting all the relevant constraints, i.e. the theoretical constraints from vacuum stability conditions and the experimental constraints, such as those from $K$- and $B$-meson data and electroweak precision data, as well as recent limits on SUSY particle masses and the 125 GeV Higgs boson data from LHC experiments. From the parameter scan we find the following: (1) The MSSM contribution to Re($C_7(\mu_b)$) can be as large as $\sim \pm 0.05$, which could correspond to about 3$\sigma$ significance of New Physics (NP) signal in the future LHCb and Belle II experiments. (2) The MSSM contribution to Re($C'_7(\mu_b)$) can be as large as $\sim -0.08$, which could correspond to about 4$\sigma$ significance of NP signal in the future LHCb and Belle II experiments. (3) These large MSSM contributions to the WCs are mainly due to (i) large scharm-stop mixing and large scharm/stop involved trilinear couplings, (ii) large sstrange-sbottom mixing and large sstrange-sbottom involved trilinear couplings and (iii) large bottom Yukawa coupling $Y_b$ for large $\tan\beta$ and large top Yukawa coupling $Y_t$. In case such large NP contributions to the WCs are really observed in the future experiments at Belle II and LHCb Upgrade, this could be the imprint of QFV SUSY (the MSSM with general QFV).

DIGITAL GENERATORS OF A PSEUDORANDOM PULSES SEQUENCE AND THEIR MODELING WITH USE OF FPGA INTHE ENVIRONMENT CAD QUARTUS II

From the results obtained in publication [1] as well percentage between decay modes of exitated states of mesons, cited in reference book “Particle Data Group” became possible to evaluate the number of hadron final states on which the meson with hidden charm decay. In the paper is shown a rough estimate of final states number for hadron decays of mesons with hidden charm. The most statistically secured are the final states for ηс (1 S), 2 (π+π-) and π+π- K+K- for χс0 (1P) mesons.

Probing new physics effects in Λ b → Λ(→pπ −)ℓ + ℓ − decay via model-independent approach

In the last few decades, the FCNC transitions played a pivotal role in the ongoing efforts to test the Standard Model (SM) parameters. These transitions are also in the limelight to constrain the various New Physics (NP) scenarios. Regarding this, both the rare meson and baryon decays are pertinent as they occur through FCNC transitions and contain information about the heavy to light quark transition sector, where the SM has not yet examined totally. Therefore, it is interesting to analyze a phenomenological rich four-body decay channel . Here, we incorporate the NP through a model-independent approach, which modifies both the SM Wilson coefficients (WCs), and introduces the new vector, axial-vector, scalar, pseudo-scalar, and tensor operators. To check the SM and to explore the possibilities of the NP, several physical observables such as the branching ratio , forward-backward asymmetries , and , longitudinal (transverse) polarization fractions , asymmetry parameters , the angular moments, and some other angular observables, extracted from certain foldings, have been examined to compare our results with LHCb. To see which new coupling among VA, SP, and T can accommodate the available experimental data, we have examined the influence of these couplings separately to the values of these observables. For the angular moments, most of the LHCb observations lie close to the SM, and the current constraints on new VA couplings do not change the SM results significantly. For angular coefficients, , and the agreement with the experimental measurement gets improved if we invoke the tensor couplings along with SM WCs. We hope that when experimental measurements become more accurate, together with B meson decays, the will help us to put constraints on the parametric space of these WCs.

The role of right-handed neutrinos in b \u2192 c\u03c4 (\u03c0\u03bd\u03c4, \u03c1\u03bd\u03c4, \u03bc overline{nu} \u03bc\u03bd\u03c4) overline{nu} \u03c4 from visible final-state kinematics

In the context of lepton flavor universality violation (LFUV) studies, we fully derive a general tensor formalism to investigate the role that left- and right-handed neutrino new-physics (NP) terms may have in b → cτ overline{nu} τ transitions. We present, for several extensions of the Standard Model (SM), numerical results for the Λb → Λcτ overline{nu} τ semileptonic decay, which is expected to be measured with precision at the LHCb. This reaction can be a new source of experimental information that can help to confirm, or maybe rule out, LFUV presently seen in overline{B} meson decays. The present study analyzes observables that can help in distinguishing between different NP scenarios that otherwise provide very similar results for the branching ratios, which are our currently best hints for LFUV. Since the τ lepton is very short-lived, we consider three subsequent τ-decay modes, two hadronic πντ and ρντ and one leptonic μ overline{nu} μντ, which have been previously studied for overline{B} → D(*) decays. Within the tensor formalism that we have developed in previous works, we re-obtain the expressions for the differential decay width written in terms of visible (experimentally accessible) variables of the massive particle created in the τ decay. There are seven different τ angular and spin asymmetries that are defined in this way and that can be extracted from experiment. Those asymmetries provide observables that can help in constraining possible SM extensions.

Prosthetic socket rotation stability - A mock limb study on different suspension systems

Decays of mesons produced in cosmic ray induced air showers in Earth’s atmosphere can lead to a flux of light exotic particles which can be detected in underground experiments. We evaluate the energy spectra of the light neutral mesons π0, η, ρ0, ω, ϕ and J∕ψ produced in interactions of cosmic ray protons and helium nuclei with air using QCD inspired event generators. Summing up the mesons produced in the individual hadronic interactions of air showers, we obtain the resulting fluxes of undecayed mesons. As an application, we re-consider the case of millicharged particles created in the electromagnetic decay channels of neutral mesons.

Doubly charmed molecular pentaquarks

We perform a systematic exploration of the possible doubly charmed molecular pentaquarks composed of Σc(⁎)D(⁎) with the one-boson-exchange potential model. After taking into account the S−D wave mixing and the coupled channel effects, we predict several possible doubly charmed molecular pentaquarks, which include the ΣcD with I(JP)=1/2(1/2−), Σc⁎D with 1/2(3/2−), and ΣcD⁎ with 1/2(1/2−), 1/2(3/2−). The ΣcD state with 3/2(1/2−) and ΣcD⁎ state with 3/2(1/2−) may also be suggested as candidates of doubly charmed molecular pentaquarks. The ΣcD and Σc⁎D states can be searched for by analyzing the ΛcDπ invariant mass spectrum of the bottom baryon and B meson decays. The ΣcD⁎ states can be searched for in the invariant mass spectrum of ΛcD⁎π, ΛcDππ and ΛcDπγ. Since the width of Σc⁎ is much larger than that of D⁎, Σc⁎D→ΛcDπ will be the dominant decay mode. We sincerely hope these candidates for the doubly charmed molecular pentaqurks will be searched by LHCb or BelleII collaboration in the near future.

Renormalization-group evolution of the none-local matrix element of B-meson in QCD and B → π transition form factor

We consider the renormalization-group evolution of the matrix element of 〈0|q¯(z)β[z,0]b(0)α|B¯〉, which can be used to define the distribution amplitudes for B meson and widely applied in studies of B meson decays. The contribution to the renormalization constant of the non-local operator q¯(z)β[z,0]b(0)α is considered up to one-loop order in QCD. Since the quark fields in this operator are not directly coupled fields, momentum can not flow freely through this non-local operator. Momentum involved in this operator can be treated stringently in coordinate space. We find that the ultraviolet divergences regulated by dimensional parameter ϵ cancel with each other, and the evolution effect vanishes. The matrix element 〈0|q¯(z)β[z,0]b(0)α|B¯〉 escapes from the renormalization-group evolution. We then apply the matrix element in calculating B→π transition form factor, where the matrix element is obtained by using the B meson wave function calculated in QCD-inspired potential model. By comparing with experimental data for the semileptonic decay of B→πℓν and light-cone sum rule calculation, we analyze the perturbative and non-perturbative contributions to B→π transition form factor in the frame work of perturbative QCD approach. We find that the effectiveness of the suppression of Sudakov factor to soft contribution depends on the end-point behavior of B meson wave function, and with the B-meson wave function used in this work, soft contribution can not be well suppressed. The hard contribution to the B→π transition form factor is about 59%, and soft contribution can be as large as 41% in the naive calculation. To make the perturbative calculation reliable, a soft momentum cutoff in the calculation and soft form factor have to be introduced.

Searching for light long-lived neutralinos at Super-Kamiokande

Light neutralinos could be copiously produced from the decays of mesons generated in cosmic-ray air showers. These neutralinos can be long-lived particles in the context of R-parity violating (RPV) supersymmetric models, implying that they could be capable of reaching the surface of the earth and decay within the instrumental volume of large neutrino detectors. In this letter, we use atmospheric neutrino data from the Super-Kamiokande experiment to derive novel constraints for the RPV couplings involved in the production of long-lived light neutralinos from the decays of charged $D$-mesons and kaons. Our results highlight the potential of neutrino detectors to search for long-lived particles, by demonstrating that it is possible to explore regions of parameter space that are not yet constrained by any fixed-target nor collider experiments.

Test of quantum nonlocality via vector meson decays to KSKS

In the system of a pair of quantum-entangled neutral kaons from meson decays, when one kaon collapses into the [Formula: see text] state, the other will collapse instantaneously into the [Formula: see text] state, due to entanglement and nonlocality. However, if the alternative hypothesis is correct and there is a time window during which one kaon is unaware that the other has decayed, some quantum mechanically prohibited [Formula: see text] decays may occur. We calculate the branching ratios of [Formula: see text] in vector meson decays under locality hypothesis and compare them with experimental results. We show that the branching ratio of [Formula: see text] under locality assumption is already excluded by the BESIII experimental upper limit. Additional experimental results are proposed to perform this test in the future.

Unitarity bounds for semileptonic decays in lattice QCD

In this work we discuss in detail the nonperturbative determination of the momentum dependence of the form factors entering in semileptonic decays using unitarity and analyticity constraints. The method contains several new elements with respect to previous proposals and allows to extract, using suitable two-point functions computed nonperturbatively, the form factors at low momentum transfer ${q}^{2}$ from those computed explicitly on the lattice at large ${q}^{2}$, without any assumption about their ${q}^{2}$-dependence. The approach will be very useful for exclusive semileptonic $B$-meson decays, where the direct calculation of the form factors at low ${q}^{2}$ is particularly difficult due to large statistical fluctuations and discretization effects. As a testing ground we apply our approach to the semileptonic $D\ensuremath{\rightarrow}K\ensuremath{\ell}{\ensuremath{\nu}}_{\ensuremath{\ell}}$ decay, where we can compare the results of the unitarity approach to the explicit direct lattice calculation of the form factors in the full ${q}^{2}$-range. We show that the method is very effective and that it allows to compute the form factors with rather good precision.

Leptoquarks and matter unification: Flavor anomalies and the muon g−2

We discuss the minimal theory for quark-lepton unification at the low scale. In this context, the quarks and leptons are unified in the same representations and neutrino masses are generated through the inverse seesaw mechanism. The properties of the leptoquarks predicted in this theory are discussed in detail and we investigate the predictions for the leptonic and semi-leptonic decays of mesons. We study the possibility to explain the current value of $\mathcal{R}_K$ reported by the LHCb collaboration and the value of the muon anomalous magnetic moment reported by the Muon $g-2$ experiment at Fermilab.

Comprehensive study of light axial vector mesons with the presence of triangle singularity

We present a systematic study of the productions and decays of light axial vector mesons with $J^{PC}=1^{+\pm}$ in charmonium decays. In the quark model scenario, the two axial vector nonets are connected with each other by the Gell-Mann-Okubo mass relation through the mixing between two $K_1$ states (i.e. $K_1(1270)$ and $K_1(1400)$) with configurations of $^3P_1$ and $^1P_1$. The mixing angles between $f_1$ and $f_1'$ (i.e. $f_1(1285)$ and $f_1(1420)$), and between $h_1$ and $h_1'$ (i.e. $h_1(1170)$ and $h_1(1415)$) can be reliably constrained. We then introduce the intermediate $K^*\bar{K}+c.c.$ meson loop transitions in the description of the productions and decays of these axial vector mesons. The presence of the nearby $S$-wave $K^*\bar{K}+c.c.$ to which these axial vector mesons have strong coupling strengths, turns out to be crucial for understanding many puzzling questions related to their productions and decays. This is because that the $S$-wave $K^*\bar{K}+c.c.$ rescatterings by the kaon exchange satisfy the triangle singularity (TS) condition in some of these cases and the TS mechanism can introduce special interference effects in the exclusive decays of these light axial vector mesons.

Weak value amplification in high energy physics: A case study for precision measurement of CP violation in B meson decays

The technique of weak value amplification, proposed by Aharonov et al. in 1988, has been applied for various fields of physics for the purpose of precision measurement, which is made possible by exploiting the freedom of `postselection' specifying actively the final state in the physical process. Here we report for the first time the feasibility of utilizing the technique of weak value amplification in high energy particle physics, especially in measuring the CP-violating parameters in B meson decays, where the effective lifetime of the decay mode is expected to be prolonged statistically due to the postselection. Our analysis shows that, when adopted in the Belle II experiment at the SuperKEKB collider, the effective lifetime may be prolonged up to 2.6 times, and that the measurement precision of the CP-violating parameters will also be improved by its effect.

Glauber gluons in annihilation amplitudes for heavy meson decays

We investigate the Glauber divergences in nonfactorizable annihilation amplitudes for two-body hadronic heavy meson decays in the kT factorization theorem at one-loop level. These divergences can be absorbed into the Glauber factors in the dominant kinematic regions of small parton momenta, which modify the interference between a nonfactorizable annihilation amplitude and other amplitudes by rotating it with a phase. We postulate that only the Glauber effect associated with a pion is significant, due to its special role as a qq̄ bound state and as a pseudo Nambu–Goldstone boson simultaneously. It is elaborated that the data of the D→ππ and πK branching ratios have revealed prominent Glauber effects. This work provides a solid theoretical ground for the factorization-assisted topological-amplitude parametrization of two-body hadronic D meson decays.