Differential Decay Width Research Articles

New constraints on CPT symmetry violation in charm mesons

Small CPT-violating effects are admissible in several theories beyond the Standard Model of interactions. We analyze experimental data obtained with neutral flavored meson mixing and place bounds on the scale of such phenomena. The constraints on the CPT-violating parameter z are derived by reinterpreting the LHCb measurement of the time-dependent asymmetry in the Cabbibo-favored D0→K−π+ and D0¯→K+π− decay rates. The bounds provided in this paper are 2 orders of magnitude stricter compared to the results obtained by the FOCUS Collaboration. Among other constraints, we report bounds on the differences in the decay widths and masses of the neutral D meson flavor states at a 95% confidence level. The decay width difference is bounded by (−4.7<δΓD<2.1)×10−16 GeV. The mass difference lies within (−2.0<δmD<2.0)×10−15 GeV for 95% of arg(z) values. The paper includes an assessment of the influence of CP violation on the results and a discussion of the future prospects. Published by the American Physical Society 2024

Exploring scalar contributions with K+ → π+ℓ+ℓ−

The rare kaon decay K+→π+ℓ+ℓ− offers insights into Standard Model (SM) physics and beyond. Driven by vector form factor in the SM, it can also probe non-standard contributions. In this letter we study the scalar contribution, fS. Using differential decay width and Forward-Backward Asymmetry we propose a simultaneous fit to vector and scalar contributions which is necessary for a consistent analysis. Novel bounds on |fS| are presented for the first time through a reinterpretation of the E865, NA48/2, and NA62 experimental results. The analysis results in the most precise bound fS<7.9×10−6 at 90% confidence level.

A measurement of ∆Γs

Using a dataset corresponding to 9 fb−1 of integrated luminosity collected with the LHCb detector between 2011 and 2018 in proton-proton collisions, the decay-time distributions of the decay modes Bs0→J/ψη′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0\ o J/{\\psi \\eta}^{\\prime } $$\\end{document} and Bs0→J/ψπ+π−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0\ o J/\\psi {\\pi}^{+}{\\pi}^{-} $$\\end{document} are studied. The decay-width difference between the light and heavy mass eigenstates of the Bs0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {B}_s^0 $$\\end{document} meson is measured to be ∆Γs = 0.087 ± 0.012 ± 0.009 ps−1, where the first uncertainty is statistical and the second systematic.

Probing quantum decoherence at Belle II and LHCb

With the advent of Belle II and the LHCb upgrade, the precision measurements of various B-Physics observables are on cards. This holds significant potential for delving into physics beyond the standard model of electroweak interactions. These measurements can also serve as means to establish limits on phenomena occurring at much finer length scales, such as quantum decoherence, which may arise due to potential discreteness in space-time or non-trivial topological effects. In this work, we set up the formalism to investigate the impact of quantum decoherence on several potential observables in B meson systems. The approach employs the trace-preserving Kraus operator formalism, extending unitary evolution to non-unitary dynamics while maintaining complete positivity. In this formalism, the decoherence effects are parametrized in terms of a single parameter. Through the analysis of purely leptonic, semileptonic, and non-leptonic decays of B mesons, we identify observables that could, in principle, be influenced by decoherence. The theoretical expressions are provided without neglecting the impact of decay width difference (∆Γ) and CP violation in mixing. Considering that many of these observables can be measured with high precision using the abundant data collected by LHCb and Belle II, our formalism can be applied to establish constraints on the decoherence parameter through multiple decay channels. This offers an alternative set-up for such studies, which, at present, are predominantly conducted in the neutrino sector.

Decay process within the QCDSR approach* *Supported in part by the National Natural Science Foundation of China (12265010, 12265009) and the Project of Guizhou Provincial Department of Science and Technology (ZK[2021]024, ZK[2023]142)

In this paper, we investigate the charmed meson rare decay process using an approach based on QCD sum rules. First, the pion twist-2, 3 distribution amplitude (DA) moments and are calculated up to the tenth and fourth orders, respectively, in the QCD sum rules according to the background field theory. After constructing the light-cone harmonic oscillator model for the pion twist-2, 3 DAs, we obtain their behaviors by matching the calculated ξ-moments. Then, the transition form factors (TFFs) are calculated using an approach based on QCD light-cone sum rules. The vector form factor at the large recoil region is . Using the rapidly converging simplified series expansion of , we present the TFFs and corresponding angular coefficients in the whole squared momentum transfer physical region. Based on non-standard neutrino interactions, the decay can be related to the decay indirectly. Thus, we first describe the semileptonic decay process , differential decay widths, and branching fraction with . The differential/total predictions for forward-backward asymmetry, -differential flat terms, and lepton polarization asymmetry are also reported. The prediction for the branching fraction is .

Constraints on subleading interactions in beta decay Lagrangian

We discuss the effective field theory (EFT) for nuclear beta decay. The general quark-level EFT describing charged-current interactions between quarks and leptons is matched to the nucleon-level non-relativistic EFT at the OMeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O}\\left(\ extrm{MeV}\\right) $$\\end{document} momentum scale characteristic for beta transitions. The matching takes into account, for the first time, the effect of all possible beyond-the-Standard-Model interactions at the subleading order in the recoil momentum. We calculate the impact of all the Wilson coefficients of the leading and subleading EFT Lagrangian on the differential decay width in allowed beta transitions. As an example application, we show how the existing experimental data constrain the subleading Wilson coefficients corresponding to pseudoscalar, weak magnetism, and induced tensor interactions. The data display a 3.5 sigma evidence for nucleon weak magnetism, in agreement with the theory prediction based on isospin symmetry.

Further study on the production of P-wave doubly heavy baryons from Z-boson decays

In this paper, we carried out a systematic investigation for the excited doubly heavy baryons production in Z-boson decays within the NRQCD factorization approach. Our investigation accounts for all the P-wave intermediate diquark states, i.e.〈cc〉[P11]3¯, 〈cc〉[PJ3]6, 〈bc〉[P11]3¯/6, 〈bc〉[PJ3]3¯/6, 〈bb〉[P11]3¯, and 〈bb〉[PJ3]6 with J=(0,1,2). The results show that contributions from all diquark states in P-wave were 7%, 8%, and 3% in comparing with S-wave for the production of Ξcc, Ξbc and Ξbb via Z-boson decay, respectively. Based on these results, we predicted about 0.539×103(106) events for Ξcc, 1.827×103(106) events for Ξbc, and 0.036×103(106) events for Ξbb can be produced annually at the LHC (CEPC). Additionally, we plot the differential decay widths of Ξcc, Ξbc and Ξbb as a function of the invariant mass s23 and energy function z distributions, and analyze the theoretical uncertainties in decay width arising from the mass parameters of heavy quark.

Form factors in HQEFT and model independent analysis of relevant semileptonic decays with NP effects* *Supported in part by the National Natural Science Foundation of China (12147214)

The form factors of decays into P-wave excited charmed mesons (including , , , and their strange counterparts, denoted generically as ) are systematically calculated via QCD sum rules in the framework of heavy quark effective field theory (HQEFT). We consider contributions up to the next leading order of heavy quark expansion and give all the relevant form factors, including the scalar and tensor ones only relevant for possible new physics effects. The expressions for the form factors in terms of several universal wave functions are derived via heavy quark expansion. These universal functions can be evaluated through QCD sum rules. Then, the numerical results of the form factors are presented. With the form factors given here, a model independent analysis of relevant semileptonic decays is performed, including the contributions from possible new physics effects. Our predictions for the differential decay widths, branching fractions, and ratios of branching fractions may be tested in more precise experiments in the future.

Role of triangle singularity in the decay process D0→π+π−f0(980) , f0→π+π−

We study the process $D^0 \to \pi^+ \pi^- f_0(980),\ f_0 \to \pi^+ \pi^-$ by introducing the triangle mechanism, in which $f_0(980)$ is considered to be dynamically generated from the meson-meson interaction. For the total contribution of this process, the contribution of the triangular loop formed by $K^{*} \bar{K} K$ particles could generate a triangular singularity of about 1418 MeV. We calculate the differential decay width of this process and show a narrow peak of about 980 MeV in the $\pi^+ \pi^-$ invariant mass distribution, which comes from $f_0$ decay. For the $M_{inv}(\pi f_0)$ invariant mass distribution, we obtain a finite peak at 1418 MeV, which is consistent with the triangle singularity.

Investigation of Z-boson decay into and baryons within the NRQCD factorization approach* *Supported in part by the Natural Science Foundation of China (12265010) and the Project of Guizhou Provincial Department of Education (KY[2021]030)

Z-boson decay provides a good opportunity to search for the baryon because a large number of its events can be collected at high energy colliders. In this paper, we perform a complete investigation of the indirect production of the and baryons via the Z-boson decay process with a quark under the NRQCD factorization approach. After considering the contribution from the diquark states , , , and , the calculated branching fractions are and . Furthermore, the and production events are predicted to be of the order of and at the LHC collider, and the order of and for the CEPC collider. We then estimate the production ratio for with in Z-boson decay, that is, and , respectively. Finally, we present the differential decay widths of and with respect to and z distributions and analyze the uncertainties.

NP effects in Λb → Λc(*) semileptonic decays

In the context of lepton flavor universality violation (LFUV) studies, we study different observables related to the b → cτν¯τ semileptonic decays. These observables are expected to help in distinguishing between different New Physics (NP) scenarios. Since the τ lepton is very short-lived, we consider three subsequent τ-decay modes, two hadronic πντ and ρντ and one leptonic µν¯µντ. This approach enables the differential decay width to be written in terms of visible (experimentally accessible) variables of the massive particle created in the τ decay. We present numerical results for the observables that can be accessed through the visible kinematics for the Λb → Λc and the Λb → Λ˚c p2595q transitions. This work is based on Refs.[1–3].

Is the Λc(2625)+ the heavy quark spin symmetry partner of the Λc(2595)+ ?

We use a $\mathcal{O}(\Lambda_\text{QCD}/m_c)$ heavy quark effective theory scheme, where only $\mathcal{O}(\Lambda_\text{QCD}/m_b)$ and perturbative QCD short distance corrections are neglected, to study the matrix elements of the scalar, pseudoscalar, vector, axial-vector and tensor currents between the $\Lambda_b$ ground state and the odd parity charm $\Lambda_c(2595)^+$ and $\Lambda_c(2625)^+$ resonances. We show that in the near-zero recoil regime, the scheme describes reasonably well, taking into account uncertainties, the results for the 24 form-factors obtained in lattice QCD (LQCD) just in terms of only 4 Isgur-Wise (IW) functions. We also find some support for the possibility that the $\Lambda_c(2595)^+$ and $\Lambda_c(2625)^+$ resonances might form a heavy-quark spin symmetry (HQSS) doublet. However, we argue that the available LQCD description of these two resonances is not accurate enough to disentangle the possible effects of the $\Sigma_c \pi$ and $\Sigma_c^*\pi$ thresholds, located only a few MeV above their position, and that it cannot be ruled out that these states are not HQSS partners. Finally, we study the ratio $\frac{d\Gamma[\Lambda_b\to \Lambda_{c,1/2^-}^* \ell \bar\nu_\ell]/dq^2}{d\Gamma[\Lambda_b\to \Lambda_{c,3/2^-}^*\ell \bar\nu_\ell]/dq^2}$ of the Standard Model differential semileptonic decay widths, with $q^\mu$ the momentum transferred between the initial and final hadrons. We provide a natural explanation for the existence of large deviations, near the zero recoil, of this ratio from 1/2 (value predicted in the infinite heavy quark mass limit, assuming that the $\Lambda_{c,1/2^-}^*$ and $\Lambda_{c,3/2^-}^*$ are the two members of a HQSS doublet) based on S-wave contributions to the $\Lambda_b\to \Lambda_{c,1/2^-}^*$ decay amplitude driven by a sub-leading IW function.

Searching for new physics in the differential decay width of a Λb semi-leptonic decay

We propose to investigate the effects of new physics in the semi-leptonic sequential decay [Formula: see text]. First, we write the general, model-independent, non-covariant expression of the differential decay width of the process. Then, we calculate that observable according to three different types of new physics interactions, which might explain the tension of data with the Standard Model predictions. We find that some coefficients of the differential decay width are sensitive to the kind of interaction that is assumed. The measurements that we suggest seem to be feasible.

Next-to-leading order QCD corrections to Z→ηQ+Q+Q¯

It has been found that at a high luminosity $e^+ e^-$ collider, sizable $\eta_c+c\bar{c}X$ and $\eta_b+b\bar{b}X$ events can be produced when it works around the $Z$ peak. In this paper, we calculate the decay widths of $Z \to \eta_c+c+\bar{c}+X$ and $Z \to \eta_b+b+\bar{b}+X$ up to next-to-leading order (NLO) accuracy. We find that the NLO corrections are significant in these two processes. After including the NLO corrections, the decay widths of $Z \to \eta_c+c+\bar{c}+X$ and $Z \to \eta_b+b+\bar{b}+X$ are enhanced by about $37\%$ and $28\%$ for the case of $\mu_R=2m_c$ and $\mu_R=2m_b$, respectively. The differential decay widths $d\Gamma/ds_1$ and $d\Gamma/dz$ for these two decay processes are also analyzed.

Light-cone sum rule analysis of semileptonic decays varLambda _b^0 rightarrow varLambda _c^+ ell ^- {overline{nu }}_ell

In this work, we analyze the semileptonic decay processes of varLambda _b rightarrow varLambda _c in the light-cone sum rule approach. In order to calculate the form factors of the varLambda _b baryon transition matrix element, we use the light-cone distribution amplitudes of varLambda _b obtained from the QCD sum rule in the heavy quark effective field theory framework. With the calculation of the six form factors of the varLambda _b rightarrow varLambda _c transition matrix element, the differential decay widths of varLambda _b^0 rightarrow varLambda _c^+ ell ^- {overline{nu }}_ell (ell = e, ~mu , ~tau ) and their absolute branching fractions are obtained. Additionally, the ratio of R(varLambda _c^+) equiv {mathcal {B}}r(varLambda _b^0 rightarrow varLambda _c^+ tau ^- {overline{nu }}_tau )/{mathcal {B}}r(varLambda _b^0 rightarrow varLambda _c^+ mu ^- {overline{nu }}_mu ) is also obtained in this work. Our results are in accord with the newest experimental result and other theoretical calculations and predictions.

New gauge boson Z′ and the rare decay H→μ+μ−γ in the minimal U(1)Lμ−Lτ model

The rare decay [Formula: see text] is an interesting and characteristic process, which is starting to become experimentally accessible at the Large Hadron Collider (LHC) and the upcoming high-luminosity LHC. In this note, we consider the resonant contributions of the new gauge boson [Formula: see text] to the rare decay [Formula: see text] in the framework of the minimal [Formula: see text] model. Its differential decay rate and decay width are calculated. Our numerical results show that the new gauge boson [Formula: see text] can generate smaller contributions to this decay process.

Recent advances in charm mixing and CP violation at LHCb

After playing a pivotal role in the birth of the Standard Model in the 70s, the study of charm physics has undergone a revival during the last decade, triggered by a wealth of precision measurements from the charm and B factories, and from the CDF and especially the LHCb experiments. In this paper, we sum up how the unique phenomenology of charmed hadrons can be used to test the Standard Model and we review the latest measurements performed in this field by the LHCb experiment. These include the historic first observations of CP violation and of a nonzero mass difference between the charmed neutral-meson mass eigenstates, the most precise determination of their decay-width difference to date, and a search for time-dependent CP violation reaching the unprecedented precision of [Formula: see text]. These results challenge our comprehension of nonperturbative strong interactions, and their interpretation calls for further studies on both the theoretical and experimental sides. The upcoming upgrades of the LHCb experiment will play a leading role in this quest.

Visible neutrino decays and the impact of the daughter-neutrino mass

We compute the differential decay width of two- and three-body neutrino decays, assuming neutrinos are Dirac fermions and allowing for the possibility that the decay-daughters have nonzero masses. We examine different hypotheses for the interaction that mediates neutrino decay and concentrate on identifying circumstances where the decay-daughters can significantly impact the neutrino-decay signature at different experiments. We are especially interested in decay daughters produced by right-chiral neutrino fields, when the mass of the daughter plays a decisive role. As a concrete example, we compare the effects of visible and invisible antineutrino decays at the JUNO experimental setup.

Visible energy and angular distributions of the charged particle from the τ −decay in bto ctau left(mu {overline{nu}}_{mu }{nu}_{tau },{pi nu}_{tau },{rho nu}_{tau}right){overline{nu}}_{tau } reactions

We study the d2Γd/(dωd cos θd), dΓd/d cos θd and dΓd/dEd distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the τ −decay in bto ctau left(mu {overline{nu}}_{mu }{nu}_{tau },{pi nu}_{tau },{rho nu}_{tau}right){overline{nu}}_{tau } reactions. These differential decay widths could be measured in the near future with certain precision. The first two contain information on the transverse tau-spin, tau-angular and tau-angular-spin asymmetries of the {H}_bto {H}_ctau {overline{nu}}_{tau } parent decay and, from a dynamical point of view, they are richer than the commonly used one, d2Γd/(dωdEd), since the latter only depends on the tau longitudinal polarization. We pay attention to the deviations with respect to the predictions of the standard model (SM) for these new observables, considering new physics (NP) operators constructed using both right- and left-handed neutrino fields, within an effective field-theory approach. We present results for {Lambda}_bto {Lambda}_ctau left(mu {overline{nu}}_{mu }{nu}_{tau },{pi nu}_{tau },{rho nu}_{tau}right){overline{nu}}_{tau } and overline{B}to {D}^{left(ast right)}tau left(mu {overline{nu}}_{mu }{nu}_{tau },{pi nu}_{tau },{rho nu}_{tau}right){overline{nu}}_{tau } sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that dΓd/d cos θd, which should be measured with sufficiently good statistics, becomes quite useful, especially in the τ → πντ mode. The study carried out in this work could be of special relevance due to the recent LHCb measurement of the lepton flavor universality ratio {mathrm{mathcal{R}}}_{Lambda_c} in agreement with the SM. The experiment identified the τ using its hadron decay into π−π+π−ντ, and this result for {mathrm{mathcal{R}}}_{Lambda_c} , which is in conflict with the phenomenology from the b-meson sector, needs confirmation from other tau reconstruction channels.

One-loop contributions to the decay H → νl̅νlγ in the Standard Model revisited

Abstract One-loop contributions to the decay H → νl̅νlγ with l = e, μ, τ within the Standard Model framework are revisited in this paper. We derive two representations for the form factors in this calculation. As a result, the computations are not only checked numerically by verifying the ultraviolet finiteness of the results but also confirming the ward identity of the amplitude. We find that the results have good stability with varying ultraviolet cutoff parameters as well as satisfying the ward identity. In phenomenological results, we study the partial decay widths for the decay channels in the two cases of the detected photon and invisible photon. Differential decay widths are also generated as a function of the energy of the final photon.