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Fu-Sheng Yu

Publications and source records attributed to Fu-Sheng Yu.

At least 37 records · Page 2Linked to original sources

Establishing CP Violation in $b$-Baryon Decays

It is a long-standing puzzle why the {\it CP} violation (CPV) in the baryon system has not yet been definitively established as in the meson one. We demonstrate that individual partial-wave CPV in the $Λ_b\to pπ^-$ and $pK^-$ decays can exceed $10\%$, but the destruction between the partial waves (the suppression by the small partial-wave weight) results in a small net direct CPV in the former (the latter) as measured currently. Our finding highlights the different dynamics responsible for CPVs in baryon and meson decays. We propose to probe the CPV observables associated with the angular distributions of the $Λ_b\to pa_1(1260)$, $pK_1(1270)$ decay products, which are large enough for being identified experimentally.

hep-ph

Final-state rescattering mechanism of double-charm baryon decays: $\mathcal{B}_{cc}\to\mathcal{B}_{c}P$

In this study, we examine the non-leptonic weak decays of doubly charmed baryons, denoted as ${\cal B}_{cc}\to{\cal B}_{c}P$, where ${\cal B}_{cc}$ represents the doubly charmed baryons, specifically $(Ξ_{cc}^{++},Ξ_{cc}^{+},Ω_{cc}^{+})$. The notation ${\cal B}_{c}$ denotes the singly charmed baryons, specifically $({\cal B}_{\bar{3}},{\cal B}_{6})$, while $P$ signifies the light pseudoscalar. These terms are pertinent to the non-leptonic decay modes under discussion. While the short-distance contributions can be precisely estimated through theoretical calculations, addressing the long-distance contributions for final-state-interaction effects presents a significant challenge. In order to address this issue, we utilize the rescattering mechanism of final state interaction effects to compute the long-distance contributions. We initially derive the entire hadronic loop contributions for these two-body nonleptonic decays of doubly charmed baryons. In subsequent analyses, we are able to calculate relative strong phases. As a result, we can provide predictions for their decay asymmetry parameters and CP violations. Furthermore, we employ experimental data from the LHCb collaboration, specifically the ratio \(Br(Ξ_{cc}^{++}\toΞ_{c}^{\prime+}π^{+})/Br(Ξ_{cc}^{++}\toΞ_{c}^{+}π^{+})=(1.41\pm0.17\pm0.10)\), to ascertain the model parameters \(η=0.9\pm0.2\). Consequently, we present the predictions of branching ratios and decay asymmetry parameters for 67 distinct decay processes and $CP$ violations for the singly Cabibbo suppressed channels. This not only strengthens the validity of our theoretical predictions, but also provides a more comprehensive theoretical framework for the future identification of other doubly charmed baryons.

hep-ph

CP violation studies at Super Tau-Charm Facility

Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($τ$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $τ$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.

hep-ex

Transition form factors of the $Λ_b \rightarrow Λ(1520)$ in QCD light-cone sum rules

In this work, we investigate the transition form factors for $Λ_b\rightarrow{Λ(1520)}$ within the framework of light-cone sum rules (LCSR), using the light-cone distribution amplitudes (LCDAs) of the $Λ_b$-baryon. In the hadronic representation of the correlation function, we carefully select the appropriate Lorentz structures and isolate the contributions from both the $Λ(1520)(J^P=(3/2)^-)$ and the $Λ(1890)(J^P=(3/2)^+)$, ensuring that the form factors for $Λ_b\rightarrow{Λ(1520)}$ can be calculated unambiguously. We also provide predictions for various physical observables in the decay $Λ_b\rightarrow{Λ(1520)}l^+l^-$, including the differential branching fraction, the lepton-side forward-backward asymmetry, the longitudinal polarization fraction, and the CP-averaged normalized angular observable. Our prediction for the differential branching fraction of $Λ_b\rightarrow{Λ(1520)}μ^+μ^-$ is in good agreement with the LHCb measurement within the uncertainties.

hep-ph

CP violation observables in baryon decays

The era of baryon physics is on the horizon with the accumulation of increasing data by collaborations such as LHCb, Belle II, and BESIII. Despite the wealth of data, one of the critical issues in flavor physics, namely CP violation in baryon decays, still awaits experimental confirmation. It is evident that the development of formulas and phenomenological analyses will play a pivotal role in advancing theoretical investigations and experimental measurements in this domain. In this work, we discuss the fundamental definitions and properties of polarization, asymmetry parameters and their associated CP violating observables that may arise in baryon decays. Additionally, we provide a detailed analysis of b-baryon quasi-two and -three body decays based on angular distributions. We highlight the significance of CP asymmetries defined by spin and momentum correlations, as non-trivial spin distributions are expected in baryon decays due to their non-zero polarization in productions and decays. Of particular importance is a complementary relation can be establised for two different types of observables, that are $\mathcal{T}$-even and -odd CP asymmetries respectively. The complementarity indicates that one observable exhibits the sine dependence on strong phase $Δδ$, while another exhibits as cosine. This gives us an distinctive opportunity to avoid the potential large suppression to CP asymmetries from small phase $Δδ$. Two points (\textbf{i}) the exact proof of strong phase dependence behaviour, and (\textbf{ii}) the criterion for complementary observables are clarified. Based on these arguments from theoretical aside, some brief discussions and suggestions on experimental measurements are offered in the final discussions. Lastly, we present a pedagogical introduction to angular distribution techniques based on helicity descriptions for both two and three body decays.

hep-ph

Final-state rescattering mechanism of charmed baryon decays

The dynamical studies on the non-leptonic weak decays of charmed baryons are always challenging, due to the large non-perturbative contributions at the charm scale. In this work, we develop the final-state rescattering mechanism to study the two-body non-leptonic decays of charmed baryons. The final-state interaction is a physical picture of long-distance effects. Instead of using the Cutkosky rule to calculate the hadronic triangle diagrams which can only provide the imaginary part of decay amplitudes, we point out that the loop integral is more appropriate, as both the real parts and the imaginary parts of amplitudes can be calculated completely. In this way, it can be obtained for the non-trivial strong phases which are essential to calculate CP violations. With the physical picture of long-distance effects and the reasonable method of calculations, it is amazingly achieved that all the nine existing experimental data of branching fractions for the $Λ_c^+$ decays into an octet light baryon and a vector meson can be explained by only one parameter of the model. Besides, the decay asymmetries and CP violations are not sensitive to the model parameter, since the dependence on the parameter is mainly cancelled in the ratios, so that the theoretical uncertainties on these observables are lowered down.

hep-ph

CP Violation of Baryon Decays with $Nπ$ Scatterings

There is a long-standing puzzle that the CP violation (CPV) in the baryon systems has never been well established in experiments, while the CPV of mesons have been observed by decades. In this paper, we propose that the CPV of baryon decays can be generated with the rescatterings of a nucleon and a pion into some final states, i.e. $Nπ\to Nπ$ or $Nππ$. Benefited by the fruitful data of $Nπ$ scatterings, we can model-independently analyse the strong phases of $b$-baryon decays using the partial wave amplitudes of $Nπ$ scatterings. Avoiding the most difficult problem of non-perturbative dynamics, it makes a great advantage to predict the CPV of baryon decays with a relatively reliable understanding of the decay dynamics. We study the processes of $Λ_b^0\to (pπ^+π^-)h^-$ and $(pπ^0)h^-$ with $h=π$ or $K$. It is found that the global CPV of the above processes in the invariant mass regions of $Nπ$ scatterings are at the order of several percent. More importantly, the local CPV in some regions of the Dalitz plots can reach the order of $10\%$, or be even larger. Considering the predicted results and the experimental data samples, we strong suggest to measure the CPV of $Λ_b^0\to (pπ^+π^-)K^-$, which has a large possibility to achieve the first observation of CPV in the baryon system.

hep-ph

Complementary $CP$ violation induced by $T$-odd and $T$-even correlations

In this letter, we propose a novel approach to concurrently measure the complementary $CP$ violation observables induced by $T$-odd correlations and their corresponding $T$-even counterparts, where $T$ represents time reversal. Our analysis demonstrates that $T$-odd and -even correlations, when satisfying specific conditions, result in cosine and sine strong phase dependencies of the corresponding $CP$ violation, respectively. Additionally, we identify pairs of these $CP$ violation observables in hadron decays depend on precisely the same strong phases within the helicity amplitude scheme. This complementarity effectively reduces the strong phase reliance in the study of $CP$ violation, while also mitigating the risk of suppressed $CP$ violation due to exceptionally small strong phases. Furthermore, our proposal holds potential for uncovering $CP$ violation in baryon decays that have not yet been observed in experiments.

hep-ph

Invisible and Semi-invisible Decays of Bottom Baryons

The similar densities of dark matter and baryons in the universe imply that they might arise from the same ultraviolet model. The B-Mesogenesis, which assumes dark matter is charged under the baryon number, attempts to simultaneously explain the origin of baryon asymmetry and dark matter in the universe. In particular, the B-Mesogenesis might induce bottom-baryon decays into invisible or semi-invisible final states, which provide a distinctive signal for probing this scenario. In this work, we systematically study the invisible decays of bottom baryons into dark matters, and semi-invisible decays of bottom baryons into a meson or a photon together with a dark matter particle. In particular, the fully invisible decay can explore the stable particles in B-Mesogenesis. Some QCD-based frameworks are used to calculate the hadronic matrix elements under the B-Mesogenesis model. We estimate the constraints on the Wilson coefficients or the product of some new physics couplings with the Wilson coefficients by the semi-invisible and invisible decays of bottom baryons at future colliders.

hep-ph

Probing hyperon electric dipole moments with a full angular analysis

The electric dipole moment (EDM) of elementary particles, arising from flavor-diagonal $CP$ violation, serves as a powerful probe for new physics beyond the Standard Model and holds the potential to provide novel insights in unraveling the puzzle of the matter-dominated Universe. Hyperon EDM is a largely unexplored territory. In this paper, we present a comprehensive angular analysis that focuses on entangled hyperon-antihyperon pairs in $J/ψ$ decays for the indirect extraction of hyperon EDM. The statistical sensitivities are investigated for BESIII and the proposed Super Tau-Charm Facility (STCF). Leveraging the statistics from the BESIII experiment, the estimated sensitivity for $Λ$ EDM can reach an impressive level of $10^{-19}$ $e$ cm, achieving a 3-orders-of-magnitude improvement over the only existing measurement in a fixed-target experiment at Fermilab with similar statistics. The estimated sensitivities for the $Σ^+$, $Ξ^-$, and $Ξ^0$ hyperons at the same level of $10^{-19}$ $e$ cm will mark the first-ever achievement and the latter two will be the first exploration of hyperons with two strange valence quarks. The EDM measurements for hyperons conducted at the BESIII experiment will be a significant milestone and serve as a litmus test for new physics such as supersymmetry and the left-right symmetrical model. Furthermore, at the STCF experiment, the sensitivity of hyperon EDM measurements can be further enhanced by 2 orders of magnitude. Additionally, this angular analysis enables the determination of $CP$ violation in hyperon decays, the effective weak mixing angle, and beam polarization.

hep-ex

$Λ_b \to p, N^\ast(1535)$ Form Factors from QCD Light-Cone Sum Rules

In this work we calculate the transition form factors of $Λ_b$ decaying into proton and $N^*(1535)$ ($J^P={1/2}^+$ and ${1/2}^-$ respectively), within the framework of light-cone sum rules with the distribution amplitudes (DAs) of $Λ_b$-baryon. In the hadronic representation of the correlation function, we have isolated both the proton and the $N^*(1535)$ states so that the $Λ_b \rightarrow p, N^*(1535)$ form factors can be evaluated simultaneously. Due to the less known properties of baryons, we investigate three interpolating currents of the light baryons and five parametrization models for DAs of $Λ_b $. Numerically, our predictions on the $Λ_b \rightarrow p$ form factors and the branching fractions of $Λ_b\to p\ell ν$ from the Ioffe or the tensor currents are consistent with the Lattice simulation and the results from the light-baryon sum rules, as well as the experimental data of $Br(Λ_b^0\to pμ^-\barν)$. The predictions on the form factors of $Λ_b \rightarrow N^*(1535)$ are very sensitive to the choice of the interpolating currents so that the relevant measurement could be helpful to clarify the properties of baryons.

hep-ph

Diagrammatic analysis of hidden- and open-charm tetraquark production in $B$ decays

Discoveries of tetraquarks not only enrich the hadronic spectrum but also provide more platforms to understand quantum chromodynamics. We study the production processes of hidden-charm and open-charm tetraquarks in $B$ decays by analyzing their topological amplitudes. Relations between different channels are found, which confront tests by experiments to probe the nature of the tetraquarks. Furthermore, promising channels to find more tetraquarks are proposed.

hep-ph

Discovery of $T_{c\bar s 0}^a(2900)^{0,++}$ implies new charmed-strange pentaquark system

Inspired by the very recently discovered tetraquark states $T_{c\bar s 0}^a(2900)^{0,++}$ from the LHCb Collaboration, we predict the existence of a new charmed-strange pentaquark system, $c\bar s nnn$, which is closely connected to $c\bar s n\bar n$ by exchanging $\bar n$ into $nn$ with $n=u,d$. Especially, it is suggested to experimentally search for the predicted new pentaquark system via the weak decays of $B$ mesons or $b$-baryons, with the support from the study of the mass spectrum and the decay properties. The predicted new pentaquark system must attract extensive attention from experimentalists and theorists when it constructs the ``particle zoo 2.0" in the near future.

hep-ph

Inverse Problem Approach for Non-Perturbative QCD: Theoretical Foundation

A novel theoretical framework, the inverse problem approach, is proposed to calculate non-perturbative quantities in quantum chromodynamics (QCD). Based on the dispersion relation of quantum field theory, this approach determines unknown low-energy non-perturbative quantities from known high-energy perturbative inputs via solving an inverse problem. The resulting inverse problem is rigorously proven to be ill-posed, with the solutions being unique but unstable. To address this instability, the well-established Tikhonov regularization is employed, yielding stable approximate solutions that converge to the true values as input errors vanish. The key features of this approach are illustrated through three toy models, demonstrating that solution precision can be systematically improved through reduced input errors and optimized regularization strategies.

hep-th

Probing hyperon CP violation from charmed baryon decays

CP violation (CPV) in the baryon sectors has not yet been established experimentally. In this work, we propose to search for the hyperon CPV through the Cabibbo-favored charm-baryon decaying processes involving a hyperon in the final states, such as $Λ_c^+\to Λ^0π^+, Λ^0\to pπ^-$. The CPV of the hyperon decays are purely revealed in these chain processes, since the CPV in the Cabibbo-favored charm decays are vanishing in the Standard Model (SM). The hyperons are polarized in the weak charm decays, so that we can measure the Lee-Yang asymmetric parameter $α$ by the angular distributions, and then can measure the $α$-induced CPV. It can be found that it is accessible for Belle II and LHCb to reach the SM prediction of the hyperon CPV in the near future.

hep-ph

$Λ_b\to p$ transition form factors in perturbative QCD

We reanalyze the $Λ_b\to p$ transition form factors in the perturbative QCD (PQCD) approach by including higher-twist light-cone distribution amplitudes (LCDAs) of a $Λ_b$ baryon and a proton. The previous PQCD evaluation performed decades ago with only the leading-twist $Λ_b$ baryon and proton LCDAs gave the form factors, which are two orders of magnitude smaller than indicated by experimental data. We find that the twist-4 $Λ_b$ baryon LCDAs and the twist-4 and -5 proton LCDAs contribute dominantly, and the enhanced form factors become consistent with those from lattice QCD and other nonperturbative methods. The estimated branching ratios of the semileptonic decays $Λ_b\to p\ell\barν_\ell$ and the hadronic decay $Λ_b\to pπ$ are also close to the data. It implies that the $b$ quark mass is not really heavy enough, and higher-power contributions play a crucial role, similar to the observation made in analyses of $B$ meson transition form factors. With the formalism established in this work, we are ready to study various exclusive heavy baryon decays systematically in the PQCD approach.

hep-ph

Weak-decay searches for $Qs\bar u\bar d$ tetraquarks

We propose to search for the open heavy-flavor exotic states with the quark components of $Qs\bar u\bar d$ with $Q=b,c$ via their weak decays. If there exist such exotic states below the $BK$ or $DK$ thresholds, they can only decay weakly. The advantages include: (i) the experimental backgrounds from the secondary decay vertex are much lower due to the long lifetimes, (ii) the productions are large enough for only one heavy quark in such states, (iii) the thresholds of $BK$ or $DK$ are about 260 MeV higher compared to the $B_sπ$ or $D_sπ$ thresholds of the configurations of $Qu\bar s\bar d$ or $Qd\bar s\bar u$ , with a higher possibility to exist such weakly-decay particles, and (iv) if observed, their inner structures are easier understood since they can not be induced by the kinematic effects.

hep-ph

Inclusive approach to hunt for the beauty-charmed baryons $Ξ_{bc}$

With a distinctive internal structure from all established hadrons, the beauty-charmed baryons $Ξ_{bc}$ can provide us with new points of view to decipher the strong interaction. In this work, we point out that the inclusive $Ξ_{bc} \to Ξ_{cc}^{++}+X$ decay is a golden channel for the experimental discovery of $Ξ_{bc}$ at the LHC. A unique feature of this process is that the $Ξ_{cc}^{++}$ is displaced, which greatly reduces the combinatorial background. A feasibility analysis is performed on the $Ξ_{bc}^+$ search, which is expected to have a longer lifetime than $Ξ_{bc}^0$ and thus a better displacement resolution. The $Ξ_{bc}^+ \to Ξ_{cc}^{++}+X$ branching ratio is calculated within the heavy diquark effective theory. Combining the $Ξ_{bc}$ production rate and the $Ξ_{cc}^{++}$ detection efficiency, we anticipate that hundreds of signal events will be collected during LHCb Run 3.

hep-ph