We investigate the $Λ_b\toΛ_cπ^-f_0(980)$ production with a $f_0(980)$ decay into $π^+π^-$ via the $K^{*0}K^-K^+$ and $K^{*-}K^0\bar{K}^0$ triangle loops. These loops produce a peak around 1.42 GeV in the $π^-f_0(980)$ invariant mass distribution, which is the same mechanism as the one considered to explain the $a_1(1420)$ peak. In the $π^+π^-$ distribution obtained by fixing the $π^-f_0(980)$ invariant mass to some values, a clear peak of $f_0(980)$ is seen, and the $π^-f_0(980)$ distribution has a peak around $M_{π^-f_0}=1.42$ GeV, which is caused by the triangle mechanism of the $K^*\bar KK$ loop. The branching ratio of $Λ_b\rightarrowΛ_cπ^-f_0(980)$ with $f_0(980)\rightarrowπ^+π^-$ by the triangle mechanism, obtained by integrating the $π^-f_0(980)$ distribution from 1 to 1.6 GeV, is estimated to be the order $10^{-4}$. Future measurements of the $Λ_b\toΛ_cπ^-f_0(980)$ branching ratio and the $π^-f_0(980)$ invariant mass distribution predicted in this work would give further clues to clarify the nature of the $a_1(1420)$ peak.
The possible role of the triangle mechanism in the $B^-$ decay into $D^{*0}π^-π^0η$ and $D^{*0}π^-π^+π^-$ is investigated. In this process, the triangle singularity appears from the decay of $B^-$ into $D^{*0}K^-K^{*0}$ followed by the decay of $K^{*0}$ into $π^-K^+$ and the fusion of the $K^+K^-$ which forms the $a_0(980)$ or $f_0(980)$ which finally decay into $π^0η$ or $π^+π^-$ respectively. The triangle mechanism from the $\bar{K}^*K\bar{K}$ loop generates a peak around 1420 MeV in the invariant mass of $π^-a_0$ or $π^-f_0$, and gives sizable branching fractions $Br(B^-\rightarrow D^{*0}π^…
We have investigated the cross section for the $π^-p\rightarrow K^0πΣ$ and $pp\rightarrow pK^+πΣ$ reactions paying attention to a mechanism that develops a triangle singularity. The triangle diagram is realized by the decay of a $N^*$ to $K^*Σ$ and the $K^*$ decay into $πK$, and the $πΣ$ finally merges into $Λ(1405)$. The mechanism is expected to produce a peak around $2140$ MeV in the $KΛ(1405)$ invariant mass. We found that a clear peak appears around $2100$ MeV in the $KΛ(1405)$ invariant mass which is about $40$ MeV lower than the expectation, and that is due to the resonance peak of a $N^…
We show the effects of a triangle singularity mechanism for the $γp \to K^+Λ(1405)$ reaction. The mechanism has a $N^*$ resonance around 2030 MeV, which decays into $K^* Σ$. The $K^*$ decays to $K^+ π$, and the $πΣ$ merge to form the $Λ(1405)$. This mechanism produces a peak around $\sqrt{s} = 2110$ MeV, and has its largest contribution around cos$θ=0$. The addition of this mechanism to other conventional ones, leads to a good reproduction of ${\rm d}σ/{\rm dcos}θ$ and the integrated cross section around this energy, providing a solution to a problem encountered in previous theoretical models.
The decay of $Λ_c^+$ into $π^+π^0Λ(1405)$ with the $Λ(1405)$ decay into $π^0Σ^0$ through a triangle diagram is studied. This process is initiated by $ Λ_c^+ \to π^+ \bar{K}^*N $, then the $\bar{K}^*$ decays into $\bar{K} π$ and $\bar{K} N$ produce the $Λ(1405)$ through a triangle loop containing $\bar{K}^*N\bar{K}$ which develops a singularity around $1890$ MeV. This process is prohibited by the isospin symmetry, but the decay into this channel is enhanced by the contribution of the triangle diagram, which is sensitive to the mass of the internal particles. We find a narrow peak in the $π^0Σ^0…
We investigate roads for evaluating model-independent cross-section distributions for the sequential hyperon decay $Σ^0\rightarrowΛγ;Λ\rightarrow pπ^- $ and its corresponding antihyperon decay. The hyperons are produced in the reaction $e^+e^-\rightarrow J/ψ\rightarrow Σ^0\barΣ^0$. Cross-section distributions are calculated using the folding technique.
We report on a study of the sequential hyperon decay $Σ^0\rightarrowΛγ;Λ\rightarrow pπ^- $ and its corresponding anti-hyperon decay. We derive a multi-dimentional and model-independent formalism for the case when the hyperons are produced in the reaction $e^+e^-\rightarrowΣ^0\barΣ^0$. Cross-section distributions are calculated using the folding technique. We also study sequential decays of single-tagged hyperons.
We have done a study of the $B^- \to K^- π^0 X(3872)$ reaction by means of a triangle mechanism via the chain of reactions: $B^- \to K^- D^{*0}\bar D^{*0}$; $D^{*0} \to π^0 D^0$; $D^0\bar D^{*0}\to X(3872)$. We show that this mechanism generates a triangle singularity in the $π^0 X(3872)$ invariant mass for a very narrow window of the $X(3872)$ mass, around the present measured values, and show that the peak positions and the shape of the mass distributions are sensitive to the $X(3872)$ mass, such that a measurement of the reaction can serve to improve on the present values of this mass. In p…
Cross-section distributions are calculated for the reaction $e^+ e^- \rightarrow J/ψ\rightarrow \barΛ(\rightarrow \bar{p}π^+) Λ(\rightarrow pπ^-)$, and related annihilation reactions mediated by vector mesons. The hyperon-decay distributions depend on a number of structure functions that are bilinear in the, possibly complex, psionic form factors $G_M^ψ$ and $G_E^ψ$ of the Lambda hyperon. The relative size and relative phase of these form factors can be uniquely determined from the unpolarized joint-decay distributions of the Lambda and anti-Lambda hyperons. Also the decay-asymmetry parameters…
We study the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ reaction and find that the mechanism to produce this decay develops a triangle singularity around $M_{\rm inv}(K^- f_0/K^- a_0) \approx 1515$~MeV. The differential width $dΓ/ dM_{\rm inv}(K^- f_0/K^- a_0)$ shows a rapid growth around the invariant mass being 1515~MeV as a consequence of the triangle singularity of this mechanism, which is directly tied to the nature of the $f_0(980)$ and $a_0(980)$ as dynamically generated resonances from the interaction of pseudoscalar mesons. The branching ratios obtained for the $J/ψ\rightarrow K^+ K^…
The BESIII Collaboration recently reported the observation of the $a_0(980)^0-f_0(980)$ mixing in the isospin breaking decay $J/ψ\to ηπ^0ϕ$. In the Dalitz plot for that decay with the $η$ reconstructed from two photons, there is a band around $1.4$~GeV on the $π^0 ϕ$ distribution. In general, this peak can be due to a resonance or a kinematic effect. In this paper, we study the effects of a set of $K^*K\bar K$ triangle diagrams, and show that due to triangle singularities such diagrams can lead to a peak around 1.4~GeV in the $π^0ϕ$ invariant mass distribution. The Dalitz plot induced by such …
We study the production of a tensor glueball in the reaction $γγ\rightarrow G_2π^0$. We compute the cross section at higher momentum transfer using the collinear factorisation approach. We find that for a value of the tensor gluon coupling of $f^T_g\sim 100$~MeV, the cross section can be measured in the near future by the Belle~II experiment.
The Standard Model calculation of $H\rightarrowγγ$ has the curious feature of being finite but regulator-dependent. While dimensional regularization yields a result which respects the electromagnetic Ward identities, additional terms which violate gauge invariance arise if the calculation is done setting $d=4$. This discrepancy between the $d=4-ε$ and $d=4$ results is recognized as a true ambiguity which must be resolved using physics input; as dimensional regularization respects gauge invariance, the $d=4-ε$ calculation is accepted as the correct SM result. However, here we point out another …
The polarization observables in the elastic scattering of polarized deuterons on a polarized hydrogen target, with measurement of the recoil proton polarization, are considered. The observables are calculated in the one-neutron exchange approximation, for the special case of backward scattering ($θ_{c.m.} = 180^{\circ}$). Several new relations between polarization observables of the reaction are derived within the framework of this approximation.
We study the appearance of structures in the decay of the $B^-$ into $K^- π^- D_{s0}^+(2317)$ and $K^- π^- D_{s1}^+(2460)$ final states by forming invariant mass distributions of $π^- D_{s0}^+$ and $π^- D_{s1}^+$ pairs, respectively. The structure in the distribution is associated to the kinematical triangle singularity that appears when the $B^- \to K^- K^{*\,0} D^0$ ($B^- \to K^- K^{*\,0} D^{*\,0}$) decay process is followed by the decay of the $K^{*\,0}$ into $π^- K^+$ and the subsequent rescattering of the $K^+ D^0$ ($K^+ D^{*\,0}$) pair forming the $D_{s0}^+(2317)$ ($D_{s1}^+(2460)$) reso…
We have analyzed the singularities of a triangle loop integral in detail and derived a formula for an easy evaluation of the triangle singularity on the physical boundary. It is applied to the $Λ_b \rightarrow J/ψK^{-} p$ process via $Λ^*$-charmonium-proton intermediate states. Although the evaluation of absolute rates is not possible, we identify the $χ_{c1}$ and the $ψ(2S)$ as the relatively most relevant states among all possible charmonia up to the $ψ(2S)$. The $Λ(1890)\, χ_{c1}\, p$ loop is very special as its normal threshold and triangle singularities merge at about 4.45 GeV, generating…
We compare contributions from the triangle diagram and the $D\bar D^*$ bubble chain to the processes of $e^{+}e^{-}\rightarrow J/ψπ^{+}π^{-}$ and $e^{+}e^{-}\rightarrow (D\bar D^*)^\mpπ^{\pm}$. By fitting the $J/ψπ$ maximum spectrum and the $D\bar D^*$ spectrum, we find that the triangle diagram cannot explain the new data from BESIII Collaboration at center of mass at 4.23GeV and 4.26GeV, simultaneously. On the contrary, the molecular assignment of $Z_c(3900)$ gives a much better description.
We calculate the neutral pion photoproduction on the proton near threshold in covariant baryon chiral perturbation theory, including the $Δ(1232)$ resonance as an explicit degree of freedom, up to chiral order $p^{7/2}$ in the $δ$ counting. We compare our results with recent low-energy data from the Mainz Microtron for angular distributions and photon asymmetries. The convergence of the chiral series of the covariant approach is found to improve substantially with the inclusion of the $Δ(1232)$ resonance.
The differential cross section and some polarization observables have been calculated for the $e^+\,e^-\to γ\,γ$ reaction taking into account the contribution of the heavy excited electron and the general form $e\,e\,γ\,γ$ contact interaction. The spin correlation coefficients are calculated for the case when both beams have arbitrary polarization. The so called left-right asymmetry is estimated if only one beam is polarized. Numerical estimations are given for the excited electron contribution to the differential cross section and spin correlation coefficients for various values of the electr…
We develop a model for the $pp \to π^+ d$ reaction based on the $pp \to Δ(1232) N$ transition followed by $Δ(1232) \to πN'$ decay and posterior fusion of $N N'$ to give the deuteron. We show that the triangle diagram depicting this process develops a triangle singularity leading to a large cross section of this reaction compared to ordinary fusion reactions. The results of the calculation also show that the process is largely dominated by the $pp$ system in $L=2, S=0$, which transfers $J=2$ to the final $π^+ d$ system. This feature is shown to be well suited to provide $L=2,S=1$, $J^\mathrm{to…
We study the meson-baryon interaction in S-wave in the strangeness S=-1 sector using a chiral unitary approach based on a next-to-leading order chiral SU(3) Lagrangian. We fit our model to the large set of experimental data in different two-body channels. We pay particular attention to the $\bar{K} N \rightarrow K Ξ$ reaction, where the effect of the next-to-leading order terms in the Lagrangian are sufficiently large to be observed, since at tree level the cross section of this reaction is zero. For these channels we improve our approach by phenomenologically taking into account effects of th…
Study of the $e^+e^- \to ϕK^+K^-$ reaction within triangle dynamics and its implications for the $ϕ(2170)$
State Key Laboratory of Heavy Ion Science and Technology, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）；College of Physics and Engineering, Qufu Normal University（曲阜师范大学物理工程学院）；Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University（天津大学理学院量子联合研究中心与物理系）
Strangness production processes can balance natural strangeness decay in the early hadronic Universe. Comparing to the characteristic Hubble time $1/H$, the reaction rates for $μ^\pm+ν_μ\rightarrow K^\pm$, $l^-+l^+\rightarrowϕ$, and $π+π\rightarrow K$ in sequence become slower than expansion rate at $T=33.9\,\mathrm{MeV}$, $T=25\,\mathrm{MeV}$ and $T=20\,\mathrm{MeV}$ respectively. This means that in the antibaryon annihilation epoch near to $T\simeq 40\,\mathrm{MeV}$ strangeness is in chemical equilibrium.
We have performed the calculations for the nonleptonic $Ξ_b^- \rightarrow π^- \ Ξ_c^0 (2790) \left(J=\frac{1}{2}\right)$ and $Ξ_b^- \rightarrow π^- \ Ξ_c^0 (2815) \left(J=\frac{3}{2}\right)$ and the same reactions replacing the $π^-$ by a $D_s^-$. At the same time we evaluate the semileptonic rates for $Ξ_b^- \rightarrow \barν_l l \ Ξ_c^0 (2790)$ and $Ξ_b^- \rightarrow \barν_l l \ Ξ_c^0 (2815)$. We look at the reactions from the perspective that the $Ξ_c^0 (2790)$ and $Ξ_c^0 (2815)$ resonances are dynamically generated from the pseudoscalar-baryon and vector-baryon interactions. We evaluate ra…
The reaction $np \rightarrow np π^+ π^-$ was studied at the various momenta of incident neutrons. It was shown that the characteristics of the reaction at the momenta above 3 GeV/c could be described by the model of reggeized $π$ exchange (OPER). At the momenta below 3 GeV/c, it was necessary to use additionally the mechanism of one baryon exchange (OBE).
We have studied the $γp \to p π^0 η$ reaction paying attention to the two main mechanisms at low energies, the $γp \to Δ(1700) \to ηΔ(1232)$ and the $γp \to Δ(1700) \to πN(1535)$. Both of them are driven by the photoexcitation of the $Δ(1700)$ and the second one involves a mechanism that leads to a triangle singularity. We are able to evaluate quantitatively the cross section for this process and show that it agrees with the experimental determination. Yet, there are some differences with the standard partial wave analysis which does not include explicitly the triangle singularity. The exercis…
We apply the generalized Veneziano model ($B_5$ model) in the double-Regge exchange limit to the $γp \to K^+ K^- p$ reaction. Four different cases defined by the possible combinations of the signature factors of leading Regge exchanges (($K^*,a_2/f_2$), ($K^*,ρ/ω$), ($K_2^*,a_2/f_2$), and ($K_2^*,ρ/ω$)) have been simulated through the Monte Carlo method. Suitable event candidates for the double-Regge exchange high-energy limit were selected employing \textit{Van Hove} plots as a better alternative to kinematical cuts in the $K^+ K^- p$ Dalitz plot. In this way we predict and analyze the double…
The cross sections for the reaction $γγ\rightarrow 4\ell$ in proton--proton collisions are calculated at the LHC energies. We show that the purely electroweak process $γγ\rightarrow 4\ell$ can be studied at the LHC and can constitute a background to other processes with $4\ell$ or $2\ell$ final states.
Within a specific texture of the quark mass matrix the notion of a maximal violation of the $CP$ symmetry can be defined. The experimental constraints from weak decays imply that in reality one is close to the case of maximal $CP$ violation, which vanishes as the mass of the $u$--quark approaches zero. The unitarity triangle of the Cabibbo--Kobayashi--Maskawa matrix elements is determined. It is related to the triangle relating the Cabibbo angle to the quark mass ratios in the complex plane. The angle $α$ describing the $CP$ violation in the decay $B_d \rightarrow π^+ π^-$ is close to 90$^{\ci…
For an electron-photon collider the complete tree-level cross sections of the reaction $γe \rightarrow νb \bar{b} W$ are computed at center-of-mass energies between 0.5 and 2.0 TeV, for top masses of 160 to 200 GeV and Higgs masses between 80 and 140 GeV within the Standard Model. It is shown that most of the $νb \bar{b}$ events are due to Higgs and $Z/γ^*$ production (with $H, Z/γ^* \rightarrow b \bar{b}$ decay) while top production (with $t \rightarrow bW$ decay) is about 50% smaller. Multiperipheral background and interferences are small, respectively negligible, in the energy range studied…
The reaction $np \rightarrow np π^+ π^-$ was studied at the various momenta of incident neutrons. It was shown that the characteristics of the reaction at the momenta above 3 GeV/c could be described by the model of reggeized $π$ exchange (OPER). At the momenta below 3 GeV/c, it was necessary to use additionally the mechanism of one baryon exchange (OBE).
We study the cross sections for the production of a neutral, intermediate mass Higgs boson in the processes $pp\rightarrow tq'Φ$, $pp\rightarrow tW^-Φ$ and $pp\rightarrow bZ^0Φ$ in the Minimal Supersymmetric Standard Model ($Φ=H^0,h^0$ and $A^0$) at Supercollider energies. The additional heavy particles ($t$, $W$, $Z$) in the final state can be used for tagging purposes, increasing the signal to background ratio. These reactions are dominated by $bq$ and $bg$ fusion. Their relevance for Higgs particle searches is discussed taking into account the expected efficiencies and purities for $b$--tag…
We have chosen the reactions $D_s^+ \to π^+ π^0 a_0(980) (f_0(980))$ investigating the isospin violating channel $D_s^+ \to π^+ π^0 f_0(980)$. The reaction was chosen because by varying the $π^0 a_0(980) (f_0(980))$ invariant mass one goes through the peak of a triangle singularity emerging from $D_s^+ \to π^+\bar K^* K$, followed by $\bar K^* \to \bar K π^0$ and the further merging of $K \bar K$ to produce the $a_0(980)$ or $f_0(980)$. We found that the amount of isospin violation had its peak precisely at the value of the $π^0 a_0(980) (f_0(980))$ invariant mass where the singularity has its…
In this work, we make a theoretical study on the $p \bar p \rightarrow Λ\barΛη$ reaction for antiproton beam energy from threshold to 4GeV within an effective Lagrangian approach and isobar model. By assuming this reaction is dominated by the excitation of $Λ$ and $\bar Λ$ resonances in intermediate states, we calculate the total cross sections and give the predictions of the angular distribution and invariant mass spectrum of final particles. In particular, we discuss the possibility to verify the existence of a narrow $Λ$ resonance found in the process of $K^- p\to ηΛ$ in the present reactio…
The main dynamical mechanisms of the reaction $π^-p \rightarrow a^0_0 (980)n \rightarrow π^0ηn$ at high energies, currently investigated at Serpukhov and Brookhaven, are considered in detail. It is shown that the observed forward peak in its differential cross section can be explained within the framework of the Regge pole model only by the conspiring $ρ_2$ Regge pole exchange. The tentative estimates of the absolute $π^-p \rightarrow a^0_0(980)n \rightarrow π^0ηn$ reaction cross section at $P_{lab}^{π^-} = 18$ GeV/c are obtained: $σ\approx200$ nb and, in the forward direction, $dσ/dt\approx94…
Dielectron production in reactions $π^- p \rightarrow n e^+e^-$ and $π^- p \rightarrow n e^+e^- γ$ at energies less than 1 GeV is studied assuming electron-positron pair production to occur in the virtual time-like photon splitting process. Theoretical predictions of the effective mass distribution of dielectrons and their angular dependence are presented. Extraction of the electromagnetic form factor of baryon transition in the time-like region from future experiments of the HADES Collaboration is discussed.
We evaluate the contribution to the $X(3872)$ width from a triangle mechanism in which the $X$ decays into $D^{*0}\bar{D}^0 -cc$, then the $D^{*0} (\bar{D}^{*0})$ decays into $D^0 π^0$ ($\bar{D}^0 π^0$) and the $D^0 \bar{D}^0$ fuse to produce $π^+ π^-$. This mechanism produces an asymmetric peak from a triangle singularity in the $π^+ π^-$ invariant mass with a shape very sensitive to the $X$ mass. We evaluate the branching ratios for a reaction where this effect can be seen in the $B^- \to K^- π^0 π^+ π^-$ reaction and show that the determination of the peak in the invariant mass distribution…
By using resonance model, we investigate $K^+ N \rightarrow K N η$ reactions with the assumption that these reactions are dominated by the excitation of $N^*(1535)$ near threshold. It is found that the hyperon and $ρ$ exchange diagrams give the most important contributions to these reactions. Thus these reactions may be a good place to study the coupling of $N^*(1535)$ with $KΛ$, $KΣ$ and $Nρ$ channels. We demonstrate that the angular distributions of final particles provide useful information about the different mechanisms of the $N^*(1535)$ excitations, which could be useful for future exper…
We investigate the charmed baryon production reaction $p\bar{p}\rightarrowΛ_c\barΛ_c$ in an effective Lagrangian approach. Besides the $t$-channel $D^0$ and $D^{*0}$ mesons exchanges, the $s$-channel $Y(4630)$ meson exchange is taken into account. For the total cross sections, the $D^0$ and $D^{*0}$ mesons provide minor background contributions, while the $Y(4630)$ state gives a clear peak structure with the magnitude of 10 $μ$b at center of mass energy 4.63 GeV. Basing on the results, we suggest that the reaction of $p\bar{p}\rightarrowΛ_c\barΛ_c$ can be used to search for the $1^{--}$ charmo…
In this work we present the results of a complete calculation of the $γ γ\rightarrow π^0π^0$ amplitude to leading order in the large $N$ approximation ($N$ being the number of Goldstone bosons) up to order $m^2_π/F^2$. The amplitude turns to be proportional to that of $π^+π^-\rightarrow π^0π^0$. In spite of the fact that this factorization property cannot hold in general (as it was recently pointed out by Morgan and Penington), it appears here since in the large $N$ limit only the $I=J=0$ channel contributes to the $γγ\rightarrow π^0π^0$ reaction. Moreover it seems to be a reasonable approxima…
The meson-baryon interaction in s-wave in the strangeness S=-1 sector has been studied, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the Lagrangian have been fitted to a large set of experimental data in different two-body channels, paying special attention to the $\bar{K} N \rightarrow K Ξ$ reaction, which is particularly sensitive to the NLO terms. With the aim of improving the model in the $KΞ$ production channels, effects of the high spin hyperon resonances $Σ(2030)$ and $Σ(2250)$ have been taken…
The $Λ(1405)$ resonance production reaction is investigated within the framework of the coupled-channels Alt-Grassberger-Sandhas (AGS) equations. We perform full three-body calculations for the $\bar{K}NN-πYN$ amplitudes on the physical real energy axis and investigate how the signature of the $Λ(1405)$ appears in the cross sections of the $K^-d\rightarrow πΣn$ reactions, also in view of the planned E31 experiment at J-PARC. Two types of meson-baryon interaction models are considered: an energy-dependent interaction based on chiral $SU(3)$ effective field theory, and an energy-independent vers…
The spectrum of hadrons is the manifestation of color confinement of quantum chromodynamics. Hadronic resonances correspond to poles of the S-matrix. Since 2003, lots of new hadron resonant structures were discovered in the mass regions from light mesons to hadrons containing a pair of a heavy quark and an antiquark. Many of them are candidates of exotic hadrons, and they are usually observed as peaks in invariant mass distributions. However, the S-matrix also has kinematical singularities due to the on-shellness of intermediate particles for a process, such as two-body thresholds and triangle…
The lowest-lying resonance in the QCD spectrum is the $0^{++}$ isoscalar $σ$ meson, also known as the $f_0(500)$. We augment SU(2) chiral perturbation theory ($χ$PT) by including the $σ$ meson as an additional explicit degree of freedom, as proposed by Soto, Talavera, and Tarrús and others. In this effective field theory, denoted $χ$PT$_S$, the $σ$ meson's well-established mass and decay width are not sufficient to properly renormalize its self energy. At $\mathcal{O}(p^4)$ another low-energy constant appears in the dressed $σ$-meson propagator; we adjust it so that the isoscalar pion-pion sca…
The reaction $e^+e^-\rightarrow Λ^+_c\barΛ^-_c$ is investigated at energies close to the threshold with emphasis on the role played by the $X(4630)$ resonance. The interaction in the final $Λ^+_c \barΛ^-_c$ system, constructed within chiral effective field theory and supplemented by a pole diagram that represents a bare $X(4630)$ resonance, is taken into account rigorously. The pole parameters of the $X(4630)$ are extracted and found to be compatible with the ones of the $X(4660)$ resonance that have been established in the reaction $e^+e^- \to π^+π^-ψ(2S)$. The actual result for the $X(4630)$…
By using an effective Lagrangian method, we study the effects of a newly proposed $Σ^*(1/2^-)$ state with mass around 1380 MeV in the initial-state polarized $γN\rightarrow K^{+} Σ^*(1385) \rightarrow K^{+} πΛ$ process near threshold. The theoretical predictions for the helicity cross sections $σ_{3/2}$, $σ_{1/2}$ as well as their ratios, and the angular distributions of $π$ in the $πΛ$ center-of-mass system are given. It is found that assuming $Σ^*(1/2^-)$ exists or not, these physical quantities are distinctly different. So our results could be useful for the investigation of the existence o…
We investigate the problem of identifying $ν_τ$-induced reactions in large neutrino telescopes. We concentrate on events with tracks and showers where the respective energies $E_μ$ and $E_X$ are measured separately. Then we compute analytically and numerically event distributions in two variables $r_l = E_X/E_l$ and $y'=E_{\text{X}}/(E_μ+E_{X})$. We find that the $y'$-distribution is especially useful because in the $ν_τ$-induced reactions the distribution has a minimum at $y'=0.75$ and then increases as $y'\rightarrow1$. This is different in $ν_μ$-induced reactions where the $y'$-distribution…
We study the $Λ_{b}\rightarrow J/ψK^{0}Λ$ reaction considering both the $K^{0}Λ$ interaction with its coupled channels and the $J/ψΛ$ interaction. The latter is described by taking into account the fact that there are predictions for a hidden-charm state with strangeness that couples to $J/ψΛ$. By using the coupling of the resonance to $J/ψΛ$ from these predictions we show that a neat peak can be observed in the $J/ψΛ$ invariant mass distribution, rather stable under changes of unknown magnitudes. In some cases, one finds a dip structure associated to that state, but a signal of the state show…
A search for the axioelectric absorption of 5.5-MeV solar axions produced in the $p+d\rightarrow \rm{^3He}+γ(5.5 \rm{MeV})$ reaction was performed with two BGO detectors placed inside a low-background setup. A model independent limit on axion-photon and axion-nucleon couplings was obtained: $|g_{Ae}\times g_{AN}| \leq 3.2\times 10^{-9} (m_A=0)$. Constraints on the axion-electron coupling constant were obtained for axions with masses in the $(0.1-1.0)$ MeV range: $g_{Ae}\leq (1.8-9.0)\times 10^{-7}$. The solar positron flux from $A\rightarrow e^-+e^+$ decay was determined for axions with masses…
The expressions for the differential cross section and of the polarization observables for the reaction $\bar p+p\rightarrow e^++e^-$ are given in terms of the nucleon electromagnetic form factors in the laboratory system. Radiative corrections due to the emission of virtual and real soft photons from the leptons are also calculated. Unlike the center-of- mass system case, they depend on the scattering angle. Polarization effects are derived in the case when the antiproton beam, the target and the electron in the final state are polarized. Numerical estimations have been done for all observabl…
We report on the first results of a full three-body calculation of the $\bar{K}NN$-$πYN$ amplitude for the $K^-d\rightarrowπΣn$ reaction, and examine how the $Λ(1405)$ resonance manifests itself in the neutron energy distributions of $K^-d\rightarrowπΣn$ reactions. The amplitudes are computed using the $\bar{K}NN$-$πYN$ coupled-channels Alt-Grassberger-Sandhas (AGS) equations. Two types of models are considered for the two-body meson-baryon interactions: an energy-independent interaction and an energy-dependent one, both derived from the leading order chiral SU(3) Lagrangian. These two models …
We investigate the two-body reactions $\bar K N\rightarrow \bar K N$, $\bar K N\rightarrow πΛ$, and $\bar K N\rightarrow πΣ$ via single-energy partial-wave analyses in the c.m.\ energy range 1480 to 2100 MeV. The partial-wave amplitudes for these reactions thus extracted were constrained by a multichannel energy-dependent model satisfying unitarity of the partial-wave $S$-matrix. We obtain excellent predictions of differential cross sections, polarizations, polarized cross sections, and cross sections for these reactions from a global energy-dependent solution.
Parametrizations of total cross sections sufficient for all channels of the $πB \rightarrow Y K$ reactions are completed using a resonance model. As well as discussing the $πN \rightarrow ΛK$ reactions, which were not presented in our previous publications, we present the differential cross section for $πN \rightarrow ΛK$. This report also aims at presenting supplementary discussions to our previous work.
We study the reactions $γγ\rightarrow π^0π^0$, $π^+π^-$, $K^0\bar{K}^0$, $K^+K^-$, $ηη$ and $π^0η$ based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains 5 unknown parameters that are relevant for the photon fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon fusion data $γγ\rightarrow π^0π^0$, $π^+π^-, π^0η$ and to the decay $η\rightarrowπ^0γγ$. In order to derive gauge invariant reaction amplitudes in t…
