We report a measurement of the exclusive e+e- -->Lambda_c+ Lambda_c- cross section as a function of center-of-mass energy near the Lambda_c+ Lambda_c- threshold. A clear peak with a significance of 8.2 sigma is observed in the Lambda_c+ Lambda_c- invariant mass distribution just above threshold. With an assumption of a resonance origin for the observed peak, a mass and width of M=(4634^{+8}_{-7}(stat.)^{+5}_{-8}(sys.))Mev/c2 and Gamma_tot=(92^{+40}_{-24}(stat.)}^{+10}_{-21}(sys.))MeV are determined. The analysis is based on a study of events with initial-state-radiation photons in a data sample collected with the Belle detector at the Υ(4S) resonance and nearby continuum with an integrated luminosity of 695/fb at the KEKB asymmetric-energy e+e- collider.
Differential cross sections and photon-beam asymmetries for the gamma p -> K+ Lambda(1520) reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump structure was found at W=2.11 GeV in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with J<=3/2. This result suggests that the bump might be produced by a nucleon resonance possibly with J>=5/2 or by a new reaction process, for example an interference effect with the phi photoproduction having a similar …
Observation of B0 to Lambda Lambdabar K0 and B0 to Lambda Lambdabar K*0 at Belle
We study the charmless decays B to Lambda Lambdabar h, where h stands for pi^+, K^+,K^0,K^{*+}, or K^{*0}, using a 605 fb^{-1} data sample collected at the Upsilon(4S)resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. We observe B0 to Lambda Lambdabar K0 and B0 to Lambda Lambdabar K*0 with branching fractions of (4.76^{+0.84}_{-0.68} (stat.) \pm 0.61 (syst.)) \times 10^{-6} and (2.46^{+0.87}_{-0.72} \pm 0.34) \times 10^{-6}, respectively. The significances of these signals in the threshold-mass enhanced mass region are 12.4 sigma and 9.3 sigma, respectively. We a…
On strangeness production in the reactions pp -> p Lambda^0 K^+ and pn -> n Lambda^0 K^+ near threshold
计算了pp -> p λ ^0 K ^+和pn -> n λ ^0 K ^+反应的截面。截面的理论比值R = sigma（pn -> n Lambda^0K^+）/ sigma（pp ->pΛ^0K^+）= 3表明，在奇异产生N Lambda^0K^+的阈值附近，pn相互作用相对于pp相互作用的增强。这种增强是由在同位旋单重态中的np相互作用的贡献引起的，其强于在同位旋三重态中的$pn$相互作用。为了证实这个结果，我们计算了反应pp -> pp pi ^0，pi ^0 p -> Lambda ^0 K^+和pi^-p -> Lambda ^0 K ^0在末态阈值附近的截面。理论截面与实验数据吻合较好。
We report the exclusive photoproduction cross sections for the Sigma(1385), Lambda(1405), and Lambda(1520) in the reactions gamma + p -> K+ + Y* using the CLAS detector for energies from near the respective production thresholds up to a center-of-mass energy W of 2.85 GeV. The differential cross sections are integrated to give the total exclusive cross sections for each hyperon. Comparisons are made to current theoretical models based on the effective Lagrangian approach and fitted to previous data. The accuracy of these models is seen to vary widely. The cross sections for the Lambda(1405) re…
We report the results of a high-statistics search for H-dibaryon production in inclusive Y(1S) and Y(2S) decays. No indication of an H-dibaryon with mass near the M_H=2m_Lambda threshold is seen in either the H-> Lambda p pi- or Lambda-Lambda decay channels and 90% confidence level branching-fraction upper limits are set that are between one and two orders of magnitude below the measured branching fractions for inclusive Y(1S) and Y(2S) decays to antideuterons. Since Y(1,2S) decays produce flavor-SU(3)-symmetric final states, these results put stringent constraints on H-dibaryon properties. Th…
The reaction gamma + p -> K+ + Sigma + pi was used to determine the invariant mass distributions or "line shapes" of the Sigma+ pi-, Sigma- pi+ and Sigma0 pi0 final states, from threshold at 1328 MeV/c^2 through the mass range of the Lambda(1405) and the Lambda(1520). The measurements were made with the CLAS system at Jefferson Lab using tagged real photons, for center-of-mass energies 1.95 < W < 2.85 GeV. The three mass distributions differ strongly in the vicinity of the I=0 Λ(1405), indicating the presence of substantial I=1 strength in the reaction. Background contributions to the data fro…
We have analyzed the reaction $χ_{c0}\to \bar{p} K^+Λ$ reported by the BESIII Collaboration, taking into account the contributions from the intermediate $K(1830)$, $N(2300)$, and $Λ(1520)$ resonances. Our results are in good agreement with the BESIII measurements, and it is found that the anomalous enhancement near the $\bar{p}Λ$ threshold is mainly due to the contribution of the $K(1830)$ resonance. We also show that the interference of the high-mass $N^*$ and $Λ^*$ can not produce the anomalous enhancement near the $\bar{p}Λ$ threshold.
We demonstrate that triangle singularity (TS) and box singularity (BS) mechanisms can produce unique narrow enhancements at the $Λ_c\bar{D}$ and $Λ_c\bar{D}^*$ thresholds in the invariant mass spectra of $J/ψp$ and $J/ψpπ$, respectively. Taking into account that such mechanisms only depend on the initial $Σ_c^{(*)}\bar{D}^{(*)}$ interactions near threshold within the TS or BS kinematic regimes, the $Λ_c\bar{D}$ and $Λ_c\bar{D}^*$ threshold enhancements can be regarded as a feed-down phenomenon originated from both the heavier pentaquark decays and the $Σ_c^{(*)}\bar{D}^{(*)}$ scatterings from …
The observed enhancement of $p\bar p$-production near the threshold in radiative decays of $J/ψ$ and $e^+e^-$-annihilations can be explained with final state interactions among the produced $N\bar N$ system, where the enhancement is essentially determined by $N\bar N$ elastic scattering amplitudes. We propose to use an effective theory for interactions in a $N\bar N$ system near its threshold. The effective theory is similar to the well-known one for interactions in a $NN$ system but with distinctions. It is interesting to note that in the effective theory some corrections to scattering amplit…
Focusing on recent measurement of $B^+ \to D_s^+D_s^-K^+$ process given by the LHCb Collaboration, we propose that this newly observed near the $D_s^+D_s^-$ threshold enhancement can be due to the contribution of the $χ_{c0}(2P)$, which is a $P$-wave charmonium below the $D_s^+D_s^-$ threshold. By performing a combined fit to the measured $D_s^+D_s^-$, $D_s^+K^+$, and $D_s^-K^+$ invariant mass spectra, introducing the $χ_{c0}(2P)$ can well reproduce the near threshold enhancement in the $D_s^+D_s^-$ invariant mass spectrum. When depicting the whole $D_s^+D_s^-$ invariant mass spectrum, the con…
One of the main issues in hadron spectroscopy is to identify the origin of threshold or near-threshold enhancement. Prior to our study, there is no straightforward way of distinguishing even the lowest channel threshold-enhancement of the nucleon-nucleon system using only the cross-sections. The difficulty lies in the proximity of either a bound or virtual state pole to the threshold which creates an almost identical structure in the scattering region. Identifying the nature of the pole causing the enhancement falls under the general classification problem and supervised machine learning using…
In the $J/ψ$ radiative decay channels $J/ψ\to γV\bar{V}$, the result of partial wave analysis indicates that the $V\bar{V}$ systems are predominately pseudoscalar component, and most of these channels have relatively large branching ratios at an order of $10^{-3}$. Meanwhile, vector mesons, such as $ρ$, $ω$ and $K^*$, have strong couplings with nucleons and/or hyperons. This suggests a dynamical mechanism describing the $ηp\bar{p}$ form factors for higher $η$ mesons, such as $η(1405/1475)$ and $η(1760)$. It is thus natural to expect that rescatterings of these vector meson pairs into $p\bar{p}…
It is shown that a recent extraction of the total cross section for pp->K+ n Sigma+ from inclusive K+ production data is in conflict with experimental data on the exclusive pp->K+ p Lambda reaction. The result may be interpreted as an upper bound which is not inconsistent with the much lower values that already exist in the literature.
We analyse electron-positron data for b-bbar production published by the BABAR Collaboration, in the invariant-mass interval delimited by the B-Bbar and Lambda(b)-Lambda(b) thresholds. In particular, we describe the Upsilon(10580) enhancement, not as a b-bbar resonance, but rather as a threshold phenomenon due to the opening of the B-Bbar decay channel and enhanced by the Upsilon(2D) bound-state pole not far below this threshold. The same data provide evidence for the true Upsilon(4S) resonance, which we find at 10.735 GeV with a width of 38 MeV. At higher energies, two more known Upsilon reso…
We study the reaction mechanism of K*Lambda(1116) photoproduction off the proton target near threshold considering the contributions from nucleon-resonances. Employing the effective Lagrangian method at the tree-level Born approximation, we investigate the role of the D13(2080) and the D15(2200). We found that the D13 plays a crucial role to reproduce the experimental data well in the forward scattering region at low energy. We also present theoretical predictions on the single photon-beam asymmetry as well as the energy and angular dependence for the cross sections of this reaction.
The Lambda(1405) baryon resonance plays an outstanding role in various aspects in hadron and nuclear physics. It has been considered that the Lambda(1405) resonance is generated by the attractive interaction of the antikaon and the nucleon, as a quasi-bound state below the threshold decaying into the pi Sigma channel. Thus, the structure of Lambda(1405) is closely related to the Kbar N interaction which is the fundamental ingredient to study few-body systems with antikaon. In this paper, after reviewing the basic properties of the Lambda(1405) resonance, we introduce the dynamical coupled-chan…
