Production Mechanism of the Charmed Baryon Λc+

As the lightest charmed baryon, precision measurement of the pair production cross section of provides unprecedented experimental information for the investigation of baryon production mechanism. In addition, the extraction of the polar angle distributions of the outgoing in the annihilation of the electron–positron help to determine its electromagnetic form factors, which is currently the unique key to access the internal structure of the baryons. In this article, the measurement of process via the initial state radiation technique at Belle detector and direct electron–positron annihilation at BESIII with discrete center-of-mass energies near threshold are briefly reviewed. In addition, the electromagnetic form factor ratios of measured by BESIII are also investigated. A few theoretical models that parameterize the center-of-mass energy dependence of the cross section and electromagnetic form factors of baryon are introduced and the contributions of data to them are discussed.

Search for the doubly charmed baryon $$ {\varXi}_{cc}^{+} $$ in the $$ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} $$ final state

A search for the doubly charmed baryon $$ {\varXi}_{cc}^{+} $$ Ξ cc + is performed in the $$ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} $$ Ξ c + π − π + invariant-mass spectrum, where the $$ {\varXi}_c^{+} $$ Ξ c + baryon is reconstructed in the pK−π+ final state. The study uses proton-proton collision data collected with the LHCb detector at a centre- of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb−1. No significant signal is observed in the invariant-mass range of 3.4–3.8 GeV/c2. Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the $$ {\varXi}_{cc}^{++} $$ Ξ cc + + → ($$ {\varXi}_c^{+} $$ Ξ c + → pK−π+)π+ decay for different $$ {\varXi}_{cc}^{+} $$ Ξ cc + mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/c. The results from this search are combined with a previously published search for the $$ {\varXi}_{cc}^{+} $$ Ξ cc + →$$ {\varLambda}_c^{+} $$ Λ c + K−π+ decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/c2, including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5–3.7 GeV/c2 mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.

Search for the doubly charmed baryon Ω+cc

A search for the doubly charmed baryon Ω cc + with the decay mode Ω cc + → Ξ c + K−π+ is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb−1. No significant signal is observed within the invariant mass range of 3.6 to 4.0GeV/c2. Upper limits are set on the ratio R of the production cross-section times the total branching fraction of the Ω cc + → Ξ c + K−π+ decay with respect to the $$\Xi _{cc}^{ + + } \to \Lambda _c^ + {K^ - }{\pi ^ + }{\pi ^ + }$$ Ξ c c + + → Λ c + K − π + π + decay. Upper limits at 95% credibility level for R in the range 0.005 to 0.11 are obtained for different hypotheses on the Ω cc + mass and lifetime in the rapidity range from 2.0 to 4.5 and transverse momentum range from 4 to 15 GeV/c.

Lattice QCD study of the elastic and transition form factors of charmed baryons

Composite nature of a particle can be probed by electromagnetic interactions and information about their structure is embedded in form factors. Most of the experimental and theoretical efforts on baryon electromagnetic form factors have been focused on nucleon while the data on charmed sector are limited to spectroscopy, and weak and strong decays. Forthcoming experiments with a heavy-hadron physics program at major experimental facilities are expected to provide a wealth of information on charmed baryons, which calls for a better understanding of the heavy-sector dynamics from theoretical grounds. We review the progress in calculating the elastic and transition form factors of charmed baryons in lattice QCD. A collection of static observables, e.g. charge radii, multipole moments, are presented along with the elastic form factors up to [Formula: see text]. As one would expect the charmed baryons are compact in comparison to nucleon and this is due to the presence of valence charm quark(s). The elastic and transition magnetic moments are both suppressed. The lattice results provide predictions for the transition magnetic moments, transition and helicity amplitudes and consequentially the decay widths of some singly and doubly charmed baryons. In general, lattice results are consonant with the qualitative expectations of quark model and heavy-quark symmetry, although there are apparent quantitative differences up to two orders of magnitude in some cases. There are, however, indications that the lattice results can be utilized to improve the model predictions. Nevertheless, discrepancies between the lattice and nonlattice calculations need to be understood better to have a solid insight into the dynamics of the heavy sector. Furthermore, reliably determined charmed baryon observables would be invaluable input to investigate the nature of exotic states, which further emphasizes the importance of rigorous, first-principles calculations to advance our understanding of the dynamics of the heavy quarks and strong interactions.

Exploring charm decays with missing energy in leptoquark models

We investigate the possibility that scalar leptoquarks generate consequential effects on the flavor-changing neutral-current decays of charmed hadrons into final states with missing energy "Image missing" carried away by either standard model or sterile neutrinos. We focus on scenarios involving the R2, $$ {\tilde{R}}_2 $$ R ˜ 2 , and $$ {\overline{S}}_1 $$ S ¯ 1 leptoquarks and take into account various pertinent constraints, learning that meson-mixing ones and those inferred from collider searches can be of significance. We find in particular that the branching fractions of charmed meson decays D →"Image missing", M = π, ρ, and Ds→"Image missing" and singly charmed baryon decays $$ {\Lambda}_c^{+} $$ Λ c + →"Image missing" and Ξc→"Image missing" are presently allowed to attain the 10−7-10−6 levels if induced by R2 and that the impact of $$ {\tilde{R}}_2 $$ R ˜ 2 is comparatively much less. In contrast, the contributions of $$ {\overline{S}}_1 $$ S ¯ 1 , which couples to right-handed up-type quarks and the sterile neutrinos, could lead to branching fractions as high as order 10−3. This suggests that these charmed hadron decays might be within reach of the BESIII and Belle II experiments or future super charm-tau factories and could serve as potentially promising probes of leptoquark interactions with sterile neutrinos.