Abstract
As the lightest charmed baryon, precision measurement of the pair production cross section of Λc+ provides unprecedented experimental information for the investigation of baryon production mechanism. In addition, the extraction of the polar angle distributions of the outgoing Λc+ 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 e+e−→Λc+Λ¯c− 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 Λc+ 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 Λc+ data to them are discussed.
Highlights
One of the challenging question in particle physics, how quarks and gluons form hadrons, has not been understood in experimental or theoretical points of view
Taking advantage of the large statistic energy scan data collected at c.m. energies = 4574.5, 4580.0, 4590.0 and 4599.5 MeV, the process e+e− → Λ+c Λ −c is studied by BESIII both in the production cross section and electromagnetic form factor ratio [13], where the first energy is only 1.6 MeV above the kinematic threshold of Λ+c Λ −c
Experimental measurements of the production and decay properties of Λ+c could definitely provide crucial information for the study of both strong and weak interactions; the current measurement of Belle suffers from relatively large uncertainty and that of BESIII is limited in a small c.m. energy region near threshold
Summary
One of the challenging question in particle physics, how quarks and gluons form hadrons, has not been understood in experimental or theoretical points of view. Under the hypothesis that the one-photon exchange process dominates the production of spin-1/2 baryon B, the differential cross section of the time-like process e+e− → BBis expressed in terms of electromagnetic FFs [3]: dσBBd cos θ After integrating over the po√lar angle θ in Equation (1), the total production cross section of baryon B at c.m. energy s takes the form σBB (s). For the charged spin-1/2 baryon, β in Equation (2) is canceled by that in the Coulomb factor at any c.m. energy; a non-zero cross section at the very beginning of the kinematic threshold of process e+e− → BBis expected. The production cross section and electromagnetic form factor ratios of the lightest charmed baryon Λ+c are discussed based on the published results
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