Hyperon Structure and Decay with BESIII

• In these proceedings, we report on the Lambda hyperon structure and decay, studied through two different processes: i) the resonant e(+)e(-) -> J/psi -> Lambda(Lambda) over bar, using a data sample of 1.31 x 10(9) J/psi events and ii) the non -resonant e(+)e(-) -> gamma* > Lambda(Lambda) over bar, using a 66.9 pb(-1) data sample collected at root s = 2.396 GeV. In e(+)e(-) -> J/psi -> Lambda(Lambda) over bar, the phase between the hadronic form factors is measured for the first time to be 42.3 degrees +/- 0.6 degrees +/- 0.5 degrees. The large data sample enabled a multi-dimensional analysis and hence a model-independent measurement of the decay parameters for Lambda -> p pi(-) (alpha(-)), Lambda(Lambda) over bar -> (p) over bar pi(+) (alpha(+)) and (Lambda) over bar -> (n) over bar pi(0) ((pi) over bar (0)). The value obtained, alpha(-) = 0.750 +/- 0.009 +/- 0.004, differs with 50- from the PDG value. The simultaneous measurement for the A, i.e. alpha(+) = 0.758 +/- 0.010 +/- 0.007, allows for the most precise test of CP violation in A decays so far: A(CP) = (alpha(-) + alpha(+))/(alpha(-) - alpha(+)) of -0.006 +/- 0.012 +/- 0.007. Furthermore, the decay asymmetry (kappa) over bar (0) = 0.692 0.016 0.006 is measured for the first time. The large data sample at Ars = 2.396 GeV of the e+ > AA reaction enabled the first complete measurement of the time-like electric and magnetic form factors GE and GM of any baryon. This includes the modulus of the ratio R = vertical bar G(E)/G(M)vertical bar and the relative phase, Delta Phi = Phi(E) - Phi(M). Using the decay asymmetry parameters from the J/psi data as input, the obtained values of R and Delta Phi are R = 0.96 +/- 0.14 +/- 0.02 and Delta Phi = 37 degrees +/- 12 degrees +/- 6 degrees, respectively. In addition, the cross section has been measured to unprecedented precision too sigma = 119.0 +/- 5.3 +/- 5.1 pb, corresponding to an effective form factor value of vertical bar G vertical bar = 0.123 +/- 0.003 +/- 0.003.

Ämnesord

NATURVETENSKAP  -- Fysik -- Subatomär fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Subatomic Physics (hsv//eng)

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