Abstrakt
Using 980 fb(-1) of data collected with the Belle detector operating at the KEKB asymmetric-energy e(+) e(-) collider, we report a study of the electromagnetic decays of excited charmed baryons Xi(c)(2790) and Xi(c)(2815). A clear signal (8.6 standard deviations) is observed for Xi(c)(2815)(0) -> Xi(0)(c)gamma, and we measure: B[Xi(c)(2815)(0) -> Xi(0)(c)gamma]/B[Xi(c)(2815)(0) -> Xi(c)(2645)(+)pi(-) -> Xi(0)(c)pi(+)pi(-)] = - 0.41 +/- 0.05 +/- 0.03.
We also present evidence (3.8 standard deviations) for the similar decay of the Xi(c)(2790)(0) and measure:B[Xi(c)(2790)(0) -> Xi(0)(c)gamma]/B[Xi(c)(2790)(0) -> Xi(c)'(+)pi(-) -> Xi(+)(c)gamma pi(-)] = 0.13 +/- 0.03 +/- 0.02. The first quoted uncertainties are statistical and the second systematic.
We find no hint of the analogous decays of the Xi(c)(2815)(+) and Xi(c)(2790)(+) baryons and set upper limits at the 90% confidence level of: B[Xi(c)(2815)(0) -> Xi(0)(c)gamma]/B[Xi(c)(2815)(0) -> Xi(c)(2645)(0)pi(+) -> Xi(+)(c)pi(-)pi(+)] Xi(0)(c)gamma]/B[Xi(c)(2815)(+) -> Xi(c)'(0)pi(+) -> Xi(0)(c)gamma pi(+)] < 0.06. Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states.