"First Obseration of Doubly Cabibbo-Suppressed Decay of a Charmed Baryon"
Comments:
* What is the meaning of the "doubly Cabibbo-Suppressed decay" ?
-- the quark's flavor changes via the emission(exchange) of W boson,
and the amplitude is represented by Cabibbo angle (if generation is two) theta_c.
The amplitude is actually propotional to cosine(theta_c) for
u->d, c->s, within the same flavor, and sine(theta_c) for u->s, c->d,
therefore, the latter is smaller than the former, since the theta_c is small.
This is called as Cabibbo suppression.
[ Cabibbo Flavor (CF) decay ]
Lambda_c-> p, K-, pi+ case, only c->s, u->d (W->u,dbar) ,
[ Doubly Cabibbo Suppressed (DCS) decay ]
Lambda_c-> p, K+, pi- case, c->d, u->s (W->u,sbar)
* The meaning of the expression of (0.82+-0.12)*tan(theta_c)^{4} ?
-- the vertex coupling ratio between DCS & CF can be expected to
be propotional to sin(theta_c)/cos(theta_c) * 2 = tan(theta_c)^{2},
and the final cross-section can be square of it, tan(theta_c)^{4}.
Therefore, if it is the only mechanism, it should be 1*tan(theta_c)^{4},
and the experimental result show us that the internal W boson exchange can be
play a role a little bit, and not so much.
P.S. from Ryuta
Just after closing the JC, I recognized author's name of this paper,
and this is my comment after the JC.
The first auther of this paper (S. B. Yang, Korean guy, he once told his ancestor
came from China) is my collegue at J-PARC, Japan,
and the second author (K. Tanida) is my one of strong advisors.
I worked with Dr. Yang about 1 year very closely, especially about the drift chamber,
and also we were know each other more than 4 years.