Giulia Ricciardi Università di Napoli “Federico II”, Italy. XLIst Rencontres de Moriond- March 19th, 2006. Introduction. Semileptonic B decays spectra LD effects due to soft interactions between the heavy quark and the light degrees of freedom.
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Università di Napoli “Federico II”, Italy
XLIst Rencontres de Moriond- March 19th, 2006
LD effects due to soft interactions between the heavy quark and the light degrees of freedom.
Large perturbative (PT) contributions at threshold
large logs in PT “signal” LD effects
Q always indicates the hardest scale Q= 2 EX
one can obtain a general resummation formula for the triple
where w=2EX/mb and x=2 El/mb and
The infrared logs can be organized in a series and factorized
into the universal form factor S
where Q = 2 EX and by definition
Q= w mb = 2 EX
can be divided into two classes, according to the fact that it is necessary or not to integrate over the hadron energy,
1) no integration over EX-directly related via short distance (SD) coefficients to the photon spectrum in the radiative decay.
the same structure of threshold logs
f.i. single distribution in EX
2) obtained by integrating over EX— CANNOT be directly related via SD coefficients to the photon spectrum in the radiative decay.
not same structure of threshold logs
f.i. single distributions in the invariant hadronic mass mX2, in the charged electron energy, in the lightcone variable p+
Example: spectrum in hadron energyw=2 EX/mb
Two integrations from the triple differential factorized form, but EX
not integrated over
Since the coefficient function does not depend on u, the second
integration only involves the QCD form factor and the remainder
w= 2 EX/mb
order to the distribution in the light cone momentum (Hoang, Ligeti and Luke);
with such scale correctly prediction of
1) Distributions not integrated over EXLD structure comparable directly with radiative decay
2) opposite behaviour respect to
distributions integrated over EXLD structure not directly