|Title: ||Taming the anti-B ---> X(s) gamma spectrum by dressed gluon exponentiation.|
|Authors: ||Andersen, Jeppe R|
|Keywords: ||inclusive B decay, renormalons, heavy quarks|
|Issue Date: ||Feb-2005|
|Publisher: ||HEP, Cavendish Laboratory, University of Cambridge|
|Series/Report no.: ||Cavendish-HEP-05-05|
|Abstract: ||We show that the ¯B −→ Xsγ photon energy (E
) spectrum can be reliably
computed by resummed perturbation theory. Our calculation is based on Dressed
Gluon Exponentiation (DGE) incorporating Sudakov and renormalon resummation. It is
shown that the resummed spectrum does not have the perturbative support properties: it
smoothly extends to the non-perturbative region E
> m/2, where m is the quark pole
mass, and tends to zero near the physical endpoint. The calculation of the Sudakov factor,
which determines the shape of the spectrum in the peak region, as well as that of the
pole mass, which sets the energy scale, are performed using Principal–Value Borel summation.
By using the same prescription in both, the cancellation of the leading renormalon
ambiguity is respected. Furthermore, in computing the Sudakov exponent we go beyond
the formal next–to–next–to–leading logarithmic accuracy using the large–order asymptotic
behavior of the series, which is accurately determined from the relation with the pole mass.
Upon matching the resummed result with the next–to–leading order expression we compute
the spectrum, obtain its moments as a function of a minimum photon energy cut,
analyze sources of uncertainty and show that our predictions are in good agreement with
|Appears in Collections:||Scholarly works - High Energy Physics|
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