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Title: Shape functions from B{yields}X{sub c}l{nu}{sub l}

Abstract

We study inclusive semileptonic B{yields}X{sub c}l{nu}{sub l} decay using the power counting m{sub c}{approx}{radical}({lambda}{sub QCD}m{sub b}). Assuming this scaling for the charm-quark mass, the decay kinematics can be chosen to access the shape-function region even in b{yields}c transitions. To apply effective field theory methods in this region we extend soft-collinear effective theory to describe massive collinear quarks. We calculate the tree-level decay rate, including O({lambda}{sub QCD}/m{sub b}) power corrections, and show that it factorizes into a convolution of jet and shape functions. We identify a certain kinematical variable whose decay spectrum is proportional to the universal leading-order shape function familiar from b{yields}u decay, and speculate as to whether information about this shape function can be extracted from data on b{yields}c decay.

Authors:
; ; ;  [1]
  1. Theoretische Physik 1, Fachbereich Physik, Universitaet Siegen, D-57068 Siegen (Germany)
Publication Date:
OSTI Identifier:
20776695
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevD.73.036003; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; B MESONS; C QUARKS; CORRECTIONS; JET MODEL; NEUTRINOS; QUANTUM CHROMODYNAMICS; REST MASS; S QUARKS; SEMILEPTONIC DECAY

Citation Formats

Boos, H., Feldmann, T., Mannel, T., and Pecjak, B.D.. Shape functions from B{yields}X{sub c}l{nu}{sub l}. United States: N. p., 2006. Web. doi:10.1103/PhysRevD.73.036003.
Boos, H., Feldmann, T., Mannel, T., & Pecjak, B.D.. Shape functions from B{yields}X{sub c}l{nu}{sub l}. United States. doi:10.1103/PhysRevD.73.036003.
Boos, H., Feldmann, T., Mannel, T., and Pecjak, B.D.. Wed . "Shape functions from B{yields}X{sub c}l{nu}{sub l}". United States. doi:10.1103/PhysRevD.73.036003.
@article{osti_20776695,
title = {Shape functions from B{yields}X{sub c}l{nu}{sub l}},
author = {Boos, H. and Feldmann, T. and Mannel, T. and Pecjak, B.D.},
abstractNote = {We study inclusive semileptonic B{yields}X{sub c}l{nu}{sub l} decay using the power counting m{sub c}{approx}{radical}({lambda}{sub QCD}m{sub b}). Assuming this scaling for the charm-quark mass, the decay kinematics can be chosen to access the shape-function region even in b{yields}c transitions. To apply effective field theory methods in this region we extend soft-collinear effective theory to describe massive collinear quarks. We calculate the tree-level decay rate, including O({lambda}{sub QCD}/m{sub b}) power corrections, and show that it factorizes into a convolution of jet and shape functions. We identify a certain kinematical variable whose decay spectrum is proportional to the universal leading-order shape function familiar from b{yields}u decay, and speculate as to whether information about this shape function can be extracted from data on b{yields}c decay.},
doi = {10.1103/PhysRevD.73.036003},
journal = {Physical Review. D, Particles Fields},
number = 3,
volume = 73,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2006},
month = {Wed Feb 01 00:00:00 EST 2006}
}
  • Owing to the fact that m{sub c}{sup 2}{approx}m{sub b}{lambda}{sub QCD}, the end point region of the charged lepton energy spectrum in the inclusive decay B{yields}X{sub c}l{nu}{sub l} is affected by the Fermi motion of the initial-state b quark bound in the B meson. This effect is described in QCD by shape functions. Including the mass of the final-state quark, we find that a different set of operators as employed in previous work is needed for a consistent matching, when incorporating the subleading contributions in B{yields}X{sub q}l{nu}{sub l} for both q=u and q=c. In addition, we modify the usual twist expansionmore » in such a way that it yields a description of the lepton energy spectrum which is not just valid in the end point region, but over the entire phase space.« less
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  • We report the results of a study of the exclusive charmless semileptonic decays, B{sup +}{yields}{eta}(')l{sup +}{nu} and B{sup 0}{yields}{pi}{sup -}l{sup +}{nu}, undertaken with approximately 464x10{sup 6} BB pairs collected at the {Upsilon}(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions for B{sup +}{yields}{eta}l{sup +}{nu} and B{sup 0}{yields}{pi}{sup -}l{sup +}{nu} decays in three and 12 bins of q{sup 2}, respectively, from which we extract the f{sub +}(q{sup 2}) form-factor shapes and the total branching fractions B(B{sup +}{yields}{eta}l{sup +}{nu})=(0.36{+-}0.05{sub stat}{+-}0.04{sub syst})x10{sup -4}more » and B(B{sup 0}{yields}{pi}{sup -}l{sup +}{nu})=(1.42{+-}0.05{sub stat}{+-}0.07{sub syst})x10{sup -4}. We also measure B(B{sup +}{yields}{eta}'l{sup +}{nu})=(0.24{+-}0.08{sub stat}{+-}0.03{sub syst})x10{sup -4}. We obtain values for the magnitude of the CKM matrix element |V{sub ub}| using three different QCD calculations.« less
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  • The inclusive decay B{yields}X{sub u}l{nu} is of much interest because of its potential to constrain the CKM element |V{sub ub}|. Experimental cuts required to suppress charm background restrict measurements of this decay to the shape-function region, where the hadronic final state carries a large energy but only a moderate invariant mass. In this kinematic region, the differential decay distributions satisfy a factorization formula of the form H{center_dot}J x S, where S is the nonperturbative shape function, and the object H{center_dot}J is a perturbatively calculable hard-scattering kernel. In this paper, we present the calculation of the hard function H at next-to-next-to-leadingmore » order (NNLO) in perturbation theory. Combined with the known NNLO result for the jet function J, this completes the perturbative part of the NNLO calculation for this process.« less