1,410 research outputs found
Measurement of the Width Difference of B_d Mesons
We estimate \Delta Gamma_d/\Gamma_d, including 1/m_b contributions and part
of the next-to-leading order QCD corrections, and find it to be around 0.3%. We
show the methods to measure \Delta Gamma_d/\Gamma_d by using at least two
different final states on the untagged B_d decay. The nonzero width difference
can also be used to identify new physics effects and to resolve a twofold
discrete ambiguity in the B_d-\bar{B}_d mixing phase. With the high statistics
and accurate time resolution of the upcoming LHC experiment, the measurement of
\Delta Gamma_d seems to be possible. This measurement would be important for an
accurate measurement of \sin2\phi_1 at the LHC. We also derive an upper bound
on the value of \Delta Gamma_d/\Gamma_d in the presence of new physics.Comment: 3 pages, LaTeX, Presented at the 5th KEK Topical Conference(KEKTC5
Renormalons and confinement
We compute the renormalon ambiguity of the static potential, in the limit of
a large number of flavors. An extrapolation of the QED result to QCD implies
that the large distance behavior of the quark potential is arbitrary in
perturbation theory, as there are an infinite number of prescriptions to
assign. The shape of the potential at large distances is not only affected by
the renormalon pole closest to the origin of the Borel plane, but a resummation
of all renormalon contributions is required. In particular, confinement can be
accommodated, but it is not explained. At short distances there is no
indication of a linear term in the potential.Comment: 7 pages revtex; major changes: list of authors corrected, title,
abstract, body of paper changed
On The Difficulty of Computing Higher-Twist Corrections
We discuss the evaluation of power corrections to hard scattering and decay
processes for which an operator product expansion is applicable. The Wilson
coefficient of the leading-twist operator is the difference of two perturbative
series, each of which has a renormalon ambiguity of the same order as the power
corrections themselves, but which cancel in the difference. We stress the
necessity of calculating this coefficient function to sufficiently high orders
in perturbation theory so as to make the uncertainty of the same order or
smaller than the relevant power corrections. We investigate in some simple
examples whether this can be achieved. Our conclusion is that in most of the
theoretical calculations which include power corrections, the uncertainties are
at least comparable to the power corrections themselves, and that it will be a
very difficult task to improve the situation.Comment: 27 pages, uuencoded file containing latex source and axodraw.sty fil
Conceptual aspects of QCD factorization in hadronic B decays
I review the meaning of ``QCD factorization'' in hadronic two-body B decays
and then discuss recent results of theoretical (rather than phenomenological)
nature: the proof of factorization at two loops; the identification of
``chirally enhanced'' power corrections; and the role of annihilation
contributions.Comment: 10 pages, LaTeX. Based on talks presented at the UK Phenomenology
Workshop on Heavy Flavour and CP Violation, 17 - 22 September 2000, Durham,
proceedings to appear in J. Phys. G; the 5th International Symposium on
Radiative Corrections (RADCOR2000), Carmel, California, September 11 - 15,
2000; the 4th Workshop on Continuous Advances in QCD, Minneapolis, 12-14 May
2000; the Vth International Workshop on Heavy Quark Physics, Dubna, 6-8 April
200
Power corrections and renormalons in Drell-Yan production
The resummed Drell-Yan cross section in the double-logarithmic approximation
suffers from infrared renormalons. Their presence was interpreted as an
indication for non-perturbative corrections of order \lqcd/(Q(1-z)). We find
that, once soft gluon emission is accurately taken into account, the leading
renormalon divergence in the resummed cross section is cancelled by
higher-order perturbative contributions in the exponent of the resummed cross
section. From this evidence, `higher twist' corrections to the hard cross
section in Drell-Yan production should therefore intervene only at order
\lqcd^2/((Q^2 (1-z)^2) in the entire perturbative domain Q (1-z) > \lqcd.
We compare this result with hadronic event shape variables, comment on the
potential universality of non-perturbative corrections to resummed cross
sections, and on possible implications for phenomenology.Comment: 37 pages, LATEX, 3 figures as uudecoded fil
The nature of power corrections in large approximation
We investigate the nature of power corrections and infrared renormalon
singularities in large approximation. We argue that the power
correction associated with a renormalon pole singularity should appear at O(1),
in contrast to the renormalon ambiguity appearing at , and give
an explanation why the leading order renormalon singularities are generically
poles.Comment: 6 page
Enhanced electroweak penguin amplitude in B-->VV decays
We discuss a novel electromagnetic penguin contribution to the transverse
helicity amplitudes in B decays to two vector mesons, which is enhanced by two
powers of mB/Lambda relative to the standard penguin amplitudes. This leads to
unique polarization signatures in penguin-dominated decay modes such as B-->rho
K* similar to polarization effects in the radiative decay B-->K*gamma, and
offers new opportunities to probe the magnitude and chirality of
flavour-changing neutral current couplings to photons.Comment: 4 pages, 1 figur
NNLO vertex corrections to non-leptonic B decays: Tree amplitudes
The colour-suppressed tree amplitude in non-leptonic B decays is particularly
sensitive to perturbative and non-perturbative corrections. We calculate the
two-loop (NNLO) vertex corrections to the colour-suppressed and colour-allowed
tree amplitudes in QCD factorization. Our results are given completely
analytically, including the full dependence on the charm quark mass. We then
update theoretical predictions for a range of interesting observables derived
from pi pi, pi rho, and rho rho final states that do not depend (significantly)
on penguin contributions, and hence are now available with NNLO accuracy. We
observe good agreement with experimental data within experimental and
theoretical errors, except for observables involving the pi^0 pi^0 branching
fraction.Comment: 52 pages, 8 figures, 3 tables. Equations (42) and (84) are contained
in electronic form in the source file of the present submissio
Bloch-Nordsieck cancellations beyond logarithms in heavy particle decays
We investigate the one-loop radiative corrections to the semileptonic decay
of a charged particle at finite gauge boson mass. Extending the Bloch-Nordsieck
cancellation of infrared logarithms, the subsequent non-analytic terms are also
found to vanish after eliminating the pole mass in favor of a mass defined at
short distances. This observation justifies the operator product expansion for
inclusive decays of heavy mesons and implies that infrared effects associated
with the summation of the radiative corrections are suppressed by at least
three powers of the mass of the heavy decaying particle.Comment: LATEX, 7 pages, one figure appended as uu-encoded ps-file,
MPI-PhT/94-1
Polarization of Upsilon(nS) at the Tevatron
The polarization of inclusive Upsilon(nS) at the Fermilab Tevatron is
calculated within the nonrelativistic QCD factorization framework. We use a
recent determination of the NRQCD matrix elements from fitting the CDF data on
bottomonium production from Run IB of the Tevatron. The result for the
polarization of Upsilon(1S) integrated over the transverse momentum bin 8 < p_T
< 20 GeV is consistent with a recent measurement by the CDF Collaboration. The
transverse polarization of Upsilon(1S) is predicted to increase steadily for
p_T greater than about 10 GeV. The Upsilon(2S) and Upsilon(3S) are predicted to
have significantly larger transverse polarizations than Upsilon(1S).Comment: 15 pages, 3 figure
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