38 research outputs found
Higher Order Power Corrections in Inclusive B Decays
We discuss order 1/m_b^4 and 1/m_b^5 corrections in inclusive semileptonic
decay of a meson. We identify relevant hadronic matrix elements of
dimension seven and eight and estimate them using the ground-state saturation
approximation. Within this approach the effects on the integrated rate and on
kinematic moments are estimated. The overall relative shift in V_{cb} turns out
about +0.4% as applied to the existing fits. Similar estimates are presented
for B -> X_s+\gamma decays.Comment: 30 pages, 16 figure
Conclusions from CDF Results on CP Violation in D^0 \to \pi^+\pi^-, K^+K^- and Future Tasks
Within the Standard Model (SM) one predicts both direct and indirect CP
violation in D^0 \to \pi^+\pi^-, K^+K^- transitions, although the effects are
tiny: Indirect CP asymmetry cannot exceed O(10^{-4}), probably even O(10^{-5});
direct effects are estimated at not larger than 10^{-4}. At B factories direct
and indirect asymmetries have been studied with /\tau_{D^0} ~ 1; no CP
asymmetry was found with an upper bound of about 1%. CDF has shown intriguing
data on CP violation in D^0 \to \pi^+\pi^- [K^+K^-] with /\tau_{D^0} ~ 2.4
[2.65]. Also, CDF has not seen any CP violation. For direct CP asymmetry, CDF
has a sensitivity similar to the combination of the B factories, yet for
indirect CP violation it yields a significantly smaller sensitivity of
a_{cp}^{ind}=(-0.01 +- 0.06_{stat} +- 0.05_{syst})% due to it being based on
longer decay times. New Physics models (NP) like Little Higgs Models with
T-Parity (LHT) can produce an indirect CP asymmetry up to 1%; CDF's findings
thus cover the upper range of realistic NP predictions ~ 0.1 - 1%. One hopes
that LHCb and a Super-Flavour Factory will probe the lower range down to
~0.01%. Such non-ad-hoc NP like LHT cannot enhance direct CP violation
significantly over the SM level in D^0 \to \pi^+\pi^-, K^+K^- and D^{\pm} \to
\pi^{\pm}K^+K^- transitions, but others might well do so.Comment: 11 pages, 1 figure. V2 has minor corrections and corresponds to the
published versio
Second order QCD corrections to inclusive semileptonic b \to Xc l \bar \nu_l decays with massless and massive lepton
We extend previous computations of the second order QCD corrections to
semileptonic b \to c inclusive transitions, to the case where the charged
lepton in the final state is massive. This allows accurate description of b \to
c \tau \bar \nu_\tau decays. We review techniques used in the computation of
O(\alpha_s^2) corrections to inclusive semileptonic b \to c transitions and
present extensive numerical studies of O(\alpha_s^2) QCD corrections to b \to c
l \bar \nu_l decays, for l =e, \tau.Comment: 30 pages, 4 figures, 5 table
Probing top charged-Higgs production using top polarization at the Large Hadron Collider
We study single top production in association with a charged Higgs in the
type II two Higgs doublet model at the Large Hadron Collider. The polarization
of the top, reflected in the angular distributions of its decay products, can
be a sensitive probe of new physics in its production. We present theoretically
expected polarizations of the top for top charged-Higgs production, which is
significantly different from that in the closely related process of t-W
production in the Standard Model. We then show that an azimuthal symmetry,
constructed from the decay lepton angular distribution in the laboratory frame,
is a sensitive probe of top polarization and can be used to constrain
parameters involved in top charged-Higgs production.Comment: 22 pages, 18 Figures, Discussions about backgrounds and NLO
corrections added, figures modified, references added, Version published in
JHE
Minimal Flavour Violation with hierarchical squark masses
In a supersymmetric model with hierarchical squark masses we analyze a
pattern of flavour symmetry breaking centered on the special role of the top
Yukawa coupling and, by extension, of the full Yukawa couplings for the up-type
quarks. For sufficiently heavy squarks of the first and second generation this
leads to effective Minimal Flavour Violation of the Flavour Changing Neutral
Current amplitudes. For this to happen we determine the bounds on the masses of
the heavy squarks with QCD corrections taken into account, properly including
previously neglected effects. We believe that the view presented in this paper
altogether strengthens the case for hierarchical sfermions.Comment: 13 pages, 1 figure. v2: an equation correcte
Neutron Electric Dipole Moment Constraint on Scale of Minimal Left-Right Symmetric Model
Using an effective theory approach, we calculate the neutron electric dipole
moment (nEDM) in the minimal left-right symmetric model with both explicit and
spontaneous CP violations. We integrate out heavy particles to obtain
flavor-neutral CP-violating effective Lagrangian. We run the Wilson
coefficients from the electroweak scale to the hadronic scale using one-loop
renormalization group equations. Using the state-of-the-art hadronic matrix
elements, we obtain the nEDM as a function of right-handed W-boson mass and
CP-violating parameters. We use the current limit on nEDM combined with the
kaon-decay parameter to provide the most stringent constraint yet on
the left-right symmetric scale TeV.Comment: 20 pages and 8 figure
Factorization at Subleading Power and Irreducible Uncertainties in Decay
Using methods from soft-collinear and heavy-quark effective theory, a
systematic factorization analysis is performed for the
photon spectrum in the endpoint region . It is proposed that, to all orders in , the spectrum obeys a
novel factorization formula, which besides terms with the structure
familiar from inclusive decay
distributions contains "resolved photon" contributions of the form and . Here and
are new soft and jet functions, whose form is derived. These
contributions arise whenever the photon couples to light partons instead of
coupling directly to the effective weak interaction. The new contributions
appear first at order and are related to operators other than
in the effective weak Hamiltonian. They give rise to
non-vanishing corrections to the total decay rate, which cannot be
described using a local operator product expansion. A systematic analysis of
these effects is performed at tree level in hard and hard-collinear
interactions. The resulting uncertainty on the decay rate defined with a cut
GeV is estimated to be approximately . It could be
reduced by an improved measurement of the isospin asymmetry to
the level of . We see no possibility to reduce this uncertainty further
using reliable theoretical methods.Comment: 63 pages, 11 Figures, Journal Versio
Top Quarks as a Window to String Resonances
We study the discovery potential of string resonances decaying to
final state at the LHC. We point out that top quark pair production is a
promising and an advantageous channel for studying such resonances, due to
their low Standard Model background and unique kinematics. We study the
invariant mass distribution and angular dependence of the top pair production
cross section via exchanges of string resonances. The mass ratios of these
resonances and the unusual angular distribution may help identify their
fundamental properties and distinguish them from other new physics. We find
that string resonances for a string scale below 4 TeV can be detected via the
channel, either from reconstructing the semi-leptonic
decay or recent techniques in identifying highly boosted tops.Comment: 22 pages, 6 figure
Averages of b-hadron, c-hadron, and tau-lepton properties as of 2018 Heavy Flavor Averaging Group (HFLAV)
This paper reports world averages of measurements of b-hadron, c-hadron, and
Ï
-lepton properties obtained by the Heavy Flavour Averaging Group using results available through September 2018. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters,
C
P
violation parameters, parameters of semileptonic decays, and CabibboâKobayashiâMaskawa matrix elements