610 research outputs found
Enhanced subleading structure functions in semileptonic B decay
The charged lepton spectrum in semileptonic decay near
maximal lepton energy receives important corrections from subleading structure
functions that are formally suppressed by powers of but are
enhanced by numerical factors. We investigate the series of higher order terms
which smear over a region of width near the
endpoint the contributions proportional to times (i)
the matrix element of the chromomagnetic operator, and (ii) four-quark
operators. These contribute to the total rate at the few percent level, but
affect the endpoint region much more significantly. Implications for the
determination of are discussed.Comment: 12 page
Recent Progress in Heavy Quark Physics
Some of the recent progress in heavy quark physics is reviewed. Special
attention is paid to inclusive methods for determining Vub and factorization in
nonleptonic B decays. Theoretical predictions for top-antitop production near
threshold are also discussed.Comment: talk given at 2001 Lepton Photon Meeting, 10 pages, 5 figure
Chiral Perturbation Theory for phi -> rho gamma gamma and phi -> omega gamma gamma
We predict differential decay distributions for phi->rho gamma gamma and phi
-> omega gamma gamma using chiral perturbation theory. We also consider the
isospin violating decay phi -> omega pi^0. Experimental information on these
decays can be used to determine couplings in the heavy vector meson chiral
Lagrangian.Comment: It was shown by P. Ko et al., hep-ph/9510205 (Phys. Lett. B366 (1996)
287), that there is a etaprime pole contribution that dominates over what we
calculate
Resumming the color-octet contribution to e+ e- -> J/psi + X
Recent observations of the spectrum of J/psi produced in e+ e- collisions at
the Upsilon(4S) resonance are in conflict with fixed-order calculations using
the Non-Relativistic QCD (NRQCD) effective field theory. One problem is that
leading order color-octet mechanisms predict an enhancement of the cross
section for J/psi with maximal energy that is not observed in the data.
However, in this region of phase space large perturbative corrections (Sudakov
logarithms) as well as enhanced nonperturbative effects are important. In this
paper we use the newly developed Soft-Collinear Effective Theory (SCET) to
systematically include these effects. We find that these corrections
significantly broaden the color-octet contribution to the J/psi spectrum. Our
calculation employs a one-stage renormalization group evolution rather than the
two-stage evolution used in previous SCET calculations. We give a simple
argument for why the two methods yield identical results to lowest order in the
SCET power counting.Comment: 27 pages, 7 figure
The adjuvant treatment of kidney cancer: a multidisciplinary outlook
Approximately 70% of cases of kidney cancer are localized or locally advanced at diagnosis. Among patients who undergo surgery for these cancers, 30â35% will eventually develop potentially fatal metachronous distant metastases. Effective adjuvant treatments are urgently needed to reduce the risk of recurrence of kidney cancer and of dying of metastatic disease. To date, almost all of the tested adjuvant agents have failed to demonstrate any benefit. Only two trials of an autologous renal tumour cell vaccine and of the vascular endothelial growth factor receptor (VEGFR) tyrosine kinase inhibitor sunitinib have shown positive results, but these have been criticized for methodological reasons and conflicting data, respectively. The results of two additional trials of targeted agents as adjuvant therapies have not yet been published. Novel immune checkpoint inhibitors are promising approaches to adjuvant therapy in kidney cancer, and a number of trials are now underway. An important component of the management of patients with kidney cancer, particularly those who undergo radical resection for localized renal cell carcinoma, is the preservation of kidney function to reduce morbidity and mortality. The optimal management of these patients therefore requires a multidisciplinary approach involving nephrologists, oncologists, urologists and pathologists
Semileptonic B Decays into Excited Charmed Mesons (, ) in HQEFT
Exclusive semileptonic B decays into excited charmed mesons (, )
are studied up to the order of in the framework of the heavy quark
effective field theory (HQEFT), which contains the contributions of both
particles and antiparticles. Two wave functions and ,
which characterize the contributions from the kinematic operator at the order
of , are calculated by using QCD sum rule approach in HQEFT. Zero recoil
values of other two wave functions and are extracted
from the excited charmed-meson masses. Possible effects from the spin-dependent
transition wave functions which arise from the magnetic operators at the order
of are analyzed. It is shown that the experimental measurements for the
branching ratios of and can be understood
in the framework of HQEFT.Comment: 27 pages, RevTex, 4 figures, 3 tables, to be published in IJMP
Semileptonic B decays into excited charmed mesons from QCD sum rules
Exclusive semileptonic decays into excited charmed mesons are studied
with QCD sum rules in the leading order of heavy quark effective theory. Two
universal Isgur-Wise functions \tau and \zeta for semileptonic B decays into
four lowest lying excited mesons (, , , and ) are
determined. The decay rates and branching ratios for these processes are
calculated.Comment: RevTeX, 17 pages including 2 figure
Object knowledge modulates colour appearance
We investigated the memory colour effect for colour diagnostic artificial objects. Since knowledge about these objects and their colours has been learned in everyday life, these stimuli allow the investigation of the influence of acquired object knowledge on colour appearance. These investigations are relevant for questions about how object and colour information in high-level vision interact as well as for research about the influence of learning and experience on perception in general. In order to identify suitable artificial objects, we developed a reaction time paradigm that measures (subjective) colour diagnosticity. In the main experiment, participants adjusted sixteen such objects to their typical colour as well as to grey. If the achromatic object appears in its typical colour, then participants should adjust it to the opponent colour in order to subjectively perceive it as grey. We found that knowledge about the typical colour influences the colour appearance of artificial objects. This effect was particularly strong along the daylight axis
Reducing theoretical uncertainties in mb and lambda1
We calculate general moments of the lepton energy spectrum in inclusive
semileptonic B -> X_c l \nu decay. Moments which allow the determination of
mb^{1S} and lambda1 with theoretical uncertainties Delta(mb^{1S}) ~ 0.04 GeV
and Delta(lambda1) ~ 0.05 GeV^2 are presented. The short distance 1S mass is
used to extract a mass parameter free of renormalon ambiguities. Moments which
are insensitive to mb and lambda1 and therefore test the size of the 1/mb^3
matrix elements and the validity of the OPE are also presented. Finally, we
give an expression for the total branching ratio with a lower cut on the lepton
energy, which allows one to eliminate a source of model dependence in current
determinations of |Vcb| from B -> X_c l \nu decay.Comment: 8 pages, one figur
Increased Yield of ttbb at Hadron Colliders in Low-Energy Supersymmetry
Light bottom squarks and gluinos have been invoked to explain the b quark
pair production excess at the Tevatron. We investigate the associated
production of ttbb at hadron colliders in this scenario, and find that the
rates for this process are enhanced over the Standard Model prediction. If
light gluinos exist, it may be possible to detect them at the Tevatron, and
they could easily be observed at the LHC.Comment: 5p, references added, version accepted to PR
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