396 research outputs found
Factorization theorems for exclusive heavy-quarkonium production
We outline the proofs of the factorization theorems for exclusive two-body
charmonium production in B-meson decay and e^+e^- annihilation to all orders in
perturbation theory in quantum chromodynamics. We find that factorized
expressions hold up to corrections of order m_c/m_b in B-meson decay and
corrections of order m_c^2/s in e^+e^- annihilation, where m_c is the
charm-quark mass, m_b is the bottom-quark mass, and root-s is the e^+e^-
center-of-momentum energy.Comment: 4 pages, 2 figure
Factorization of low-energy gluons in exclusive processes
We outline a proof of factorization in exclusive processes, taking into
account the presence of soft and collinear modes of arbitrarily low energy,
which arise when the external lines of the process are taken on shell.
Specifically, we examine the process of e^+e^- annihilation through a virtual
photon into two light mesons. In an intermediate step, we establish a
factorized form that contains a soft function that is free of collinear
divergences. In contrast, in soft-collinear effective theory, the low-energy
collinear modes factor most straightforwardly into the soft function. We point
out that the cancellation of the soft function, which relies on the
color-singlet nature of the external hadrons, fails when the soft function
contains low-energy collinear modes.Comment: 18 pages, 10 figures, 2 tables, version published in Physical Review
Factorization in exclusive quarkonium production
We present factorization theorems for two exclusive heavy-quarkonium
production processes: production of two quarkonia in e^+e^- annihilation and
production of a quarkonium and a light meson in B-meson decays. We describe the
general proofs of factorization and supplement them with explicit one-loop
analyses, which illustrate some of the features of the soft-gluon
cancellations. We find that violations of factorization are generally
suppressed relative to the factorized contributions by a factor v^2m_c/Q for
each S-wave charmonium and a factor m_c/Q for each L-wave charmonium with L>0.
Here, v is the velocity of the heavy quark or antiquark in the quarkonium rest
frame, Q=sqrt{s} for e^+e^- annihilation, Q=m_B for B-meson decays, sqrt{s} is
the e^+e^- center-of-momentum energy, m_c is the charm-quark mass, and m_B is
the B-meson mass. There are modifications to the suppression factors if
quantum-number restrictions apply for the specific process.Comment: 69 pages, 12 figures, 2 tables. v2: Version published in Physical
Review
Comparison of the color-evaporation model and the NRQCD factorization approach in charmonium production
We compare the color-evaporation model (CEM) and nonrelativistic QCD (NRQCD)
factorization predictions for inclusive quarkonium production. Using the NRQCD
factorization formulas for quarkonium production and for perturbative QQ-bar
production, we deduce relationships that are implied by the CEM between the
nonperturbative NRQCD matrix elements that appear in the factorization formula
for quarkonium production. These relationships are at odds with the
phenomenological values of the matrix elements that have been extracted from
the Tevatron data for charmonium production at large transverse momentum. A
direct comparison of the CEM and NRQCD factorization predictions with the CDF
charmonium production data reveals that the CEM fits to the data are generally
unsatisfactory, while the NRQCD factorization fits are generally compatible
with the data. The inclusion of k_T smearing improves the CEM fits
substantially, but significant incompatibilities remain. The NRQCD
factorization fits to the chi_c data indicate that multiple gluon radiation is
an essential ingredient in obtaining the correct shape of the cross section as
a function of p_T.Comment: 26 pages, 6 figures, 7 tables, Some changes of emphasis in the
conclusions, additional discussion of theoretical uncertainties, minor
revisions and corrections, version to be published in Physical Review
Inclusive Charm Production in chi_b Decays
We calculate the inclusive decay rate of the spin-triplet bottomonium states
chi_{bJ} into charm hadrons, including the leading-order color-singlet and
color-octet bb-bar annihilation mechanisms. We also calculate the momentum
distribution of the charm quark from the decay of chi_{bJ}. The infrared
divergences from the color-singlet process bb-bar -> cc-bar g are factored into
the probability density at the origin for a bb-bar pair in a color-octet state.
That probability density can be determined phenomenologically from the fraction
of decays of chi_{bJ} that include charm hadrons. It can then be used to
predict the partial widths into light hadrons for all four states in the P-wave
bottomonium multiplet.Comment: 39 pages, 3 figures, Minor corrections, Version published in Phys.
Rev.
Enceladus' south polar sea
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Icarus 189: 72-82, doi:10.1016/j.icarus.2007.01.010.Recent observations of the south pole of Saturn’s moon Enceladus by the Cassini
spacecraft have revealed an active world, powered by internal heat. In this paper, we
propose that localized subsurface melting on Enceladus has produced an internal south
polar sea. Evidence for this localized sea comes from the shape of Enceladus, which
does not match a differentiated body at its current orbital position. We show that melting
induced by the observed heat flow at the south pole produces a large enough pit to match
the shape of Enceladus with a differentiated rock and ice interior. Numerical modeling of
melting and ice flow shows that the sea produced beneath the south pole is stable against
inflow of ductile ice from its surroundings for the duration of the heating. The shape
modification due to melting also produces a negative degree-two gravity anomaly, which
can reorient the spin axis of Enceladus in order to place the sea at the pole
Material Units, Structures/Landforms, and Stratigraphy for the Global Geologic Map of Ganymede (1:15M)
In the coming year a global geological map of Ganymede will be completed that represents the most recent understanding of the satellite on the basis of Galileo mission results. This contribution builds on important previous accomplishments in the study of Ganymede utilizing Voyager data and incorporates the many new discoveries that were brought about by examination of Galileo data. Material units have been defined, structural landforms have been identified, and an approximate stratigraphy has been determined utilizing a global mosaic of the surface with a nominal resolution of 1 km/pixel assembled by the USGS. This mosaic incorporates the best available Voyager and Galileo regional coverage and high resolution imagery (100-200 m/pixel) of characteristic features and terrain types obtained by the Galileo spacecraft. This map has given us a more complete understanding of: 1) the major geological processes operating on Ganymede, 2) the characteristics of the geological units making up its surface, 3) the stratigraphic relationships of geological units and structures, and 4) the geological history inferred from these relationships. A summary of these efforts is provided here
Factors influencing time to diagnosis and initiation of treatment of endemic Burkitt Lymphoma among children in Uganda and western Kenya: a cross-sectional survey
BACKGROUND: Survival rates for children diagnosed with Burkitt lymphoma (BL) in Africa are far below those achieved in developed countries. Late stage of presentation contributes to poor prognosis, therefore this study investigated factors leading to delays in BL diagnosis and treatment of children in Uganda and western Kenya.
METHODS: Guardians of children diagnosed with BL were interviewed at the Jaramogi Oginga Odinga Teaching and Referral Hospital (JTRH) and Uganda Cancer Institute (UCI) from Jan-Dec 2010. Information on sociodemographics, knowledge, attitudes, illness perceptions, health-seeking behaviors and prior health encounters was collected using a standardized, pre-tested questionnaire.
RESULTS: Eighty-two guardians were interviewed (20 JTRH, 62 UCI). Median total delay (1st symptoms to BL diagnosis) was 12.1 weeks [interquartile range (IQR) 4.9-19.9] in Kenya and 12.9 weeks (IQR 4.3-25.7) in Uganda. In Kenya, median guardian delay (1st symptoms to 1st health encounter) and health system delay (1st health encounter to BL diagnosis) were 9.0 weeks (IQR 3.6-15.7) and 2.0 weeks (IQR 1.6-5.8), respectively. Data on guardian and health system delay in Uganda were only available for those with \u3c 4 prior health encounters (n = 26). Of these, median guardian delay was 4.3 weeks (range 0.7-149.9), health system delay 2.6 weeks (range 0.1-16.0), and total delay 10.7 weeks (range 1.7-154.3). Guardians in Uganda reported more health encounters than those in Kenya (median 5, range 3-16 vs. median 3, range 2-6). Among Kenyan guardians, source of income was the only independent predictor of delay, whereas in Uganda, guardian delay was influenced by guardians\u27 beliefs on the curability of cancer, health system delay, by guardians\u27 perceptions of cancer as a contagious disease, and total delay, by the number of children in the household and guardians\u27 role as caretaker. Qualitative findings suggest financial costs, transportation, and other household responsibilities were major barriers to care.
CONCLUSIONS: Delays from symptom onset to BL treatment were considerable given the rapid growth rate of this cancer, with guardian delay constituting the majority of total delay in both settings. Future interventions should aim to reduce structural barriers to care and increase awareness of BL in particular and cancer in general within the community, as well as among health professionals
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