202 research outputs found
Drell-Yan Massive Lepton-Pair's Angular Distributions at Large
By measuring Drell-Yan massive lepton-pair's angular distributions, we can
identify the polarization of the virtual photon of invariant mass which
decays immediately into the lepton-pair. In terms of a modified QCD
factorization formula for Drell-Yan process, which is valid even if ,
we calculate the massive lepton-pair's angular distributions at large . We
find that the virtual photons produced at high are more likely to be
transversely polarized. We discuss the implications of this finding to the
J/ mesons' polarization measured recently at Fermilab.Comment: Latex, 10 pages including 4 figure
Otitis Media in Sperm-Associated Antigen 6 (Spag6)-Deficient Mice
Mammalian SPAG6 protein is localized to the axoneme central apparatus, and it is required for normal flagella and cilia motility. Recent studies demonstrated that the protein also regulates ciliogenesis and cilia polarity in the epithelial cells of brain ventricles and trachea. Motile cilia are also present in the epithelial cells of the middle ear and Eustachian tubes, where the ciliary system participates in the movement of serous fluid and mucus in the middle ear. Cilia defects are associated with otitis media (OM), presumably due to an inability to efficiently transport fluid, mucus and particles including microorganisms. We investigated the potential role of SPAG6 in the middle ear and Eustachian tubes by studying mice with a targeted mutation in theSpag6 gene. SPAG6 is expressed in the ciliated cells of middle ear epithelial cells. The orientation of the ciliary basal feet was random in the middle ear epithelial cells of Spag6-deficient mice, and there was an associated disrupted localization of the planar cell polarity (PCP) protein, FZD6. These features are associated with disordered cilia orientation, confirmed by scanning electron microscopy, which leads to uncoordinated cilia beating. The Spag6 mutant mice were also prone to develop OM. However, there were no significant differences in bacterial populations, epithelial goblet cell density, mucin expression and Eustachian tube angle between the mutant and wild-type mice, suggesting that OM was due to accumulation of fluid and mucus secondary to the ciliary dysfunction. Our studies demonstrate a role for Spag6 in the pathogenesis of OM in mice, possibly through its role in the regulation of cilia/basal body polarity through the PCP-dependent mechanisms in the middle ear and Eustachian tubes
The charged-hadron/pion ratio at the Relativistic Heavy Ion Collider
The hadron/pion ratio is calculated in 200 GeV AuAu collisions at
midrapidity, applying pQCD and non-universal transverse-momentum broadening.
Arguments are presented for such non-universality, and the idea is implemented
in a model, which explains the enhancement of the hadron/pion ratio in central
AuAu collisions. The model also describes the qualitative difference between
the recently-measured dAu nuclear enhancement factors for pions and charged
hadrons.Comment: 4 pages, 3 figure
QCD Factorized Drell-Yan Cross Section at Large Transverse Momentum
We derive a new factorization formula in perturbative quantum chromodynamics
for the Drell-Yan massive lepton-pair cross section as a function of the
transverse momentum of the pair. When is much larger than the
pair's invariant mass , this factorization formula systematically resums the
logarithmic contributions of the type to all
orders in the strong coupling . When , our formula yields
the same Drell-Yan cross section as conventional fixed order QCD perturbation
theory. We show that resummation is important when the collision energy
is large enough and , and we argue that perturbative
expansions are more stable and reliable in terms of the modified factorization
formula.Comment: 36 pages, latex, including 16 figure
Recommended from our members
Spatial variations of N2O fluxes across the waterâair interface of mariculture ponds in a subtropical estuary in southeast China
While aquaculture ponds are potentially important sources of atmospheric N2O, the magnitude and variability of N2O concentrations and fluxes both within and across the ponds remain poorly understood. In this study, we examined the smallâscale spatial variations of dissolved N2O concentrations in water and N2O fluxes across the waterâair interface from three mariculture ponds in a subtropical estuary in southeast China. Our results showed that the dissolved concentrations and diffusive fluxes of N2O in the shrimp ponds ranged between 2.3â19.2 nM and 16.4â589.7 nmol mâ2 hrâ1, respectively, over the culture period. Significant variations of N2O concentrations and fluxes were observed within the ponds, with higher values being observed in the aeration area that could be attributed to the high rates of nitrification in the water column, as well as sediment N2O production and diffusive flux into the overlying water. Also, N2O concentrations and fluxes varied significantly among the three ponds as a result of the difference in NâNO3â and NâNH4+ concentrations in the water column. The large fineâscale spatial variations of N2O concentrations and fluxes observed in our aquaculture ponds suggested that management practices such as aeration and bait feeding could largely affect the extent that aquaculture activities have on N2O emissions and climate change through their influence on the physicochemical environment (e.g., oxygen and NâNH4+ concentrations) of the ponds
Nuclear dependence coefficient for the Drell-Yan and J/ production
Define the nuclear dependence coefficient in terms of ratio
of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon
collisions: . We argue that in small region, the
for the Drell-Yan and J/ production is given by a universal function:\
, where parameters a and b are completely determined by either
calculable quantities or independently measurable physical observables. We
demonstrate that this universal function is insensitive to the
A for normal nuclear targets. For a color deconfined nuclear medium, the
becomes strongly dependent on the A. We also show that our
for the Drell-Yan process is naturally linked to perturbatively
calculated at large without any free parameters, and the
is consistent with E772 data for all .Comment: latex, 28 pages, 10 figures, updated two figures, and add more
discussion
Role of the nonperturbative input in QCD resummed Drell-Yan -distributions
We analyze the role of the nonperturbative input in the Collins, Soper, and
Sterman (CSS)'s -space QCD resummation formalism for Drell-Yan transverse
momentum () distributions, and investigate the predictive power of the CSS
formalism. We find that the predictive power of the CSS formalism has a strong
dependence on the collision energy in addition to its well-known
dependence, and the dependence improves the predictive power
at collider energies. We show that a reliable extrapolation from perturbatively
resummed -space distributions to the nonperturbative large region is
necessary to ensure the correct distributions. By adding power
corrections to the renormalization group equations in the CSS formalism, we
derive a new extrapolation formalism. We demonstrate that at collider energies,
the CSS resummation formalism plus our extrapolation has an excellent
predictive power for and production at all transverse momenta . We also show that the -space resummed distributions provide a good
description of Drell-Yan data at fixed target energies.Comment: Latex, 43 pages including 15 figures; typos were correcte
Universality in nuclear dependence coefficient
We derive the nuclear dependence coefficient for Drell-Yan and
J/ production. We show that at small , the is given by
an universal functional form: , and the parameters
and are completely determined by either perturbatively calculable or
independently measurable quantities. This universal functional form
is insensitive to the , and is consistent with existing data.Comment: latex, 4 pages, 3 figures, slightly revise
- âŠ