491 research outputs found
Production of -pairs at HERA-
The production of -pairs as a possible measure of the polarized gluon
distribution is studied for proton--nucleon collisions at
\sqrt{s} =40\;\mbox{GeV}^2 (HERA-). Possibilities of
reconstructing the helicity state of at least one of the 's are
critically reviewed. The observation of production asymmetries in the single
polarized mode of HERA- is found to be not feasible.Comment: 8 pages, LATeX, 3 figures availabe as .uu-fil
Social determinants of content selection in the age of (mis)information
Despite the enthusiastic rhetoric about the so called \emph{collective
intelligence}, conspiracy theories -- e.g. global warming induced by chemtrails
or the link between vaccines and autism -- find on the Web a natural medium for
their dissemination. Users preferentially consume information according to
their system of beliefs and the strife within users of opposite narratives may
result in heated debates. In this work we provide a genuine example of
information consumption from a sample of 1.2 million of Facebook Italian users.
We show by means of a thorough quantitative analysis that information
supporting different worldviews -- i.e. scientific and conspiracist news -- are
consumed in a comparable way by their respective users. Moreover, we measure
the effect of the exposure to 4709 evidently false information (satirical
version of conspiracy theses) and to 4502 debunking memes (information aiming
at contrasting unsubstantiated rumors) of the most polarized users of
conspiracy claims. We find that either contrasting or teasing consumers of
conspiracy narratives increases their probability to interact again with
unsubstantiated rumors.Comment: misinformation, collective narratives, crowd dynamics, information
spreadin
Photoproduction of J/psi mesons at high energies in parton model and k_t-faktorization approach
We consider J/psi meson photoproduction on protons at high energies at the
leading order in alpha_s using conventional parton model and k_t-factorization
approach of QCD. It is shown that in the both cases the colour singlet
mechanism gives correct description for experimental data from HERA for the
total cross section and for the J/psi meson z-spectrum at realistic values of a
c-quark mass and meson wave function at the origin Psi (0). At the same time
our predictions for p_t-spectrum of J/psi meson and for p_t dependence of the
spin parameter alpha obtained in k_t-factorization approach are very different
from the results obtained in conventional parton model. Such a way the
experimental study of a polarized J/psi meson production at the large p_t
should be a direct test of BFKL gluons.Comment: LaTeX2e, 11 pages plus 8 fig. using epsfig.st
Fibrocyte accumulation in the lungs of cystic fibrosis patients
Background: Cystic fibrosis (CF) patients develop severe lung disease including chronic airway infections, neutrophilic inflammation, and progressive fibrotic remodeling in airways. However, cellular and molecular processes that regulate excessive collagen deposition in airways in these patients remain unclear. Fibrocytes are bone marrow (BM)-derived mesenchymal cells that express the hematopoietic cell marker CD45, and mesenchymal cell markers and implicated in collagen deposition in several fibrotic diseases. It is unknown whether fibrocytes accumulate in the lungs of CF patients, so the current study evaluates the presence of fibrocytes in the fibrotic lesions of airways in explanted CF lungs compared to non-CF unused donor lungs (control). Methods: We used immunofluorescence staining to determine if fibrocytes accumulate in explanted CF lungs compared to healthy donor lungs. Simultaneously, we evaluated cells collected by bronchoalveolar lavage (BAL) in CF patients using multi-color flow cytometry. Finally, we analyzed transcripts differentially expressed in fibrocytes isolated from the explanted CF lungs compared to control to assess fibrocyte-specific pro-fibrotic gene networks. Results: Our findings demonstrate fibrocyte accumulation in CF lungs compared to non-CF lungs. Additionally, fibrocytes were detected in the BAL of all CF children. Transcriptomic analysis of fibrocytes identified dysregulated genes associated with fibrotic remodeling in CF lungs. Conclusions: With significantly increased fibrocytes that show increased expression of pro-fibrotic gene transcripts compared to control, our findings suggest an intervention for fibrotic remodeling as a potential therapeutic target in CF
Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation
The transverse momentum distribution is computed for inclusive Higgs
boson production at the energy of the CERN Large Hadron Collider. We focus on
the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and
incorporate contributions from the quark-gluon and quark-antiquark channels.
Using an impact-parameter -space formalism, we include all-orders
resummation of large logarithms associated with emission of soft gluons. Our
resummed results merge smoothly at large with the fixed-order
expectations in perturbative quantum chromodynamics, as they should, with no
need for a matching procedure. They show a high degree of stability with
respect to variation of parameters associated with the non-perturbative input
at low . We provide distributions for Higgs boson masses
from to 200 GeV. The average transverse momentum at zero rapidity
grows approximately linearly with mass of the Higgs boson over the range ~GeV. We provide analogous results
for boson production, for which we compute GeV. The
harder transverse momentum distribution for the Higgs boson arises because
there is more soft gluon radiation in Higgs boson production than in
production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in
wording. Published in Phys. Rev. D67, 034026 (2003
Diffractive Photoproduction of Jets with a Direct Pomeron Coupling at HERA
We investigate in detail the effect of a direct pomeron coupling to quarks on
the production of jets in scattering with almost real photons. Jet
production via a direct pomeron coupling is compared with the resolved--pomeron
mechanism. We consider both direct and resolved photoproduction. Rapidity and
transverse momentum distributions are calculated and compared with preliminary
H1 and ZEUS data.Comment: 21 pages, Latex file, 7 figures (uuencoded) enclosed, Preprint DESY
94-140, KEK-TH-407 and KEK Preprint 94-7
Direct J/psi and psi' hadroproduction via fragmentation in the collinear parton model and k_T-factorization approach
The p_T-spectra for direct J/psi and psi' in hadroproduction at Tevatron
energy have been calculated based on NRQCD formalism and fragmentation
approximation in the collinear parton model and k_T-factorization approach. We
have described the CDF data and obtained a good agreement between the
predictions obtained in the parton model and k_T-factorization approach. We
performed the calculations using the relevant leading order in alpha_s hard
amplitudes and the equal values of the color-octet long-distance matrix
elements for the both models.Comment: 10 pages, Latex, 4 eps figures, epsfig.sty, graphics.st
B Production Asymmetries in Perturbative QCD
This paper explores a new mechanism for B production in which a b quark
combines with a light parton from the hard-scattering process before
hadronizing into the B hadron. This recombination mechanism can be calculated
within perturbative QCD up to a few nonperturbative constants. Though
suppressed at large transverse momentum by a factor Lambda_QCD m_b/p_t^2
relative to b quark fragmentation production, it can be important at large
rapidities. A signature for this heavy-quark recombination mechanism in
proton-antiproton colliders is the presence of rapidity asymmetries in B cross
sections. Given reasonable assumptions about the size of nonperturbative
parameters entering the calculation, we find that the asymmetries are only
significant for rapidities larger than those currently probed by collider
experiments.Comment: 17 pages, LaTeX, 4 ps figures, tightenlines, sections added, final
version accepted for publication in Phys. Rev.
Isolating a light Higgs boson from the di-photon background at the LHC
We compute the QCD corrections to the gluon fusion subprocess gg to gamma
gamma, which forms an important component of the background to the search for a
light Higgs boson at the LHC. We study the dependence of the improved pp to
gamma gamma X background calculation on the factorization and renormalization
scales, on various choices for photon isolation cuts, and on the rapidities of
the photons. We also investigate ways to enhance the statistical significance
of the Higgs signal in the di-photon channel.Comment: Additional reference included, 17 pages, 16 figure files, revte
The fully differential single-top-quark cross section in next-to-leading order QCD
We present a new next-to-leading order calculation for fully differential
single-top-quark final states. The calculation is performed using phase space
slicing and dipole subtraction methods. The results of the methods are found to
be in agreement. The dipole subtraction method calculation retains the full
spin dependence of the final state particles. We show a few numerical results
to illustrate the utility and consistency of the resulting computer
implementations.Comment: 37 pages, latex, 2 ps figure
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