32,919 research outputs found
Study of heavy meson production in p-Pb collisions at =5.02 TeV in the general-mass variable-flavour-number scheme
We study inclusive charm and bottom production, for both D and B mesons, in
p-Pb collisions at the LHC. Numerical results for p_T-differential production
cross sections are obtained at next-to-leading-order in the general-mass
variable-flavor-number scheme. We compare our results with recent data from
ALICE, LHCb and CMS at a center-of-mass energy of 5 TeV and find good
agreement. A comparison with p-p cross sections does not reveal the presence of
nuclear initial-state interaction effects that could be expected to become
visible as deviations of the ratio of p-Pb and p-p cross sections from one.Comment: 20 pages, extended discussion, agrees with published version in
Nucl.Phys.
b-Hadron production in the general-mass variable-flavour-number scheme and LHC data
We study inclusive b-hadron production in pp collisions at the LHC at
different center-of-mass energies and compare with experimental data from the
LHCb and CMS collaborations. Our predictions for cross sections differential in
the transverse momentum and (pseudo-)rapidity agree with data within
uncertainties due to renormalization scale variations. A small tension is found
if data and theory predictions are compared for cross section ratios at
different center-of-mass energies.Comment: 22 pages. Replaced LHCb data: now match with revised version (v9) of
arXiv:1612.0514
Inclusive D* production in gamma-gamma collisions: including the single-resolved contribution with massive quarks
We have calculated the next-to-leading order cross section for the inclusive
production of charm quarks as a function of the transverse momentum p_T and the
rapidity in two approaches using massive or massless charm quarks. For the
single-resolved cross section we have derived the massless limit from the
massive theory. We find that this limit differs from the genuine massless
version with MS-bar factorization by finite corrections. By adjusting
subtraction terms we establish a massive theory with MS-bar subtraction which
approaches the massless theory very fast with increasing transverse momentum.
With these results and including the equivalent results for the direct cross
section obtained previously as well as double-resolved contributions, we
calculate the inclusive D*+- cross section in gamma-gamma collisions using
realistic evolved non-perturbative fragmentation functions and compare with
recent data from the LEP collaborations ALEPH, L3 and OPAL. We find good
agreement.Comment: 34 pages including postscript figure
Inclusive D* Production in Photon-Photon Collisions at Next-to-Leading Order QCD
The next-to-leading order cross section for the inclusive production of charm
quarks in gamma-gamma collisions is calculated as a function of the transverse
momentum pT and the rapidity y in approaches using massive or massless charm
quarks. For the direct cross section we derive the massless limit from the
massive theory with the result that this limit differs from the massless
version with MSbar factorization by finite corrections. Subtracting or adding
these corrections allows us to compare the two approaches on equal footing. We
establish massless and massive versions with 3 and 4 initial flavours which are
shown to approach the massless approximations very fast with increasing pT.
With these results we calculate the inclusive D* cross section in gamma-gamma
collisions using realistic evolved fragmentation functions with appropriate
factorization scales and compare with recent data for dsigma/dpT from three LEP
collaborations after single- and double-resolved contributions have been added.Comment: 27 pages, 8 figures, LaTe
LARGE LOGARITHM BEHAVIOUR OF e^+e^- JET CROSS SECTIONS AND EVENT SHAPE DISTRIBUTIONS IN O(alpha_s^2)
We have calculated the leading and next-to-leading logarithm coefficients of
annihilation jet cross sections, thrust distribution
and energy-energy correlation in the two-jet limit when the jet resolution and
the event shape variables vanish. We have compared our results with
expectations based on leading logarithm approximations used to resum the
pertubative cross sections where this is possible. There is good agreement for
the leading and next-to-leading coefficients of jet cross sections in the
Durham scheme. Also for the thrust distribution and energy-energy correlation
we find results which are consistent with the leading logarithm predictions.Comment: 22 pages, uuencoded postscript, no figure
Inclusive photoproduction of bottom quarks for low and medium pT in the general-mass variable-flavour-number scheme
We present predictions for b-quark production in photoprodcution and compare
with experimental data from HERA. Our theoretical predictions are obtained at
next-to-leading-order in the general-mass variable-flavor-number scheme, an
approach which takes into account the finite mass of the b quarks. We use
realistic evolved nonperturbative fragmentation functions obtained from fits to
e+e- data. We find in general good agreement of data with both the GM-VFNS and
the FFNS calculations, while the more precise ZEUS data seem to prefer the
GM-VFNS predictions.Comment: 11 page
Power supply Patent
Power supply with automatic power factor conversion syste
T cell-specific suppressor factor(s) with regulatory influence on interleukin 2 production and function
In this study we report that alloantigen-activated spleen cells produce both amplifying and suppressive factors under the same conditions. Both types of soluble mediators--as detected in different assay systems-- were present in the supernatants of in vivo sensitized and in vitro restimulated spleen cell populations and were separable by gel filtration. As shown by others, the amplifying factor (IL 2) was eluted in the size range of 30,000 m.w. The suppressive factor(s) (SF) was eluted in the size range of 10,000 m.w. SF was shown to inhibit the proliferative response of T cells to alloantigen, as well as the generation of regulatory T cells and cytotoxic T cells from their precursors when added at the beginning of the in vitro culture. Furthermore, SF inhibited the release of IL 2 from producer T cells but had no detectable effect on the interaction of IL 2 with receptive T cells. In addition it was shown that SF does not affect the generation of PFC from their precursors after activation by T cell-independent antigens. The results indicate that SF selectively acts on T cells and that it is involved in the regulation of the immune response by modulating early events in T cell activation
Nanometer lithography on silicon and hydrogenated amorphous silicon with low-energy electrons
We report the local oxidation of hydrogen terminated silicon (Si) surfaces induced with the scanning-tunneling microscope (STM) operating in air and by a beam of free low-energy electrons. With STM, oxide lines were written in Si(100) and Si(110) and transferred into the substrate by wet etching. In case of Si(110) trenches with a width as small as 35 nm and a depth of 300 nm were made. The same process has also successfully been applied to the patterning of hydrogenated amorphous silicon (a-Si:H) thin films. We demonstrate the fabrication of metallic ânanowiresâ using a-Si:H as resist layer. With regard to the process of oxidation, it is found that the oxide written with STM is apparently not proportional to the electron current, in contrast to results obtained with a beam of free electrons in an oxygen gas-environment. The dose needed to remove the hydrogen was determined as a function of electron energy. This dose is minimal for 100 eV electrons amounting to 4 mC/cm2
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