80 research outputs found
An explanation of the ABC enhancement in the dd -> alpha X reaction at intermediate energies
The dd -> alpha X reaction is studied in a model where each pair of nucleons
in the projectile and target deuterons undergoes pion production through the NN
-> d pi reaction. The condition that the two deuterons fuse to form an
alpha-particle then leads to peaks at small missing masses, the well-known ABC
enhancement, but also a broad structure around the maximum missing mass. With a
simplified input amplitude the model gives a quantitative description of both
the alpha-particle momentum and angular distributions for a deuteron beam
energy of 1250 MeV.Comment: 10 pages, Latex2e, 1 eps figure, submitted to Phys. Lett.
Planar box diagram for the (N_F = 1) 2-loop QED virtual corrections to Bhabha scattering
In this paper we present the master integrals necessary for the analytic
calculation of the box diagrams with one electron loop (N_{F}=1) entering in
the 2-loop (\alpha^3) QED virtual corrections to the Bhabha scattering
amplitude of the electron. We consider on-shell electrons and positrons of
finite mass m, arbitrary squared c.m. energy s, and momentum transfer t; both
UV and soft IR divergences are regulated within the continuous D-dimensional
regularization scheme. After a brief overview of the method employed in the
calculation, we give the results, for s and t in the Euclidean region, in terms
of 1- and 2-dimensional harmonic polylogarithms, of maximum weight 3. The
corresponding results in the physical region can be recovered by analytical
continuation. For completeness, we also provide the analytic expression of the
1-loop scalar box diagram including the first order in (D-4).Comment: Misprints in Eqs. (36), (38), (39), and (B.9) have been corrected.
The results are now available at http://pheno.physik.uni-freiburg.de/~bhabha,
as FORM input file
Two-Loop N_F=1 QED Bhabha Scattering Differential Cross Section
We calculate the two-loop virtual, UV renormalized corrections at order
\alpha^4 (N_F=1) in QED to the Bhabha scattering differential cross section,
for arbitrary values of the squared c.m. energy s and momentum transfer t, and
on-shell electrons and positrons of finite mass m. The calculation is carried
out within the dimensional regularization scheme; the remaining IR divergences
appear as polar singularities in (D-4). The result is presented in terms of 1-
and 2-dimensional harmonic polylogarithms, of maximum weight 3.Comment: 61 pages, 4 figures. Overall sign mistakes in some formulas in
appendix corrected, references adde
Two-Loop N_F =1 QED Bhabha Scattering: Soft Emission and Numerical Evaluation of the Differential Cross-section
Recently, we evaluated the virtual cross-section for Bhabha scattering in
pure QED, up to corrections of order alpha^4 (N_F =1). This calculation is
valid for arbitrary values of the squared center of mass energy s and momentum
transfer t; the electron and positron mass m was considered a finite, non
vanishing quantity. In the present work, we supplement the previous calculation
by considering the contribution of the soft photon emission diagrams to the
differential cross-section, up to and including terms of order alpha^4 (N_F=1).
Adding the contribution of the real corrections to the renormalized virtual
ones, we obtain an UV and IR finite differential cross-section; we evaluate
this quantity numerically for a significant set of values of the squared center
of mass energy s.Comment: 24 pages, 15 figures. Formulas in Appendix B corrected, changes in
Section 3, references adde
Extended sudden approximation model for high-energy nucleon removal reactions
A model based on the sudden approximation has been developed to describe high
energy single nucleon removal reactions. Within this approach, which takes as
its starting point the formalism of Hansen \cite{Anne2}, the nucleon-removal
cross section and the full 3-dimensional momentum distributions of the core
fragments including absorption, diffraction, Coulomb and nuclear-Coulomb
interference amplitudes, have been calculated. The Coulomb breakup has been
treated to all orders for the dipole interaction. The model has been compared
to experimental data for a range of light, neutron-rich psd-shell nuclei. Good
agreement was found for both the inclusive cross sections and momentum
distributions. In the case of C, comparison is also made with the
results of calculations using the transfer-to-the-continuum model. The
calculated 3-dimensional momentum distributions exhibit longitudinal and
transverse momentum components that are strongly coupled by the reaction for
s-wave states, whilst no such effect is apparent for d-waves. Incomplete
detection of transverse momenta arising fromlimited experimental acceptances
thus leads to a narrowing of the longitudinal distributions for nuclei with
significant s-wave valence neutron configurations, as confirmed by the data.
Asymmetries in the longitudinal momentum distributions attributed to
diffractive dissociation are also explored.Comment: 16 figures, submitted to Phys. Rev.
Two-loop QED Corrections to Bhabha Scattering
Recent developments in the calculation of the NNLO corrections to the Bhabha
scattering differential cross section in pure QED are briefly reviewed and
discussed.Comment: 5 pages, 4 figures, to appear in the proceedings of the 7th
International Symposium on Radiative Corrections (RADCOR05), Shonan Village,
Japan, 200
Radiative Decay Width Measurements of Neutral Kaon Excitations Using the Primakoff Effect
We produce a sample consisting of 147 candidate events, with minimal
backgrounds, of the mixed axial vector pair K1(1270)-K1(1400) by exciting Kl's
in the Coulomb field of lead and report the first measurements of the radiative
widths Gamma_r(K1(1400)) = 280.8+-23.2(stat)+-40.4(syst) keV and
Gamma_r(K1(1270)) = 73.2+- 6.1(stat)+-28.3(syst) keV. We also place 90% CL
upper limits Gamma_r(K*(1410)) < 52.9 keV for the vector state and
Gamma_r(K2*(1430)) < 5.4 keV for the tensor state. These measurements allow for
significant tests of quark-model predictions of radiative widths for the
low-lying vector mesons.Comment: PRL-size article, 4 figure
The non-pathogenic mycobacteria M. smegmatis and M. fortuitum induce rapid host cell apoptosis via a caspase-3 and TNF dependent pathway
<p>Abstract</p> <p>Background</p> <p>The HIV pandemic raised the potential for facultative-pathogenic mycobacterial species like, <it>Mycobacterium kansasii</it>, to cause disseminating disease in humans with immune deficiencies. In contrast, non-pathogenic mycobacterial species, like <it>M. smegmatis</it>, are not known to cause disseminating disease even in immunocompromised individuals. We hypothesized that this difference in phenotype could be explained by the strong induction of an innate immune response by the non-pathogenic mycobacterial species.</p> <p>Results</p> <p>A comparison of two rapid-growing, non-pathogenic species (<it>M. smegmatis </it>and <it>M. fortuitum</it>) with two facultative-pathogenic species (<it>M. kansasii </it>and <it>M. bovis </it>BCG) demonstrated that only the non-pathogenic bacteria induced strong apoptosis in human THP-1 cells and murine bone marrow-derived macrophages (BMDM) and dendritic cells (BMDD). The phospho-<it>myo</it>-inositol modification of lipoarabinomannan (PI-LAM) isolated from non-pathogenic species may be one of the cell wall components responsible for the pro-inflammatory activity of the whole bacteria. Indeed, PI-LAM induces high levels of apoptosis and IL-12 expression compared to the mannosyl modification of LAM isolated from facultative-pathogenic mycobacteria. The apoptosis induced by non-pathogenic <it>M. smegmatis </it>was dependent upon caspase-3 activation and TNF secretion. Consistently, BALB/c BMDM responded by secreting large amounts of TNF upon infection with non-pathogenic but not facultative-pathogenic mycobacteria. Interestingly, C57Bl/6 BMDM do not undergo apoptosis upon infection with non-pathogenic mycobacteria despite the fact that they still induce an increase in TNF secretion. This suggests that the host cell signaling pathways are different between these two mouse genotypes and that TNF is necessary but not sufficient to induce host cell apoptosis.</p> <p>Conclusion</p> <p>These results demonstrate a much stronger induction of the innate immune response by non-pathogenic versus facultative-pathogenic mycobacteria as measured by host cell apoptosis, IL-12 and TNF cytokine induction. These observations lend support to the hypothesis that the strong induction of the innate immune response is a major reason for the lack of pathogenicity in fast-growing mycobacteria.</p
A review of the optical properties of alloys and intermetallics for plasmonics
Alternative materials are required to enhance the efficacy of plasmonic
devices. We discuss the optical properties of a number of alloys, doped metals,
intermetallics, silicides, metallic glasses and high pressure materials. We
conclude that due to the probability of low frequency interband transitions,
materials with partially occupied d-states perform poorly as plasmonic
materials, ruling out many alloys, intermetallics and silicides as viable. The
increased probability of electron-electron and electron-phonon scattering rules
out many doped and glassy metals.Comment: 26 pages, 10 figures, 3 table
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