71 research outputs found
Next-to-leading order QCD corrections to inclusive-hadron photoproduction in polarized lepton-proton collisions
We calculate the next-to-leading order QCD corrections to the `direct' part
of the spin-dependent cross section for single-inclusive charged-hadron
photoproduction. This process could be studied experimentally in future
polarized fixed-target lepton-nucleon experiments, but also at the HERA ep
collider after an upgrade to both beams being polarized. We present a brief
numerical evaluation of our results by studying the K-factors and the scale
dependence of the NLO cross section.Comment: 25 Pages, LaTeX, 4 figures as eps file
Radiation of single photons from collisions at the CERN SPS and quark hadron phase transition
The production of single photons in collisions at the CERN SPS as
measured by the WA98 experiment is analysed. A quark gluon plasma is assumed to
be formed initially, which expands, cools, hadronizes, and undergoes
freeze-out. A rich hadronic equation of state is used and the transverse
expansion of the interacting system is taken into account. The recent estimates
of photon production in quark-matter (at two loop level) along with the
dominant reactions in the hadronic matter leading to photons are used. About
50% of the single photons are seen to have a thermal origin. An addition of the
thermal and prompt photons is seen to provide a very good description of the
data. Most of the thermal photons having large transverse momenta arise from
the quark-matter, which contributes dominantly through the mechanism of
annihilation of quarks with scattering, and which in turn is possible only in a
hot and dense plasma of quarks and gluons. The results thus confirm the
formation of quark gluon plasma and the existence of this mechanism of the
production of single photons.Comment: 6 pages including 3 figures. Corrected 2-loop rates for photons are
use
Experimental investigation of transverse spin asymmetries in muon-p SIDIS processes: Collins asymmetries
The COMPASS Collaboration at CERN has measured the transverse spin azimuthal
asymmetry of charged hadrons produced in semi-inclusive deep inelastic
scattering using a 160 GeV positive muon beam and a transversely polarised NH_3
target. The Collins asymmetry of the proton was extracted in the Bjorken x
range 0.003<x<0.7. These new measurements confirm with higher accuracy previous
measurements from the COMPASS and HERMES collaborations, which exhibit a
definite effect in the valence quark region. The asymmetries for negative and
positive hadrons are similar in magnitude and opposite in sign. They are
compatible with model calculations in which the u-quark transversity is
opposite in sign and somewhat larger than the d-quark transversity distribution
function. The asymmetry is extracted as a function of Bjorken , the relative
hadron energy and the hadron transverse momentum p_T^h. The high statistics
and quality of the data also allow for more detailed investigations of the
dependence on the kinematic variables. These studies confirm the leading-twist
nature of the Collins asymmetry.Comment: 11 pages, 5 figure
Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering
We have measured the spin-dependent structure function in inclusive
deep-inelastic scattering of polarized muons off polarized protons, in the
kinematic range and . A
next-to-leading order QCD analysis is used to evolve the measured
to a fixed . The first moment of at is .
This result is below the prediction of the Ellis-Jaffe sum rule by more than
two standard deviations. The singlet axial charge is found to be . In the Adler-Bardeen factorization scheme, is
required to bring in agreement with the Quark-Parton Model. A
combined analysis of all available proton and deuteron data confirms the
Bjorken sum rule.Comment: 33 pages, 22 figures, uses ReVTex and smc.sty. submitted to Physical
Review
A new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target
New high precision measurements of the Collins and Sivers asymmetries of
charged hadrons produced in deep-inelastic scattering of muons on a
transversely polarised 6LiD target are presented. The data were taken in 2003
and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at
160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible
with zero, within the present statistical errors, which are more than a factor
of 2 smaller than those of the published COMPASS results from the 2002 data.
The final results from the 2002, 2003 and 2004 runs are compared with naive
expectations and with existing model calculations.Comment: 40 pages, 28 figure
UVA/UVA1 phototherapy and PUVA photochemotherapy in connective tissue diseases and related disorders: a research based review
BACKGROUND: Broad-band UVA, long-wave UVA1 and PUVA treatment have been described as an alternative/adjunct therapeutic option in a number of inflammatory and malignant skin diseases. Nevertheless, controlled studies investigating the efficacy of UVA irradiation in connective tissue diseases and related disorders are rare. METHODS: Searching the PubMed database the current article systematically reviews established and innovative therapeutic approaches of broad-band UVA irradiation, UVA1 phototherapy and PUVA photochemotherapy in a variety of different connective tissue disorders. RESULTS: Potential pathways include immunomodulation of inflammation, induction of collagenases and initiation of apoptosis. Even though holding the risk of carcinogenesis, photoaging or UV-induced exacerbation, UVA phototherapy seems to exhibit a tolerable risk/benefit ratio at least in systemic sclerosis, localized scleroderma, extragenital lichen sclerosus et atrophicus, sclerodermoid graft-versus-host disease, lupus erythematosus and a number of sclerotic rarities. CONCLUSIONS: Based on the data retrieved from the literature, therapeutic UVA exposure seems to be effective in connective tissue diseases and related disorders. However, more controlled investigations are needed in order to establish a clear-cut catalogue of indications
Largest ancient fortress of South-West Asia and the western world?:Recent fieldwork at Sasanian Qaleh Iraj at Pishva, Iran
The article presents recent works at Qale Iraj, near Varamin, Iran. My short contribution is on the Middle Persian ostraka found at the site
Collins and Sivers asymmetries for pions and kaons in muon-deuteron DIS
The measurements of the Collins and Sivers asymmetries of identified hadrons
produced in deep-inelastic scattering of 160 GeV/c muons on a transversely
polarised 6LiD target at COMPASS are presented. The results for charged pions
and charged and neutral kaons correspond to all data available, which were
collected from 2002 to 2004. For all final state particles both the Collins and
Sivers asymmetries turn out to be small, compatible with zero within the
statistical errors, in line with the previously published results for not
identified charged hadrons, and with the expected cancellation between the u-
and d-quark contributions.Comment: 16 pages, 9 figures, added author Efremov, calculated pure kaon
asymmetries instead of those for experimental kaon/pion mixture (mainly error
affected
Theory of hard photoproduction
The present theoretical knowledge about photons and hard photoproduction
processes, i.e. the production of jets, light and heavy hadrons, quarkonia, and
prompt photons in photon-photon and photon-hadron collisions, is reviewed.
Virtual and polarized photons and prompt photon production in hadron collisions
are also discussed. The most important leading and next-to-leading order QCD
results are compiled in analytic form. A large variety of numerical predictions
is compared to data from TRISTAN, LEP, and HERA and extended to future electron
and muon colliders. The sources of all relevant results are collected in a rich
bibliography.Comment: Habilitationsschrift, scheduled for publication in Rev. Mod. Phys.,
126 pages, 61 figure
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