58,717 research outputs found
Universality of soft and collinear factors in hard-scattering factorization
Universality in QCD factorization of parton densities, fragmentation
functions, and soft factors is endangered by the process dependence of the
directions of Wilson lines in their definitions. We find a choice of directions
that is consistent with factorization and that gives universality between
e^+e^- annihilation, semi-inclusive deep-inelastic scattering, and the
Drell-Yan process. Universality is only modified by a time-reversal
transformation of the soft function and parton densities between Drell-Yan and
the other processes, whose only effect is the known reversal of sign for T-odd
parton densities like the Sivers function. The modifications of the definitions
needed to remove rapidity divergences with light-like Wilson lines do not
affect the results.Comment: 4 pages. Extra references. Text and references as in published
versio
A model-independent analysis of the dependence of the anomalous J/psi suppression on the number of participant nucleons
A recently published experimental dependence of the J/psi to Drell-Yan ratio
on the measured, by a zero degree calorimeter, forward energy E_ZDC in Pb+Pb
collisions at the CERN SPS is analyzed. Using a model-independent approach it
is shown that the data are at variance with an earlier published experimental
dependence of the same quantity on the transverse energy of neutral hadrons
E_T. The discrepancy is related to a moderate centrality region: 100 < N_p <
200 (N_p is the number of participant nucleons) and is peculiar only to the
data obtained within the `minimum bias' analysis (using the `theoretical
Drell-Yan'). This could result from systematic experimental errors in the
minimum bias sample. A possible source of the errors is discussed.Comment: 10 pages, LaTeX, 3 PS-figures. V2: Misprints are correcte
Polarized Drell-Yan at COMPASS-II: Transverse Spin Physics Program
Successful realization of polarized Drell-Yan physics program is one of the
main goals of the second stage of the COMPASS experiment. Drell-Yan
measurements with high energy (190 GeV/c) pion beam and transversely polarized
NH3 target have been initiated by a pilot-run in the October 2014 and will be
followed by 140 days of data taking in 2015. In the past twelve years COMPASS
experiment performed series of SIDIS measurements with high energy muon beam
and transversely polarized deuteron and proton targets. Results obtained for
Sivers effect and other target transverse spin dependent and unpolarized
azimuthal asymmetries in SIDIS serve as an important input for general
understanding of spin-structure of the nucleon and are being used in numerous
theoretical and phenomenological studies being carried out in the field of
transvers-spin physics. Measurement of the Sivers and all other azimuthal
effects in polarized Drell-Yan at COMPASS will reveal another side of the
spin-puzzle providing a link between SIDIS and Drell-Yan branches. This will be
a unique possibility to test universality and key-features of transverse
momentum dependent distribution functions (TMD PDFs) using essentially same
experimental setup and exploring same kinematic domain. In this review man
physics aspects of future COMPASS polarized Drell-Yan measurement of azimuthal
transverse spin asymmetries will be presented, giving a particular emphasis on
the link with very recent COMPASS results obtained for SIDIS transverse spin
asymmetries from four "Drell-Yan" -ranges.Comment: 6 pages, 7 plots. SPIN-2014, Beijing, China. arXiv admin note: text
overlap with arXiv:1411.156
A possible nuclear effect on the NuTeV sin^2 theta_W anomaly
We investigate a possible explanation for the NuTeV anomaly in terms of a
nuclear correction difference between u_v and d_v distributions. Analyzing deep
elastic scattering and Drell-Yan data for nuclear targets, we try to determine
the correction difference and its effect on the anomaly. We find that the
difference cannot be precisely determined at this stage due to the lack of data
which are sensitive to the difference. Therefore, it is difficult to draw a
solid conclusion about its effect although the anomaly could be explained, at
least partially, by this kind of nuclear correction.Comment: 3 pages, 1 figure, to be published in the proceedings of the XVIIth
Particles and Nuclei International Conference (PANIC), Santa Fe, New Mexico,
USA, October 24-28, 200
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