156 research outputs found
QCD coupling constant value and deep inelastic measurements
We reanalyze deep inelastic scattering data of BCDMS Collaboration by
including proper cuts of ranges with large systematic errors. We perform also
the fits of high statistic deep inelastic scattering data of BCDMS, SLAC, NM
and BFP Collaborations taking the data separately and in combined way and find
good agreement between these analyses. We extract the values of the QCD
coupling constant \alpha_s(M^2_Z) up to NLO level.Comment: 7 pages, 4 figures, latex. Talk presented at the 5-th International
Conference "Renormalization Group 2002", High Tatras, Slovakia, March 200
A systematic study of QCD coupling constant from deep inelastic measurements
We reanalyze deep inelastic scattering data of BCDMS Collaboration by
including proper cuts of ranges with large systematic errors. We perform also
the fits of high statistic deep inelastic scattering data of BCDMS, SLAC, NM
and BFP Collaborations taking the data separately and in combined way and find
good agreement between these analyses. We extract the values of both the QCD
coupling constant \alpha_s(M^2_Z) up to NLO level and of the power corrections
to the structure function F_2. The fits of the combined data for the nonsinglet
part of the structure function F_2 predict the coupling constant value
\alpha_s(M^2_Z) = 0.1174 \pm 0.0007 (stat) \pm 0.0019 (syst) \pm 0.0010
(normalization) (or QCD parameter \Lambda^{(5)}_{MSbar} = 204 \pm 25 (total
exper.err.) MeV). The fits of the combined data for both: the nonsinglet part
and the singlet one, lead to the values \alpha_s(M^2_Z) = 0.1177 \pm 0.0007
(stat) \pm 0.0021 (syst) \pm 0.0009 (normalization) (or QCD parameter
\Lambda^{(5)}_{MSbar} = 208 \pm 27 (total exper.err.) MeV). Both above values
are in very good agreement with each other. We estimate theoretical
uncertainties for \alpha_s(M^2_Z) as +0.0047 and -0.0057 from fits of the
combine data, when complete singlet and nonsinglet Q^2 evolution is taken into
account.Comment: 47 pages, 14 figures, late
Transverse-target-spin asymmetry in exclusive -meson electroproduction
Hard exclusive electroproduction of mesons is studied with the
HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and
electron beams off a transversely polarized hydrogen target. The amplitudes of
five azimuthal modulations of the single-spin asymmetry of the cross section
with respect to the transverse proton polarization are measured. They are
determined in the entire kinematic region as well as for two bins in photon
virtuality and momentum transfer to the nucleon. Also, a separation of
asymmetry amplitudes into longitudinal and transverse components is done. These
results are compared to a phenomenological model that includes the pion pole
contribution. Within this model, the data favor a positive
transition form factor.Comment: DESY Report 15-14
Longitudinal double-spin asymmetries in semi-inclusive deep-inelastic scattering of electrons and positrons by protons and deuterons
A comprehensive collection of results on longitudinal double-spin asymmetries is presented for charged pions and kaons produced in semi-inclusive deep-inelastic scattering of electrons and positrons on the proton and deuteron, based on the full HERMES data set. The dependence of the asymmetries on hadron transverse momentum and azimuthal angle extends the sensitivity to the flavor structure of the nucleon beyond the distribution functions accessible in the collinear framework. No strong dependence on those variables is observed. In addition, the hadron charge-difference asymmetry is presented, which under certain model assumptions provides access to the helicity distributions of valence quarks
Bose-Einstein correlations in hadron-pairs from lepto-production on nuclei ranging from hydrogen to xenon
Bose-Einstein correlations of like-sign charged hadrons produced in
deep-inelastic electron and positron scattering are studied in the HERMES
experiment using nuclear targets of H, H, He, He, N, Ne, Kr,
and Xe. A Gaussian approach is used to parametrize a two-particle correlation
function determined from events with at least two charged hadrons of the same
sign charge. This correlation function is compared to two different empirical
distributions that do not include the Bose-Einstein correlations. One
distribution is derived from unlike-sign hadron pairs, and the second is
derived from mixing like-sign pairs from different events. The extraction
procedure used simulations incorporating the experimental setup in order to
correct the results for spectrometer acceptance effects, and was tested using
the distribution of unlike-sign hadron pairs. Clear signals of Bose-Einstein
correlations for all target nuclei without a significant variation with the
nuclear target mass are found. Also, no evidence for a dependence on the
invariant mass W of the photon-nucleon system is found when the results are
compared to those of previous experiments
Flavor decomposition of the sea quark helicity distributions in the nucleon from semi-inclusive deep-inelastic scattering
Double-spin asymmetries of semi-inclusive cross sections for the production
of identified pions and kaons have been measured in deep-inelastic scattering
of polarized positrons on a polarized deuterium target. Five helicity
distributions including those for three sea quark flavors were extracted from
these data together with re-analyzed previous data for identified pions from a
hydrogen target. These distributions are consistent with zero for all three sea
flavors. A recently predicted flavor asymmetry in the polarization of the light
quark sea appears to be disfavored by the data.Comment: 5 pages, 3 figure
First Measurement of the Tensor Structure Function of the Deuteron
The \Hermes experiment has investigated the tensor spin structure of the
deuteron using the 27.6 GeV/c positron beam of \Hera. The use of a tensor
polarized deuteron gas target with only a negligible residual vector
polarization enabled the first measurement of the tensor asymmetry \At and
the tensor structure function \bd for average values of the Bj{\o}rken
variable and of the squared four-momentum transfer . The quantities \At and \bd are found to be
non-zero. The rise of \bd for decreasing values of can be interpreted to
originate from the same mechanism that leads to nuclear shadowing in
unpolarized scattering
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