260 research outputs found
High-temperature oxidation of nuclear graphite with account of movement of the surface layer of oxidator
At high-temperature oxidation of nuclear graphite, the oxidant flow in the near-surface region is taken into account. Macro- and microscopic modeling of the oxidation of the near-surface layer was carried out. The calculation of the diffusion coefficient of gaseous components as a function of temperature and concentration is given. The influence of the motion of the surface layer of the oxidizer on the concentration of gaseous components is studied.При високотемпературному окисленні ядерного графіту врахований потік окислювача в приповерхневій області. Проведено макро- і мікроскопічне моделювання окислення приповерхневого шару. Наведено розрахунок коефіцієнта дифузії газоподібних компонент у залежності від температури і концентрації. Досліджено вплив обліку руху приповерхневого шару окислювача на концентрацію газоподібних компонентів.При высокотемпературном окислении ядерного графита учтен поток окислителя в приповерхностной области. Проведено макро- и микроскопическое моделирование окисления приповерхностного слоя. Приведен расчет коэффициента диффузии газообразных компонент в зависимости от температуры и концентрации. Исследовано влияние учета движения приповерхностного слоя окислителя на концентрацию газообразных компонентов
Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs
We present a determination of the gluon polarization Delta G/G in the
nucleon, based on the helicity asymmetry of quasi-real photoproduction events,
Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final
state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV
polarized muon beam scattered on a polarized 6-LiD target. The helicity
asymmetry for the selected events is = 0.002 +- 0.019(stat.) +-
0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta
G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3
(GeV}/c)^2.Comment: 10 pages, 3 figure
Measurement of the Spin Structure of the Deuteron in the DIS Region
We present a new measurement of the longitudinal spin asymmetry A_1^d and the
spin-dependent structure function g_1^d of the deuteron in the range 1 GeV^2 <
Q^2 < 100 GeV^2 and 0.004< x <0.7. The data were obtained by the COMPASS
experiment at CERN using a 160 GeV polarised muon beam and a large polarised
6-LiD target. The results are in agreement with those from previous experiments
and improve considerably the statistical accuracy in the region 0.004 < x <
0.03.Comment: 10 pages, 6 figures, subm. to PLB, revised: author list, Fig. 4,
details adde
Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2
We present a precise measurement of the deuteron longitudinal spin asymmetry
A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1
GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS
experiment at CERN during the years 2002 and 2003. The statistical precision is
tenfold better than that of the previous measurement in this region. The
measured A_1^d and g_1^d are found to be consistent with zero in the whole
range of x.Comment: 17 pages, 10 figure
Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering
First measurements of azimuthal asymmetries in hadron-pair production in
deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron)
and NH_3 (proton) targets are presented. The data were taken in the years
2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c
at the CERN SPS. The asymmetries provide access to the transversity
distribution functions, without involving the Collins effect as in single
hadron production. The sizeable asymmetries measured on the NH_ target indicate
non-vanishing u-quark transversity and two-hadron interference fragmentation
functions. The small asymmetries measured on the ^6LiD target can be
interpreted as indication for a cancellation of u- and d-quark transversities.Comment: 13 pages, 4 figures, updated to the published versio
The Spin-dependent Structure Function of the Proton g_1^p and a Test of the Bjorken Sum Rule
The inclusive double-spin asymmetry, A_1^p, has been measured at COMPASS in
deepinelastic polarised muon scattering off a large polarised NH3 target. The
data, collected in the year 2007, cover the range Q2 > 1 (GeV/c)^2, 0.004 < x <
0.7 and improve the statistical precision of g_1^p(x) by a factor of two in the
region x < 0.02. The new proton asymmetries are combined with those previously
published for the deuteron to extract the non-singlet spin-dependent structure
function g_1^NS(x,Q2). The isovector quark density, Delta_q_3(x,Q2), is
evaluated from a NLO QCD fit of g_1^NS. The first moment of Delta_q3 is in good
agreement with the value predicted by the Bjorken sum rule and corresponds to a
ratio of the axial and vector coupling constants g_A/g_V =
1.28+-0.07(stat)+-0.10(syst).Comment: 12 pages, 5 figure
Leading order determination of the gluon polarisation from DIS events with high-p_T hadron pairs
We present a determination of the gluon polarisation Delta g/g in the
nucleon, based on the longitudinal double-spin asymmetry of DIS events with a
pair of large transverse-momentum hadrons in the final state. The data were
obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon
beam scattering off a polarised ^6LiD target. The gluon polarisation is
evaluated by a Neural Network approach for three intervals of the gluon
momentum fraction x_g covering the range 0.04 < x_g < 0.27. The values obtained
at leading order in QCD do not show any significant dependence on x_g. Their
average is Delta g/g = 0.125 +/- 0.060 (stat.) +/- 0.063 (syst.) at x_g=0.09
and a scale of mu^2 = 3 (GeV/c)^2.Comment: 13 pages, 6 figures and 3 table
Measurement of the Collins and Sivers asymmetries on transversely polarised protons
The Collins and Sivers asymmetries for charged hadrons produced in deeply
inelastic scattering on transversely polarised protons have been extracted from
the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At
large values of the Bjorken x variable non-zero Collins asymmetries are
observed both for positive and negative hadrons while the Sivers asymmetry for
positive hadrons is slightly positive over almost all the measured x range.
These results nicely support the present theoretical interpretation of these
asymmetries, in terms of leading-twist quark distribution and fragmentation
functions.Comment: 9 Pages, 5 figure
Exclusive rho^0 muoproduction on transversely polarised protons and deuterons
The transverse target spin azimuthal asymmetry A_UT in hard exclusive
production of rho^0 mesons was measured at COMPASS by scattering 160 GeV/c
muons off transversely polarised protons and deuterons. The measured asymmetry
is sensitive to the nucleon helicity-flip generalised parton distributions E^q,
which are related to the orbital angular momentum of quarks in the nucleon. The
Q^2, x_B and p_t^2 dependence of A_UT is presented in a wide kinematic range.
Results for deuterons are obtained for the first time. The measured asymmetry
is small in the whole kinematic range for both protons and deuterons, which is
consistent with the theoretical interpretation that contributions from GPDs E^u
and E^d approximately cancel.Comment: 20 pages, 9 figures and 4 tables, updated author lis
Quark helicity distributions from longitudinal spin asymmetries in muon-proton and muon-deuteron scattering
Double-spin asymmetries for production of charged pions and kaons in
semi-inclusive deep-inelastic muon scattering have been measured by the COMPASS
experiment at CERN. The data, obtained by scattering a 160 GeV muon beam off a
longitudinally polarised NH_3 target, cover a range of the Bjorken variable x
between 0.004 and 0.7. A leading order evaluation of the helicity distributions
for the three lightest quarks and antiquark flavours derived from these
asymmetries and from our previous deuteron data is presented. The resulting
values of the sea quark distributions are small and do not show any sizable
dependence on x in the range of the measurements. No significant difference is
observed between the strange and antistrange helicity distributions, both
compatible with zero. The integrated value of the flavour asymmetry of the
helicity distribution of the light-quark sea, \Delta u-bar - \Delta d-bar, is
found to be slightly positive, about 1.5 standard deviations away from zero.Comment: 13 pages, 5 figure
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