QCD analysis of DIS and SIDIS data

The combined analysis of polarized DIS and SIDIS data is performed in NLO QCD using two alternative procedures: standard fitting procedure and the recently developed direct new method. The results from two methods are compared. The especial attention is paid to the light sea and strange PDFs.     

A QCD analysis of diffractive deep-inelastic scattering data

We perform a novel type of analysis of diffractive deep-inelastic scattering data, in which the input parton distributions of the pomeron are parameterised using the perturbative QCD expressions. In particular, we treat individually the components of the pomeron of different size. We are able to describe simultaneously both the recent ZEUS and H1 diffractive data. In addition to the usual two-gluon model for the perturbative pomeron, we allow for the possibility that it may be made from two sea quarks.Received: 12 July 2004, Revised: 3 September 2004, Published online: 24 September 2004     

QCD analysis of the semi-inclusive COMPASS and HERMES data

The first moments of polarized valence parton distribution functions truncated to the wide Bjorken x region 0.004 < x < 0.7 are directly (without any fitting procedure) extracted in the NLO QCD from combined semi-inclusive DIS data of COMPASS and HERMES collaborations. Two scenarios for fragmentation functions are considered. Applying the proposed original procedure to these results we estimate the contributions of sea u and d quarks to the proton spin, which turn out to be simply zero within the errors.     

QCD asymmetry and polarized hadron structure function measurement

It is shown that in hard processes with a single polarized particle contributions proportional to two-arguments distribution functions (parton correlation densities) can receive imaginary parts even from the Born subprocess. This results in large (not proportional to α_s) single asymmetries. Such an asymmetry is calculated in the process λN↑ → λX, which can serve as a good parton meter for the correlation densities.     

QCD versus recent experimental data on lepton pair production at accelerator energies

New and precise experimental results on Drell-Yan pair production at accelerator energies are now available, both in π^? andp-nucleus interactions. These data are analyzed within the QCD framework including soft gluon resummation. It is shown that a quantitative agreement of the theory with experimental data can be reasonably managed. In particular, the soft gluon resummation is shown to build up nicely the so-calledK-factor. The pion formfactor is deduced from experimental data, but is rather sensitive to the nuclear structure functions we use. Definite nuclear structure functions are needed.     

QCD analysis of DIS and SIDIS data with two alternative methods

The global fit analysis of all published data on DIS and semi-inclusive DIS (SIDIS) asymmetries is performed in the next to leading (NLO) QCD order. The respective parameterization on polarized PDFs is constructed. The especial attention is paid to the impact of novel SIDIS data on the polarized distributions of light sea and strange quarks as well as on the polarized gluon distributions. The first moments of these distributions entering the nucleon spin are found to be surprisingly small quantities. The alternative direct (free of any fitting procedure) method of NLO QCD analysis is elaborated. Method is especially important for analysis of SIDIS data because it allows to avoid the problems arising in the conventional fitting procedure: functional arbitrariness at initial scale and ambiguities in the error band calculation. Within the alternative method the central values and uncertainties of the measured asymmetries directly propagate to the central values and uncertainties of the polarized PDFs we are interested in. The method is applied to all existing SIDIS data on pion production for an estimation in NLO QCD of the valence and sea quark contributions to the proton spin. As a result one arrives at the conclusion that, contrary to the valence contributions, the sea contributions to the proton spin are compatible with zero within the errors.     

A QCD analysis of HERA and fixed target structure function data

The parton momentum density distributions of the proton are determined from a next-to-leading order QCD analysis of structure functions measured at HERA and by fixed target experiments. Also included are data on the difference of the up and down anti-quark distributions. The uncertainties in the parton densities, structure functions and related cross sections are estimated from the experimental errors and those on the input parameters of the fit. Several QCD predictions based on the parton densities obtained from this analysis are calculated and compared to data. Received: 21 December 1999 / Published online: 6 April 2000     

QCD vacuum tensor susceptibility and properties of transversely polarized mesons

We re-estimate the tensor susceptibility of the QCD vacuum, , and to this end, we re-estimate the tensor coupling constants for the transversely polarized -, - and -mesons. The origin of the susceptibility is analyzed using (anti-)duality between the - and - channels in the 2-point correlator of the tensor currents. We conclude that the origin of the differences in - and -meson masses and tensor couplings is the (anti-)duality breakdown in QCD due to the 4-quark condensate. We confirm the results of Govaerts et al. for the 2-point correlator of the tensor currents and disagree with Belyaev and Oganesyan on both the OPE expansion and the value of the QCD vacuum tensor susceptibility. Using our value for the latter we determine new estimations of the nucleon tensor charges related to the first moment of the transverse structure function of a nucleon. Received: 17 May 2000 / Published online: 9 August 2000     

Results from a QCD analysis of the new deep inelastic scattering data

Results from a numerical evolution of the Altarelli-Parisi equations are presented, covering the full range 0<x<1. The predictions of leading order and next-to-leading order in perturbative QCD, are compared with the most precise currently available data. All necessary assumptions are quantitatively discussed.     

Nuclear size and rapidity dependence of the saturation scale from QCD evolution and experimental data

The solutions of the Balitsky-Kovchegov evolution equations are studied numerically and compared with known analytical estimations. The rapidity and nuclear size dependences of the saturation scale are obtained for the cases of fixed and running coupling constant. These same dependences are studied in experimental data, on lepton-nucleus, deuteron-nucleus and nucleus-nucleus collisions, through geometric scaling and compared with the theoretical calculations.Arrival of the final proofs: 18 March 2005PACS: 12.38.Bx - 13.60.Hb - 12.38.CyJoint contribution to the proceedings of the Hard Probes 2004 Conference based on the oral presentations by J.G. Milhano and C.A. Salgado     

QCD higher-order effects in polarized electroproduction: Flavour singlet coefficient functions

the QCD corrections of order g^?2 to the coefficient functions in polarized electroproduction are calculated for the flavour singlet part. The full g^?2 corrections to the sum rule corresponding to the first moment of the structure functions are also discussed. In the singlet case there appears the Adler-Bell-Jackiw anomaly which forces the relevant anomalous dimension to be non-zero. Thus the form of the corrections in the singlet part is different from that in the non-singlet part. Their magnitude turns out to depend on the number of flavours.     

QCD effects in semi-inclusive deep inelastic scattering from a polarized target

The next-to-leading logarithmic corrections to cross-sections for semi-inclusive deep inelastic scattering from a polarized target are worked out. Predictions for pion asymmetries and pion charge ratios are given.     

Top-quark pair production via polarized and unpolarized protons in the supersymmetric QCD

The QCD corrections to the top-quark pair production via both polarized and unpolarized gluon fusion in pp collisions are calculated in the minimal supersymmetric model (MSSM). We find that the MSSM QCD corrections can reach 4% and may be observable in future precise experiments. Furthermore, we studied CP violation in the MSSM. Our results show that the CP-violating parameter is sensitive to the masses of SUSY particles (it becomes zero when the c.m. energy is less than twice the masses of both the gluino and the stop quarks) and may reach . Received: 30 September 1998 / Revised version: 21 January 1999 / Published online: 28 May 1999     

An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment

The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e ⁺ and e^- beams, together with differential cross-section data on inclusive jet production in e ⁺ p scattering and dijet production in scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet-production data constrains the gluon and allows an accurate extraction of at NLO; An additional uncertainty from the choice of scales is estimated as . This is the first extraction of from HERA data alone.     

Recurrence analysis of quasiperiodicity in experimental fluid data

We propose a procedure to analyze experimental data which exhibit different dynamical regimes, namely, periodicity, chaoticity and quasiperiodicity by means of Recurrence Plots (RPs). We show that, based on the recurrence properties captured by RPs, we are able to characterize successfully the type of dynamics. This approach is particularly useful for detecting the existence of quasiperiodic motion in short time series. We show the capability and validity of this method by analyzing time series from fluid experiments.     

Interpreting data from polarized proton beams

The reactions pp → pp and pp → Δ⁺⁺n with polarized beam and/or polarized target are currently under investigation at the Argonne ZGS. We discuss how to interpret various measured quantities in terms of amplitudes whose behavior is familiar (as functions of s, t). For pp total cross sections and elastic scattering, Argonne measurements will yield Im ?₂ (s,t = 0) and the rather complicated combination $\text{2|?}{}_5\text{|}{}^2\text{+}\text{Re}\text{(?}{}_1\text{?}{}_2{}^1\text{? ?}{}_3\text{?}{}_4{}^1\text{)}$, where ?_i (i = 1, … 5) are conventional s-channel helicity amplitudes. The forward direction (t = 0) is of special interest. We find that for both pp → pp and pp → Δ⁺⁺n, polarized beam — polarized target experiments plus the rather general (testable) assumption that amplitudes with the same s-channel helicity flip quantum numbers are proportional, are sufficient to fully determine all non-vanishing amplitudes at t = 0. Numerical estimates of some observables, based on calculations in a specific model, are also given.     

Determination of QCD condensates from τ decay data

We have used the latest data from the ALEPH Collaboration to extract values for QCD condensates up to dimension d=12 in the V-A channel and up to dimension d=8 in the V, A and V+A channels. Performing two- and three-parameter fits, we obtain new results for the correlations of condensates. The results are consistent and agree with most of the previous results found in the literature.