arXiv subjects

M. Osipenko

Publications and source records attributed to M. Osipenko.

At least 91 records · Page 5Linked to original sources

arXiv2009

Measurement of unpolarized semi-inclusive pi+ electroproduction off the proton

Semi-inclusive pi+ electroproduction on protons has been measured with the CLAS detector at Jefferson Lab. The measurement was performed on a liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold differential cross sections were measured over a wide kinematic range including the complete range of azimuthal angles between hadronic and leptonic planes, phi, enabling us to separate the phi-dependent terms. Our measurements of phi-independent term of the cross section at low Bjorken x were found to be in fairly good agreement with pQCD calculations. Indeed, the conventional current fragmentation calculation can account for almost all of the observed cross section, even at small pi+ momentum. The measured center-of-momentum spectra are in qualitative agreement with high energy data, which suggests a surprising numerical similarity between the spectator diquark fragmentation in the present reaction and the anti-quark fragmentation measured in e+e- collisions. We have observed that the two phi-dependent terms of the cross section are small. Within our precision the cos(2phi) term is compatible with zero, except for low-z region, and the measured cos(phi) term is much smaller in magnitude than the sum of the Cahn and Berger effects.

hep-ex↗

arXiv2009

Lowest order QED radiative corrections to five-fold differential cross section of hadron leptoproduction

The contribution of exclusive radiative tail to the cross section of semi-inclusive hadron leptoproduction has been calculated exactly for the first time. Although the experience of inclusive data analyses suggests us that the contribution of radiative tail from the elastic peak is of particular importance, similar effects in the semi-inclusive process were only recently estimated in the peaking approximation. The explicit expressions for the lepton part of the lowest order QED contribution of exclusive radiative tail to the five-fold differential cross section are obtained and discussed. Numerical estimates, provided within Jefferson Lab kinematic conditions, demonstrate rather large effects of the exclusive radiative tail in the region at semi-inclusive threshold and for high energy of detected hadron.

hep-ph↗

arXiv2007

Structure Function Moments of Proton and Neutron

QCD-inspired phenomenological analysis of experimental moments of proton and deuteron structure functions F2 have been presented. The obtained results on the d/u ratio at large-x, isospin dependence of higher twists and comparison with Lattice QCD calculations were discussed. We remind shortly these results: the obtained ratio is consistent with the asymptotic limit d/u-->0 at x-->1, the total contribution of higher twists is found to be isospin independent and the non-singlet moments are in excellent agreement with the Lattice data. We present here some details of the analysis triggered by the public discussion.

hep-ph↗

arXiv2006

Neutron structure function moments at leading twist

The experimental data on F2 structure functions of the proton and deuteron were used to construct their moments. In particular, recent measurements performed with CLAS detector at Jefferson Lab allowed to extend our knowledge of structure functions in the large-x region. The phenomenological analysis of these experimental moments in terms of the Operator Product Expansion permitted to separate the leading and higher twist contributions. Applying nuclear corrections to extracted deuteron moments we obtained the contribution of the neutron. Combining leading twist moments of the neutron and proton we found d/u ratio at x->1 approaching 0, although 1/5 value could not be excluded. The twist expansion analysis suggests that the contamination of higher twists influences the extraction of the d/u ratio at x->1 even at Q2-scale as large as 12 (GeV/c)^2.

hep-ph↗

arXiv2006

Elastic and Resonance contributions to moments of the proton structure function F2

We discuss the role of nucleon and its excited state poles in the twist expansion of the nucleon structure function moments. We find that the nucleon pole contribution was overestimated in previous analyses by a factor of two. Inclusion of this missing factor makes the duality appear for all moments at least down to Q2=1 GeV2. For resonance poles the time reversal invariance together with unitarity demand at least four of them in the forward Compton scattering amplitude. These poles as well as the elastic pole can be propagated separately through the standard Operator Product Expansion derivation for DIS. This part of the amplitude gives a coherent, positive, higher twist contribution, which can be singled out of the total and compared with the remaining one given mostly by threshold effects. A comparison of the estimated resonance contribution to the data on structure function moments allows to test large-Q2 behavior of proton-resonance transition form-factors.

hep-ph↗

arXiv2006

Experimental moments of the nucleon structure function F2

Experimental data on the F2 structure functions of the proton and deuteron, including recent results from CLAS at Jefferson Lab, have been used to construct their n<=12 moments. A comprehensive analysis of the moments in terms of the operator product expansion has been performed to separate the moments into leading and higher twist contributions. Particular attention was paid to the issue of nuclear corrections in the deuteron, when extracting the neutron moments from data. The difference between the proton and neutron moments was compared directly with lattice QCD simulations. Combining leading twist moments of the neutron and proton we found the d/u ratio at x->1 approaching 0, although the precision of the data did not allow to exclude the 1/5 value. The higher twist components of the proton and neutron moments suggest that multi-parton correlations are isospin independent.

hep-ph↗

arXiv2006

Measurement of the Deuteron Structure Function F2 in the Resonance Region and Evaluation of Its Moments

Inclusive electron scattering off the deuteron has been measured to extract the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement covers the entire resonance region from the quasi-elastic peak up to the invariant mass of the final-state hadronic system W~2.7 GeV with four-momentum transfers Q2 from 0.4 to 6 (GeV/c)^2. These data are complementary to previous measurements of the proton structure function F2 and cover a similar two-dimensional region of Q2 and Bjorken variable x. Determination of the deuteron F2 over a large x interval including the quasi-elastic peak as a function of Q2, together with the other world data, permit a direct evaluation of the structure function moments for the first time. By fitting the Q2 evolution of these moments with an OPE-based twist expansion we have obtained a separation of the leading twist and higher twist terms. The observed Q2 behaviour of the higher twist contribution suggests a partial cancellation of different higher twists entering into the expansion with opposite signs. This cancellation, found also in the proton moments, is a manifestation of the "duality" phenomenon in the F2 structure function.

hep-ex↗

arXiv2005

Leading twist moments of the neutron structure function F2n

We perform a global analysis of neutron F2n structure function data, obtained by combining proton and deuteron measurements over a large range of kinematics. From these data the lowest moments (n <= 10) of the leading twist neutron F2n structure function are extracted. Particular attention is paid to nuclear effects in the deuteron, which become increasingly important for the higher moments. Our results for the nonsinglet, isovector (p - n) combination of the leading twist moments are used to test recent lattice simulations. We also determine the lowest few moments of the higher twist contributions, and find these to be approximately isospin independent, suggesting the possible dominance of ud correlations over uu and dd in the nucleon.

hep-ph↗

arXiv2005

The deuteron structure function F2 with CLAS

The inclusive, inelastic eD scattering cross section has been measured with the CLAS detector in Hall B of the Thomas Jefferson National Accelerator Facility (TJNAF). Combining these data and previously measured world data we have extracted Nachtmann moments of the deuteron structure function F2 in the region 0.4 < Q2 < 100 GeV2/c2. These results are published in hep-ex/0506004. The purpose of the present CLAS-Note is to tabulate the CLAS deuteron F2 data. A description of the data analysis is reported in hep-ex/0506004.

hep-ex↗

arXiv2005

Global Analysis of Data on the Proton Structure Function g1 and Extraction of its Moments

Inspired by recent measurements with the CLAS detector at Jefferson Lab, we perform a self-consistent analysis of world data on the proton structure function g1 in the range 0.17 < Q2 < 30 (GeV/c)**2. We compute for the first time low-order moments of g1 and study their evolution from small to large values of Q2. The analysis includes the latest data on both the unpolarized inclusive cross sections and the ratio R = sigmaL / sigmaT from Jefferson Lab, as well as a new model for the transverse asymmetry A2 in the resonance region. The contributions of both leading and higher twists are extracted, taking into account effects from radiative corrections beyond the next-to-leading order by means of soft-gluon resummation techniques. The leading twist is determined with remarkably good accuracy and is compared with the predictions obtained using various polarized parton distribution sets available in the literature. The contribution of higher twists to the g1 moments is found to be significantly larger than in the case of the unpolarized structure function F2.

hep-ph↗

arXiv2005

Higher twist analysis of the proton g_1 structure function

We perform a global analysis of all available spin-dependent proton structure function data, covering a large range of Q^2, 1 < Q^2 < 30 GeV^2, and calculate the lowest moment of the g_1 structure function as a function of Q^2. From the Q^2 dependence of the lowest moment we extract matrix elements of twist-4 operators, and determine the color electric and magnetic polarizabilities of the proton to be χ_E = 0.026 +- 0.015 (stat) + 0.021/-0.024 (sys) and χ_B = -0.013 -+ 0.007 (stat) - 0.010/+0.012 (sys), respectively.

hep-ph↗

arXiv2004

Self-Consistent Data Analysis of the Proton Structure Function g1 and Extraction of its Moments

The reanalysis of all available world data on the longitudinal asymmetry A|| is presented. The proton structure function g1 was extracted within a unique framework of data inputs and assumptions. These data allowed for a reliable evaluation of moments of the structure function g1 in the Q2 range from 0.2 up to 30 GeV2. The Q2 evolution of the moments was studied in QCD by means of Operator Product Expansion (OPE).

hep-ex↗

arXiv2004

The CLAS Electromagnetic Calorimeter at Large Angles

The study of the response of the two modules of the large-angle electromagnetic shower calorimeter (LAC) of the CLAS detector to charged and neutral particles is reported. The results agree very well with the Monte Carlo simulation. The procedures adopted for the energy and timing calibration are also discussed, proving that the module geometry allows for simple self-calibrating energy and timing algorithms.

nucl-ex↗

arXiv2004

Evaluation of the Higher Twist Contribution to the Moments of Proton Structure Functions F2 and g1

We performed the measurement of the inclusive electron scattering off the proton in the resonance region (W<2.5 GeV) at momentum transfer Q2 below 4.5 (GeV/c)^2 with the CLAS detector. The large acceptance of CLAS provided an access to a large, continuous two-dimensional kinematic domain in Q2 and x, allowing therefore an integration of the data at fixed Q2 over x-interval. The covered x-interval at each measured Q2 value is sufficient for an evaluation of the higher moments (n>2). From these data we extracted the structure function F2 and, by including other world data, we studied the Q2 evolution of its moments, Mn(Q2), in order to estimate the higher twist contributions. A similar experiment with polarized proton target is completed at CLAS. These new data allow an accurate determination of higher moments of the proton structure function g1. A preliminary phenomenological analysis indicates an excess of the higher twist contribution in the spin-dependent structure function with respect to the spin-independent one.

hep-ph↗

arXiv2003

The proton structure function F2 with CLAS

Here we publish experimental data on the proton structure function F2 measured with CLAS detector during February and March 1999 in Thomas Jefferson National Accelerator Facility (Virginia, USA).

hep-ex↗

arXiv2003

New extraction of alpha_s(MZ) from proton DIS data

An exploratory study for a new determination of the strong coupling constant alpha_s(MZ) from existing world data on the proton structure function F2p in the Q**2-range from ~ 5 to ~ 120 (GeV/c)**2 is presented. The main features of our approach are: 1) the use of low-order Nachtmann moments evaluated with a direct contribution from data larger than 70% of the total; 2) the inclusion of high-order perturbative effects through the soft gluon resummation technique; 3) a direct control over higher-twist effects; and 4) the independence from any specific choice of the x-shape of the input parton distributions. At next-to-leading order we get alpha_s(MZ) = 0.1209 +/- 0.0010 (stat.) +/- 0.0015 (syst.) with a significant dependence upon the order of the moment used. Including soft gluon effects we obtain alpha_s(MZ) = 0.1188 +/- 0.0010 (stat.) +/- 0.0014 (syst.) with a remarkable better stability against the order of the moment. Our findings are compared with recent DIS determinations of alpha_s(MZ) and directions for future improvements are discussed.

hep-ph↗

arXiv2003

A Kinematically Complete Measurement of the Proton Structure Function F2 in the Resonance Region and Evaluation of Its Moments

We measured the inclusive electron-proton cross section in the nucleon resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2 with the CLAS detector. The large acceptance of CLAS allowed for the first time the measurement of the cross section in a large, contiguous two-dimensional range of Q**2 and x, making it possible to perform an integration of the data at fixed Q**2 over the whole significant x-interval. From these data we extracted the structure function F2 and, by including other world data, we studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate higher twist contributions. The small statistical and systematic uncertainties of the CLAS data allow a precise extraction of the higher twists and demand significant improvements in theoretical predictions for a meaningful comparison with new experimental results.

hep-ph↗

arXiv2003

The proton structure function F2 in the resonance region

Unique measurement of the proton structure function F2 in a wide two-dimensional region of x and Q**2 has been reported. The accessible kinematics covers entire resonance region up to W=2.5 GeV in the Q**2 interval from 0.1 to 4.5 GeV**2. Obtained data allowed for the first time an evaluation of moments of the structure function F2 directly from experimental data as well as an intensive study of the Bloom-Gilman duality phenomenon.

hep-ex↗