NLO QCD procedure of the semi-inclusive deep inelastic scattering data analysis with respect to the light quark polarized sea

Sissakian, A.; Shevchenko, O.Yu.; Ivanov, О. N.

doi:10.1103/physrevd.70.074032

Cited by 18 publications

(5 citation statements)

References 29 publications

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“…The unpolarised distributions s(x) and G(x) used in this test are taken from the MRST parametrisation [26]. This procedure leads to asymmetric errors on the parameters when the fitted value is close to the allowed limit.The fits have been performed with two different programs: the first one uses the DGLAP evolution equations for the spin structure functions [27], the other one, referred to in [28], uses the evolution of moments. The fitted PDF parameters are compatible within one standard deviation and the two programs give the same χ 2 -probabilities.…”

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confidence: 99%

The deuteron spin-dependent structure function g1d and its first moment

Alexakhin¹,

Alexandrov²,

Alexeev³

et al. 2007

Physics Letters B

275

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We present a measurement of the deuteron spin-dependent structure function g d 1 based on the data collected by the COMPASS experiment at CERN during the years [2002][2003][2004]. The data provide an accurate evaluation for Γ d 1 , the first moment of g d 1 (x), and for the matrix element of the singlet axial current, a 0 . The results of QCD fits in the next to leading order (NLO) on all g 1 deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function ∆G positive or negative, which describe the data equally well. In both cases, at Q 2 = 3(GeV/c) 2 the first moment of ∆G(x) is found to be of the order of 0.2 -0.3 in absolute value.Keywords: Deep inelastic scattering; Spin; Structure function; QCD analysis; A1; g1 (To be Submitted to Physics Letters B)The COMPASS Collaboration [4]. Due to the relatively low incident energy, the DIS events collected in those experiments cover only a limited range of x for Q 2 > 1(GeV/c) 2 , x > 0.015 and x > 0.03, respectively. Further measurements covering the low x region were also performed at CERN (see [5] and references therein). Besides its general interest for the understanding of the spin structure of the nucleon, g d 1 is specially important because its first moment is directly related to the matrix element of the singlet axial vector current a 0 . A precise measurement of g d 1 can thus provide an evaluation of the fraction of nucleon spin carried by quarks, on the condition that the covered range extends far enough to low x to provide a reliable value of the first moment.Here we present new results from the COMPASS experiment at CERN on the deuteron spin asymmetry A As previous fits were found to be in disagreement with our data at low x, we have performed a new QCD fit at NLO. The resulting polarised parton distribution functions (PDF) are also presented in this paper and discussed in relation with the new data, however without a full investigation of the theoretical uncertainties due, for instance, to the values of the factorisation and renormalisation scales.The COMPASS data acquisition system is triggered by coincidence signals in hodoscopes, defining the direction of the scattered muon behind the spectrometer magnets, and by signals in the hadron calorimeters [7]. Triggers due to halo muons are eliminated by veto counters installed upstream of the target. Inclusive triggers, based on muon detection only, cover the full range of x and are dominant in the medium (x, Q 2 ) region. Semi-inclusive triggers, based on the muon energy loss and the presence of a hadron signal in the calorimeters, contribute mainly at low x and low Q 2 . Purely calorimetric triggers, based on the energy deposit in the hadron calorimeter without any condition on the scattered muon, account for most events at large Q 2 . The relative contributions of these three trigger types are shown in Fig. 1 as a function of x. The minimum hadron energy deposit required for the purely calorimetric trigger has been reduced to 10 GeV for the...

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confidence: 99%

The deuteron spin-dependent structure function g1d and its first moment

Alexakhin¹,

Alexandrov²,

Alexeev³

et al. 2007

Physics Letters B

275

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“…moments ∆ 1 ū and ∆ 1 d even in the case of rather narrow HERMES x-range, while for the wide COMPASS x-range we deal with here this approximation works very well -see the respective numerical tests in Ref. [5]. The point is that since the valence PDFs (contrary to the sea PDFs) are suppressed near the low boundary x = 0 (so that ∆q = ∆q V + ∆q → ∆q as x → 0), the omitted in r.h.s.…”

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confidence: 58%

“…For the scenario preserving SU f (2) symmetry (AKK08 parametrization for FFs here) the procedure of direct extraction in NLO QCD of n-th moments of the valence PDFs from the measured difference asymmetries is described in Refs. [5], [7] in details. Let us recall the key necessary equations.…”

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confidence: 99%

“…A lot of numerical tests performed in Refs. [5,7] have shown that Eqs. (11) allow to reconstruct the truncated moments of polarized valence PDFs with a high precision even in the case of rather narrow HERMES x region 0.023 < x < 0.6, divided on relatively small number of bins (nine bins only).…”

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confidence: 99%

“…Bjorken sum rule (23) rewritten in terms of valence and sea distributions produces quite good approximation [5,23] (see Ref. [4] for review)…”

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Valence and sea contributions to the nucleon spin

2011

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The first moments of the polarized valence parton distribution functions (PDFs) truncated to the wide Bjorken x region 0.004 < x < 0.7 are directly (without any fitting procedure) extracted in the next to leading order (NLO) QCD from both COMPASS and HERMES data on pion production in polarized semi-inclusive DIS (SIDIS) experiments. The COMPASS and HERMES data are combined in two ways and two scenarios for the fragmentation functions (FFs) are considered. Two procedures are proposed for an estimation of light sea quark contributions to the proton spin. Both of them lead to the conclusion that these contributions are compatible with zero within the errors.

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Spin structure function of deuteron g 1 d from COMPASS

Korzenev¹

The IVth International Conference on Quarks and Nuclear Physics

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NLO QCD procedure of the semi-inclusive deep inelastic scattering data analysis with respect to the light quark polarized sea

Cited by 18 publications

References 29 publications

The deuteron spin-dependent structure function g1d and its first moment

The deuteron spin-dependent structure function g1d and its first moment

Valence and sea contributions to the nucleon spin

Spin structure function of deuteron g 1 d from COMPASS

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