共查询到20条相似文献,搜索用时 31 毫秒
1.
A. S. Gorski B. L. Ioffe A. Yu. Khodjamirian 《Zeitschrift fur Physik C Particles and Fields》1992,53(2):299-303
The twist-4 corrections to the photon structure function are calculated by the method previously suggested by the authors [1], using the operator expansion in the photon virtualityp
2 and correct analytical properties of photon-photon scattering amplitude inp
2.Work supported in part by Schweizerischer Nationalfonds 相似文献
2.
S.I. Alekhin 《The European Physical Journal C - Particles and Fields》2000,12(4):587-593
We perform the NLO QCD fit to the combined deep inelastic scattering (DIS) data at high x from the SLAC, BCDMS, and NMC collaborations. The model-independent x shape of the high-twist contribution to structure function is extracted. The twist-4 contribution to is found to be in a qualitative agreement with the predictions of the infrared renormalon model. The twist-6 contribution
exhibits a weak trend to negative values, although on the whole, it is compatible with zero within the errors.
Received: 21 April 1999 / Revised version: 17 June 1999 / Published online: 27 January 2000 相似文献
3.
K. Golec-Biernat M. Wüsthoff 《The European Physical Journal C - Particles and Fields》2001,20(2):313-321
We review diffractive deep inelastic scattering (DIS) in the light of the collinear factorization theorem. This theorem allows
one to define diffractive parton distributions in the leading twist approach. Due to its selective final states, diffractive
DIS offers interesting insight into the form of the diffractive parton distributions which we explore with the help of the
saturation model. We find Regge-like factorization with the correct energy dependence measured at HERA. A remarkable feature
of diffractive DIS is the dominance of the twist-4 contribution for small diffractive masses. We quantify this effect and
make a comparison with the data.
Received: 22 February 2001 / Revised version: 22 March 2001 / Published online: 3 May 2001 相似文献
4.
5.
Fu-Guang Cao Yuan-Ben Dai Chao-Shang Huang 《The European Physical Journal C - Particles and Fields》1999,7(3):501-506
Non-leading contribution to the pion electromagnetic form factor which comes from the pion twist-3 wave function is analyzed
in the modified hard scattering approach (MHSA) proposed by Li and Sterman. This contribution is enhanced significantly due
to bound state effect (the twist-3 wave function is independent of the fractional momentum carried by the parton and has a
large factor with being the pion meson mass and being the mean u- and d-quark masses). Consequently, although it is suppressed by the factor , the twist-3 contribution is comparable with and even larger than the leading twist (twist-2) contribution at intermediate
energy region of being .
Received: 23 March 1998 / Published online: 3 November 1999 相似文献
6.
We study the single transverse-spin asymmetry for the Drell-Yan lepton pair production based on the twist-3 mechanism in the collinear factorization. We calculate all the hard-pole (HP) and the soft-fermion-pole (SFP) contributions to the single-spin-dependent cross section originating from the quark-gluon correlation functions in the transversely polarized nucleon in the leading order with respect to the QCD coupling constant. Combined with the soft-gluon-pole (SGP) contribution, this completes the corresponding twist-3 cross section. In the real photon limit, where all the HP contributions are transformed into the SFP contribution, we find that the SFP partonic hard cross section for the two independent quark-gluon correlation functions coincides in each scattering channel, as in the case of the inclusive light-hadron production. Our result enables one to extract the quark-gluon correlation functions from the forthcoming experiments at several facilities such as RHIC and J-PARC. 相似文献
7.
We evaluate in the next-to-leading approximation the forward impact factor for the virtual photon to light vector meson transition in the case of longitudinal polarization. We find that in the hard kinematic domain, both in the leading and in the next-to-leading approximation, the expression for the impact factor factorizes, up to power suppressed corrections, into the convolution of a perturbatively calculable hard-scattering amplitude and a meson twist-2 distribution amplitude.Received: 20 May 2004, Revised: 28 September 2004, Published online: 15 November 2004 相似文献
8.
S.L. Cherkas 《The European Physical Journal C - Particles and Fields》2001,19(3):471-476
T-violating P-even magnetism is considered. The magnetism arises from the T-violating P-conserving vertex of a spin 1/2 particle interaction with the electromagnetic field. The vertex vanishes for a particle on
the mass shell. Considering the particle interaction with a point electric charge we have obtained the T-violating P-even spin dependent potential, which is inversely proportional to the cubed distance from the charge. The matrix element
of this potential is zero for particle states on the mass shell; nevertheless, the potential contributes to the T-odd P-even neutron forward elastic scattering amplitude by a deformed nucleus with spin . The contribution arises if we take into account incident neutron plane wave distortion by the strong neutron interaction
with the nucleus.
Received: 29 August 2000 / Revised version: 22 January 2001 / Published online: 23 March 2001 相似文献
9.
E.R. Berger A. Donnachie H.G. Dosch W. Kilian O. Nachtmann M. Rueter 《The European Physical Journal C - Particles and Fields》1999,9(3):491-501
We investigate the reaction where PS denotes a pseudoscalar meson , , , or and X either a proton or resonance or continuum state into which the proton can go by diffractive excitation. At high energies
photon and odderon exchange contribute to the reaction. The photon exchange contribution is evaluated exactly using data for
the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative
QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark
structure as suggested by the small odderon amplitude in pp and forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic PS production cross section.
Observation of our reaction at HERA would establish the soft odderon as an exchange object on an equal footing with the soft
pomeron and would give us valuable insight into both the nucleon structure and the mechanism of high energy diffractive scattering.
Received: 2 February 1999 / Revised version: 22 March 1999 / Published online: 28 May 1999 相似文献
10.
N. Jaouen J.M. Tonnerre D. Raoux L. Ortega E. Bontempi M. Münzenberg W. Felsch M. Suzuki H. Maruyama H.A. Dürr E. Dudzik G. van der Laan 《Applied Physics A: Materials Science & Processing》2001,72(6):711-715
The element and electronic shell specificities of X-ray resonant magnetic scattering have been used to investigate the magnetization
of Ce 5d and Fe 3d states in [CeH2(19.6 ?)/Fe(25.4 ?)]*38 a multilayer. We show that the measurement of the magnetic contribution to the intensities reflected
at low angles at the Ce L2 and Fe L2,3 edges allows us to investigate the profile of the Ce 5d and Fe 3d magnetic polarization. The Fe 3d polarization is found
to be uniform across the Fe layer and the Ce 5d polarization appears to be restricted close to the interface with Fe.
Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001 相似文献
11.
K. Prytz 《The European Physical Journal C - Particles and Fields》2001,22(2):317-321
The notion of a pomeron structure function arises in a model of electromagnetic diffractive scattering based on Regge factorization.
Due to its small size we expect gluon recombination to occur significantly in the pomeron. The latest data from H1 (1999)
show a evolution in qualitative accordance with the GLR-MQ equations; these are the DGLAP (Altarelli–Parisi) equations corrected
for the effect of gluon recombination.
Received: 9 October 2000 / Revised version: 25 July 2001 / Published online: 5 November 2001 相似文献
12.
B.Z. Kopeliovich A.V. Tarasov O.O. Voskresenskaya 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):345-356
The Born approximation, one photon exchange, used for DIS (deep inelastic scattering) is subject to virtual radiative corrections
which are related to the long-range Coulomb forces. They may be sizeable for heavy nuclei since Zα is not a small parameter. So far, these corrections are known only for two processes, elastic scattering and bremsstrahlung
on the Coulomb field of a point-like target. While the former amplitude acquires only a phase, in the latter case also the
cross-section is modified. Although the problem of Coulomb corrections for DIS on nuclei is extremely difficult, it should
be challenged rather than “swept under the carpet”. The importance of these radiative corrections is questioned in the present
paper. We show that, in the simplest case of a constant hadronic current, the Coulomb corrections provide a phase to the Born
amplitude, therefore the cross-section remains the same. Inclusion of more realistic hadronic dynamics changes this conclusion.
The example of coherent production of vector mesons off nuclei reveals large effects. So far a little progress has been made
deriving lepton wave functions in the Coulomb field of an extended target. Employing available results based on the first-order
approximation in Zα, we conclude that the Coulomb corrections are still important for heavy nuclei. We also consider an alternative approach
for extended nuclear targets, the eikonal approximation, which we demonstrate to reproduce the known exact results for Coulomb
corrections. Calculating electroproduction of vector mesons, we again arrive at a large deviation from the Born approximation.
We conclude that one should accept with caution the experimental results for nuclear effects in DIS based on analyses done
in the Born approximation.
Received: 16 May 2001 / Accepted: 4 July 2001 相似文献
13.
The single-spin asymmetries for a longitudinally polarized lepton beam or a longitudinally polarized nucleon target in semi-inclusive deep-inelastic scattering are twist-3 observables. We study these asymmetries in a simple diquark spectator model of the nucleon. Analogous to the case of transverse target polarization, non-vanishing asymmetries are generated by gluon exchange between the struck quark and the target system. It is pointed out that the coupling of the virtual photon to the diquark is needed in order to preserve electromagnetic gauge invariance at the twist-3 level. The calculation indicates that previous analyses of these observables are incomplete. 相似文献
14.
We prove the collinear factorization theorem for the process
at the twist-3 level in the covariant gauge by means of the Ward identity, concentrating on the two-parton case. It is shown that soft divergences cancel and collinear divergences are grouped into the pseudo-scalar and pseudo-tensor two-parton twist-3 pion distribution amplitudes. The delicate summation of a complete set of diagrams for achieving factorization in momentum, spin, and color spaces is emphasized. The proof is then extended to the exclusive semileptonic decay
, assuming the hard scale to be of
, where
is a hadronic scale and M
B
the B meson mass. We explain the distinction between the factorization of collinear divergences for a pion distribution amplitude and of soft divergences for a B meson distribution amplitude. The gauge invariance and universality of the two-parton twist-3 pion distribution amplitudes are confirmed. The proof presented here can accommodate the leading twist-2 case. We then compare our proof with that performed in the framework of soft-collinear effective theory.Received: 8 June 2004, Revised: 10 December 2004, Published online: 3 March 2005PACS:
12.38.Bx 相似文献
15.
A. Angelopoulos et al. M.P. Locher V.E. Markushin 《The European Physical Journal C - Particles and Fields》1999,10(1):19-25
We apply a forward dispersion relation to the regeneration amplitude for kaon scattering on C using all available data. The CPLEAR data at low energies allow the determination of the net contribution from the subthreshold
region which turns out to be much smaller than earlier evaluations, solving a long standing puzzle.
Received: 26 February 1999 / Published online: 15 July 1999 相似文献
16.
A. Nehme 《The European Physical Journal C - Particles and Fields》2002,23(4):707-718
We use chiral perturbation theory to evaluate the scattering amplitude for the process at leading and next-to-leading orders in the chiral counting and in the presence of isospin breaking effects. We also discuss
the influence of the latter on the combination of the -wave scattering lengths which is relevant for the 2S–2P energy level shift of atoms.
Received: 19 November 2001 / Revised version: 21 December 2001 / Published online: 5 April 2002 相似文献
17.
We present a detailed next-to-leading order (NLO) leading twist QCD analysis of deeply virtual Compton scattering (DVCS)
observables, for several different input scenarios, in the scheme. We discuss the size of the NLO effects and the behavior of the observables in skewedness , momentum transfer,t, and photon virtuality, . We present results on the amplitude level for unpolarized and longitudinally polarized lepton probes, and unpolarized and
longitudinally polarized proton targets. We make predictions for various asymmetries and for the DVCS cross section and compare
with the available data.
Received: 30 November 2001 / Revised version: 12 February 2002 / Published online: 15 March 2002 相似文献
18.
Hiroyuki Kawamura 《Zeitschrift fur Physik C Particles and Fields》1997,75(1):27-33
We analyze the twist-4 contributions to Bjorken and Ellis-Jaffe sum rules for spin-dependent structure function g 1(x, Q 2). We investigate the anomalous dimensions of the twist-4 operators which determine the logarithmic correction to the 1/Q 2 behavior of the twist-4 contribution by evaluating off-shell Green’s functions in both flavor non-singlet and singlet case. It is shown that the operators which are proportional to the equation of motion play an important role to extract the anomalous dimensions of physical operators. The calculations to solve the operator mixing of higher-twist operators are given in detail 相似文献
19.
A systematic derivation is presented of the twist-2 anomalous dimensions of the general quark and gluon light-ray operators in the generalized Bjorken region in leading order both for unpolarized and polarized scattering. Various representations of the anomalous dimensions are derived in the non-local and local light cone expansion and their properties are discussed in detail. Evolution equations for these operators are derived using different representations. General two- and single-variable evolution equations are presented for the expectation values of these operators for non-forward scattering. The Compton amplitude is calculated in terms of these distribution amplitudes. In the limit of forward scattering a new derivation of the integral relations between the twist-2 contributions to the structure functions is given. Special limiting cases which are derived from the general relations are discussed, as the forward case, near-forward scattering, and vacuum-meson transition. Solutions of the two-variable evolution equations for non-forward scattering are presented. 相似文献
20.
Simplified dark matter models with loop effects in direct detection and the constraints from indirect detection and collider search
下载免费PDF全文
![点击此处可从《中国物理C(英文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
《中国物理C(英文版)》2019,(11)
We reexamine the simplified dark matter(DM) models with fermionic DM particle and spin-0 mediator.The DM-nucleon scattering cross sections in these models are low-momentum suppressed at tree-level,but receive sizable loop-induced spin-independent contribution.We perform one-loop calculations for scalar-type and twist-2 DM-quark operators,and complete two-loop calculations for scalar-type DM-gluon operator.Analyzing the looplevel contribution from new operators,we find that future direct detection experiments could be sensitive to a fraction of the parameter space.The indirect detection and collider search also provide complementary constraints on these models. 相似文献