Q2 Dependence Research Articles

Anomalous diffusion in random pores

Molecular dynamics simulations are performed for binary liquids confined in the pores of Vycor glass. The individual molecular motions are studied by computing Fs, the self-part of the concentration fluctuation autocorrelation function. The results for Fs(q,t) show that the diffusion is anomalous as its relaxation rate does not follow the usual q2 dependence on the probing wave vector q. This is explained as a confining effect of the glass walls.

Measurement of η′(958) formation in two-photon collisions at LEP1

Abstract The formation of the η′ in the reaction e+e−→e+e−η′→e+e−π+π−γ has been measured by the L3 detector at a centre-of-mass energy of 91 GeV . The radiative width of the η′ has been found to be Γ γγ =4.17±0.10 (stat.) ±0.27 (sys.) keV . The Q2 dependence of the η′ formation cross section has been measured for Q 2 ≤10 GeV 2 and the η′ electromagnetic transition form factor has been determined. The form factor can be parametrised by a pole form with Λ=0.900±0.046 (stat.) ±0.022 (sys.) GeV . It is also consistent with recent non-perturbative QCD calculations.

Next-to-leading order QCD analysis of polarized deep inelastic scattering data

Abstract We present a next-to-leading order perturbative QCD analysis of world data on the spin dependent structure functions g1p, g1n, and g1d, including the new experimental information on the Q2 dependence of g1n. Careful attention is paid to the experimental and theoretical uncertainties. The data constrain the first moments of the polarized valence quark distributions, but only qualitatively constrain the polarized sea quark and gluon distributions. The NLO results are used to determine the Q2 dependence of the ratio g 1 F 1 and evolve the experimental data to a constant Q2 = 5 GeV2. We determine the first moments of the polarized structure functions of the proton and neutron and find agreement with the Bjorken sum rule.

Diffractive open charm production at HERA

We use perturbative QCD to calculate the cross sections σLT for the diffractive production of open charm (cc) from longitudinally and transversely polarised photons (of virtuality Q2) incident at high energy (√S) on a proton target. We study both the Q2 and M2 dependence of the cross sections, where M is the invariant mass of the cc pair. Surprisingly, the result for σT, as well as for σL, is perturbatively stable. We estimate higher-order corrections and find a sizeable enhancement of the cross sections. The cross sections depend on the square of the gluon density g(x, K2), and we show that the observation of open charm at the HERA electron-proton collider can act as a sensitive probe of the gluon distribution for x = (Q2 + M2)/s and scale K2 = (M2c + )(1 + Q2/M2) where the average quark transverse momentum squared 〈k2t~ (M2c . As compared to diffractive J/#x03C8; production, open charm has the advantage that it is independent of the non-perturbative ambiguities arising from the J/#x03C8; wave function. We estimate the fraction of diffractive events that arise from cc¯ production.

Diffractive heavy flavour production at the Tevatron and the LHC

We give predictions for diffractive heavy flavour production at the Tevatron and the LHC in leading-order approximation. In the framework of these studies we use three different models for the partonic structure of the Pomeron recently proposed by Stirling and Kunszt. These Pomeron models are, despite being fitted to the same diffractive deep inelastic HERA data, very different in their parton content and taken together provide a powerful tool to probe the structure of the Pomeron. All models satisfy GLAP evolution and show a significant Q2 dependence. We give numerical predictions for single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor.

The Q2 dependence of the structure function ratio ? and the difference RSn − RC in deep inelastic muon scattering The New Muon Collaboration (NMC)

The Q2 dependence of the structure function ratio ? and the difference RSn − RC in deep inelastic muon scattering The New Muon Collaboration (NMC)

Structure and dynamics of polyelectrolyte solutions with multivalent salts

AbstractAqueous solutions of highly charged polyelectrolyte solutions phase separate in the presence of multivalent salts. Phase diagrams of sodium polystyrene sulfonate (Na+PSS−) with LaCl3, Th(NO3)4 were studied over a wide range of polyelectrolyte and salt concentrations. The concentration of salt at the transition C was found to be proportional to the monomer concentration Cm and nearly molecular weight independent: C/Cm≅0.23 for La3+ and C/Cm≅0.12 for Th4+. With further addition of salt a new transition from a two phase system back to a single phase was observed at constant salt concentration independent of NaPSS concentration but sensitive to molecular weight. A theoretical model which explains this behavior in termes of electrostatic attractive interaction between monomers due to the high valency of condensated counterions has been developped recently. The form of the phase diagram results from a competition between the classical long range Coulombic interaction, the short range bridging attraction via the condensed counterion and the electrostatic screening.Dynamic light scattering measurements were performed in the lower monophase solution as a function of NaPSS concentration and over a wide LaCl3 concentration range. Two relaxation times were observed at very low salt concentration.The dynamic studies reveal some interesting behaviours of apparent diffusion coefficient as a function of polyelectrolyte and salt concentrations (Cm, Cs): i) a q2 dependence of the fast mode and a q3 dependence of the slow mode; ii) the power law Dfast varies approximately as C1/2m at constant low salt concentration. This mode can be explained assuming cooperative diffusion in a transient polyelectrolyte network.The slow mode of the bimodal decay disappears increasing the added salt (LaCl3) concentration at constant Cm. It is concluded that the slow mode is related to labile clusters or temporal domains of polyelectrolyte chains which are formed in solutions at low concentration of added salt. Both the disappearance of the slow mode on a very long time scale and the non reappearance of this mode when cycling at constant Cs/Cm between high and low salt concentration indicate that low salt or salt free polyelectrolyte solutions tend very slowly to thermodynamic equilibrium.

Measurement of the Q2 dependence of the charged and neutral current cross sections in e±p scattering at HERA

The Q 2 dependence and the total cross sections for charged and neutral current processes are measured in e ± p reactions for transverse momenta of the outgoing lepton larger than 25 GeV. Comparable size of cross sections for the neutral current process and for the weak charged current process are observed above Q 2 ∥ 5000 GeV 2. Using the shape and magnitude of the charged current cross section we determine a propagator mass of m W = 84 −7 +10 GeV.

Aggregation Behavior in the Semidilute Poly(N-vinyl-2-pyrrolidone)/Water System

Dynamic and static light scattering experiments were performed on aqueous solutions of poly(N-vinyl-2-pyrrolidone) in the dilute and semidilute regime. In the dilute regime, typical good solvent behavior is found. In the semidilute regime, we observe two relaxation times in the autocorrelation functions and intense forward scattering. The short time relaxation has a typical q2 dependence, characteristic of diffusion, and the long time relaxation an approximately q3 dependence, characteristic of intraparticle dynamics. This behavior is not consistent with predicted semidilute, good solvent system behavior but instead indicates the presence of aggregates. Using combined static and dynamic scattering, we show these aggregates to be approximately 2−3 times the size of the dilute-solution radius of gyration. We attribute this anomalous behavior to the unique, tetrahedral hydrogen bond network of water and show that denaturing the water through the addition of denaturing agents known to disrupt the water structure significantly diminishes the aggregate size. We also show through pressure denaturation that the aggregation process is reversible.

Phenomenology of nuclear shadowing in deep-inelastic scattering

We investigate shadowing effects in deep-inelastic scattering from nuclei at small valuesx < 0.1 of the Bjorken variable. Unifying aspects of generalized vector meson dominance and color transparency we first develop a model for deep-inelastic scattering from free nucleons at smallx. In application to nuclear targets we find that the coherent interaction of quark-antiquark fluctuations with nucleons in a nucleus leads to the observed shadowing atx < 0.1. We compare our results with most of the recent data for a large variety of nuclei and examine in particular the Q2 dependence of the shadowing effect. While the coherent interaction of low mass vector mesons causes a major part of the shadowing observed in the Q2 range of current experiments, the coherent scattering of continuum quark-antiquark pairs is also important and guarantees a very weak overall Q2 dependence of the effect. We also discuss shadowing in deuterium and its implications for the quark flavor structure of nucleons. Finally we comment on shadowing effects in high-energy photon-nucleus reactions with real photons.

Model for the Q2 dependence of polarized structure functions.

We present an update of a phenomenological model for the spin-dependent structure functions ${\mathit{g}}_{1}$(x,${\mathit{Q}}^{2}$) of the proton and neutron. This model is based on a broken SU(6) wave function parametrized by the unpolarized structure functions. The two free parameters of the model are chosen to satisfy the Bjorken and Ellis-Jaffe sum rules. The model respects isospin symmetry and has zero strange sea polarization. Using new values for F/D from hyperon \ensuremath{\beta} decay the resulting ${\mathit{Q}}^{2}$-dependent asymmetries ${\mathit{A}}_{1}$ are in perfect agreement with the existing data. Therefore we do not see any evidence for a ``spin crisis.'' With two choices for ${\mathit{g}}_{2}$ the ${\mathit{Q}}^{2}$ dependence of ${\mathit{A}}_{1}$(x,${\mathit{Q}}^{2}$) and ${\mathit{A}}_{2}$(x,${\mathit{Q}}^{2}$) \ensuremath{\surd}${\mathit{Q}}^{2}$/M is predicted and shown to be small for both cases.

Measurements of the proton elastic form factors for 1

We report measurements of the proton form factors GEp and GMp extracted from elastic scattering in the range 1≤Q2≤3 (GeV/c)2 with total uncertainties < 15% in GEp and < 3% in GMp. Comparisons are made to theoretical models, including those based on perturbative QCD, vector-meson dominance, QCD sum rules, and diquark constituents in the proton. The results for GEp are somewhat larger than indicated by most theoretical parametrizations, and the ratios of the Pauli and Dirac form factors Q2(F2pF1p) are lower in value and demonstrate a weaker Q2 dependence than those predictions. A global extraction of the elastic form factors from several experiments in the range 0.1 0.1<Q2<10 (GeV/c)2 is also presented.Received 4 November 1993DOI:https://doi.org/10.1103/PhysRevD.49.5671©1994 American Physical Society

Q2 dependence of the average squared transverse energy of jets in deep-inelastic muon-nucleon scattering with comparison to perturbative QCD predictions.

The average squared transverse energy of jets in deep-inelastic muon-nucleon scattering is measured as a function of the momentum transfer squared ([ital Q][sup 2]), in the range 3[lt][ital Q][sup 2][lt]25 GeV[sup 2]. Perturbative QCD predicts that the average squared parton transverse energy will depend upon the strong coupling constant ([alpha][sub [ital S]]). Identifying the transverse energy of the jets with those of the corresponding partons, [alpha][sub [ital S]] is found to vary with [ital Q][sup 2] as predicted by QCD.

On the Q2 dependence of the measured polarized structure functions

We analyse the available data on the polarized asymmetries A 1 for proton, neutron and deutron targets. We use a homogeneous and updated set of unpolarized structure functions to derive g 1 from A 1, and we accurately correct for the scaling violations in order to obtain g 1( x, Q 2) with the same Q 2 for all x values. The contribution to the Q 2 evolution of a possible large gluon polarized density is also considered. The implications for the Ellis-Jaffe and for the Bjorken sum rules are discussed.

Small-x structure functions from NMC

The NMC measurements of the proton and deuteron structure functions for 0.006<x<0.6 and 0.5<Q2<55 GeV2 and of the neutron-to-proton structure function ratio down to x=0.0008 are presented. The data agree very well with the earlier results of the BCDMS, SLAC (reanalysed) and EMC NA28 experiments, but disagree with the reanalysed results of the EMC NA2. A parametrization of the low-x structure function F2, incorporating vector meson dominance dynamics and the QCD-improved parton model, valid at arbitrary Q2 and reproducing well the data, is also presented. Results of a quantitative analysis of the shadowing effect in the deuteron are given. The shadowing is found to be about a 2% effect, in qualitative agreement with the NMC results on the neutron-to-proton structure function ratio at low x. The NMC results on the Q2 dependence of the structure functions are compared with the predictions of perturbative QCD in next-to-leading order. Parton distributions and the strong coupling constant are determined from the data. The QCD evolution in the low-x region is driven largely by gluons, and shows only a moderate contribution of 'higher twists' at scales around 1 GeV2.

Nuclear effects in deep inelastic scattering

Measurements of the structure function F2D from deep inelastic muon scattering extending down to x=0.008 are presented. These are the first precise measurements at low x. The results on EMC effect are presented from deep inelastic scattering experiments NMC and E665 and compared with those from Drell-Yan processes. The saturation of the shadowing is seen for x below 0.003. No significant Q2 dependence of the F2A/F2D ratio is observed. Short description of possible mechanisms describing the effect in different kinematic regions is also given.

The q2 dependence of DIS structure functions at small x

The new NMC data at very small x (up to x=0.008) are compared with the parameter free prediction of the modified GLR evolution equation. Fair agreement is found.

Two-centre effects in ejected-electron spectra from ionization of helium atoms in collisions with fast, fully stripped ions

A joint experimental and theoretical study of the double-differential cross sections (DDCS) for ejection of electrons from helium by 1.00 and 1.84 MeV amu-1 p+, He2+, C6+ and O8+ is presented. Electron-emission angles from 20' to 160' are surveyed, and the electron energies range from 4 to 2500 eV. Single-differential and total cross sections, obtained by integrating the DDCS over angle and electron energy, are also presented. Large departures from the q2 dependence (where q is the projectile charge) predicted by the first Born approximation are observed in the cross sections. The deviations, which are seen to increase with projectile charge are discussed and compared with calculations, using the first Born approximation and a continuum-distorted-wave eikonal-initial-state model.

THE EMC EFFECT IN A NUCLEONIC DESCRIPTION

Deep inelastic lepton-nucleus scattering is treated by considering the nucleus as a bound system of nucleons based on the light-cone quantum field theory. This method has the advantages that the impulse approximation is justified and that baryon number conservation is guaranteed. However, the ambiguities in identifying the structure function for bound nucleons in the conventional nucleonic approach seem not to have been avoided. It is also shown that a consistent calculation gives an unreasonably large Q2 dependence in the calculated nuclear structure function if one makes the most natural assumption to identify the off-"energy"-shell structure function for bound nucleons.

Static and dynamic light scattering of poly‐(α‐methyl styrene) in toluene in the dilute region

AbstractThe scattered intensity function S(q, c) and the intermediate scattering function S(q, c, τ) of poly‐(α‐methyl styrene) (Mω = 5.71 × 105, 1.17 × 106, and 2.96 × 106) in toluene in the dilute concentration region were measured as functions of concentration and scattering vector q. In infinitely dilute solution, the intensity function S(q, 0) agrees well with the Debye function for u &lt; 7, where u is (qRg)2. At finite concentration S(q, c) varies from its thermodynamic value at low u to the single chain value at high u. Theoretical calculations of S(q, c) are in quantitative agreement with the observed scattering function in very dilute solutions. The intermediate scattering function S(q, c, τ) is a single exponential decay with decay rate Dmq2 for u ≪ 1. For u &gt; 1, S(q, c, τ) is nonexponential, and when analyzed with a discrete inversion method, yields a bimodal distribution of decay rates. Both components are well represented as single exponential decays. D0 can be obtained from the slower component. The decay rate of the faster component is a continuous function of u and approaches q2 dependence at high u.