Nuclear shadowing in Glauber–Gribov theory with Q 2-evolution

We consider deep inelastic scattering off nuclei in the Regge limit within the Glauber–Gribov model. Using unitarized parton distribution functions for the proton, we find sizeable shadowing effects on the nuclear total and longitudinal structure functions, $F_{2}^{A}$ and $F_{L}^{A}$ , in the low-x limit. Extending a fan-diagram analysis for the large-mass region of coherent diffraction off nuclei to high Q ², we also find significant shadowing effects in this kinematical regime. Finally, we discuss the shortcomings of our approach and possible extensions of the model to other kinematical regimes.     

Pomeron structure function and diffraction dissociation of virtual photons in perturbative QCD

We study scaling properties of the diffraction dissociation of virtual photons in a deep inelastic scattering. We concentrate on the total diffraction dissociation rate, diffraction excitation mass spectrum and the pomeron structure function to the lowest order in perturbative QCD. We calculate the valence structure function and the strangeness and charm content of the pomeron and estimate the ocean structure function using the pomeron factorization property. We find that quarks carry ≈ 10% of pomeron's momentum. Differential cross section of the (virtual) photon-pomeron scattering is found to exhibit features typical of the hadronic two-body reactions, supporting a treatment of the Pomeron as a particle, whereas the flavor dependence of structure functions does not support the particle treatment of the pomeron. Diffraction dissociation of photons is predicted to make ≈ 15% of the total deep inelastic scattering rate at smallx and largeQ ². Detailed predictions for the mass spectrum and angular distribution of jets produced on the valence component of the pomeron are presented.     

Structure functions of nuclei for all x and Q 2

We propose a modified version of the quark cluster model to describe the structure functions of nuclei over the complete kinematical region of the variables x = Q ²/2m _N ν and Q ². The model accounts for shadowing effects at very small x and anti-shadowing in the region 0.1 ≤ x ≤ 0.3. The experimental observation that the ratio of structure functions F ₂ ^A /F ₂ ^D is less than unity in the region x ? 0.5 is related to the influence of multiquark clusters. The model agrees with all available data on nuclear structure fuctions for a large variety of nuclei, and can be used to make predictions for kinematical regions not yet studied experimentally.     

Scaling properties of nuclear shadowing in deep inelastic scattering

We present the perturbative QCD analysis of nuclear shadowing in deep inelastic scattering and prove it to be the scaling, rather than the higher twist, 1/Q², effect, contrary to numerous recent claims. We argue in favor of the scaling triple-pomeron contribution to the nuclear shadowing and comment on the mass spectrum of diffraction excitation by highly virtual photons. Our numerical predictions for shadowing are in good agreement with the recent EMC data.     

Hard bremsstrahlung photons in thet\bar t production anddecay: A background for the intermediate Higgs search

We discuss the radiation of hard photons in the $t\bar t$ production anddecay as a background for the intermediate Higgs search at LHC/SSC experiments. For the purpose of experimental simulation of this process we propose to use the approximate Monte Carlo algorithm together with any physics Monte Carlo not including QED corrections. We verify, by comparison with the exact matrix element Monte Carlo TOPKI, that this method can be used to generate single- and double-photon bremsstrahlung in the $t\bar t$ production process with a precision of 10% for experimental cuts. The predictions for the ψψl background from photons radiated in theproduction of $t\bar t$ pair and their cascadedecays, within simplified experimental cuts, are presented for the first time. We show that, even after additional cuts on the minimal lepton-photon mass, photons radiated in the productionand decay of a $t\bar t$ pair increase this background by a factor of 2 with respect to previous estimates from radiation in the $t\bar t$ production alone.     

Effect of parton shadowing on the distributions of global observables

The effect of parton shadowing on the distributions of global observables (total transverse energy E _T and charged-particle multiplicity n _ch) is investigated on the basis of the HIJING model of nucleus-nucleus interactions. It is shown that, for the interaction of lead nuclei at $\sqrt s = 5$ TeV per nucleon, the shadowing effect results in a considerable reduction of the cross section for (mini)jet production (approximately by a factor of 4); this in turn reduces the total transverse energy and the charged-particle multiplicity by a factor of 2.7. Upon taking into account the QCD evolution of nuclear structure functions in Q ², the shadowing effect becomes less pronounced (by a factor of 1.9 for PbPb interactions). It is shown that global observables can be used to test models of parton shadowing.     

Unusual effects of diffraction dissociation for multiproduction in deep inelastic scattering on nuclei

In hadron-nucleus interactions, the stronger is nuclear shadowing in the total cross section the higher is the multiplicity of secondary hadrons. In deep inelastic scattering nuclear shadowing at smallx is associated with the hadronlike behaviour of photons as contrasted to the pointlike behaviour in the non-shadowing region of largex. In this paper we predict dilution of multiproduction of secondary hadrons, and weaker fragmentation of the target nucleus, in deep inelastic leptoptoproduction on nuclei in the shadowing region of smallx as compared to the non-shadowing region of largex. This paradoxial conclusion has its origin in nuclear enhancement of the coherent diffraction dissociation of photons which affects multiproduction in the shadowing region and does not contribute in the non-shadowing region. We present numerical predictions for multiproduction in theμXe interactions studied by the Fermilab E665 collaboration.     

The nucleon structure functions in deep inelastic scattering off deuterium: nuclear shadowing and the Gottfried sum rule

The perturbative QCD is applied to calculation of nuclear shadowing correction to the deuterium structure functionF ₂ ^D (x) atx«1. This correction is shown to be numerically large. It is emphasized that the neglect of nuclear shadowing leads to underestimating of the neutron structure functionF ₂ ⁿ (x) and, as a result, to gross overestimating of the Gottfried integral \(\int_0^1 {\left[ {F_2^P (x) - F_2^n (x)} \right]} dx/x\)      

The role of screening corrections in smallx-behaviour of structure functions

We consider the influence of shadowing effects on the proton structure function in the small-x interval. The gluon-gluon shadowing are noticeable in the HERA kinematical region while the screening of the quark component of the structure function effects negligibly the gluon distribution. The only noticeable effect is the decreasing of sea quark densities at small-x. The explicit form of the gluon distribution in the proton depends significantly on the form of used boundary condition atQ ²=Q ₀ ² . We consider also difference of results obtained with the help of Kuraev-Lipatov-Fadin and Altarelli-Parisi evolution equations.     

The role of gluon-gluon shadowing in smallx-behaviour of structure functions

We consider influence of gluon shadowing effects on the proton structure function in the smallx interval. These effects are noticeable in the HERA kinematical region. The explicit form of the gluon distribution in the proton depend significantly on the form of used boundary condition atQ ²=Q ₀ ² . We consider also difference of results obtained with the help of Kuraev-Lipatov-Fadin and Altarelli-Parisi evolution equations.     

Hyperfeinstrukturaufspaltung und Lebensdauer des 72 P 3/2-Terms von Rb85 und Rb87

The hyperfine structure splitting of the 7² P _3/2 state of Rb⁸⁵ and Rb⁸⁷ has been measured with optical double resonance. The following hfs interaction constants have been obtained: Rb⁸⁵:A _7p ⁸⁵ =3.71(1) MHz;B _7p ⁸⁵ =3.68 (8)MHz. Rb⁸⁷:A _7p ⁸⁷ =12.57(1) MHz;B _7p ⁸⁷ =1.71 (3)MHz. These values yield quadrupole moments ofQ _7p,hfs ⁸⁵ =+0.316(7) barn andQ _7p,hfs ⁸⁷ =+0.147(2)barn which are reduced by application of the Sternheimer correction toQ _7p ⁸⁵ =+0.267(6) barn andQ _7p ⁸⁷ =+0.124(2) barn. The averaged ratio of the uncorrected values of Q_hfs in the 5p and 7p ² P _3/2 stake isQ _5p,hfs/Q _7p,hfs=1.07(3). This has to be compared with the correction factors for polarization of the core of electrons by the nuclear quadrupole moment (1?R)_5p/(1?R)_7p=1.07. The agreement between the measured and calculated ratio indicates a net antishielding of the nuclear quadrupole moments of rubidium by the core of electrons as has been predicted bySternheimer. The lifetime of the 7² P _3/2 state of the RbI-spectrum is:τ(7² P _3/2, Rb)=2.4(2)·10^?7 sec.     

Decay energy of183Re→183W

The electron capture decay energy of¹⁸³Re has been determined from the fraction ofK-capture in the transition to the 453.08 keV level in¹⁸³W by delayed coincidences. From this value the total decay energy from₁₈₃Re→¹⁸³W is obtained to beQ=555 _?7 ⁺⁹ keV according to the theory ofBrysk andRose with corrections ofBahcall. The resulting logft values and consequences for the decay scheme are discussed.     

Higher-twist effects in QCD,deep inelastic scattering,and the Drell-Yan process

Inclusion of specific effects associated with constituent binding in hadronic wave functions is shown to lead to important non-scaling, nonfactorizing 1/Q ² contributions to cross sections for semi-inclusive deep-inelastic scattering, the Drell-Yan process, and other hard scattering reactions. These 1/Q ² higher-twist terms are predicted to be dominant in well defined kinematic regions such as largex and/or largez. The provide angular distributions typical of longitudinally polarized virtual photons andW's, including sin² θ terms in meson induced Drell-Yan processes and ine ⁺ e ^?→πX, as well as unusual (1?y) terms in deep-inelastic scattering. Calculations are also presented of the quark structure functions of the pionq _π(x, Q ²) and for the quark to pion fragmentation functionD _π(z, Q ²). Predictions are made for the azimuthal angle dependence of the cross sections for \(\pi N \to \mu {\text{ }}\bar \mu X\) andlN→l′πX.     

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.     

Q^2 \to A\sqrt s Scaling law fore + e −→hadrons andpp collisions at high energy

It has been conjectured recently that multiparticle production in low momentum transfer hadronic collisions is due to gluon bremsstrahlung off highly virtual (mass \(\mu ^2 \sim \sqrt s \) ) quarks. The model gives a new scaling law: \(Q^2 \to A\sqrt s \) , for comparinge ⁺ e ^?→hadrons andpp non-diffractive inelastic data. The scaling law is tested for average multiplicities, plateau height and 〈p ₂ ^⊥ 〉. Fore ⁺ e ^? annihilation a parametrization of data based on perturbative QCD approach is used.     

The electric field gradient at the nuclear site of177Lu in Zn and In

The electric quadrupole interaction frequencyν _Q =eQV _zz /h of¹⁷⁷Lu in single crystals of Zn and In has been measured by the method of low temperature nuclear orientation. The results are $$\begin{gathered} v_Q ({}^{177}Lu\underline {Zn} ) = - 180(5)MHz \hfill \\ v_Q ({}^{177}Lu\underline {In} ) = - 19(5)MHz. \hfill \\ \end{gathered} $$ With the known quadrupole moment of¹⁷⁷LuQ=3.39 (2) b we derive for the electric field gradientV _zz (Lu Zn)=?2.20 (5)×10¹⁷ V/cm² andV _zz (Lu In)=?0.23 (6)×10¹⁷ V/cm². The results are compared with magnetostriction measurements of silver single crystals doped with rare earth atoms.     

The determination by an independent method ofP k electron capture probabilities in133Ba and139Ce decays gamma decay of133Ba

The electron capture decays of¹³³Ba (10.4 y) and¹³⁹Ce (140 d) were investigated with high resolution Ge(Li) detectors. By x-ray — γ-ray coincidences values of the quantityP _k ω _k ? _k for various transitions in the decay of¹³³Ba and¹³⁹Ce are obtained. The factor ω _k ? _k was measured independently by means ofK-conversion electron-K x-ray coincidences and was then used to determineP _k , theK-capture probability. The independent measurement of the product ω _k ? _k , together with recent accurate values of ω _k , provides a new method for the accurate calibration of semiconductor x-ray detectors. In the decay of¹³⁹Ce, a value ofP _k =0.78±0.03 is found (where the error represents twice the standard deviation) from whichQ _ec =326 _?30 ⁺⁷⁰ keV to the¹³⁹La ground-state is found by use of theory. In¹³³Ba decay, values are found ofP _k 1=0.72±0.04 for theEC transition to the 437 keV level in¹³³Cs,P _k 2=0.80±0.07 to the 384 keV level, and from an independent measurement, the ratioP _k 1/P _k 2=0.87±0.07. From these results the ground-state value ofQ _ec =522 _?10 ⁺²⁰ keV is derived from theory for¹³³Ba decay. The gamma spectrum of¹³³Ba also was remeasured. From the present gamma intensities and previous conversion electron intensities, new values forK-shell conversion coefficients are obtained. Previously reported γ-rays at 35 and 391 keV are not confirmed.