On the Proton charge extensions
It is shown that the recent determination of the various proton charge extensions is compatible with Standard Model expectations.
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arXiv subjects
M. Gluck
Publications and source records attributed to M. Gluck.
On the charged current neutrino-nucleon total cross section at high energies
We evaluate the charged current neutrino-nucleon total cross section up to neutrino energies of 10^{12} GeV in the LO and NLO of perturbative QCD within the framework of two different factorization schemes. The numerical implications of some inconsistent QCD calculations are illustrated.
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The Lamb shift contribution of very light millicharged particles
The leading order vacuum polarization contribution of very light millicharged fermions and scalar (spin-0) particles with charge εe and mass μto the Lamb shift of the hydrogen atom is shown to imply universal, i.e. μ-independent, upper bounds on ε: ε\lsim 10^{-4} for μ\lsim 1 keV in the case of fermions, and for scalars this bound is increased by a factor of 2. This is in contrast to expectations based on the commonly used approximation to the Uehling potential relevant only for conventionally large fermion (and scalar) masses.
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The Photon Structure Function at Small-x
It is shown that recent small-x measurements of the photon structure function F_2^γ(x,Q^2) by the LEP-OPAL collaboration are consistent with parameter-free QCD predictions at all presently accessible values of Q^2.
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Spin-Dependent Structure Functions of Real and Virtual Photons
The implications of the positivity constraint, $|g_1^{γ(P^2)}(x,Q^2)| \leq F_1^{γ(P^2)}(x,Q^2)$, on the presently unknown spin--dependent structure function $g_1^{γ(P^2)}(x,Q^2)$ of real and virtual photons are studied at scales $Q^2\gg P^2$ where longitudinally polarized photons dominate physically relevant cross sections. In particular it is shown how to implement the physical constraints of positivity and continuity at $P^2=0$ in NLO calculations which afford a nontrivial choice of suitable (DIS) factorization schemes related to $g_1^γ$ and $F_1^γ$ and appropriate boundary conditions for the polarized parton distributions of real and virtual photons. The predictions of two extreme `maximal' and `minimal' saturation scenarios are presented and compared with results obtained within the framework of a simple quark `box' calculation expected to yield reasonable estimates in the not too small regions of $x$ and $P^2$.
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Spin-Dependent Structure Functions of the Photon
The implications of the positivity constraint on the presently unknown polarized structure function of the photon, $g_1^γ(x,Q^2)$, are studied in detail. In particular the non-trivial consequences of this constraint, $|g_1^γ(x,Q^2)|\leq F_1^γ(x,Q^2)$, in the next-to-leading order analysis of $g_1^γ$ are pointed out by employing appropriate (DIS) factorization schemes related to $g_1^γ$ and $F_1^γ$ (rather than to $F_2^γ$).
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On the Determination of the Polarized Sea Distributions of the Nucleon
The possibilities to determine the flavor structure of the polarized sea (antiquark) distributions of the nucleon via vector boson $(γ^*, W^{\pm}, Z^0)$ production at high energy polarized hadron--hadron colliders, such as the Relativistic Heavy--Ion Collider (RHIC), are studied in detail. In particular the perturbative stability of the expected asymmetries in two representative models for the (un)broken flavor structure are investigated by confronting perturbative QCD leading order predictions of the expected asymmetries with their next--to--leading order counterparts.
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Models for the Polarized Parton Distributions of the Nucleon
Polarized deep inelastic scattering (DIS) data are analyzed in leading and next-to-leading order of QCD within the common `standard' scenario of polarized parton distributions with a flavor-symmetric light sea (antiquark) distribution $δ\bar{q}$, and a completely SU(3)$_f$ broken `valence' scenario with totally flavor-asymmetric light sea densities $(δ\bar{u}\neqδ\bar{d}\neqδ\bar{s})$. The latter flavor-broken light sea distributions are modelled with the help of a Pauli-blocking ansatz at the low radiative/dynamical input scales of $μ_{\rm LO(NLO)}^2=0.26$ (0.40) GeV$^2$ which complies with predictions of the chiral quark-soliton model and expectations based on the statistical parton model as well as with the corresponding, well established, flavor-broken unpolarized sea ($\bar{d}>\bar{u}$). Present semi-inclusive DIS data cannot yet uniquely discriminate between those two flavor-symmetric and flavor-broken polarized light sea scenarios.
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Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?
It is demonstrated that present $e^+e^-$ and DIS ep data on the structure of the virtual photon can be understood entirely in terms of the standard `naive' quark--parton model box approach. Thus the QCD renormalization group (RG) improved parton distributions of virtual photons, in particular their gluonic component, have not yet been observed. The appropriate kinematical regions for their future observation are pointed out as well as suitable measurements which may demonstrate their relevance.
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Phenomenology of the Flavor-Asymmetry in the Light-Quark Sea of the Nucleon
A phenomenological ansatz for the flavor-asymmetry of the light sea distributions of the nucleon, based on the Pauli exclusion principle, is proposed. This ansatz is compatible with the measured flavor-asymmetry of the unpolarized sea distributions, $\bar{d}>\bar{u}$, of the nucleon. A prediction for the corresponding polarized flavor-asymmetry is presented and shown to agree with predictions of (chiral quark--soliton) models which successfully reproduced the flavor-asymmetry of the unpolarized sea.
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Radiatively Generated Parton Distributions of Real and Virtual Photons
The parton content of real (P^2=0) and virtual (P^2\neq 0) transverse photons γ(P^2) is expressed in terms of perturbative pointlike and nonperturbative hadronic (VMD) components, employing recently updated parton distributions of pions and protons. The resulting parameter-free and perturbatively stable LO and NLO parton densities f^{γ(P^2)}(x,Q^2) are smooth in P^2 and apply to all P^2 >= 0 whenever γ(P^2) is probed at scales Q^2 >> P^2 where transverse photons also dominate physically relevant cross sections. Predictions are given for the structure function F_2^{γ(P^2)}(x,Q^2) and f^{γ(P^2)}(x,Q^2), and are compared with all relevant data for real photons as well as with recent data for virtual photons as extracted from DIS ep dijet events. Simple analytic parametrizations of our predicted parton distributions are presented for the real photon in LO and NLO, and for the virtual photon in LO which, within sufficient accuracy, may be also used in NLO-QCD.
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Pionic Parton Distributions Revisited
Using constituent quark model constraints we calculate the gluon and sea-quark content of pions solely in terms of their valence density (fixed by πN Drell-Yan data) and the known sea and gluon distributions of the nucleon, using the most recent updated valence-like input parton densities of the nucleon. The resulting small-x dynamical QCD predictions for g^π(x,Q^2) and \bar{q}^π(x,Q^2) are unique and parameter free. Simple analytic parametrizations of the resulting parton distributions of the pion are presented in LO and NLO. These results and parametrizations will be important, among other things, for updated formulations of the parton distributions of real and virtual photons.
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Mesonic Parton Densities Derived From Constituent Quark Model Constraints
Using constituent quark model constraints we calculate the gluon and sea content of pions solely in terms of their valence density and the known sea and gluon densities of the nucleon. The resulting small-x predictions for g^{pi}(x,Q^2) and \bar{q}^{pi}(x,Q^2) are unique and parameter free, being entirely due to QCD dynamics. Similar ideas are applied for calculating the gluon and sea content of kaons which, for our suggested choice of the kaon's valence densities, turn out to be identical to the ones of the pion.
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Detailed Next-to-Leading Order Analysis of Deep Inelastic Neutrino Induced Charm Production off Strange Sea Partons
Neutrino induced deep inelastic charm production off strange sea partons in the nucleon is studied in the framework of the MSbar fixed flavor factorization scheme. The momentum (z) distributions of the produced D mesons as calculated in the next-to-leading order QCD analysis are presented and compared to their leading order counterparts. Perturbative stability within this formalism is demonstrated and the compatibility of recent next-to-leading order (NLO) strange quark distributions with available dimuon data is investigated. Our NLO (MSbar) results provide, for the first time, the tools required for a consistent and complete NLO (MSbar) analysis of charged current dimuon data in order to extract the strange sea density in NLO. It is furthermore shown that the absolute predictions of radiatively (dynamically) generated strange sea densities are in agreement with all present measurements.
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Probing the Parton Densities of Virtual Photons at ep Colliders
The feasibility of an experimental determination of the parton distributions of virtual photons at high energy $ep$ colliders is studied in the context of the DESY-HERA collider. Recently proposed parton densities of virtual photons are utilized to evaluate the appropriate production processes and their relevant kinematical regions. It is demonstrated that high $E_T$ jet production with $E_T\,\simeq 5-7\, {\rm{GeV}}$ and $b\bar{b}$ production can probe the parton distributions of virtual photons up to virtualities of a few ${\rm{GeV}}^2$. A useful leading order parametrization of our proposed photonic parton densities, suitable for further studies of these issues, is presented.
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The Strange Sea Density and Charm Production in Deep Inelastic Charged Current Processes
Charm production as related to the determination of the strange sea density in deep inelastic charged current processes is studied predominantly in the framework of the $\overline{\rm{MS}}$ fixed flavor factorization scheme. Perturbative stability within this formalism is demonstrated. The compatibility of recent next-to-leading order strange quark distributions with the available dimuon and $F^{νN}_2$ data is investigated. It is shown that final conclusions concerning these distributions afford further analyses of presently available and/or forthcoming neutrino data.
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Next-to-Leading Order Radiative Parton Model Analysis of Polarized Deep Inelastic Scattering
A next-to-leading order QCD analysis of spin asymmetries and structure functions in polarized deep inelastic lepton nucleon scattering is presented within the framework of the radiative parton model. A consistent NLO formulation of the $Q^2$-evolution of polarized parton distributions yields two sets of plausible NLO spin dependent parton distributions in the conventional $\overline{\rm{MS}}$ factorization scheme. They respect the fundamental positivity constraints down to the low resolution scale $Q^2=μ^2_{NLO}=0.34\,{\rm{GeV}}^2$. The $Q^2$-dependence of the spin asymmetries $A_1^{p,n,d}(x,Q^2)$ is similar to the leading-order (LO) one in the range $1\le Q^2\le 20\,{\rm{GeV}}^2$ and is shown to be non-negligible for $x$-values relevant for the analysis of the present data and possibly forthcoming data at HERA.
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Radiative Parton Model Analysis of Polarized Deep Inelastic Lepton Nucleon Scattering
A leading order QCD analysis of spin asymmetries in polarized deep inelastic lepton nucleon scattering is presented within the framework of the radiative parton model. Two resulting sets of plausible leading order spin dependent parton distributions are presented, respecting the fundamental positivity constraints down to the low resolution scale $Q^2=μ_{LO}^2=0.23$ GeV$^2$. The $Q^2$ dependence of the spin asymmetries $A_1^{p,n,d}(x,Q^2)$ is investigated in the range $1 \leq Q^2 \leq 20$ GeV$^2$ and shown to be non-negligible for $x$-values relevant for the analysis of present data and possibly forthcoming data at HERA.
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