arXiv subjects

W. Greiner

Publications and source records attributed to W. Greiner.

242 records · Page 14Linked to original sources

arXiv1995

QCD sum rules with finite masses

The concept of QCD sum rules is extended to bound states composed of particles with finite mass such as scalar quarks or strange quarks. It turns out that mass corrections become important in this context. The number of relevant corrections is analyzed in a systematic discussion of the IR- and UV-divergencies, leading in general to a finite number of corrections. The results are demonstrated for a system of two massless quarks and two heavy scalar quarks.

hep-ph↗

arXiv1995

Azimuthal correlations of pions in relativistic heavy ion collisions at 1 GeV/nucl.

Triple differential cross sections of pions in heavy ion collisions at 1 GeV/nucl. are studied with the IQMD model. After discussing general properties of $Δ$ resonance and pion production we focus on azimuthal correlations: At projectile- and target-rapidities we observe an anticorrelation in the in-plane transverse momentum between pions and protons. At c.m.-rapidity, however, we find that high $p_t$ pions are being preferentially emitted perpendicular to the event-plane. We investigate the causes of those correlations and their sensitivity on the density and momentum dependence of the real and imaginary part of the nucleon and pion optical potential.

nucl-th↗

arXiv1994

Pion and thermal photon spectra as a possible signal for a phase transition

We calculate thermal photon and neutral pion spectra in ultrarelativistic heavy-ion collisions in the framework of three-fluid hydrodynamics. Both spectra are quite sensitive to the equation of state used. In particular, within our model, recent data for $S+Au$ at $200$ AGeV can only be understood if a scenario with a phase transition (possibly to a quark-gluon plasma) is assumed. Results for $Au+Au$ at $11$ AGeV and $Pb+Pb$ at $160$ AGeV are also presented.

hep-ph↗

arXiv1994

QCD Sum Rule Calculation of Twist-3 Contributions to Polarized Nucleon Structure Functions

Using the framework of QCD sum rules we predict the twist-3 contribution to the second moment of the polarized nucleon structure function $g_2(x)$. As the relevant local operator depends explicitely on the gluon field, we employ a recently studied interpolating nucleon current which contains three quark field and one gluon field operator. Despite the fact that our calculation is based on the analysis of a completely different correlation function, our estimates are consitent with those of Balitsky, Braun and Kolesnichenko who used a three-quark current.

hep-ph↗

arXiv1994

Diffractive Meson Production and the Quark-Pomeron Coupling

Diffractive meson production at HERA offers interesting possibilities to investigate diffractive processes and thus to learn something about the properties of the pomeron. The most succesful phenomenological description of the pomeron so far assumes it to couple like a $C = +1$ isoscalar photon to single quarks. This coupling leads, however, to problems for exclusive diffractive reactions. We propose a new phenomenological pomeron vertex, which leads to very good fits to the known data, but avoids the problems of the old vertex.

hep-ph↗

arXiv1993

The connection between single transverse spin asymmetries and the second moment of $g_2$

We point out that the size of the photon single spin asymmetry in high--energy proton proton collisions with one transversely polarized proton can be related to $d^{(2)}$, the twist three contribution to the second moment of $g_2$. Both quantities should be measured in the near future. The first was analysed by Qiu and Sterman, the second was estimated by Balitsky, Braun, and Kolesnichenko. Both experiments measure effectively the strength of the collective gluon field in the nucleon oriented relative to the nucleon spin. The sum rule results suggest that the single spin asymmetry is rather small for the proton, but could be substantial for the neutron.

hep-ph↗

arXiv1993

Finite Volume Effect of Nucleons and the Formation of the Quark-Gluon Plasma

We study a thermodynamically consistent implementation of the nucleon volume in the mean field theory, and find that this volume has large consequences on the properties of hadronic matter under extreme conditions such as in astrophysical objects and high energy heavy-ion collisions. It is shown that we can reproduce the critical temperature $T_{c}\simeq 200$ MeV predicted by lattice QCD calculations for the phase transition from hadronic matter to quark-gluon plasma, by using parameters which are adjusted to fit all empirical data for normal nuclear matter.

nucl-th↗

arXiv1993

The phase-space structure of the Klein-Gordon field

The formalism based on the equal-time Wigner function of the two-point correlation function for a quantized Klein--Gordon field is presented. The notion of the gauge-invariant Wigner transform is introduced and equations for the corresponding phase-space calculus are formulated. The equations of motion governing the Wigner function of the Klein--Gordon field are derived. It is shown that they lead to a relativistic transport equation with electric and magnetic forces and quantum corrections. The governing equations are much simpler than in the fermionic case which has been treated earlier. In addition the newly developed formalism is applied towards the description of spontaneous symmetry breakdown.

hep-ph↗