12 research outputs found
Atomic Mass Dependence of Hadron Production in Deep Inelastic Scattering on Nuclei
Hadron production in lepton-nucleus deep inelastic scattering is studied in
an absorption model. In the proposed model, the early stage of hadronization in
the nuclear medium is dominated by prehadron formation and absorption,
controlled by flavor-dependent formation lengths and absorption cross sections.
Computations for hadron multiplicity ratios are presented and compared with the
HERMES experimental data for pions, kaons, protons and antiprotons. The
mass-number dependence of hadron attenuation is shown to be sensitive to the
underlying hadronization dynamics. Contrary to common expectations for
absorption models, a leading term proportional to A^{2/3} is found. Deviations
from the leading behavior arise at large mass-numbers and large hadron
fractional momenta.Comment: 30 pages, 10 figures, v2: minor changes (legend in figs 5 & 6 is
added), v3: additional explanations are added, v4: Version combines v3 and
the erratum hep-ph/050803
Photoproduction of phi mesons from nuclei
We investigate the consequences of possible medium modifications of the phi
meson at finite nuclear matter density on the K+K- mass distribution in
photonuclear reactions. The inclusive cross sections for K+K- pair production
are calculated within a semi--classical BUU transport model, which combines the
initial state interaction of the incoming photon with the final state
interactions of the produced particles. The effects of final state interactions
on the invariant mass distribution of the observed K+K- pairs are discussed in
detail. In addition we calculate the Coulomb correction and possible effects of
hadronic kaon potentials on the K+K- mass spectrum. Due to the large cross
sections for reactions of the final state particles with the surrounding
nuclear medium and the influence of the Coulomb potential we find no measurable
sensitivity of the observables to the phi properties at finite baryon density.Comment: revtex4, 24 page
Transverse Momentum Broadening in Semi-inclusive DIS on Nuclei
Using a three stage model of hadron formation we calculate the change of the
transverse momentum distribution of hadrons produced in semi-inclusive deep
inelastic scattering (SIDIS) on nuclei. In the first stage after its
interaction with the virtual photon, the struck quark propagates quasi free in
the nuclear environment undergoing multiple collisions with nucleons. During
this stage it can acquire transverse momentum. In the second stage a prehadron
is formed which has a very small elastic cross section with the nucleons. In
the third stage the prehadron turns into a hadron. For HERMES energies,
prehadron elastic scatterings contribute little to -broadening. The
acquired extra of hadrons can therefore be deduced entirely
from the first stage of quasi free quark propagation with quark-nucleon
collisions. We use this model to describe -production on Ne, Kr, Xe and
compare with the most recent HERMES preliminary data.Comment: 17 pages, 9 figures, Slightly modified plot legends to indicate that
HERMES data are preliminar
Flux Phase as a Dynamic Jahn-Teller Phase: Berryonic Matter in the Cuprates?
There is considerable evidence for some form of charge ordering on the
hole-doped stripes in the cuprates, mainly associated with the low-temperature
tetragonal phase, but with some evidence for either charge density waves or a
flux phase, which is a form of dynamic charge-density wave. These three states
form a pseudospin triplet, demonstrating a close connection with the E X e
dynamic Jahn-Teller effect, suggesting that the cuprates constitute a form of
Berryonic matter. This in turn suggests a new model for the dynamic Jahn-Teller
effect as a form of flux phase. A simple model of the Cu-O bond stretching
phonons allows an estimate of electron-phonon coupling for these modes,
explaining why the half breathing mode softens so much more than the full
oxygen breathing mode. The anomalous properties of provide a coupling
(correlated hopping) which acts to stabilize density wave phases.Comment: Major Revisions: includes comparisons with specific cuprate phonon
modes, 16 eps figures, revte
Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
We review the most important experimental results from the first three years
of nucleus-nucleus collision studies at RHIC, with emphasis on results from the
STAR experiment, and we assess their interpretation and comparison to theory.
The theory-experiment comparison suggests that central Au+Au collisions at RHIC
produce dense, rapidly thermalizing matter characterized by: (1) initial energy
densities above the critical values predicted by lattice QCD for establishment
of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by
constituent interactions of very short mean free path, established most
probably at a stage preceding hadron formation; and (3) opacity to jets. Many
of the observations are consistent with models incorporating QGP formation in
the early collision stages, and have not found ready explanation in a hadronic
framework. However, the measurements themselves do not yet establish
unequivocal evidence for a transition to this new form of matter. The
theoretical treatment of the collision evolution, despite impressive successes,
invokes a suite of distinct models, degrees of freedom and assumptions of as
yet unknown quantitative consequence. We pose a set of important open
questions, and suggest additional measurements, at least some of which should
be addressed in order to establish a compelling basis to conclude definitively
that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.