Beside its intrinsic interest for the insights it can give into color confinement, knowledge of the space-time evolution of hadronization is very important for correctly interpreting jet-quenching ...data in heavy-ion collisions and extracting the properties of the produced medium. On the experimental side, the cleanest environment to study the space-time evolution of hadronization is semi-inclusive deeply inelastic scattering on nuclear targets. On the theoretical side, two frameworks are presently competing to explain the observed attenuation of hadron production: quark energy loss (with hadron formation outside the nucleus) and nuclear absorption (with hadronization starting inside the nucleus). I will discuss recent observables and ideas which will help to distinguish these two mechanisms and to measure the time scales of the hadronization process.
A
bstract
The spin-dependent cross sections for semi-inclusive lepton-nucleon scattering are derived in the framework of collinear factorization, including the effects of masses of the target and ...produced hadron at finite momentum transfer squared
Q
2
. At leading order the cross sections factorize into products of parton distribution and fragmentation functions evaluated in terms of new, mass-dependent scaling variables. The size of the hadron mass corrections is estimated at kinematics relevant for future semi-inclusive deepinelastic scattering experiments.
A polarized
ep
/
eA
collider (Electron-Ion Collider, or EIC) with variable center-of-mass energy √
s
∼ 20–70 GeV and luminosity ∼10
34
cm
−2
s
−1
would be uniquely suited to address several ...outstanding questions of Quantum Chromodynamics (QCD) and the microscopic structure of hadrons and nuclei: i) the three-dimensional structure of the nucleon in QCD (sea quark and gluon spatial distributions, orbital motion, polarization, correlations); ii) the fundamental color fields in nuclei (nuclear parton densities, shadowing, coherence effects, color transparency); iii) the conversion of color charge to hadrons (fragmentation, parton propagation through matter, in-medium jets). We briefly review the conceptual aspects of these questions and the measurements that would address them, emphasizing the qualitatively new information that could be obtained with the collider. Such a medium-energy EIC could be realized at Jefferson Lab after the 12GeV Upgrade (MEIC), or at Brookhaven National Lab as the low-energy stage of eRHIC.
A
bstract
We explore the sensitivity of
W
and
Z
boson production in hadronic collisions to uncertainties in parton distribution functions (PDFs) at large
x
arising from uncertainties in nuclear ...corrections when using deuterium data in global QCD fits. The
W
and
Z
differential cross sections show increasing influence of nuclear corrections at high boson rapidities, particularly for the
d
quark, which is diluted somewhat in the decay lepton rapidity distributions. The effects of PDF uncertainties on heavy
W
′ and
Z
′ bosons beyond the Standard Model become progressively more important for larger boson masses or rapidities, both in
pp
collisions at the LHC and in
scattering at the Tevatron.
Multiple initial state parton interactions in p(d)+Au collisions are calculated in a Glauber–Eikonal formalism. The convolution of perturbative QCD parton–nucleon cross sections predicts naturally ...the competing pattern of low-pT suppression due geometrical shadowing, and a moderate-pT Cronin enhancement of hadron spectra. The formal equivalence to recent classical Yang–Mills calculations is demonstrated, but our approach is shown to be more general in the large x>0.01 domain because it automatically incorporates the finite kinematic constraints of both quark and gluon processes in the fragmentation regions, and accounts for the observed spectra in elementary pp→πX processes in the RHIC energy range, s∼20–200 GeV. The Glauber–Eikonal formalism can be used as a baseline to extract the magnitude of dynamical shadowing effects from the experimental data at different centralities and pseudo-rapidities.
Articular cartilage lesions are a particular challenge for regenerative medicine strategies as cartilage function stems from a complex depth-dependent organization. Tissue engineering scaffolds that ...vary in morphology and function offer a template for zone-specific cartilage extracellular matrix (ECM) production and mechanical properties. We fabricated multi-zone cartilage scaffolds by the electrostatic deposition of polymer microfibres onto particulate-templated scaffolds produced with 0.03 or 1.0mm3 porogens. The scaffolds allowed ample space for chondrocyte ECM production within the bulk while also mimicking the structural organization and functional interface of cartilage’s superficial zone. Addition of aligned fibre membranes enhanced the mechanical and surface properties of particulate-templated scaffolds. Zonal analysis of scaffolds demonstrated region-specific variations in chondrocyte number, sulfated GAG-rich ECM, and chondrocytic gene expression. Specifically, smaller porogens (0.03mm3) yielded significantly higher sGAG accumulation and aggrecan gene expression. Our results demonstrate that bilayered scaffolds mimic some key structural characteristics of native cartilage, support in vitro cartilage formation, and have superior features to homogeneous particulate-templated scaffolds. We propose that these scaffolds offer promise for regenerative medicine strategies to repair articular cartilage lesions.
Baseline computations of the Cronin effect in nuclear collisions at energies spanning the SPS and the RHIC accelerators are performed in the Glauber-Eikonal model, which ascribes the effect to ...initial-state incoherent multiple parton scatterings. The model accounts very well for the mid-rapidity Cronin effect in hadron-nucleus collisions in the \(\sqrt{s} = 27\)-200 GeV center of mass energy range, and will be extended to nucleus-nucleus collisions. The computations are performed under the assumption that the partons do not interact with the medium produced in the collision. Therefore, medium effects such as energy loss in a quark-gluon plasma may be detected and measured as deviations from the presented baseline computation of the “naked” Cronin effect.
Predictions for semi-inclusive deep inelastic lepton–nucleus scattering are presented. Both the effects of gluon radiation by the struck quark and the absorption of the produced hadron are ...considered. The gluon radiation covers a larger window in virtuality
Q
2 because of the increased deconfinement of quarks inside nuclei. The absorption of hadrons formed inside the nucleus is described with a flavor dependent cross-section. Calculations for rescaled fragmentation functions and nuclear absorption are compared with the EMC and HERMES data for N, Cu and Kr targets with respect to the deuteron target. Predictions for Ne and Xe targets in the HERMES kinematic regime are given.
A five-dimensional reaction surface-vibronic coupling model is introduced to describe the B- to C-state predissociation dynamics of Br2 occupying a double substitutional lattice site in a ...face-centered cubic argon crystal at low temperatures. The quantum dynamics driven by a Franck−Condon vertical excitation is investigated, revealing the role of matrix cage compression for efficient nonadiabatic transitions. Vibrational preexcitation of the Br2 bond in the electronic ground state can be used to access a different regime of predissociation which does not require substantial matrix compression because the Franck−Condon window shifts into the energetic range of the B−C level crossing. Using optimal control theory, it is shown how vibrational preexcitation can be achieved via a pump−dump-type mechanism involving the repulsive C state.
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