Project 5: Heavy flavour production vs charged-particle multiplicity with ALICE
Supervisors: Dr Zinhle Buthelezi ([email protected] )
Nuclear Physics Department
1 PhD
Heavy-flavours (charm and beauty) are produced in the early stages of ultrarelativistic collisions via hard scatterings
and are important tools for studying different aspects of QCD in hadronic collisions.
Charged-particle multiplicity gives information on the global characteristics of the event and could be used to
characterize particle production mechanisms. In pp collisions at LHC energies, there is a significant contribution of
multi-parton interactions (MPIs). The measurement of heavy-flavours as a function of charged particle multiplicity
gives insight into the mechanisms influencing their production in hadronic collisions at these energies and is a tool to
test the influence of MPIs. Charged-particle multiplicity dependence of heavy-flavours is used to test the ability of
QCD theoretical models to reproduce data. Heavy flavours will be studied via muonic decays as a function of
charged-particle multiplicity in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC.
In this project we want to study the production yield of muons from decays of charm and beauty hadrons as a
functions of multiplicity in ALICE (A Large Ion Collider Experiment) detector at the CERN Large Hadron Collider
(LHC). ALICE is a dedicated heavy-ion detector studying strongly-interacting QCD matter knows as the quark gluon
plasma (QGP). The aim is to understand particle production processes involved and this will help tune pQCD
theoretical models used to predict the production of these particles. We will focus on high multiplicity data collected
by ALICE during Run 1 (2010 - 2013) and available data from Run 2 (2015 ongoing) in pp, p-Pb and PbPb collisions
at LHC energies. We will measure charged-particle multiplicity using central barrel detectors (Silicon Pixel, VZERO
and TZERO scintillators) and muon candidates using the Muon Spectrometer in ALICE.
As indicated in this short description the project requires high level of competence in particle and nuclear physics
theories (deep inelastic scattering, quantum field, special relativity, etc.), understanding of how accelerators and
detectors work (LHC and ALICE). The physics involved in this study entails analysis of large amounts of data using
high performance tools ALIROOT (based on ROOT frameworks) and associated packages. As both data and
analysis tools are available on the CERN GRID (distributed computer clusters) therefore the candidate is required
have competent programming skills. Furthermore, the involved scientist from iThemba LABS contribute are also
involved in the maintenance and operations of the ALICE Muon Spectrometer.
Project 6: Fast timing measurements with the iThemba LABS Facility for Low Spin
Structure Studies of Exotic States
Supervisors: Dr Pete Jones ( [email protected] )
Nuclear Physics Department
1 PhD
An NEP proposal has been accepted and is funded to provide iThemba LABS with a new unique instrument to
measure properties that are out of our reach with our current equipment i.e. the ability for fast-lifetime measurements
providing information on quadrupole moments, and high efficiency providing measurements of very weak decay
branches.
The work is encompassed by the theme of the study of excited 0+ states, their population mechanism (such as using
the K600 spectrometer), and the study of a range of nuclei through the RIB project. Recent developments with the
K600 magnetic spectrometer have enabled not only 0-degree measurements but an investment in a new aluminium
reaction chamber has allowed particle-gamma-ray coincidence studies using silicon detectors combined with
gamma-ray detectors. The use of the K600 magnetic spectrometer allows for firm selectivity on the populated state in
the final nucleus. The major advantage of the use of the 0-degree mode, of which the K600 spectrometer is the only
other device in the world, is the suppression of higher L-value transitions and the selection of low-spin states in the
final nuclide. In a similar manner to (3He,n) reactions, (p,t) and (4He,6He) reactions transfer of a pair of neutrons
from the target nuclei onto the beam nuclei to selectively populate low-spin, natural- parity states. States with 0+ can
be easily identified by looking for states for which the cross section shows a pronounced peak at 0-degrees and
drops away at higher angles. The coupling of the Facility to the K600 spectrometer will promote these studies.
The study of the evolution of the Z=28, N=50 and N=82 closed shells by studying the beta-decay of neutron-rich
nuclei is a proposal led by South African scientists. As part of the iThemba LABS RIB project, a beam of protons
would be used to fission uranium atoms and produce neutron-rich species along N=82. The fission products will be
selectively and efficiently ionized using lasers. The desired radioactive neutron-rich atoms are accelerated by a small
~50 keV potential, to create a low- energy radioactive beam, then mass selected by a dipole magnet, to be implanted
at an analysis station. The fast-timing properties of LaBr3 will allow nuclear lifetimes to measured, giving critical
information on collectivity and single particle structure in the neutron-rich region.
Project 7: Study of Excited 0+ States via Electron Spectroscopy
Supervisors: Dr Pete Jones ( [email protected] )
Nuclear Physics Department
1 PhD
A CPRR proposal has been accepted and is funded to refurbish an existing electron spectrometer for conversionelectron studies. The spectrometer will establish and perform an experimental programme for nuclear structure
studies in this field of research. The main focus will be on education, research and training young scientists and
Ph.D. students using this cutting-edge research platform. There will be a direct contribution to the local and national
knowledge economy, and open new avenues of collaboration with other world-class research institutes.
In association with the project, another spectrometer was donated from the University of Bonn to add to the arsenal
of equipment. This superconducting spectrometer can be also used to study the same area of nuclear physics,
however at higher electron energies and even covers the extremely rare-production detection region. The project will
investigate the areas of physics and niches of interest for such a spectrometer and it will be used to study the nuclear
configuration of multiple excited 0+ states such as in Cd nuclei
Project 10: Nanoscale Patterning by Atomic Force Microscope Nanolithography
Supervisor: Dr Mlungisi Nkosi ([email protected] )
Materials Research Department
1 PhD
Nanostructures have attracted increasing interest because of their unique properties and their tremendous
potential for applications in advanced microelectronic and optoelectronic devices. The major challenge in
fabricating nanostructures is to form structures and control their positions on the nanometer scale. In the
past, the lithographic method using focused beams of high-energy electrons has been the most popular
approach for this purpose. However, the ultimate resolution is limited not only by the beam diameter but
also by the proximity effects, phenomena originating from the scattering of high-energy electrons in the
resist and from the substrate. Therefore, the smallest possible feature size can only be achieved with
limited resist materials and certain substrate materials.
Nanolithography, where a proximal probe tip is used to provide a local intense electric field or a low-energy
electron beam near the sample surface to be modified, has been developed as an alternative way. In
particular, electric-field-induced anodic oxidation using a conductive-probe atomic force microscope (AFM)
under ambient conditions has been widely applied to metals and semiconductors, and insulators. Because
of its inherent simplicity and generality, this method has been regarded as a key technology for the
development of future nanoscale electronics.
The objective of this project is to use thin silicon-nitride dielectric films grown on doped silicon substrate as
a mask for selective-area epitaxial growth. Silicon nitride is widely used as a dielectric material for both
silicon and gallium arsenide very large scale integration processing due to its many superior material
properties. It has also been used for diffusion, ion implant masks, and passivation layers. Because of the
large selectivities of many etchants of silicon and SiO2 over Si3N4, it can be a versatile wet- or dry-etching
mask for nanofabrication if a local oxidation scheme can be developed. Moreover, both Si 3N4 and SiO2 are
important mask materials for selective-area growth of semiconductors and metals. Therefore,
nanolithography using nitride masks could open up new possibilities for a wide variety of nanofabrication
applications.
The successful candidate will build on a strong experimental program emphasizing the application of
scanning probe methods to nanoscale materials processing and device fabrication. The candidate will also
be responsible for operation, maintenance, and user training for the Atomic Force Microscope.