Understanding the origins of the universe
The switching on of the Large Hadron Collider (LHC) at CERN in Switzerland has generated exciting new particle physics data.
A front view of the ATLAS detector under construction. Image courtesy of CERN (www.cern.ch)
Searching for new subatomic particles
A new research group at Sussex is part of the ATLAS experiment running at the LHC, and is involved in the search for new subatomic particles that may help us learn about the nature of dark matter and the forces that have shaped our universe from the beginning of time.
Particle physics has been the hot science topic in the mainstream media for the last year or so, most famously with the search for the Higgs boson particle closing in on its elusive target.
Much of this cutting-edge physics research is being carried out at the LHC – a particle accelerator that has broken all records in terms of its size and power.
Based at CERN (the European Organization of Nuclear Research) in Geneva, the LHC produces high-energy states that recreate conditions that existed at the birth of the universe shortly after the Big Bang.
The ATLAS experiment
ATLAS is one of four main experiments being conducted at the LHC, and the ATLAS detector is searching for new subatomic particles that arise from high-speed, head-on collisions between two beams of protons (hydrogen atoms with their electrons stripped off). Led by Dr Antonella De Santo, Reader in Experimental Particle Physics, and Dr Fabrizio Salvatore, Senior Lecturer in Experimental Particle Physics, a team from the Department of Physics and Astronomy at Sussex is part of the ATLAS collaboration.
In simple terms, the collisions at the LHC result in the breaking apart of colliding protons to create a profusion of subatomic particles.
In the millionths of seconds after the collisions take place, the resulting particles and their decay products are analysed by the ATLAS detector.
Because of the massive amounts of data that are generated by these collisions, it is not possible to store all of the information owing to limitations of technology and disc space. Thus, the detector relies on a sensitive and sophisticated 'trigger system' that must decide rapidly which data to keep and which to discard.
The role of the Sussex ATLAS team is two-fold.
Firstly, they are involved in writing software that is required for the good functioning of the trigger system. At any one time, a member of the group (often a postdoctoral fellow or graduate student) is on site at CERN for an extended period, to participate in the running of the experiment.
The second major role of the group is to search for new physics that will help expand our knowledge of the nature and origins of the universe. This includes the search for particles that fit the theory of supersymmetry, specifically the neutralino, which could help explain the nature of dark matter.
Neutralinos and dark matter
Physicists estimate that a quarter of the universe is made of dark matter which, in essence, describes material of which we don't know the composition and which we are, at present, unable to detect directly.
The known universe is made up of a variety of subatomic particles classified as bosons or fermions.
The theory of supersymmetry predicts that for every known particle there is a corresponding unknown particle – for every boson a fermion, and vice versa – predicting a mirror-like world that establishes symmetry in the universe.
One of these unknown particles is dubbed the neutralino, the discovery of which is the one of the main objectives of the Sussex group.
If they exist, these unknown supersymmetric particles are expected to be much heavier than their known counterparts.
Because of the relationship between energy and mass, high energy would be required to produce these massive particles, which is why it is expected that they might be seen for the first time at the LHC.
Another function of the experiment is the search for extra dimensions of space, which, although we do not experience them directly, could produce microscopic effects that might be detected at the LHC.
The impact of such exotic findings may not appear immediately obvious to most people. However, the ATLAS experiment, in its search for new physics, is pushing back the boundaries of scientific knowledge to help us understand the fundamental nature of our universe and, therefore, ourselves. In more practical terms, such experimental physics has an impact on our world in other ways.
Much of the technology arising from the construction of the LHC and its detectors has found practical application in everyday life, including technology used in medical applications and in homeland security.
CERN is also a training ground for a highly computer-literate and numerate work force that is in high demand.
Sussex and the Grid
In addition CERN was the birthplace of the World Wide Web, which now permeates every aspect of our daily lives.
The next generation of the Web, the 'Grid', also has great relevance for CERN-based research.
The Grid allows the storage and sharing of the vast amounts of data generated at the LHC (too vast to be hosted on any single institution's computer system) on a federation of computers in scientific institutions around the globe, fostering a truly international collaboration.
The start-up of the ATLAS group at Sussex in 2009 gave the University a presence on the Grid for the first time, and is instrumental in raising the profile of physics at Sussex and attracting high-calibre students and staff.
This project has been supported by the Science and Technology Facilities Council (STFC) and the South East Physics Network (SEPnet)
Anthony's perspective
Anthony Rose, PhD student and Associate Tutor in Physics and Astronomy said: "This is a hugely exciting time to be working in high energy particle physics, and at the ATLAS detector in particular.
"With each passing day, the detectors at the Large Hadron Collider are collecting more data at a higher energy than it has ever previously been possible to explore, and new discoveries are imminent.
"Our current theory of fundamental particles and their interactions, known as the Standard Model, has stood undefeated by experiment since it was devised in the 1970s, and it is a hugely rewarding experience to be part of a team that is trying to break new ground in our understanding of the building blocks of the universe. My work at Sussex has focused on a search for supersymmetry, a proposed new symmetry of spacetime that results in many new particles.
"Earlier this year we placed the world's most stringent limits on the particular model that we are investigating, and this summer expect to do even better.'"