High Energy Physics - CMS
- CMS cavern radiation detection
- Medipix imaging
- Dr Orlon Petterson
- Alan Bell
(MSc submitted 28 Feb 2008)
- CMS Beam Scintillation Counter
The universities of Canterbury and Auckland have been members of the CERN CMS collaboration since December 2003 when a Memorandum of Understanding was signed between the New Zealand government and CERN (the European Organisation for Nuclear Research). This MoU granted the NZ institutes access to CERN facilities and programmes. Since then NZCMS, a collaboration of NZ scientists participating in the CMS experiment, has been formed with members in UC, UA and Massey University, to oversee NZ's activities within the CMS collaboration.
CMS is CERN's Compact Muon Solenoid detector - a general-purpose particle physics detector built at one of the four interaction points of the Large Hadron Collider (LHC) proton collider. When the LHC begins operation in December 2007, it will be the largest energy machine in the world. "CMS" also refers to the 2000 person CMS Collaboration which will build, operate and analyse data from the machine. New Zealand makes up about 0.2% of the CMS collaboration in manpower, but has still managed to make a very visible contribution to the project.
The primary aim of the LHC experiments, CMS included, is to search for the elusive Higgs boson. The Higgs boson is the final particle required to complete the Standard Model of Particle Physics - a model which has been highly effective in describing the particles and interactions which have been observed to date. The Higgs boson is predicted by the theory of spontaneous summetry breaking, which is a process by which particles can attain non-zero masses while still allowing a mathematical predictive theory (other means of giving particles mass tend to result in calculations breaking down with unmanageable infinities and thereby losing their predictive ability).
While the Higgs is the main focus of CMS, there are also very large groups within the collaboration who will use the CMS data to seek other new particles, for example Supersymmetric particles (supersymmetry is a theory which unites the families of half-integer spin matter particles (electrons, quarks, ...) with the integer-spin exchange particles (photons, gluons, ...) by hypothesising the existence of a new super-particle (sparticle) for each known particle). Also we will work to understand the nature of Dark Matter and Canterbury University will contribute towards the study of the cosmologically-observed excess of matter over antimatter by looking for asymmetries in the decays of B mesons.
Other CMS studies will focus on searches for "new physics" interactions, improved measurements of Standard Model parameters and Heavy Ion interactions. After about 18 months of 14 TeV proton-proton collision data-taking, the LHC will switch to colliding ions of heavier species, e.g. lead and gold nuclei. Collisions at the LHC energies are predicted to produce a new matter state known as Quark-Gluon Plasma (QGP) which is believed to be the state of matter in the earliest instances of the universe, before the quarks and gluons bound themselves into the colourless states that are observed today.
CERN, the European Centre for Nuclear Research, is located in Geneva, Switzerland near the French border. The facility actually has two sites, the largest being in Meyrin, in Switzerland, and the second in Previsson, in France. The LHC's 27km collider rings run underneath both sites in a tunnel 100m below ground.
CMS is a multipurpose particle physics detector build at one of the proton-proton collision points of the LHC. Physically, it is several kilometers away from the main CERN site at the opposite side of the LHC's 27km circumference ring.
Fortunately most of the operations using the CERN LHC experiments are remote controlled, with most research buildings and detector monitoring labs being together in the Meyrin site.
The Worldwide Large Hadron Collider Computing GRID (WLCG) is an international project to harness the computing power of thousands of CPUs and many petabytes of storage space to store, process and analyse data from the CERN LHC detector.
New Zealand can join the WLCG by providing a Tier2 data centre - this will involve storing several terabytes of CMS data, and providing 100-200 CPUs to analyse data. Connecting this modest site to the WLCG will then enable us to access the vast computing power and storage of the world's GRID computing resources.
Once the LHC begins taking physics data (early/mid-2008) it will log 12 Petabytes of raw data a year. This data needs to be processed to select collision events in which interesting interactions have occured (very few needles in a vast haystack), and to reconstruct physics objects such as the pions, kaons, B mesons, ... which have been produced - not to mention the search for the Higgs Boson!
All this data is too much to store at CERN, so it will be distributed among approximately a dozen "Tier 1" computing centres around the world (including Fermilab in Chicago, Italy, Taiwan, ...) and smaller subsets of data wit specific selected features will be sent out to smaller "Tier 2" centres which will serve local communities and provide both storage and a large amount of computing power for all GRID members. The user will simply have to plug into the grid, fill in an online form saying which type of data they want to analyse, and submit the analysis job with their user-specific code. A resource broker will find a site with the appropriate data, and a nearby site with some computing power - somewhere in the world - and will send the job, collate the result, and deliver them to the user who doesn't have to know anything about which country had which set of data.
Grid certificates will be used to identify users and provide security.
Aided by colleagues on the LHC ATLAS detector project from Melbourne University, Orlon Petterson has already established a miniGrid in the UC Physics and Astronomy department. We are working towards establishing a partnership with a Tier 1 centre in either Korea or Taiwan to source CMS data through the KAREN network once the LHC switches on.
While we await the turn-on of the LHC there are many urgent tasks occupying the detector collaborations. Three of these which UC is actively involved in within the CMS collaboration are:
With hundreds of physicists poised to analyse the vast datasets which will be recorded by the CMS detector, analysis software needs to be written, tested and documented. CMS delivers a series of monthly tutorials to help users get to grips with asects of data-taking and analysis. UC takes a leading role i nproviding online documentation of these tutorials and introductory material through editing the CMS "WorkBook" - an online how-to manual for all aspects of data analysis with the CMS experiment. For more advanced users, a Sofware Manual is also maintained with indepth instructions and coding guidance. (There is also a self-documenting "reference manual" which contains explicit information about classes and packages in the CMS analysis suite.)
UC has contributed to the UA-led effort on the beam protection system for CMS. The system is designed to provide early warning of unfavourable/unsafe conditions in the LHC proton beams to enable shut-down of the beams before the sensitive detector components are damaged.
The NZCMS collaboration is also working on building the "Beam Scintillator Counter System" - a low-luminosity detector system to study the beams at the earliest running period of the LHC and to detect the clouds of muons which travel with the beams. It consists of panels of scintillation material at either end of the CMS detector. The scintillator panels are connected to photo-multiplier tubes which use optical fibres to feed their responses out to the data acquisition system.
In 2007, Masters student Alan Bell will be based at CERN to complete the construction of the BSC in time for the startup of the LHC.
See GRID computing notes on this page.
Other Projects with CMS
- UC is currently looking into projects which involve measuring the radiation produced in the cavern housing the CMS detector when the collider and detector are fully operational.
- Auckland University is developing analysis programmes for the Heavy Ion running of the LHC which will occur after a large amount of proton-proton collision data has been taken.
- UC and Massey are working with CERN colleagues to look into possible theoretical physics studies involving interactions which may be seen at the LHC
In October 2006, NZCMS held an international conference in High Energy Physics and Medical Physics at the Chateau-on-the-Park hotel in Christchurch. 50 scientists from around NZ and abroad attended and presentations included talks on CERN, the LHC and the CMS experiment, the Australian Synchrotron, Medipix and RICE/ICECUBE. The conference was sponsored by CERN, the Royal Society of New Zealand, CMSAlphatech, and the universities of Canterbury and Auckland. The conference website, with links to presentation abstracts is, at http://www2.phys.canterbury.ac.nz/~jcw83/conf/agenda.php.
CERN offers a number of educational and research opportunities each year to member state nationals (there are about 20 European "member states"), as well as to non-member state participants. The CERN management have been particularly encouraging and welcoming to New Zealand in enabling us to have students from UC and UA contribute in their programmes.
CERN Summer Studentship Programme
The CERN Summer Studentship Programme runs between June and September and provides an opportunity for students to attend lecture courses given by leading researchers. In addition, CERN organises several workshops and all participants are assigned to research/development groups to work on an assigned project during their stay. The projects vary from hardware and electronics to detector monitoring, software design and writing simulations and accelerator physics.
Recent NZ CERN summer students:
- 2009:Hamish Silverwood (UC) and Jason Tam (AUT)
- 2007: Sam Whitehead -
- 2006 Giles Reid - simulation using GEANT
- 2005 Karla Kincaid - Medipix imaging project
Applications for the summer studentship programme are invited in December for the following year, with a deadline of mid-January. Presently NZ's CERN summer studentship coordinator is Prof Phil Butler.
Other CERN student programmes
CERN also runs an Accelerator School and an annual School of Computing (both of which are generally held offsite in a different European location each year).
As well as this, CERN offers a Technical Studentship for students based overseas to spend up to a year working on an approved CERN project.
Other student visits to CERN
From time to time we are able to offer short (2-6 week) placements at CERN to work on specific NZCMS projects with other NZCMS scientists and/or CERN scientists. If you are interested in such an opportunity, it is useful to let the UC academics on CMS know in advance so that we know there is manpower available if an opportunity arises.
Student visitors to CERN tend to stay either in the CERN hostel onsite, or in St Genis, just over the border in France in accommodation which is within walking distance of the CERN facility.
More information about CERN can be found at: http://www.cern.ch/