Illustration of the possible layout of the quarks in a pentaquark particle such as those discovered at LHCb.
The LHCb experiment has reported the discovery of a class of particles known as pentaquarks.
“The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson (Oxford). “It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over 50 years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.”
Our understanding of the structure of matter was revolutionized in 1964 when American physicist Murray Gell-Mann proposed that a category of particles known as baryons, which includes protons and neutrons, are comprised of three fractionally charged objects called quarks, and that another category, mesons, are formed of quark-antiquark pairs. Antiquarks are quarks of antimatter. Gell-Mann was awarded the Nobel Prize in physics for this work in 1969. This quark model also allows the existence of other quark composite states, such as pentaquarks composed of four quarks and an antiquark.
Earlier experiments that have searched for pentaquarks have proved inconclusive. Where the LHCb experiment differs is that it has been able to look for pentaquarks from many perspectives, with all pointing to the same conclusion. It’s as if the previous searches were looking for silhouettes in the dark, whereas LHCb conducted the search with the lights on, and from all angles. The next step in the analysis will be to study how the quarks are bound together within the pentaquarks.
This year’s biggest gathering of physicists took place at the European Physical Society conference on high energy physics in Vienna. It’s an opportunity for experiments around the world to present results and discuss developments in high energy physics.
A summary of the conference is available, where you can find out about the research highlights from EPS. Here are two results that were also of interest:
The LHC experiments only started taking data on 4 June but teams at all four experiments have been working hard to be the first to release a result featuring 13TeV collision data. This time, the honour went to the CMS experiment, with a measurement of the number and trajectories of charged hadrons produced in the proton collisions.
The conference also coincided with the publication of a paper in Nature Physics confirming, intriguingly, that the Universe is left-handed. The result, from LHCb, was led by a team from Imperial College and is based on a precise measurement of one the properties of beauty quark decays.
The weak force is the only one of the four fundamental forces of nature which has the strange property that it would act differently on the mirror image of our Universe. For subatomic particles, this introduces the concept of ‘handedness’, which connects how a particle spins in relation to its direction of travel. The Standard Model of particle physics predicts that the weak force only interacts with left-handed particles. This phenomenon can be tested by measuring the rate at which beauty quarks change flavour into up quarks via the weak force. The measurement was made possible by the exceptional levels of precision available with the LHCb detectors.
Ulrik Egede (Imperial and LHCb) explains: “The LHCb results are consistent with a perfectly left-handed weak force as expected from the Standard Model, in contradiction with previous hints. While we know that the Standard Model can’t explain why the Universe is dominated by matter and not antimatter, it seems like a right-handed coupling of quarks is not part of the explanation. ”
The paper does not indicate whether the Universe has the usual leftie problems with using scissors, tin openers and finding a seat in a lecture theatre with a left-leaning desk.
SpecTrometer for Exotic Fission Fragments
(Credit: University of Manchester/A Smith)
Sometimes it’s not just scientists who move from lab to lab, it’s also the experiments. Preparations are underway at CERN to install an unusual experiment that was previously collecting data at a nuclear reactor in Grenoble.
STEFF (the SpecTrometer for Exotic Fission Fragments) is helping to make making nuclear energy safer and more efficient by looking at the gamma decay of the products of fission reactions. The experiment measures both the velocity of the fragments and their energy, giving the mass and the total kinetic energy of the reaction, along with the energies of the emitted gamma rays.
The experiment was designed and built by the University of Manchester in response to the Nuclear Energy Agency’s (NEA) request for more nuclear data about gamma ray emission.
Gavin Smith leads the team, “In a nuclear reactor, the core structure gets heated by gamma rays. If you’re thinking of building a nuclear power station, or even looking at the lifetime of an existing one, you need to know that it will operate safely within its design parameters. The NEA’s data on gamma ray emission is thought have an accuracy of only 15%, with the data coming from experiments carried out in the 1970s. STEFF is going to provide more detailed and much needed data.”
The experiment was originally installed at the Institut Laue Langevin, the reactor-based neutron source in Grenoble. There, it was looking a low energy thermal neutron induced fission. The move to CERN, where the experiment will be installed in the n_TOF facility (see UKNFC 8),will allow the team to take data across a wider range of neutron energies.
“Our intention was always to move the experiment to a different type of neutron source,” explains Gavin. “We want STEFF to collect data over a range of neutron energy appropriate for future reactor designs.”
STEFF will be one of the first experiments to use n-TOF’s new experimental area, EAR2. It is currently being set-up off-line at CERN but installation of the kit in EAR2 will start in October and the experiment will start taking data in the spring 2016. The data will be reviewed and added to the NEA’s database by the UK’s National Nuclear Laboratory.
M Squared Titanium Sapphire Laser
A new laser, supplied by M Squared Lasers from Glasgow, is set to open up new capabilities on the CRIS beamline in the ISOLDE nuclear physics facility.
The titanium sapphire laser is a turn-key system requiring minimal intervention by the beamline users. That means that not only can it offer the team a range of wavelengths that were previously unavailable, it’s much safer for them to use. This state-of-the-art laser technology and automation recently led to M Squared Lasers winning an Institute of Physics Innovation award.
The £135,000 laser was funded through an ERC grant to Kieran Flanagan (Manchester and ISOLDE) and is currently being commissioned.
Congratulations to the recipients of the 2015 awards from the ATLAS collaboration, Institute of Physics and Royal Society!
The excellent work carried out by members of the ATLAS Collaboration during the Long Shutdown has been recognised. 92 people were nominated, 26 awards were made and UK institutes were well-represented.
James Frost (Oxford) was recognised for his contribution to data preparation. His Oxford colleague, Koichi Nagai was acknowledged for his dedication to Semiconductor Tracker operations and Run 2 commissioning.
Warwick post-docs, Tim Martin and Elisabetta Pianori received awards for their dedication to the implementation and commissioning of the highly complex Run 2 trigger menu.
Mark Sutton (Sussex), Jiri Masik (Manchester), Dmitry Emeliyanov (STFC) and Stewart Martin-Haugh (STFC) were recognised for the significant improvements in the performance, timing and flexibility of the trigger tracking software.
It was a bumper crop of awards for STFC - Bruce Barnett’s contribution to the Level 1 calorimeter trigger over many years, and in particular during LS1, was also celebrated.
The awards were presented by ATLAS Spokesperson, Dave Charlton (Birmingham).
Amanda Cooper-Sarkar (Oxford and ATLAS) has been awarded the Chadwick Medal and Prize for her study of deep inelastic scattering (DIS) of leptons on nuclei which has revealed the internal structure of the proton. Her expertise in the area of DIS, gained from the Hadron Electron Ring Accelerator at the German Electron Synchrotron (DESY), will be applied to the Large Hadron Collider, where the techniques of structure function data analysis are essential for virtually all precision measurements, including in the area of Higgs physics.
Jim Virdee (Imperial) has been awarded the Glazebrook Medal and prize for his leadership of the CMS experiment. Jim was one of the physicists who first proposed the experiment and is a former Spokesperson of CMS.
Chris Lintott (Oxford) has been awarded the Kelvin Medal and Prize for his major contributions to public engagement with science through conventional media (especially through television) and by leading citizen science projects through Zooniverse, where hundreds of thousands of people can participate in the process of scientific discovery. Via Zooniverse, everyone can become a Higgs Hunter!
Nobel Laureate Peter Higgs has been awarded the Copley Medal for his fundamental contribution to particle physics with his theory explaining the origin of mass in elementary particles. The announcement of the discovery of a Higgs-like particle was made by the ATLAS and CMS collaborations in 2012. One of the LHC experimental goals for Run 2 is to find out more about the properties of the Higgs particle.
Chris Llewellyn Smith (Oxford) has been awarded the Royal Medal for his major contributions to the development of the Standard Model, particularly his success in making the case for the building the LHC. Chris is president of the SESAME Council and a former Director General of CERN.
CERN Summer School 2015
Tom Parton and Benjamin Perceval, along with more than 280 fellow students from around the world, are enjoying the unique combination of lectures, activities and hands-on research projects.
Tom has just completed his degree at UCL and will start a Masters in theoretical physics at Cambridge in October. He’s been very impressed by the lectures, “they are very well-presented – I’ve got new insights into my existing knowledge. They’ve covered general physics, the nuts and bolts of the experiments as well as detector technology and applications.”
Students spend the first few weeks of their time at CERN attending lectures in the morning, and doing their projects in the afternoon. Tom is working on an essential project to upgrade the ATLAS end cap muon detectors, “The original detectors pick up lots of background noise. When the LHC increases luminosity, it would be impossible to detect the muon signal.” The new technology will be installed ready for Run 3 in around five years’ time
Tom has been surprised by the people that he’s met, “I came here with a sense of trepidation – I thought everyone would be very technical and only interested in their own project. Whilst they obviously love what they do, they also do so many other things outside work.”
The social side of the Summer Student Programme shouldn’t be underestimated; this is, after all, an important networking opportunity. Most of the students who take part in the programme are planning a career in physics, engineering or computer science, and the class of 2015 will kick-start their international contacts list.
The range of social activities has certainly surprised Benjamin Perceval – he’s a new recruit for the CERN cricket team (the second oldest club in Switzerland). Benjamin is about to go into the final year of an integrated masters in maths and physics at Durham University.
Benjamin is particularly interested in theoretical particle physics and his project is modelling the effects of magnets on beam extraction from the PS accelerator into the SPS. “It’s about managing the oscillation of the beam – the particles in the beams undergo perturbations about their circular orbit - and we want to optimise the magnetic field to control the beam. I’ve been really lucky with the project that I’ve got – it suits me very well!”
Benjamin’s lecture highlight has been Yuval Grossman’s series of talks on theoretical concepts in particle physics. The programme includes many of the world’s leading exponents in their fields, and Benjamin appreciated the chance to chat to Yuval after the talk.
Both Benjamin and Tom are hoping to go on to study PhDs, but what about the students that UKNFC met last year ?
Harry Cutts took part in the OpenLab programme for IT students. One of the visits included in the programme turned out to be unexpectedly inspiring; “In October, I'm moving to California to work as a Graduate Software Engineer for Google (whose Zurich office the OpenLab students toured last summer). My time at CERN, as well as being extremely enjoyable, was what got my CV noticed in Google's pile of applications, I suspect. I'd highly recommend applying for CERN's summer programmes, as it'll be an unforgettable experience.”
For Constantin Weisser, being a summer student at CERN and working on hardware for ATLAS was an invaluable experience, “While I was a summer student I met Markus Klute from MIT and made my mind up about possible PhD projects. Currently, I am taking part in a summer school organised by the European Space Agency and am preparing for my PhD with Markus at MIT which will start in August. For that I will work on data analysis for CMS, but the exact topic has not been decided upon. Being a summer student was certainly one of best things I have done so far - it continues to open doors to new experiences for me. See you soon, CERN!”