Experimental Particle Physics

Flavour physics describes the different types of matter particles (quarks and leptons) and flavour-changing interactions. We are striving to answer fundamental questions such as why particles have different masses and why the Universe is made of matter (or where is the anti-matter)? Lancaster investigates these questions through research involving both quarks and leptons. We also use particles containing heavy quark flavours to examine the nature of the strong interaction that binds quarks and antiquarks together to form hadrons and holds together protons and neutrons to form atomic nuclei.

We study the fundamental properties of neutrinos at the Tokai to Kamioka (T2K) experiment in Japan, the MicroBooNE and MINOS+ experiments at Fermilab, USA and the SNO+ experiment in SNOLab, Canada. By studying neutrinos from a wide range of sources, both natural and man-made, the transformation of one neutrino into another (oscillations) can be investigated. Such oscillations can be used to search for CP violation in the lepton sector, which may explain the observed dominance of matter in our universe. They also permit a search for physics that is not defined by the Standard Model. The T2K experiment has shown the first hints that this CP violation is non-zero through precise measurements of the appearance of electron neutrinos in a muon-neutrino beam. The SNO+ experiment in Canada studies oscillations of neutrinos emitted by our Sun.

We are also studying the matter anti-matter asymmetry using the ATLAS experiment via decays of particles containing bottom (b)-quarks. The primary process examined is the decay of the Bs or its antiparticle to a J/ψ and a φ particle. In our Standard Model of particle physics, this decay can behave differently for the particle and antiparticle. Our studies attempt to measure the difference and are an indirect way of searching for new particles 'beyond the Standard Model', which can enhance or reduce the difference through quantum mechanical effects. We also study the decays of other particles containing beauty quarks, looking both for expected and unexpected states.

Lancaster is also making precision measurements of the decay of the top quark to tau leptons.

Team

• Dr Andrew Blake
• Professor Guennadi Borissov
• Professor Roger Jones
• Professor Vakhtang Kartvelishvili
• Dr Laura Kormos
• Dr Jaroslaw Nowak
• Dr Helen O'Keeffe

The Standard Model of particle physics cannot wholly explain the observed Universe. For example, it cannot explain the existence of dark matter and dark energy. Lancaster is carrying out an extensive programme searching for phenomena that are not included in the Standard Model.

The NA62 experiment will search for new physics at energy scales up to 100 TeV by observing and studying the ultra-rare decay of a charged kaon (K±) to a charged pion (π±), a neutrino and an anti-neutrino (which only occurs in one in 1010 decays). NA62 is also searching for dark matter candidates such as heavy neutral leptons, dark photons and axion-like particles as well as looking for differences between matter and anti-matter.

The study of neutrino oscillations also enables searches for new physics. For example, the MicroBooNE experiment is searching for oscillations mediated by hypothesised 'sterile' neutrinos, which cannot be detected directly. Both T2K and MINOS+ (which has now completed its data-taking phase) are also conducting searches for sterile neutrinos.

The SNO+ experiment will be used to search for neutrinoless double-beta decay and invisible modes of nucleon decay. An observation of neutrinoless double-beta decay would indicate that neutrinos are their own antiparticles, with wide-ranging implications for both particle physics and cosmology.

On the ATLAS experiment, we are searching for new massive particles that decay to a pair of particles, for example, two quark jets, two Higgs or two J/ψ particles. In all of these analyses, we are searching for a resonance (peak) in a mass spectrum.

We are searching for:

• excited quarks
• quantum black holes and additional bosons that can decay to two jets
• gravitons that can decay to two Higgs particles
• hidden supersymmetric particles that can decay to two J/ψ particles (or other onia)

Team

• Professor Iain Bertram
• Dr Andrew Blake
• Professor John Dainton
• Dr Harald Fox
• Professor Roger Jones
• Professor Vakhtang Kartvelishvili
• Dr Jaroslaw Nowak
• Dr Helen O'Keeffe
• Dr Giuseppe Ruggiero

We are investigating the properties of the recently-discovered Higgs boson. In particular, we measure the CP properties of the Higgs boson and the fraction of Higgs particles that decay to taus. When the LHC is running at High Luminosity, the measurement of the cross-section of two-Higgs events will be used to determine the shape of the Higgs potential. We are also working on the International Linear Collider, a Higgs factory that is planned to be built in Japan. The Higgs boson properties will be measured with high precision when this e+ e- collider is made.

We are searching for unusual or exotic combinations of quarks which can shed light on the strong interaction. During the few first years of LHC running, we were pleased to discover the first new particle seen at the LHC, the χb(3P). To study the strong interaction, we focus on particles called ‘onia’ that are made up of quark-antiquark pairs. Their production and various ways of decaying act as a very precise test of theories of the strong interaction. We also study the creation of pairs of onia and onia in association with other objects such as W and Z bosons. These can test essential processes such as double parton scattering, which is a necessary background to understand when searching for new particles and when studying the decays of the Higgs boson. Such studies can also reveal the unexpected; in the D0 experiment, we have observed a state, the X(5568), which we interpret as a combination of two quarks and two anti-quarks.

An understanding of how neutrinos interact with matter is essential for current and future neutrino oscillation experiments as well as for testing the Standard Model of particle physics. Because neutrinos only interact via the weak force, they are challenging to study, resulting in limitations to current neutrino interaction cross-section data and models. Using data and measurements from existing experiments such as MicroBooNE and T2K, neutrino interaction models can be investigated and improved. These experiments will lead to a better understanding of neutrinos and improved precision for future investigations. We measure neutrino interaction cross-sections as well as develop the Monte Carlo models that allow us to test our understanding.

Team

• Professor Iain Bertram
• Dr Harald Fox
• Professor Roger Jones
• Professor Vakhtang Kartvelishvili
• Dr Jaroslaw Nowak
• Dr Laura Kormos
• Dr Helen O'Keeffe

Lancaster plays critical roles in the research and development for upcoming neutrino experiments DUNE and SBND in the USA, and Hyper-Kamiokande in Japan, as well as on upgrades for the ATLAS detector at the LHC at CERN. Using our extensive experience of and understanding from existing experiments, we are helping to shape the future of particle physics, keeping Lancaster at the forefront of the field for years to come. This work includes not only hands-on hardware development and construction, but also data simulations and sensitivity studies, detector design optimisation, quality assurance, data acquisition and triggering methods, and particle reconstruction algorithms.

Upgrades to the LHC accelerator are planned to increase the luminosity, which will enable the experiments to collect up to 3000 fb-1 of data. This will lead to severely increased occupancy and radiation damage of the tracking detectors.

The ATLAS experiment plans to introduce an all-silicon inner tracker to cope with the elevated luminosity. Lancaster is involved in several aspects of the construction of the new sub-detector. We will test all UK pixel endcap sensors before they are assembled and are developing expertise with FPGA-based readout systems to be able to test individual pixel modules and the detector during assembly – with up to 5 Gbit/s. We are also leading experts for bending the CO2 cooling pipes made from Titanium with only 100 µm wall thickness into the required shapes and will pressure-test them to make sure they are safe at up to 100 atmospheres.

One recurring challenge for future particle physics investigations is that the experiments are getting larger and larger. Instrumenting of larger and larger volumes with existing technology is very costly – therefore, new ideas for cost-efficient particle detectors have to be pursued, and we believe that the key to realising significant savings is to use industrially available technologies for our purposes. One example of industrially available technology is HV-CMOS processes that are typically used to produce ASICs (application-specific integrated circuits) for the automotive industry. We found that they can also be used to create outstanding particle detectors. Lancaster is focusing on understanding the radiation damage to the silicon bulk of these sensors.

Another example is to assess whether thin-film technology – capable of producing square-meter-size panels for TFT-screens and solar cells at a little cost – could be used to create particle detectors. To this end, Lancaster has teamed up with collaborators in Mexico, the USA and Germany; our expertise is in exploring sensors based on GaAs and c-Si (single-crystalline silicon) thin films. We are also looking into the option to create cost-efficient scintillation detectors from a cheap, everyday plastic: PEN (Polyethylene naphtalate). In this project, we are collaborating with colleagues in Dortmund, Munich, Prague and at Oak Ridge National Laboratory.

Team

• Dr Andrew Blake
• Dr Harald Fox
• Dr Laura Kormos
• Dr Daniel Muenstermann
• Dr Jaroslaw Nowak
• Dr Helen O'Keeffe

To do all of this exciting physics, advanced software and a global computing system are required. At Lancaster, we are developing tracking tools for the high luminosity future running of ATLAS, as well as the software frameworks to exploit new computing techniques and architectures. We also develop the job management software required to simulate, process and analyse LHC data in a comprehensive computing system. We provide one of the most extensive computing and data storage facilities for particle physics and participate in the management and operation of the distributed computing for particle physics and other physical sciences in the UK.

Team

• Professor Roger Jones

Supervisor

Professor Roger Jones

Description

The PhD will analyse new data from the world’s largest collider, LHC, situated in CERN. The data are taken after the LHC upgrade to an energy of 13 TeV. After the enormous success of the LHC in 2010-2012, culminating with finding the Higgs particle, we have now opened a new chapter in the search for New Physics. The high precision measurements of B-hadron decays allow for indirect searches for new physics, where new particles that are produced virtually alter the decays so they do not follow rules of the Standard Model. This builds on Lancaster’s leading role in the ATLAS analysis of the 2010-2012 data to search for SUSY in CP-violating of Bs-decays, which led to 3 publications in influential journals. From 2015 ATLAS has an upgraded Inner Detector with additional pixel layer (IBL), which has substantially increased a lifetime measurement precision. This change will allow ATLAS to measure CP violation in Bs meson decays with unprecedented precision and will increase the potential for finding possible SUSY effects.

We propose two distinct physics measurements, both searching for New Physics in CP violation. They study the decay channels Bs ➔J/ψφ and Bs ➔J/ψKK. The methodology is similar, while a physics potential is different. These two measurements are complementary to each other, and the conclusion on CP effects can be only done by performing both. Also, we propose a high precision measurement in channel B+ ➔J/ψK+, which is both a stringent test of the detector performance and calibration and has new interesting physics information in its own right.

Supervisor

Professor Roger Jones

Description

The PhD will analyse new data from the world’s largest collider, LHC, situated in CERN. The data are taken after the LHC upgrade to an energy of 13 TeV. After the enormous success of the LHC in 2010-2012, culminating with finding the Higgs particle, we have now opened a new chapter in the search for New Physics. This proposed search for displaced supersymmetric (SUSY) particles is an example of a “direct search” in which the signal would be distinguished by an excess of displaced vertices relative to those coming from Standard Model. The search will look for events with a pair of leptons (muons, electrons) produced at a point between 0.01 cm and 2 cm from the original collision sideways from the beams. The search will be designed to be sensitive to a wide range of SUSY models with non-prompt di-lepton final states. From 2015 has an upgraded Inner Detector with additional pixel layer (IBL) that has substantially increased the precision with which the production point of the lepton pair can be resolved. This change will allow ATLAS to hugely improve the signal/ background separation for SUSY particles decaying in the range we will study.

The PhD will study two decay channels, searching for displaced supersymmetry in oppositely charged muon-muon pairs and electron-muon pairs. While the selections are different, the methodology is similar: in both cases, the central part of the analysis is the reconstruction of the displaced vertex and the impact parameters of leptons.

Supervisor

Dr Vakhtang Kartvelishvili

Description

A heavy quark-antiquark bound state - has been an object of experimental and theoretical investigations over more than 40 years. Apart from an insight into the workings of Quantum Chromodynamics (QCD, the theory of strong interactions) quarkonium production at the LHC appears to be exceptionally useful in a wide variety of tasks, ranging from detector performance and trigger efficiency studies to the determination of the Higgs boson couplings to fermions. Members of the Lancaster group have been instrumental in the vast majority of quarkonium studies performed in ATLAS.

Recently a variety of "new observables" in quarkonium production studies have been suggested, some of which - the production of vector quarkonium in association with a vector boson - have been performed in ATLAS. They showed a large excess over the expectation of theoretical calculations, thus injecting new interest into quarkonium physics. Other similar measurements are planned using the data from Run II of the LHC. A new PhD student will be expected to play a major role in one or more of these analyses.

Supervisor

Dr Harald Fox

Description

At Lancaster, we work on the Higgs boson decay mode into two tau leptons. With this channel, we contributed to the Higgs discovery in 2012. There are two projects possible exploiting this particular final state.

The first project is investigating the Higgs boson further. The di-tau final state is the most accessible fermionic final state. Measuring the Higgs branching ratio into fermions directly is one of the tests of the Standard Model. Anomalous couplings of the Higgs boson would be a hint of new physics. The di-tau signal also allows one to measure the CP properties of the Higgs boson.  The Standard Model predicts a CP-even (scalar) Higgs with no CP violation in the production or decay. On the other hand, we know that there is not enough CP violation in the quark sector of the Standard Model to explain the existence of the universe. Observation of a new source of CP violation is hence necessary. Measuring the Higgs couplings and its CP properties is hence an important test for the Standard Model.

The second project uses the Higgs boson as a portal to new physics beyond the Standard Model. Here we are investigating the production of two Higgs bosons together, where one decays into a pair of b-quarks and the other into a pair of tau leptons. Di-Higgs production is predicted by the Standard Model and will be used to determine the exact shape of the Higgs (Mexican hat) potential. However, other processes predict an enhancement of this signal, e.g. the decay of Randall-Sundrum gravitons or the decay of further, heavy Higgs bosons. In this project, you will be looking for new physics beyond the Standard Model in this decay mode.

Supervisor

Professor Iain Bertram

Description

Currently, our best description of the theory of fundamental interactions of particles, the standard model of particle physics (SM), does not describe the Universe we live in. The SM cannot explain the observed matter-antimatter asymmetry of the Universe. This is before we consider the problem the 95% of the Universe that is made up of "dark" matter and energy of which the SM has nothing to say.

The LHC is currently the highest energy accelerator in the world, the probing centre of mass energies up to 13 TeV. Jets of hadronic particles with transverse momenta of several TeV are produced in these collisions and are sensitive to the presence of physics beyond the SM. You will be searching for new particles that will appear as a peak in the mass spectrum or as a deviation from the predictions of the standard model (for example the angular distribution of the jets). These searches will be carried out by using jets that contain b-mesons (heavy quarks) and/or using multi-jet events to search for more esoteric particles.

Supervisor

Dr Daniel Muenstermann

Description

Future particle experiments will impose extreme requirements on their tracking detectors, taking today's silicon sensor technology to the very limit. To extend the physics reach of the LHC for example, upgrades to the accelerator are planned which will increase the peak luminosity by a factor 5 to 10. This will lead to much-increased occupancy and radiation damage of the sub-detectors, requiring the exchange of the current inner trackers with all-silicon ones.

Lancaster has a long-standing tradition of silicon detector R&D in CERN's RD50 collaboration and is now focusing on R&D for future pixel detectors – the innermost sub-detector of particle physics experiments and thus exposed to the harshest conditions. Possible PhD projects would include irradiation and characterisation of prototype planar pixel sensors, which are the baseline choice for all LHC detector upgrades and CLIC.

Beyond those, the PhD project may also involve the characterisation of novel HV-CMOS pixel sensors which promise very good radiation tolerance while being extremely lightweight and cost-efficient. The first large-area prototype chip has just been received from the foundry; initial results from this chip are eagerly awaited by the community and could be part of the PhD project.

Supervisor

Dr Laura Kormos

Description

The Tokai-to-Kamioka (T2K) long-baseline neutrino oscillation experiment sited in Japan is well-established and was the first experiment to indicate that mixing occurs between all three neutrino flavours.  This finding opened the door to leptogenesis, in which neutrinos play a major role in the formation and evolution of our matter-dominated universe, which as yet is unexplained. Recent results from T2K suggest that we may be on the brink of discovering yet another necessary ingredient for this hypothesis: CP violation in the lepton sector.  However, at present T2K cannot make a definitive statement because it doesn't have enough data. As we collect more data, we also must reduce our systematic uncertainties to ensure that they don't become the limiting factor in our understanding of the matter-antimatter asymmetry.  One of the largest uncertainties is our understanding of neutrino interactions.  The student on this project would work on this problem in two ways:  by measuring the rates in the T2K off-axis near detector of neutrino interactions on various nuclei that result in the production of specific particles, and by comparing the results to the predictions of the models and subsequently playing a role in modifying the models.  This will lead to a published cross-section measurement in an area where there are few or even none. T2K has had impressive success with using data from the near detector to constrain the uncertainties in their oscillation results (it halves them), and the constraints provided by measurements such as the ones above are key to measuring matter-antimatter asymmetry via neutrino oscillations.  The student also will spend some months on-site in Japan, acting as a detector expert and doing data-taking shifts.

Supervisor

Dr Laura Kormos

Description

The SNO+ experiment, sited at SNOLab in Canada, aims to search for neutrinoless double-beta decays in Te-130.  If observed, these decays would demonstrate that neutrinos are Majorana particles, a necessary condition for a theoretical hypothesis called leptogenesis in which neutrinos provide enough matter-antimatter asymmetry in the early universe to explain its existence.  But SNO+ can address many other areas of neutrino and particle physics as well.  Detector commissioning began in November 2016, to be followed with some months of data-taking with the detector full of ultra-pure water, then with the scintillator, and finally, the Te-130 will be added.  This large, deep-underground detector allows us to search for nucleon decay, dark matter candidates, and make significant contributions to our understanding of geophysical, reactor and solar neutrinos.  The student on this project would explore one or more of these topics using the SNO+ data, leading to a publication.  The student will also spend some months on-site in Canada, operating the detector and doing data-taking shifts.

Supervisor

Dr Helen O'Keeffe

Description

The SNO+ experiment is a multi-purpose 1 ktonne liquid scintillator experiment that will study low energy neutrinos from a variety of sources.  With the addition of 130Te to the scintillator, a search for neutrinoless double-beta decay will be performed to yield information on whether the neutrino is a Dirac or Majorana particle.  Possible PhD projects include the study of low energy radioactive backgrounds and their impact on the sensitivity to neutrinoless double beta decay and/or solar neutrino physics.  The project would include aspects of laboratory work, data analysis and computer simulation.   It is expected that PhD students would spend 9-12 months on-site in Canada.

Supervisor

Dr Helen O'Keeffe

Description

The Tokai to Kamioka (T2K) experiment is a long-baseline neutrino oscillation experiment located in Japan.  An intense beam of muon neutrinos is created in Tokai and its composition is measured 280 m and 295 km downstream of the neutrino production point.  Comparison of the beam composition measured by the two detectors yields information on whether neutrino oscillations have occurred.  Hyper-Kamiokande is the next-generation experiment planned to follow on from T2K.  Possible PhD projects include measurements of (anti)-neutrino neutral pion production in the T2K near detector and sensitivity studies for the Hyper-Kamiokande experiment.

It is expected that PhD students would spend 9-12 months on-site at the near detector in Japan supporting ECal and/or DAQ operations.

Supervisor

Dr Andrew Blake

Description

The MicroBooNE experiment has recently begun operating in the Booster neutrino beamline at the Fermi Laboratory near Chicago USA. Its 100-ton detector is pioneering the use of Liquid Argon Time-Projection technology and offers the ability to measure neutrino interactions with unprecedented spatial and calorimetric precision. Over the coming years, MicroBooNE will perform new measurements of accelerator neutrinos and will demonstrate the exquisite imaging capabilities of Liquid Argon technology. It will also shed new light on previous experimental results from the MiniBooNE and LSND experiments, which hint at the existence of a fourth species of sterile neutrino, a potentially major discovery. In 2018, MicroBooNE will be joined in the beamline by the Short-baseline Near Detector (SBND), providing a high-statistics neutrino data set and a powerful multi-detector search for sterile neutrinos. The Lancaster neutrino group is currently working on neutrino event reconstruction and data analysis for MicroBooNE, and detector construction and software development for SBND. A new PhD student would collaborate on the operation of MicroBooNE, commissioning of SBND, analysis of data, and publication of neutrino physics results. It is expected that the student would spend a long-term attachment at the Fermi Laboratory.

Supervisor

Dr Jaroslaw Nowak

Description

The protoDUNE is a full-scale engineering prototype of the DUNE far detector and will be the largest Liquid Argon Time Projection Chamber (LArTPC) detector with almost 1kTon mass. protoDune will be placed at CERN on a test beam to aid the future long-baseline experiments with reduction of the systematic uncertainties. One of the highest uncertainties comes from hadrons interaction in the medium after they are produced in the neutrino interactions. The PhD projects will focus on the measurement of the pion and kaon cross-sections on argon for particles with momenta from about 500MeV/c to 7GeV/c. PhD candidates will be required to spend significant time at CERN and help with the installation and operation of the detector.

Supervisor

Dr Jaroslaw Nowak

Description

In the last decade measurements from several neutrino experiments (MiniBooNE, NOMAD, MINERvA, T2K) showed that our understanding of neutrino cross-sections is limited. The introduction of new processed (MEC, 2p-2h) which caused a paradigm shift in the way we think about the nuclear effects. Our understanding of the neutrino interaction cross-sections and cross-sections of the hadrons with the medium after they are created in the neutrino interactions are necessary to achieve a reduction of the systematic uncertainties required by the future long-baseline experiments, which will measure CP violation in the neutrino sector.

Several PhD projects are available: precise neutrino cross-section measurements with any of the experiments the Lancaster group is a member (T2K, MicroBooNE, SBND), development of NuWro neutrino Monte Carlo generator, measurement of proton and pion interactions on argon with the two test beam experiments at CERN (protoDUNE and HPTPC). PhD candidates will be required to spend about one year overseas to help with the operation of the experiment.