UCL HEP Seminars 2010
: John Baines (RAL)
Performance of the ATLAS Trigger in 2010 running
The ATLAS trigger has been used very successfully to collect collision data during 2009 and 2010 LHC running at centre-of-mass energies of 900 GeV, 2.36 TeV, and 7 TeV. The trigger system reduces the event rate, from the design bunch-crossing rate of 40 MHz, to an average recording rate of 200 Hz. The ATLAS trigger is composed of three levels. The first (L1) uses custom electronics to reject most background collisions, in less than 2.5 us, using information from the calorimeter and muon detectors. The upper two trigger levels, known collectively as the High Level Trigger (HLT), are software-based triggers. As well as triggers using global event features, such as missing transverse energy, there are selections based on identifying candidate muons, electrons, photons, tau leptons or jets. I will give an overview of the performance of these trigger selections based on extensive online running during LHC collisions and describe how the trigger has evolved with increasing LHC luminosity. I will end with a brief overview of plans for forthcoming LHC running including future trigger upgrades.
: Justin Evans (UCL)
Latest Results from the MINOS experiment.
The MINOS experiment uses a muon neutrino beam, over a baseline of 735 km, to measure neutrino oscillation parameters. A number of new results have been released this year. The observation of muon neutrino disappearance has allowed the world's most precise measurement of the largest neutrino mass splitting, and a competitive measurement of the mixing angle θ_23. A search for the appearance of electron neutrinos yields limits on the as-yet-unmeasured mixing angle θ_13. A measurement of the neutral current interaction rate allows limits to be placed on the existence of sterile neutrinos. Data has also been taken with a dedicated muon antineutrino beam. This data has been used to make the first precision measurement of the muon antineutrino oscillation parameters; any observed difference from the neutrino parameters would be evidence for physics beyond the standard model.
: Gunther Roland (MIT)
Long-range correlations in high-multiplicity proton-proton collisions at the LHC
The CMS collaboration recently announced the observation of long-range near-side angular correlations in proton-proton collisions at LHC. In this measurement, we have found a novel correlation where particles produced in the collision are aligned in their azimuthal angle over a large pseudorapidity region. This "ridge"-like structure is absent in minimum bias events but emerges as the produced particle multiplicity reaches very high values. This phenomenon has not been observed before in proton-proton collisions but resembles similar effects seen in collisions of nuclei such as copper and gold ions at RHIC. In this talk, I will report on the experimental aspects of this measurement and discuss some of the recent proposals regarding the physical origin of the effect.
: Adam Davison (UCL)
Exciting results from the ICHEP 2010 conference
A review of the exciting results presented at this year's International Conference on High Energy Physics in Paris this summer.
: Subir Sarkar
Antimatter in cosmic rays: new physics or old astrophysics?
There has been considerable excitement generated by recent 'anomalies' in galactic cosmic ray and gamma-ray observations, indicative of dark matter annihilation or decay. It is essential to have a reliable evaluation of the astrophysical 'background' in order to evaluate such claims. I will focus on the PAMELA, Fermi and HESS data and discuss whether these can be accommodated in the 'standard model' of galactic cosmic ray origin and propagation or whether new physics is needed.
: Krisztian Peters (University of Manchester)
Higgs searches - latest results from the Tevatron
The current status of Standard Model Higgs searches at the Tevatron is presented. A comprehensive program of searches in many Higgs boson production and decay channels is underway, with recent results using up to 5.4/fb of data collected with the CDF and D0 detectors. The major contributing processes include associated production (WH→lνbb, ZH→ννbb, ZH→llbb) and gluon fusion (gg→H→WW). Improvements across the full accessible mass range resulting from the larger data sets, improved analyses techniques and increased signal acceptance will be discussed. A new CDF and D0 combined result with the updated data set will also be presented. Finally, I will discuss prospects for Higgs searches at the Tevatron.
: Steve Biller (University of Oxford)
The SNO+ Project
The continuously surprising and peculiar nature of neutrinos and the weak interaction have been a source of puzzlement since they were first discovered. In recent years, a remarkable paradigm has emerged that seeks to explain hidden symmetries, the scale of neutrino masses and the reason for the imbalance between matter and antimatter in the universe. A cornerstone of this includes the notion that the physical neutrinos we see are their own antiparticles. The only viable mechanism known to have a chance of testing this is the process of neutrinoless double beta decay (0nbb). A pioneering new approach to searching for this rare process involves a novel use of the unique SNO detector in Canada as part of the SNO+ programme, which has a large UK involvement. In concert with other experiments using different isotopes, Phase I aims to convincingly establish or bound 0nbb for equivalent neutrino masses in excess ~100meV and, if seen, constrain the physics mechanism by 2015. Methods to push beyond this are also being explored. In addition, SNO+ will perform precision measurements of solar neutrinos at the transition between matter and vacuum-dominated oscillations to critically test fundamental neutrino couplings as well as studing geo-neutrinos, reactor neutrinos and a variety of other physics.
: Yoshi Uchida (Imperial College London)
Charged Lepton Flavour Violation: a factor one million improvement
Flavour-changing transitions of charged leptons have been a topic of experimental investigation since the early days of particle physics, and this helped shape some of the basic laws that any successful model of particle physics would have to obey, including what we now call the Standard Model. While such phenomena have never been observed to date, when the discovery of neutrino masses and oscillations broke the Standard Model, it transformed the question "Does charged lepton flavour violation exist?" into "How much?" and "How?", and even "Why haven't we seen it yet?". In this seminar, I will describe the current experimental and theoretical state of the field, and why the next generation of experiments could hold the keys that lead the way to a fuller understanding of our universe, offering complementary discoveries that experiments at the high-energy frontier cannot reach. I will then focus on mu-e conversion experimentation, and specifically the COMET/PRISM programme which is promising a sensitivity improvement of four orders of magnitude compared to the current record, potentially improving to six orders, which could open the path to precision measurements with multiple lepton flavour-violating probes of Physics Beyond the Standard Model.
: Friedrich Hehl, University of Cologne (M304 Kathleen Lonsdale Building - Origins Seminar)
Nonlocal gravity simulates dark matter
A nonlocal generalization of Einstein's theory of gravitation is constructed within the framework of the translational gauge theory of gravity. In the linear approximation, the nonlocal theory can be interpreted as linearized general relativity but in the presence of dark matter that can be simply expressed as an integral transform of matter. It is shown that this approach can accommodate the Tohline-Kuhn treatment of the astrophysical evidence for dark matter.
: Friedrich Hehl, University of Cologne (Maths room 500 - Origins Seminar)
On the change in form of Maxwell's equations during the last 150 years --- spotlights on the history of classical electrodynamics ---
Starting with Maxwell's equations for the electromagnetic field (1865), we first point out how Maxwell brought his system of equations into quaternionic form. Subsequently, we recognize that what we call Maxwell's equation nowadays is a creation of Heaviside and Hertz. We touch the development of vector calculus (Hamilton, Grassmann, Gibbs, Foeppl) and of tensor calculus (Riemann, Christoffel, Ricci, Levi-Civita) both around 1900. Then we study the impact of special and of general relativity on Maxwell's equations. In particular we follow up the metric-free and topological version of Maxwell's equations via exterior differential forms and period integrals. Some alternative formulations via spinors, Clifford algebras, chains and cochains... are mentioned.
: Jon Butterworth (UCL)
Subjet structure as physics tool at the LHC: and some early LHC Data
I will show some of the first jet data from the 2009 LHC run, and discuss the prospects for using jet substructure to search for new physics in high energy running.
: Adrian Bevan (Queen Mary)
Super Flavour Factories: SuperB
The Standard Model of particle physics is the pinnacle of achievements of science. In one simple model we can describe the behaviour of all known particles extremely well. However we know that there are missing pieces to this puzzle. We can use SuperB to learn about the missing pieces through a multi-prong approach: i) study rare decays, ii) search forbidden decays, and iii) over-constrain measurements of Standard Model sensitive observables to see if they all agree. I will discuss just a few of the many measurements that can be made at SuperB and how these can be used to improve our understanding of particle physics. Having motivated the reasons for a new experiment, I will briefly discuss some of the aspects of such a proposed facility.
: Morgan Wascko (Imperial College London)
Neutrino Cross Section Measurements at SciBooNE
As we enter the era of precision neutrino oscillation measurements, the need to improve neutrino interaction cross section measurements is paramount. SciBooNE at Fermilab uses a fine grained tracking detector to make precise neutrino and antineutrino cross section measurements on carbon and iron. I will present SciBooNE's latest physics results, which are measurement of neutral current neutral pion production by neutrinos. These measurements are of direct relevance to the future global long baseline accelerator neutrino program, especially the T2K experiment in Japan.