τ\tau physics at LHCb

We report on the first searches for lepton flavour violating $\tau^-$ decays at a hadron collider. These include searches for the lepton flavour violating decay $\tau^-\to \mu^+\mu^-\mu^-$ and the lepton flavour and baryon number violating decays $\tau^-\to \bar{p}\mu^+\mu^-$ and $\tau^-\to p\mu^-\mu^-$. Upper limits of ${\cal B}(\tau^-\to \mu^+\mu^-\mu^-) < 4.6 \times 10^{-8}$, ${\cal B}(\tau^-\to \bar{p}\mu^+\mu^-) < 3.4 \times 10^{-7}$ and ${\cal B}(\tau^-\to p\mu^-\mu^-) < 4.6 \times 10^{-7}$ are set at 90% confidence level. A measurement of the inclusive $Z\to\tau^+\tau^-$ cross-section at 7 TeV is also reported and is found to be consistent with the Standard Model. The ratio of the $Z\to\tau^+\tau^-$ cross-section to the $Z\to\mu^+\mu^-$ cross-section is found to be consistent with lepton universality.Comment: To be published in the proceedings of CHARM-2015, Detroit, MI, 18-22 May 201

CN excitation and electron densities in diffuse molecular clouds

Utilising previous work by the authors on the spin-coupled rotational cross-sections for electron-CN collisions, data for the associated rate coefficients is presented. Data on rotational, fine-structure and hyperfine-structure transition involving rotational levels up to $N$=20 are computed for temperatures in the range 10 -- 1000~K. Rates are calculated by combining Born-corrected R-matrix calculations with the infinite-order-sudden (IOS) approximation. The dominant hyperfine transitions are those with $\Delta N=\Delta j= \Delta F=1$. For dipole-allowed transitions, electron-impact rates are shown to exceed those for excitation of CN by para-H$_2$($j=0$) by five orders of magnitude. The role of electron collisions in the excitation of CN in diffuse clouds, where local excitation competes with the cosmic microwave background (CMB) photons, is considered. Radiative transfer calculations are performed and the results compared to observations. These comparisons suggest that electron density lies in the range $n(e)\sim 0.01-0.06$~cm$^{-3}$ for typical physical conditions present in diffuse clouds.Comment: 6 pages, 8 figures, accepted 14/08/201

An automatic adaptive method to combine summary statistics in approximate Bayesian computation

To infer the parameters of mechanistic models with intractable likelihoods, techniques such as approximate Bayesian computation (ABC) are increasingly being adopted. One of the main disadvantages of ABC in practical situations, however, is that parameter inference must generally rely on summary statistics of the data. This is particularly the case for problems involving high-dimensional data, such as biological imaging experiments. However, some summary statistics contain more information about parameters of interest than others, and it is not always clear how to weight their contributions within the ABC framework. We address this problem by developing an automatic, adaptive algorithm that chooses weights for each summary statistic. Our algorithm aims to maximize the distance between the prior and the approximate posterior by automatically adapting the weights within the ABC distance function. Computationally, we use a nearest neighbour estimator of the distance between distributions. We justify the algorithm theoretically based on properties of the nearest neighbour distance estimator. To demonstrate the effectiveness of our algorithm, we apply it to a variety of test problems, including several stochastic models of biochemical reaction networks, and a spatial model of diffusion, and compare our results with existing algorithms

The impact of temporal sampling resolution on parameter inference for biological transport models

Imaging data has become widely available to study biological systems at various scales, for example the motile behaviour of bacteria or the transport of mRNA, and it has the potential to transform our understanding of key transport mechanisms. Often these imaging studies require us to compare biological species or mutants, and to do this we need to quantitatively characterise their behaviour. Mathematical models offer a quantitative description of a system that enables us to perform this comparison, but to relate these mechanistic mathematical models to imaging data, we need to estimate the parameters of the models. In this work, we study the impact of collecting data at different temporal resolutions on parameter inference for biological transport models by performing exact inference for simple velocity jump process models in a Bayesian framework. This issue is prominent in a host of studies because the majority of imaging technologies place constraints on the frequency with which images can be collected, and the discrete nature of observations can introduce errors into parameter estimates. In this work, we avoid such errors by formulating the velocity jump process model within a hidden states framework. This allows us to obtain estimates of the reorientation rate and noise amplitude for noisy observations of a simple velocity jump process. We demonstrate the sensitivity of these estimates to temporal variations in the sampling resolution and extent of measurement noise. We use our methodology to provide experimental guidelines for researchers aiming to characterise motile behaviour that can be described by a velocity jump process. In particular, we consider how experimental constraints resulting in a trade-off between temporal sampling resolution and observation noise may affect parameter estimates.Comment: Published in PLOS Computational Biolog

Comparing the effectiveness of explicit EAL feedback through slideshow (text+audio) and captioned video

Research seems to show that captions and subtitles are generally beneficial to learners of English as an Additional Language (EAL), but some research does contradict this. Research on slideware and slide design seems to focus more on attractiveness of slides and less on educational effectiveness. However, research on slide design and specific approaches to slide design continue to become more detailed. This study compared comprehension of explicit feedback received through either slideshow (text+audio) video or captioned video on an EAL writing task in an on-demand university setting. Results (n=163) indicated that approximately 50% of learners clicked the feedback video to advance to the quiz without viewing it completely. Of the learners with at least one full viewing (n=86), slideshow video seems to have engaged students for a longer duration than captioned video. The quiz items were easier for the slideshow video groups, and the quiz items performed better for these groups. The slideshow video groups had slightly higher means, but a significant difference between the effectiveness of slideshow video and captioned video to transmit feedback to students was not found

The Rise of Jim Crow in Fort Myers, 1885-1930

The power and opportunities of African Americans in Florida between the 1880s and 1920s fluctuated across time and location and were affected by variations in local economic structures, migration patterns and cultural histories. Black property ownership, political participation and social prestige were in flux, impacted by such factors as the availability of public land for cultivation by blacks, the cultures of the places from which new residents had migrated, and whether the area was a new settlement or one that was carrying forward a set of social relationships that had been formed during the slavery period. Each of these factors can be documented in the case of Fort Myers in a way that throws additional new light on the nuances involved in racial interactions during this era. The picture that emerges is one in which the path to segregation was not a straight line, nor were African Americans passive in their responses to the processes taking place

Radiation damage studies in the LHCb VELO detector and searches for lepton flavour and baryon number violating tau decays

This thesis presents work carried out using data from the LHCb experiment during the first three years of data taking, 2010 - 2012. A study of the effects of radiation damage on the silicon sensors of the LHCb Vertex Locator is performed, with an emphasis on the implications for the long term performance of the detector. Following three years of operation the sensors have received a maximum delivered neutron equivalent fluence of $\sim1.6 \times 10^{12}$ per square centimetre, leading to a number of radiation induced effects. In particular the change in charge collection efficiency and signal/noise with fluence is compared to theoretical expectations, and the current trends are extrapolated to the fluences expected at the end of the LHCb detector lifetime. The development of an unexpected effect due to the structure of the routing lines in the sensors is described in detail. Searches for lepton flavour and baryon number violating decays of the $\tau$ lepton using the 2011 LHCb dataset are described. Observation of any lepton flavour or baryon number violation would be an unambiguous sign of new physics, whilst setting improved limits helps to constrain a number of Beyond the Standard Model theories. First LHCb limits are set on the branching fractions of the decays $\tau^-\rightarrow \mu^-\mu^+\mu^-$, $\tau^-\rightarrow \overline{p}\mu^+\mu^-$ and $\tau^-\rightarrow p\mu^-\mu^-$, with these results also representing the first limits on lepton flavour violating tau decays at a hadron collider. The limit on $\tau^-\rightarrow \mu^-\mu^+\mu^-$ is expected to approach the world's best result from Belle in the coming years whilst the $\tau^-\rightarrow \overline{p}\mu^+\mu^-$ and $\tau^-\rightarrow p\mu^-\mu^-$ results constitute the first limits on the branching fractions of these decays. The future prospects for these measurements with further data are briefly described