Fast algorithm for real-time rings reconstruction

The GAP project is dedicated to study the application of GPU in several contexts in which real-time response is important to take decisions. The definition of real-time depends on the application under study, ranging from answer time of μs up to several hours in case of very computing intensive task. During this conference we presented our work in low level triggers [1] [2] and high level triggers [3] in high energy physics experiments, and specific application for nuclear magnetic resonance (NMR) [4] [5] and cone-beam CT [6]. Apart from the study of dedicated solution to decrease the latency due to data transport and preparation, the computing algorithms play an essential role in any GPU application. In this contribution, we show an original algorithm developed for triggers application, to accelerate the ring reconstruction in RICH detector when it is not possible to have seeds for reconstruction from external trackers

Scalable framework for heterogeneous clustering of commodity FPGAs

A combination of parallelism exploitation and application specific hardware is increasingly being used to address the computational requirements of a diverse and extensive set of application areas. These targeted applications have specific computational requirements that often are not able to be implemented optimally on general purpose processors and have the potential to experience substantial speedup on dedicated hardware. While general parallelism has been exploited at various levels for decades, the advent of heterogeneous cluster computing has allowed applications to be accelerated through the use of intelligently mapped computational tasks to well-suited hardware. This trend has continued with the use of dedicated ASIC and FPGA coprocessors to off-load particularly intensive computations. With the inclusion of embedded microprocessors into otherwise reconfigurable FPGA fabric, it has become feasible to construct a heterogeneous cluster composed of application specific hardware resources that can be programatically treated as fully functional and independent cluster nodes via a standard message passing interface. The contribution of this thesis is the development of such a framework for organizing heterogeneous clusters of reconfigurable FPGA computing elements into clusters that enable development of complex systems delivering on the promise of parallel reconfigurable hardware. The framework includes a fully featured message passing interface implementation for seamless communication and synchronization among nodes running in an embedded Linux operating system environment while managing hardware accelerators through device driver abstractions and standard APIs. A set of application case studies deployed on a test platform of Xilinx Virtex-4 and Virtex-5 FPGAs demonstrates functionality, elucidates performance characteristics, and promotes future research and development efforts

Single Photon Interferometry and Quantum Astrophysics

abstract: This thesis contains an overview, as well as the history of optical interferometers. A new approach to interferometric measurements of stars is proposed and explored. Modern updates to the classic techniques are described along with some theoretical derivations showing why the method of single photon counting shows significant promise relative to the currently used amplitude interferometry. Description of a modular intensity interferometer system using commercially available single-photon detectors is given. Calculations on the sensitivity and \emph{uv}-plane coverage using these modules mounted on existing telescopes on Kitt Peak, Arizona is presented. Determining fundamental stellar properties is essential for testing models of stellar evolution as well as for deriving physical properties of transiting exoplanets. The proposed method shows great promise in measuring the angular size of stars. Simulations indicate that it is possible to measure stellar diameters of bright stars with AB magnitude 5% in a single night of observation. Additionally, a description is given of a custom time-to-digital converter designed to time tag individual photons from multiple single-photon detectors with high count rate, continuous data logging, and low systematics. The instrument utilizes a tapped-delay line approach on an FPGA chip which allows for sub-clock resolution of <100 ps. The TDC is implemented on a Re-configurable Open Architecture Computing Hardware Revision 2 (ROACH2) board which allows for continuous data streaming and time tagging of up to 20 million events per second. The functioning prototype is currently set-up to work with up to ten independent channels. Laboratory characterization of the system, including RF, pick up and mitigation, as well as measurement of in-lab photon correlations from an incoherent light source (artificial star), are presented. Additional improvements to the TDC will also be discussed, such as improving the data transfer rate by a factor of 10 via an SDP+ Mezzanine card and PCIe 2SFP+ 10 Gb card, as well as scaling to 64 independent channels. Furthermore, a modified nulling interferometer with image inversion is proposed, for direct imaging of exoplanets below the canonical Rayleigh resolution limit. Image inversion interferometry relies on splitting incoming radiation from a source, either spatially rotating or reflecting the electric field from one arm of the interferometer before recombining the signals and detecting the resulting images in the two output ports with an array of high-speed single-photon detectors. Sources of incoming radiation that have cylindrical symmetry and are centered on the rotation axis will cancel in one of the output ports and add in the other output port. The ability to suppress light from a host star, as well as the ability to resolve past the Rayleigh limit, enables sensitive detection of exoplanets from a stable environment without the need for a coronagraph. The expected number of photons and the corresponding variance in the measurement for different initial contrast ratios are shown, with some first-order theoretical instrumental errors. Lastly, preliminary results from a sizeable photometric survey are presented. This survey is used to derive bolometric flux alongside from angular size measurements and the effective stellar temperatures.Dissertation/ThesisDoctoral Dissertation Astrophysics and Astronomy 201

Measurement of the production cross section of four top quarks in proton-proton collisions at 13 TeV

The field of particle physics involves not only searches for new particles and measurements of their interactions, but also the design and construction of advanced particle detectors. This thesis presents the measurement of the production cross section of four top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV using 137 fb$^{-1}$ of integrated luminosity recorded by the CMS experiment at the LHC. This analysis considers events in the final state of a same-sign pair of leptons, notable for being a final state with relatively few Standard Model background events. A boosted decision tree is utilized to discriminate four top quark events from background events. The four top quark production cross section is measured to be $12.6^{+5.8}_{-5.2}$ fb, consistent with the Standard Model prediction. This measurement is used to constrain the top quark\u27s Yukawa coupling as well as various theories beyond the Standard Model. This thesis also describes the construction and testing of silicon pixel detector modules used in the Phase I upgrade of the CMS pixel detector, and optimization of electron reconstruction methods using the new detector. The role of automated module assembly and quality assurance will be discussed, as well as work towards the construction of a high precision silicon strip detector based telescope. Adviser: Professor Frank Gol

Measurement of the production cross section of four top quarks in proton-proton collisions at 13 TeV

The field of particle physics involves not only searches for new particles and measurements of their interactions, but also the design and construction of advanced particle detectors. This thesis presents the measurement of the production cross section of four top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV using 137 fb$^{-1}$ of integrated luminosity recorded by the CMS experiment at the LHC. This analysis considers events in the final state of a same-sign pair of leptons, notable for being a final state with relatively few Standard Model background events. A boosted decision tree is utilized to discriminate four top quark events from background events. The four top quark production cross section is measured to be $12.6^{+5.8}_{-5.2}$ fb, consistent with the Standard Model prediction. This measurement is used to constrain the top quark\u27s Yukawa coupling as well as various theories beyond the Standard Model. This thesis also describes the construction and testing of silicon pixel detector modules used in the Phase I upgrade of the CMS pixel detector, and optimization of electron reconstruction methods using the new detector. The role of automated module assembly and quality assurance will be discussed, as well as work towards the construction of a high precision silicon strip detector based telescope. Adviser: Professor Frank Gol

Design Studies for a Tracking Upgrade of the Crystal Barrel Experiment at ELSA and Installation of a Tracking Test Bench

Ever since mankind was interested in the understanding of the universe and especially the matter in it. The fundamental building blocks of matter seem to be quarks and gluons, whose interactions are investigated in hadron physics. To study this strong interaction different experimental approaches can be used. One way is to do spectroscopy similar to atomic physics. The Crystal Barrel experiment at ELSA performs spectroscopy of nucleons to learn more about the strong interaction. A major improvement of this experimental setup will be the introducing of charged particle tracking as it will be shown in this thesis. Different detector concepts will be discussed concerning feasibility, material budget and especially momentum resolution. It will turn out that a Time Projection Chamber (TPC) is the optimal solution. Then it will be shown how a prototype TPC is tested using a newly installed tracking test bench with an electron beam and obtained results will be presented. The design of the final TPC and its integration into the Crystal Barrel experiment will be discussed as well as methods to calibrate the detector

Resolution studies and performance evaluation of the LHCb VELO upgrade

The LHCb detector at CERN is scheduled to undergo an upgrade during the second long shutdown of the LHC. As part of this upgrade, the vertex detector (VELO) will be replaced with a new hybrid pixel detector, based on an evolution of the Timepix ASIC. The performance of this detector should improve upon that achieved by the current VELO, in addition to facilitating the complete detector readout at 40 MHz. As part of the preparation for this upgrade, this thesis presents the results of studies carried out on the single hit resolution of silicon hybrid pixel detectors. The development of a particle beam telescope has been carried out to allow these studies, shown to operate with track rates in excess of 45 kHz and with a pointing resolution at the device under test of less than 2 μm. A wide range of sensor types, thicknesses and resistivities have then been tested under different operating conditions and the results presented, with single hit resolutions varying between 4 μm and 12 μm depending on the conditions and incident angle. The resistivity of the devices is observed to have a significant effect on the single hit resolution, with high resistivity substrates allowing operation at lower bias voltages. This facilitates increased charge sharing, and the corresponding improvement in resolution. At sufficiently large incident angles however, the resolution becomes independent of the electric field, being instead dominated by the sensor geometry and variations in the charge deposited along the track length. No significant differences were found between the various detector technologies (n-on-n, n-on-p and p-on-n) though a difference in performance is expected for low-voltage operation of higher resistivity samples. A simplified model of the physical processes contributing to the detector resolution has been constructed, shown to reasonably reproduce the observed resolution as a function of angle and bias voltage. This model is extrapolated to potential future directions in the design of pixel sensors, highlighting the differences between various technology choices. The integration of the ATLAS FE-I4 ASIC into the telescope has been carried out, and the performance of an unirradiated planar silicon sensor was shown in order to verify this. Efficiency measurements show that the device is fully efficient in the angular range measured. The tracking performance of two irradiated sensors mounted on FE-I4 ASICs has been investigated, in addition to the mapping of collected charge over the pixel unit cell under various biasing conditions and at varying incident angles with respect to the incoming particles. For the sample irradiated to 2e15 1 MeV neq /cm2 the single hit resolution was 12.5 μm at perpendicular incidence, dropping to 8 μm at 22 degrees. The sample irradiated to 4e15 1 MeV neq /cm2 was found to have a resolution of around 13.5 μm, which remained relatively insensitive to the incident track angle. The conclusions drawn suggest that the upgraded VELO detector will be able to overcome the difficult radiation environment if it is able to reach the high voltage operation required. The implementation of these observations in the LHCb simulation environment has allowed some initial studies on the likely degradation of the detector performance to take place, showing that the high tracking efficiency (99.4 % for Long tracks) is likely to be maintained throughout the full lifetime of the upgrade. The impact parameter resolution was not observed to vary significantly. These studies have been carried out alongside simulations to gauge the expected compression that can be achieved in the data transmission of the VELOPix ASIC. Different designs of the front-end have been implemented, leading to the adoption of binary readout for the upgraded VELO. The uniformity of the pixel pitch across the detector has additionally been used to show the sensitivity of the system to multiple scattering, shown to be a credible tool with which to control the event reconstruction in the online LHCb trigger. A reduction of the number of VELO tracks passed to the forward reconstruction of almost 50 % has been shown, for the loss of only 5 % of tracks with momentum above 20 GeV/c. This could potentially replace the lifetime biasing cuts currently envisaged in the trigger