arXiv subjects

Marco Gersabeck

Publications and source records attributed to Marco Gersabeck.

14 recordsLinked to original sources

arXiv2025

Wavelength-tunable femtosecond pulsed laser for the characterisation of solid-state sensors

The Two-Photon Absorption (TPA) process provides an excellent method for the characterisation of solid-state sensors due to its intrinsic 3D resolution for the excitation of electron-hole pairs. This paper presents the commissioning of a system composed of a Light Conversion PHAROS laser read out with an ORPHEUS optical parametric amplifier with tuneable output wavelength across $310-16000$ nm. This is one of the few facilities suitable for particle physics detector applications with a very wide wavelength range and ultra short pulses. The voxel characterisation shows a Rayleigh length of $12.20 \pm 0.47$ $~μ$m and the beam radius at the waist of $1.53 \pm 0.04$$~μ$m. Initial measurements with silicon and diamond samples are described. The apparatus is characterised with both devices, demonstrating the expected quadratic dependency with the energy per pulse, and different models are presented to explain the signal generated due to reflection. The signal generated in the silicon diode is in good agreement with one dimension voxel model predictions.

physics.ins-det↗

arXiv2023

GPU-based optical photon simulation for the LHCb RICH 1 Detector

We present the investigation of the use of Opticks, a GPU-accelerated optical photon interface with the LHCb detector simulation, to improve computation time of optical photon propagation. The hybrid workflow, combining the particle simulation package Geant4 and Opticks, offloads optical photon propagation to GPUs, thereby accelerating the overall simulation process. The consistency of the results obtained from Geant4 and Opticks simulations is verified with a simplified LHCb RICH 1 detector geometry, demonstrating the feasibility of the proposed approach. In addition, the ongoing transition to the NVIDIA OptiX 7 API and re-structuring of Opticks code is discussed within the context of HEP simulation workflows, with caveats explored.

hep-ex↗

arXiv2023

Optical Photon Simulation with Mitsuba3

Optical photon propagation is an embarrassingly parallel operation, well suited to acceleration on GPU devices. Rendering of images employs similar techniques -- for this reason, a pipeline to offload optical photon propagation from Geant4 to the industry-standard open-source renderer Mitsuba3 has been devised. With the creation of a dedicated plugin for single point multi-source emission, we find a photon propagation rate of $2\times10^{5}$ photons per second per CPU thread using LLVM and $1.2\times10^{6}$ photons per second per GPU using CUDA. This represents a speed-up of 70 on CPU and 400 on GPU over Geant4 and is competitive with other similar applications. The potential for further applications is discussed.

physics.comp-ph↗

arXiv2017

Flavour Anomalies in $b\to s\ell^+\ell^-$ Processes - a round table Discussion

Precision measurements of flavour observables provide powerful tests of many extensions of the Standard Model. This contribution covers a range of flavour measurements of $b\to s\ell^+\ell^-$ transitions, several of which are in tension with the Standard Model of particle physics, as well as their theoretical interpretation. The basics of the theoretical background are discussed before turning to the main question of the field: whether the anomalies can be explained by QCD effects or whether they may be indicators of effects beyond the Standard Model.

hep-ph↗

arXiv2017

On model-independent searches for direct CP violation in multi-body decays

Techniques for performing model-independent searches for direct CP violation in three and four-body decays are discussed. Comments on the performance and the optimisation of a binned chisquare approach and an unbinned approach, known as the energy test, are made. The use of the energy test in the presence of background is also studied. The selection and treatment of the coordinates used to describe the phase-space of the decay are discussed. The conventional model-independent techniques, which test for P-even CP violation, are modified to create a new approach for testing for P-odd CP violation. An implementation of the energy test using GPUs is described.

hep-ex↗

arXiv2015

Introduction to Charm Physics

This paper gives an overview of charm physics. It is a lecture write-up aimed at students with a minimum of prior knowledge in particle physics, but at the same time provides a state-of-the art review of the field. The main focus is on mixing and CP violation, which is a field with ever growing attention since first evidence for charm mixing was observed in 2007. Other areas covered are charm spectroscopy, production, as well as rare decays.

hep-ex↗

arXiv2014

HFAG-charm averages

The extraction of charm mixing and CP violation parameters requires the combination of many measurements. The latest averages are reviewed and the contribution of individual measurements is discussed. While it is established that the CP-even eigenstate is the shorter lived, the oscillation frequency of charm mesons is still not known to high accuracy. All CP asymmetries are found to be compatible with zero within less than 3 sigma.

hep-ex↗

arXiv2012

The charm physics programme at the LHCb upgrade, and Atlas and CMS upgrades

Charm physics has been established at the LHC based on several high-precision measurements. The future of charm physics at the LHC experiments is discussed in detail. The bulk of the charm physics programme will be performed by LHCb and the LHCb upgrade. In particular, the impact of the LHCb upgrade on mixing and \CP violation measurements is presented.

hep-ex↗

arXiv2012

Brief Review of Charm Physics

Charm physics has attracted increased attention after first evidence for charm mixing was observed in 2007. The level of attention has risen sharply after LHCb reported first evidence for CP violation in the charm sector. Neither mixing nor CP violation have been established by a single unambiguous measurement to date. This review covers the status of mixing and CP violation measurements and comments on the challenges on the road ahead, both on the experimental and theoretical side, and on ways to tackle them.

hep-ex↗

arXiv2012

Experimental constraints from flavour changing processes and physics beyond the Standard Model

Flavour physics has a long tradition of paving the way for direct discoveries of new particles and interactions. Results over the last decade have placed stringent bounds on the parameter space of physics beyond the Standard Model. Early results from the LHC, and its dedicated flavour factory LHCb, have further tightened these constraints and reiterate the ongoing relevance of flavour studies. The experimental status of flavour observables in the charm and beauty sectors is reviewed in measurements of CP violation, neutral meson mixing, and measurements of rare decays.

hep-ex↗

arXiv2012

On the interplay of direct and indirect CP violation in the charm sector

Charm mixing and CP violation observables are examined in the light of the recently reported evidence from LHCb for CP violation in the charm sector. If the result is confirmed as being due to direct CP violation at the 1% level, its effect will need to be taken into account in the interpretation of CP violation observables. The contributions of direct and indirect CP violation to the decay rate asymmetry difference DeltaACP and the ratios of effective lifetimes AGamma and yCP are considered here. Terms relevant to the interpretation of future high precision measurements which have been neglected in previous literature are identified.

hep-ex↗

arXiv2011

Charged Particle Tracking with the Timepix ASIC

A prototype particle tracking telescope has been constructed using Timepix and Medipix ASIC hybrid pixel assemblies as the six sensing planes. Each telescope plane consisted of one 1.4 cm2 assembly, providing a 256x256 array of 55 micron square pixels. The telescope achieved a pointing resolution of 2.3 micron at the position of the device under test. During a beam test in 2009 the telescope was used to evaluate in detail the performance of two Timepix hybrid pixel assemblies; a standard planar 300 micron thick sensor, and 285 micron thick double sided 3D sensor. This paper describes a detailed charge calibration study of the pixel devices, which allows the true charge to be extracted, and reports on measurements of the charge collection characteristics and Landau distributions. The planar sensor achieved a best resolution of 4.0 micron for angled tracks, and resolutions of between 4.4 and 11 micron for perpendicular tracks, depending on the applied bias voltage. The double sided 3D sensor, which has significantly less charge sharing, was found to have an optimal resolution of 9.0 micron for angled tracks, and a resolution of 16.0 micron for perpendicular tracks. Based on these studies it is concluded that the Timepix ASIC shows an excellent performance when used as a device for charged particle tracking.

physics.ins-det↗

arXiv2010

Searches for CP Violation in Charm Mixing at LHCb

LHCb has started its charm physics programme using the data taken at the LHC. The first measurements of open charm production cross-sections for proton proton collisions at $\sqrt{s}=7 \tev$ are presented. The cross-sections of the \PDzero, $\PDstar^+$, \PDplus, and \PDsplus mesons are found to be in broad agreement with theory predictions. The prospects for measurements of charm mixing, CP and T violation in decays of neutral \PD mesons at LHCb are discussed. Furthermore, plans for CP violation measurements using charged \PD mesons are presented. Most analyses are expected to yield results improving the current world averages based on the data expected to be taken in 2011.

hep-ex↗

arXiv2008

Alignment of the LHCb Vertex Locator

LHCb will commence data taking as the first dedicated heavy flavour experiment at a hadron collider in 2008. A very high hit precision from its vertex detector (VELO) is essential to meet the tight requirements of vertex reconstruction in B-physics. The single hit precision of the VELO is better than 10 micron. However, the VELO is operated only 8 mm from the beam and must be retracted and reinserted each LHC fill. Hence, the detector places unique demands on its alignment algorithm. The partially assembled VELO system has already been tested in a beam test. The novel software alignment methods are presented together with their interplay with the metrology measurements. Results from Monte Carlo simulation studies are discussed and recent beam test results are shown that prove the method's precision at the micron level.

physics.ins-det↗