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Richard Nisius

Publications and source records attributed to Richard Nisius.

At least 19 recordsLinked to original sources
arXiv2020

BLUE: combining correlated estimates of physics observables within ROOT using the Best Linear Unbiased Estimate method

This software performs the combination of $m$ correlated estimates of $n$ physics observables ($m\ge n$) using the Best Linear Unbiased Estimate (BLUE) method. It is implemented as a C++ class, to be used within the ROOT analysis package. It features easy disabling of specific estimates or uncertainty sources, the investigation of different correlation assumptions, and allows performing combinations according to the importance of the estimates. This enables systematic investigations of the combination on details of the measurements from within the software, without touching the input.

physics.data-an↗
arXiv2018

TCAD simulations of pixel sensors for the ATLAS ITk upgrade and performance of annealed planar pixel modules

For the high luminosity phase of the Large Hadron Collider to start operation around 2026, a major upgrade of the ATLAS Inner Tracker (ITk) is in preparation. Thanks to their low power dissipation and high charge-collection efficiency after irradiation, thin planar pixel modules are the baseline option to instrument all, except for the innermost layer of the pixel detector. To optimise the sensor layout for a pixel cell size of $50\times50\,μm^2$, TCAD simulations are being performed. Charge-collection efficiency, electronic noise and electrical-field properties are investigated. A radiation-damage model is employed in TCAD simulations to estimate the performance before- and after irradiation. The impact of storage time at room temperature for the ITk pixel detector during maintenance periods are estimated using sensors irradiated up to a fluence of 5$\times10^{15}\,$n$_\text{eq}$/cm$^2$. Pixel sensors of $100-150\,μm$ thickness, interconnected to FE-I4 read-out chips with pixel dimensions of $50\times250\,μm^2$, are characterised using the testbeam facilities at the CERN-SPS and DESY. The charge-collection and hit efficiencies are compared before and after annealing at room temperature for up to one year.

physics.ins-det↗
arXiv2017

Measurements of the top quark mass with the ATLAS detector

The measurements of the top quark mass given are obtained from ATLAS data taken at proton--proton centre-of-mass energies of $\sqrt{s}=7$ and $8$ TeV. An extraction of the top quark pole mass ($m_{\mathrm{top}}^{\mathrm{pole}}$) at next-to-leading order (NLO) is presented. This result is obtained from normalised differential cross-sections in the $t\bar{t}\to\mbox{dilepton}$ channel leading to: $m_{\mathrm{top}}^{\mathrm{pole}} = 173.2 \pm 0.9 (\mathrm{stat.}) \pm 0.8 (\mathrm{syst.}) \pm 1.2 (\mathrm{theo.})$ GeV. In addition, measurements of $m_{\mathrm{top}}$ are discussed that are based on the template method performed in three $t\bar{t}$ decay channels. For all results the uncertainty is dominated by systematic effects. Finally, the 2016 ATLAS combined value of $m_{\mathrm{top}}$ is: $m_{\mathrm{top}}=172.84 \pm 0.34 (\mathrm{stat.}) \pm 0.61 (\mathrm{syst.})$ GeV,with a total uncertainty of 0.70 GeV, i.e. a precision of 0.4$\%$.

hep-ex↗
arXiv2017

Performance of irradiated thin n-in-p planar pixel sensors for the ATLAS Inner Tracker upgrade

The ATLAS collaboration will replace its tracking detector with new all silicon pixel and strip systems. This will allow to cope with the higher radiation and occupancy levels expected after the 5-fold increase in the luminosity of the LHC accelerator complex (HL-LHC). In the new tracking detector (ITk) pixel modules with increased granularity will implement to maintain the occupancy with a higher track density. In addition, both sensors and read-out chips composing the hybrid modules will be produced employing more radiation hard technologies with respect to the present pixel detector. Due to their outstanding performance in terms of radiation hardness, thin n-in-p sensors are promising candidates to instrument a section of the new pixel system. Recently produced and developed sensors of new designs will be presented. To test the sensors before interconnection to chips, a punch-through biasing structure has been implemented. Its design has been optimized to decrease the possible tracking efficiency losses observed. After irradiation, they were caused by the punch-through biasing structure. A sensor compatible with the ATLAS FE-I4 chip with a pixel size of 50x250 $\mathrmμ$m$^{2}$, subdivided into smaller pixel implants of 30x30 $\mathrmμ$m$^{2}$ size was designed to investigate the performance of the 50x50 $\mathrmμ$m$^{2}$ pixel cells foreseen for the HL-LHC. Results on sensor performance of 50x250 and 50x50 $\mathrmμ$m$^{2}$ pixel cells in terms of efficiency, charge collection and electric field properties are obtained with beam tests and the Transient Current Technique.

physics.ins-det↗
arXiv2017

Optimization of thin n-in-p planar pixel modules for the ATLAS upgrade at HL-LHC

The ATLAS experiment will undergo around the year 2025 a replacement of the tracker system in view of the high luminosity phase of the LHC (HL-LHC) with a new 5-layer pixel system. Thin planar pixel sensors are promising candidates to instrument the innermost region of the new pixel system, thanks to the reduced contribution to the material budget and their high charge collection efficiency after irradiation. The sensors of 50-150 $μ$m thickness, interconnected to FE-I4 read-out chips, have been characterized with radioactive sources and beam tests. In particular active edge sensors have been investigated. The performance of two different versions of edge designs are compared: the first with a bias ring, and the second one where only a floating guard ring has been implemented. The hit efficiency at the edge has also been studied after irradiation at a fluence of $10^{15}$ \neqcm. Highly segmented sensors will represent a challenge for the tracking in the forward region of the pixel system at HL-LHC. In order to reproduce the performance of 50x50 $μ$m$^2$ pixels at high pseudo-rapidity values, FE-I4 compatible planar pixel sensors have been studied before and after irradiation in beam tests at high incidence angles with respect to the short pixel direction. Results on the hit efficiency in this configuration are discussed for different sensor thicknesses.

physics.ins-det↗
arXiv2016

Characterization of Novel Thin N-in-P Planar Pixel Modules for the ATLAS Inner Tracker Upgrade

The ATLAS experiment will undergo a major upgrade of the tracker system in view of the high luminosity phase of the LHC (HL-LHC) to start operation in 2026. The most severe challenges are to be faced by the innermost layers of the pixel detector which will have to withstand a radiation fluence of up to $1.4\times10^{16}\,$n$_\text{eq}$/cm$^{2}$. Thin planar pixel modules are promising candidates to instrument these layers, thanks to the small material budget and their high charge collection efficiency after irradiation. Sensors of $100-200\,μ$m thickness, interconnected to FE-I4 read-out chips, are characterized with radioactive sources as well as testbeams at the CERN-SPS and DESY. The performance of sensors irradiated up to a fluence of $5\times 10^{15}\,$n$_\text{eq}$/cm$^{2}$ is compared in terms of charge collection and hit efficiency. Highly segmented sensors are a challenge for the tracking in the forward region of the pixel system at the HL-LHC. To reproduce the performance of $50$x$50\,μ$m$^2$ pixels at high pseudo-rapidities, FE-I4 compatible planar pixel sensors are studied before and after irradiation in beam tests at high incidence angle ($80^\circ$) with respect to the short pixel direction. Results on cluster shape and hit efficiency will be shown.

physics.ins-det↗
arXiv2016

Development of n-in-p pixel modules for the ATLAS Upgrade at HL-LHC

Thin planar pixel modules are promising candidates to instrument the inner layers of the new ATLAS pixel detector for HL-LHC, thanks to the reduced contribution to the material budget and their high charge collection efficiency after irradiation. 100-200 $μ$m thick sensors, interconnected to FE-I4 read-out chips, have been characterized with radioactive sources and beam tests at the CERN-SPS and DESY. The results of these measurements are reported for devices before and after irradiation up to a fluence of $14\times10^{15}$ n$_{eq}$/cm$^2$. The charge collection and tracking efficiency of the different sensor thicknesses are compared. The outlook for future planar pixel sensor production is discussed, with a focus on sensor design with the pixel pitches (50x50 and 25x100 $μ$m$^2$) foreseen for the RD53 Collaboration read-out chip in 65 nm CMOS technology. An optimization of the biasing structures in the pixel cells is required to avoid the hit efficiency loss presently observed in the punch-through region after irradiation. For this purpose the performance of different layouts have been compared in FE-I4 compatible sensors at various fluence levels by using beam test data. Highly segmented sensors will represent a challenge for the tracking in the forward region of the pixel system at HL-LHC. In order to reproduce the performance of 50x50 $μ$m$^2$ pixels at high pseudo-rapidity values, FE-I4 compatible planar pixel sensors have been studied before and after irradiation in beam tests at high incidence angle (80$^\circ$) with respect to the short pixel direction. Results on cluster shapes, charge collection and hit efficiency will be shown.

physics.ins-det↗
arXiv2014

On the combination of correlated estimates of a physics observable

The combination of a number of correlated estimates of a given observable is frequently performed using the Best Linear Unbiased Estimate (BLUE) method. Most features of such a combination can already be seen by analysing the special case of a pair of estimates from two correlated estimators of the observable. Two important parameters of this combination are the weight of the less precise estimate and the ratio of uncertainties of the combined result and the more precise estimate. Derivatives of these quantities are derived with respect to the correlation and the ratio of uncertainties of the two estimates. The impact of using either absolute or relative uncertainties in the BLUE combination is investigated on a number of examples including Peelle's Pertinent Puzzle. Using an example, a critical assessment is performed of suggested methods to deal with the fact that both the correlation and the ratio of uncertainties of a pair of estimates are typically only known with some uncertainty. Finally, a proposal is made to decide on the usefulness of a combination and to perform it. The proposal is based on possible improvements with respect to the most precise estimate by including additional estimates. This procedure can be applied to the general case of several observables.

physics.data-an↗
arXiv2014

NLO QCD corrections to W+ W- b anti-b production with leptonic decays in the light of top quark mass and asymmetry measurements

We present the NLO QCD corrections to the processes p p and p anti-p to W+ W- b anti-b including leptonic decays of the W bosons. Non-resonant contributions as well as diagrams with doubly resonant and singly resonant top quark propagators are fully taken into account. We employ the narrow width approximation to perform the decays of the W bosons; spin correlations are however preserved. We also calculate observables relevant for top quark mass measurements, and study the impact of kinematical requirements and different scale choices on t anti-t asymmetries.

hep-ph↗
arXiv2012

QCD results from the LHC

A selection of results from the 2010 data taking period of the ATLAS and CMS experiments at the LHC at a proton-proton centre-of-mass energy of 7 TeV is presented. These results comprise differential jet cross sections for varying jet multiplicities, the investigation of properties of large rapidity gaps spanned by a dijet system, the production of heavy gauge bosons together with jets, and finally the investigations of properties of top quark pair production.

hep-ex↗
arXiv2011

Characterization and Performance of Silicon n-in-p Pixel Detectors for the ATLAS Upgrades

The existing ATLAS Tracker will be at its functional limit for particle fluences of 10^15 neq/cm^2 (LHC). Thus for the upgrades at smaller radii like in the case of the planned Insertable B-Layer (IBL) and for increased LHC luminosities (super LHC) the development of new structures and materials which can cope with the resulting particle fluences is needed. N-in-p silicon devices are a promising candidate for tracking detectors to achieve these goals, since they are radiation hard, cost efficient and are not type inverted after irradiation. A n-in-p pixel production based on a MPP/HLL design and performed by CiS (Erfurt, Germany) on 300 μm thick Float-Zone material is characterised and the electrical properties of sensors and single chip modules (SCM) are presented, including noise, charge collection efficiencies, and measurements with MIPs as well as an 241Am source. The SCMs are built with sensors connected to the current the ATLAS read-out chip FE-I3. The characterisation has been performed with the ATLAS pixel read-out systems, before and after irradiation with 24 GeV/c protons. In addition preliminary testbeam results for the tracking efficiency and charge collection, obtained with a SCM, are discussed.

physics.ins-det↗
arXiv2009

Experimental Review of Photon Structure Function Data

The present knowledge of the structure of the photon is presented based on results obtained by measurements of photon structure functions at e+e- collider. Results are presented both for the QED structure of the photon as well as for the hadronic structure, where the data are also compared to recent parametrisations of the hadronic structure function F2gamma(x,Q^2). Prospects of future photon structure function measurements, especially at an International Linear Collider are outlined.

hep-ex↗
arXiv2003

End-cap Modules for the ATLAS SCT

The performance of prototype end-cap modules of the ATLAS SemiConductor Tracker (SCT) are discussed. The results are obtained in stand-alone as well as test beam measurements performed on modules both before and after irradiation with protons with a total dose corresponding to the expectation for ten years of operation at the LHC. Finally, the present status of construction is summarised.

physics.ins-det↗
arXiv2001

Summary of the structure function session at PHOTON 2001

The status of and ongoing developments in the measurements and theoretical studies of the structure of the photon have been presented at the PHOTON 2001 conference in Ascona. The results presented in the structure function session are briefly summarised.

hep-ex↗
arXiv2000

First Measurement of the Photon Structure Function F_2,c^gamma

The first measurement of F_2,c^gamma is presented. At low x the measurement indicates a non-zero hadron-like component to F_2,c^gamma. At large x the measurement constitutes a test of perturbative QCD at next-to-leading order, with only m_c and alpha_s as free parameters, with a precision of O(40%).

hep-ex↗