Oberseminar des II. Physikalischen Instituts

Termin: Freitags, 10:30 - 11:30 Uhr, virtual
Kontaktperson: Stan Lai (stan.lai *at* cern.ch)
Dozentinnen/Dozenten: A. Frey, H. Hofsäss, S. Lai, A. Quadt

Sommersemester 2021

16. April 2021 Dr. Jörn Große-Knetter II. Physikalisches Institut Safety Briefing - Sicherheitsbelehrung
25. June 2021 Dr. Fabian Hügging University of Bonn The new ATLAS ITk-Pixel read-out chip (aka RD53B)
09. July 2021 Prof. Jyothsna Rani Komaragiri Indian Institute of Science, Bengaluru Searches for Higgs boson pair production and Dark Matter with the CMS experiment
16. July 2021 Bachelor student presentations II. Physikalisches Institut various talks

Wintersemester 2019/20

DateSpeakerAffiliationTitle (click for abstract)
25.10.2019 Hans Hofsäss II. Physikalisches Institut radiation safety instruction – Sicherheitsbelehrung
No abstract provided.

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01.11.2019 cancelled (Brückentag)
08.11.2019 Günther Dollinger Bundeswehr University Munich Positron Lifetime Microscopy
15.11.2019 T.B.A.
22.11.2019 Tianyang Wang Univ. of Bonn CMOS pixel development
29.11.2019 Jay Howarth Univ. of Manchester top properties/spin with ATLAS
06.12.2019 Johannes Erdmann TU Dortmund top properties/BSM with ATLAS
13.12.2019 Antonia Struebig Univ. of Edinburgh SUSY searches and MET triggers at ATLAS
20.12.2019 cancelled (Xmas break)
10.01.2020 Peter Schaaf TU Ilmenau T.B.A.
17.01.2020 Stella Orfanelli CERN CMS pixel electronics system
24.01.2020 Anna Kaczmarska Institute of Nuclear Physics, Polish Academy of Sciences Searches for charged Higgs bosons at ATLAS
31.01.2020 Frank Simon MPI for Physics, Munich Future electron-positron colliders
07.02.2020 Fabian Hügging Univ. of Bonn New ATLAS ITk-Pixel read-out chip (aka RD53B)

Somersemester 2019

DateSpeakerAffiliationTitle (click for abstract)
26.04.2019 Jörn Große-Knetter II. Physikalisches Institut Sicherheitsbelehrung – Safety briefing
Safety briefing.

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03.05.2019 Hans Hofsaess II. Physikalisches Institut PIXE analysis of antique pottery from the Mediterranean sea area
S. Rösemeier 1 , H. Hofsäss 1 , C. B. Fantauzzi 2 , S. Bergemann 2

1) 2nd Institute of Physics, Georg-August-University Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

2) Archeological Institute, Georg-August-University Göttingen, Nikolausberger Weg 15 37073 Göttingen, Germany

Contact and presenting person: H. Hofsäss, hans.hofsaess[AT]phys.uni-goettingen.de

We have used the external proton beam setup at Göttingen University to analyze the elemental composition of about 600 antique pottery samples collected in Sicily and neighboring islands. The samples can be categorized in groups of Terra Sigillata (roman ceramic table ware), Mediterranean cooking ware, African cooking ware, amphores, greek laquer ware (greek fine ceramics), domestic pottery, ceramics from Pantelleria (Italy), and pre-historic pottery. For each recovered pottery fragment representative small pieces of few mm diameter were collected and analyzed using PIXE with a 2.5 MeV proton beam of 1 mm 2 size and 5 nA beam current, extracted into air through a 200 nm Si 3 N 4 membrane. Relative concentrations of elements starting from Si up to Pb were analyzed, including oxygen as additional invisible element. Besides the main components Si, K, Ca and Fe we focus on the concentrations of trace elements (few hundered ppm) like Ti, V, Sc, Sr, Sn and the metals Cr, Ni, and Zn, which show significant variations even within one group of pottery samples. The results are discussed and compared with literature data from neutron activation analysis.

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10.05.2019 Enrico Bothmann Univ. of Goettingen Bounding the Higgs width at the HL-LHC through interference effects
The Higgs decay width can be constrained by exploiting interference effects of the pp -> H->γγ signal with the pp->γγ continuum background, which yields a width-dependent shift of the observed Higgs mass peak. I review a study in which my collaborators and I investigate the HL-LHC reach of an analysis that determines the reference mass from the di-photon final state at high transverse momenta, where the shift is less pronounced. As an alternative strategy, we also propose a yet more powerful technique based on a direct fit to the distorted m_γγ line shape. Both approaches employ particle-level predictions calculated with the Monte-Carlo event generator Sherpa, and I will take time to introduce some of the relevant concepts.

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17.05.2019 Daniel Primetzhofer Uppsala University Ion physics & ion beam-based materials research at Uppsala University
The presentation will highlight both the available infrastructure at the tandem laboratory as well as ongoing research projects in the ion physics research group at Uppsala University. The existing infrastructure for accelerator mass spectrometry (AMS), ion beam analysis (IBA) and ion beam modification of materials (IBMM) comprises of a 175 keV MICADAS compact radiocarbon dating system, a 5 MV pelletron tandem accelerator with in total 6 beam lines, a 350 kV implanter with 3 beam lines as well as a system for Low-Energy Ion Scattering. The existing infrastructure and its potential for fundamental research and applied studies will be exemplified by research results recently obtained using the available instrumentation. Also, a series of very recent upgrades in instrumentation will be introduced, with a focus on in-situ characterization and multi-method approaches. Examples from applied research comprise of characterization of thin films containing light and heavy constituents as used for hard-coatings and in optical applications, high-resolution depth profiling of light elements such as hydrogen and lithium in energy materials, but also investigations of sensitive materials such as metal-organic frameworks. Furthermore, different results from in-situ studies of materials growth and modification will be shown. Finally, also an overview of the ongoing fundamental studies of ion-solid interaction will be presented, with a focus on lower ion energies.

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24.05.2019 No seminar
31.05.2019 May Bank Holiday
07.06.2019 Jay Howarth Univ. of Manchester Talk cancelled
14.06.2019 Anastasia.Karavdina DESY Search for resonant ttbar production in proton-proton collisions at √s= 13 TeV with CMS data
The top quark (t) is the most massive known fundamental particle in the standard model. It has a Yukawa coupling to the Higgs field that is near unity. It is also closely connected to the hierarchy problem, where the largest corrections to the Higgs mass arise from top quark loops. Furthermore, studies of the top quark may provide insight into the mechanism of electroweak(EW) symmetry breaking. Many theories beyond the standard model (SM) predict heavy resonances at the TeV scale, which would decay to top quark and antiquark (tt) pairs. In this talk the search for the resonant ttbar production with the dataset collected with the CMS detector will be discussed. The analysis considers three exclusive final states and uses reconstruction techniques that are optimized for top quarks with high Lorentz boosts, which requires the use of nonisolated leptons and jet substructure techniques.

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21.06.2019 Teng Jian (TJ) Khoo Univ. of Geneva Challenges and opportunities in hadronic reconstruction with ATLAS
Recording and reconstructing data from the upcoming Large Hadron Collider runs poses monumental difficulties, which demand innovative solutions in hardware and software. This seminar will review progress made by the ATLAS collaboration in devising methods to precisely reconstruct hadronic observables in the face of large pileup backgrounds. Strategies for pileup mitigation in online and offline reconstruction will be presented in the context of important searches and measurements featuring jets and missing transverse momentum.

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28.06.2019 Ludovica Aperio Bella IHEP Electroweak precision physics at the LHC
Precision measurements of electroweak observables offer a viable option for finding indications of new physics and also guidance for the next big discovery. In the past, precise measurements of the fundamental parameters of the standard model were used to successfully predict the existence of new particles, the most recent examples being the top quark and the Higgs boson. The large samples of data collected at the LHC enable measuring some of the fundamental parameters of the standard model with even higher precision.

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05.07.2019 Matt LeBlanc Univ. of Arizona Inside and Out: Precision Jet Physics in ATLAS Run 2
Collimated jets of particles are the signature of quarks and gluons with high energy, such as those produced in hadron collisions at CERN's LHC. Despite challenging Run 2 conditions, the precision of the ATLAS jet energy scale measurement has reached the percent-level across a wider kinematic range than ever before. Meanwhile, theoretical advances have also enabled the first calculations of jet substructure beyond leading log accuracy, which have been recently compared to LHC data. In this talk, I will review the ATLAS jet reconstruction and energy scale calibration procedure for small- and large-radius jets, then discuss recent precision measurements of jet substructure performed by ATLAS at sqrt(s)=13 TeV.

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12.07.2019 Summer Blot DESY Neutrino oscillations with IceCube DeepCore
The IceCube Neutrino Observatory is a pioneering, cubic kilometre-sized neutrino telescope located at the geographic South Pole. Since its discovery of the astrophysical neutrino flux, IceCube has continued to provide invaluable knowledge about both potential neutrino sources and neutrino properties at the GeV-PeV scale through its detection of neutrino interactions via Cherenkov radiation in the optically clear, deep ice. In this talk I will discuss the most recent measurements of neutrino oscillations with DeepCore. I will also describe our progress on a near-future detector extension, the IceCube Upgrade, which will deploy new optical modules into the ice along with improved calibration devices to further enhance the performance of the IceCube Neutrino Observatory.

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19.07.2019 BSc Students II. Physikalisches Institut Presentation of their thesis projects
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Wintersemester 2018/19

DateSpeakerAffiliationTitle (click for abstract)
19.10.2018 Hans Hofsäss II. Physikalisches Institut Sicherheitsbelehrung - Radiation Safety Briefing
09.11.2018 Xingguo Li DESY Searches for new physics with same-sign leptons, jets and missing transverse momentum at the ATLAS experiment
The production of same-sign lepton pairs from proton-proton collisions occurs rarely in the Standard Model (SM). However, physics Beyond Standard Model (BSM) can significantly enhance the cross section of these production processes. The final state is favoured in many BSM searches because of its relatively low background. In this seminar, I will focus on new physics searches with same-sign leptons and missing transverse momentum at the ATLAS experiment.

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16.11.2018 Katharina Bierwagen Mainz Searches for Dark Matter with the ATLAS detector
Cosmological and astrophysical observations indicate the presence of Dark Matter in the universe which cannot be explained by the Standard Model. Searches for Dark Matter are performed by both the ATLAS and CMS experiment in events involving large missing transverse momentum in the final state. So far no signal for physics beyond the Standard Model has been found. An overview of the most recent results by the ATLAS collaboration based on the full proton-proton collision dataset collected at a centre-of-mass energy of 13 TeV in 2015 and 2016 will be presented. A major focus is on the search for DM in final states with an energetic jet and large missing transverse momentum. In addition, the prospects for the future will be discussed.

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23.11.2018 Tamara Vazquez Schroeder CERN Search for the associated production of a Higgs boson and a top quark pair with the ATLAS experiment at the LHC
One of the important tests of the SM is the measurement of the top quark Yukawa coupling, directly measured via the associated production process pp→tt̄H. The fourfold increase of the tt̄H cross section from √s=8 to 13 TeV and the high statistics of top quark sample collected by the LHC experiments allow to increase the sensitivity of the search of this process. Both ATLAS and CMS have performed searches of tt̄H targeting the most relevant Higgs decays modes in final states with multi leptons, high b-jet multiplicity or containing two photons at √s=13 TeV. In this talk, the latest results on the search for the tt̄H process with the ATLAS experiment will be discussed, together with a comparison to the CMS performance and an outlook of these measurements with higher statistics.

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30.11.2018 Chaowaroj "Max" Wanotayaroj DESY Building the local electronic support for the ATLAS strip detector
For the ATLAS experiment a new Silicon tracker is necessary for the High-Lumimosity Upgrade of the LHC. The main building blocks for the strip tracker is a module which consists of a silicon sensor, readout ASICs and a hybrid PCB. Up to 28 modules are placed on long substructures. An End-of-Substructure (EoS) card provides common connections for data, commands, and power to the off-detector systems. Prototypes has been developed based on the GBTx and GBT-SCA chip family and SFP+ optical links. In this talk, I will present the design of the communication protocol, the hardware, as well the tests for both electrical performance and physical properties of the EoS.

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07.12.2018 Rafael Gama II. Physikalisches Institut Muon trigger assisted by calorimetry at the ATLAS experiment
With the increase of the luminosity provided by the LHC, throughout its upgrade phases, studies predicted that the available bandwidth for the muon trigger system, at the ATLAS experiment, would be exceeded due to background noise. To help overcoming this issue, the concept of using the Tile Hadronic calorimeter (TileCal) information to assist the muon trigger system was proposed and it's known as the Tile-Muon trigger. A new electronic instrumentation system had to be developed to enable the deployment of the Tile-Muon trigger in the experiment. Details about the Tile-Muon trigger, as well as its current performance, will be presented. Moreover, a study regarding the potential of using the TileCal information to increase the muon trigger efficiency in the ATLAS central region will be shown. This study considers the experimental environment after the ATLAS phase-II upgrade for the High-Luminosity LHC.

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14.12.2018 Jörn Lange II. Physikalisches Institut Time for High Luminosity – a new Detector for ATLAS
A new detector is being proposed for the High-Luminosity-LHC upgrade of ATLAS to complement precise tracking with ultra-fast timing for pile-up removal: the High Granularity Timing Detector (HGTD). It will exploit the fact that the primary vertices where the individual interactions take place are not only distributed in space, but also in time. Hence, measuring the time of each particle with about 30 ps precision allows to further suppress backgrounds from pile-up and restore the reconstruction performance of b-tagging, jets and isolated leptons, which is crucial for many physics analyses. The HGTD will cover a pseudo-rapidity range of 2.4 to 4.0 with a granularity of 1.3x1.3 mm2. It is only made possible by the rapid advance of a new silicon detector technology, namely Low Gain Avalanche Detectors (LGAD), which have been developed by CNM Barcelona and the CERN RD50 Collaboration and are now also produced by Hamamatsu, FBK, BNL and Micron. Also the University of Göttingen recently joined LGAD sensor R&D efforts. The current status of the project and detector development will be presented.

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11.01.2019 María Cepeda CERN Higgs Physics at the HL/HE-LHC
One of the central goals of the physics program at the Large Hadron Collider is the study of the origin of electroweak symmetry breaking. The upgrade of the LHC to a High Luminosity Machine (HL-LHC) at 14 TeV center-of-mass energy, expected to collect 3 ab-1 of proton-proton collision data, will provide an extensive data sample with which to characterize the properties of the Higgs boson with unprecedented precision. In this seminar, I will present the state-of-the-art expected sensitivities of Higgs boson measurements at the HL-LHC, which combine the potential of ATLAS and CMS and take into account future upgraded detector performance and foreseen theoretical developments. They are the culmination of the experimental and theoretical collaborative effort documented by the Higgs working group of the "Workshop on Physics at HL-LHC, and perspectives on HE-LHC”.

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18.01.2019 Oleg Brandt Heidelberg Dark Sector Vistas Through the Higgs Window
The Higgs boson plays a central role in the Standard Model of Elementary Particle Physics, through spontaneous electroweak symmetry breaking and by providing masses to fermions. Similarly, the Higgs boson plays a special role in many extensions of the Standard Model. In particular, the Higgs boson represents an extraordinary window to search for extensions of the Standard Model that feature a Dark Matter particle candidate. I will review such searches for Dark Matter through the Higgs window at colliders, with a particular focus on the contribution of our group using the ATLAS detector at the Large Hadron Collider at CERN, and will give an outlook into the future at the High-Luminosity LHC.

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Somersemester 2018

DateSpeakerAffiliationTitle (click for abstract)
13.04.2018 Jörn Große-Knetter II. Physikalisches Institut Sicherheitsbelehrung – Safety briefing
20.04.2018 Lucia Masetti Univ. of Mainz Towards 4D tracking and 5D calorimetry: the ATLAS high granularity timing detector and more
After the upgrade of the LHC to its high luminosity phase (HL-LHC) on average 200 collisions will take place every 25 ns. In order to correctly recognise the detector signals generated from the high energy process, timing detectors with a resolution of few tenths of picoseconds are proposed for both ATLAS and CMS, additionally to a higher spatial resolution in the tracker. In this talk the requirements, available technologies, detector designs and expected performance will be presented. Applications in luminosity detectors will be shortly discussed as well.

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27.04.2018 Dimitar Yordanov Univ. of Göttingen A single element of matrix source of negative hydrogen ions
The presented work is within the scope of plasma sources of negative hydrogen ions, based on volume-production. The design of the studied source is for a matrix of small radius discharges with planar-coil inductive driving and single aperture extraction of the ions from each discharge. The concept of the source is based on the nonlocality in the discharge, which leads to the accumulation of negative ions in the peak of the plasma potential. Since, in planar coil discharges the maximum of the plasma potential is in the vicinity of the coil, thus an appropriate profile of the plasma potential is required for the efficient extraction of the ions, which determines the aim of the work: investigation of the extraction of volume-production negative ions from a single element of a matrix source. As a result of the studies, it has been shown that the efficient extraction of negative ions requires a high potential applied to the first electrode of the extraction system. Thus, a new type of discharge is formed, which constitutes a hybrid gas discharge structure, which is a combination of an inductive discharge with a planar coil and a DC discharge providing the plasma potential, required for efficient ion extraction.

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04.05.2018 Sam Meehan Univ. of Washington Finding the Next Einstein
The African Institute of Mathematical Sciences (AIMS) was founded in 2008 by Neil Turok with a simple yet profoundly ambitious goal; to find the next Einstein in Africa. More broadly speaking, the AIMS organization works to improve the overall level of math and scientific education throughout the African continent while building a sustainable pan-African academic network that will enable future generations of scientists to succeed. In this talk, I will introduce you to this unique academic institution through the lens of my own experiences, having been involved with AIMS in a variety of roles in South Africa, Rwanda, and most recently Ghana, and how an investment of oneself in this endeavor has amazing potential for the broader scientific community throughout the 21st century. (Note : There will be minimal discussion of jet substructure in this talk.)

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18.05.2018 Tomas Jezo Univ. of Zürich State of the art POWHEG generators for Top Mass Measurements at the LHC
We study the theoretical uncertainties in the determination of the top-quark mass using next-to-leading-order (NLO) generators interfaced to parton showers (PS) that have different levels of accuracy. Specifically we consider three generators: one that implements NLO corrections in the production dynamics, one that includes also NLO corrections in top decay in the narrow width approximation, and one that implements NLO corrections for both production and decay including finite-width and interference effects. Our aim is to provide an assessment of the uncertainties of purely theoretical origin, we thus consider simplified top-mass related observables that are broadly related to those effectively used by experiments, eventually modelling experimental resolution effects with simple smearing procedures. Examining these observables with generators of increasing accuracy allows us to assess the theoretical errors due to the use of the less accurate generators. Furthermore, we estimate theoretical uncertainties associated with the variation of scales and with the choice of parton distribution functions. In order to give an indicative assessment of the uncertainties due to the shower and to the modelling of non-perturbative effects, we interface our NLO+PS generators to several shower Monte Carlos, with various settings, and compare the results.

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01.06.2018 James Ferrando DESY Searches for new particles decaying to top-quark pairs at the LHC
The top quark plays an important role in many theoretical models of physics beyond the Standard Model. A typical, striking signal of such models is the production of new heavy particles (resonances) which decay into top quark pairs. This seminar reviews searches at the Large Hadron Collider (LHC) for top-antitop resonances from the start of LHC running up to the present day. The development of techniques to address the particular challenges of identifying high-energy top quarks, the latest search results from the ATLAS and CMS experiments, and a look towards the prospects for future searches at the upgraded high-luminosity LHC are presented.

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08.06.2018 Jeanette Lorenz LMU Munich Direct Searches for SUSY at LHC
Supersymmetry is an appealing extension beyond the Standard Model of particle physics which could provide e.g. a candidate for Dark Matter. Both the ATLAS and the CMS experiments at the Large Hadron Collider, CERN, carry out a comprehensive search program, addressing many different signatures that supersymmetric particles could result in. Some of the recent highlights of these searches will be presented along with the assumptions made in the interpretation of these results. Although these searches did not result in a discovery yet, there are many ways in which Supersymmetry could hide, which guide us to new directions in future searches. Some of these future directions will be discussed.

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22.06.2018 Ewen Maclean CERN Beam optics studies at the LHC
Accelerator beam optics is, broadly speaking, the study of the dynamics of charged particle beams as they travel through a particle accelerator and interact with its magnetic lattice. Precise control of accelerator optics is essential for the safe and efficient operation of modern colliders such as the LHC. One of the key tools at our disposal to understand and improve the optics at the LHC are studies utilizing the beams themselves. Since the start of operation an active program of beam-based study has been in place. This talk aims to give a flavour of some of the optics studies which are conducted on the LHC accelerator.

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29.06.2018 Marcus Morgenstern Nikhef From light to heavy states - How ATLAS can contribute to flavour physics
In the recent years, several anomalies showed up in semi-leptonic rare B decays pointing to violation of Lepton Flavour Universality which put Physics Beyond the Standard Model (BSM) in favour. In this talk the measurements of the LHCb and BELLE experiments will be reviewed and an outline of corresponding efforts by the ATLAS collaboration will be given. Measurements involving low momentum muons comes with its own challenges, in particular on the trigger system and muon reconstruction. These challenges will be addressed in the context of Lepton Flavour violating decays of tau leptons. Based on the B anomalies Leptoquarks recently attracted significant attention as a potential explanation of these anomalies. Leptoquarks, predicted by several BSM models, like SU(5) Grand Unified Theories or SU(4) Pati-Salam model, are new heavy colour charged particles carrying both lepton and baryon numbers. Current and planned search efforts by the ATLAS collaboration will be discussed in the second part.

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06.07.2018 Michael Lupberger CERN A next generation readout system and its application at the NMX instrument for ESS
The European Spallation Source ERIC (ESS) currently under construction in Lund will become the brightest neutron source in the world opening new opportunities in different fields of research like material science or biology once the user program starts in 2023. Due to the Helium-3 crisis, several instruments will employ new detector technologies with solid converters. A prototype for one instrument, the NMX macromolecular diffractometer, developed by the gaseous detector group at CERN is based on Micro Pattern Gaseous Detectors (MPGDs). The detector with an active area of 50 x 50 cm² uses a Gadolinium neutron converter as cathode of a micro-TPC with 10 mm drift, a triple Gaseous Electron Multiplier (GEM) amplification stage and a two-dimensional strip anode. Data are collected by the multi-purpose Scalable Readout System (SRS) of the RD51 Collaboration. Within the Horizon2020 projects BrightnESS and AIDA2020, RD51 has decided to implement the VMM ASIC developed by BNL for the ATLAS New Small Wheel (NSW). The SRS-VMM will become the backbone of R&D in MPGDs for the next decade and replace the successful APV25 based readout, which was used in many projects like the CMS GEM upgrade QA, ATLAS NSW and drove the research within RD51 in the last eight years. My presentation will introduce the ESS and developments for NMX at CERN and then focus on the SRS-VMM readout system in general also giving an overview of the current APV25 standard readout. Several groups have signed up to apply SRS-VMM in their experiments and some of those applications will be presented briefly as well as upgrade plans for the readout system.

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13.07.2018 BSc Students II. Physikalisches Institut Presentation of their thesis projects
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Wintersemester 2017/18

DateSpeakerAffiliationTitle (click for abstract)
20.10.2017 Hans Hofsäss II. Physikalisches Institut Sicherheitsbelehrung - Radiation Safety Briefing
27.10.2017 Felipe Bregolin II. Physikalisches Institut Development of an enhanced ion source for accelerator mass spectrometry
The origin and the irradiation age of micrometeorites are of great interest for astrophysical questions, which indirectly allow new statements and insights into the variation of galactic cosmic radiation in the past millions of years. This information can be reconstructed by the determination of so-called long-lived cosmogenic radionuclides obtained in micrometeorites. Since their amount in the samples is quite low, the only analytical technique sensitive enough is the accelerator mass spectrometry (AMS). However, even AMS encounters its technological limits for the quantitative determination of these extremely small sample quantities. By increasing the efficiency of the negative ion generation from AMS samples, a more sensitive detection can be achieved. The overall objective of the project is to develop a high-current ion source specifically for the detection of these radionuclides for studies on micrometeorites and other condensed matter samples of small volume to be installed at the Dresden Accelerator Mass Spectrometry facility (DREAMS) located at the Helmholtz-Zentrum Dresden Rossendorf.

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03.11.2017 Hannes Vennekate Univ. of Dresden Emittance Compensation for SRF Photoinjectors
The advantages of contemporary particle injectors are high bunch charges and good beam quality in the case of normal conducting RF guns and increased repetition rates in the one of DC injectors. The technological edge of the concept of superconducting radio frequency injectors is to combine the strengths of both these sides. As many future accelerator concepts, such as energy recovery linacs, high power free electron lasers and certain collider designs, demand particle sources with high bunch charges and high repetition rates combined, applying the superconductivity of the accelerator modules to the injector itself is the next logical step. However, emittance compensation — the cornerstone for high beam quality — in case of a superconducting injector is much more challenging than in the normal conducting one. The use of simple electromagnets generating a solenoid field around the gun’s resonator interferes with its superconducting state. Hence, it requires novel and sophisticated techniques to maintain the high energy gain inside the gun cavity, while at the same time alleviating the detrimental fast transverse emittance growth of the bunch.
In the case of the ELBE accelerator at the Helmholtz-Zentrum Dresden- Rossendorf, a superconducting electron accelerator provides beam for several independent beamlines in continuous wave mode. The applications include IR to THz free electron lasers, neutron and positron generation, to Thompson backscattering with an inhouse TW laser, and hence, call for a flexible CW injector. Therefore, the development of a 3.5 cell superconducting electron gun was initiated in 1997.
The focus of this thesis lies on three approaches of transverse emittance compensation for this photoinjector: RF focusing, the installation of a su- perconducting solenoid close to the cavity’s exit, and the introduction of a transverse electrical mode of the RF field in the resonator. All three methods are described in theory, examined by numerical simulation, and experimen- tally reviewed in the particular case of the ELBE SRF Gun II at HZDR and a copy of its niobium resonator at Thomas Jefferson National Laboratory, Newport News, VA, USA.

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10.11.2017 T. Theveneaux-Pelzer DESY Highlights of recent ATLAS results in the top-quark sector
The top quark is the heaviest particle in the Standard Model, and the only one with a mass larger than the Higgs boson mass. Therefore, it plays an important role in several scenarios Beyond the Standard Model. New physics may be found either by the observation of new processes involving top quarks - in which Standard Model top-quark processes are backgrounds - or indirectly by finding deviations of measured observables with respect to Standard Model predictions. In both cases, it is crucial to perform precision measurements of all top-quark processes, in the widest possible phase-space. The Large Hadron Collider has already produced about 380 billions top quarks in proton-proton collisions since the startup in 2009, and this unprecedented amount of Data lead to a wide range of measurements and searches. A selection of recent results by the ATLAS collaboration in the top-quark sector will be presented.

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17.11.2017 Lidia Dell’Asta Boston University Measurement of the production cross-section of a single top quark in association with a Z boson at 13 TeV with ATLAS
The seminar will describe the evidence for the production of a top quark in association with a Z boson. This rare Standard Model process, involving WWZ and tZ couplings, has not been observed so far. The proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of sqrt(s) = 13 TeV are used, corresponding to an integrated luminosity of 36.1 fb^(−1). Events containing three identified leptons (electrons and/or muons) and two jets, one of which is identified as a b-quark jet are selected. The major backgrounds are diboson, ttbar and Z+jets production. A neural network is used to improve the background rejection and extract the signal. The resulting significance is 4.2sigma in the data and the expected significance is 5.4sigma. The measured cross-section for tZq production is 600 +/- 170 (stat.) +/- 140 (syst.) fb.

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24.11.2017 Malte Backhaus Univ. of Zurich Design, construction, and performance of the new CMS pixel detector: conceptual differences to ATLAS pixels on micro- and macroscopic level
The instantaneous luminosity of the Large Hadron Collider is gradually increased above the nominal luminosity. The result is that already in 2016 the experiments needed to cope with luminosities exceeding the design values. While ATLAS inserted a new B-Layer at smaller radius in 2014, the CMS experiment constructed and inserted a completely new pixel detector during the winter shutdown of LHC in 2016/2017. This upgrade ensures efficient data taking until the long shutdown in 2023. Several evolutions of the detector design - most prominent a fourth barrel layer, a third disc and new readout chips - improve the detector performance. Despite the similarity of the challenges in the ATLAS and CMS experiments, the technical solutions used in the CMS pixel detector differ significantly from those implemented in ATLAS. The talk motivates the conceptual differences on the ATLAS and CMS detector design and the constraints they set on the pixel system. Then key parameters of the tracking system are introduced and the techniques used in ATLAS and CMS to optimize the performance are explained. The impact of the used solutions on the tracking performance is demonstrated based on data that was recently recorded with the new CMS pixel detector.

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01.12.2017 Peter Loch Univ. of Arizona Calorimetry in high energy and high intensity particle physics applications
Calorimeters are the prevalent detector choice in particle physics experiments requiring precision energy and direction reconstruction for even the highest energy particles escaping an interaction. In this talk we briefly review the basic principles of signal generation and signal features for these detectors, and discuss their application at the world’s highest energy and intensity hadron collider in operation today, the Large Hadron Collider (LHC) at CERN. Some emphasis is put on the reflection of the typical detector signal characteristics onto the methods applied to reconstruct the collision products and extract the underlying physics in an environment characterized by a significant background arising from diffuse lower energy particle flow surrounding the interaction of interest. The paramount examples guiding this part of the talk are the calorimeter systems and the corresponding reconstruction techniques employed by the two large multi-purpose experiments at the LHC, ATLAS and CMS. Additional considerations include a brief outlook on the application of calorimeters in the even more challenging environments of future lepton and hadron colliders, and their application in non-collider experiments at the intensity frontier, like MINOS and NOvA.

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08.12.2017 no seminar
15.12.2017 James Robinson DESY Di-Higgs searches at the LHC
The production of Higgs pairs is extremely rare within the Standard Model. Several beyond the Standard Model theories predict enhancements to this rate either through a resonance decaying directly to a Higgs pair or through changes to coupling strengths. Searches for Higgs pairs can thus probe a variety of new physics models and provide a unique direct test of the Higgs self-coupling. In this talk, I will present the latest results from ATLAS and CMS across a variety of different decay channels.

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05.01.2018 Georges Aad CNRS Probing the coupling of the two heaviest particles in the Standard Model: search for the associated production of a Higgs boson and a top quark pair with ATLAS
After the discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations, attention has turned to more detailed measurements of its properties and couplings as a means of testing the predictions of the Standard Model (SM). In particular, the coupling to the top quark, the heaviest particle in the SM, could be very sensitive to effects of physics beyond the SM. The most precise measurement of the top-quark Yukawa coupling relies largely on the gluon–gluon fusion production mode and on the decay mode to photons, which both depend on loop contributions with a top quark. Higgs-boson production in association with a pair of top quarks, ttH, is the most favorable production mode for a direct measurement of the top-quark’s Yukawa coupling. This mode is not yet observed at the LHC while a recent evidence of this production mode was published by ATLAS. In this seminar I will present the recent ATLAS results for the various ttH channels and their combination leading to this evidence. I will concentrate on the critical points for each of the channels and discuss the possible improvements that can lead to a discovery with the full Run 2 dataset.

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12.01.2018 Benedict Winter Univ. of Bonn Tau polarisation measurements at the LHC
Tau leptons are important probes for electroweak and top quark production processes as well as in searches for physics beyond the Standard Model at the LHC. One of the unique properties of taus is that their polarisation can be measured because they decay before exiting the detector volume. After introducing the basic concepts of tau polarisation measurements, the talk focuses on the measurements in W and Z boson decays at ATLAS, which are the first tau polarisation measurements in hadron collisions. Possible future tau polarisation measurements at the LHC are discussed.

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19.01.2018 Lucia Masetti Univ. of Mainz Talk cancelled
26.01.2018 Anna Macchiolo MPP Munich Pixel Sensors Developments for the ATLAS ITk
The entire tracking system of the ATLAS experiment will be replaced during the LHC Phase II shutdown by an all-silicon detector called the ITk (Inner Tracker). The pixel detector will comprise the five innermost layers, and will be instrumented with new sensor and readout electronics technologies to improve the tracking performance and cope with the HL-LHC environment, which will be severe in terms of occupancy and radiation. An overview of the last phases of the R&D activities for the new pixel system will be given, with particular emphasis on the different sensor options being explored. Their relative performance will be discussed, together with the path towards the final technological decisions to be made.

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02.02.2018 Olaf Nackenhorst Univ. of Dortmund Talk cancelled

Sommersemester 2017

DateSpeakerAffiliationTitle (click for abstract)
21.04.2017 Jörn Grosse-Knetter II. Physikalisches Institut Sicherheitsbelehrung - Safety Briefing
28.04.2017 Florian Bernlochner Univ. of Bonn Belle II and the flavour frontier of the search for New Physics
Belle II is a future flavour factory that will produce large numbers of B-Mesons and study their decay. Such precision studies are complementary to new physics searches at the LHC and in the precision laboratory provided by the Belle II detector, new physics can be probed to scales beyond the direct detection potential of the ATLAS and CMS experiments. Belle II will record first collisions in 2018 and I'll provide a brief overview in what analyses Bonn will be involved using first data and beyond. In addition, I'll provide details on the physics focus of my Emmy Noether group and give a sneak peak on interesting theory and analysis projects I'm involved in.

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05.05.2017 Mathieu Pellen Univ. of Würzburg NLO corrections for processes involving off-top quarks at the LHC
With Run II, the Large Hadron Collider (LHC) is entering the precision era. In order to match the experimental measurements, precise and appropriate theoretical predictions should be computed. In that respect, the assessment of electroweak (EW) corrections and off-shell effects for Standard Model (SM) processes is of prime importance. EW corrections can grow large in particular phase space regions which are usually the one where new physics is expected to appear. This makes them particularly relevant for precise SM measurements as well as for SM background estimate in new physics searches. In addition to allow for a direct comparison with experiments, off-shell computations provide realistic estimate of the high energy tail of distributions. The latter will be probed during Run II thanks to a never accessed centre-of-mass energy. To illustrate this, I present two recent computations where NLO EW corrections have been calculated for processes involving off-shell top quarks: the production of top-quark pairs decaying fully leptonically and the same production process in association with a Higgs Boson. In this two examples, I discuss the impact of EW corrections and off-shell effects.

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12.05.2017 Johannes Albrecht Univ. of Dortmund Challenging the Standard Model with LHCb data
The LHCb experiment at CERN has in the past years recorded the world's largest sample of beauty mesons. Their decays can be precisely measured with the LHCb detector, thanks to its unique geometry as forward spectrometer. Rare leptonic and semi- leptonic beauty decays are excellent probes for yet unknown heavy particles. Measurements of decay rates and angular distributions of these processes can be used to test the Standard Model of particle physics with unprecedented sensitivity. This seminar puts a focus on recent measurements of the LHCb collaboration, including a discussion of the recent tensions in tests of lepton flavour universality.

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19.05.2017 Sergio Diez Cornell DESY Hamburg The new silicon microstrip detector of the ATLAS ITk tracker
The inner detector of the present ATLAS detector has been designed and developed to function in the environment of the present Large Hadron Collider (LHC). At the next-generation tracking detector proposed for the High Luminosity LHC (HL-LHC), the so-called ATLAS Phase-II Upgrade, the particle densities and radiation levels will be higher by as much as a factor of ten. The new detectors must be faster, they need to be more highly segmented, and covering more area. They also need to be more resistant to radiation, and they require much greater power delivery to the front-end systems. At the same time, they cannot introduce excess material which could undermine performance. For those reasons, the inner tracker of the ATLAS detector must be redesigned and rebuilt completely. The design of the ATLAS Upgrade inner tracker (ITk) has already been defined. It consists of several layers of silicon particle detectors. The innermost layers will be composed of silicon pixel sensors, and the outer layers will consist of silicon microstrip sensors.

The talk will be focused on the strip region of the ITk. The central part of the strips tracker (the "barrel") will be composed of rectangular "short" (~ 2.5 cm) and "long" (~5 cm) strip sensors. The forwards regions of the strips tracker (the "endcaps") consist of 6 disks per side, with trapezoidal shaped microstrip sensors of various lengths and strip pitches. In response to the needs of the strip region for the ITk, highly modular structures are being studied and developed, called "staves" for the central region (barrel) and "petals" for the forward regions (end-caps). These structures integrate large numbers of sensors and readout electronics, with precision light weight mechanical elements and cooling structures. The silicon modules are directly glued onto low-mass, carbon fiber-based stave and petal core structures, with embedded titanium cooling pipes and data and power buses. The staves and petals are then arranged into cylinders and disks, respectively, by means of the integration and global structures. The service module elements, part of the global structure, provide data, power, and cooling to groups of petals and staves. A strong prototyping effort has been put in place over the course of the last years in order to optimize the design and construction methods of the ATLAS Strips ITk tracker. The Collaboration reached an important milestone recently with release of the ATLAS Strips ITk Technical Design Report (TDR).

The instrumentation effort in the ATLAS group at DESY focuses on the end-cap region of the strips tracker. A fully instrumented end-cap will be assembled and tested at DESY. The end-cap will then be transported to CERN for its final installation and commissioning. The talk will also detail the infrastructure and QA/QC methods envisioned for this challenging task.

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02.06.2017 Dan Guest UC Irvine and CERN Machine Learning for Object Identification at the LHC
(no abstract provided)

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09.06.2017 Steffen Schaepe Univ. of Bonn Searching SUSY with ATLAS
The Standard Model (SM) of particle physics is one of the best tested and most successful theories in modern physics. However, several fundamental problems indicate that there must be some physics beyond the well known SM. Despite its ongoing non-discovery, Supersymmetry (SUSY) remains one of the most compelling ideas for a natural extension of the SM. The Large Hadron Collider LHC and it's two general purpose detectors are ideal tools to search for SUSY in proton-proton collisions. In my talk, I will present some basics of SUSY, how it is searched for and how the results can be interpreted. Moreover, I will present a few selected results from recently published ATLAS searches for SUSY.

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16.06.2017 Darren Scott IPPP Durham Resummation for top quark pair production at the LHC at NNLO+NNLL
With top quark physics now entering the precision era, the need for ever more accurate theory calculations is greater than ever. In this talk we present a formalism, derived from SCET, for the simultaneous resummation of soft and small mass logarithms present in top quark pair production at the LHC. By matching this simultaneous resummation with standard soft gluon resummation and recent exact NNLO results, we present differential cross sections of the pair invariant mass and top quark transverse momentum which are applicable to the entire phase space with an accuracy of NNLO+NNLL'. Finally, we will also comment on the choice of factorisation scale.

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30.06.2017 Andrea Knue MPI for Physics, Munich Search for rare process involving top quarks in the Standard Model and Beyond
(no abstract provided)

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07.07.2017 Christian Grefe Univ. of Bonn Leptonic Higgs decays: status and outlook
Evidence of the decay of the Higgs boson into two tau leptons has been observed by the ATLAS and CMS experiments at the LHC. To date this is the strongest evidence of the Yukawa coupling of the Higgs boson to fermions but it is only a first step into exploring this sector of Higgs physics. The latest results of searches and measurements of leptonic Higgs decays will be presented and prospects for future measurements will be discussed.

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14.07.2017 BSc Students II. Physikalisches Institut Presentation of their thesis projects
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Wintersemester 2016/17

21.10.2016 Hans Hofsäss II. Physikalisches Institut Sicherheitsbelehrung - Radiation Safety Briefing
28.10.2016 Flavia Dias Univ. of Edinburgh Fast simulation/ new physics
04.11.2016 Frank Siegert Univ. of Dresden A practical guide to event generation for prompt photon production
02.12.2016 Quentin Buat Simon Fraser University TBA
09.12.2016 Arnaud Ferrari Univ. of Uppsala Searches for beyond-the-Standard Model Higgs bosons in ATLAS
16.12.2016 Felipe Bregonlin II. Physikalisches Institut Development of an efficient high current ion source for Accelerator Mass Spectrometry
13.01.2017 Tobias Flick Univ. of Wuppertal Phase-2 upgrade of the ATLAS tracker readout
20.01.2017 Ben Nachman Berkeley Lab (LBNL) Grand Challenges for Jet Substructure
20.01.2017 Juergen Reuter DESY Searching New Particles in Vector Boson Scattering at the LHC
03.02.2017 Steve Muanza Univ. of Marseille Using integral and differential charge asymmetries in searches for BSM physics at the LHC

Sommersemester 2016

15.04.2016 Jörn Grosse-Knetter II. Physikalisches Institut Sicherheitsbelehrung - Safety Briefing
22.04.2016 Peter Wagner Univ. of Bonn Particle Flow Reconstruction of Tau Lepton Decays and Analysis Prospects
29.04.2016 Tobias Bisanz II. Physikalisches Institut Code Quality: Modern C++
13.05.2016 Joshua Wyatt Smith II. Physikalisches Institut Code Quality 2
20.05.2016 Louis Helary Boston University and CERN Review of recent Electroweak results from the LHC
03.06.2016 Marek Schoenherr Univ. of Zürich Electroweak corrections for the LHC
17.06.2016 Alexander Oh Univ. of Manchester 3D diamond detectors for particle tracking and dosimetry
24.06.2016 Volker Metag Univ. of Gießen Experimental tests of QCD at the low energy frontier
01.07.2016 Mads Frandsen CP3-Origins, Southern Univ. of Denmark Dynamical electroweak symmetry breaking in light of LHC results
08.07.2016 Christoph Englert Univ. of Glasgow Effective Theories at the LHC
15.07.2016 BSc Students II. Physikalisches Institut Presentation of their thesis projects

Wintersemester 2015/16

30.10.2015 Hans Hofsäss II. Physikalisches Institut Sicherheitsbelehrung - Radiation Safety Briefing
13.11.2015 Christian Grefe Univ. of Bonn Higgs physics at linear colliders
04.12.2015 Jennifer Thompson II. Physikalisches Institut Electroweak corrections in Monte Carlo simulations
11.12.2015 Christoph Falk Anders Univ. of Heidelberg Boosted top quark reconstruction and searches with boosted objects at ATLAS
15.01.2016 Jason Veatch II. Physikalisches Institut A search for ttbar resonances: 1-lepton channel
22.01.2016 Pier Monni Univ. of Oxford Event shape resummation and/or jet vetoes
05.02.2016 Marie-Hélène Genest CNRS LPSC Grenoble Searches for Dark Matter and Extra Dimensions with mono-X signatures at ATLAS
12.02.2016 Hans Peter Beck Univ. of Bern Higgs Boson - Year four after its discovery

Sommersemester 2015

24.04.2015 Jörn Grosse-Knetter II. Physikalisches Institut Sicherheitsbelehrung - Safety Briefing
08.05.2015 Nathan Hartland Univ. of Oxford Parton distributions for the LHC
15.05.2015 Matthias Hamer CBPF - Brazilian Center for Physics Research A Global Fit of the CMSSM after the LHC Run I
22.05.2015 Iacopo Vivarelli Univ. of Sussex Searches for 3rd generation SUSY particles
29.05.2015 Lorenzo Bianchini ETH Zurich MEM for the ttH search in CMS
05.06.2015 Susanne Kuehn Univ. of Freiburg Silicon Strip Detectors for the ATLAS upgrade project
19.06.2015 Rebeca Gonzalez Suarez Univ. of Nebraska Overview of single top physics in CMS with Run-1 data
26.06.2015 Yves Kemp DESY Interactive Analysis Facilities: from NAF to NAF 2.0
03.07.2015 Silke Merchel Helmholtz-Zentrum Dresden-Rossendorf Cutting-edge analytics at DREAMS: Cool application stuff using tandem accelerators
17.07.2015 BSc students II. Physikalisches Institut Presentation of their thesis projects

Inhalt der Übersichtsseite des Oberseminars