Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

AFP detectors - first experience with data

The ATLAS Forward Proton (AFP) is a forward detector using a Roman Pot technique, recently installed in the LHC tunnel. It is aiming at registering protons that were diffractively or electromagnetically scattered in soft and hard processes. AFP plans to take data both in standard high-luminosity periods, as well as in dedicated runs, where colliding beams are separated in order to decrease the luminosity. The advantage of dedicated running is that pile-up is small and in consequence, in the majority of registered events there is only one proton-proton interaction. By combining AFP data together with the data from the ATLAS Inner Detector, it is possible to have insight on what happens in diffractive events in the whole available acceptance. In 2016 the AFP detectors were present only on one side of the interaction point. The collected data can be used for studies of single diffractive processes. In 2017 the detectors on the other side have been installed, which allows studies of central diffractive production. This poster presents the construction and principle of operation of the AFP detector. First experience from operation and first physics results obtained from 2016 data will be presented

Measurements of single diffraction using forward proton tagging at the ATLAS detector

Inclusive single diffractive dissociation (pp$\rightarrow$pX) at 8 TeV is studied using data collected by the ATLAS experiment at the LHC. The intact proton is reconstructed and measured in the ALFA forward spectrometer, while charged particles from the dissociative system (X) are reconstructed and measured using the ATLAS detector. Differential cross sections are presented as a function of the proton fractional momentum loss, the four-momentum transfer squared and the size of a rapidity gap measured from the edge of the ATLAS Inner Detector. The results are interpreted in the framework of Regge phenomenology

Detector Control System for the ATLAS Forward Proton detector

The ATLAS Forward Proton (AFP) is a forward detector using a Roman Pot technique, recently installed in the LHC tunnel. It is aiming at registering protons that were diffractively or electromagnetically scattered in soft and hard processes. Infrastructure of the detector consists of hardware placed both in the tunnel and in the control room USA15 (about 330 meters from the Roman Pots). AFP detector, like the other detectors of the ATLAS experiment, uses the Detector Control System (DCS) to supervise the detector and to ensure its safe and coherent operation, since the incorrect detector performance may influence the physics results. The DCS continuously monitors the detector parameters, subset of which is stored in data bases. Crucial parameters are guarded by alarm system. A detector representation as a hierarchical tree-like structure of well-defined subsystems built with the use of the Finite State Machine (FSM) toolkit allows for overall detector operation and visualization. Every node in the hierarchy is described in an easy-to-understand way reflecting the detector structure by a graphical user interface called FSM panel. This poster presents the AFP DCS system, an overview of the detector and description of its hierarchical representation with particular emphasis on FSM panels

Study of Diffractive Bremsstrahlung at 13 TeV LHC

Feasibility studies of the diffractive bremsstrahlung measurement at the LHC at $\sqrt s$ = 13 TeV are presented. The method considered for this measurement uses the ATLAS detector and, in particular, the Zero Degree Calorimeter and the ATLAS Forward Proton detectors. The signal and background processes were generated with GenEx and PYTHIA 8.2 generators, respectively. The obtained fiducial cross sections are 1.2 ub for the signal and 6 ub for the background. Further reduction of the background is possible by the optimisation of event selection cuts

Estimation of track reconstruction efficiency for ALFA detectors for data collected in 2012

Całkowity przekrój czynny na oddziaływanie hadronów jest jednym z podstawowych parametrów oddziaływań silnych. Jest on wyznaczany w akceleratorach, w których zderzane są protony, w tym w akceleratorze LHC. Jedną z metod jego otrzymania jest zastosowanie twierdzenie optycznego, które łączy część urojoną amplitudy na rozpraszanie elastyczne w przód przy zerowym przekazie czteropędu z całkowitym przekrojem czynnym. Oznacza to rozpraszanie pod bardzo małymi kątami, bliskimi zeru. Rejestracje protonów rozproszonych elastycznie pod tak małymi kątami wykonywane są z dala od punktu oddziaływania. Od liczby przypadków elastycznych mierzonych przez dedykowane do tego celu, odległe detektory, zależy wartość wyznaczonego przekroju czynnego. Jednym z czynników, jakie należy uwzględnić przy tych pomiarach, jest wydajność rekonstrukcji śladów protonów w detektorach. Pozwala ona na określenie, o jaką wartość powinna zostać poprawiona wyznaczona wartość amplitudy na rozpraszanie elastyczne, aby odpowiadała ona wartości prawdziwej.Celem niniejszej pracy jest wyznaczanie wydajności rekonstrukcji dla przypadków elastycznych w danych zebranych w 2012 roku, przy energii zderzenia wynoszącej 8 TeV.W pracy opisano eksperyment ATLAS oraz jego detektory, w szczególności detektory ALFA. Przedstawiona sposób rekonstrukcji śladów oraz selekcji przypadków elastycznych. Główna część pracy zawiera opis wyznaczania wydajności rekonstrukcji oraz analizę danych, wraz z analizą niepewności.The total hadronic cross section is a fundamental parameter of strong interactions. It is determined by the use of accelerators colliding protons - one of them is Large Hadron Collider. One of the method is based on the use of the optical theorem, which combines the imaginary part of the forward elastic scattering amplitude extrapolated to zero momentum transfer with the total cross section.Zero momentum transfer implies measurements performed at very small angles, close to zero. They are carried out far from the interaction point with the use of special detectors dedicated for that purpose: ALFA detectors. Designated number of elastic events decides about the determined value of the cross section. One of the factors, that should be taken into account during these measurements, is the track reconstruction efficiency in detectors.The aim of this thesis is estimation of track reconstruction efficiency for elastic events for data collected in 2012, at the collision energy of 8 TeV.This thesis includes description of the ATLAS experiment and its detectors, especially ALFA detectors. The tracking algorithm is described in details and the method of elastic event selection is presented. The main part centers on the description of the method to determine the reconstruction efficiency and on carrying out the analysis, including uncertainty analysis

Inelastic proton-proton interactions in data collected with ALFA Detectors at the ATLAS Experiment.

W laboratorium CERN pod Genewą, na akceleratorze LHC, uruchomionym w 2008 roku, prowadzone są liczne eksperymenty mające pomóc w znalezieniu odpowiedzi na nurtujące pytania dotyczące budowy materii. Jednym z nich jest eksperyment ATLAS, dzięki któremu udało się potwierdzić istnienie bozonu Higgsa. W eksperymencie tym zderzane są ze sobą wiązki protonów. Zderzenia te mogą zachodzić jako elastyczne bądź, z większym prawdopodobieństwem, jako nieelastyczne. Do analizy użyto danych pochodzących z kilku różnych rodzajów detektorów. Jednym z nich są detektory ALFA, usytuowane ok. 240 m od miejsca zajścia oddziaływania między protonami. Z tego względu mogą one rejestrować jedynie cząstki poruszające się pod bardzo małymi kątami.W niniejszej pracy skupiono się przede wszystkim na analizie oddziaływań nieelastycznych. Podstawowym źródłem informacji były dane dostarczone przez detektory ALFA.Opisano pokrótce eksperyment ATLAS - jego sposób prowadzenia oraz używane w nim detektory. Omówiono możliwe rodzaje oddziaływań protonów, a następnie przeanalizowano w jaki sposób na podstawie posiadanych danych można rozróżnić między sobą rodzaje zachodzących oddziaływań. Następnie skupiono się na wybranych aspektach obserwowanych zderzeń nieelastycznych, które w trakcie analizy danych uznane zostały za interesujące.In the LHC accelerator (CERN Laboratory at Geneva) numerous experiments investigating the structure of matter take place. The main goal of these experiments is to help answering some fundamental questions. One of these experiments is the ATLAS Experiment, which has managed to confirm the existence of the Higgs boson. The idea of that experiment is to collide proton beams. These collisions may occur as flexible, or more likely, as inflexible.Different types of detectors were used to analyse collected data. Among them are the ALFA Detectors, situated at about 240 metres from the interaction point. Because of their location, they can register only particles that move at very small angles.This study is concentrated mostly on the analysis of inelastic interactions. The most basic source of information was the data collected by the ALFA Detectors.The ALFA Experiment is outlined - the way it is conducted and the detectors that are used. Possible types of interactions between protons are discussed and it is examinated how the available data can be distinguished in terms of interactions that occurred. Selected aspects of the observed inelastic collisions, which during the analysis seemed to be interesting, are discussed in detail

Detector Control System for the AFP detector in ATLAS experiment at CERN

The ATLAS Forward Proton (AFP) detector consists of two forward detectors located at 205 m and 217 m on either side of the ATLAS experiment. The aim is to measure the momenta and angles of diffractively scattered protons. In 2016, two detector stations on one side of the ATLAS interaction point were installed and commissioned. The detector infrastructure and necessary services were installed and are supervised by the Detector Control System (DCS), which is responsible for the coherent and safe operation of the detector. A large variety of used equipment represents a considerable challenge for the AFP DCS design. Industrial Supervisory Control and Data Acquisition (SCADA) product Siemens WinCCOA, together with the CERN Joint Control Project (JCOP) framework and standard industrial and custom developed server applications and protocols are used for reading, processing, monitoring and archiving of the detector parameters. Graphical user interfaces allow for overall detector operation and visualization of the detector status. Parameters, important for the detector safety, are used for alert generation and interlock mechanisms

The AFP detector control system

The ATLAS Forward Proton (AFP) detector is one of the forward detectors of the ATLAS experiment at CERN aiming at measuring momenta and angles of diffractively scattered protons. Silicon Tracking and Time-of-Flight detectors are located inside Roman Pot stations inserted into beam pipe aperture. The AFP detector is composed of two stations on each side of the ATLAS interaction point and is under commissioning. The detector is provided with high and low voltage distribution systems. Each station has vacuum and cooling systems, movement control and all the required electronics for signal processing. Monitoring of environmental parameters, like temperature and radiation, is also available. The Detector Control System (DCS) provides control and monitoring of the detector hardware and ensures the safe and reliable operation of the detector, assuring good data quality. Comparing with DCS systems of other detectors, the AFP DCS main challenge is to cope with the large variety of AFP equipment. This paper describes the AFP DCS system: a detector overview, the operational aspects, the hardware control of the AFP detectors, the high precision movement, cooling, and safety vacuum systems