Search for Rare B Decays into Two Muons with the ATLAS Detector.

PhDThe impressive progress that elementary particle physics made in the second half of the last century led to the formulation of a comprehensive theory, known as the Standard Model (SM), which correctly describes all fundamental interactions in nature, except for the gravitational one. Indirect discoveries have always played an important role in high energy physics scenario and indirect research can be considered to all intents and purposes complementary to the direct one, since allows to test much higher energy scales than those the current colliders are able to reach. This is very important now that electroweak precision tests and measurements on Flavour Changing Neutral Currents (FCNC) processes put very stringent constraints on physics beyond the SM, requiring it to appear at scales O(10 TeV). On the other hand, New Physics (NP) is expected already at scales O(1 TeV) in order to offer a natural explanation to the smallness of the Higgs mass. This scale is also confirmed by recent constraints on thermal dark matter [1] which show how new physics should manifest not far above the electroweak scale. Rare B decays have always played a crucial role in shaping the flavour structure of the SM and particle physics in general. Since the first measurement of rare radiative B æ Kú“ decays by the CLEO Collaboration [2] this area of particle physics has received much experimental and theoretical attention. In particular, FCNC B decays, involving the b-quark transition b æ (s, d) + “ and b æ (s, d) + ¸+¸≠(¸ = e, μ, ·, ‹), provided crucial tests for the SM at the quantum level since they proceed through loop or box diagrams, and they are highly suppressed in the SM (also by helicity). Hence, these rare B decays are characterised by their high sensitivity to NP. The B0 s æ μ+μ≠ channel is the most direct example of the b æ s ¸¸ transitions. The SM predicted branching ratio [3] can be enhanced by coupling to non-SM heavy particles, such as those predicted by the Minimal Supersymmetric Standard Model (MSSM) and other extensions. Updated measurements on the B0 s æ μ+μ≠ branching ratio have been presented by ATLAS [4], LHCb [5] and CMS [6] collaborations. In this thesis I will report all the studies I performed within the rare B decays ATLAS group, measuring the branching ratio of the B0 s æ μ+μ≠ channel on data collected during LHC Run 1. The first chapter provides a general introduction to the SM, focusing in particular on the flavour sector and the possible new physics scenarios. Chapter 2 briefly introduces the LHC collider and the ATLAS detector, detailing the muon and trigger systems, fundamental for the rare B decays measurements. In chapters 3 and 4, I will summarise the work done, during my presence at CERN, on the ATLAS semiconductor strip detector, monitoring the Lorentz angle during Run 1 and measuring the backplane resistance of the silicon modules installed in the ATLAS cavern. In chapter 5, I will review the strategy adopted to measure the B0 s æ μ+μ≠ branching ratio, reporting all the studies I performed on the combinatorial background, and the results obtained on 4.9 fb≠1 of data collected in 2011. Chapters 6 and 7 detail respectively the additional studies I performed on the 2011 datasets and all the tests I made in preparation for the analysis on 20 fb≠1 of data collected in 2012. I will show the studies on the discriminating variables for the rejection of the background, the tests on the multivariate analysis and on the possible strategies for the invariant mass fit for the extraction of the signal yield. All these studies proved to be fundamental for the 2012 measurement detailed in chapter 8

Cold atoms in space : community workshop summary and proposed road-map

We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies

The MATHUSLA Test Stand

The rate of muons from LHC $pp$ collisions reaching the surface above the ATLAS interaction point is measured and compared with expected rates from decays of $W$ and $Z$ bosons and $b$- and $c$-quark jets. In addition, data collected during periods without beams circulating in the LHC provide a measurement of the background from cosmic ray inelastic backscattering that is compared to simulation predictions. Data were recorded during 2018 in a 2.5 $\times$ 2.5 $\times$ 6.5~$\rm{m}^3$ active volume MATHUSLA test stand detector unit consisting of two scintillator planes, one at the top and one at the bottom, which defined the trigger, and six layers of RPCs between them, grouped into three $(x,y)$-measuring layers separated by 1.74 m from each other. Triggers selecting both upward-going tracks and downward-going tracks were used.Comment: 18 pages, 11 figures, 1 tabl

Cosmic-ray searches with the MATHUSLA detector

The performance of the proposed MATHUSLA detector as an instrument for studying the physics of cosmic rays by measuring extensive air showers is presented. The MATHUSLA detector is designed to observe and study the decay of long-lived particles produced at the pp interaction point of the CMS detector at CERN during the HL-LHC data-taking period. The proposed MATHUSLA detector will be composed of many layers of long scintillating bars that cannot measure more than one hit per bar and correctly report the hit coordinate in case of multiple hits. This study shows that adding a layer of RPC detectors with both analogue and digital readout significantly enhances the capabilities of MATHUSLA to measure the local densities and arrival times of charged particles at the front of air showers. We discuss open issues in cosmic-ray physics that the proposed MATHUSLA detector with an additional layer of RPC detectors could address and conclude by comparing with other air-shower facilities that measure cosmic rays in the PeV energy range.Comment: 64 pages, 58 figure

Cold atoms in space: community workshop summary and proposed road-map

We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies

Recent Progress and Next Steps for the MATHUSLA LLP Detector

We report on recent progress and next steps in the design of the proposed MATHUSLA Long Lived Particle (LLP) detector for the HL-LHC as part of the Snowmass 2021 process. Our understanding of backgrounds has greatly improved, aided by detailed simulation studies, and significant R&D has been performed on designing the scintillator detectors and understanding their performance. The collaboration is on track to complete a Technical Design Report, and there are many opportunities for interested new members to contribute towards the goal of designing and constructing MATHUSLA in time for HL-LHC collisions, which would increase the sensitivity to a large variety of highly motivated LLP signals by orders of magnitude.Comment: Contribution to Snowmass 2021 (EF09, EF10, IF6, IF9), 18 pages, 12 figures. v2: included additional endorser

Report from Working Group 3: Beyond the standard model physics at the HL-LHC and HE-LHC

This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3$ ab$^{-1}$ of data taken at a centre-of-mass energy of 14 TeV, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15$ ab$^{-1}$ of data at a centre-of-mass energy of 27 TeV. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will, generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics