ALICE has observed that strangeness production increases with multiplicity in
small collision systems (proton-proton and proton-lead collisions) at LHC energies.
This means that proton-proton collisions cannot be seen as
incoherent sums of parton-parton collisions, an idea that has been central in
most proton-proton generators, for example PYTHIA. To accommodate the new ALICE results,...
The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable...
The presentation will summarize the scope and status of the SHIFT project, which is a collaboration between experimental and theoretical particle physicists at Chalmers, Stockholm and Uppsala. The focus is to search for top partners that can protect the mass of the Higgs boson from large quantum corrections. We study possible signatures of such top partners and search for them using data from...
Conventional dark matter (DM) searches are looking for scattering events between DM particles of the galactic halo and nuclei in a detector target. For kinematic reasons, they lose sensitivity to masses below typically a few GeV. The most prominent strategy to probe sub-GeV masses is to search for DM-electron scatterings.
In modelling these interactions, the literature has been dominated by...
We study the consequences of the hadron-quark phase transition in failing core-collapse supernovae, which lead to the stellar-mass black-hole formation. For progenitor models with a range of compactness, the supernova core collapses and bounces for a second time due to the appearance of quarks. However, this second bounce cannot overcome the ram pressure of the envelope and result in the...
In the years following the initial discovery of a new scalar boson, data-analyses related to the Higgs sector in and beyond the Standard Model continue to be a central part of the ATLAS physics program. A number of new results have recently become available, following the exploitation of the full Run 2 proton-proton collision dataset recorded by the ATLAS experiment at the LHC. This talk...
While the LHC completed its second run in 2018, analyses of the 140 fb⁻¹ data recorded by the ATLAS experiment during that period are in full swing. In order to provide the best possible sensitivity to Standard Model and new physics, the collaboration is reprocessing the full Run-2 dataset with improved calibrations as well as simulations in all relevant areas.
The four ATLAS-Sweden groups...
Electromagnetic form factors serve to explore the intrinsic structure of nucleons and their strangeness partners. With electron scattering at low energies the electromagnetic moments and radii of nucleons can be deduced. The corresponding experiments for hyperons are limited because of their unstable nature. Only for one process this turns to an advantage: the decay of the neutral Sigma...
In recent papers we proposed the Chirality-flow method, a novel method that allows a one-line journey from a Standard-Model Feynman diagram to a complex number, which can then be easily squared. In this talk I will describe this method and show its power in some representative examples.
The European Consortium for Astroparticle Theory (EuCAPT) was founded in 2019 with the aim of supporting and bringing together the European community of theoretical astroparticle physicists and cosmologists. This short talk will explain the organisational structure, scope and plans of EuCAPT.
Gamma ray bursts (GRBs) have long been considered as a possible source of ultra high energy cosmic rays, which makes them a promising neutrino source candidate. Previous IceCube searches for neutrino correlations with GRBs focused on the prompt phase of the GRB and found no significant correlation between neutrino events and the observed GRBs. This motivates us to extend our search beyond the...
Abstract
A new type of short beam separation scans (“Emittance Scans”) was initiated at the ATLAS Experiment, at the CERN LHC, in 2018. Emittance scans are beam separation scans in which the beams are scanned across each other in the x and y planes. At every separation point we estimate the average interactions, also called the luminosity of the accelerator. These studies involved searching...
Starting in 2027, the HL-LHC will begin operation and deliver unprecedented luminosities allowing higher-precision measurements and searches for new physics processes. One central problem that arises in the ATLAS detector when reconstructing event information is to separate the interesting hard scatter (HS) vertex from uninteresting pileup (PU) vertices in a spatially compact environment. This...
The current ATLAS inner detector provided tracking and vertex reconstruction with high precision and efficiency during Run 1 and Run 2, and will continue to provide similar performance for Run 3 of the Large Hadron Collider (LHC). However, with the increased radiation damage and bandwidth requirements from the future High Luminosity LHC (HL-LHC), the ATLAS inner detector needs to be upgraded....
The High-Luminosity LHC (HL-LHC) is expected to provide a data set of 4000 fb-1 allowing precision Higgs physics and search for deviations from the Standard Model. The HL-LHC poses new challenges in terms of radiation hardness and requires an unprecedented ability to select interesting collisions (trigger) at the collision frequency with a fully digital trigger.
The ATLAS Hadronic Tile...
We calculate fixed-order electroweak corrections to the angular coefficients parameterizing the Drell-Yan process in the Z-boson mass range. We examine how the electroweak corrections affect the Lam-Tung relation, which was measured at the LHC to deviate from the SM predictions. For the calculations, we introduce a technical single lepton cut in order to avoid a double-soft/collinear...
In this session session discusses funding strategies for large accelerator-based infrastructures, as it is the case for particle physics, with authors of the report and Swedish scientists. Anyone is welcome to add questions for the panel at [this link] and to contribute to the discussion during the session.
The recent report by VR can be found here:...
Machine learning has been successfully used in physics research for decades. With the advent of deep learning methods in computer science, a renaissance of machine learning in physics occurred in recent years. The seminar explains the basic ideas of deep learning, distinguishes deep learning from the classic data analysis and classic machine learning approaches and explains concepts and...
IceCube is an astrophysical neutrino detector that uses photosensors embedded in a cubic kilometer of glacial ice at the South Pole. Over the past decade, IceCube has discovered a diffuse, high-energy flux of extragalactic neutrinos, and has reported the first likely multimessenger association involving high energy neutrinos.
In light of these findings, we are now looking towards the...
Ultra-high energy (UHE) neutrinos (E > 1e16 eV) are connected to the most energetic phenomena in our universe and neutrino astronomy is a powerful tool to study the high-energy universe. Neutrinos can escape dense source environments and point back to their sources with sub-degree accuracy. In particular, multi-messenger analyses that combine neutrino detection with electromagnetic (e.g. gamma...
In the presence of an external magnetic field, the axion and the photon mix. In particular, the dispersion relation of a longitudinal plasmon always crosses the dispersion relation of the axion (for small axion masses), thus leading to a resonant conversion. While often neglected in the literature, these conversions can dominate axion production or absorption. Using thermal field theory and...
The IceCube detector has components drilled 2 km into the ice. While the depth has been calibrated so far there is no calibration for any horizontal shift from nominal. I will present the idea behind my calibration project and some results from proof of concepts.
High-energy neutrino astronomy has become a powerful tool to explore the most extreme environments in our universe. High energy neutrinos are detected most efficiently via the Askaryan effect in ice, where a particle cascade induced by the neutrino interaction produces coherent radio emission. There are several pilot radio arrays at the moment, among them ARIANNA at the Ross Ice Shelf and the...
IceCube monitors our galaxy for supernovae using neutrinos with energies of tens of MeV. However, the shock between the ejecta and the progenitor star's circumstellar material can create a high flux of neutrinos with energies on the order of TeV and above. These neutrinos would reach Earth 0.1 day - 1 year after the low-energy neutrinos. I will describe an analysis aimed to investigate whether...
Blazars are among the most powerful emitters in the Universe over a broad range of wavelengths. The recent association of TXS 0506+056 with an astrophysical neutrino and observation of a neutrino excess from its direction by IceCube has further strengthened the case for the presence of a hadronic component in their emission, and paved way for efforts to detect this component by linking it to...
In this collaboration between pure mathematics and cosmology we show that in de Sitter, bounce solutions, or the instanton configurations that trigger vacuum decay during inflation, are O(4) symmetric. This fact has so far been assumed through analogy with the flat spacetime case but never proved. The proof follows from recent progress in geometric PDE and min-max methods
Beyond the Standard Model physics (BSM) is one of the major contributions from the ATLAS groups in Sweden. This talk highlights recent BSM analyses, such as searches for dark matter and long-lived particles, in R-parity conserving and R-parity violating scenarios. Other results from the 139 fb-1 LHC data collected by the ATLAS detector are also presented, such as the search for massive...
The ATLAS experiment, located at the Large Hadron Collider (LHC) at CERN, uses a detector design optimized for the collection of data for a wide range of physics studies.
The experiment will benefit greatly from the upcoming High Luminosity LHC (HL-LHC) upgrade, which will provide higher luminosities, making new discoveries and higher-precision measurements possible.
Higher luminosity...
The existence of baryon number violating processes is considered a necessary condition to explain the observed matter-antimatter asymmetry in the universe. The construction of the European Spallation Source (ESS) provides a unique opportunity to exploit a high intensity beam of free, cold neutrons to perform searches for baryon number violation. The NNBAR/HIBEAM experiment will be the...
Traditional decision-making processes require that data is collected first, then analyzed. This model is not sustainable when the quantity of data is too large to be recorded for subsequent analysis. The Large Hadron Collider at CERN collides protons up to 30 million times per second: the majority of these events need to be rejected to comply with data processing and storage constraints. While...
The Tile Calorimeter (TileCal) of ATLAS is a hadronic calorimeter system placed in the central region of the detector. Muons deposit energy according to a well known distribution as ionization, which makes them ideal particles for energy calibration. The study is performed using muons produced in decays of
Several HH searches are already being performed in ATLAS with different final states, but no evidence of SM-like HH production is expected until High-Luminosity LHC. The associated production of a single Higgs boson via ZH is a background in HH searches. When considering ZH, the cross-section is larger than for the corresponding SM-like HH channel. A slight modification of the HH searches to...
One of the unanswered questions remaining in particle physics is “What is Dark Matter?”. There are many different ways of searching for it; directly, indirectly, and in colliders. However, since so little is still known about it, theoretical attempts to describe it are as different as they are many. In my talk, I will describe the analysis that I am performing within the ATLAS experiment at...
The NNBAR experiment would look for neutrons transforming to antineutrons with a sensitivity improvement of three orders of magnitude compared with the previous search. At the last search, cosmic particles were the dominant background. Understanding the signature that cosmic particles leave in the NNBAR detector is therefore crucial. In this talk, predictions of cosmic ray backgrounds made...
The existence of a light sterile species of neutrino is still under consideration, as it may offer an explanation to anomalies in short-baseline neutrino oscillation experiments. However, among the difficulties encountered in including such an extra neutrino species in the zoo of well-motivated new particles, the strongest restriction may come from cosmological observations. As the light...
Liquid xenon time-projection chambers are the world’s most sensitive detectors for a wide range of dark matter candidates. We show that the statistical analysis of their data can be improved by replacing detector response Monte Carlo simulations with an equivalent deterministic calculation. This allows the use of high-dimensional undiscretized models, yielding up to ∼2times better...
It is well known that quantum and temperature corrections to the scalar potential are important when considering vacuum dynamics and phase transition phenomena. It is also true that a naive application of perturbation theory gives gauge dependent results. Further complications arise when one is considering dim
In this work we present an extended...
Astrophysical jets in active galaxies and gamma-ray bursts (GRBs) accelerate charged particles, giving rise to fluxes of very-high-energy (VHE) gamma-rays. While observing high redshift GRBs on Earth, the photon spectrum gets softer at VHEs due to the extra-galactic background light (EBL) absorption. Additionally, detecting such VHE gamma-rays is a probe to search for axion-like particles and...
The ground-based ALTO array is being developed for observation of atmospheric air showers induced by very-high-energy (VHE) gamma-rays at energies above ~200 GeV, thus covering emission spectra of soft-spectrum sources. Its particle detector array, consisting of water Cherenkov detectors and scintillation detectors, overlooks a large portion of the sky and enables detection of VHE gamma-rays...
Direct detection experiments probing dark matter scattering off electrons in semiconductors provide leading constraints on sub-GeV dark matter. In this work, we model these interactions using non-relativistic effective operators, and identify and compute five dark matter and crystal response functions, four of them for the first time. We then use these responses to calculate the expected...
As a newly appointed professor in the nuclear physics division in Uppsala I would like present some recent results from my research in LHCb. I will give a brief introduction to LHCb and my main involvements the construction of the detector. Then I’ll give a brief summary of two research topics that I have been involved in recently. The first topic is the discovery of the first doubly-charmed...
The ALICE experiment is currently undergoing a major detector upgrade during LS2 in order to make full use of the planned LHC luminosity increase for heavy-ion collisions from 2022. The Lund group has been active in the main ALICE tracking detector (TPC) from the start, and I wish to give an overview on the Lund group's activities both related to ALICE upgrades and physics analyses.
Cosmic-ray positron measurements provide a powerful probe of dark matter annihilation. A possible contribution to the measured positron flux could come from dark matter annihilating or decaying into e+e- pairs. In this work, we combine a detailed scan of the cosmic-ray propagation parameter space using Galprop with a new time-, charge- and rigidity-dependent model for solar modulation to...
In this contribution, I will outline three ongoing efforts revolving around dark matter complementarity, in the spirit of fostering cross-talk and engagement between different communities.
The first topic of this contribution is the [initiative for Dark Matter in Europe and Beyond][1]. It aims to create a permanent and common platform to exploit synergies and complementarities in dark...
One overarching objective of science is to further our understanding of the Universe and its composition. The nature of dark matter (DM), corresponding to 85% of the matter currently present in the universe is still unknown. The presence and distribution of DM is detected through its gravitational interactions by observatories and experiments, while the interactions of DM with ordinary matter...
The advent of deep learning has yielded powerful tools to automatically compute gradients of computations. This is because 'training a neural network' equates to iteratively updating its parameters using gradient descent to find the minimum of a loss function. Deep learning is then a subset of a broader paradigm; a workflow with free parameters that is end-to-end optimisable, provided one can...
