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Searches for supersymmetric dark matter in semileptonic final states at the CMS experiment employing angular correlation and deep learning techniques followed by a reinterpretation in the pMSSM19 framework
No full textThe nature of dark matter (DM) remains one of the most compelling mysteries in modernphysics. Despite DM exceeding the visible (baryonic) matter by a factor of four, itsorigin and properties are yet to be understood. This thesis explores the dark matterproblem through the framework of supersymmetry (SUSY), a theoretical extension ofthe Standard Model of particle physics. Using data collected during the Large HadronCollider (LHC) Run 2 (2016-2018) by the Compact Muon Solenoid (CMS) experiment,with an integrated luminosity of L = 138 fb−1, multiple analysis strategies are employedto search for signatures of SUSY particles that present viable DM candidates.The first analysis utilizes a cut-and-count approach targeting the m˜g-m˜χ01 mass planevia angular correlation between selected physics objects, combined with a data-drivenmethod to address limitations in background modeling via transfer factors and correc-tions. This analysis achieved exclusion limits for gluino masses up to 2050 GeV andneutralino masses up to 1070 GeV. Subsequently, these results were reinterpreted withinthe phenomenological MSSM framework (pMSSM19), constraining additional SUSY pa-rameters and highlighting potential regions of interest based on observed data excesses.To further enhance the sensitivity, a machine learning-based approach was developed,utilizing a deep neural network (DNN) to classify collision events and define signal regionsbased on DNN scores. This novel methodology expands the exclusion limits up to 1450GeV for m˜χ01 and up to 2230 GeV for m˜g and demonstrates the advantages of sophisticatedcomputational techniques in modern collider analyses.Also, the HO, the outer hadron calorimeter of the CMS detector, was evaluated as apotential trigger system for long-lived particle (LLP) detection, addressing challenges inidentifying signatures predicted by SUSY theories
Early Career Researcher Input to the European Strategy for Particle Physics Update: White Paper
No full textThis document, written by early career researchers (ECRs) in particle physics, aims to represent the perspectives of the European ECR community and serves as input for the 2025--2026 update of the European Strategy for Particle Physics. With input from a community-wide survey, it highlights key challenges faced by ECRs -- career stability, funding access and long-term research opportunities -- while proposing policy recommendations and targeted initiatives. It underscores the importance of practices fostering diverse, equitable, inclusive and healthy workplaces, as well as of stronger ECR communities, and highlights how effective communication and interdisciplinary collaborations reinforce the societal relevance of particle physics and promote continued support for large-scale and long-term projects. Finally, the future of both collider and beyond-collider experiments is addressed, emphasising the critical role of ECRs in shaping future projects. The ECR contribution is formed of two parts: the ten-page executive summary submitted as input to the European Strategy for Particle Physics Update and, as backup document, this extended white paper providing additional context
Search for long-lived supersymmetric decays in CMS using machine learning methods
No full textAs the search for physics beyond the Standard Model continues, this thesis presentsan analysis in the long-lived particle (LLP) supersymmetry sector. A Boosted DecisionTree (BDT) classifier was developed to enhance the search for long-lived supersymmetricpartner particles of the tau lepton (stau) particles in the muon-hadronic tau channel at theCMS detector in LHC, motivated by Gauge Mediated Supersymmetry Breaking (GMSB)scenarios. The signal region is characterized by the staus decaying to a muon and hadronictau. These displaced topologies were analyzed with the help of machine learning tools. Usingsimulated Run 2 CMS data, a BDT was constructed, including input feature selection, eventweighting, cross-validation, and model optimization. It demonstrates strong performance,achieving up to 90% signal efficiency while maintaining background misidentification ratesbelow 10−4, depending on the chosen working point. These results demonstrate the BDT’spotential for deployment in ongoing and future searches for long-lived particles at the LHC.Future work will address systematic uncertainties and integrate the BDT into the full eventselection workflow to further improve sensitivity to GMSB-inspired new physics
The mechanism of pathogenic α 1 -antitrypsin aggregation in the human liver
No full textOriginating 2 to 3 millennia ago in a Scandinavian population, the SERPINA1 Z allele (Glu342Lys) is present in up to 2.5% of populations of Northern European descent and accounts for 95% of severe α1-antitrypsin deficiency. The α1-antitrypsin Z variant self-assembles into polymer chains that deposit within hepatocytes, predisposing to liver disease. Here, the 4.0Å subunit structure of polymers isolated directly from human liver tissue has been determined using cryoelectron microscopy. Challenges of flexibility, small subunit size, heterogeneous length, and preferred orientations were mitigated using antibody Fab domains and sample preparation strategies. This structure demonstrates that the formation of polymers in vivo involves self-incorporation of an exposed structural element (the reactive center loop) as an additional β-strand into the central β-sheet of α1-antitrypsin and displacement of a C-terminal region from one subunit with incorporation into the next. Unlike amyloid aggregation, this well-folded structure partially recapitulates a conformation adopted during normal function of the protein. These perturbations to the constituent α1-antitrypsin subunits of human tissue-derived polymers are consistent with a pronounced stability, their tendency toward long-chain forms, the ability of a subset to undergo canonical secretion, and the action of a class of small molecules that block polymerization in vivo
IPPOG: a global network for particle physics outreach and education
No full textWe present the International Particle Physics Outreach Group (IPPOG), a global network dedi- cated to connecting students, educators, and the general public with the world of particle physics. In this paper, we outline the need to bridge the existing gap between the particle physics community and the wider audience, and we present the solutions that IPPOG has implemented to overcome it through three pillar Activities: the International Masterclasses and the Global Cosmics hands-on activities network, which have engaged together over 200 000 high-school students to date, and the curation of an Outreach Resource Database and web portal
Insights from the first flaring activity of a high synchrotron peaked blazar with X-ray polarization and VHE gamma rays
No full textContext. Blazars exhibit strong variability across the entire electromagnetic spectrum, including periods of high-flux states commonly known as flares. The physical mechanisms in blazar jets responsible for flares remain poorly understood to date.Aims. Our aim is to better understand the emission mechanisms during blazar flares using X-ray polarimetry and broadband observations from the archetypical TeV blazar Mrk 421, which can be studied with higher accuracy than other blazars that are dimmer and/or located farther away.Methods. We studied a flaring activity from December 2023 that was characterized from radio to very high-energy (VHE; E > 0.1 TeV) gamma rays with MAGIC, Fermi-LAT, Swift, XMM-Newton, and several optical and radio telescopes. These observations included, for the first time for a gamma-ray flare of a blazar, simultaneous X-ray polarization measurements with IXPE, in addition to optical and radio polarimetry data. We quantify the variability and correlations among the multi-band flux and polarization measurements, and describe the varying broadband emission within a theoretical scenario constrained by the polarization data.Results. We find substantial variability in both X-rays and VHE gamma rays throughout the campaign, with the highest VHE flux above 0.2 TeV occurring during the IXPE observing window, and exceeding twice the flux of the Crab Nebula. However, the VHE and X-ray spectra are on average softer, and the correlation between these two bands is weaker than those reported in the previous flares of Mrk 421. IXPE reveals an X-ray polarization degree significantly higher than that at radio and optical frequencies, similar to previous results for Mrk 421 and other high synchrotron peaked blazars. Differently to past observations, the X-ray polarization angle varies by ∼100° on timescales of days, and the polarization degree changes by more than a factor of 4. The highest X-ray polarization degree, analyzed in 12 h time intervals, reaches 26 ± 2%, around which an X-ray counter-clockwise hysteresis loop is measured with XMM-Newton. It suggests that the X-ray emission comes from particles close to the high-energy cutoff, hence possibly probing an extreme case of the Turbulent Extreme Multi-Zone model for which the chromatic trend in the polarization may be more pronounced than theoretically predicted. We model the broadband emission with a simplified stratified jet model throughout the flare. The polarization measurements imply an electron distribution in the X-ray emitting region with a very high minimum Lorentz factor (γ′min≳104), which is expected in electron-ion plasma, as well as a variation of the emitting region size of up to a factor of 3 during the flaring activity. We find no correlation between the fluxes and the evolution of the model parameters, which indicates a stochastic nature of the underlying physical mechanism that likely explains the lack of a tight X-ray/VHE correlation during this flaring activity. Such behavior would be expected in a highly turbulent electron-ion plasma crossing a shock front.Key words: acceleration of particles / radiation mechanisms: non-thermal / galaxies: active / BL Lacertae objects: individual: Markarian 421 / gamma rays: general / X-rays: genera
Commissioning of the new FLASHlab@PITZ Beamline Extension: First Results
No full textBackground and Aims:Over the past year a new beamline dedicated to R&D for electron FLASH cancer radiation therapy and radiation biology was set up at the Photo Injector Test facility at DESY in Zeuthen (PITZ). Utilizing the uniquely wide parameter range of the PITZ accelerator, the FLASH effect can be studied systematically for an extremely wide range of beam conditions. This should help to understand the mechanisms of the FLASH effect.Methods:The buildup of an electron beam delivery system for radiation therapy was done in a 2-step approach: in 2022 a preliminary beamline extension was realized, allowing a first set of experiments with a limited range of doses and dose rates available for CONV and UHDR irradiations. In 2025 the full beamline with optimized beam properties was built and commissioned.Results:Once, all beamline components were installed and connected, they are put into operation and are tested one by one and, finally, an electron beam will be delivered to the experimental station with a beam energy around 20 MeV. The bunch charge will be varied from ~1 pC to more than 1 nC. The beam size at the exit is controlled with quadrupole magnets installed in the new beamline section. Resulting irradiation parameters are characterized with dosimetric methods available at FLASHlab@PITZ, including gafchromic films, a diamond detector and an ionization chamber. This confirms the wide range of doses and dose rates available. Ongoing work is the implementation of a robotic arm for increased sample throughput and the installation of a SARRP.Conclusion:FLASHlab@PITZ is a new R&D platform for electron beam irradiation experiments, which is now capable of delivering ~20 MeV electrons into a flexible experimental area. Commissioning has started with beam transport to the experimental area and dosimetric characterization
Measurement of the jet mass and W boson mass in hadronic decays of boosted W bosons at 13 TeV
No full textThe jet mass of W bosons decaying to a quark-antiquark pair is measured in W+jet events from proton-proton collisions in the LHC at a center-of-mass energy of = 13 TeV. W bosons with large transverse momentum (boost) produce strongly collimated decay products reconstructed as single large-radius jets. Jets initiated by W bosons with a characteristic two-prong substructure are distinguished from single quark- and gluon- initiated jets in background using a jet substructure observable. We report the double-differential cross section in bins of jet transverse momentum and jet soft drop mass. A first measurement of the W mass in an all-jets final state at a hadron collider is reported