L. Beresford

The anomalous magnetic moment of the tau lepton $a_\tau = (g_\tau -2)/2$ strikingly evades measurement, but is highly sensitive to new physics such as compositeness or supersymmetry. We propose using ultraperipheral heavy ion collisions at the LHC to probe modified magnetic $\delta a_\tau$ and electric dipole moments $\delta d_\tau$. We introduce a suite of one electron/muon plus track(s) analyses, leveraging the exceptionally clean photon fusion $\gamma\gamma \to \tau\tau$ events to reconstruct both leptonic and hadronic tau decays sensitive to $\delta a_\tau, \delta d_\tau$. Assuming 10% systematic uncertainties, the current 2 nb$^{-1}$ lead-lead dataset could already provide constraints of $-0.0080 < a_\tau < 0.0046$ at 68% CL. This surpasses 15 year old lepton collider precision by a factor of three while opening novel avenues to new physics.

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS experiment to mitigate pile-up effects during the High Luminosity (HL) phase of the Large Hadron Collider (LHC) at CERN. Low Gain Avalanche Detectors (LGADs) will provide high-precision measurements of the time of arrival of particles at the HGTD, improving the particle-vertex assignment. To cope with the high-radiation environment, LGADs have been optimized by adding carbon in the gain layer, thus reducing the acceptor removal rate after irradiation. Performances of several carbon-enriched LGAD sensors from different vendors, and irradiated with high fluences of 1.5 and 2.5 x 10^15 neq/cm2, have been measured in beam test campaigns during the years 2021 and 2022 at CERN SPS and DESY. This paper presents the results obtained with data recorded by an oscilloscope synchronized with a beam telescope which provides particle position information within a resolution of a few um. Collected charge, time resolution and hit efficiency measurements are presented. In addition, the efficiency uniformity is also studied as a function of the position of the incident particle inside the sensor pad.

Abstract In the past years, it has been observed at several beam test campaigns that irradiated LGAD sensors break with a typical star shaped burn mark when operated at voltages much lower than those at which they were safely operated during laboratory tests. The study presented in this paper was designed to determine the safe operating voltage that these sensors can withstand. Many irradiated sensors from various producers were tested in two test beam facilities, DESY (Hamburg) and CERN-SPS (Geneva), as part of ATLAS High Granularity Timing Detector (HGTD) beam tests. The samples were placed in the beam and kept under bias over a long period of time in order to reach a high number of particles crossing each sensor. Both beam tests lead to a similar conclusion, that these destructive events begin to occur when the average electric field in the sensor becomes larger than 12 V/μm.

We propose a search strategy using the LHC as a photon collider to open sensitivity to scalar lepton (slepton ℓ[over ˜]) production with masses around 15 to 60 GeV above that of neutralino dark matter χ[over ˜]_{1}^{0}. This region is favored by relic abundance and muon (g-2)_{μ} arguments. However, conventional searches are hindered by the irreducible diboson background. We overcome this obstruction by measuring initial state kinematics and the missing momentum four-vector in proton-tagged ultraperipheral collisions using forward detectors. We demonstrate sensitivity beyond LEP for slepton masses of up to 200 GeV for 15≲Δm(ℓ[over ˜],χ[over ˜]_{1}^{0})≲60 GeV with 100 fb^{-1} of 13 TeV proton collisions. We encourage the LHC collaborations to open this forward frontier for discovering new physics.

A bstract Measuring the Higgs trilinear self-coupling λ hhh is experimentally demanding but fundamental for understanding the shape of the Higgs potential. We present a comprehensive analysis strategy for the HL-LHC using di-Higgs events in the four b -quark channel ( hh → 4 b ), extending current methods in several directions. We perform deep learning to suppress the formidable multijet background with dedicated optimisation for BSM λ hhh scenarios. We compare the λ hhh constraining power of events using different multiplicities of large radius jets with a two-prong structure that reconstruct boosted h → bb decays. We show that current uncertainties in the SM top Yukawa coupling y t can modify λ hhh constraints by ∼ 20%. For SM y t , we find prospects of − 0 . 8 &lt; $$ {\lambda}_{hhh}/{\lambda}_{hhh}^{\mathrm{SM}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>λ</mml:mi><mml:mi>hhh</mml:mi></mml:msub><mml:mo>/</mml:mo><mml:msubsup><mml:mi>λ</mml:mi><mml:mi>hhh</mml:mi><mml:mi>SM</mml:mi></mml:msubsup></mml:math> &lt; 6 . 6 at 68% CL under simplified assumptions for 3000 fb − 1 of HL-LHC data. Our results provide a careful assessment of di-Higgs identification and machine learning techniques for all-hadronic measurements of the Higgs self-coupling and sharpens the requirements for future improvement.

Measuring the tau-lepton ($\tau$) anomalous magnetic moment $a_\tau=(g_\tau-2)/2$ in photon fusion production ($\gamma\gamma\to\tau\tau$) tests foundational Standard Model principles. However, $\gamma\gamma\to\tau\tau$ eludes observation in LHC proton collisions (pp) despite enhanced new physics sensitivity from higher-mass reach than existing probes. We propose a novel strategy to measure $\text{pp}\to\text{p}(\gamma\gamma\to\tau\tau)\text{p}$ by introducing the overlooked electron-muon signature with vertex isolation for signal extraction. Applying the effective field theory of dipole moments, we estimate 95% CL sensitivity of $-0.0092<a_{\tau}<0.011$ assuming 300 fb$^{-1}$ luminosity and 5% systematics. This fourfold improvement beyond existing constraints opens a crucial path to unveiling new physics imprinted in tau-lepton dipoles.

Parental substance use is a substantial public health and safeguarding concern. Research examining the impact of parental substance use upon children is well-established, but there is a lack of research examining how parents/caregivers cope with their parenting role within the context of another parent's substance use, or how best to support these parents/caregivers. This paper examines the experiences and support needs of parents/caregivers impacted by another parent's substance use. and Settings: Nineteen parents/caregivers from substance exposed families via local community-based voluntary sector support organizations, in urban and rural settings in northeast England. Qualitative, in-depth interviews with caregivers (mothers/fathers/grandparents/aunts/uncles/siblings, aged 25-65+) of dependent aged children (aged 4-17) in substance exposed families. Thematic analysis explored their experiences and support needs. Cumulative stress impacted parents/caregivers in their parenting role, creating further challenges in caring for children impacted by another parent's substance use. Parents/caregivers felt their needs went unrecognized by support services, and interactions with statutory services frequently exacerbated their stress. Parents/caregivers worried about what to disclose to children about substance use and how and when to do this. Parents/caregivers attempted to mitigate the risk of another parent's substance use upon the children in their care. They often perceived lack of appropriate support specifically for parents/caregivers, particularly considering the extra challenges they faced caring for children in the context of parental substance use. Resources to support parents/caregivers in talking with children about these issues may offer guidance and reassurance to caregivers to alleviate some of their stress.

Received 19 July 2022DOI:https://doi.org/10.1103/PhysRevD.106.039902Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectric momentMagnetic momentRelativistic heavy-ion collisionsPhysical SystemsTau leptonsTechniquesHadron collidersNuclear PhysicsParticles & Fields

A group of Early-Career Researchers (ECRs) has been given a mandate from the European Committee for Future Accelerators (ECFA) to debate the topics of the current European Strategy Update (ESU) for Particle Physics and to summarise the outcome in a brief document [1]. A full-day debate with 180 delegates was held at CERN, followed by a survey collecting quantitative input. During the debate, the ECRs discussed future colliders in terms of the physics prospects, their implications for accelerator and detector technology as well as computing and software. The discussion was organised into several topic areas. From these areas two common themes were particularly highlighted by the ECRs: sociological and human aspects; and issues of the environmental impact and sustainability of our research.

This thesis presents three searches for new resonances in dijet invariant mass spectra. The spectra are produced using √s = 13 TeV proton-proton collision data recorded by the ATLAS detector. New dijet resonances are searched for in the mass range 200 GeV to 6.9 TeV in mass. Heavy new resonances, with masses above 1.1 TeV, are targeted by a high mass dijet search. Light new resonances, with masses down to 200 GeV, are searched for in dijet events with an associated high momentum object (a photon or a jet) arising from initial state radiation. The associated object is used to efficiently trigger the recording of low mass dijet events. All of the analyses presented in this thesis search for an excess of events, localised in mass, above a data-derived estimate of the smoothly falling QCD background. In each search no evidence for new resonances is observed, and the data are used to set 95% C.L. limits on the production cross-section times acceptance times branching ratio for model-independent Gaussian resonance shapes, as well as benchmark signals. One particular benchmark signal which is considered in all of the searches is an axial-vector Z' dark matter mediator model whose parameter space is reduced due to the results presented in this thesis.

The common goal of the high mass dijet analysis and the dijet $$+$$ ISR analyses is to determine if there is evidence for resonances being present in the spectra, and to assess their significance. In order to determine if such resonances are present it is necessary to compare the spectra produced in Chap. 5 to an estimate of the background produced via Standard Model processes.

Object reconstruction is a vital component of all analyses. It is the crucial step in which the electronic signals read out from the detector are combined to form objects which can be identified as particles. Once identified, the objects are then calibrated, such that their physical attributes (for example, their energy) are corrected for known detector effects. The calibrated objects can then be used in physics analyses. This chapter outlines the reconstruction and calibration of the objects utilised in the analyses in this thesis.

The well calibrated jets can now be used to construct dijet invariant mass spectra. New BSM particles or interactions can then be searched for by looking for resonance ‘bumps’ above the smoothly falling spectra predicted by QCD. In order to perform such searches experimentally, events which contain at least two jets are selected. The invariant mass of the pair of jets (dijet) which is most likely to have been produced by the decay of the resonance is then calculated by summing together the calibrated four-momentum vectors of the two jets.

In order to search beyond the Standard Model of particle physics, and to study the Standard Model itself, a particle detector is needed. The ATLAS (A Toroidal LHC ApparatuS) detector is a large general-purpose particle detector which records the proton-proton collisions produced by the Large Hadron Collider (LHC). The analyses presented in this thesis utilise data which is recorded by the ATLAS detector.

In 2015 and 2016, the LHC delivered proton-proton collisions with an unprecedented centre-of-mass energy of $$\sqrt{s}=13$$ TeV. In this thesis results are shown from the analysis of the high energy collision data recorded by the ATLAS detector.

The theoretical description of particles and their interactions is provided by the Standard Model of particle physics, also referred to as the Standard Model in this thesis. This theory was finalised in the 1970s, and has been extremely successful, with experimental results confirming the predictions of the Standard Model to increasing degrees of precision [1]. Despite the huge successes of the Standard Model, there are many reasons to believe that this theory is incomplete, and that there is new physics ‘beyond’ the Standard Model.

The search results obtained in Chap. 6 indicated that there is no evidence for local excesses due to BSM phenomena in the mass spectra. The analyses proceed by using the data to derive limits on physical quantities for theoretical models of new physics. This enables us to quantify the phase space excluded by the analyses, allowing us to measure our progress and to compare our results with other experiments.

In the quest to further our knowledge about what the universe is made from, and the forces which hold it together, humans have built particle accelerators with increasing centre-of-mass energies ( $$\sqrt{s}$$ ), to try to discover new particles and interactions. In 2015, the Large Hadron Collider (LHC) based at the European Organisation for Nuclear Research (CERN), managed to reach the highest centre-of-mass energy ever achieved by a particle accelerator, $$\sqrt{s}=13$$ TeV. This allows us to explore higher energy scales, and to search for new heavy particles whose production may have previously been kinematically forbidden.

This book presents a significant and substantial contribution to the search for new physics at the Large Hadron Collider, in particular for new particles which couple to dark matter, and utilises a novel technique to efficiently gather low mass dijet events

Measuring the Higgs trilinear self-coupling $\lambda_{hhh}$ is experimentally demanding but fundamental for understanding the shape of the Higgs potential. We present a comprehensive analysis strategy for the HL-LHC using di-Higgs events in the four $b$-quark channel ($hh \to 4b$), extending current methods in several directions. We perform deep learning to suppress the formidable multijet background with dedicated optimisation for BSM $\lambda_{hhh}$ scenarios. We compare the $\lambda_{hhh}$ constraining power of events using different multiplicities of large radius jets with a two-prong structure that reconstruct boosted $h \to bb$ decays. We show that current uncertainties in the SM top Yukawa coupling $y_t$ can modify $\lambda_{hhh}$ constraints by $\sim 20\%$. For SM $y_t$, we find prospects of $-0.8 < \lambda_{hhh} / \lambda_{hhh}^\text{SM} < 6.6$ at 68% CL under simplified assumptions for 3000~fb$^{-1}$ of HL-LHC data. Our results provide a careful assessment of jet substructure and machine learning techniques for all-hadronic measurements of the Higgs self-coupling and sharpens the requirements for future improvement.