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W and Z boson production in p-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV

The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at √ s NN = 5.02 TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward (–4.46 < y cms < –2.96) and forward (2.03 < y cms < 3.53) rapidity regions, corresponding to Pb-going and p-going directions, respectively. The Z-boson production cross section, with dimuon invariant mass of 60 < m μμ < 120 GeV/c 2 and muon transverse momentum (p T μ ) larger than 20 GeV/c, is measured. The production cross section and charge asymmetry of muons from W-boson decays with p T μ > 10 GeV/c are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Measurements of electroweak W ± Z boson pair production in association with two jets in pp collisions at $ \sqrt{s}$ = 13 TeV with the ATLAS detector

Measurements of integrated and diferential cross-sections for electroweak W ± Z production in association with two jets (W ± Zjj) in proton-proton collisions are presented. The data collected by the ATLAS detector at the Large Hadron Collider from 2015 to 2018 at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV are used, corresponding to an integrated luminosity of 140 fb -1 . The W ± Zjj candidate events are reconstructed using leptonic decay modes of the gauge bosons. Events containing three identifed leptons, either electrons or muons, and two jets are selected. Processes involving pure electroweak W ± Zjj production at Born level are separated from W ± Zjj production involving a strong coupling. The measured integrated fducial cross-section of electroweak W ± Zjj production per lepton favour is σ W Zjj-EW→ℓ' νℓℓjj = 0.368 ± 0.037 (stat.) ± 0.059 (syst.) ± 0.003 (lumi.) fb, where ℓ and ℓ' are either an electron or a muon. Respective cross-sections of electroweak and strong W ± Zjj production are measured separately for events with exactly two jets or with more than two jets, and in three bins of the invariant mass of the two jets. The inclusive W ± Zjj production cross-section, without separating electroweak and strong production, is also measured to be σ W Zjj→ℓ ' νℓℓjj = 1.462 ± 0.063 (stat.) ± 0.118 (syst.) ± 0.012 (lumi.) fb, per lepton favour. The inclusive W ± Zjj production cross-section is measured diferentially for several kinematic observables. Finally, the measurements are used to constrain anomalous quartic gauge couplings by extracting 95% confdence level intervals on dimension-8 operators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

The Mu2e experiment

Mu2e will search for coherent, neutrinoless conversion of muons into electrons in the nucleus field of aluminum with a sensitivity improvement of a factor of 10,000 over existing limits. Probing the charged lepton flavor-violating reaction at such sensitivity may uncover new physics at a scale unreachable by direct searches at current or planned high-energy colliders. The experiment complements and extends the current studies at MEG-II and the LHC. I will present the physics motivation for Mu2e, as well as the design and construction status of the experiment.

Gaponenko, Andrei↗

Leptonic scalars at the LHC

We explore the collider prospects of neutrino non-standard interaction with a Standard Model (SM) gauge-singlet leptonic scalar &straightphi; carrying two units of lepton-number-charge. These leptonic scalars are forbidden from interacting with the SM fermions at the renormalizable level and, if one allows for higher-dimensional operators, couple predominantly to SM neutrinos. For masses at or below the electroweak scale, &straightphi; decays exclusively into neutrinos. Its characteristic production signature at hadron collider experiments like the LHC would be via the vector boson fusion process and leads to same-sign dileptons, two forward jets in opposite hemispheres, and missing transverse energy, i.e., $$ pp\to {\mathrm{\ell}}_{\alpha}^{\pm }{\mathrm{\ell}}_{\beta}^{\pm } jj+{E}_T^{\mathrm{miss}}\left(\alpha, \beta =e,\mu, \tau \right) $$ pp → ℓ α ± ℓ β ± jj + E T miss α β = e μ τ . Exploiting the final states of electrons and muons, we estimate, for the first time, the sensitivity of the LHC to these lepton-number-charged scalars. We show that the LHC sensitivity is largely complementary to that of low-energy precision measurements of the decays of charged leptons, charged mesons, W , Z and the SM Higgs boson, as well as the neutrino beam experiments like MINOS, and searches for neutrino self-interactions at IceCube and in cosmological observations. For &straightphi; mass larger than roughly 10 GeV, our projected LHC sensitivity would surpass all existing bounds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Measurement of the top-quark mass using a leptonic invariant mass in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A measurement of the top-quark mass ($m_t$) in the $t\overline{t}$ → lepton+jets channel is presented, with an experimental technique which exploits semileptonic decays of $b$-hadrons produced in the top-quark decay chain. The distribution of the invariant mass $m_{{\ell}µ}$ of the lepton, $\ell$ (with $\ell$ = $e, µ$), from the $W$-boson decay and the muon, $µ$, originating from the b-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract $m_t$. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb –1 of $\sqrt{s}$ = 13 TeV $pp$ collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is $m_t$ = 174.41 ± 0.39 (stat.) ± 0.66 (syst.) ± 0.25 (recoil) GeV, where the third uncertainty arises from changing the Pythia8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Measurements of the W production cross sections in association with jets with the ATLAS detector

This paper presents cross sections for the production of a W boson in association with jets, measured in proton–proton collisions at \(\sqrt{s} = 7\) TeV with the ATLAS experiment at the large hadron collider. With an integrated luminosity of 4.6fb -1 , this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of 1TeV and multiplicities up to seven associated jets. The production cross sections for W bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. As a result, the measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Same sign dimuon search for heavy majorana mass neutrinos at the CMS experiment at CERN and design studies of a quartz plate calorimeter prototype

This paper consists of two studies: the results of a search for heavy Majorana neutrinos (N) using an event signature defined by two like-sign charged muons and two jets, and the results from studies of a prototype quartz plate calorimeter. The data in the Majorana search correspond to an integrated luminosity of 5.0 fb$^{−1}$ of pp collisions at a centre-of-mass energy of 7 TeV collected with the CMS detector at the Large Hadron Collider. No excess of events are observed beyond the expected standard model background and therefore upper limits are set on the square of the mixing element, $|V_{\mu N} |$as a function of Majorana neutrino mass. These are the first direct upper limits on the heavy Majorana-neutrino mixing for m$_N$ > 90 GeV . The second part of this thesis is the results of performance tests of a 20-layer quartz plate calorimeter prototype. The calorimeter prototype was tested at the CERN H2 area in hadronic and electromagnetic configurations, at various en ergies of pion and electron beams. The beam test and simulation results of this prototype are reported.

43 PARTICLE ACCELERATORS↗

Particle Theory and Cosmology

This project covered theoretical studies in particle physics, particle astrophysics and cosmology, aiming to bridge theoretical models with observable phenomena. The central focus was on exploring innovative mechanisms that could simultaneously address several outstanding puzzles in these areas, including the nature of dark matter, the muon g-2 anomaly, the existence of topologically stable monopoles, the generation of observable gravitational waves from early universe phenomena and high energy cosmic rays. One of the major achievements of this project was the development of models that predict new physics accessible through current and forthcoming experimental setups, both in particle colliders and astrophysical observations. These models have been instrumental in proposing verifiable predictions concerning supersymmetric extensions, the dynamics of cosmic strings and monopoles, and the intricate processes underpinning baryogenesis and reheating post-inflation. In tackling the dark matter conundrum, the project proposed several candidates within extended frameworks, such as light Z' models, pseudo-Goldstone dark matter, and scenarios integrating dark matter with inflationary cosmology. Each model outlined pathways for detection through direct, indirect, and collider search strategies, marking significant strides in the hunt for dark matter. Another cornerstone of the project was the in-depth analysis of inflationary models compliant with the Trans-Planckian Censorship Conjecture, highlighting the compatibility of axion dark matter within such frameworks. This not only provided a coherent picture of early universe cosmology but also delineated clear experimental signatures. The exploration of grand unified theories yielded insights into the potential discovery of monopoles and novel particle configurations at energy scales accessible to current and future colliders. This endeavor expanded the predictive power of these theories, particularly in the context of proton decay and the properties of Higgs-portal dark matter. Throughout the project, significant emphasis was placed on ensuring the theoretical developments were grounded in experimental testability. This led to a series of publications across prestigious journals, each contributing to the vibrant discourse at the intersection of particle physics and cosmology. In summary, this project has elucidated pathways beyond the Standard Model that are ripe for exploration through both ongoing and upcoming experimental efforts. The comprehensive approach adopted herein not only enhances our understanding of the fundamental forces and constituents of the universe but also propels the field towards new frontiers in high-energy physics and cosmology.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Constraining neutrinophilic mediators at FASER ν , FLArE, and FASER ν 2

High energy collider neutrinos have been observed for the first time by the FASER ν experiment. The detected spectrum of collider neutrinos scattering off nucleons can be used to probe neutrinophilic mediators with GeV-scale masses. We find that constraints on the pseudoscalar (axial vector) neutrinophilic mediator are close to the scalar (vector) case since they have similar cross section in the neutrino massless limit. We perform an analysis on the measured muon spectra at FASER ν , and find that the bounds on the vector mediator from the current FASER ν data are comparable to the existing bounds at m Z ′ ≈ 0.2 GeV . We also study the sensitivities to a neutrinophilic mediator at future Forward Physics Facilities including FLArE and FASER ν 2 by using both the missing transverse momentum and the charge identification information. We find that FLArE and FASER ν 2 can impose stronger bounds on both the scalar and vector neutrinophilic mediators than the existing bounds. The constraints on the scalar mediator can reach 0.08 (0.1) for m ϕ ≲ 1 GeV with (without) muon charge identification at FASER ν 2 . Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Measurements of the W production cross sections in association with jets with the ATLAS detector

This paper presents cross sections for the production of a W boson in association with jets, measured in proton--proton collisions at sqrt(s)=7 TeV with the ATLAS experiment at the Large Hadron Collider. With an integrated luminosity of 4.6 fb^{-1}, this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of 1 TeV and multiplicities up to seven associated jets. The production cross sections for W bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. The measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Performance of b-jet identification in the ATLAS experiment

The identification of jets containing b hadrons is important for the physics programme of the ATLAS experiment at the Large Hadron Collider. Several algorithms to identify jets containing b hadrons are described, ranging from those based on the reconstruction of an inclusive secondary vertex or the presence of tracks with large impact parameters to combined tagging algorithms making use of multi-variate discriminants. An independent b-tagging algorithm based on the reconstruction of muons inside jets as well as the b-tagging algorithm used in the online trigger are also presented. The b-jet tagging efficiency, the c-jet tagging efficiency and the mistag rate for light flavour jets in data have been measured with a number of complementary methods. The calibration results are presented as scale factors defined as the ratio of the efficiency (or mistag rate) in data to that in simulation. In the case of b jets, where more than one calibration method exists, the results from the various analyses have been combined taking into account the statistical correlation as well as the correlation of the sources of systematic uncertainty.

43 PARTICLE ACCELERATORS↗

An Improved W Boson Mass Measurement Using the Collider Detector at Fermilab

The mass of the W boson is one of the most important parameters in the Standard Model. A precise measurement of the W boson mass, together with a precise measurement of the top quark mass, can constrain the mass of the undiscovered Higgs boson within the Standard Model framework or give a hint for physics beyond the Standard Model. This dissertation describes a measurement of the W boson mass through its decay into a muon and a neutrino using ~ 2.2 fb -1 of √ s = 1.96 TeV p$\bar{p}$ data taken with the CDF II detector at Fermilab. We measure the W boson mass to be (80.374 ± 0.015 stat . ± 0.016 syst. ) GeV/c 2 . This result, when combined with the W mass measurement in the electron channel, leads to the single most precise mW value and greatly constrains the possible mass range of the undiscovered Higgs boson. iv

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb -1 of $\sqrt{s}=13 $ TeV pp collision data with the ATLAS detector

The results of a search for the direct pair production of top squarks, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, several energetic jets, and missing transverse momentum are reported. The analysis also targets spin-0 mediator models, where the mediator decays into a pair of dark-matter particles and is produced in association with a pair of top quarks. The search uses data from proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of s√=13 TeV and recorded by the ATLAS detector, corresponding to an integrated luminosity of 36 fb -1 . A wide range of signal scenarios with different mass-splittings between the top squark, the lightest neutralino and possible intermediate supersymmetric particles are considered, including cases where the W bosons or the top quarks produced in the decay chain are off-shell. No significant excess over the Standard Model prediction is observed. The null results are used to set exclusion limits at 95% confidence level in several supersymmetry benchmark models. For pair-produced top-squarks decaying into top quarks, top-squark masses up to 940 GeV are excluded. In conclusion, stringent exclusion limits are also derived for all other considered top-squark decay scenarios. For the spin-0 mediator models, upper limits are set on the visible cross-section.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for displaced leptons in $\sqrt{𝑠}$ =13 TeV and 13.6 TeV 𝑝⁢𝑝 collisions with the ATLAS detector

A search for leptons displaced from the primary vertex is performed with the ATLAS detector at the Large Hadron Collider. The search includes the full proton-proton collision dataset collected during Run 2 at $\sqrt{𝑠}$ = 13 TeV and a partial dataset collected during Run 3 in 2022–2023 at $\sqrt{𝑠}$ = 13.6 TeV, corresponding to integrated luminosities of 140 fb −1 and 56.3 fb −1 , respectively. Final states with displaced electrons or muons are considered, and novel triggers introduced in Run 3 are employed that use large impact parameter tracking to reconstruct displaced tracks with low momentum. In addition, photon reconstruction and multivariate techniques are employed to broaden the sensitivity to channels with large background rates or highly displaced electrons, respectively. The results are consistent with the Standard Model background expectations and are used to set model-independent limits on the production of displaced electrons and muons. The analysis is also interpreted in the context of a gauge-mediated supersymmetry breaking model with pair-produced long-lived sleptons and a dark sector model with pair-produced chargino-like states. The results include 95% confidence level exclusions of selectrons with lifetimes from 4 ps to 60 ns and a mass of 150 GeV, and exclusions of selectrons, smuons, and staus with a lifetime of 0.3 ns for masses up to 740, 830, and 440 GeV, respectively. Dark charginos with masses up to 380 GeV are excluded for a mass difference with the neutral state of 40 GeV, and mass differences down to 17 GeV are excluded for dark charginos with a 100 GeV mass.

supersymmetric models↗

Search for flavor-changing neutral-current couplings between the top quark and the Z boson with proton-proton collisions at s = 13 TeV with the ATLAS detector

A search for flavor-changing neutral-current couplings between a top quark, an up or charm quark, and a $Z$ boson is presented, using proton-proton collision data at $\sqrt{s}$ = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The analyzed data set corresponds to an integrated luminosity of 139 fb -1 . The search targets both single-top-quark events produced as $gq$ → $tZ$ (with $q$ = $u, c$) and top-quark-pair events, with one top quark decaying through the $t$ → $Zq$ channel. The analysis considers events with three leptons (electrons or muons), a $b$-tagged jet, possible additional jets, and missing transverse momentum. The data are found to be consistent with the background-only hypothesis and 95% confidence-level limits on the $t$ → $Zq$ branching ratios, assuming only tensor operators of the Standard Model effective field theory framework contribute to the $tZq$ vertices. These are 6.2 x 10 -5 (13 x 10 -5 ) for $t$ → $Zu$ ($t$ → $Zc$) for a left-handed $tZq$ coupling, and 6.6 x 10 -5 (12 x 10 -5 ) in the case of a right-handed coupling. These results are interpreted as 95% CL upper limits on the strength of the corresponding couplings, yielding limits for |${C}^{(13)*}_{uW}$| and |${C}^{(13)*}_{uB}$| (|${C}^{(31)}_{uW}$| and |${C}^{(31)}_{uB}$|) of 0.15 (0.16), and limits for |${C}^{(23)*}_{uW}$| and |${C}^{(23)*}_{uB}$| (|${C}^{(32)}_{uW}$| and |${C}^{(32)}_{uB}$|) of 0.22 (0.21), assuming a new-physics energy scale Λ NP of 1 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Forecasting dark showers at Belle II

Dark showers from strongly interacting dark sectors that confine at the GeV scale can give rise to novel signatures at e + e - colliders. In this work, we study the sensitivity of B factory experiments to dark showers produced through an effective interaction arising from a heavy off-shell mediator. We show that a prospective search for displaced vertices from GeV-scale long-lived particles at Belle II can improve the sensitivity to dark showers substantially compared to an existing search at BaBar. We compare the sensitivity of searches for displaced signals to searches for promptly produced resonances at BaBar and KLOE and calculate sensitivity projections for a single-photon search at Belle II to invisible dark showers produced through an effective interaction. The underlying structure of the effective interaction can be resolved at higher-energy experiments, where the mediator can be produced on-shell. To study the resulting constraints, we update electroweak precision bounds on kinetically mixed Z' bosons and reinterpret a search for low-mass di-muon resonances at LHCb in terms of dark showers. We find that LHCb and Belle II are most sensitive to different particle decay lengths, underscoring the complementarity of LHC and intensity frontier experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for heavy right-handed Majorana neutrinos in the decay of top quarks produced in proton-proton collisions at s = 13 TeV with the ATLAS detector

A search for heavy right-handed Majorana neutrinos is performed with the ATLAS detector at the CERN Large Hadron Collider, using the 140 fb -1 of proton–proton collision data at $\sqrt{s}$ =13 TeV collected during Run 2. This search targets $t\overline{t}$ production, in which both top quarks decay into a bottom quark and a W boson, where one of the W bosons decays hadronically and the other decays into an electron or muon and a heavy neutral lepton. The heavy neutral lepton is identified through a decay into an electron or muon and another W boson, resulting in a pair of same-charge same-flavor leptons in the final state. This paper presents the first search for heavy neutral leptons in the mass range of 15–75 GeV using $t\overline{t}$ events. No significant excess is observed over the background expectation, and upper limits are placed on the signal cross sections. Assuming a benchmark scenario of the phenomenological type-I seesaw model, these cross section limits are then translated into upper limits on the mixing parameters of the heavy Majorana neutrino with Standard Model neutrinos.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Search for decays of the Higgs boson into pair-produced pseudoscalar particles decaying into τ+τ−τ+τ− using pp collisions at s=13 TeV with the ATLAS detector

A search for a pair of low-mass pseudoscalars a that promptly decay into τ-leptons is presented using 140 fb −1 of proton–proton collision data at 13 TeV centre-of-mass energy recorded with the ATLAS detector at the Large Hadron Collider. The result is used to place constraints on exotic decays of the Higgs boson into four τ-leptons, H→aa→τ+τ−τ+τ−. This search focuses on events with either one or two τ-leptons decaying into hadrons and neutrinos, and the remaining three or two τ-leptons decaying into either electron or muon and neutrinos. No significant excess is observed above the expected Standard Model background and upper limits at the 95% confidence level on B(H→aa→τ+τ−τ+τ−) are set ranging from 0.06 to 0.23, depending on the mass ma ranging from 15 to 60 GeV.

Source record↗