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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Measurements and interpretations of W ± Z production cross-sections in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Measurements of integrated and differential cross-sections for W ± Z production 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 ± Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons or muons. The integrated cross-section per lepton flavour for the production of W ± Z is measured in the detector fiducial region with a relative precision of 4%. The measured value is compared with the Standard Model prediction at a precision of up to next-to-next-to-leading-order in QCD and next-to-leading-order in electroweak. Cross-sections for W + Z and W − Z production and their ratio are presented. The W ± Z production is also measured differentially as functions of various kinematic variables, including new observables sensitive to CP-violation effects. All measurements are compared with state-of-the-art Standard Model predictions from fixed-order calculations or Monte Carlo generators based on next-to-leading-order matrix elements interfaced with parton showers. An effective field theory interpretation of the measurements is performed, considering both CP-conserving and CP-violating dimension-6 operators modifying the W ± Z production. In the absence of observed deviations from the Standard Model, limits on CP-conserving Wilson coefficients are extracted using the transverse mass of the W ± Z system. For CP-violating coefficients a machine learning approach is used to construct an observable with enhanced sensitivity to CP-violation effects.

hadron-hadron scattering↗
DOE OSTI2026

Towards a self-driving trigger at the LHC: adaptive response in real time

Real-time data filtering and selection—or trigger—systems at high-throughput scientific facilities such as the experiments at the Large Hadron Collider must process extremely high-rate data streams under stringent bandwidth, latency, and storage constraints. Yet these systems are typically designed as static, hand-tuned menus of selection criteria grounded in prior knowledge and simulation. In this work, we further explore the concept of a self-driving trigger, an autonomous data-filtering framework that reallocates resources and adjusts thresholds dynamically in real-time to optimize signal efficiency, rate stability, and computational cost as instrumentation and environmental conditions evolve. We introduce a benchmark ecosystem to emulate realistic collider scenarios and demonstrate real-time optimization of a menu including canonical energy sum triggers as well as modern anomaly-detection algorithms that target non-standard event topologies using machine learning. Using simulated data streams and publicly available collision data from the Compact Muon Solenoid experiment, we demonstrate the capability to dynamically and automatically optimize trigger performance under specific cost objectives without manual retuning. Our adaptive strategy shifts trigger design from static menus with heuristic tuning to intelligent, automated, data-driven control, unlocking greater flexibility and discovery potential in future high-energy physics analyses.

Emami, Shaghayegh [Michigan U.] (ORCID:00090007589↗
DOE OSTI2016

Measurement of the forward-backward asymmetry of top-quark and antiquark pairs using the full CDF Run II data set

In this study, we measure the forward--backward asymmetry of the production of top quark and antiquark pairs in proton-antiproton collisions at center-of-mass energy $\sqrt{s} = 1.96~\mathrm{TeV}$ using the full data set collected by the Collider Detector at Fermilab (CDF) in Tevatron Run II corresponding to an integrated luminosity of $9.1~\rm{fb}^{-1}$. The asymmetry is characterized by the rapidity difference between top quarks and antiquarks ($\Delta y$), and measured in the final state with two charged leptons (electrons and muons). The inclusive asymmetry, corrected to the entire phase space at parton level, is measured to be $A_{\text{FB}}^{t\bar{t}} = 0.12 \pm 0.13$, consistent with the expectations from the standard-model (SM) and previous CDF results in the final state with a single charged lepton. The combination of the CDF measurements of the inclusive $A_{\text{FB}}^{t\bar{t}}$ in both final states yields $A_{\text{FB}}^{t\bar{t}}=0.160\pm0.045$, which is consistent with the SM predictions. We also measure the differential asymmetry as a function of $\Delta y$. A linear fit to $A_{\text{FB}}^{t\bar{t}}(|\Delta y|)$, assuming zero asymmetry at $\Delta y=0$, yields a slope of $\alpha=0.14\pm0.15$, consistent with the SM prediction and the previous CDF determination in the final state with a single charged lepton. The combined slope of $A_{\text{FB}}^{t\bar{t}}(|\Delta y|)$ in the two final states is $\alpha=0.227\pm0.057$, which is $2.0\sigma$ larger than the SM prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

University-Based Detector Research and Development for the International Linear Collider (Final Report)

The U.S Linear Collider Detector R&D program, supported by the DOE and NSF umbrella grants to the University of Oregon, made significant advances on many critical aspects of the ILC detector program. Progress advanced on vertex detector sensor development, silicon and TPC tracking, calorimetry on candidate technologies, and muon detection, as well as on beamline measurements of luminosity, energy, and polarization.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

CRIC and Rucio integration for CMS Data Management

The Large Hadron Collider (LHC) at CERN smashes protons together at close to the speed of light with seven times the energy of the most powerful accelerators built up to now. Some of the collision energy is turned into mass, creating new particles which are observed in the Compact Muon Solenoid (CMS) particle detector. CMS data is analyzed by scientists around the world to build up a picture of what happened at the heart of the collision. This will help us answer questions such as: ”what is the Universe really made of and what forces act within it?” and ”what gives everything substance?”. All the data produced by the experiment are collected and stored in a distributed system, since it must provide an high throughput and performing access to these data to scientists and physicists spread all over the world. In order to answer the previous questions and many others, CMS users must first obtain a copy of a portion of these data, and then to analyze it, therefore the first challenge is to decide in which storage site to save this duplicate so they can access it as quickly as possible. The second issue is each storage site shares a limited memory space with many CMS users, and each one needs to be assigned to a well defined personal amount of storage to pin data he needs. The main goal of my Summer Internship is to make scalable and automatic this user-site mapping which is based on a preexisting policy, proving a structured and organized algorithm to accomplish this task. Hence we are going to define, and solve, the main challenges encountered, and the technical solution used to generalize the algorithm to handle different policies for different countries.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Measurement of jet activity produced in top-quark events with an electron, a muon and two b -tagged jets in the final state in pp collisions at √s = 13 TeV with the ATLAS detector

Measurements of jet activity in top-quark pair events produced in proton–proton collisions are presented, using 3.2 fb –1 of pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Events are chosen by requiring an opposite-charge eμ pair and two b-tagged jets in the final state. The normalised differential cross-sections of top-quark pair production are presented as functions of additional-jet multiplicity and transverse momentum, p T . The fraction of signal events that do not contain additional jet activity in a given rapidity region, the gap fraction, is measured as a function of the p T threshold for additional jets, and is also presented for different invariant mass regions of the eμbb¯ system. All measurements are corrected for detector effects and presented as particle-level distributions compared to predictions with different theoretical approaches for QCD radiation. While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Search for dark photons from neutral meson decays in p+p and d+Au collisions at √s NN = 200 GeV

In this study, the standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g-2) μ deviates from SM calculations by 3.6σ. Several theoretical models attribute this to the existence of a “dark photon,” an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in π⁰, η → γe⁺e⁻ decays and obtained upper limits of O(2×10⁻⁶) on U-γ mixing at 90% CL for the mass range 30 < m U < 90 MeV/c². Combined with other experimental limits, the remaining region in the U-γ mixing parameter space that can explain the (g-2) μ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29 < m U < 32 MeV/c² remaining.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Final state radiation from high and ultrahigh energy neutrino interactions

Charged leptons produced by high-energy and ultrahigh-energy neutrinos have a substantial probability of emitting prompt internal bremsstrahlung ν ℓ + N → ℓ + X + γ . This can have important consequences for neutrino detection. We discuss observable consequences at high- and ultrahigh-energy neutrino telescopes and the Large Hadron Collider’s (LHC’s) Forward Physics Facility. Logarithmic enhancements can be substantial (e.g., ∼ 20 % ) when either the charged lepton’s energy or the rest of the cascade is measured. We comment on final state radiation’s impacts on measuring the inelasticity distribution, ν / ν ¯ flux ratio, throughgoing muons, and double-bang signatures for high-energy neutrino observation. Furthermore, for ultrahigh-energy neutrino observation, we find that final state radiation increases the overall detectable energy by as much as 20%, affects flavor measurements, and decreases the energy of both Earth-emergent tau leptons and regenerated tau neutrinos. Many of these have significant impacts on measuring neutrino fluxes and spectra. Finally, for the LHC’s Forward Physics Facility, we find that final state radiation will impact future extractions of strange quark parton distribution functions. Final state radiation should be included in future analyses at neutrino telescopes and the Forward Physics Facility. Published by the American Physical Society 2025

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Constraints on models of the Higgs boson with exotic spin and parity using decays to bottom-antibottom quarks in the full CDF data set

In this study, a search for particles with the same mass and couplings as those of the standard model Higgs boson but different spin and parity quantum numbers is presented. We test two specific alternative Higgs boson hypotheses: a pseudoscalar Higgs boson with spin-parity J P = 0 – and a gravitonlike Higgs boson with J P = 2 + , assuming for both a mass of 125 GeV/c 2 . We search for these exotic states produced in association with a vector boson and decaying into a bottom-antibottom quark pair. The vector boson is reconstructed through its decay into an electron or muon pair, or an electron or muon and a neutrino, or it is inferred from an imbalance in total transverse momentum. We use expected kinematic differences between events containing exotic Higgs bosons and those containing standard model Higgs bosons. The data were collected by the CDF experiment at the Tevatron proton-antiproton collider, operating at a center-of-mass energy of √s = 1.96 TeV, and correspond to an integrated luminosity of 9.45 fb –1 . We exclude deviations from the predictions of the standard model with a Higgs boson of mass 125 GeV/c 2 at the level of 5 standard deviations, assuming signal strengths for exotic boson production equal to the prediction for the standard model Higgs boson, and set upper limits of approximately 30% relative to the standard model rate on the possible rate of production of each exotic state.

Aaltonen, Timo Antero↗
DOE OSTI2021

Search for heavy resonances decaying into a pair of Z bosons in the $\ell ^+\ell ^-\ell '^+\ell '^-$ and $\ell ^+\ell ^-\nu {{\bar{\nu }}}$ final states using 139 $\mathrm {fb}^{-1}$ of proton–proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

A search for heavy resonances decaying into a pair of Z bosons leading to $\ell ^+\ell ^-\ell '^+\ell '^-$ and $\ell ^+\ell ^-\nu {{\bar{\nu }}}$ final states, where ℓ stands for either an electron or a muon, is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV collected from 2015 to 2018 that corresponds to the integrated luminosity of 139 fb -1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Different mass ranges spanning 200 GeV to 2000 GeV for the hypothetical resonances are considered, depending on the final state and model. In the absence of a significant observed excess, the results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, and the limits for the spin-2 resonance are used to constrain the Randall–Sundrum model with an extra dimension giving rise to spin-2 graviton excitations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Vectorlike leptons and long-lived bosons at the LHC

We study a renormalizable theory that includes a heavy weak-singlet vectorlike lepton, $\tau$', that decays into a pseudoscalar boson and a tau lepton. We show that this can be the dominant decay mode of $\tau$' provided the pseudoscalar couplings deviate from the case of a Nambu-Goldstone boson. For a range of parameters, the pseudoscalar is long-lived, and mainly decays into a photon pair at one loop, or into a tau pair at tree level. Electroweak production of $\tau$' + $\tau$' - leads to a rich phenomenology at colliders, including signals with many taus or photons. We analyze in detail the LHC signal involving two prompt taus and two displaced photon pairs. Particularly interesting is the case where the pseudoscalar has a decay length of a few meters and thus would typically deposit energy in the muon chambers of the CMS or ATLAS detectors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the Higgs boson mass in the H → ZZ*→ 4ℓ decay channel using 139 fb –1 of s = 13 TeV pp collisions recorded by the ATLAS detector at the LHC

The mass of the Higgs boson is measured in the H→ZZ * →4ℓ decay channel. The analysis uses proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb –1 . The measured value of the Higgs boson mass is 124.99 ± 0.18(stat.) ± 0.04(syst.) GeV. In final states with muons, this measurement benefits from an improved momentum-scale calibration relative to that adopted in previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass of 124.94 ± 0.17(stat.) ± 0.03(syst.) GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Production and tests of the ADDC for the Micromegas detector of the ATLAS New Small Wheel

The Large Hadron Collider (LHC) at CERN will perform a series of upgrades to allow luminosity increases during the next physics runs expected from 2022 on. These will also significantly increase the trigger rates of all the detectors. As part of the ATLAS Phase-I upgrade, the current Small Wheel muon detectors will be replaced with state-of-the-art New Small Wheel (NSW) detectors to cope with the increased luminosity of the LHC. The Address in Real Time Data Driver Card (ADDC) is designed to transmit the trigger data from the resistive Micro-Mesh Gaseous Structure (Micromegas) detectors of the NSW. The ART ASIC on the ADDC is a customdesigned chip to receive theAddress in Real Time (ART) signals from theVMMfront-end ASIC and perform hit-selection processing. The processed trigger data is then sent to the Trigger Processor (TP) through optical links. A total of 512 ADDCs will be installed on the detector close to the front-end boards. Therefore, those cards must be able to work properly in a high radiation and magnetic field environment. Furthermore, after four rounds of prototyping, the ADDC production was launched in January of 2019. 600 ADDC boards have been produced and tested with an automated test stand. This test setup can simulate the front-end signals and provide "Level-1 Data Driver Card" (L1DDC) functions as well as part of the TP functions. Thus, the ADDC functionality and stability can be verified without the remaining NSW electronics. This paper describes the ADDC hardware prototype development, radiation and integration testing, and the ADDC automated production test procedure.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Collider Phenomenology with Split-UED

We investigate the collider implications of Split Universal Extra Dimensions. The non-vanishing fermion mass in the bulk, which is consistent with the KK-parity, largely modifies the phenomenology of Minimal Universal Extra Dimensions. We scrutinize the behavior of couplings and study the discovery reach of the Tevatron and the LHC for level-2 Kaluza-Klein modes in the dilepton channel, which would indicates the presence of the extra dimensions. Observation of large event rates for dilepton resonances can result from a nontrivial fermion mass profile along the extra dimensions, which, in turn, may corroborate extra dimensional explanation for the observation of the positron excess in cosmic rays. The Minimal Universal Extra Dimensions scenario has received great attention. Recently non-vanishing bulk fermion masses have been introduced without spoiling the virtue of KK-parity. The fermion profiles are no longer simple sine/cosine functions and depend upon the specific values of bulk parameters. The profiles of fermions are split along the extra dimensions while the wave functions of the bosons remain the same as in UED. A simple introduction of a KK-parity conserving bulk fermion mass has significant influences on collider aspects as well as astrophysical implications of UED. For instance, the DM annihilation fraction into certain SM fermion pairs is either enhanced or reduced (compared to the MUED case) so that one can perhaps explain the PAMELA positron excess while suppressing the anti-proton flux. In this paper, we have concentrated on collider phenomenology of Split Universal Extra Dimensions. We have revisited the KK decomposition in detail and analyzed wave function overlaps to compute relevant couplings for collider studies. We have discussed general collider implication for level-1 KK modes and level-2 KK with non-zero bulk mass and have computed LHC reach for the EW level-2 KK bosons, {gamma}{sub 2} and Z{sub 2}, in the dilepton channel. The LHC should able to cover the large parameter space (up to M{sub V{sub 2}} {approx} 1.5 TeV for {mu}L {ge} 1) even with early data assuming {approx}100 pb{sup -1} or less. The existence of double resonances is one essential feature arising from extra dimensional models. Whether or not one can see double resonances depends both on how degenerate the two resonances are and on the mass resolution of the detector. The very high P{sub T} from the decay makes resolution in dimuon channel worse than in dielectron final state. This is because one can reconstruct electron from ECAL but muon momentum reconstruction relies on its track, which is barely curved in this case. Further indication for SUED might be the discovery of W'-like signature of mass close to Z{sub 2}. The MUED predicts a somewhat lower event rate due to 1-loop suppressed coupling of level-2 bosons to SM fermion pair, while it exists at tree level in SUED. Therefore in UED, one has to rely on indirect production of level-2 bosons, whose collider study requires complete knowledge of the model: the mass spectrum and all the couplings. On the other hand, in the large {mu} limit of SUED, the dependence on mass spectrum is diminished since level-2 KK bosons decay only into SM fermion pairs. This allows us to estimate the signal rate from their direct production, so that they can be discovered at the early phase of the LHC. The indirect production mechanism only increases production cross sections, improving our results. Once a discovery has been made, one should try to reconstruct events and do further measurements such as spin and coupling determination, with more accumulated data, which might discriminate KK resonances from other Z' models. The coupling measurement is directly related to the determination of the bulk masses. A challenging issue might be the existence of two resonances which are rather close to each other.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Search for a new $Z$' gauge boson in 4$μ$ events with the ATLAS experiment

This paper presents a search for a new Z' vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 139 fb -1 . The new gauge boson Z' is predicted by Lμ - Lτ models to address observed phenomena that cannot be explained by the Standard Model. The search examines the four-muon (4μ) final state, using a deep learning neural network classifier to separate the Z' signal from the Standard Model background events. The di-muon invariant masses in the 4μ events are used to extract the Z' resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z' production cross-section times the decay branching fraction of pp → Z'μμ → 4μ are set from 0.31 to 4.3 fb for the Z' mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, g Z' , of the Z' boson to the second and third generation leptons above 0.003 – 0.2 have been excluded.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Beam-induced and cosmic-ray backgrounds observed in the ATLAS detector during the LHC 2012 proton-proton running period

This paper discusses various observations on beam-induced and cosmic-ray backgrounds in the ATLAS detector during the LHC 2012 proton-proton run. Building on published results based on 2011 data, the correlations between background and residual pressure of the beam vacuum are revisited. Ghost charge evolution over 2012 and its role for backgrounds are evaluated. New methods to monitor ghost charge with beam-gas rates are presented and observations of LHC abort gap population by ghost charge are discussed in detail. Fake jets from colliding bunches and from ghost charge are analysed with improved methods, showing that ghost charge in individual radio-frequency buckets of the LHC can be resolved. Some results of two short periods of dedicated cosmic-ray background data-taking are shown; in particular cosmic-ray muon induced fake jet rates are compared to Monte Carlo simulations and to the fake jet rates from beam background. A thorough analysis of a particular LHC fill, where abnormally high background was observed, is presented. Correlations between backgrounds and beam intensity losses in special fills with very high β* are studied.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Measurements of double-helicity asymmetries in inclusive J / ψ production in longitudinally polarized p + p collisions at s = 510 GeV

We report the double-helicity asymmetry, A J/ψ LL , in inclusive J/ψ production at forward rapidity as a function of transverse momentum p T and rapidity |y|. The data analyzed were taken during √s = 510 GeV longitudinally polarized p + p collisions at the Relativistic Heavy Ion Collider in the 2013 run using the PHENIX detector. At this collision energy, J/ψ particles are predominantly produced through gluon-gluon scatterings, thus A J/ψ LL is sensitive to the gluon polarization inside the proton. We measured A J/ψ LL by detecting the decay daughter muon pairs μ + μ – within the PHENIX muon spectrometers in the rapidity range 1.2 < |y| < 2.2. In this kinematic range, we measured the A J/ψ LL to be 0.012 ± 0.010 (stat) ±0.003 (syst). The A J/ψ LL can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken x: one at moderate range x ≈ 5 × 10 –2 where recent data of jet and π 0 double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-x region x ≈ 2 × 10 –3 . Furthermore, our new results could be used to further constrain the gluon polarization for x < 5 × 10 –2 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Micromegas chambers for the experiment ATLAS at the LHC (A Brief Overview)

The increase in luminosity and energy of the Large hadron collider (LHC) in the next upgrade (Phase-1) in 2018–2019 will lead to a significant increase in radiation load on the ATLAS detector, primarily in the areas close to the interaction point of the LHC proton beams. One of these regions is the Small Wheel of the ATLAS Muon Spectrometer. It is planned to be replaced with the New Small Wheel that will have Micromegas chambers as main coordinate detectors. The paper gives an overview of all existing types of Micromegas detectors with special focus on the Micromegas chambers for the ATLAS detector upgrade.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗